My first winter in Oregon came and went. The weather’s been fairly nice leading into spring, or at least my surroundings look just as they did in Washington, so I feel right at home and often forget I jumped states. Many aspects of my life are different and yet things feel the same—and yet better. Comfortable. I still work with the same people and Brian still calls me to chat every time he hops in his Jeep, even when he’s headed home for lunch. “You realize you’ll see me in five?” I’ll ask. “So the stabilator…” he’ll continue, disregarding my subtle nudge to postpone the RV-15 talk until after I’ve eaten.

I don’t leave the house a whole lot—a major aid in my recent increase in comfort. I buckled into my car the other day only to find the battery was dead. “I didn’t want to leave anyway,” I smirked, crawling up the stairs to return to my sweatpants or, in my case, work pants. The same image was drawn three weeks later, a jump-start occurring somewhere in between. Oops!

Brian and I spent the past few months indoors, ripping down wallpaper and making things pretty. I haven’t gotten to fully take advantage of our hangar because there currently aren’t any projects in there for me to work on, so there were a handful of days where I forgot where we live—that there’s a runway out there. One day I found a plastic bag in our crawl space that read Cleveland Brakes under a fine layer of dust. “What are the odds!” I thought, before remembering the previous owners were airplane nuts too. A short while later Brian tossed a Basler Aircraft keychain down from the attic. High. The odds are high.

My People

As you know, there are many general aviation businesses in Oregon and with that a large number of airparks nestled between cities, crawling with homebuilders. It’s a short drive from here to Rob Hickman’s house, where his children and I steal beer he brews in his hangar. He makes it using an all-grain process just like the pros, not with extract, which is the more common method among home brewers because the all-grain method requires more specialized equipment. Speaking of special equipment, Rob couldn’t help himself and added some automation driven off of an AF-5000 prototype EFIS, complete with a 3D-printed bezel. On nice days we hang out in the driveway and Greg Hughes, another member of the Van’s Aircraft crew, wanders over to chat. All are based at a grass strip called Dietz Airpark, which lies just to the east of Aurora’s Class D boundaries.

How many airports in this part of the world? If you drew a circle with a 40-mile radius centered on Portland International, there would be more than 50—yes, five-oh—airports inside it. Some are sleepy farmer’s fields that don’t see much activity. Some, like Hillsboro and McMinnville (home of the Evergreen Aviation & Space Museum and the Spruce Goose), are overflowing with training activity when the weather permits. On a sunny weekend day, the patterns are packed.

My airpark is pretty sleepy in comparison. There are fewer active pilots than at Dietz and not many people fly in to sample the crabgrass. When I am serenaded by that familiar engine sound it’s almost always the one and only high-wing RV followed by a low-wing one. Van’s test pilot Axel Alvarez and Brian chase each other to “collect data” while I peer out my east-facing window and enter yet another purchase order. “All work and no play,” I’ll say to the cats who have no idea their owners have hobbies that don’t pertain to them and who can’t appreciate the desire to replace the computer keyboard with a control stick most every day.

Axel flew the RV-15 over on one of his few unaccompanied flights. I stood in my lawn and watched him execute a handful of simulated engine-outs on either end of the runway since winds were calm. This was my first time seeing the -15 in action and I must say, I want one. Brian’s landing gear looked great—perfect for the grass runway our 95-year-old neighbor sometimes lets get a little tall. (We cut him some slack.) From my vantage point, the airplane sure looked slow on approach and stopped quickly. Our runway is 2200 feet long and all I can say is, Axel certainly didn’t need much of it.

The Van’s employees aren’t the only ones having fun around here. Marc Cook and I went up in his GlaStar a couple times so I could knock out my required six instrument approaches for currency. He played safety pilot while I got used to slowing down a slippery airplane with a fixed-pitch propeller—the trickiest part about shooting approaches in his plane. I had to shake some rust off, of course, but overall everything felt great and I was thrilled I still knew how to chase the needle.

This was my first time flying a GlaStar. I have over 50 hours in the larger, more powerful Sportsman and roughly 250 in a C-172. Initially, the GlaStar felt more like the C-172, which I mostly chalk up to horsepower and the little wheel being up front, since all of my Sportsman time is in a taildragger. With a fixed-pitch prop, Marc’s GlaStar is more like the Cessna in that it doesn’t slow down as easily as the Sportsman. I also got my first landing at home, which was exciting! I had to go around on my first attempt because I came in a little low and slow, but avoided making that mistake on my second attempt, the bossman coaching me down. It felt great to be using my new home runway, finally, and not have it seem like an abstract thing—nice grass for someone else to mow.

Out on the Town

Canby is really small, but charming. We’ve got some good restaurants, which make for a nice escape when I’ve had it with pajamas. Brian and I often run into members of the Pudding River Bearhawk Gang. “What are the odds!” we’ll say, sidling up to Ken Scott and Rion Bourgeois for a beer and quick chat—about airplanes, of course. It seems there’s no escaping aviation around here and I’m OK with it. This surprised me at first—even the local news meteorologist is a pilot—but it helps reinforce why I moved to this part of Oregon.

I suppose the odds of bumping into a homebuilder are fairly high since Oregon played a major role in establishing what would become the Experimental/Amateur-Built class of aircraft—and helping to set in motion the vital industry that supports it today. George Bogardus flew his homebuilt airplane, the Little Gee Bee, from Oregon to Washington, D.C., on three separate occasions to convince the Civil Aeronautics Administration and the Civil Aeronautics Board that people could and should be able to build and fly their own airplanes under the guidance of sensible rules and regulations. In 1952 the CAA enacted the legislation and a year later Paul Poberezny founded the Experimental Aircraft Association. It’s true: We have aviation in our veins—and Basler keychains in our attics to prove it.

Photos: Ariana Rayment and Brian Hickman.

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We often treat the propeller as a uniform “actuator disc” and the slipstream as a uniform stream tube of accelerated and swirling air. While this simplification is valid for many types of analysis, a propeller is composed of discrete blades. Each blade generates force and also sheds an individual aerodynamic wake downstream.

The discrete nature of the propeller blades has several effects on the propeller, the engine and the airframe.

Blade Loads

The loads on the propeller blades are not constant in flight. There are several conditions that change the aerodynamic environment of a blade as a function of its angular position along the orbit of the propeller. This variation produces a cyclic change in the force generated on the blade.

Angle of Attack

As we saw in last month’s Wind Tunnel about P-factor, the lift on the blade can vary as it goes around its orbit, even if the propeller is rotating at a constant rpm. There can be several causes for this variation in blade lift.

The first is the effect of the angle of attack of the airplane on the angle of attack and airspeed the blades encounter over a full rotation of the propeller.

A positive airplane angle of attack tilts the prop axis relative to the wind. Individual propeller blades encounter different conditions at different points in the propeller rotation. An up-going blade has a lower blade AOA and airspeed than if the shaft were parallel to the wind. A down-going blade has a higher blade AOA and airspeed. This causes the lift of each blade to vary cyclically within a period of one cycle per revolution.

Wake Impingement

If the wake of any part of the airframe impinges on the propeller, it affects the forces on the blades. This is particularly true on pusher configurations because the propeller is some combination of the wing, tail or engine support structure.

The frequency of the perturbations to the forces on a blade depends on how the blade passes behind an airframe component. For example, if the engine is pylon-mounted, as is the case on the Lake Amphibian, each blade passes through the wake of the pylon once per revolution. If the engine is in line with a wing, like on the Rutan canard designs such as the Long-EZ or on an airplane with wing-mounted pusher engines like the Piaggio Avanti or Beech Starship, each blade passes through the wing wake twice per revolution.

Upwash and Downwash

A lifting wing deflects the airstream. There is an upwash ahead of the wing and a downwash behind it.

On a multi-engined airplane with wing-mounted engines and tractor propellers, the props are immersed in the upwash ahead of the wing. This means that the propeller axis of rotation is tilted upward relative to the local airflow at the plane of the prop, even if the propeller shafts are physically aligned with the direction of flight. The blades will encounter the same variation of local angle of attack and airspeed around the prop orbit as we saw in our discussion of the effect of airplane angle of attack.

The downwash behind a lifting wing changes the angle of attack of the parts of the airplane behind the wing. On a pusher configuration, wing downwash affects the inclination of the oncoming airstream relative to the propeller axis of rotation. This produces the same type of once-per-revolution variation of blade forces as we saw as a result of airplane angle of attack.

Effects of Blade Force Variations

The aerodynamic effects we have just discussed produce cyclic variations of the loads on each propeller blade. The characteristic frequencies of the variations in blade load are multiples of the propeller rate of rotation.

Resonance and Blade Fatigue

The cyclic changes in blade thrust can excite flapping oscillations of the blade. This can be a significant problem if the natural frequency of a flapping mode of the blade is at or near the same frequency as the excitation caused by the fluctuation of the aerodynamic loads on the blade.

If the two frequencies couple, the blade will experience a resonance. The cyclic aero load will excite the structural flapping mode of the blade, causing the flexing of the blade to grow and the transient forces on the blade to increase far above the initial magnitude of the aerodynamic load. This can cause fatigue failure of the blades and is a particular problem for metal propellers or props with metallic shanks holding on wooden or composite blades.

It’s important that the propeller blades be stiff enough so that their natural frequencies are well separated (usually higher frequency) from at least one-per-revolution and two-per-revolution blade-passing frequencies. Certified propellers are tested extensively to ensure that they do not suffer from resonance issues within their normal operating range. There have been problems in the past with Experimental props with metal blades that were not so extensively tested, and at least two early attempts at variable-pitch props for homebuilts had to be withdrawn from the market after a series of in-flight blade failures.

Cyclic Loadings From the Prop

In addition to affecting the blades themselves, the cyclic variations of blade loading are transmitted into the propeller hub, the prop shaft and eventually the airframe via the engine and engine mount. This creates structure-borne vibration in the airframe and also cyclic loads that can fatigue mounting bolts and other structural components.

The frequency of these vibrations is different than that experienced by a single blade because it also depends on the number of blades. In essence, the characteristic frequency is multiplied by the number of blades. If, for example, a single blade experiences a one-per-revolution variation of load, a two-blade prop will put a two-per-revolution force variation into its hub and a three-blade prop will generate a three-per-revolution excitation.

The number of blades also affects the amplitude of the vibration caused by blade-force variations.

The amplitude of the propeller-induced vibration is a function of the loading of the individual blades. The cyclic loading on each blade is proportional to the nominal or average load the blade is carrying.

To the first order, the thrust generated by the propeller is divided equally between the blades. Increasing the number of blades reduces the load carried by each individual blade and therefore reduces the amplitude of the cyclic variation of load on each blade.

The result of these phenomena is that as the blade count increases, the frequency of the propeller-induced vibrations increases and its amplitude decreases. With more blades, the propeller will generate higher-frequency, lower-amplitude vibration.

The lower amplitude and higher frequency of the prop-induced vibrations are one reason to use a prop with more blades. In general, using fewer blades and more diameter is more efficient until the blade tip Mach number becomes the limiting factor on diameter, but the reduction in vibration amplitude with more blades is often worth the slight reduction in efficiency. Also, higher-frequency vibrations are less objectionable to people, so both effects make the propeller seem “smoother” to the occupants of the airplane.

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It could be you’ve heard the Brennand name associated with the idyllic floatplane base southeast of Oshkosh, on Lake Winnebago. Beginning in the 1970s, Bill donated the use of his waterfront land for floatplane operations and chaired the base for 20 years. Maybe you are acquainted with the Brennand
Airport, equally idyllic, a short hop north of Oshkosh. Both locales are linked to the Brennand name, though neither define the man. Nor does the fact he dated Betty Skeleton.

To my recollection, I first saw Bill Brennand in the 1990s, at a grassroots aviation gathering that happened spontaneously every Saturday morning, west of Oshkosh, on the farm of Munsil and Shirley Williams. The weekly gathering attracted all manner of aviators and aviation enthusiasts, their spouses and their children. It was everything aviation should be: accessible, friendly, diverse and fueled by coffee and donuts and, occasionally, accordion music. Stories were told. Lies repeated. Air medals re-earned. Munsil’s, as it was known, went on with or without its namesake. It was at Munsil’s that I first approached Bill Brennand. The conversation was likely brief. I didn’t know what to say to him and he was a quiet man. The ice, however, was broken by coffee. Over time our conversations expanded to include the donuts and the weather. On a lucky day, Bill would accidentally share one of his flying stories.

A Pivotal Pairing

In 1943, with a service deferment to work the family farm, 19-year-old Brennand began taking flying lessons at Wittman Flying Services. Steve Wittman—you’ve certainly heard his name—was, at that time, training pilots for the military. Prior to the war, Wittman had established a successful air racing career with two aircraft that sprang from his own mind and hands (Wittman was homebuilding in Oshkosh before EAA founder Paul Poberezny was 3 years old). His first racer, Chief Oshkosh, was raced from 1931 until 1938, when it was heavily damaged near Oakland, California. It was trailered home to Oshkosh and placed in the rafters of Wittman’s hangar while he concentrated on campaigning his other racer, Bonzo, a Thompson Trophy contender that was faster than the military aircraft of the day. Wittman had also designed a two-place aircraft, Buttercup, the predecessor to his Tailwind, which he licensed to Fairchild Aircraft. The onset of WW-II, however, brought both civilian aircraft production and air racing to a full ground stop.

By April 1944, Brennand had earned his pilot certificate and was working part time for Wittman. Brennand said the first thing he worked on with Wittman was a four-place airplane Wittman designed and designated Big-X. Fairchild, like every other aircraft manufacturer pivoting to a post-war economy, envisioned returning military pilots wanting their own aircraft. But, as with Buttercup, Fairchild never put Big-X in production. For Bill, however, building an airplane with Wittman was “amazing in every way.”

All the while the injured Chief perched in the rafters. Wittman reminisced about it. Brennand dreamed about it. They both talked about fixing and flying it. In the summer of 1945, with Wittman uttering, “Yeah, I suppose that’s something for me to get killed in,” Chief Oshkosh was lowered from the rafters. Brennand knew that statement—a statement he never forgot—was meant for him. By the summer of 1946, Chief Oshkosh was reborn as Buster.

In September 1947 Bill Brennand, age 23, lowered his 100-pound frame into Buster’s cramped cockpit to compete in the Goodyear-sponsored Midget class race at the National Air Races in Cleveland. Lockheed test pilot Tony LeVier idled nearby. LeVier was experienced at both racing and winning. His airplane, Cosmic Wind, had the full, though unofficial, backing of Lockheed Aircraft and its vast resources. Brennand, a farm-boy-turned-flight instructor, had never raced. Ever. Brennand’s steed was a homebuilt aircraft built during the Depression (when it is said Wittman lived on $1 per day, including what he spent on building his airplanes). It was raced, wrecked and raftered before being resurrected in its new configuration. Bill had only flown Buster 10 hours for recreation before being sent to compete in Cleveland.

September Surprises

A rescue crew arrived as Brennand swung Buster’s canopy open. Buster’s propeller broke during Bill’s final qualifying flight, forcing him to pull up and glide over the grandstand for an emergency landing. “What happened?” the rescue crew asked. “I don’t know,” Bill replied, “I just got here myself.” The next day, with a borrowed propeller, Brennand won the inaugural closed-course Goodyear Trophy race with an average speed of 165.8 mph. Tony LeVier finished fourth, at 159.1 mph.

Some 60 years later, in September 2007, Bill Brennand, age 83, his storied air racing, barnstorming and aviation career behind him, lowered himself into the right seat of Metal Illness. I swung the canopy shut.

When offered control of an airplane many passengers, even pilots, demur. Those who accept often hold the controls neutral, altering neither altitude nor heading and certainly not piloting. Bill was an exception. He flew with skill and confidence. He didn’t move the controls tentatively. He wholly and instinctively piloted the aircraft without overcontrolling it. If Bill was happy to be piloting again, I didn’t see it. His eyes were outside the cockpit, where all good pilots’ eyes should be. Where an air racer’s eyes must be. My eyes were on Bill. Not out of concern, but out of awe. If Bill had performed an aileron roll or pulled up into a stall before spinning earthward I was all in. If I had any concerns they were in my ability to get Bill back on the ground with both him and my pride intact.

“I was not one to ride around the patch very much; the flight had to have a purpose. I guess 65 years of flying was enough.” Those words are recorded on the final page of Brennand’s biography. (Bill Brennand: Air Racing and Other Aerial Adventures by Bill Brennand and Jim Cunningham, ISBN: 0971163766, published by Airship International Press.) He may have spoken those words often, after health issues grounded him. While I helped Bill off my wing he said, quietly, as was his way, “I really don’t miss it. I did it for so many years.”

I was at once taken aback and relieved. I had often thought about what it would be like to have my wings clipped, to age out of ability if not desire. A few weeks later, Bill’s girlfriend gripped my forearm, held my eyes hostage with hers and delivered unexpected news. “Bill has not stopped talking about the airplane ride you gave him!” Turns out, Bill Brennand lied to me—and likely himself.

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My choice for new ignition was to install a pair of E-MAG Electronic Ignition 114 Series P-MAG units. These units, which have been around for more than a decade, are designed to be as simple as possible to install. Each takes the physical space of a magneto—slightly less, actually. There are, of course, a few more wires to run through the firewall, plus you’ll have to route new spark-plug wires, make a connection to a manifold-pressure source and install new automotive plugs and the associated adapters. (See Paul Dye’s story for some tools and techniques around those adapters.) I also used some corrugated plastic tube for cooling the units, which is considered mandatory by E-MAG. I would say the retrofit was involved but not difficult. The documentation is extensive.

As with many aspects of my airplane, I’m installing over existing systems. So I kept the keyed ignition switch­—first removing the jumper whose normal function is to keep the non-impulse-coupled mag from firing while starting—though I also advocate using one because it’s like so many certified airplanes, which makes it easier for other pilots to transition into.

A note about power for the P-MAGs. They need ship’s power only to start and in the event of the internal supply’s failure; in fact, during normal operation they’re not even using main-bus power. This is how I justify not having a truly redundant electrical system. In fact, I have considerable avionics redundancy because many pieces either have their own backup batteries or are powered through a TCW Technologies IBBS.

The P-MAGs’ internal power can be relied upon as low as 850 rpm. Below that, the internal generator can’t keep up and the system falls back on external power. Some builders wire momentary switches to test this function periodically but I used pullable breakers located right next to the ignition switch to do the same thing. (And partly so I wouldn’t have to run power all the way from the other side of the panel.) The procedure for landing with a total aircraft electrical failure is to maintain 850 rpm or greater until the runway is made, a small change from the SOP.

Advance and Performance

P-MAGs have two internal advance curves, chosen by a jumper; I used the less aggressive one. I also attempted to set the baseline timing to coincide with my engine’s spec, which is 20° before top dead center (BTDC). The P-MAGs are designed with an internal 25° BTDC timing, the most common, and are set with TDC as a reference. By setting mine 5° after TDC, the system fires at the correct timing for my engine.

The two main functional advantages of electronic ignition include variable timing and a stronger spark on all plugs during start. Agreed on the strong start. My engine has never been easier to light off, hot or cold, first thing in the morning or right after a quick refueling—that aspect has been a solid win.

The variable timing comes into play at altitude and, especially, when running lean-of-peak mixture settings, which I almost always do in cruise. A lean mixture takes longer to burn, so advancing the timing helps move the peak of the power pulse back to where it does more good.

Once flying, I compared before-and-after engine data and was surprised to see higher EGTs with the P-MAGs. Retarded spark usually raises EGTs—it’s why a mag check sees the EGTs rise on one ignition source—so I was surprised when the P-MAGs seemed to be running late. I double-checked the timing and it was right where I wanted it. But the advance curves follow both engine speed and manifold pressure. With my fixed-pitch prop, I’m way down on the rpm-based advance curve for takeoff and the initial climb compared to an engine with a constant-speed prop that can turn 2700 rpm for takeoff.

After a lot of head scratching, I began incrementally advancing the installed timing to get the real-world spark near where it would be with magnetos. The engine remained happy with nearly all the offset removed. This is another reason to watch your data and try to interpret what it’s telling you. In addition, my experience speaks to the value of really understanding how systems work.

After tweaking the overall timing, I tried a prop adjustment. Because, well, everything is interconnected. By reducing prop pitch by “one number” in the Sensenich ground-adjustable, I was able to get static rpm up above 2200 and climb in the 2350–2400 rpm range, which made the airplane a bit more sprightly off the runway and during the climb to cruise—though I did lose 2–3 knots in cruise at any given engine speed.

More Testing…

I thought I was done. But one nice spring day I decided to take Charlie up to altitude to fill out missing fields in my cruise data. It revealed a couple of things. First, the timing advance really begins to show by about 5000 feet in the climb. At first you think the engine’s too rich because the EGTs are falling, but it’s really just the advance moving the combustion event ahead. I’ll have to recalibrate my sense of absolute EGTs to fuel flow during the climb phase. That’s not a bug, just a matter of learning the system. I do see higher cylinder-head temps later in the climb as the manifold-pressure-based ignition advance starts to take hold, but it’s been manageable so far.

In cruise flight, two characteristics stand out. First is that the engine will run much deeper lean-of-peak EGT prior to roughness. In fact, most of the time, as you lean, the engine just quietly stops making power. No fuss at all. The other change is that the engine is definitely making more power at altitude—not orders of magnitude but enough to show up as greater engine speed on any given prop setting. I’m now thinking I should have moved to electronic ignition sooner—but I also know exactly why I didn’t.

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A few months ago, we visited our friends at the Tempest Aero Group and watched as they made hundreds of oil filters and spark plugs every hour. Watching filter production (in the post-COVID world) was like watching wartime production in action; it was all hands to the pumps, getting as many out the door in as short a time as possible. The spark plug area was more sedate but equally interesting—a mainly automated process with a large machine centered around a carousel where the plugs grew before your eyes as components were added. As I said, very interesting…but at the same time, amusing because while there will always be a great demand for the products in the certified airplane world where aviation spark plugs are mandatory, the Experimental world is quickly leaving them behind in exchange for the ubiquitous BR8ES automotive spark plug because so many builders and owners are switching to electronic ignition systems and leaving their old Slick and Bendix mags behind.

The NGK BR8ES (or DENSO W24ESR-U) can be purchased in quantity from many sources and in a couple of different flavors. First tip: The BR8ES (also search for as BR8-ES, BR-8ES or any other variation of where the dash goes) comes in two different types—one with a screw-on tip for the spark plug wire and one with a solid tip. The first has a part number of 5422 and is very common. The other has a part number of 3961 and is less common, but it is the one you want for your airplane. Why? Because some folks have reported that the screw-on end can get loose and cause RFI that shows up as radio noise. The solid tip can’t do this. Whether this is true or just an old wives’ tail, it is not that hard to find the 3961s (as I write this, www.rockauto.com has them for $1.88 each), and there is no disadvantage to the solid tip so, why not?

Of course, you can use aviation plugs with some electronic ignitions, but with aviation plugs going for north of $30 each, it’s hard to pass up those $1.88 plugs and throw them away each time. I personally have four Lycoming engines, all with electronic ignitions, so I buy several dozen BR8ES plugs at a time and keep a bunch on the shelf. All my wonderful aviation spark plug tools (used for cleaning and gapping) sit in a drawer, used only when I have to work on someone else’s plane that still has mags. The NGKs are so cheap that while you can clean them, it is simply easier to throw them away every couple hundred hours and drop in new ones. It’s just economics.

Adapting

Of course, automotive spark plugs don’t just screw into a Lycoming engine—they are too small. Automotive plugs screw into a 14mm hole, whereas aviation plugs traditionally are 18mm. That means you’ll need an adapter for each plug, and these are usually supplied by your electronic ignition provider. They are generally made of brass, but some have been known to be steel. We’ve used both, but generally use the brass sets because they are more generally supplied.

Using an adapter means that there are two seals for every spark plug: one that seals the plug to the adapter and one that seals the adapter to the cylinder head. The first comes on the automotive plug and is generally a crush washer—hollow soft steel that crushes down when you torque the plug in place. While most mechanics will remove a plug and put it back in place again, the engineer who designed them probably considers these crush washers to be single use. I haven’t heard of problems (such as leakage or a plug backing out) from reusing them; I generally will only put one of these plugs in and out a couple of times. Again, they are cheap to simply replace.

The seal between the adapter and the cylinder head is accomplished the old-fashioned way—with a copper gasket. These gaskets come with aviation plugs (and can be bought separately by the thousands) and when new are in an annealed condition, which is to say “soft.” Using them properly (with a torque wrench) crushes them, providing a seal and adding tension that prevents the spark plug (or adapter) from backing out. Many mechanics routinely reanneal old gaskets and use them over, while many others declare that those who reuse them are just cheapskates—so why not use new ones every time? I personally reuse them sometimes because I enjoy the process of heating them up with a torch, watching them change color and then letting them cool down. Of course then you have to clean them to make them pretty…the whole process taking more time than simply buying a bag of new ones from Aircraft Spruce. It’s a religious argument; do what you’d like!

The Torque Problem

Automotive spark plugs get torqued to 18–25 foot-pounds. Aircraft spark plugs get torqued to about 35 foot-pounds. The difference is in the size of the thread (14mm versus 18mm) as well as the type of gasket used that provides a sort of spring retaining force. This means that to make everything happy in your Lycoming installation, you have two different torques in the assembly. If you torque both the plug and the adapter to 18 foot-pounds, you haven’t preloaded the copper gasket on the adapter sufficiently. If you torque the assembly to 35 foot-pounds, you’ve crushed the heck out of the spark plug’s built-in gasket. So what to do?

The answer is to torque them both separately, in series—but to do this, you need a couple of different wrenches. One thing you don’t want to do is torque the brass adapter in place without a spark plug screwed in; the soft adapter can be twisted and crushed out of true if there is nothing in the hole. The different electronic ignition builders have different techniques they recommend, but surveying the various options and simply looking at the joints has helped us build this procedure. The advantage is that it gives each “joint” the proper torque (not over, not under) and allows for easy removal of the plugs for maintenance. Ideally, once you have used this method, the adapters will stay in the engine—and we find that works about 70% of the time.

The Process—and Tools!

The way we do it is this: Take a new plug out of the box and screw it hand tight into the adapter using the appropriate anti-seize (which is the topic of an entirely different article!). Now screw the assembly finger-tight into the cylinder (same comment on anti-seize). Now take out your automotive spark plug socket, slide it on the plug and torque it to 18 foot-pounds. The net result is that both the plug and the adapter will be torqued into their holes at 18 ft-lb.

Next, take that automotive socket and put it aside. What you want next is a 7/8-inch deep socket that is long enough to allow it to fully cover the “flats” on the adapter, yet let the spark plug nest inside. The socket we have found that does this is a Craftsman 1/2-inch drive deep socket—ours is probably 40 years old, but it appears they still make the same thing. Note that a standard aircraft spark plug socket from Champion, Tempest or Autolite doesn’t work because it has a shoulder about 3/4 inch inside that will interfere with the automotive plug and not let the socket sit full down onto the adapter. You need a 7/8-inch socket that has “flats” all the way from the mount to the top (see picture). Now you probably don’t have a 1/2-inch torque wrench—or if you do, it will not work down at 35 foot-pounds, as it’s designed to work on big tractors—so find a “cheater” adapter to fit your ⅜-inch drive wrench onto the 1/2-inch drive socket.

Now you can slide this deep socket over the plug and onto the adapter and torque the adapter to the appropriate 35 foot-pounds to crush the copper washer properly—and you’re done. Next time you pull the plugs, you should theoretically be able to use an automotive plug socket and simply remove the plugs since they are torqued to a lower value than the adapters. This means you’re going to need a 14mm compression tester spud, of course. And as we noted, sometimes the adapters will still come out—so you’ll need both spuds for compression testing…maybe.

The Baffling Question

OK, so the process described above works fine until you get to a spot where the baffles (think top plugs) get in the way of that long 7/8-inch socket. Sure, it fits in place, but you don’t have room to put the torque wrench on there! What you need is a much “shorter” way to drive the big socket—and for this, you can make a special tool—if you have a lathe and welder (or know someone with the right skills and tools). The idea is to make something short that plugs into the ½-inch drive and allows you to use a crowfoot on the end of your torque wrench.

What we did was take a cheap 1/2-inch to 3/8-inch drive adapter and a short 1/2-inch bolt from the hardware store. We chucked the bolt up in the lathe and cut off all the threads, leaving a 3/4-inch hex head with a cylindrical 3/8-inch diameter shaft. We then chucked up the adapter and drilled out the inside about 1/4 inch deeper using a 3/8-inch drill bit. We cut as much off the open end of the adapter as we dared while leaving enough material to create a sturdy assembly, then cut enough of the “shaft” off the ¾-inch hex head so that it nested fully down into the adapter. Then it was a simple stop at the TIG welding table to join the two things together, and we had a 3/4-inch hex head to pop into the big socket. Use the 3/4-inch crowfoot on your torque wrench, and you’re ready to go.

An alternative is to use a mill to put “flats” on the end of the big socket and use the appropriate (larger) crowfoot directly on the socket. Essentially, it duplicates the configuration of a standard aircraft plug socket wrench that has both a ratchet drive socket and a hex head (usually for a 7/8-inch wrench) as well. This is easier if you don’t have access to a welder, but you have a friend with a mill—or you have a vise, a mill bastard file and some patience. You can start with a Craftsman CMMT47528 (1/2-inch drive, 7/8-inch deep socket—available at Ace Hardware or your favorite online retailer) and use a carbide end mill to do the work. The socket is very hard and it simply laughed at our regular (cheap) end mills that we use for aluminum. This solution gives you the best fit for top plugs where cooling baffles might be in the way, while also preserving the option of using a 1/2-inch-drive torque wrench directly. The spark plug and adapter fit snuggly inside this particular Craftsman socket.

One final solution is the cheapest (but won’t always work with baffles). Harbor Freight sells a set of square-drive socket caps (part number 67011) that give you the same thing as the welded adapter we described above—but where’s the building fun in that?

The Simple Solution

Automotive plugs are a simple solution for experimental Lycomings when using any of the popular electronic ignition systems. They fire great with a factory gap of about 0.032 inch, and they are cheap so that you will never worry about maintaining them. I have heard less discussion about lead fouling with these plugs than in the old days, when everyone used massive-electrode aviation plugs. I don’t know if this is because people do a better job of leaning on the ground, the plugs are less prone to fouling or people just throw them away before fouling becomes an issue!

It’s hard to break the habits of decades of aircraft maintenance, but not having to clean and re-gap plugs is a boon to those of us that have spent years of our lives digging out little lead balls and sandblasting expensive plugs. I first used the BR8ES in two-stroke jet skis, where the tuning process was to run the engine hard, then pull the safety lanyard off at high rpm, killing the motor instantly and preserving the combustion signatures on the plugs. You pulled the plugs, looked at the color of the deposits, threw the plug away, retuned, put in a new plug and did it over. Yeah, we went through a ton of plugs, but they were even cheaper back then.

Experimental aviators now have the option of using and throwing away plugs the same way—but we should always remember that the consequences of a blown-out plug in an airplane are much more dire than having to swim your jet ski back to shore or coast your late-model car to the side of the road. So use proper techniques and torques when installing plugs, and enjoy the convenience and savings of the modern ignition world!

Photos: Paul Dye and Marc Cook (sidebar).

The post Automotive Plugs in Lycomings appeared first on KITPLANES.

“Some wounds never heal, and for me it was the Honda Mini Trail I couldn’t have,” says seven-time Reno Sport class champion Jeff LaVelle. “It was $280 back then and it might as well have been $280 million.” And so began Jeff’s obsession with speed and freedom and winning and, eventually, airplanes. He couldn’t swing that little Mini Trail burning a hole in his heart as a boy and it’s been bugging him ever since. “Yeah, fill that damn hole up with stuff you don’t need.”

At least Jeff has been filling it with some pretty interesting stuff. The Glasair III we’re looking at here is just one of Jeff’s hole fillers, one that’s been the contender at the Reno National Air Races for years.

Besides unfortunately marking the end of the Reno era, this September also denotes the first quarter century of Sport class racing and our last chance to see this highly developed machine in action around the sport’s modern temple in the Nevada desert. So it’s time we take a close look at the class’s winningest combination of pilot and plane: Jeff LaVelle and Race 39.

Certainly Jeff is the logical candidate to represent the exciting, relevant Sport action. His debut in 2007 was during the transition from Sport’s putative years into a mature, stable class. He’s been active ever since, so his experience spans flying with the immortal Darryl Greenamyer and early Sport-class kingpin Jon Sharp to giving today’s developing crop of Sport racers the target to hit. He’s run the same Glasair III throughout—it’s a man-and-machine pairing with the stats to back up the reputation.

To hit the statistical highlights, Jeff has entered 14 of the 24 Sport races run to date, qualifying on the pole an amazing 10 times and winning seven. When Jeff shows up, odds are he’ll be on the pole nearly three quarters of the time and win half of the races against meaningful competition. When he finishes, he’s never been lower than second in 13 years—so your only real hope of beating him is to have him not show up or break. Good luck. He was the second inductee to Sport’s exclusive 400-mph club—Jon Sharp and Andrew Findlay are the only other members. (Jim Rust should join this September if he brings his own Glasair III.) And it’s possible Jeff’s Glasair has run more of those thrilling all-out laps than any other Sport racer.

Jeff LaVelle

A Seattle native who never left, there isn’t much aviation predestination in LaVelle’s background. Neither parent was a pilot or worked in aviation, other than his dad built and flew U-control balsa-and-tissue airplanes. As for schooling, Jeff laughs, “the school of hard knocks…I think I drove past a college once.” Instead he latched onto machining in high school, progressively turning that talent and experience into owning a series of machine shops, some rather large, before retiring to commercial real estate.

Like many, Jeff had a passing interest in airplanes but found motorcycles a more accessible and engaging passion, especially dirt bikes. “I had a bunch of them,” he says, and was neck deep in wrenching and racing them (and is still riding). Busy with work and life, Jeff didn’t have any money for airplanes as a young adult.

But in the latter 1980s he was constantly driving by Paine Field, as his machine shop was located next to the airport, and his customers were aerospace companies. And he was eyeing the Cessna 150s and such that were around in those days because they looked kind of fun. It took a few years and growing success in business but stressed by work and an ongoing divorce he impulsively blurted, “Oh, screw it!” during his commute and steered into the FBO’s parking lot. It didn’t take more than a few lessons in a little Cessna for Jeff’s initiative and performance lust to kick in. “So I bought a Mooney 201.”

The complex speedster required a new instructor—Jeff was still working on his private ticket—which led him to Bob Chase, an ex-Navy Corsair jockey. “He couldn’t hear very well,” says Jeff, “but he had all the skills he’d never lost.” We suppose drumming around behind a Pratt & Whitney R-2800 really would keep you on your toes—and your ears ringing.

After flying the Mooney for maybe five years—Jeff is too engaged in the present to keep a diary of the past—he ordered his Glasair III kit, the same airplane he’s racing today. “There was no Sport class racing then or it was just getting started, so I didn’t build the plane to race it. I wanted it because it was small, aerobatic and fun looking.”

While the Glasair was under construction Jeff, no doubt gnawed by a racer’s need to keep moving, also bought a Decathlon to horse around in and, like a proven planeaholic, he still has it. Still not sated, Jeff also bought an RV-4 and fell in with the Black Jacks, a regionally famous formation flying group working out of Arlington, Washington. Jeff cites his time with the Black Jacks as fundamental to building his airmanship and professionalism due to the large number of battle-hardened Vietnam-era military vets running the show. “They’d just love to kick your ass,” says Jeff about the Black Jack culture. “I can’t tell you what an opportunity that was.”

Race 39

Built with low weight and maximum performance in mind, Jeff’s Glasair is a product of his motorcycle racing mindset, even if it was intended for general duty, not air racing. Constructed via Glasair’s builder-assist program, his plane started with kit purchase in May 1998 and took only about a year and a half to completion, sans paint. Although Jeff was a frequent participant at the Arlington build center, “Jim Muldoon, the leader at Glasair’s assist program, built the fuselage and did the final assembly,” says Jeff. “I’d go up there and he’d laugh at me because I was chasing all the details.” The Glasair shop was a laid-back, fun-loving place, resorting to the occasional tape ball fight, says Jeff, who’d interrupt with his hard-core dirt bike racing mindset. Sweating weight details, he played the concerned customer. Or, as Jeff put it, “They thought I was a lunatic.”

While the fuselage was going together in Arlington, Ted Backus of Emerald Aircrafters in Troutdale, Oregon, built the all E-glass wing. This is an involved task because of the large number of parts the builder actually lays up, along with the responsibility to square them into a straight wing. At least the design is straightforward, with the spars and ribs taking shape as foam core and E-glass sandwiches with vinyl ester resin. But by today’s standards there’s plenty of hand fitting required to arrive at a straight, untwisted airfoil. It’s also worth noting that if such slow-build kits take time and build skills, they also give the builder more control over the finished product. In Jeff’s case that meant an emphasis on stopping weight creep.

Glasair shipped wing kits with the full-span, one-piece main spar built and bonded to the lower wing skin with the rest done by the builder. Thus, the builder’s critical first task is to construct a full-span table to serve both as a workbench and jig for the one-piece wing. As the table determines many wing characteristics, including dihedral and washout, it has to be exact. In practice that means a good amount of measuring, shims and tweaks until it’s right.

Rib formation begins by cutting out paper patterns supplied by Glasair and bonding those to whatever rigid material the builder chooses. This produces the stiff templates used to cut out the foam cores, which are then glassed over to make a rib, and then are finished with the addition of separate rib caps. Once these ribs and the rear spar are glassed into the wing they’re followed by precisely fitting the upper skin to the rib caps via numerous trial fits. Gaps between the rib caps and upper skin are checked with clay while temporarily laying on the upper skin. This reveals the high and low spots, which are either sanded or built up with micro or flox. As the wing is wet with fuel, there is the added issue of sealing the fuel bays from the dry areas. Jeff added to this by closing out the aileron bays for extra tankage near the wingtips. His wing holds 33 gallons of fuel per side.

Finally, the big day came when the upper skin was bonded to the wing assembly, closing the entire wing. This involves wetted, heavy, thick structural cloth along with a lightweight top skin.  As the final skin goes on it’s a blind job as the skin covers up the structure. Not only is getting the wing’s top skin accurately placed critical for achieving the best wing shape possible, it’s also a difficult step requiring “a lot of touch labor and eyeball…it’s a craftsman thing to put this on correctly,” says Jeff. “You’ve got to make it perfect the first time because it’s a done deal” once the upper skin has bonded in place.

When it was time to close out his wing Jeff brought Jim Muldoon to Emerald Aircrafters alongside Backus, a bit of dirty pool as Jeff figured having two principal builders on hand would spur each to their best and thus produce the lightest, strongest, straightest and smoothest wing. It seems to have worked.

Once together in early 2000, Jeff flew his Glasair for a couple of years in primer behind a stock 300-hp, IO-540 Lycoming. From the first flight Jeff was pleased to find he had achieved his goal of building an exceptional Glasair III airframe. Crediting the main builders, Backus and Muldoon, Jeff found his plane just a little bit lighter and a touch faster than other Glasairs he came across. “It’s above average speed-wise,” he says. “It’s lighter and straighter…a little better than average.”

While enjoying his new go-fast machine, Jeff found himself assisting an Unlimited air-racing team based nearby. He sped parts from Seattle to Reno during the Pylon Racing Seminar, and there he saw the Sport class in action. You can guess what happened next.

Race Power

Jeff’s first Reno race was in 2007. He ran his stock, naturally aspirated 540 Lycoming, giving us an accurate baseline on what a stock Glasair III can do around Reno’s pylons. The effort netted an 11th-place qualifying speed of 292.193 mph and a sixth-place finish in the Sport Gold race at 283.251 mph.

This was one of the four years where the Sport racers were broken into Sport Gold and either Sport Super Gold in 2007 and 2008 or Super Sport in 2009 and 2010. Thus, for comparison we’ll note Jon Sharp qualified his twin-turbo Nemesis NXT first at 387 mph and won the Sport Super Gold race in 2007 while Jeff was puttering around at 292 mph.

Clearly needing turbo power, for 2008 Jeff’s then crew chief Grant Semanskee “bought a cheap engine out of Spokane,” recalls Jeff. A company was converting Piper Mirages to PT-6A power and “were almost giving them away,” LaVelle notes. This stone-stock Lycoming TIO-540-AE2A angle-valve engine was rated at 350 hp (for five minutes) using 42 inches of manifold pressure. What do you think—did Jeff run it longer than that?

For packaging the intercooled Mirage engine in a Glasair, a new intake plenum was built by John Kerner while Bruce Hamilton fabbed a new carbon fiber cowling. Jeff said the combination “was fine…a good starter package” with its stock 7.3:1 compression ratio and running 100LL fuel. In 2008 he “got into first but detonated, maybe an injector clogged. I had just passed Lee Behel and was going to get my watch (Reno has awarded custom Breitling watches to race winners for many years) and then I detonated a jug and had to land the airplane.”

Now past the getting-started phase, Jeff’s next move was to call Ken Tunnell at engine shop Ly-Con to have him prep the Lycoming. This confederacy of Ly-Con building the core power section out of stock Lycoming engine cases, crankshafts and angle-valve jugs (with plenty of Ly-Con speed secrets) coupled to Jeff’s turbo and systems installation has remained his power source to this day. Ly-Con has Jeff ship them the core engine every year for inspection and freshening, a process that actually shows little wear (unless a connecting rod is sticking out) but lately includes a brand-new crankshaft out of hard-earned caution. That’s what running an engine at three times its rated power does to durability.

In 2008 and ’09, these were 540-cubic-inch engines but since 2010 they’ve been 580s. As usual, Ken Tunnell just goes “aw shucks” when pestered about how much power the deep-breathing 580 makes. In truth he doesn’t really know. “My dyno only reads to 1200 foot-pounds of torque and Jeff’s 540 pegged my dyno way below race power. Now he’s running a 580.” Like other Sport racers, Jeff says his current engine makes 850 hp or so. It could be over 900 hp but whatever the number is, it’s stout and a real accelerated wear test of everything inside it.

As for the 580 internals, they are mainly stock Lycoming bits augmented with Ly-Con’s cryogenic heat treatment, anti-friction and heat-barrier coatings, a custom-grind camshaft, CNC-ported heads, an O-ring case treatment and a subterranean 5.8:1 compression ratio via Ly-Con’s custom NFS pistons. The super-low compression greatly supports elevated manifold pressure while racing, but makes for a lazy dog with a fuel drinking habit at low or no boost. A fly-to-breakfast engine this is not, even if Tunnell says it’s “basically a drive-around-the-block engine,” when referencing its lack of exotic high-rpm parts.

ADI

Jeff followed the lead of many Unlimited and other Sport Gold racers in 2021 by removing air-to-air intercoolers in favor of increased ADI flow. ADI—anti-detonation injection—is a 50/50 water/methanol mix sprayed into the intake manifold. As the water evaporates it provides a powerful cooling effect that keeps combustion temperatures from spiking. It provides more combustion cooling than intercooling with much less aerodynamic drag.

Originally Jeff had a single ADI lawn sprinkler in the intake manifold but found it gave poor distribution among cylinders and was essentially impossible to tune. So, from a central ADI manifold he plumbed “water” lines to each intake runner, giving six tunable nozzles for much more efficiency. Two other lines feed the turbo outlets for additional general cooling as well. ADI fluid is kept in a 5-gallon tank in the cockpit for weight and balance reasons. It sits next to a 12-gallon spray-bar tank that spritzes distilled water onto the outside of the engine and oil cooler to increase heat rejection via evaporation. Like the ADI tank, the plastic spray bar tank is, “straight out of the Summit [Racing] catalog.” Distilled water is used in both to reduce nozzle clogging and water spots all over the engine compartment. “We go to Walmart and clean the shelves off,” says Jeff when asked where he gets his water.

Fuel System

To get sufficient fuel flow and control over 65 inches of manifold pressure, racers have successfully abandoned mechanical fuel injection for electronic injection (and ignition), mainly from SDS and EFII. Busy with other issues and an old-school guy at heart anyway, so far Jeff has stuck with Bendix mechanical fuel injection modified by Precision Airmotive in Arlington. Jeff Sitter at Precision has specified an RSA-10 fuel servo, along with a Romec fuel pump running a nominal 90 psi but sometimes hitting upward of 100 psi. That’s nearly three times the stock pressure. This extra pressure is used to both supply more fuel and overcome the boost pressure in the intake manifold. The rear-entry fuel servo layout dates from the original Mirage engine, with the servo rotated 180° to ease packaging the throttle linkage and fuel lines, which feed larger injector jets.

A fuel system improvement came during Jeff’s major landing gear upgrade in 2021. This required removing the wing, allowing enlarging the tank-to-fuselage fuel lines from 3/8- to 1/2-inch diameter plus replacing the stock Glasair 90° bulkhead fittings (where the fuel lines pass from the wings to the fuselage) in favor of mandrel-bent tubing. Seemingly minor, this change eliminated a fundamental stumbling block to achieving sufficient fuel flow.

Also of note, the stock Glasair III fuel system uses two wing tanks, plus a header tank in front of the instrument panel. Not wanting a lap full of fuel, Jeff eliminated the header tank during the plane’s initial build, saying they tend to leak and make working on the avionics more difficult. Jeff has no preference which wing fuel tank he draws from while racing, even admitting that prior to enlarging the fuel lines he did race in the “both” position, a desperate move in a low-wing airplane as it might unport the fuel pickup. It never did and he now runs just fine off of one tank with the enlarged fuel lines.

As for the fuel itself, 100LL was good when naturally aspirated, but his minimum fuel for high-boost operation is the old 115/145 purple avgas, which VP Racing Fuel mixes for Reno racers. VP also developed 160-octane Strega fuel for that P-51 team in the 1980s and several teams run it today, including Jeff for 2023. And what’s “high boost?” At least 85 inches of manifold pressure—likely into the low 90s when pressed.

Ignition

What’s remarkable about Jeff’s ignition system is how stock it is: a pair of Bendix 1200 magnetos timed to 20° in deference to all that manifold pressure, igniting AC Delco twin-electrode iridium spark plugs. Jeff actually has had an SDS electronic ignition system in-house for several years, but wants to run it on a non-race engine first to learn its ways. He hasn’t had the time so far. One ignition curiosity is that the Unlimited folks say the Strega fuel rapidly eats the iridium off the ground electrode and they’re constantly installing new spark plugs. Jeff hasn’t had that issue and runs the same plugs all year. Must have something to do with the huge boost the Merlin boys run.

Wing and Gear Modification

If Jeff did everything he could during his plane’s build to ensure a perfectly formed wing, it was still a stock Glasair III wing fitted with slotted flaps and stock Glasair landing gear. As soon as he began racing the under-wing flap tracks had to go due to their great aero drag, so he bolted the flaps shut and cut off the flap tracks. No other changes were made to Race 39’s wing for years, but entering the COVID era Jeff was suffering gear doors hanging open and the easy fixes weren’t working. A solution came from an unexpected source, Robbie Grove at Grove Aircraft. Unexpected because Robbie and partner Jim Rust from Whirlwind Propellers are direct competitors to Jeff in Sport Gold, running their own very fast Glasair III. But if they’re competitors they’re also part of the tight racing brotherhood, and where Grove and Rust had borrowed many firewall forward ideas from Jeff, they were ready to reciprocate with Grove’s redesigned Glasair landing gear.

Recognizing the stock Glasair III gear was unsuitable at high speeds, Grove had already developed and installed on his Glasair racer a totally new gear door and gear actuation system, retaining the stock Glasair gear legs and not much more. Grove’s goal was to completely enclose the gear when retracted—stock Glasair practice exposes some of the main gear tires—using flat, flush, tightly closed doors held shut with hydraulic pressure. This requires new half forks, hydraulic cylinders, sequencing valves and supporting pieces. But that’s just half of it as the Grove system interferes with the flap linkage and even the aileron linkage. Thus, the flaps must be abandoned and an all-new control system fitted, starting with the control stick, torque tube and extending all the way to a reversing bell crank in the aft fuselage for the elevators!

Grove built the new system for his and Jim Rust’s racer with no intention of offering it as a kit. But they had a few spare hydraulic cylinders (Grove makes his own) and he gave these to Jeff, along with sketches, tooling and other bits so he could replicate the system in Race 39. Installing the Grove gear should take place during the initial build before the wing is joined to the fuselage, not on a flying Glasair. But with the 2020 races canceled due to COVID, Jeff opted to take the huge step of separating the wing from 39’s fuselage to install the Grove gear. With a weary tone Jeff says the wing and gear job, “is a horrifically involved process. The [new] actuator requires a whole new flight control system, and a new fuel system to clear the flight control system. The time to do this is when you’re building; to convert an existing wing involves a lot of demolition. I did a lot of research before we just started hacking away at stuff, but man, I could have built a whole RV.” Yes, but the Grove gear works flawlessly.

While he was there, Jeff could also tend to other details. The bolted-shut flaps were removed and the area glassed-in using hot-wired foam shapes provided by Grove. Also, the stall strips were sanded off and new root fairings developed. Barely finishing in time for the 2021 races, Jeff was pleased to find his plane flew better than ever and to have his gear door issues a thing of the past. He was even more pleased to win convincingly—over Grove and Andrew Findlay—that year, too.

Continuous Improvement

A casual observer might think Race 39 hadn’t changed in years as it’s always worn the same paint job and has seen no highly visible changes such as wing clipping, but Jeff says it’s changed “radically” since he started racing it. Of course there have been many engine improvements over the years, plus the Grove landing gear, and these are not visually apparent from the grandstands.

But what we’ve been missing is Jeff’s tireless pursuit of weight reduction. Built lightly from the beginning, Race 39 has not seen the usual weight creep of developing airplanes thanks to Jeff’s constant efforts. Replacing aluminum and E-glass with carbon fiber is one reason. The cowling, wingtips, gear doors, seatback and belly pan have all gone to carbon, as have other hidden parts. As Jeff was the first Sport racer to dedicate his airplane to racing and give up sport flying it the rest of the year—a highly desirable move almost all his competitors were late to adopt themselves, if ever—this has enabled less weight and arguably greater safety. The nav lights and wiring were removed, the instrument panel pared to the minimum and the cockpit stripped to single-seat utility, all weight-saving moves. Ditching the intercoolers was another big help, as was closing out the flaps, which eliminated the flap structure, hinges, linkage and body filler used to fair in the bolted-shut flaps.

Even Jeff has been amazed at how lightweight his plane has become. When first turbocharged it scaled just over 1700 pounds, but “after COVID and the big mods I thought it might be 1700 pounds and under, but wow, it was 1570 pounds without the water tanks. I was really wondering after glassing the flaps [shut]; before it was always pulling right, but after the wing mod it felt really light and flew straight.”

2023 & Beyond?

With one more Reno race to run, Jeff is still improving. He’s working on downsizing his engine-cooling exhaust tunnels and trying new tailpipes. Different brand turbo wastegates are going on—one failed last year, causing him to mayday out of the Gold race—and there is the usual engine overhaul at Ly-Con yet to go at our deadline. The plane will definitely be a contender at the last-ever Reno speed fest.

After that, the entire sport of air racing faces an unknown future. The Sport class is working on new races around North America—see the Rear Cockpit column—and the Reno organizers are searching for a new venue. Whether these stimulating, expensive, all-out Sport Gold contenders can survive the new order remains to be seen. But, somehow, we don’t think we’ve seen the last of Jeff or heard Race 39 making that delicious, deep thrumming moan as man and machine zoom by at 400-plus mph.

The Woodshed

In our July 2023 issue we stumbled over our own wheel chock in our story on Jeff LaVelle and his Reno-winning Glasair lll. On page 13 in the Multi-time Sport Class Champions sidebar we correctly listed Darryl Greenamyer’s 4 Sport + 5 Unlimited championships, but credited Jon Sharp with just his 4 Sport championships, overlooking his unprecedented 11(!) Formula 1 wins. Kitplanes regrets the oversight, especially as Sharp’s combined 15 Gold wins is the all time Reno win record.
Photos: Tom Wilson and Tim O’Brien (action).

The post La Zoom! appeared first on KITPLANES.

The arrival of the engine also seems to be a common turning point with this type of project, providing a needed boost in builder dedication and the drive for completion. That has been the case for me as well with this one. I have been dreaming and thinking about how the relatively lightweight 220-hp turbo engine will perform in my 750SDX. I want to see this thing in the air!

Putting on Pounds

There are plenty of other small weight gains in the works as well between adding plumbing for fuel and getting the wiring into the wings. Even though I have taken extra time to lighten certain kit parts (as discussed in the previous article in the April 2023 issue), most of those are now being installed. I’m happy to report that it’s coming together really nicely.

Working on this project, I continue to find it truly amazing how far the latest CNC’d kits have come when you compare them to early airplane kits. The CNC final-size match-drilled parts allow you to simply Cleco parts together. Many of them have hole spacings that only allow the part to be put together in the correct position or orientation and it is spectacular to see these pieces go together so precisely without any cutting or drilling required. I’ve been able to leave a lot of my old building tools in the toolbox while doing the basic assembly because they just aren’t needed for the 750SD.

There is really no comparison between the newer Zenith kits and the 701 kit I bought in 2016 (which eventually turned into the Super701). The older kit took a lot of extra time and tools to achieve a similar-quality fit and finish to what I am now getting easily on the 750SD with only a set of Cleco pliers. Remembering how I spent all day building the older rudder and then being able to assemble a rudder from a new kit in only 10 minutes has left me very appreciative of the improvements made by the technology Zenith is now using in manufacturing its kits.

Wing Work

I am getting very close to permanently buttoning up the wings. The fuel system in an airplane is something that needs a great deal of consideration because it has to work, period. I used rubber hoses to plumb the fuel system in the Super701, but am planning to build aluminum fuel lines to connect the wing tanks in the 750SD build.

If done correctly, the aluminum lines should require less maintenance over the life of the airplane whereas hoses would need to be inspected and replaced periodically. The aluminum lines also have a mostly uniform inside diameter even through the fittings. Since sometimes fittings for a rubber hose can have a much smaller diameter port inside the barbed nipple, I am hoping using the aluminum lines will optimize fuel flow in the relatively small-diameter tubes by eliminating that potential bottleneck. In addition, the aluminum lines should have the benefit of being slightly lighter.

I will be running a header tank in the rear fuselage, just like I have done before. All the venting in the tanks will be handled through the vented fuel caps, leaving only one wing tank outlet for the main fuel supply line to the header tank and one small drain/check valve in the bottom of the wing. Although not having an extra vent line running from the header tank back to the wing tank is probably a hot topic, this setup has worked without a glitch in my Super701 for 700 hours and it really helps to keep things simple by eliminating the extra return lines and several connections.

The only other thing required before final assembly of the wings is installing the wiring for navigation, strobe and landing lights. This is a relatively easy task but it is taking some careful planning to install everything correctly through the spars and ribs and to get it all secured properly across the length of the wing. I will be using AeroLEDs lighting, just as I did on the Super701. In my experience, it is an excellent lightweight, bright and effective lighting system that requires less power consumption than most of the older bulbs.

I catch myself thinking a lot about how to make the wiring and plumbing connections as clean as possible, especially where the wings join the fuselage. I have several ideas in mind, but integrating an idea into a finished product can sometimes be a challenge. While I tend to like challenges, I also want to get this thing in the air—and challenges always cost time.

Forward Fuselage Planning

Getting closer to having fully assembled wings is also forcing me to start looking at the forward fuselage again. It is about time to get more things moving along there, like preparing the upper cabin area for the upcoming wing joining. At the moment, the forward fuselage is all Clecoed together and not yet riveted because I am still doing some planning.

On the list of stuff I’m still figuring out in this area are things like the instrument panel, engine mount, controls, seat and several other things. Some of it may require modifications to the cabin frame and other chrome-moly components that I’d like to paint before they are assembled. There is also some work to do with the landing gear, firewall and pedal assembly.

Weight and Balance

While my current focus has been on the wings, once the engine is delivered I will most definitely switch to working on the fuselage. On the top of that task list is figuring out the engine mount and trying to make sure things come out the way I want with the weight and balance of this airplane. I created a weight and balance spreadsheet on my computer and have been crunching all kinds of numbers so I can get the center of gravity positioned just where I want it.

It shouldn’t surprise anyone at this point that I’m aiming for a CG that is optimal for STOL operations. In my opinion, there is a fine line between having the CG optimally located and keeping it just forward of the rear CG limit. Basically, I want this airplane to be right at the rear CG limit when it is loaded in its most aft load configuration—buying myself some “margin” by having the airplane more nose-heavy doesn’t do its STOL performance any favors.

There is an engine mount available for the 750SD/520T combination. However, with my very specific ops in mind, I am looking at custom-building a shorter engine mount in order to move the empty CG back and make this plane handle just the way I want for my mission. ULPower, which makes the mount, has made it work for more of a real-world kind of loading. I have a feeling creating my own mount will involve a lot of work, but I am almost ready to tackle it!

Circuit Breaker System

Pretty soon, I will be looking at the interior and working on things like seats, controls, the door assembly, the instrument panel and electrical system. Among the growing pile of electronics on the back workbench waiting to be installed is a Vertical Power electronic circuit breaker system. I am excited about this particular system because I have used it before on the Super701 and it definitely helps to clean up the instrument panel real estate and the wiring.

The Vertical Power system eliminates the need for a bunch of individual mechanical circuit breakers and many of the switches by replacing them with one small, remotely mounted solid-state module controlled through the EFIS. From the EFIS screen, you can monitor the current (amps) of each electronic device, reset any circuit and also turn circuits on and off without the need for any external switches or breakers.

The Vertical Power website has a very thorough planning tool that works great for electrical systems. Once you plug in all your desired electronics and enter the parameters for each device, the tool will configure it and give you a map of how to put everything together. This even includes wire sizing, pinouts and planning for the connectors. The online planner creates a config file for you to download that will program all of your preplanned parameters into the Vertical Power system and configure it, eliminating the need to sit in the cockpit pondering how to integrate everything. I can’t say enough good things about this system. It has performed amazingly well in my Super701 and I am looking forward to continuing that trend with another VP-X in the 750SDX.

Taking Advantage of Show Season

I plan to be at Sun ’n Fun  2023, where I will talk with vendors such as Beringer, DUC Propellers, Garmin and Levil Aviation in hopes of figuring out exactly what I need to complete this project and securing the products necessary to keep it moving along. If you are looking at building an airplane, I highly recommend you to go to shows like SnF and AirVenture to check out all the planes and vendors and to talk with other builders and flying enthusiasts. There is a huge wealth of knowledge—and also some extra motivation—at these events to help you get going with your own project.

Videos of Humberd’s builds—and some of the fun that can be had with flying a STOL airplane—can be found at www.youtube.com/@TNFlyingFarmer.

The post Building the 750SD XTREME: Part 6 appeared first on KITPLANES.

The good news is that the dreary weather has made for some consistently long days in the hangar making great progress on the Hummingbird. I am beginning to get optimistic about an early spring 2023 completion—if I don’t cause any more problems for myself. Did I tell you I cracked the left windshield while installing it? A new set cost $1800! I realized why when I saw the part number was for a Bell helicopter. I like the idea that the Hummingbird is stout and made with a lot of FAA/PMA parts, but I did forget about the pricing that comes with that. I was very careful cutting and installing the new ones and managed to get them completed without any problems, except for a lot of stress!

Engine and Avionics Update

Lycoming completed my Thunderbolt engine in December, as promised. I will detail all of that in a future update, but suffice it to say that I had it completely installed and ready to run and decided to remove the exhaust system and have it ceramic coated to help get rid of some heat. I saw a picture of a recently completed Hummingbird in flight at dusk and the exhaust system was glowing red! I’ve seen turbocharged engines do that in a test cell, but not normally aspirated engines. Perhaps it is due to the engine running at 3200 rpm in the helicopter, as well as there not being the same amount of cooling air going over the exhaust system as in a more tightly cowled aircraft installation. I don’t really know, but I do know it is best to have the exhaust ceramic coated before it is used.

Speaking of heat, there weren’t any provisions for cabin heat. So, I sent the mufflers off to Vetterman Exhaust and Clint Busenitz welded some fittings on the muffler and installed a heat muff.

The other good thing is that Advanced Flight Systems delivered on the promise to code some software to display the transmission oil pressure on the EFIS. I really didn’t want an analog oil pressure gauge on the panel.

I also managed to get all the electrical completed. The Advanced Control Module and associated components were all installed, and then the instrument panels were sent off to AFS for powder coating and labeling. They came back looking beautiful, were accompanied with the long-awaited AF-6600 EFIS and now are completely installed. Everything powered up without any smoke, and I even have traffic displaying on the screen in the hangar! Seeing everything working was quite motivational, especially since I ran many individual wires, such as the intercom and engine sensors. I must admit I did install the wrong wire from the EMS to the manifold pressure sensor but realized that as soon as I powered it up, as there was no value displayed. It was a quick fix, and I sure felt relieved.

Fuel System and Interior

Toward the end of any aircraft I’ve built, it seems like the need for project management and forward thinking increases dramatically. Some things need to get done in an order such that they don’t cause delays in other areas. Paint and interior seem to cause a lot of consternation. The interior certainly needs to be built and then taken completely apart to paint those pieces that aren’t covered. Even the painting process for the outside of the aircraft seems to take some planning.

To start the interior required completing the fuel cell. On the Hummingbird, the fuel tank is a large 57-gallon bladder underneath the rear seats. It is protected by sheets of Conolite on the bottom and sides to help prevent a puncture in the event of an accident. Once all of that was installed, the fuel cell area was cleaned, vacuumed and wiped multiple times. You don’t want any metal shavings or rivet stems abrading the rubber bladder. Then, all seams and protrusions, such as rivet heads, bolt heads and nuts, were generously covered in multiple layers with very high-quality duct tape. I used almost two complete very large rolls. Then, some very strong Velcro pieces were added to the tops and sides of the cell that matched the Velcro on the bladder. The Velcro holds the fuel bladder in place and keeps it from collapsing when it is empty.

Next, it was time to close out the fuel cell. I installed the float-type quantity sensor and adjusted it for the best low-quantity reading. The instructions called for cork gaskets and Permatex for all of the access panels to the fuel cells, including the sensor, but I used Pro-Seal without gaskets instead. My experience is that the cork and Pro-Seal seem to dry out over time and leak. I haven’t put any fuel in it yet, as I plan to calibrate the sensor when I do that.

One of the main contributions to accidents in the amateur-built aircraft world is modification of the fuel system. As a DAR I always ask if any modifications have been made. In this case, I admit that I have made one modification, as I added the ability to remotely turn the fuel supply off. Since the fuel tank is at the aft end of the cabin, and there is only one tank, there are no fuel lines to route to a fuel-selector valve. There’s no sense routing fuel lines unnecessarily, but I wanted the ability to turn the fuel off in case of an accident and for maintenance. In this installation the fuel was routed from the bottom of the tank at the rear of the aircraft directly to the gascolator on the aft side of the firewall. It was simple enough to place a high-quality cutoff valve right where the connection is made to the sump. I worked out the geometry on the bench such that the slipstream and cable are always working to keep it in the open position.

There are a lot of cables routed on the exterior bottom of the cabin, such as brake lines, control cables, throttle/mixture, etc. Again, the gantry crane I’ve mentioned in earlier columns came in very handy. The cabin sits pretty low to the ground, so lying underneath it was not very comfortable. Raising it using the gantry crane made the work very easy, including installing the chin windows, parking brake and landing lights. Yes, I added a parking brake, which I intend to use for rotor start-up and shutdown. Since this helicopter is on wheels, not skids, the initial torque at rotor engagement will cause the nose to turn without using the brakes. As a funny side note, I don’t think I ever broke the habit of stepping on the pedals in the Hughes 269 helicopter whenever I started the engine, even though it was on skids and had no brakes. Some habits die hard from flying fixed-wing aircraft. Now, it will seem natural to check the brakes.

Once everything was installed we took the time to make templates for the interior panels and carpet, allowing Carol to get started on fabricating them. The cabin is huge, so it required a number of complex panels in order to have an organized installation process.

Another area that I needed to address was cockpit ventilation. Yes, we can fly it with the doors off, which is a lot of fun in a helicopter, but there’s a good portion of the time that the doors remain installed, and that huge bubble canopy makes for a really hot cabin on sunny days. Luckily, I had two Snapvents left over from an earlier project, as that company doesn’t seem to be in business any longer; they don’t answer the phone and every distributor shows them as indefinite backorder. I will install the two I have in the front door windows, and I added sidewall vents from Van’s Aircraft on each of the doors. I also designed the cabin heat system so that I can route cool air through it in the summer months.

I painted the interior of the doors first, so that I could get the plexiglass installed. When installing plexiglass, don’t forget to use a plexiglass drill bit, and drill the hole larger than the diameter of the fastener so that there is room for expansion. Otherwise, there’s a high probability that it will crack.

Painting the Tail Cone. Again.

In Part 4, I mentioned that I had painted the tail cone, but I wasn’t happy with the way it turned out. It’s my own fault, as this was the first time I was using Superflite paint. I’ve painted all my own aircraft over the years, but painting is one of those skills that deteriorates if you don’t use it regularly. Once every five to six years is probably not enough and coupled with a different brand of paint than I had previously used, it showed. As I progressed through painting the rest of the aircraft, my results improved. Unfortunately, that tail cone was staring us in the face as we walked by it every time on our way to the hangar. Carol was kind enough to not say anything, but I knew she wanted to.

Then a lightbulb went off, or on, as I should say. I thought we had lit up the paint booth well and had even added some extra lights outside the booth shining into the windows. But the paint was black, and it was hard to see. Perhaps it’s my old eyes, and I’ll use that as an excuse, but I decided to try something different. The bottom of the cabin was going to be quite hard to paint, and I was wrestling with how to do it. The gantry crane process I had been using to work underneath it was not going to work in the paint booth, so I decided I needed to raise it another way. Brad Clark mentioned that pumping the struts up all the way would help, and I decided that jacking it just a little higher would even be better. I figured out a way to do that, but it still left me with the hard-to-see black paint.

I needed more light and it had to be underneath the helicopter. I don’t know when it hit me, but the brightest light I know is the sun. So, one evening when the weather conditions were perfect—no wind, low humidity, no bugs, etc.—we placed a big tarp on the taxiway, and as the sun got lower on the horizon it lit up the bottom of the cabin beautifully. I managed to get a gorgeous paint job on the bottom that exceed my expectations. The trick was the light, so we found the brightest LED cone lights we could find for the booth, and it made a huge difference.

I know you are wondering, and yes, I sanded down the tail cone and repainted it in the booth with all the extra lighting. It’s gorgeous now, too.

From there we proceeded to paint the red and silver on the rest of the aircraft. Painting is very time-consuming and tedious work, especially with multiple colors. You end up going through a lot of consumables, such as tape, masking paper and filters, coupled with a lot of extra time cleaning the booth between colors. Carol is ruthless about cleaning the booth, and it really makes a difference. I do wear paint suits, along with a fresh-air breathing system, gloves and head covers, so no skin is exposed. It’s kind of cumbersome in the booth dragging the hoses around and trying not to bump into the pieces as you paint them. Carol stays outside the booth and constantly drains the compressor of any moisture every few minutes, even though I have moisture traps and in-line desiccant filters.

While it’s not perfect, we are pleased with the results. It looks so different now that it is painted, but it’s also added to the stress of being more careful to not scratch anything.

Next update I will highlight the engine installation for you, and by then the engine should be making good noises. I’ve even started the paperwork for an airworthiness inspection, just to keep the fun factor alive. Did I tell you we received the registration? The FAA completed it in less than 10 days. I had heard they give new amateur-built applications a sense of urgency, and I was shocked at the turnaround. The Hummingbird is a model 300L, so we have N300VC, a 300 for Vic and Carol.

The post Building the ‘Beater – Part 5 appeared first on KITPLANES.

Question:

Answer: The regulations do not differentiate between gliders with or without an engine. There should be no problem with adding an engine as you propose. However, since this will be a very major modification, you should talk with your local FSDO or proposed DAR and see how they want to handle it. You will definitely need to submit a new airworthiness application because of the “change of engine type” aspects of this modification.

Question: I bought a Sonex that was completed in 2007. The builder received the initial airworthiness certificate but passed away four days later. The aircraft was never flown and one year later the family donated it to a museum where it sat until being given away in 2022. It was then sold to me a month later. I’ve been able to transfer registration and ownership but all builder’s logs have been lost long ago. Can this aircraft ever be certified for flight without any documentation of the build?

Answer: I’m not sure I understand the question. If the original airworthiness certificate was issued then the airplane is certified for flight. The only reason you would need the build documentation would be to apply for the repairman certificate, but you are not eligible for that anyway. Depending on your location, you may need to have the operating limitations amended to change the flight test area for Phase I. Also the airplane will need a current condition inspection before flight.

Question: When you’re looking at an airplane of a known design and the builder has decided to increase the maximum gross weight above the factory’s number, what is your response? Do you approve this because he’s the builder? Do you ask for documentation? Do you tell him tough luck?

Answer: Typically I ask to see documentation. If he cannot provide some kind of engineering documentation, I will discuss how he justifies such a change. If he cannot convince me that the increase is safe, I will ask him to redo the weight and balance to match the designer’s limits. What he does after I leave is between the builder and the FAA. I have no control after certification. I only have what I approved (with backup data in my records).

Question: What date of manufacture is used on the E-LSA Airworthiness Certificate 8130-6 application and on the aircraft data plate? Must the date of manufacture listed on the Statement of Compliance (Box 4) be used or may I use the date close to the date I expect DAR airworthiness issuance? The date on the Statement of Compliance 8130-15 from Van’s Aircraft for my RV-12 is the date they signed this statement.

Answer: For kitbuilt E-LSAs, the date the airworthiness certificate is issued is the date of manufacture for aircraft. This information is not required on the data plate. The only information required on the data plate is make (for E-LSAs this is the kit manufacturer), model (this is the model designated by the kit manufacturer) and serial number (this is designated by the kit manufacturer).

The post Sailplane to Motorglider, Museum Rescue, Gross Weight Change appeared first on KITPLANES.

Just like every other metal-aircraft builder, I have had to develop fiberglass skills—doing layups, filling pinholes and smoothing out contours with resin and micro (or other fillers). It’s a love/hate relationship. I actually love the fact that you can do pretty much anything with fiberglass—and if you aren’t happy with the results, you can “erase” it with a sanding tool and start again. But I simply hate the mess and the repetitive nature of sanding, filling, sanding, filling…ad infinitum.

I have had to make composite tips (tail and wing) fit by cutting and re-bonding. I have had to fix warped parts with  filler and lots of sanding. And I have performed major surgery on cowls and fairings to get the air to move past discontinuities properly. It’s just part of the road to finishing—a road with few shortcuts. Unless you know a good glass airplane builder who will trade you their skills for a nice set of engine baffles.

Today’s Challenge

So what prompted this particular set of musings on the “joys” of composite work? Well, it turned out that the cowling for our eXenos project needed to be lengthened as part of the process of mounting a completely different powerplant than what the original design called for.

Why? It’s the pain of being an early adopter. As one, I received an engine mount for the electric propulsion system that was longer than intended. Bad news for me but the good news is that all of the production versions will be the correct length to allow use of the standard, unmodified Xenos cowling. Progress!

When all was said and done, with the early, too-long motor/battery mount and installing the electrics, the stock cowling was about 2.5 inches short of reaching the firewall when the front was butted up against the back of the propeller. Rather than wait for the new mount, we modified the cowling.

While we could have attached the cowling to the firewall and done considerable re-contouring up front, the thought of forming shapes in foam and reworking contour lines lost out to the simple task of bonding in flat strips on the sides and bottom to match the slab nature of the fuselage. We had to do some work to make the curved top fit properly, but at least we could do that without making molds.

So let’s take a walk through the process we used to lengthen the cowling for this project. You will be tempted to say, “Hang on, this simply isn’t relevant to me. I am going completely stock and my factory cowl will fit perfectly!” Let me point out that a lot of metal airplane builders over-trim their stock cowl and end up making it too short—so they need to add some back in. Why does this happen? Composite cowlings are a little like octopus skins—they keep changing shape until they are in their absolute final position. So trimming a little that seems just right when the cowl is not in its final position often means you end up a quarter-inch too short. It doesn’t fit until it, uh, doesn’t fit! Love/hate, remember?

Establishing “Truth”

In many airplanes, both the fuselage and the cowling are tapering toward the nose, so getting a good fit is not always easy. Tapers and compound curves are hard to fit. Add to that the fact that most cowls are split—either top to bottom or side to side (ours is side to side). As a result, you quickly find that the cowling doesn’t want to hold any particular shape until it is actually mounted—but you can’t mount it until you freeze the shape. Catch 22. (If you caught Larry Larson’s multipart series in our March, April and May 2023 issues on fitting the RV cowling, you know part of the story already.)

The way to deal with this is to figure out how to establish a baseline, a “truth,” if you will. Once you pin the cowling in a specific position, you can then adjust from there to get a good fit. With a cowling that is too short, the problem is compounded because it is literally floating in space until you lengthen it somewhere.

For our project, the slab side of the fuselage provided a good place to establish truth, so the first point of attack was to add some material to the back edge of the sides. Once we added material to the sides, we could trim and fit those to where it could be Clecoed in place. Then we could deal with the curved top or the flat bottom—whichever seemed more appropriate when we got to that point. But once the sides we pinned, we had truth and everything else could be adjusted to fit.

Lengthening With Scarf Joints

How do you add material? Well when it is flat, it’s pretty easy—you start with a scarf joint. What this means is that you want to taper the surface to which you want to attach the new material. An aggressive sanding disk on an angle grinder or hand sander will generally do the trick. We laid the cowl on the workbench, outside down, then ran the sander along the edge, tapering it to a fine knife edge. With a layer of gelcoat on the outside, this was easy—you could tell that you were down to the knife edge when you saw the white appear. We then tapered the joint in about an inch, uncovering the layers of the original cowl like sedimentary rock on the edge of a reservoir. This taper is the key to a good scarf joint—the added material will be tapered in the opposite direction and the overall thickness will remain the same all the way from the old part to the new part, with the outside edges lining up due to the knife-edge taper.

With the joint prepared, I now needed a mold—this was nothing but a backing surface that was straight and flat, covered in something to which the fiberglass resin wouldn’t bond. Plastic sheeting or clear packing tape is good for this. I found a nice flat piece of particle board in my scrap bin, laid it on the workbench, then laid the cowl “side down” on that, leaving sufficient board sticking out to add the 3 inches of glass that I needed. I then drilled a couple of #40 holes in the cowl and through into the board and used silver Clecoes to hold the cowl to the board.

Yes, I’m drilling extra holes in the cowling I won’t need later. Not a big deal. You are going to be doing a lot of finishing and filling on the cowl anyway so filling a couple of tiny holes is in the noise. Make your job easier—fasten things down now and fill the holes later. It’s really better this way.

With the cowl and mold prepared, it was time to cut some fabric and make a mess! I used a roll of BID (bidirectional) cloth and cut progressively narrower layers—because I wanted an overlap of 3 inches, I started with two layers 3 inches wide, then one layer 3.5 inches wide, another 4 inches wide, one more 4.5 inches wide and then, finally, one 5 inches wide. This gave me a taper to match the scarf on the existing cowl. This bundle of layups went on plastic sheeting to be saturated by activated resin, another layer of plastic, complete wetting out of the matrix and finally, application to the cowl and the mold sheet. A layer of Dacron peel-ply finished it off, with a final squeegeeing of excess resin.

Curing time complete, it was a simple matter of separating the peel ply from one side, then popping the cowl with its new 3-inch extension off of the mold. I now had 3 more inches to work with on the sides (I repeated the process for the other half of the cowl of course).

Now came the usual fit/trim cycle—using the back of the prop as “truth,” I trimmed the new back edge (on each side) until it was close enough to Cleco to the cowling’s attach points (in this case, hinges). Two holes drilled for silver Clecoes held each side rigidly in position so that I could continue trimming and fitting, eventually drilling all of the holes to the attaching hinges. I now had the cowl positioned so that I could work on the top. The bottom was going to be a simple job and its final position might depend on how the top turned out, so I left it for last.

Getting in Deeper

Creating the curved extension on the top was similar to the process for the sides, except that the “mold” needed to be curved to follow the contours of the existing cowl. A curved backing isn’t all that hard to create, however, so long as you’re dealing with a single curvature—or something close to it. I suspect that there is a bit of compound curving going on with the Sonex cowl, but it was small enough that we could get away with using a piece of heavy poster board for the curved mold, taping it securely to the outside of the top portion of the cowl, then laying the material into it. Care had to be taken in trimming because this truly is a case of “it doesn’t fit until it fits,” so you have to sneak up on the final trim.

Once the sides and top were more or less in place, we fit the center seam—which, in all the perversity of working with fiberglass, now had a gap that had to be filled. We did this to a final fit by building a “bridge” of scrap aluminum, Clecoed in place on the outside after covering it with packing tape. Working inside the joined cowl, I laid in the necessary glass to re-joint the two halves. When it was all set, the entire cowl gets Clecoed back in place to check the fit, then split the cowl down the middle, leaving the specified 1/16-inch gap. You’ll see in the pictures that we made a strip of aluminum match-drilled to our hinge and used that on the outside instead of trying to use the hinge on the inside during all this fitting. The same thing was done on the bottom.

Finally, the bottom needed to be extended and, again, this was as simple as the sides. With some rough trimming and aluminum splices holding the bottom center seam together, we simply added 4 inches to the back of the bottom, then trimmed to fit. Since an exit is required for cooling air, we simply didn’t do the extension in the middle area as shown on the plans and finished the back with hinge material as per the standard Sonex design. We now had a cowl that fit all the way around and matched the fuselage nicely.

One Step at a Time

When first faced with a project like lengthening a cowl, it seems like a daunting challenge and trying to figure out how it is all going to fit is a puzzle. But just like all aircraft building, you have to stop trying to look at the whole picture at once—you need to break the project down into single steps. Determine how much you have to add all around and add some margin for error—maybe 20%–25%. Figure out the easiest place to add material so that you can “pin” the project in position to figure out the next step. Scarf your joining surface. Prepare your layout. Saturate with resin. Lay it in place. Let it cure. Then mount and trim to fit. Now begin the next area.

It isn’t all that hard, just messy. But so is drilling lots of repetitive holes or spraying metal primer—or if you’re doing tube and fabric, sanding all that area again and again! If you’re a wood builder, tell me about all those rib pieces and gussets! Airplane building is messy, no matter the material. In the case of fiberglass, wear old clothes, cover anything in the shop that doesn’t react well to dust and find yourself a good set of safety glasses and a dust mask. Then have at it!

And as I said at the start—if you don’t like the results, sand or cut them away and start again. That’s the beauty of non-structural fiberglass work—it’s all art and it can all be fixed.

The post Love and Hate appeared first on KITPLANES.