Kitfox Model IV with Corvair mount

Note, new picture added two thirds of the way down….


This weekend, 3,000 cc Corvair builder Thomas DeBusk drove down from Virgina with a friend and his Kitfox Model IV fuselage. We had planned this for a while. We had first spoken about it all the way back at Corvair College #16, but what really got things in high gear was Thomas running his 3,000 cc Corvair at College #19, and all of a sudden he got a look at the light at the end of his building tunnel. It was still far off, but he could certainly look at his running engine and a lot clearer picture of his plane getting done.

Below are a couple of photos I shot of his plane in my workshop on Saturday morning. The project took all day and a chunk of the next because we have no tooling or fixture to make this mount, everything had to be developed from scratch. The good part is that it was very easy to picture how this aircraft is going to climb like a homesick angel with 120 hp on tap. The Model IV is an earlier, smaller model, significantly lighter than modern Kitfoxes. The Corvair is right on the upper limit of weight for the airframe, but we were able to preserve the CG of the plane by backing the engine right up to the firewall. This was made possible by using a Reverse Gold Oil Filter Housing, normally only seen on Cleanex and Waiex installations. The additional weight of the engine is offset by Thomas being in excellent shape. If he was a boxer, he would fight as a super welterweight. In the big picture, he is going to have a very smooth running hot rod, in correct CG, with a useful load that makes practical sense for his weight and the smaller dimensions of the Model IV cabin.


Above, we built the mount directly on the fuselage, seen upside down in this photo. Vern is laying don a bead, Thomas is in the middle, and his friend Mark is on the left.


Above, Vern in a close up of the inverted mount. All of the welding we do is high quality TIG. Note the very unusual layout of the mount. It took a while to figure this out: It is a standard tray with a lot of 5/8-.058″ elements, and two 3/4-.049″ compression legs. We added the lower lug to the airframe. It may look heavy, but it is hollow, a 7/8-.058″ tube with a hidden internal NAS nut. What makes the Kitfox unusual is the lack of mounting points on the lower longeron corners. The rudder pedals actually stick past the lower ends of the fuselage structure and are housed in pedal boxes, thus the mount only has one central lower lug. The design checked out when we loaded it to 5 Gs; the deflection on the tray was only .016″.


Another angle of the top mount. The 16 x 30′ workshop is adjacent to our 40 x 50′ hangar. The hangar is a basic wood framed metal clad building. It isn’t open to the elements, but it has no measurable insulation “R” value either. Big projects and all cleaning are done in the hangar. In reasonable weather (50F to 90F), working in the hangar is nice, I like to be “outdoors” for a lot of the working day. For most welding and fine work, we function in the climate controlled workshop. It has a 4′ x 5′ hinged hatch in the end wall which makes it easy to bring something big like a fuselage inside. Looking at the photos, I can tell it’s time to take 3 hours off and clean the shop.


Above is a shot of a welded cluster on the fuselage. All Kitfoxes are MIG welded. Nothing wrong with this if it is done correctly. This particular fuselage was made in 2005. It is one of the last ones made by “Skystar.” While many people think “Kitfox, they have been around since the 1980s,” this isn’t exactly true. The name has had three distinctly different owners. Skystar, the middle owner, had two phases themselves. The current owners are good people whom we know. They run a solid operation.

If you look at the joint, there are a number of places that were missed on welding. Plenty of Kitfoxes have flown this way, and this isn’t related to MIG welding. This is indifferent quality control at the factory. This particular fuselage had to be retrieved as an asset by the original buyer from Skystar’s bankruptcy. To get a picture of the limitations of magazines in our industry, read the Wikipedia page on Kitfox history, then go to your stack of old magazines from the same year, and note how almost nothing was said about the early versions of the company tanking. Part of this is because the magazines had long lead times (loads of glowing articles hit the newsstands the month after the company in the article went Chapter 11), but the other half of the story was that “journalists” didn’t ask any questions as long as the company was buying $4,000/month full-page color ads.

I don’t point this stuff out to make builders cynical or depressed, I do it so that you understand that the only person who is looking out for you the builder in this industry is you. Do some homework: develop a handful of trusted friends with more experience; recognize aviation’s versions of “too good to be true.”


Not a perfect picture, but it gives an idea of what a MIG weld on thin wall 4130 looks like. This is done by a technique called “pulsing,” where the operator repeatedly taps the trigger to form the ringlets in the weld. Conventionally switched equipment didn’t like this pulsing; MIG welders since the early 1990s are not bothered by it. I don’t recommend that people new to welding try to use a MIG on their project. It is the wrong tool in the hands of a beginner. Most new people using them produce brittle welds by letting the puddle cool too fast. (You can slow this by using bigger beads and having more mass in the weld than the surrounding tubing area.)


Above, mock up engine sits on the mount so we can develop the special intake manifold for this installation. Thomas is planning on a Rotec or Ellison carb which will be mounted horizontally under the engine. I don’t view the Kitfox IV as a big untapped market, this may be the only installation we do. The project got one big step closer to being done, and I look forward to having Thomas among the Corvair flyers. 

On the Internet you can find a steady stream of negative comments about me and my work with Corvairs from a vocal minority that have two common traits: they have never met me, and they have never assisted another builder in learning or achieving anything. While occasionally annoying, it doesn’t have much credibility. Any reasonable person can review my Web sites and find 100 stories much like Thomas DeBusk’s that define my work as a valuable contributor to real homebuilders. Do I deserve some special award for this? Yes, and I already have it….the real friendship of a great number of quality people like Thomas.

Blast from the past: Thomas at Corvair College #19. The caption below the photo is from the event in 2010.

Thomas DeBusk, above, with his very potent powerplant that will find a home on the front of his Kitfox Model IV. While it was running, we had a chuckle over the old wives’ tales that Corvairs are heavy engines that don’t make enough power. Thomas’ engine is the absolute upper limit of power for a Kitfox Model IV. Anyone who saw it in person would never question its performance potential in that airframe. The engine is a 3 liter with a Roy bearing, Falcon heads and a Reverse gold oil system.


Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.