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VW-Powered Single Seat, All-Metal Aircraft at AirVenture 2010

Story and photos by Rob Wyland, EAA 766676, rmwyland@gmail.com

Ultra Cruiser Plus, Hummel H5, RV-6
Near to far: Neil Byers’ Ultra Cruiser Plus, Terry Hallett’s UCP Sport (Hummel H5) and
Charles Dunlap’s rotary-powered RV-6, which has nothing to do with this article, but we thought it was still worth mentioning.

I must admit to having a bit of a love affair with single-seat Volkswagen auto conversion powered airplanes, particularly the classics like the Taylor monoplane, Jodel D9, and the Druine Turbulent. To me, these planes are the essence of what homebuilt sport flying is about: simple, economical, and fun. The downside is that they’re small in every way, and I probably would never fit in one. So I bought a more modern classic of the genre, a partially completed Corby Starlet.

However, I have come to doubt my ability to match the tenacity of the pioneer homebuilders to finish a plans-built craft, or to fit my increasingly large and overweight body into the plane. So while I should really finish my Starlet project, my eyes have strayed to more modern metal construction, more detailed construction plans, and kits or partial kits that still encompass the design philosophy of a single-seat VW-powered plane.

I’m not alone. There seems to be a rebirth of single-seat VW-powered planes, yet with modern popular aluminum sheet metal construction. Don’t get me wrong; single-seat VW planes have been around continuously since the early 1950s, some even in sheet metal (such as the Teenie Two, Mini Coupe and Quail). However, this new crop has taken advantage of the larger displacement VW conversions, pulled rivets, AL 6061 construction, and in some cases, computer-assisted designs. This gives them higher performance, more useful load, easier builds, lower maintenance, and larger cockpits.

The designs I saw at EAA AirVenture Oshkosh 2010 are Bruce King’s BK 1.3, David Thatcher’s CX4, Morry Hummel’s H5, and the Onex by Sonex. All these designs are sport pilot eligible, have a gross weight of 850 pounds, and are taildraggers. I developed my impressions of each model by either sitting in on a presentation or talking directly with the company representative.

BK Flier
Photo credit: Bruce King

Bruce King BK Flier 1.3
This Bruce King BK Flier 1.3 (BK 1 was featured in the January 2007 Air and Space) is the most beautiful out of this bunch to me. I think it has to do with the solid flush rivets and the tapered wings. What’s not to like about tapered wings, other than the difficulty of making ribs that are each a different size and tapered spars? Actually I think this is one of the most unique features about this plane.

BK Airfoil
I mustered the nerve to directly ask Bruce King, the designer, why the Clark Y airfoil he used on the plane looked as if the middle section was stretched with straight segments in the middle of it to increase the chord length. He explained that is exactly what he did. I looked puzzled, and he explained his ingenious plan. This wing form means the chord length/chord depth ratio is greater at the inboard end, causing it to stall first (since the stall angle of attack is related to the length/depth ratio). Thus without having to incorporate washout in the wing, he gets desirable stall characteristics and a wing that is easy to build because it has a spar of constant depth and a flat-bottomed airfoil that can be built on a flat table. I asked about the discontinuity in the airfoil at the “stretched” section. King chuckled and said, “It flies great, and I don’t think the airfoil is that sensitive at these sub-Mach speeds.”

Photo courtesy Cornelius Braun
Photo courtesy: Cornelius Braun

This plane appears to be a great design, simple to build with great plans and detailed instructions. Bruce’s Beta Builders, about eight of them, are on the verge of completing their planes, so the claims about the aircraft will soon be verified. King has intentions to sell not just the plans, but also to manufacture the more difficult-to-build parts. www.BKFliers.com

Click for larger image

David Thatcher, designer of the Thatcher CX4, pilots serial number one over Lake Hancock, Florida, during the 2008 Sun ’n Fun Fly-In at Lakeland, Florida, while EAA Chief Photographer Jim Koepnick squeezes the shutter. Photo plane pilot: Bruce Moore.

Thatcher CX4
The Thatcher CX4 was featured in EAA Sport Aviation and several times in Experimenter, as well as the cover story for CONTACT! Magazine, and it sure is a beauty. It’s the longest of the bunch, thus less short coupled which probably accounts for its docile ground handling, confirmed by those who have flown it, including a young 17-year-old sub-80-hour (four hours of tail wheel) pilot. The CX4 is slender all around, not only in fuselage but in wing plan as well.


This VW-powered plane is one of the few to incorporate a sliding canopy which lends it an air of sophistication found in higher-end planes. This design has many builder completions already, strong builder support and community, and prefab parts available through licensee Peter Beck. In fact, this is about as close as you can come to a kit plane without it being a kit plane. The mere fact that so many people have jumped on this bandwagon and been successful says volumes about this aircraft. It is reportedly easy to build, has great plans, performs well, and it can be built inexpensively.

Click for larger image

My only hesitation is that the plane seems to be coming out with less of a useful load than originally hoped for. Builders are getting empty weights in the high 500s, some eclipsing 600 pounds, making the useful load between 250 and 300 pounds. That range is still workable for most of us when you consider this plane has a VW engine which isn’t going to suck up too much gas and has only a 9-gallon fuel capacity. Thatcher sure knew what he was doing when he built and designed the CX4. This is a beautiful and fun plane that anyone should be able to fly. www.ThatcherCX4.com


Hummel H5
The features of the Hummel H5 (a creation of the late Morry Hummel and recently reviewed in KITPLANES) that stand out to me are the large wing with a fat airfoil, telescoping landing gear, and the fighterlike canopy. The surprises for me are the comfort in the cockpit, a bed-mounted engine, all push-pull rod controls, and the extreme lightness of the design.

H5 Engine

H5 Cockpit

H5 Engine

The narrow canopy gives it a bit of a fighter look and also gives the false impression that there won’t be much room inside the cockpit, yet when I sat inside, it was very roomy and provided an adjustable seatback. Even with the seat in the most upright position that I prefer, I still had a hands-width of space on top of my six-foot height, which is impressive, considering that I have a very long torso and neck.

The round fuselage cross section makes for plenty of elbow and shoulder room contributing to the plane’s overall comfort. One unusual feature was the rather large-diameter push-pull rod for the rudder running on the left side of the cockpit, which looked even larger as the rod was wrapped partly in pipe insulation.

H5 Engine Installation
I was surprised to see the engine was bed-mounted. Not many VWs are mounted by this method. This installation, an integral part of the fuselage (the lower half of the cowl isn’t removable), looked light yet difficult to construct with its unusual shape and use of solid rivets.

Landing gear

The landing gear employs oleo struts mounted wide at the end of the straight wing center section, one of my favorite configurations. However, the landing gear wheels and brakes look extremely light, and I wonder what kind of abuse it could withstand. All the lightness of construction appears to have paid off with a sub-500-pound empty weight and a useful load of over 350 pounds. I would be tempted to change some things for durability’s sake at the expense of useful load. The plans and kits are ready to go, so no waiting here. www.FlyHummel.com


Sonex Onex
The Onex (pronounced “One-X”) was the plane that I was most excited about seeing, even though the prototype isn’t quite complete. I really am in love with the folding-wing concept and particularly the Onex’s method of folding the wing up like the WWII Corsairs. The folding-wing concept has been around a long time, and the British in particular had many lightplane designs utilizing this feature during the ’30s. I guess hangar space was at a premium then, just as it is now. The Onex’s wing fold was simple, quick, and solid feeling.

Onex wing fold

The wing has a center section with no dihedral out to the wing hinge point, and then all the dihedral is incorporated into the wing from that junction. The aileron control linkage at the fold  is achieved with two mating bell horns, each with two push-push paddles and gap adjusters. To fold the wing, you release a locking lever. Pull another larger lever and the wings fold up, taking less than 30 seconds. It’s truly a functional foldable wing. It will definitely not create the thought, “Do I really want to spend the time to fold the wing?” Beyond the folding wing, the plane is straightforward Sonex, and in fact it looks like a narrower version of the popular two-seater.

The wing fold is quick and simple as shown in this video.

I easily fit in the Onex’s cockpit which is about 27 inches wide, and the mock canopy cover indicated I would have plenty of headroom. I would consider taking advantage of this generous headroom to install seatback padding to bring me to a more upright seating position, as I don’t like a highly reclined seat position. But I understand this has already been modified on the prototype as a result of feedback gathered at AirVenture. While Jeremy Monnett was cautious about kit release date, saying it’s approximately one year from now, I’m anxious to see it come to fruition and find what the kits really end up selling for. Official word from Sonex is, " t will be available just as soon as it’s ready."

There sure is a part of me that wishes there wasn’t a Corby Starlet in the garage waiting for me to finish it, as I sure would like to have one of these all-metal VW-powered single seaters parked in there instead. Time will determine if there really is a market for such a thing. The main drawback I hear cited is that you can’t get checked out by a certificated flight instructor sitting next to you before you take off for the first time, and there’s no room for a friend. Yet this is the ultimate economic (aka cheap!) way to satiate the selfish desire to fly for the fun of it. This type of plane has been around for a half century, and it’s a good bet there’s still some mileage left in the genre.

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