A chat with Ron Dixon

It is quite fortunate (for me) that probably the foremost active authority on the MiniCoupe, Ron Dixon, lives only an hour or so away up in Maryland.  Ron sells the MiniCoupe plans and was kind enough to offer me an hour or so to crawl around his MiniCoupe – after nearly forty years, his is now getting a bit long in the tooth, but remains an active flier, sharing flight time with Ron’s other bird, a good-looking Luscombe 8A now sporting a new wind-generator. 

After an hour or so of get-acquainted chit-chat, Ron invited me across the runway of the quiet Maryland airport to the isolated hanger where his MiniCoupe relaxes, along with assorted spare aircraft parts, propellers, tools and even a Teenie Two fuselage.  I weigh around 250lbs and my first concern was whether I’d even fit in the Coupe, but Ron without more ado assured me; “you’ll fit…” Sure enough, as soon as we got to the simple hanger, Ron slid the canopy back and instructed, “Jump in…” 

I was a tad uncertain crawling over the right wing and gingerly forcing my geriatric knees to contort a bit more than they liked, but Ron who is no small man himself knows his cockpit well after nearly forty years flying her and just as he had promised, I did indeed fit.  We’re not exactly the same dimensions, and he quickly described a few things I might consider for my own construction to tailor mine to me, but the worry over the cockpit was anticlimactic – and I was able to egress without the aid of a derrick; a really hopeful sign.  Ron may sell the plans although I doubt he makes any money at it – mostly I think he just likes the MiniCoupe and his enthusiasm can be infectious.

Some years ago Ron’s MiniCoupe was rebuilt, after a brake failure and the little bird’s unanticipated trip into the trees.  During the rebuild, he flush riveted much of the aircraft, especially the Clark-Y wings which he extended slightly incorporating the fiberglass wing-tips which he sells for any new MiniCoupe builders who would like them – the designer of the wing-tips is reputed to be none other than Dick VanGrunsven, better known as the patriarch of Van’s Air Force.  As it turned out the first MiniCoupes were originally designed in the upper North West, and the original MiniCoupe prototypes were built near the VanGrunsven farm. As a result of a few aero-improvements, some propeller tweaking and the C85 Ron’s bird now sports, he has a cruise speed closer to 125mph than the steady 95-105mph the smaller VW engined MiniCoupes generally achieve.

Anyway, what an opportunity to crawl all over Ron’s MiniCoupe with tape-measure and camera in hand – Ron was patient enough to answer a steady string of (almost certainly inane) questions which I'm sure he's probably answered time and again for newbies… I'm psyched – even though his MinCoupe is nearly 40 years old it'll hold all of my geriatric flab – and I didn't realize how many travels that little bird has been on -- it sure answered any doubts I may have had as to whether a MiniCoupe was feasible for occasional XC; he cruises at a good clip with his C85 and has been over much of the U.S. – Oshkosh several times, maybe again this year.

Probably the most reassuring issue of the afternoon, other than meeting Ron himself, was that in crawling around the MiniCoupe it was clear to me that this was a plain, simple bird designed to be built by only a modestly-skilled, backyard hobbyist – seemingly the only real decree is; don’t cut corners during construction and don’t add too many gadgets and techno-gizmos that only complicate the trouble-free structure -- and needlessly weigh down what is a honest, enormously-robust little flyer. 

The Bow-Tie Brigade

Many MiniCoupe builders successfully use the tried and true VW derived conversion for power.  That is the engine that Johnson envisioned; however, the design is robust enough that the smaller A65 and C85 Continentals have also been used with satisfactory results and Ron relates that up to an O200 is acceptable.  Needless to say these last are somewhat heavier engines, and in my case we’re going to trust the airframe with even more weight – that of a Chevrolet Corvair.  I find absolutely nothing inappropriate with the VW derived engines, it is just that I have a Corvair originally intended for a different airframe – so I’ll be adapting it for both budget and time reasons.

By now the Corvair, although nowhere near as accepted as the Volkswagen derived power plants, is not a mystery in homebuilders’ circles – with many KRs and Zenith CH600 series aircraft using this larger engine to good advantage.  The Achilles heel of the Corvair seems to be that at higher output, the crankshaft can become susceptible to vibrations and gyroscopic loadings that Chevrolet never envisioned, making the nitrated crankshaft a must for this conversion -- and increasingly the 5^th bearing (prop-hub) has become an implicit requirement for any of the higher-performance installations.

At least at the outset I’ll probably be using the trusty Keihin CV40 carburetor often used on Harley Davidson and Kawasaki motorcycles, among others.  The CV40 is a moderately altitude compensating carburetor – essentially akin to the CV Bings used by Rotax. – and again, it is what I have and am familiar with, so hope no additional investment will be required.  Further, I will be using the rare TRW forged pistons – in my case we purchased the 0.030 over-bored cylinders and pistons already painted and stored, awaiting eventual reassembly with the engine.

For the MutantCruiser, however, we will not be designing in as much Chevrolet power as is usually may be available from the Corvair.  Typical, for instance, the big 3100cc KR Corvair engines can churn out up to 135-140hp which is far in excess of what the MiniCoupe airframe can adequately use.  As I had planned in two early building attempts, my Corvair will be tuned closer to the level that Bernie Pietenpol used to good advantage in his admired AirCampers – about 85hp-88hp.  Although that is fairly small by Corvair standards, it is a nod to longevity and it is further envisioned that cruising output will be throttled back in the neighborhood of 55hp at a little less that 2700rpm, for a roughly 5-gallons an hour fuel burn. 

With reasonable consideration to aerodynamic cleanliness and a well-tuned engine, I am hopeful for a cruise in the neighborhood of 105-108mph which should offer sensible cruise fuel economy along with respectable power reserves for climb-out on hot summer afternoons -- of course faster would be better, but not at the expense of greater fuel burn.

We shall see…

MutantCruiser -- we begin again...

My design goal is for a homebuilt single-seater that fully meets the spirit of the FAA light-sport aircraft and pilot regulations -- an aircraft that remains uncomplicated to fly for a lower time pilot with a two decade hiatus and an aircraft that is easy and inexpensive to build, ultimately providing a modest cross-country ability for chasing after grandma and the grandkids, and yet is modestly capable of skirting complicated airspace which unfortunately is a fact of life where I live.

Many devotees will correctly recognize my proposed aircraft as a MiniCoupe.  The MiniCoupe is one of the oldest of the species of diminutive aluminum single-seaters such as the BK1 and the Thatcher CX4 as well as the venerable Hummel series of aircraft refined by Mory Hummel and Bill Spring.  The MiniCoupe, also know as the Chris Tena MiniCoupe, (except for its twin-tails) is visually reminiscent of the Teenie Two -- although a noticeably larger and heavier aircraft compared to the Teenie Two, to the extent that any aircraft in this size range can really be called "heavy." 

For whatever reason, far more Teenie Twos are recorded than MiniCoupes, but there remains a relatively active discussion group for both aircraft, thanks in no small part to the efforts of Ron Dixon who has kept both designs very much alive through his plans sales and vigorous encouragement.  Ron was an early builder of the MiniCoupe and decades later still maintains his in Maryland.

Designed by Bill Johnson of Oregon in 1970s, the MiniCoupe was intended to provide an amateur builder with a single-seat aircraft,  via an easy-to-build and complete materials kit where most of the hard technical work was already finished – a concept now common-place in the experimental aircraft industry under the 51% rule.  Although all contemporary MiniCoupes are now pure plans-built, Ron Dixon notes that the original MiniCoupes were the first of the modern materials kits, and at the time the notion of a "kit" was an entirely new and revolutionary home-builder’s concept.

The MiniCoupe is essentially all aluminum construction and generally uses pulled/blind rivets  with 2024T3 aluminum throughout, although some have asked about using conventional riveting, especially in high-stress areas and others have actually used flush-riveting in hopes of lowering drag and expanding the flight envelope upwards – reputedly with good success.  Like most others of this genre, the Tena MiniCoupe was primarily intended as a VW powered airplane, although other engines have been used very successfully and a few use the smaller 65hp and 85hp Continental – mine will use a Chevrolet Corvair conversion (more on this another time).

For a variety of reasons, my MiniCoupe will be whimsically known for now as a the MutantCruiser, rather than trying to convince anyone that my work is a genuine MiniCoupe – but aficionados will quickly recognize the robust MiniCoupe structure, as well as general composition and minimalist philosophy that is plagiarized throughout.  The key reason for the nomenclature tweaking is that I may end up taking a few liberties with the Johnson design and I have zero interest in debating whether my altered rendition is properly called a MiniCoupe, nor am I interested in drifting into some of the testy parochial debates that rage through aviation forums on the internet when a builder decides to stray from the established blueprints of a respected designer.  I suspect if we all wanted pure clones, we'd fly Cessnas.

In any case, because of my heavier Corvair engine and the portly geriatric pilot destined to occupy the cockpit, the poor MiniCoupe would probably be near, or at, its designed gross weight all of the time, before we added any gas – and I have no intentions of building a glider!  Nonetheless, thanks to modern calculators and readily available EAA spreadsheets, I have run dozens of possible scenarios – keeping a wary eye on the fact that I am neither an engineer nor an A&P, nor even an experienced builder -- just a wayward hobbyist.  Further, although I’ve made hesitant starts on two different aircraft in the past two years, I’m now thoroughly chastened that although it is incredibly easy to modify a proven design in the virtual-world with the aid of modern computing, unless one is extremely carful, the real-world construction complexity goes through the roof at about the same rate that the probable fly-ability plummets. 

My target is for a simple yet modestly efficient single-seater that falls under the FAA light-sport aircraft and pilot regulations; a little bird that remains comfy to fly on up to 500-miles VFR XC hops and that is quite easy and absolutely inexpensive to build.  Further it must use as much of the materials and assemblies as possible from my two abortive building efforts.  Proffesional planners will recognize this as your basic “time, scope and resources” conundrum. Because social-security is quickly approaching, we have limited time and very restricted resources, so although my dream RV-3 would be nice and a fantasy Lancair IV superb, my real-world scope must remain modest – even austere!

I’m just a geriatric first-time builder who hears the clock ticking -- and there ain’t no free lunch!

Links:
http://au.groups.yahoo.com/group/minicoupe/?yguid=244371447
http://theminicoupe.com/id2.html
http://wday6511.home.comcast.net/~wday6511/