THIS IS A TRANSCRIPT FROM EAA'S MAY '98 ISSUE OF SPORT AVIATION:
 
TWIN COZY
BY JACK COX
 
One of the most innovative home-builts we saw during all of last year was the Cozy YV-22X built by brothers Ruben Leon (EAA 546416) of Valencia, Venezuela and Carlos Leon (EAA 554073) of Caracas, Venezuela and flown by them across the Caribbean to Sun’n Fun ’97.  The Cozy airframe was essentially straight off Nat Puffer’s drawings, but everything aft of the firewall was a perfect example of why homebuilts have the word “experimental” written on their sides.

   The Leon Cozy appeared to be just another example of that popular design when it appeared in the pattern at Lakeland last spring, but when close enough to be heard, it was obvious something was different about it.  Whatever lurked beneath its cowling was definitely not the usual Lycoming!  A further difference was apparent when it came whistling by on final: it had counter rotating propellers.  Joining the crowd that quickly swarmed around the airplane when it was shut down at its parking spot, I soon learned that it was powered by two little four-cylinder 1,600 cc Suzuki Swift auto engines, each independently driving its own Warp Drive three-blade propeller through a shaft-within-a shaft or coaxial drive mechanism.  One engine faced forward and the other aft,  and each drove its own drive shaft through four Micro-V belts.  Just getting two of the engines and their drive systems into a space normally occupied by a four-cylinder Lycoming was obviously quite a feat of engineering, and it seemed redundant to the point of embarrassment to ask about the feasibility of the configuration...after all, the Leons had just flown over some 1,200 miles of open ocean to get to Lakeland, hadn’t they?

Later in the week, I had the opportunity to talk to the Leons about their aircraft and found that its engine installation is still another validation of the old chestnut, “necessity is the mother of invention.” First, you should know that the Leons are not rank amateurs.  Ruben Leon, who is 43, is an aerospace engineering graduate of Catholic University in Washington, DC and has a Masters degree from Princeton University in both aerospace and mechanical engineering.  He is the president of his own company, Centro de Mecanizado Levil, C. A. in Valencia, Venezuela. Carlos Leon, 34, was educated in England and has a degree in computer systems engineering from Warwick University.  He is the head of the numerical control service department of Maquinaria Diekmann SA, a machine tool sales company in Caracas.

 
Ruben learned to fly in the mid-1970s while in college at Catholic University – in a Cessna 150 at the Freeway Airport in Maryland.   He always wanted to own an airplane and managed to buy a Stinson project, but had to sell it because he couldn’t afford to buy an engine for it.  He later started a KR-2, but never finished it; about half way through, his head was turned by the VariEze, which he began to build instead.  He finished the airframe in about three years, but, again, couldn’t afford an engine.  He ultimately carried the parts and pieces home to Venezuela, but the Eze continued to languish as he married, began a family and struggled through the early years of establishing his own machine shop and manufacturing business.  He had attempted to find a challenging job in Venezuela in some area of aviation, but, unable to do so, started his own machine shop operation instead.  He began with a small lathe and a milling machine and made hydraulic lifters for engine companies.  He later made a deal to have a CNC lathe placed in his shop, which he paid for by working it.  Eventually he developed a CNC system of his own that works with a PC computer and adapted it to all his equipment... which put him on the road to success.

   Carlos learned to fly in England in a Cessna 152 and upon his return to Venezuela, began flying a Cessna 182 that Ruben had purchased in poor condition and rebuilt for use in his business.  It was later traded for a Cessna 337 in order to have two engines – but has been plagued by a problem familiar to U.S. owners of the type: landing gear system failures.  As of last spring, Ruben had made three belly landings because the main gear would not come down.

 
 Aircraft engines are not easy to come by in Venezuela, but a few years ago, Ruben and Carlos finally managed to locate a high time Lycoming O-320 and installed it in Ruben’s by then 12 year old VariEze airframe.  They flew it for the first time in 1992 and subsequently enjoyed some 350 hours in the little pusher-until the day Carlos was flying and had the Lycoming swallow a valve.  He attempted to glide back to the airport but run out of altitude about two miles short and ended up wiping the gear off the airplane.  Fortunately unhurt, his first words to Ruben were, “We’ve got to put two engines in that thing!”

   Deciding not to rebuild the VariEze, the Leons chose to build a four-place Cozy Mk IV instead...and try to come up with the way to power it with two engines.  Aircraft engines were eliminated from consideration early in the game because there were none available to them that were small or light enough for two to be mounted in as relatively small an airframe as a Cozy.  They also had to be economical, which eliminated virtually everything with an “aircraft” label.  A primary criterion was that anything used in the engine installation had to either be available in Venezuela or readily available from foreign sources.  Practically, that meant engines (and, ultimately, parts) in Venezuela and props and some specialty items from the U.S.  Their first choice of engines was the Subaru, but getting no cooperation from a local dealer, they decided on the Suzuki Swift engine instead, which was available from a local GM dealer.  Two of the 100h.p., aluminum block, four-cylinder, inline, liquid-cooled, 1,600cc engines were purchased new for $2,200 each and work was immediately begun to find a way to install them in the Cozy airframe, which was already underway at this point.

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   All the design work for the engine installation was done on CAD.   The engines were drawn into the computer program, which allowed them to be turned and tilted in any manner in order to determine the optimum position for each in terms of overall compactness of the engine package and for the best location and alignment of the drive shafts.  They considered all sorts of configurations, one of which was to mount the engines sideways in the fuselage, with drive shafts out to nacelles on the wings, then turning backwards to drive pusher props.  After further consideration of the weight and complexity of 90 degree elbows in the drive lines and the problems of asymmetric thrust, they quickly abandoned that idea.  After about six months of such deliberation, they finally settled on a shaft-within-a-shaft, centerline thrust arrangement, and it took another three months to actually design it.

   As can be seen in the accompanying photos taken at Sun’n’Fun ’97, the engines were placed side-by-side and mounted on the longitudinal axis of the fuselage.   Standing  behind the airplane and looking forward toward the nose, the left engine was mounted with the power output end facing aft, and the right engine was turned in the opposite direction.  Massive structures of flat metal plates bolted on each of the ends of the engines to connect them and serve as the supports for the prop drive shafts that extended fore and aft between the engines.  One of the shafts rode in bearings within the other.   The left engine drove the forward-most propeller through four Micro-V belts, and the right engine drove the aft prop through its own set of belts and pulleys.   As viewed from the rear of the airplane, the front prop turned counterclockwise and the aft one turned clockwise.  Both engines turned the same way, of course, but with one pointed forward and the other aft, the belt-driven shafts and the props counter-rotated.

   A lot of problems were encountered in the manufacturing of the parts for the engine package.   The type of aluminum needed to make the belt drive pulleys, for instance, was not readily available in Venezuela, so they had to be made of steel.  Cog belts were the first choice, but not having them readily available, the Leons used Micro-V belts instead.  Four belts were utilized when three would have been adequate to handle the engine loads, but with four, less stress was placed on each belt during operation and in case one broke, the remaining three could still handle full engine power.  The original reduction ratio was 2 to 1.

   The two engines and their drive trains were completely separate in the Leon Cozy.  Each had its own complete set of accessories and operated independently of the other.   If on engine quit (or was intentionally shut down), its prop simply windmilled while the other did all the work.  One interconnection was between the engine’s electrical systems.  They were wired so if the electrical system of one engine failed, the other would power both engines.  This was not an automatic function, however.  Switches on the instrument panel allowed the pilot to cause one engine’s electrical system to operate both engines.  Because of this interconnection, some weight was saved by virtue of using one full-size battery and a smaller back-up, rather than two full sized ones.   There was also an extra electric fuel pump.  Each engine had its own electrical pump, but a third one that could operate both engines simultaneously was also employed.

   Initially, the Leons wanted to use magnetos, but trying to come up with a way to make one set operate both engines became so complex that they ultimately reverted to the stock automotive electronic ignitions...and they have always worked perfectly.   They also considered electronic fuel injection, but ended up with Ellison throttle body carbs, and they, too, have worked perfectly from the start.

   The Twin Cozy was finally completed and test flown on February 1, 1997, but there were problems to overcome before Ruben and Carlos could seriously consider their hoped-for goal of making Sun’n Fun a month and a half later.   The brothers charmed even the most hardened skeptic at Lakeland last spring with the forthright manner in which they related all the initial glitches they had to identify and solve.   As professional engineers, they had a realistic attitude toward a project as complex as their engine intallation and knew from the beginning that despite their best design efforts, there would be real world surprises once they fired up the Suzukis...and they were right.

   Cooling raised its ugly head on the first flight , but the problem was solved by switching from their original radiator to an air conditioner evaporator from a Chevy Blazer.  Ruben and Carlos had to chuckle when they told of this change, because at that point (during Sun’n Fun ’97) they really didn’t know why the first radiator failed to cool adequately and why the second one did.  Both had the same area and liquid capacity, but for whatever reason the Chevy unit worked better.

   The next major problem involved the bearings in which the drive shafts were mounted.  Despite their best efforts to perfectly align the shafts and thus be able to use fixed-race ball bearings, it was soon evident that something was causing undue wear on the shafts.   It might have been tiny amounts of misalignment at either end of the shafts adding up to an excessive total, or it might have been a bit of wiggle caused by so many reciprocating parts thrusting in so many directions, whatever, the resulting wear could not be tolerated.  The solution was to substitute for self-aligning spherical bearings.

   The most maddening problem, however, was vibration.   Four-cylinder inline engines are not noted for electric motor-like smoothness, but the two Suzukis certainly did not pound the airframe like a big bore four-cylinder Lycoming.   The problem was a higher frequency buzz that managed to crack something...an exhaust stack or alternator bracket...every few hours or so.   Ruben and Carlos kept changing the resonant frequency of those components by beefing them up, and finally got a four hour crack-free run before deciding to strike out across the Caribbean for Florida.   Perhaps predictably they discovered another cracked alternator bracket when they landed for fuel in the Dominican Republic, but they were able to make the repair and continue to Lakeland.  At Sun’n Fun they readily acknowledged that a lot more scientific investigation and just plan trial and error would likely be needed to bring this problem within acceptable bounds.  Those of us who own aircraft that were FAA certified decades ago and have supposedly benefited from the experience of millions of hours of combined fleet operation, yet still are subject to regular craking of  exhaust stacks and other engine components, nodded in agreement.

   The most often asked question at Lakeland was the weight of the twin Suzuki  power package.  Although they had not included every hose clamp and washer used in attaching and plumbing the engines,  Ruben and Carlos had weighed the major components and they totaled about 380 pounds.  That did not include oil in both engines or the two and a half gallons of coolant (a 50/50 mix of water and Prestone).  Assuming 200h.p. from the two Suzukis, that compares to the 298 pound dry weight Lycoming quotes for its 200 h.p. IO-360C – although the installed weight of the Lycoming, with accessories, exhaust system, baffling, etc., is much closer to the weight of the Leon’s twin engine package.  The total weight of the aircraft is 1,250 pounds.   Nat Puffer lists 1,050 pounds as the desirable empty weight target for a Lycoming O-360 powered Cozy Mk. IV, but we’ve seen weights as high as 1,340 pounds or so on prop cards at Oshkosh, so the Leons are well within the weight range of Mk. IV’s that have been successively flown. (Nat is still out there shaking a paternalistic “naughty boy”  finger at all of them, however.)

   As the Twin Cozy was configured at Lakeland in April of 1997, and at its still very early stage of development (flying for only a month and a half), it was cruising at 150 kts (172.7 mph) and burning a total of 10 gallons per hour.  At gross weight, 2,050 pounds, it was climbing at between 600 and 700 fpm at 120 kts.  (138 mph).  This was with the Warp Drive ground adjustable propellers set as a result of calculations only.  There had not been sufficient time to experiment with different blade settings,  reduction ratios for the belt drives,  tweaking of the carbs, etc., so all the performance figures had to be considered preliminary.   Ruben and Carlos were quite pleased with the numbers they were seeing, however, especially the cruise speed.
   Following Sun’n Fun ’97 Ruben and Carlos retraced their trans-Caribbean route home to Venezuela, with a fuel stop a Puerto Plata on the north shore of the Dominican Republic.  The twin Suzukis never missed a beat during their over-ocean passage, and when they landed at Valencia, the brothers were surprised to find they had become local celebrities.  They were on TV and were featured in the local newspaper.  In an update obtained in late March of this year,  Ruben revealed that the Twin Cozy had been flown a total of 120 hours – 60 since Sun’n Fun ’97 – but at that point was down for modification.   The engines themselves and their coaxial drive system had continued to perform flawlessly, he said, but the resonant frequency problem had remained.  The culprit, they had determined, was the rigid attachment of the two engines by the interconnecting flat plates, which was creating harmonics that were cracking the brackets of nearly everything attached to the engine.  Their stopgap measures to change the resonant frequencies of the various brackets increased the time between cracking,  but was not a permanent solution.   As a result, they have gone back to their computer to redesign the engine package,  with the primary focus on separating the two engines.   Their plan is to remove the interconnecting flat plates and redesign the tubular engine mount so that each engine will be free to shake, rattle and roll completely on its own.  The coaxial prop drive will be attached to the engine mount and the belts will be fitted with idler pulleys to maintain proper tension.  While they are at it, they also plan to switch to cog belts and to change the reduction ratio to 2.2 to 1, which they believe will increase the total power available.
 
   Unfortunately, the modifications and additional test time could not be completed in time to make Sun ‘n Fun this year,  but Ruben and Carlos are hoping to fly their Twin Cozy to Oshkosh this summer.

   As EAAers surely recognize, the work Ruben and Carlos Leon have undertaken to create a twin engine, coaxial drive, centerline thrust power package for their Cozy is highly complex and requires a high level of design creativity, engineering expertise and parts manufacturing capability.  The potential payoff is great, however.  When perfected, they will have the peace of mind they seek when flying over oceans – because they will have two engines; they will have two engines for a fraction of the price of one new aircraft engine of  comparable power; and, with centerline thrust, they will have eliminated the aircraft handling problems caused by the asymmetric thrust of conventional twins.  This is experimentation in the finest EAA tradition, and we wish them every success.