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Twin engine RV-6A...or not

George, lots of Corvairs flying and they work well. The conversion process has been refined for a couple decades now and is well understood.

The engines are quite robust at the 110-120hp level. I've owned several cars, built a number of the engines, including a 300hp turbocharged one and some road racing ones.
 
gmcjetpilot said:
If a single 160HP engine can make an RV scoot along, a twin RV with two 100 to 120 HP engines will result in good performance. Single engine performance? Well what people might not know, twins under 6000lbs only have to demonstrate single engine rate of climb for certification. Demonstrate does not mean positive ROC. You just have to demonstrate it, which can be negative ROC. Yes you can have a zero single engine service celling. It is just the regulations for light twins. Once you get over 6000lbs you have to climb single engine.

In a Jet you lose an engine in high altitude cruise, you start to DRIFT DOWN. You can't hold altitude. Same with a light twin you need to drift down to SE service ceiling. SE operations can extend your range before the ground comes up, but given conditions you may be able to maintain altitude. People think two engines is great. It is great, but with serious limits unless you are in larger heavy twins.

All light twins I flew can climb slightly below say 5000 ft DA. When I say slightly I mean 50 FPM. I can tell you my beloved Piper PA-23-160 (Apache) did well single engine, solo, half fuel sea level conditions. Two people, full 108 gal, baggage, high density altitude, loss of engine means pulling the good engine back and making a forced landing. Trying to fly it would result in loss of control.

You also have to worry about Vmc as I am sure you know. You can have too much power from the standpoint of single engine operations. The whole problem is asymmetric thrust. Reducing that helps control. Also adding more yaw stability helps. Did you consider a bigger Vertical Stab/ rudder or ventral fin? Have you estimated Vmc? Vyse (blue line). I think keeping it light (O200 or Rotax) is goodness. I don't think a Convair is heavy but guessing (forgive me no time to research) it is not lighter than a O200 and Rotax. I know the Convair is claimed to make 100 to 120HP. With non feathering prop you will lose more performance and have even higher Vmc.https://www.youtube.com/watch?v=GIMVkTk26fw
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I think it would be an absolute blast to flight test engine-out handling and performance. The other benefit of experimental aviation is if it's determined there is a handling or performance characteristic that is deemed inadequate, a remedy can be part of the "experiment". Vmc too high? VGs, bigger rudder. bigger stabilizer, etc. Engine-out performance inadequate? Bigger engines, different props. Then also the experimenting and developing the performance data and procedures. Suffice to say, it's significantly more complex than a single. Twice the engines, four times the complexity. I lack both the means, and the talent to engineer, build and operate a twin. Suppose that means I'm stuck in dreamland, and in envy of those that do.
 
Wing Derringer Etc

The Wing Derringer was designed by the late John Thorp who designed a series of mostly two place airplanes including the T18.
The Piper Twin Comanche started out as a single engine Comanche converted to two engines by Ed Swearengen. Extended prop extensions integral with the then custom Hartzell props. There were no significant mods to the single Comanche airframe to "correct the CG". All of the popular twins of that era placed the main spar under the front seats. The The Twin Comanche got a VERY undeserved bad reputation mostly because of training accidents. I know of one case where the trainee feathered an engine and then proceeded to shut off the mag switches on the operating engine. Most of the training accidents were stall spin after a simulated engine failure.
I got my multi in a TC that I repaired after a landing gear retraction during the landing flare. The instructors and charter pilots knew very little about the airplanes they were flying in that era. The TC was then and still is a GREAT airplane. Comanche 180, 250 and Twin set world distance records flown by Max Conrad. TC record was Capetown S Africa to St. Petersburg FL. Max was halfway between St. Pete and New Orleans when everything ahead fogged in and he had to turn back to St. Pete. Records were for three different weight categories and I believe one still stands. The single Comanche is in the museum in Liberal KS with the extra fuel tanks.
 
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