Needed: A twin: The Airplane

[rhbelter]

Needed: A twin: The Airplane

Ahoy, EAA Engineers, Designers, Builders:
Here is an offering of a design concept which I have been considering for some time. I suggest that it is particularly applicable for folks developing and flying an alternate engine.
Needed: A twin: To mostly sidestep the reliability factors/consequences of alternative engines. Folks like a fast airplane, but a single 'developmental' engine joined with an airplane with a high landing speed is vicious in terms of safety, and the record is terrible. This push-pull airplane configuration is intended to offer a 'ride-home' on one engine, and the opportunity to use the airplane again (as contrasted with a BRS chute). And --- without the control/handling challenges of a lateral configuration twin, where the running engine drags you to the crash site. Our EAA folks insist on trying a lot of different things. This 'bird' will hopefully keep you around until you get it right.
This low wing design configuration capitalizes on the many fine airplane designs already existent, and expects that you will adapt as many pieces as you can to prove the concept. Plan to use a pair of known reliable engines to sort-out the airframe. (You never want to mate a new airframe and new engine). An appropriate 'firewall forward' installation of an existing design could be duplicated, and added to the 'backside' of the airplane, with suitable scoop/baffle changes. Cheek panels below the cowl would fair it OK, with probably not much aerodynamic penalty as compared with an optimized rear cowl. Hang some tail booms on it -w- an inverted V tail, and you have it.
I have attached a .pdf file which shows the general design, (My Excel W&B file and Autocad.dwg's which show some of the unique details will not upload). As small and clean as it is, with two engines to prove the airframe, such as 0-200's or Corvairs, or in a 'beefier' version, Lycoming O-320's or O-360's would make it a fast airplane, which will appeal to folks who are not even developing an engine. Two engines are not a bad idea, because even a 'perfect' engine is not ALWAYS perfect.
I have done some preliminary spreadsheets which put things 'in the ballpark'. These are based on work done by John Roncz, printed in Sport Aviation in 1990. It appears, (by a not very rigorous analysis), that this bird would climb on one engine -w- a feathered/braked prop, and even better with a powerful developmental engine and PSRU.
The fuselage I envision is basically a steel tube truss-work -w- fiberglass covering plus cowlings. Essentially a rectangular section -w- rounded corners. Wing, tail, booms are aluminum. Spring gear, blown canopy. Really, a pretty simple airplane. Developed, it could be as 'fancy' as one may choose.
Fast does not mean difficult to fly. This one won't go there, but: -- A thousand miles an hour is a piece of cake, and -- GREAT FUN.
OK, why not just use a Cessna 337 push-pull as a perfectly useful test bed? It would work just great, but people don't seem to do it. I don't know why. Hubris? -- Like: 'MY stuff NEVER fails, I don't need another lousy engine'! Yah!!!! Plus, it sure is not a 'go-fast'. Perhaps the paperwork to-do-such to a certificated airplane would take longer, cost more, be less fun, and yield a less useful product than just prototyping this article.
My formal engineering skills are now more than FIFTY years out of date. My analytic skills are even less refined than they were all those years ago, but the principles are still pretty much there. There are powerful tools today to do CFD, FEA, and flutter analysis compared with the limited/laborious and mostly forgotten methods of back then. Use 'em.
I'm a seriously old sucker, and I have no plan to design/build/fly this 'thing-of-beauty', but I'd sure like to see the concept move along, because I believe that we EAA guys need it. I'll be pleased to contribute my 'archaic' abilities to whoever pursues this project. If there is any consistent interest in this project, someone (not me) should start a thread or a web site, or a whatever. Please let me know, for I may not be clever enough to find it.
Please look at another post to follow this, entitled: 'Needed: A twin: The Engines'.
Enjoy /s/ Bob
Robert H. Belter
rhbelter@comast.net
EAA # 8444, EAA TC # 4561, EAA CH 204,

[crusty old aviator]

Ahoy Bob,

Every once in a while a twin homebuilt appears, there'll be a few articles written about it, and then it flies off into the sunset...and the recesses of our collective memory. Not many homebuilders are interested in twins. For all the adoring fans Burt Rutan had in the late 70's, only a handful of his tandem twin Defiant design was built. Perhaps this thread will spark someone's interest to design, build and fly a twin...who knows?

[wildhorsesracing]

Nice idea, I have always like pushers with twin boom tails.

[JJJacober]

That's a very pretty design you have there. I really like the tail configuration. It's reminiscent of a few older r/c aircraft from my younger years.

Ahoy Bob,

Every once in a while a twin homebuilt appears, there'll be a few articles written about it, and then it flies off into the sunset...and the recesses of our collective memory. Not many homebuilders are interested in twins. For all the adoring fans Burt Rutan had in the late 70's, only a handful of his tandem twin Defiant design was built. Perhaps this thread will spark someone's interest to design, build and fly a twin...who knows?

I spent a little time searching for a twin, but the offerings in the experimental realm are fairly dismal. I just assumed the sort of folks who were rated, and also looking for an affordable twin was a niche market and therefore not catered to. That's especially the case when you can find a 310 for under 100k nowadays that hasn't seen a freighters life.

Ideally, I'd Love to see a compact otter design, something a little more akin to an islander, but in the experimental category. I'd like a bush plane with float capability as well as the peace of mind that comes with two motors, but short of gambling with my own design, the twin market seems largely ignored. Probably for a good reason.

[mcrae0104]

Bob,

Have you seen this twin-Corvair RV-6 derivative? I met Jim at a Corvair College about a year ago. I think he would be a good guy for you to talk to. Personally, I'd rather focus on building one engine well than deal with the complexities of a twin, but to each his own. Good luck in your pursuit.