Homebuilt, low wing, 5+2 place, mazda powered twin

[Bill Berson]

It's neat you are in an aviation family.
My family was 8. I found that most in my family don't want to fly much. Rarely more than one at a time.

[AMDguy]

Hi all,
Thank you very much for your support. I really appreciate all the encouragement and advice. i mentioned getting a lot of hp out of the Mazda engines, and the only reason that i would think to do that would be because they are the Wankel rotary engines, not a traditional recropraciting engine. I may be wrong, but some of the research that i have done says that because the Wankels are so simple (3 critical moving parts in a 13b), that it is not excessively hard on the engines to run them at high power settings for extended periods of time. another piece of information that makes me think this is because drag racers who use the wankels run them at extreme levels of power (750-800bhp for a 13B) in a much harsher way, then especially because an aircraft engine is mostly running at a constant RPM, it would not be the end of the world. if I am wrong, then please correct me, and if you have any other engine suggestions, then please let me know. i have also considered several marine engines, as boats generally (similar to aircraft) cruise at higher power settings (greater than 60% throttle). this seems to me as if it is the perfect solution (marine engines are extremely durable and long-lasting), but there are no PSRU's available for any marine engines that i can find. I considered rebuilding an old aircraft engine, but it would limit my options to liquid cooled engines (i really want water cooled, i know that it is more complicated, but it gives you far more control over the plane) which there are not that many of, and then i would still not get the power that i want. as i mentioned before, please give any recommendations and advice that you have.

thanks,
christian L.

[thisadviceisworthles]

Just a few things:

1) I would be very interested to see the design because it sounds interesting.
2) If you are looking to save money, it would be difficult to build a twin for cheaper than you can buy one. I saw a flying Travelair on Barnstormers the other day for less than $35k, and Cessna 310s regularly go for under $70K.
3) Unlike a one-off design, a certificated airplane can be financed, which may make it more accessible than building.

Assuming you are not looking to save money:

The Mazda rotary has had limited success in aviation. I think it is related to the fact that they can be turned up to such high power levels. (I am not an expert but) based on what I have seen in RX7 and RX8s, it is really difficult to manufacture Apex seals that can stand up to constant heat of high horsepower applications. As a result high horsepower builds often work in drag cars or street cars that only use that horsepower for short amounts of time, but they are not used in circle track applications that run high, sustained load. Airplanes are more like circle track applications.

If you want to use the rotaries, I would suggest dialing back your HP goals to the 250-275 range. But rotary engines are still appealing for weight advantages.

If you can afford slightly more weight, a few Vans RV builders have had good luck with Chevy LS V8s. 400 HP, fuel injected and lighter than many aircraft engines with 1/2 the HP. Plus they are cheap, around $10K-15K for a new engine, converted for aircraft use.

If you are looking for some less conventional inspiration, take a look at some Burt Rutan designs including the Defiant and the Starship.