"Micromaster"-- Centerline twin using small industrial engines

Has anyone ever looked at asymmetrical aircraft designs for the "Micromaster" - Centreline twin using small industrial engines.
I know they don't look sexy, but with all the expertise on this site, there could be a really good concept put together that has
21st century design techniques and looks.

 

Blackhawk,
No, I don't think we've covered that ground in this particular thread.
There was some discussion of the BV. 141 in another thread (here: https://www.homebuiltairplanes.com/forums/threads/asymmetrical-homebuilt-aircraft-concepts.14722)
We had another long thread on a centerline-thrust design powered by VW engines (75 HP, so a lot bigger than these industrial engines). That design was dubbed the "Beetlemaster" and remains something I'd like to take farther someday. Within that thread we discussed the Rutan "Boomerang" asymetric design as a possible way to address some of the challenges of a conventional (non-centerline thrust) twin. Here's a post on that.
And another
And a third

With these small, heavy engines, it is challenging to get good single engine climb performance (dragging a stopped prop). To be worth pursuing, any asymmetric design would have to be truly better (more aerodynamically or structurally efficient, etc) rather than just novel. Maybe that's possible, I don't know.

 

When you say "stopped prop" are you meaning an engine malfunction in one of the two engines ???

 

Yes.
Most twin engine airplanes use propellers with variable pitch. This has two big advantages in a twin engine airplane:
1) If one engine quits, the propeller can be "feathered", and this reduces drag a lot (compared to a non-feathered prop)
2) An adjustable propeller allows the engine to produce optimum thrust at both the airplane's normal cruising speed AND at the much lower speed for optimum single engine clime (rate or angle). This second part is critical, since climbing on one engine is the most difficult performance challenge for a twin.

If we want a plane that can climb safely with one engine not running and we want to use fixed pitch props and we want to use these cheap engines that are heavy for their power output and we want very benign single-engine handling (no significant "minimum controllable airspeed"), then we have a very tight set of design parameters to meet. That means no novelty for its own sake, the design decisions have to pull their own weight on pragmatic grounds.

Maybe an asymmetric twin design can do that, and maybe it is something that an amateur could analyze and build.

 

Three engines solves more problems than it creates for multi engine.

 

Again with the three engine thing?
Like here. And here.
And here. And here.

I agree with your basic point: With three engines, it is less of an issue if one fails. We even discussed it a bit here. But a triple does create problems/potential problems: Regulatory, asymmetric thrust, regulatory, higher weight/HP, regulatory, aircraft complexity, regulatory. If I ever get a chance to discuss the regulatory issue/challenge with someone who knows how that would work, I'll be sure it bring it up (because I would really like to know).

 

I'm sure we've discussed this before--maybe in the Beetlemaster thread?--but a stopped prop is less drag than a windmilling prop. Are you sure the prop will stop on one of these little engines? The builder of the twin Corvair RV, for instance, was going to have some sort of a crankshaft brake to stop windmilling on a dead engine.

Maybe the SD guys have the answer about whether they windmill or stop. Either way, it is drag...

 

No, I'm not sure, and it is something to figure out (especially as the back prop sits in propwash of the front prop).
I was thinking the backup plan would be a simple spring-loaded arm and brake shoe from a mountain bike to press on the flywheel. Pull one pin to let the spring and arm do the stopping. If you mistakenly pull the wrong one, an engine under power should make short work of one of those little rubber brake pads. I don't think it would be hard to engineer or weigh very much, but it would be "another thing."

ETA: I think all these engines have a compression release (see here) to allow the starter to bring them up to speed--it is on the cam and keeps a valve open slightly until the engine gets up to running speed. If so, this makes it more likely that they'd windmill, since (at low windmilling speed) the prop would be working against less compression load from the cylinders.

 

If 3 motors are good then 4 is 33% better ...

 

Disc area from a windmilling prop is not fun under certain circumstances. Like engine failure after rotation during takeoff. A 42" inch prop is going to act like about a 1/3 sheet of plywood is there. You'll not want it windmilling for sure. I thought putting a mtn bike disc brake on the prop extension between the flywheel and the prop would work. If the center hole in the disc is greater in dia. than one or the other end of the prop extension a mounting surface can be machined similar to the prop flange itself. Cable or hydraulic wouldn't matter much, it would be easy to pull tension up slowly to ease the prop into a stopped condition. Pulling hard and stopping the prop quickly might alleviate the windmilling problem as well. Pulling tension on a running engine may be fun also. You'd get the "big eyes".

 

Or three engines is 25% less than four engines eh?

 

I don't want to hog up this thread with 3 and 4 engine stuff, but is my dream/fantasy and have spent some thought on it if you are interested discussing on another thread. I just firmly believe it is safer.

 

The only four engine HBA that I recall seeing - Bally Bomber - is for sale.


BJC

 

I'm interested in a triple, too, either the "Tri-Mow-tor" (Mini Ford style) or the BroncoMaster (with a pusher behind the pod). We even ran some quick back-of-the-envelope numbers on one in this thread a long time ago (here).

But if I can get safe climb with one engine out, I'd prefer to have a true centerline thrust twin. No need for any special techniques to keep the plane upright in case of an engine failure (that 1/3 sheet of plywood in the breeze that you mentioned? I'd like it to be on the aircraft centerline, thanks. Hopefully we'll get that prop stopped! ) . One less engine to convert and mount, less total weight for the same HP, and (especially important) I >think< less likelihood that I'll need or be required to get very expensive mutiengine training.

I don't own this thread, and others are free to post what they want. If you've got a triple design idea, feel free to plop it in here. I'll look at it wherever it is, it would be cool. It will probably get more notice, though, in a thread with a title that matches your project of interest.

 

Priced to sell at $225,000

 

I like the Micromaster concept. It is a solid idea. Keeping it light and simple it'll be fun to fly and should always get you home safely. I hope you assuage your concerns to be able to legally fly it for an acceptable expense and pursue building it. Woot!

 

Four legs good, two legs better!
Four legs good, two legs better!
Four legs good, two legs better!

 

It's the odd leg that's always the trouble maker eh?

 

If you're looking to use the props in small 1 or 2 seat homebuilt aircraft couldn't folding propellers similar to gliders be used for simplicity. rather than using very complicated feathering props ??

 

I had a 3 legged cat once. She was a trouble maker.