I have a pair of older OS 30's, nib, that I would love to put in a push-pull configuration like the Cessna Skymaster. These engines have strap on mufflers so I know they are old, probally from the 70's.I would like to design a plane for these boys, but am not sure of the relationship, % wise ,as to the relationship of the wing and tail section and what I should be going for in length of fuse. I have never before designed a plane before but would love to try something like this. I would appreciate any advice from you guys and gals that would help get me to the drawing stage. Thanks in advance.

Bill

Bill:

The simplest thing would be just to get a 3-view of the C-336 or 337 and size yours in proportion.

The tail moment and area proportions are the same for a multi as for a single - the air doesn't care how many fans are blowing. With conventionaly mounted multi engines it is not a bad idea to make the vertical fin and rudder a bit larger than for a single, with centerline thrust the normal size is fine since there's no chance of off center thrust.

Bill.

Bill, could you give me an idea as to where to start as in wingspan and length? I am a complete idiot as far as designing a plane is concerned. I am thinking something on the order of 60 inch span and 50 or so in length. It will not be a scale model of a 336 or337 but probally something more on the order of a stik with twin booms. Thanks much.

Bill

Bill:

With antique 30 engines 60" might be a bit too much unless you build a lot of "Lightness" in, and then you'd be limited to relatively windless days. But your overall length percentage sounds good - on a twin I generally like to be a little longer so I can get more rudder authority in case of a single engine flame out. Using the "Pushme-Pullyu" this would not be a consideration, 80% is fine.

If you want a P-P Stick you have an easy route, buy almost any 40 size stick and maintain the proportions, chop the fuselage off a little way behind the wing mount and add the second engine. Then cobble up two booms to support the tail and you're done. The pair of 30s should fly a 40 stick aggressively.

Bill.

Thanks for the reply Bill and I think you are dead on.I guess I have a deal with wantin to hear more than a single piston beating itself to death.I will take your advice and move forward. Thanks,
Bill

Here is a plane made with two "sticks" combined, as Bill suggested. That is a trainer fuse in the middle. Stop the booms on the wing, instead of putting engines on it. Make sure you have room for getting your hand into the second engine safely.
Just a thought, lengthen the center fuse, to the rear, and mount a second firewall. The trainer has a front firewall..........mmm...let's see, I left the front firewall in this..........lengthen the trainer fuse to the rear.........mmmmmmmm. have two ST 40's laying around....four?......mmmm
Check you later....uh got to go....uh look at something!!
Twinman

Balsa Brain,

If the OS .30'syou have are plain bearing engines, you probably do not want to run one of them with a pusher prop. In that mode the thrust washer will be riding on the crankcase front end. Same reason manufacturers recommend not using an electric starter on plainbearing engines. BTW I have two of these same engines on a C/L deHavilland Hornet. They are not super powerhouses, but they are easy to start and extremely reliable.