Aerodynamics really interest me, but traditional configurations don't really do too much for me considering the amount of creative freedom r/c offers. You could say I'm as much a fan of design as a fan of math! Anyhow one idea I've been throwing around is for a twin engine combat aircraft based on the Blohm & Voss BV P.170:

http://www.luft46.com/bv/bvp170.html

Some alterations I've been considering are: Removing the center engine, and introducing more stylised wingtip landing gear cowls extending from the engine pods. Has anyone successfully flown anything with wingtip mounted engines and rudders? Is such a design even feasable?

these dungarees,

Interesting aircraft; don't know anyone who has made anything even remotely similar.

If you're talking about making a "combat aircraft" as in R/C combat, it is probably doable, but also probably not a good idea. With all the bumps and taps in the furball, not to mention the wing to wing mid-airs, if one prop broke or the engine died, you'd most likely have one heck of a motorized Frisbee until you got the other engine stopped. The R/C combat twins I've seen had the engines as close together as possible in case there was a hit, so the good engine would be near the center line. That would (theoretically)help to lessen the immediate yaw problem and possibly allow the plane to keep flying with at least a little control.

I was going to build a twin SPAD DPS for my first attempt at a multi-engine, but the 170 is interesting... So many planes, so little time!

You might post your question on [link=http://spadworld.net/]SPADWORLD[/link] and see if anyone has tested the concept on a low cost coroplast design.

Let us know what you come up with!

Blue skies,

DL

Engine outage would be an instant spiral dive. But an electric version is easily doable. I'm also just guessing but if the prop rotation of the outer engines is chosen to counter the usual tip vortex rotation there may be some "free" lift to be had.

I suspect the roll rate of such a design with IC engines at least would be poor - banks would be slow to initiate and slow to stop. And the complexity of the whole thing would make it a hard combat plane to live with.

there would be big outboard loads on the wings on landing. the wing structural weight would be very high.

This design would have a low strength to weight ratio.

However I think it would be interesting to try it - and totally agree that electric is the way to go.

The lateral area on this plane seems quite minimal - I wonder if its laterally stable in the current configuration.

Fast for a piston engined plane though > 500mph!


I agree with BMatthews - the only design reason for putting the engines out there has to be related to trying to minimise (tip) vortex drag.

Thanks for the replies! What's the reason behind using electric?

Btw, my main goal is to design a working plan for this configuration that will not only fly okay (in theory), but also look good doing it.

Simple - electric makes it easy(er). Nothing to tune or adjust, no starting routine - just move the throttle up. No mess, less noise.

Consider one electric motor getting knocked off, and still attached to the plane, and still running.
Euuuuuuuuuuuuuuuu!
I have been playing with seperate ESCs on a twin, to handle the rare occasion when one motor quits,
both as a pusher and a push-pull...
With this Gentle Lady, the plane is controllable at less than 40% power on one motor.. it will turn into the running motor.
More than that amount of power, it can't do that.
With a wingtip motor running.... I think "Frisbee" is an apt description.

You never had a glow engine quit on you for no apparent reason or due to being slightly misadjusted? On a normal twin with the close spaced motors you can compensate for the offset thrust with rudder and get away with it. Some twins with one engine out will fly almost normal while others are limited to level or descending flight or a spiral dive into the dead engine results.

On a model with the engines at the tips the leverage of the running engine combined with all the drag being so offset would mean that the model would go into a death spiral at once and the only way to recover would be to put that engine to idle or kill it as well and glide back. With electric the possibility of a motor quiting is far smaller (I would have said "won't happen" until I saw Paul's post... ) so you can pretty much forget about that issue.

That plane is intended to look at one-engine flight.
Both motors have seperate speed controls, running from seperate channels.. the left motor on ch. 3, the right on ch. 6.
Using P-MIX-1, 6 is slaved to 3, with the knob on 6 set to sync the motors.
Either or both can be stopped in flight.
The plane runs out of rudder control preventing the running motor from pushing the nose towards the dead motor at about 40% power.
Adding "outthrust" of about 10 degrees to each improves that to about 50% power, before the rudder can't stop the turn.
The conclusion I draw is a power failure, glow or electric with a twin is very deadly, IF the power isn't instantly cut back to idle, and the dead motor identified so the corrective controls can be used after the live motor is slowly advanced in power to get the plane back.
The last photo shows full rudder with the plane going to the right. Pulling back power will let the plane go to the left, straight or right.
The other reason (other than because I wanted to) for the push-pull is when holding the plane prior to launch with my left hand, the right prop in the pusher mode was very close to my left ear, to which I am quite attached.
Making that motor a tractor had no effect on the flyability.