In Line Electric Cessna

[Terry Warner]

Hi to one and all

I am in the final stages of getting ready to fly my Cessna 336 but not sure of the motor set up. Any suggestions as to how to set up these motors:-

• both on the centre line using a pusher prop on rear?
• both on the centre line but reversing the rotation on rear using standard prop motor's then rotate in the same direction)
• Or offset front down and right leaving rear straight using normal props on both
  

or what do you suggest ????

Thanks in advance

[TheFlyingCrust]

Hi Terry. Have a read of this thread and have a word with Simon.

Lovely looking model. I'd have thought with props rotating in oposite directions (as viewed from the nose ie. lefthanded prop on the rear) there shouldn't be a side thrust issue - but I have no direct experience.

Ian

[Simon Chaddock]

Terry

Counter rotating props on a push/pull is a very good idea.

It does not really matter which is which but the complete absence of torque makes the plane feel very 'secure' in the air. Rapid power application even close to the stall has no effect other than it speeds up!

I can put my Cessna in a positions at slow speed that normally only a 3D plane would be happy.

On the full size the rear engine is parallel to the fuselage datum but the front has a couple of degrees down thrust, presumably to reduce 'power on' pitch changes.

On mine I set the motors zero/zero and it does have a very slight nose up pitch change at full power but to be honest for a scale type I prefer that rather than absolutely neutral.

Edited By Simon Chaddock on 10/07/2013 09:48:03

[John Olsen 1]

While counterrotating props would be ideal, it means you need a pusher prop for the back, and while these are available, there does not tend to be the same range of sizes and pitches as for standard props. Actually pusher is not really the right word, really they are left and right handed props, since on a normal (full size) twin they would both be pulling and would turn opposite ways.

So if you can get the props you want, counterrotating is the way to go. If you can't get them, then with the rear motor reversed you can use two standard props, just make sure that the lettering on the prop faces the front of the aircraft so the airfoil on the prop is the right way around. The foamy Dornier that Erfolg has and that I have as well does this, and torque effects don't seem to be a major issue.

Of course, if you use IC engines then reversing the rear motor is not quite so easy. For the ESM Do335 I am putting together I have managed to find a three bladed pusher (or "left hand" ) prop that should be about right. So it will have counterrotating props, although the engine and hence the prop at the front will be bigger. (120 on the back, 160 twin on the front. ) There is some amusing confusion on the Dornier 335 thread at the RC universe site about the effects of turning a prop around...that does not turn a puller into a pusher, it just makes it work much less efficiently.

I would suggest for simplicity that if you do need to use engine offset, just put it on the front. If you do put any offsets on both, remember they need to be reversed at the back to have the same effect.

John

Edited By John Olsen 1 on 10/07/2013 10:59:00