Twin Power

[foofighter]

Currently working on my first twin (1/8 Twin Commanche) and just got as far as the engine nacelles....

The scale thrust lines seem to be up thrust + considerable 'toe-in' (L engine has R thrust, R engine has L thrust).

I expect that the 'toe-in' is related to engine out performance which (hopefully) will not be a factor on an electric twin.

I was thinking that I should go with:

L engine 2° up, 0° lateral
R engine 2° up, 1° right

Does that sound about right?? :confused:

[AndyOne]

foofighter

Before you decide on the thrust lines you might need to take into acount the rotation of the propellers on the full scale and the model. Does the full scale plane have counterrotating props if so which one is clockwise and which is anti-clockwise, then compare this with your model set-up.

Of course none of this may make any difference at model scale but it's probably worth getting an expert opinion.

Where's Ollie when you need him.

Andy.

[foofighter]

I cant find any info for the PA-30 for the props but the last of the PA-39 Twin Commanches were the 'CR' version with counter rotating props. So I guess the PA-30 version wasnt.

I was planning 'normal' props both sides - maybe this is a bad idea? I hadnt considered that detail.

[BMatthews]

On our models it's usually not as big a deal to have counter rotating props We don't have as much torque effect to deal with. And like you said electrics don't quite on ya'.

I would use about 1 degree right thrust on both motors just to take care of what torque reaction you do have and the fact that you'll be using the same direction props. And probably go with 0 up or down thrust but allow for some modification for later.

From looking at the side thrust on the original being 0 on the left and 1 right on the right it sure sounds like the original used same direction CCW props just like we do. Perhaps you SHOULD just copy the side thrust angles.

Typical side thrust angles for most twins I've looked over shows OUTthrust on both engines when using counter rotating props.

[feihu]

foofighter -

FWIW - I have flown the full size PA-30. Both propellers rotate in the same direction, and that is CCW when viewed from the front looking aft.
Also FWIW, I would set the up/down thrust of the engines slightly above the vertical CG of your model so as to minimize pitch trim changes with power changes. And BTW, if you are going electric, then set the lateral thrust to zero on both motors since you won't be doing any single engine operation.

feihu