Motor offset guidance reqired

[Basil]

I am a newby and require some guidence re Engine offset/ down thrust.. I am using electric power.If the plan says for instance ' 1 deg right' off set , am I correct that the 'Right' is to the right of the rear of the motor from the centre so as the centre line is adhered to at the front of the motor.

If no mention of offset or down - thrust is made , on the plan, then none is made!!!!

How is this caculated , or is it derived from experience?

Your advise and guidance will be appreciated.

Barry

[Nigel R]

Experience, generally.

You are correct about the centreline at the front; the prop stays centre.

Downthrust varies, as it depends on the type of model.

[Keith England 1]

No right means point the motor to the right. Since you ideally want the propeller on the centreline of the model that would mean moving the back of the engine to the left of centre.

Downthrust can be calculated (to an extent) the thrust line should run through the centre of gravity of the model so a very high mounted engine (as on many seaplanes) may actually need upthrust but drag will have an effect too so so a degree of experimentation is going to be needed.

Sidethrust has more factors to consider. Basically there are a number of interactions but generally a conventional engine which turns clockwise viewed from the pilot’s seat will need right thrust to counteract a tendency for the plane to yaw left under power. It is always a compromise as reaction will vary with power, angle of attack and airspeed.

Of course with modern radios you could always programme elevator and rudder mixing with throttle to correct for thrust issues.

[Chris Walby]

Some designs use off set and some don't, others say the use of the rudder can be used to correct the swing to the left on take off.

Some small (indoor) models use very large amounts of down/right to "correct" a tendency to pitch up under full power.