I am buildina a pusher ! Should the engine be angled up and why ?

[mortonj69]

see below

i made my motor horizontal and got no lift

[matter]

Hi,
More details would be helpful, but here's a bit of theory:

With a plane that has the motor behind and above the center of gravity and the center of drag, engine thrust will try to make the plane pitch downward.
This happens because the line of thrust is above most of the drag-causing parts of the plane.

(if the plane is hard to keep up with full throttle, but pitches up more easily with less throttle, this is the case.)


Tilting the motor so that the prop faces upward means that you are tilting the line of thrust downward so that it passes closer to the 'center of drag'
that will reduce the plane's tendancy to nose down,
BUT it will also mean that a portion of the thrust is pushing the plane downward!

I'm guessing that those are the problems you're encountering.

If you can give me more info (cg, and what happens in the air with the motor horizontal) I'll try to give some specific advice.

[tim hooper]

mortonj69,

This thread is closed. Please do not post the same question in multiple forums.

Tim Hooper (Moderator)

[kensp]

mortonj69

When an aeroplane has a motor with a thrust line above the CG then a nose down force is developed that acts like down elevator. On your aeroplane the designer has reduced this force by making the thrust line closer to the CG point.

Ken

[Ollie]

Yes, the thrust line should be angled to provide down thrust when the motor is below the level of the center of drag and up when it it passes above the center of drag of the whole model. I'm guessing that the wing has lots of dihedral and that the wing tips are above the thrust line. At slow speeds more than half the total drag is at the wing tips. If the thrust line was at or above the wing tips, then up thrust would be required. The level of the thrust line in relation to the level of the total drag of the model determines whether the thrust produces a nose up or nose down effect. The angling of the thrust line is to compensate for the nose up or nose down tendencies. The greater the vertical distance between the thrust line and center of drag, the more angular compensation required. The best thrust line adjustment minimizes changes in pitch atitude with throttle changes.

[leccyflyer]

I've merged the five threads which were posted on this identical question into one. Please do not make duplicate postings of the same thread in different forums.

Brian