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Pusher Prop angle

Hoomi

Well-known member
#1
I'm getting ready to mount the power pod in a 3 channel pusher plane. Looking at the old Parkzone Fighterbird I found at a thrift store some years back, it has a significant up-angle on the prop, but the control on that plane was V-tail rudder only, with climb/descend based on motor thrust. That left me wondering if they had the prop angled so as to push the nose up more with power, while a true 3 channel with elevator/rudder control in the tail wouldn't need quite so much.

The nice thing about the power pod system, is that I can adjust the angle as necessary after a test flight, but I'd rather at least get in the ballpark for the first time out.

Any insights from those who have blazed this trail before, would be very much appreciated.

Thanks!
 

Hai-Lee

Old and Bold RC PILOT
#3
Simply put ideally the thrust line from the motor should pass through the planes centre of mass.
This is so there is no motor thrust tendency to want to rotate the plane around its centre of mass due to the thrust effectively pushing the plane nose down if the thrust line is above the centre of mass or nose up if the line is below.

When setup properly the amount of motor thrust will make no difference to the pitch or yaw of the plane though it may tend to push the plane downwards, (flat towards the earth), on launch where the motor is mounted above the planes centre line.

Have fun!.
 

Hoomi

Well-known member
#4
Okay, if I'm reading that right, if I have the prop angled either level or slightly down on the pusher, with the prop above the center of mass, it will tend to rotate the nose down, so I'm going to want a slight amount of up angle on the prop.
 

quorneng

Well-known member
#5
Hoomi
Correct but having the thrust line passing through the centre of mass will prevent the plane trying to pitch up (or down) as the power in increased but the plane will still tend to pitch up with the increase in the planes speed resulting from the extra thrust.

A plane has two sets of conditions. The effect of adding power and the effect of a particular speed.
The thrust angle can be set to compensate exactly for one or the other but not both, unless you add 'on board' stabilisation.;)
Normally the thrust angle is set to a compromise angle that suits how you want the plane to behave.
 

Piotrsko

Well-known member
#6
If I recall correctly, you have the same plane I have just different name. Motor is close to center of wing, but above center of mass. Mine has a couple of degrees up built in and flew decent, but if you are adding more power it may need more.
 

Hoomi

Well-known member
#7
I've set the prop angle with just a slight up angle. I'll see how it flies, and decide if I want to try and adjust it more, or leave it as-is.

This is a scratch-build plane, not the Parkjet, so it's still an unknown if it'll fly worthwhile at all. I'll have its own topic posted here shortly with a few photos.
 

BATTLEAXE

Well-known member
#8
If you look at the Explorer i think it has the answer you are looking for. It's design is similar to what you are building and has about a 15 degree down thrust line to the center of mass. The Sea Angel on the other hand has zero thrust angle as explained by Peter S. that because the tail feathers are directly behind the prop wash no angle was needed. Seems to be a few variables involved

EDIT... sorry I said Sea Angel, I meant Sea Otter, my bad