Techniques for measuring/checking engine side thrust?
 

The Robart incidence meter can be used to check for and measure +/- engine thrust. But what about side thrust? Assuming it's not so off as to be easily visible to the eye, what methods are there for checking side thrust?

Firebee (Mike P.) offered one technique, namely measuring the distances (on both sides) from the prop tip to the rudder post with a piece of (on non-stretchable) string. Are there any other methods?

*****

I just tried Mike's method using a length of wire cable with a small hook that snags the edge of the "tail post" (which technically my SE5a model doesn't have since it uses a hidden lever to actuate the elevators). I then pulled the cable taut up to the prop tip marked the spot on a bit of tape, rotated the prop 180 degrees and checked that it was at the same spot (as Mike says in case there is an issue with prop symmetry). Then I connected the cable on the other side and measured again.

And the distance is, indeed, about 2mm shorter on the port side, meaning there is some degree of bad left thrust. I'm not sure how much this amounts to. I suppose it could be worked out with a few more numbers and some geometry. But it's enough to know that it's there and needs to be corrected.

Unfortunately this won't be quite as easy as placing washers under one side of a mount since the engine is mounted on beams built into the model. But it's doable.

A drill size or so bigger than needed in the wood beam mounts will probably give enough slack for a few degrees.

That's my hope. I'm also hoping that there is enough space between the two beam to allow the engine to move. The engine is seated pretty tightly.

[h=2]The Robart incidence meter can be used to check for and measure +/- engine thrust. But what about side thrust?[/h]
Just support the plane on it's side/wingtip.

Les

I hate to think the effort needed to make sure the fuselage is level on its centerline while balanced on its wingtip. :eek: Definitely a two (or more) man operation.

Of course, ff the wirewall is perfect perpendicular to centerline (as it usually is on most models baring any building errors) then it should be possible to measure side thrust with some sort of modified triangle or protractor. I looked at several different protractors designs in the store yesterday and none of these seemed like they would allow me to measure "around" the engine. The angle might also be too small to measure with such a device.

" Definitely a two (or more) man operation"

Not at all. A string from the front of the plane (crankshaft for instance) to a hook in the sky (ceiling) and back to a pin in the tail, and you can adjust to your heart's content"-))))))

Les

2mm on a 12"(?) prop is about 1/2 degree.

Martin

That's all it looks like to me. If you know what you're looking for, you can see that it's not exactly square, but no one would casually notice it.