Thrust Line

[Kiwi55]

I'm getting close to building the engine mount for my Cabin Eagle. I maybe just missing it, but I can’t tell from the plans just where the thrust line should be. Horizontally I'll be putting it dead center of the firewall, and I have seen several references to a 0,0 offset angle. But where is it supposed to be vertically? Dead center of the fire wall? I've seen mention of it being in line with the horizontal stabilizer, and mention of it being as high as the top of the firewall.
It is true I am planning on using a nonstandard engine (Rotax 582) but I would assume the thrust line still needs to be where the plans call for it to be. So where?
Thanks...Paul

[Dan_]

I am not an engineer, so use at your own risk, and I don't have the CE plans, but assume the thrust center line is located by building the fuselage according to the plans like the rest of the Eagles, since the engine mounts to the firewall instead of a separate built up mount.

If this is the case, your task would seem to be to determine the difference in the thrust line between the 2 engines, and adjust accordingly.

You can turn the gearbox up or down on the rotax, which should put you close.

With the major difference in installed weight, it is imperative to be sure to get the longitudinal CG of the aircraft correct --goes without saying.

At any rate...  the center line of thrust should coincide with the vertical center of gravity, else you will experience pitch excursions with power changes.

I used to fly a Kolb...  It had the clutch on the gearbox, so I wanted to practice an emergency landing because of the free wheeling prop acting like a big drogue chute.

Turns out, I had went a little long and went to full power for the go around a few feet off the ground.  The big nose down pitch change caused me to make a touch and go out of it.

My guess would be the thrust line is about 2 feet too high on those airplanes, but they fly just fine if you allow for the pitch changing with the power inputs...



This is how the gyro guys find the vertical CG.  Note the thrust line comes out at pilot's belly button...

[Kiwi55]

I appreciate the reply, but my problem is I cant tell from the original plans just where the thrust line is. The fuselage is built according to the plans. It's the motor mount details that elude me. Forget for the moment that I'm using a different engine, assuming a VW mounted according to plans. Assume also the VW is direct drive. Relative to the center of the firewall, how high or low is the crankshaft center line?
Thanks...Paul

[Dan_]

Are you sure you are not missing some pages of the plans..?

I looked in the Gallery and found an interesting photo of the CE...  Seems it has a built up mount.  Thus plans pages showing it must be present to build the plane.

[Leonard]

Hi Guys
Using another engine like a two stroke you MUST double insulate the engine from the fuselage as the vibrations are complete different from the VW engine and the tube from the fuselage will get in harmony with the engine vibrations and it can be dangerous.   Leonard  2-27-19