Center line as to engine placement

[Don Chandler]

Has anyone had a plane that was flying well with the engine inverted then changed the engine to the upright position and had it want to fly tail heavy?

I see that by doing that I have actually lowered the center line of the prop shaft in reference to the center line of the fuselage by about a 1/4 inch. Could this be my problem?

Don

[Tim Wescott]

What is it doing that says "tail heavy" to you?

[Steve Helmick]

Do you mean that it seems tailheavy, or that it likes being tailheavy? Could you post a picture or two?

One thing you definitely did was to raise the CG somewhat. I'd hang it from the leadouts and see how vertical it is. You might consider raising the leadout guide to compensate. If the LO's are not in the correct place, that alone can cause instability or lack of "groove".

I wouldn't think that lowering the thrustline 1/4" (or 1/2") would do anything bad. If you put upthrust in it when you changed it over, that would be bad. Downthrust should be ok, tho. Get out the Robart Incidence Meters.  Steve

[Tim Wescott]

Steve means to look at how vertical it is when you look from the nose BTW -- he's thinking that since you moved the CG up without moving the LO guides to compensate, it may fly noticeably different.

[Don Chandler]

Going out to the shop to see how veericle it is. No, I didn't move the lead outs, wondered about that. It actually kind of porpoises, thats what makes me say tail heavy.

Don

[Mark Scarborough]

Porpoising is more commonly described as hunting,,

and leadouts, CG tip weight and handle sensitivity are to be looked at, as is control system freedom from drag

[Steve Helmick]

Steve means to look at how vertical it is when you look from the nose BTW -- he's thinking that since you moved the CG up without moving the LO guides to compensate, it may fly noticeably different.

Well, actually, no. I was suggesting that moving the leadouts up in the wingtip (or heavier wheels) might fix the vertical CG, if that has become a problem. But the main point was that the LO's position fore/aft can make a big difference in the "groove" (or lack of).

I'm really thinking that he's now got upthrust in it. That would very likely make it porpoise. I'm also wondering if the engine is mounted on the top side of the mounting lugs, because some (especially the .40LA and .46LA) have a huge draft angle on the topside of them. I'd NOT want to put that surface against any mounting beams, most especially on any one of the LA's. Then again, if it's mounted on an R/C mount, and that was also turned over, then maybe it has some angle error built into it, which could be good when inverted, but bad when upright? These are some of my questions, which might be answered by a picture or two of the engine installation, and perhaps provide a clue as to the cause & solution.  Steve








   

[Tim Wescott]

Well, actually, no. I was suggesting that moving the leadouts up in the wingtip (or heavier wheels) might fix the vertical CG, if that has become a problem. But the main point was that the LO's position fore/aft can make a big difference in the "groove" (or lack of).

Sorry to put words in your mouth.  Although, if nothing was changed but the vertical CG...

[Steve Helmick]

But if it's got upthrust, that would explain it pretty well. Could also be that a lump of lead was left off, I suppose. Maybe Don will find some forgotten nose-weight out in the shop?  Steve