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  • October 01, 2020, 01:00:25 AM

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Author Topic: unwanted pitching  (Read 285 times)

Offline Ara Dedekian

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  • Ara Dedekian
unwanted pitching
« on: September 15, 2020, 06:34:52 PM »
 

        Fixed up three '90's era hand-me-downs and although line tension is very good during maneuvers all three pitch up when entering the upwind side of the circle. I don't mean hunting; they pitch up to the top of the circle, even when entering that side of the circle on landing. It's hard to keep them down and level during flight. On one of these landings, with all line tension gone, it glided down to a perfect landing (spectra lines). So I'd say the balance is OK(?).

       The builder added reversed trailing edge stock on top of the wing trailing edge as if to act as an aileron and compensate for a warp, but I didn't detect a warp. I shaved half the thickness on one and the flight seemed slightly better. There's tip weight as the outboard wing is a bit down on landings.

       The engine thrust line is level with the fuselage centerline.

       Any ideas?

       Ara
« Last Edit: September 15, 2020, 06:52:54 PM by Ara Dedekian »

Offline Bob Mears

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Re: unwanted pitching
« Reply #1 on: September 16, 2020, 08:02:19 AM »
As heavy as that model looks, I'll bet its tail heavy. Move your push rod to the top of the control horn and cut off about half that plank of a tail, lengthwise.
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Offline Ken Culbertson

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Re: unwanted pitching
« Reply #2 on: September 16, 2020, 10:12:48 AM »
I agree that it is probably tail heavy.  If the leadouts are that far back then the CG is probably back there too.  It has been a long time since I flew fast combat but from the length of the tail arm I would guess that the CG should be somewhere around the spar.

Ken
AMA 15382
If it is not broke, don't fix it.
If it is broke, replace it.
USAF 1968-1974 TAC

Offline Ara Dedekian

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Re: unwanted pitching
« Reply #3 on: September 16, 2020, 10:36:08 AM »
As heavy as that model looks, I'll bet its tail heavy. Move your push rod to the top of the control horn and cut off about half that plank of a tail, lengthwise.

        Bob, Ken

            I can do an easy test tomorrow by moving the leadouts forward and then adding nose weight to see if things improve. If I'm going to cut into it, I may as well go all the way and cut the entire tail off, add a carbon boom and convert to pressure. I'd copy the moments on my Corehouse GX planes. Easy enough and it would be worth doing since the wings are intact. Oh, and then replace the OS 40FPs and Fox 40 plain bearings they came with.

       Thanks for the replies,

        Ara

Offline Bob Mears

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Re: unwanted pitching
« Reply #4 on: September 21, 2020, 09:10:04 AM »
Your leadouts have no bearing on your CG. You should leave them where they are. If it is tail heavy moving the leadouts forward will just make it loose on the lines.
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Offline Ara Dedekian

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Re: unwanted pitching
« Reply #5 on: September 22, 2020, 02:58:46 PM »
As heavy as that model looks, I'll bet its tail heavy. Move your push rod to the top of the control horn and cut off about half that plank of a tail, lengthwise.

        Bob

           You're right; 1-1/2oz of nose weight took care of the problem. Didn't alter the plane or control system other than removing the trailing edge pieces.

        Ara

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