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Scratch plane with big trouble

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Scratch plane with big trouble

Old 01-11-2020, 06:06 PM
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stearman70's Avatar
Join Date: May 2012
Location: GuadalajaraJalisco, MEXICO
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Default Scratch plane with big trouble

I built a high wing of Spanish plans called Pumby. 60" wingspan, balsa and ply. . The plane does not mark engine and the bench comes as for a .35 two strokes glow. I puted a .46 glow on it. His weight was 5 pounds.
The plane dials 4 degrees down trusth and 2 degrees right thrust and was what I encased the engine. I leveled according to the planes but with all the throttle, the plane taked off as if it were very heavy tail, when the throttle was lowered in half, the plane go down, as if it were somewhat heavy nose. Very very unstable, even with little elevator movement, he behaved very nervously. The only thing not attached to the planes, is that for lack of adequate wood at the time, I made the leading edge with wood a 16" thinner than the plane marked, so the edge was a little round and not as sharp as the plane marked , but I think this is not so influential as to have had such an unstable, erratic flight and almost on the verge of the accident. I will be grateful to help me define what may be the mistake I made in building it or what may be the solution to never risk it again with another bad flight. I include plan for consultation.
Thanks in advance for your help.
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Old 01-12-2020, 05:37 AM
Join Date: Feb 2007
Location: Dearborn, MI
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Nice looking plane.
I am assuming that the center of gravity is exactly what shows on the plans?
Other than that, the plans show the incidence angles of the wing and horizontal tail to be parallel. I would set the airplane so that the tail is horizontal by using a LEVEL. Then check the incidence angles of the wing with the level on both wings at center, mid, and wing tip to make sure the wing is not warped.
If not matching, you will have to do some adjustments.

Last edited by hsukaria; 01-12-2020 at 05:39 AM.

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