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Old 08-21-2005, 01:32 PM
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BMatthews
 
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Default RE: Pitch up with new prop!

I suggest you try doing a dive test with the props on the plane. For something like a Funtana you should be able to push over to a vertical dive and then neutralize the elevator stick and the model should continue in a pure vertical line or pull the nuse back up VERY slowly..... like maybe pitch up only 5 to 10 degrees over a 200 foot dive. Set the elevator trim such that it flies at 2/3 to 3/4 of max speed and dead level hands off for a good time and then do the test. If it tucks and tries to loop negatively you're tail heavy with down trim to compensate. If it pulls nose up faster than indicated then you're nose heavy and flying with too much up trim to compensate. Move the CG to fix whichever way the model reacts and re-adjust the elevator trim to restore that level mid power cruise and test again.

I'm guessing that you're nose heavy and the extra speed of the higher pitch prop is inducing a climb due to the elevator trim. If not then you have thrust line issues.

With the CG and resulting elevator trim set according to such a dive test the model should show only a very slight or no tendency to nose up with added power. If it still acts up then I suggest you check the thrust line to wing centerline angle for any upthrust. It should be 0-0 or perhaps just one degree of downthrust.