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Old Feb 02, 2013, 10:51 AM
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farmington, mn
Joined Sep 2003
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Would a oversized prop cause turning issues?

I have a 36 inch balsa DR1 that I made from aerodromerc.com I love the plane but as with all dr1's it is tail heavy and I had to add something like 4 ounces to the nose. When I went to maden flight I couldn't get it to turn right unless I was at full throttle, it would fly level and straight but just wouldn't turn right and even at full throttle at was a slow turn, never tried it dead stick. I and using a 12x6 e-flight prop. Would using this large of a prop cause this or is it more related to a cg issue? I used a large prop because the front of the cowling is huge and wanted to get more air flow past the closed up cowling.
Thanks jeff
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Old Feb 02, 2013, 11:00 AM
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Ian Easton's Avatar
United Kingdom, Scotland, Fife
Joined May 1999
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It may need some right thrust. Check that it has no warps. Check the the stab is straight relative to the wings and that it is not tilted down on right side.
Ian
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Old Feb 02, 2013, 11:16 AM
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Joensuu, Finland
Joined Mar 2002
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Well, the full-size DR1 had this tendency too - it was actually faster to turn 270 left than 90 right.

I'd check that controls move freely and there is no pushrod bending or other sources of blowback when the airflow hits a deflected control surface. If you don't already know how to do a coordinated turn using both ailerons and rudder, you will need to learn it. CG has no effect on turn rate. Prop size might have something to do with it - to test if this is the case climb high, close the throttle, push nose down to maintain airspeed and then try to turn.
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Old Feb 02, 2013, 11:50 AM
I eat glue
Canada, NS, Yarmouth
Joined Jul 2006
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The rotary powered fighters would turn faster to one direction because of the spinning mass of the rotary engine, not so much due to prop diamter. A large prop could cause a torque roll though, especially with enough power. The full size Mustangs could kill an unwary novice pilot if he rammed the throttle to full get up and go low to the ground, like in an overshoot. The combination of big prop and tons of power would roll the Stang into the ground before the pilot could react.
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Old Feb 02, 2013, 12:54 PM
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South Wales U.K.
Joined Mar 2003
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Take it high, turn the motor off, and hope it glides enough to see if it still turns left and right Ok.

If it does, it's a motor/prop/thrust line problem.

If it doesn't, then it's an aerodynamic problem, (controls, warps, twists etc).
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Old Feb 02, 2013, 03:04 PM
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Albuquerque, NM USA
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If you want to check cause first, then do what e said and put it in a glide.

I'd be using a 9-10" prop on a plane that size.

As above. Check wings and tail alignment. Also check to see if the tail surfaces are flexing. They may need rigging too.
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Old Feb 02, 2013, 05:01 PM
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farmington, mn
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Is the a good way to check the alignment of the tail to the wings? There are three wings so where do I start other then the old eye ball
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Old Feb 02, 2013, 05:18 PM
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Two (three) points to align. And start with the eyeball

1. make sure horizontal tail is 'flat'. I stand back and look at the tail to see that it is level with wings.

2. make sure vertical tail is 90deg from horizontal and is aligned straight front to rear.

3. measure horizontal tail tips to wing tips (any one will do) on both sides. they should be equal.
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Old Feb 02, 2013, 05:46 PM
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United Kingdom, Scotland, Fife
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A quick check is to hold the model and look at it from the rear.Rotate the model up and down and you should notice the TE of the wing(s) as it lines up with the tail. The same point on each side of the wing should "appear on the horizon" or the TE of the stab at the same time as it rotates. If they don't then something is twisted.You can see small differences with you eye.
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