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Old Sep 20, 2011, 08:27 PM
Sure it'll hover!
omster's Avatar
United States, MI, Sanford
Joined Jun 2007
165 Posts
Question
Can thrust angle cause rolling out of loops (unintentionally)?

So I've got an old Extreme Flight Extra 300E that I really love... in fact, the motor blew off of it (right through the cowl) mid-flight, destroying the original motor cage, but the rest of the airframe was fine - so I built my own motor cage/mount - which, so far, is holding up great.

When I rebuilt it, I'm not sure I added 3 degrees right and down thrust perfectly... it may be off one way or the other.

Now, when I try doing a somewhat tight loop - it always rolls out of it to the right. It's not just loops, anytime I pull back somewhat heavy on the elevator, it wants to roll out right - almost caused me to go in tonight

I've already checked the lateral balance and it seems fine...
Could an incorrect thrust angle cause it to behave like this???
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Last edited by omster; Sep 20, 2011 at 09:57 PM.
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Old Sep 20, 2011, 08:51 PM
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Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
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Does the elevator pushrod go to one elevator or both. If it goes to only one elevator that is connected to the other elevator with a rod, then you may be getting unequal deflection of the two elevators under heavy load.

Larry
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Old Sep 20, 2011, 08:58 PM
Sure it'll hover!
omster's Avatar
United States, MI, Sanford
Joined Jun 2007
165 Posts
Quote:
Originally Posted by Lnagel View Post
Does the elevator pushrod go to one elevator or both. If it goes to only one elevator that is connected to the other elevator with a rod, then you may be getting unequal deflection of the two elevators under heavy load.

Larry
It goes to one side - I'll double check the deflection, but I can't remember having this problem before I rebuilt the motor mount. Just wondering if incorrect thrust angles would cause it to roll out like it is...

Edit - I checked the model and the elevator linkage is on the right side, so I don't think that's the problem since it's rolling out that way...
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Last edited by omster; Sep 20, 2011 at 10:00 PM.
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Old Sep 21, 2011, 12:35 AM
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Moab, Utah, USA
Joined Apr 2003
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If the elevator control horn is attached to the bottom of the right elevator then while pulling up for a loop the right elevator could very possiblly deflect up more than the left elevator under a heavy air load. That would be the same as giving right aileron causing the plane to roll right.

I would think that your problem is more of a control surface/wing warp situation. Engine right and down thrust is more of a yaw and pitch moment rather than a roll moment. I suppose with a lot of dihedral the yaw moment of the righ thrust could induce a roll to the right. But it doesn't seem that such a situation would be limited to just doing loops. The thrust induced roll would also happen at high speed straight and level flight.

Larry
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Old Sep 21, 2011, 12:46 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
11,190 Posts
Yes, incorrect thrust angle can lead to screwing out of loops. Of course any plane will screw out of a loop if you try to loop too tight so first be sure you are not trying too loop too tight and causing a wing to stall.

Standard test for correct side thrust is as follows:

Fly your model straight into wind at full throttle and pull up into a vertical climb. The theory here is that as the airspeed bleeds off, a continued vertical climb is now fully dependent on engine power alone. Do not use rudder (or rudder trim) to correct for any deviation from the vertical. Your model will do one of three things.
  • If the model continues to climb vertically, the side thrust is correct.
  • If the model gradually, then more noticeably, veers to the right, the model has too much right thrust.
  • If the model gradually, then more noticeably, veers to the left, the model has too little right thrust.
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Old Sep 21, 2011, 12:46 AM
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ilektron's Avatar
United States, CA, Carlsbad
Joined May 2011
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I have seen several sport planes do this and never thought to check elevator deflection. I assumed it was thrust. I'll have to check this out! Thanks!
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Old Sep 21, 2011, 06:46 PM
Registered User
Wallingford, Ct
Joined Sep 2001
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Too much elevator is the first thing to look at. Then a crooked airplane( including elevator bending ). Then the thrust.
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Old Sep 23, 2011, 10:26 PM
Will fly for food
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United States, CA, Carlsbad
Joined May 2011
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Are you saying something about my plane building abilities?
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Old Sep 23, 2011, 10:32 PM
I like to fly!
United States, WI, Monona
Joined May 2011
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Quote:
Originally Posted by ilektron View Post
Are you saying something about my plane building abilities?
Hahaha! It's always good to check everything over just to make sure something's not crooked. It can take as much as nicking the plane as you take it out of your car to bend something up.

But I would definately first look at how you're doing your loops. A full elevator loop will most likely cause you to roll out. A smooth loop will allow you to have more control throughout the whole thing.

Good luck!

Alex
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Old Sep 24, 2011, 06:28 AM
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Wallingford, Ct
Joined Sep 2001
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I had an early arf that always rolled out. It took me a while to notice that one wing panel was 3/4 inch longer than the other. I also hah one plane with a heavier wing panel than the other. It had the same problem, but only slightly. It can be a hard thing to find.
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Old Sep 24, 2011, 08:37 AM
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United States, MN, Buffalo
Joined Jul 2011
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How does it stall?
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Old Sep 24, 2011, 06:37 PM
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United States, CA, Garden Grove
Joined Oct 2000
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If your model has no warps in wings, you are probably entering a loop at too slow a speed and stalling at the top of the loop where motor torque takes over and plane rolls out of the loop. The same will happen if you try to loop too tightly, wing stalls and torque takes over. If you have plenty of power, try doing larger diameter loops and reduce power when you go inverted and as you start down from the top of the loop. I have a P-26 Peashooter (own design-retired) that usually fell out of loops and rolls. It did not develop enough airspeed in the climb due to the drag of the dummy radial engine etc., and excess wing loading which caused it to be stall prone which allowed tourque to take over and make it roll out of the loop. ( That's my theory and I'm sticking to it. )
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Old Sep 26, 2011, 12:42 AM
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United States, CA, Carlsbad
Joined May 2011
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Hmm... excess wing loading has been a possibility for the planes that I have seen do this. One plane I had I tried it with the recommended setup, seemed to loop fine. I added a larger engine and more batteries. Afterwards, it started rolling out of loops. Probably added 1-1.5 lbs. I assumed it was only the torque of the larger motor.
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