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Pitch up violently

Old 09-08-2021, 07:40 PM
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kuobin
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Default Pitch up violently


Doing a loop with my high-wing trainer, just before the airplane reaches the bottom of the loop, iI feed in a little bit of elevator with throttle almost in idle, then the airplane pitch up so violently almost to vertical up.
It was like a free second loop it gives to you automatically, I really don't know what went wrong. Does anybody get the same problem before? thanks.

Last edited by kuobin; 09-08-2021 at 08:03 PM.
Old 09-08-2021, 09:07 PM
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Malcolm H
 
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Yeh, I’ve seen this when the wing bands are not strong enough to hold the wing firmly against the seating in the fuselage when subjected to the increased flight loads when looping.

From the pic your bands look pretty “skimpy”! I bet if you replace them with some heavier ones and use a few more, the problem will go away.

Malcolm
Old 09-08-2021, 09:57 PM
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kuobin
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Sounds very possible and reasonable, I will give it a try,
thank you so much.
Old 09-09-2021, 02:45 PM
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Originally Posted by Malcolm H View Post
Yeh, I’ve seen this when the wing bands are not strong enough to hold the wing firmly against the seating in the fuselage when subjected to the increased flight loads when looping.

From the pic your bands look pretty “skimpy”! I bet if you replace them with some heavier ones and use a few more, the problem will go away.

Malcolm
Yes, that brings back good memories, I've had it happen once on an old trainer.
Old 09-09-2021, 03:33 PM
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DRC1
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Originally Posted by kuobin View Post

Doing a loop with my high-wing trainer, just before the airplane reaches the bottom of the loop, iI feed in a little bit of elevator with throttle almost in idle, then the airplane pitch up so violently almost to vertical up.
It was like a free second loop it gives to you automatically, I really don't know what went wrong. Does anybody get the same problem before? thanks.
I don't think the strength of the rubber bands are an issue if your flying it as shown in the picture.

40 size should have 8 rubber bands. I have used 10 on an over powered 60 size trainer with the top of the wing beefed up to support them.

I looked up the instructions in the manual for an Avistar 40 and it states two #64 bands per pound of plane. Personally I feel that is overkill, 8 should be just fine.

My .02

Last edited by DRC1; 09-09-2021 at 03:43 PM.
Old 09-09-2021, 08:02 PM
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Ditto - with the plane on the ground, and holding the fuse, you should not be able to lift a wing tip and see any separation between the wing and the wing saddle, without so much force that you begin to think you may break something. More rubber bands.
While there is an idea that the wing is supposed to pop off in some crashes, that also allows it to pull away from the fuse in high G maneuvers. It needs to be solidly held down. Which may mean just as much damage as using wing bolts in a crash.
Old 09-10-2021, 02:40 AM
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Malcolm H
 
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He has 4 bands on that thing! Unless it weighs 2 pounds at takeoff, he’s got an issue!

M
Old 09-10-2021, 03:44 AM
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Originally Posted by tedsander View Post
Ditto - with the plane on the ground, and holding the fuse, you should not be able to lift a wing tip and see any separation between the wing and the wing saddle, without so much force that you begin to think you may break something. More rubber bands.
While there is an idea that the wing is supposed to pop off in some crashes, that also allows it to pull away from the fuse in high G maneuvers. It needs to be solidly held down. Which may mean just as much damage as using wing bolts in a crash.
It was also handy for badly built planes to be able to put the wing on a bit crooked to get it to fly straight(ish), then mark it's location with a pen for future reference.

Old 09-16-2021, 12:22 AM
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kuobin
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Originally Posted by Malcolm H View Post
Yeh, I’ve seen this when the wing bands are not strong enough to hold the wing firmly against the seating in the fuselage when subjected to the increased flight loads when looping.

From the pic your bands look pretty “skimpy”! I bet if you replace them with some heavier ones and use a few more, the problem will go away.

Malcolm
Thank you Malcolm, today I tried to fly again with two more rubber bands to attach my wing. The previous problem was gone. You are really sharp.
Old 09-16-2021, 03:58 AM
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Malcolm H
 
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Glad to help!

Nothing to do with being sharp, just been flying R/C a very long time!

Malcolm
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Old 09-16-2021, 09:26 PM
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tedsander
 
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Originally Posted by kuobin View Post
Thank you Malcolm, today I tried to fly again with two more rubber bands to attach my wing. The previous problem was gone. You are really sharp.
For a plane that size, I always use 10. 4 on each side, and the final 2 crisscrossed. I want that wing to be solid when I am training beginners, so when I have to pull out hard in a high speed dive, nothing will make it move....
Some may think it is overkill, but as long as you clean all the glow fuel off, they can be reused many times, so is very cheap insurance.

BTW - I only use the ones Sig Mfg. sells. Order on-line, or most good hobby stores have them. The ones from the big box office stores barely last one days flying session before breaking.

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