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A strangely odd occurrance

Old 09-14-2016, 03:00 PM
  #1  
Glacier Girl
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Question A strangely odd occurrance

Got my GWS Me262 done, maiden went well yesterday. Just enough to trim it out. Got more then enough power, takes off easily at half throttle. And cruised just fine at that.

Today I take it out to see what she's got. Again, take off at half throttle, and flying fine. Problem when I go full throttle. Instant I do, she snap rolls to the right. Like someone has grabbed it on the nose and spun it like a drill.

Normally on the other 262's I've had you get a nose up climb, not something like this. You have to watch them on take off as you can cause them to stall because of this.

I'm not losing a fan, she holds equal thrust static all the way up to WOT.

I'm running E-flite 66 mm 6 blade fans. 3S3000 pack, and 30 amp esc's.
Only change I made was to move the fans back further in the nacelles. They sit just in front of the CG instead of the normal right at the front of the nacelles.

Only thing I can think of is torque doing this. But man that is some serious torque if that's the problem.

Notes: This occurs on going straight from half to full throttle. I did not try it going slowly from one to the other so I'm not sure on how she would react.
Also I don't have the rudder hooked up, so I'm not thumbing it when throttling up and causing this.

Any suggestions, or ideas?
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Old 09-14-2016, 03:18 PM
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solentlife
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I'm sure you've looked at usual things :

a) Fans thrust at same angle / incidence to fuselage / wing datum.
b) Fans rpm are same at intermediate through to full throttle.
c) ESC's not on power limits that when flying any full throttle may put one over the top ?

To Snap roll to right means a high differential on lift and thrust with Left overpowering the right side. But the ROLL part is the interesting bit ... indicating a speeding up or slowing down of one wing half.

Having flown quite a few twins ... it actually takes quite a bit of difference in each side to get a serious reaction ... and you say an instant snap roll !! That's more than serious.

Interesting to know what happens when you increase slowly ... trying faster increases in stages to see at what acceleration rate the snap occurs.

Weird !

Nigel
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Old 09-14-2016, 03:26 PM
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Glacier Girl
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Nigel, yeah it's a new one on me. And yep I've been looking it over and running static tests to see if I can find anything off, since I got back. And I'm not. She's in front of me now, and she's not telling me what is going on.

Once my nerves settle, I'll go back out today and try going slow on throttle up.
At least now I know what to look for.

And that's just it, at half throttle she'll take right off and climb like nobody's business. And she flies like a cat at that throttle. Like said, I've had other GWS 262's, and even a high powered HET version. None of them ever did this.

I hope the heck I can figure this out or somebody has an idea of what is going on.

Too nice of a plane to have it be a non fun flyer.
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Old 09-14-2016, 04:27 PM
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solentlife
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Get a straight edge and check all surfaces ... moving out across wing span ... tail span ... even fin ... to see if any twists or inconsistency from side to side ...

I have a 50mm EDF that flips easily ... due to a slight twist in tail feathers ... all looks fine and she flies nice until you give it full throttle and then she develops a mind of her own. I heat and straighten those feathers ... and she's good for a day or two but then it creeps back in.
It also affects hand launches ... if I don't know its crept back in again ... she barrel rolls into the deck.

nigel
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Old 09-14-2016, 05:01 PM
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Glacier Girl
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Nigel I just had a thought. I wonder if one of the fan adapters is slipping when I hammer the throttle? When I tried it on the ground I just ran up the fans to check the amps and thrust figures. Could have been I missed a millisecond of slip when I looked at the watt meter.

Maybe it's hanging on tight enough that on low throttle speeds it's coping but the surge when the throttle is hammered causes it to slip for a bit. Just enough to cause it to spin.

I'm going back out to check that.
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Old 09-14-2016, 05:04 PM
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solentlife
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Could well be ... but I would have thought you would hear the motors / fans out of synch ... the ear in fact is one of the best friends in synch'g motors.

Nigel
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Old 09-14-2016, 07:57 PM
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No my hearing is shot, way way too many open exhaust race engines took care of that.

But anywho, right fan, held the blades and twisted the back of the motor with a pair of padded needle nose pliers. Took some force but the fan adapter was slipping. Not so on the left side. Just to be safe I pulled them both and applied green loctite to em and the set screws.

Just tried slamming the throttle from idle to WOT multiple times, watching the amp gauge and feeling the thrust. Houston I think we have a fix.

Of course the thunderstorms are rolling in now. Hopefully they'll clear out and I can get in a test flight.

Thanks for your help Nigel!
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Old 09-14-2016, 09:14 PM
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Wildflyer
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I wonder if, at high speed one of the wings is bending slightly up or down depending on which side, causing an extreme aileron effect. This might be kind of like a high speed flutter, but not a continuous effect.

I had a prop plane that flew ok at lower speeds but took more and more aileron trim the faster it went, turned out when I joined the wing halves, I got the right side LE almost 1/16" higher than the left. sawed and re-bonded the wings and it flew fine. That is until I hit a tree at 125 MPH, I didn't even have a wing to fix.
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Old 09-15-2016, 12:52 AM
  #9  
Glacier Girl
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Nah it was the fan. Like a high speed engine flame out. Instant dead on one side, and full power on the other. Just like a P-38 does. Loose an engine/motor and if you aren't quick it will go into a death spiral.

The fan adapter on the right side was just tight enough that if I eased the throttle it would hold. But when I hammed the throttle, the drag of the fan caused it to slip badly.

I flew it again tonight and problem is gone. Now she takes off like scalded rabbit when I hammer the throttle.

Well if there is a good side, along with not loosing it in a crash, I now know what will happen if I loose a fan/motor in flight.

TSB/FAA case closed.
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Old 09-15-2016, 07:15 AM
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Good news all sorted.

Nigel
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