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HelicopterAerial Photography and Video › Help with a weird tail issue
09-02-2009 01:48 AM  8 years agoPost 1
cranester

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Bogota, Colombia

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Hi, I´m finishig a new t-rex 700 cameraship, I've been testing it yesterday and today.

I got rid of all the initial bugs but the heli wobbles really bad at about 1600 head speed, then I switch to Idle up at 1740 head speed and the wobble disappears but then the tail starts to bob up and down.

What could this be? Its a brand new kit so there's nothing bent.

thanks.

Juan Crane

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09-02-2009 01:55 AM  8 years agoPost 2
nooobs

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web

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...

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09-02-2009 03:14 AM  8 years agoPost 3
SeismicCWave

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Hilo, Hawaii

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Tail bobbing up and down is definitely a case of rotor head problem. Start with the flybar then work with the rotor blades.

Things to check are the usual.
1) Main blade CG
2) Main blade weight
3) Flybar length
4) Flybar weight
5) Flybar balance
6) Softness in the teetering

A brand new kit doesn't mean all the metal shafts are perfectly straight. Don't assume anything.

Generally skid shakes, tail bobbing up and down are low frequency vibration attributable to the main rotor head. Tail fins buzzin, mid frequency vibration attributable to tail rotor shaft, tail rotor blades out of balance.

One suggestion, put a set of flybar weights on the flybar. That way even if the flybar is a little bent or out of balance you can trim it back by shifting the flybar weights.

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09-02-2009 03:50 AM  8 years agoPost 4
rerazor

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Mich.

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Is this a stretch or 700n conversion?

Robert

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09-02-2009 04:04 AM  8 years agoPost 5
cranester

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Bogota, Colombia

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Thanks SeismicWave, I have disasembeled the head to check everything and found a missing socket screw, one of the two that fix the rotor head to the shaft there was a little bit of play between the shaft and rotor head because of this, I'll have to wait till tomorrow to fly it but I'm almost sure this was the problem.

Robert it's a t-rex 700 converted to electric.

Juan Crane

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09-02-2009 02:57 PM  8 years agoPost 6
cranester

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Bogota, Colombia

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ok.. It did not solve the problem and everything else in the hesd seams to be ok.

Juan Crane

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09-02-2009 04:08 PM  8 years agoPost 7
jhamlinjr

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Milledgeville, GA, United States

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Try loosening your gear mesh at the maingear to motor pinion a bit. Just thinking that has caused me issues in the past. Hope that's the magic bullet.

HALO

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09-02-2009 07:49 PM  8 years agoPost 8
SeismicCWave

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Hilo, Hawaii

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Juan,

You need to get back to the basic of rotor head balancing. I know you have a lot of flight time under your belt so some of the things may be trivia to you. However I found that when ever I am stumped with a situation I always default back to the basic. We are not above the law of physics.

1) Let's double check the cg of the main blades. Put them on a razor blade and see if they are both at the same positions on the span. Otherwise you need to adjust. This will cause the majority of the shakes at different RPM because of centripetal force.

2) Use an accurate gram scale and weigh the blades. They have to be within .01 grams of each other or less.

3) Measure the flybar distance between the two paddles. Make sure that they are equal or at least balance without one side being heavier than the other.

4) Install a set of flybar weights. You can move them around to adjust the flybar balance.

5) Check your rotor blade tightness. Sometimes when they are too tight they can't swing out to dynamically balance themselves.

6) Check if the flybar is a little warp.

7) Make sure the flybar paddles are lined up properly with the proper angle of attack (which should be zero/zero).

8) Make sure the flybar paddles are screwed in the same amount.

9) Make sure the run out on the main gear is acceptable.

10) Make sure the main shaft is not bent.

11) Make sure the main shaft bearings are in good shape.

12) Make sure the tracking of the main blades stay the same.

Basically concentrate on the main rotor head from the main gear and up. That is the only thing spinning and giving you the vibration.

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09-02-2009 10:50 PM  8 years agoPost 9
cranester

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Bogota, Colombia

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Thanks for your time Seismicwave I will double check everything.
I appreciate your help.

Juan Crane

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09-02-2009 10:55 PM  8 years agoPost 10
jhamlinjr

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Milledgeville, GA, United States

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Did you try loosening your mesh?? I've seen this in person several times cause exactly what you are describing. Simple thing to try.

HALO

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09-02-2009 11:19 PM  8 years agoPost 11
cranester

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Bogota, Colombia

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Yeah I did, but the head is all disasembeled so I haven´t flown it yet,

I have loosened the mesh, changed dampeners for softer ones and I am balancing everything out. Tomorrow I'll test again and see.

Thanks!

Juan Crane

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09-03-2009 05:06 AM  8 years agoPost 12
Vortex Aerial

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Riverside Ca

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All though i have no first hand experience with the 700E conversions, i have been told that the 700N likes a higher head speed and during a HC setup on a friends 700N i watched it wobble while in a hover until the head speed was raised. This was with YB 710s.

Another thing to try might be running the blade drag bolts at a tightness that is just tighter than what it takes to keep the bolts from moving up and down in the grip hole in which case you’ll probably have to manually start the head spool up by hand to keep the blades from folding.

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09-03-2009 07:38 PM  8 years agoPost 13
cranester

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Bogota, Colombia

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Put everything back together and flew several batts today, tail issue is gone!

Not sure what was causing it but I suspect it was the dampners, even at very low headspeeds there is no wobble or tail bob.

Thanks for your time.

Juan Crane

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09-03-2009 10:35 PM  8 years agoPost 14
SeismicCWave

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Hilo, Hawaii

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I am glad everything worked out for you.

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