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Old 12-08-2008, 09:33 PM   #1 (permalink)
HEIM JOINT
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Default TREX250 Tail analysis, spacer upgrade and Chinese weights

These are videos of :
  • Diagnosing the tail bind problem.
  • A bearing spacer upgrade.
  • Chinese weight testing
Diagnosing the tail bind problem.
I had this tail assembly to design the chinese weights for the T250. But first I had to get the tail assembly to work smoothly enough to do the testing.
I am not bashing Align!!! The things that you see in the video are problably not typical. this was probably a bad tail. This video is just to help those who might not know how to diagnose a mechanical problem. These are areas to look at to find causes of excessive drag. Your tail may have none of the issues seen in these videos.

TAIL BINDING PART 1
T250 TAIL BINDING ANALYSIS PART 1.wmv (7 min 11 sec)

TAIL BINDING PART 2
T250 TAIL BINDING ANALYSIS PART 2.wmv (6 min 6 sec)




Comments:
  • On this tail, just replacing the blade grip bearings was 90% of the cure.
  • The spacer upgrade (video below) eliminated the severe slop in the blade grips. I think the angle that the blade grip moved to under load caused binding of the link and bushing on the blade grip.
  • The pushod forces of 10-12 oz. seen at the end are typical of a 200 size heli (Identical to a gaui 200)
  • I think the high blade grip slop may allow the grip to rub or bind on the hub under load on some helis.
  • The axial clearance gap between the hub and the blade grip was only .002" on the tail I had. That would explain why Bert's longer bolt fix worked on some helis. This is probably addressed by Aligns replacement hub.
Bearing spacer upgrade and Chinese weight test



These are videos of:
  • Why a spacer decreases the bearing loads
  • What exactly is bearing preload
  • Can Chinese weights help the T250
I designed the bearing spacer upgrade to allow the slop to be adjusted out like a Kasama grip. This was necessary to get the tail I had to behave. This also reduces the loads on the bearings from moment loads (bending) by over half. (Note: this does nothing for the centrifugal loads on the bearings, they remain unchanged) The Chinese weights are the same as all the others just scaled down for the T250

SPACER UPGRADE & CHINESE WEIGHT PART 1
TREX 250 TAIL BLADE GRIP UPGRADE & CHINESE WEIGHT PART 1 (9 min 17 sec)


SPACER UPGRADE & CHINESE WEIGHT PART 2
TREX 250 TAIL BLADE GRIP UPGRADE & CHINESE WEIGHT PART 2 (9 min 38 sec)




Comments:
  • I dont think any single bearing blade grip setup will will perform as good as two bearings preloded with spacers.
  • You will need to trim the tail blade to clear the longer blade grip screw (see picture)
  • Chinese weights will not cure a binding tail problem!!!!!!!!!!!!!! They will only improve a properly functioning tail.
  • The Chinese weights are tuned for the curved "batman" blade. They will work with the straight blade but the pushrod forces will be higher (about 5 oz.)
  • The Chinese weights reduce the pushrod force to 1/10th of original.
  • The Chinese weight nut is self locking to allow you to fly immediately (still use loctite)
  • The Chinese weight sets are matched to within 0.002g to minimize any balance problems
Both the Bearing spacer upgrade kit and the Chinese weights will be available in 1-2 weeks. I will post in this thread when they are available with more information.

PLEASE DONT PM ME OR INQUIRE IN THIS THREAD UNTIL I POST THAT THEY ARE READY!!!!!!
IT MAKES DOUBLE WORK FOR ME TO ANSWER PMS INQUIRING BEFORE I HAVE THEM AVAILABLE.

Thanks for your patience in advance,

HEIM JOINT
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Last edited by HEIM JOINT; 12-08-2008 at 10:39 PM..
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