TREX250 Tail analysis, spacer upgrade and Chinese weights

[HEIM JOINT]

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 http://www.youtube.com/watch?v=9WmzpeQY6YA
TAIL BINDING PART 2 http://www.youtube.com/watch?v=-Y1UBDJaNVo



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 http://www.youtube.com/watch?v=gP2OYVEjU0Y

SPACER UPGRADE & CHINESE WEIGHT PART 2http://www.youtube.com/watch?v=8IOXbuMOJfU



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

[12/07/41]

HEIM JOINT
thanks for all your time and work on this!

[s76 mech]

Yup thanks, that looks so cool, add me to that list!

[DesertClimber]

I watched your vids last night. Good stuff!

[NotEnoughTime]

Heim Joint,

You are undoubtedly The Man! From the time you spend to make these mods, to the time spent in explanation of theory in all you do. You and Finless are top notch examples of knowledge applied in our sport. I commend you for all you do and look forward to future advancements that you will surely take part in.

[Gutaaaooo]

Can I get on a preoder list? I want these BAAAADDDD. They do wonders on my T450, and t500. TKS MAN!!! YOU ARE GREAT!

[heli-on]

Awesome job throwing these vids together, let alone the in depth detail you go into.

I was skeptical about the effectiveness of chinese weights on a model this small. You totally blew my theory out of the water.

I was wondering if your only reason for placing the bearings in the polarity you chose was to cup the grease (as was explained in the video). It seemed to be that when simulating a load on the bearing (pressing the stack towards the head of the bolt), action seemed smoother with the open end facing the bolt head (which forces the bearings into their races). Do the bearings have polarity or are they just as effective in either orientation?

Please put me in the queue for the bearing and chinese weight mods. Again, nice work and thanks for taking the time to put together undisputable evidence of your findings.

[teshreve]

Just watched all 4 videos. Very nice work. Really, exceptionally well done.
In one of your other videos, you mentioned it was probably a good idea to keep trivial forces on the servo with any "chinese" weighting, instead of a true zero load. I tend to agree as any servo gear lash, linkage slop, etc would only be felt at the transition from/to 0 pitch (instead of throughout the range). In this video the weights pretty much show zero forces until the end (and may even go negative?).
The sheer size of the weights in relation to the grips is pretty amazing.

Thanks for the info!

[HEIM JOINT]

[quote=heli-on;998277]
I was wondering if your only reason for placing the bearings in the polarity you chose was to cup the grease (as was explained in the video). It seemed to be that when simulating a load on the bearing (pressing the stack towards the head of the bolt), action seemed smoother with the open end facing the bolt head (which forces the bearings into their races). Do the bearings have polarity or are they just as effective in either orientation?
quote]

A Standard radial bearing has no direction. Its thrust capacity is the same either direction. On larger bearings the ball cage or retainer is symetrical and the direction to cup the grease would not apply. On these very small bearings the ball cage is not symetrical and does have a "cup" direction. On some of these blade grip bearings that I have seen that I would consider poor quality, it looks like the retainer may stick outside the bearing faces under axial load and might rub whatever is next to the inner race. This may be part of the "binding problem" since just changing to another bearing set removed 90% of the drag.

HEIM JOINT

[blade strike]

SOB.... I'm sold!!! Great work man and sign me up for a kit when ready!!!!