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Other › Belt failures or belt dust in tail gearbox?
11-13-2005 03:02 AM  12 years agoPost 1
turbojoe

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Mesa, Arizona

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I crashed today. Hit tail first and bent the boom, shattered blades etc. After I replaced the boom and twisted the belt to the left as shown in the instructions I noticed some dust building up in the tail gearbox and spin down took less than half the normal time. I went ahead and replaced the gearbox halves and the tail rotor shaft, gear and bearings and still had the same problem. I must have had it apart a dozen times and couldn't find any problem. I then installed the belt with the twist opposite of what it says in the manual and viola! The belt wear is gone. Spin down now takes forever as usual. I did have to change the tail blade grips 180 degrees though. I'll fly it just long enough to get it trimmed out tomorrow. In the livingroom it doesn't seem to be out of trim by much if at all. The belt isn't that bad but I'll get a new one before I do any long flights.
Just sharing what I found that could cause others grief.

Joe

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11-13-2005 03:15 AM  12 years agoPost 2
MikeInMobile

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Mobile, Alabama

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This is a common issue. It is caused by a slightly bent tail shaft or a damaged tail shaft pulley. The vibration causes the belt to walk to one side, causing drag and excessive wear on the belt. Reversing the rotation of the tail simply reverses the wear pattern (on the Trex, reverse rotation of the tail always reduces wear on the belt). I had the same problem on one of my rexes and found this to be the issue. After replacing the shaft, I just kept the reverse rotation on the tail to reduce the wear on the system.

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11-13-2005 03:46 AM  12 years agoPost 3
Ozydego

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Westerville, Ohio

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Doesn't the opposite twist in the belt cause the blades to follow the main rotor wash instead of go up into it?? I thought that was one of the main things about tails, are the blades spinning up towards the wash, or looking through the tail to the blades... clockwise....

But Honey, I can't live with just stock.....

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11-13-2005 03:59 AM  12 years agoPost 4
turbojoe

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Mesa, Arizona

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I honestly didn't pay attention to which way the belt was twisted when I took it apart so don't know for certain that I actually reversed it from what I had originally. The tail blades rotate toward the mains. (clockwise looking from the right side). I guess I should pay more attention to what I'm doing when I take it apart huh?


Joe

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11-13-2005 05:46 AM  12 years agoPost 5
Tmaster

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TX

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I don't run a guide pulley anymore, it works better. I've had 4 flights so far without it and the belt is in the same shape. I had a problem before with the belt riding up against the edge of the guide pulley, and then the bottom of the belt was being cut on the back pulley. Belt dust all over and I crashed because the belt failed in one flight. No more guide pulley!!!!

Check out my gallery you'll see a pic of the sliced belt.

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11-13-2005 01:32 PM  12 years agoPost 6
Learn to Fly

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Yalesville Connecticut

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Tail blades should turn COUNTERCLOCKWISE. Main shaft CLOCKWISE!!!


Jeff
Believe nothing you hear, and half of what you see...

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11-13-2005 06:29 PM  12 years agoPost 7
Ozydego

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Westerville, Ohio

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Looking from the right, they should turn counterclockwise.... I Always look at it this way, because right side is a relative term... I say clockwise looking across the boom to the blades... less chance of error that way... The belt, when looking from the front should twist clockwise 90 degress....

What I would do is to replace your tail shaft, and then I would change the belt if it was my heli, but you can always take the belt out and turn it 180 degrees to get it turning right, and be on the good side of the belt.... I wouldn't chance it though....

But Honey, I can't live with just stock.....

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11-13-2005 07:00 PM  12 years agoPost 8
MikeInMobile

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Mobile, Alabama

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Reversing the rotation of the tail will not change the performance of the helicopter. The theory that the tail blade rotation should oppose the wash of the main rotor has metit on much larger helicopters, but on the small machines, the effect is not noticable due to the small amount of main rotor wash and the area (displacement) of the tail rotor blades. On a larger helicopter, the larger displacement of the tail rotor blades makes the disruption of the airflow across the tail much more noticable.

The Align tail pulleys are not really true, which causes the tail belt to walk. By reversing the rotation of the tail blades, this walk can be counteracted. It's your choice, but no damage or degradation of flight performance will occur from reversing the rotation of the tail rotor.

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11-13-2005 07:35 PM  12 years agoPost 9
turbojoe

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Mesa, Arizona

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I tried a new tail gear and shaft and it made no difference. The belt still made dust. My tail blades turn clockwise viewed from the right. (facing the tail blades). I can't run the belt the other direction or it will wear itself away. I did a short test hop this morning and it seemed to fly fine.


Joe

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11-13-2005 07:59 PM  12 years agoPost 10
Dos Equis

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Silver Spring Maryland

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The belt walk phenomenon is due to the fact that the shafts are out of perfect parallel of their respective axis to one another . The shafts should be within 1 degree or so, of each other.....

I've found a couple of reasons for this to occur, but there could easily be more.
The t/r case may have it's side plates shifted in a way that the t/r shaft is not 90 degrees to the t/r case side plates when assembled.
The bore for the boom in the tail case may itself be skewd not allowing perfect alignment.

Maybe shimstock strategically placed between the boom and the tail case could cure this.Or loosening and repositioning of components would help.

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11-13-2005 08:33 PM  12 years agoPost 11
steph

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Hampshire England

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I found with mine the outputt gear on the molding it had sharp edges after i removed the surplus plastic it was fine no more dust

The world is round you can run but you will always end up where you started from

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11-14-2005 01:19 AM  12 years agoPost 12
turbojoe

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Mesa, Arizona

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Would the metal tail case be a good idea? Would belt tracking be better with it? I already have the Micro Heli metal front belt drive gear. The prices are so good on the upgrades that my head is fully blinged now (minus the blade grips). I keep finding killer deals and snatch them up.
I'm only concerned about reliability not so much the looks. If it'll help keep me from crashing due to failures then to me it's money well spent. The only problem then is that I have to take ALL the blame when I crash!


Joe

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11-14-2005 02:18 AM  12 years agoPost 13
Ozydego

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Westerville, Ohio

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try a metal pulley for the tail blades... doesn't MH make it, that pulley may run a lot truer than the stock plastic pulley.... you already have the true front pulley... you may wanna try the true back pulley...

But Honey, I can't live with just stock.....

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11-14-2005 02:24 AM  12 years agoPost 14
MikeInMobile

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Mobile, Alabama

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The tail pulley (part of the tail shaft .... not available seperately) does run a lot truer than the stock pulley. The problem is that the case assembly is not exact and can result in offset of the tail shaft incidence. I guess if you used an incidence guage and set the angle to exactly 90 degrees when assembling the tail box, you would be OK, but as soon as you spooled the machine up, all that work would be undone (the 2mm screws used to assemble the tail gearbox will allow the incidence to change slightly due to their short length). Just a note ... the Microheli tail shaft does not work well with the stock tail case, not the Aligh metal tail case. The pulley is slightly wider than the Align one and will cause binding (I found out the hard way).

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