Gearbox clutch dissengaging

[scottessex]

I was flying the other night and I had pulled the throttle back slightly, and shortly afterwards the engine sped up as if the prop had come decoupled.
I put it down in a field, and checked everything out, all seemed ok so I flew out of the field and back to the house. :confused:
Flew fine the rest of the week. last night I was flying and had reduced power slightly, I was in a slight bank, turning into the wind. And it did it again! Engine sped up like it lost the prop, so I pulled the throttle back, and then shoved it all the way open and the clutch grabbed and held. I flew over the airstrip for about another 20 min without problem. :confused:

The engine is an Arrow GT500 65hp, with a 2.73 red ratio, The gearbox has a sprag clutch (one way clutch) I don't know what causes this, but I don't like it much. Any info would be appreciated.

[rehler]

Sounds like the sprag clutch is slipping and needs to be replaced.

This happened to me twice with a homebuilt helicopter. I finally went to a larger sprag clutch set up. The smaller ones (too small) just did not last very long.

[scottessex]

That sounds bad, seeeing how there are NO parts available for this thing!

I guess I could E-mail Doug Smith at Air command and see if they have any spares from way back.

[jos]

Repair the sprag clutch before you fly. The planetairy redrive will get destroyed with debris from the clutch if you carry on,then you'll need parts.
Give me some info regarding engine I'll have a look for a sprag.

JOS

[scottessex]

Jos, it is an Arrow 2 cyl 500cc engine with the 2.73:1 reduction drive. It has the 2 gears in the box, Not the planetary style. It has a right turning prop, same as a Rotax.Thanks.

[mceagle]

Gearboxex with sprag clutches can be oil sensitive. You shouldn't use a friction modified oil or use any oil friction modifier additives.

[scottessex]

I am using Dextron II as per the mfg's recomendation.

It did it again to me last night! :eek:

[scottessex]

Does anyone have drawings of the Arrow offset gearbox??? I have it off, but I need to know how to remove the sprag without breaking anything.!

[rehler]

Scott,

I don't know about the Arrow gearbox, but in some cases the sprag clutch is "press fit" into position with a several ton hydralic press. Sometimes an "interference fit" is used, where the sprag clutch is actually larger than the housing, so it is cooled to make it shrink and the housing is heated to make it expand. Then the clutch is pressed into place. If this is the case you may not have the equipment to change it yourself and have to send it out to have it done. I hope this is not the case.

[scottessex]

I hope that That ins't the case, I just have to figure out the proper order to take things apart, and if there is a snap ring or two hiding inside before I get pressing too much. I have a 20 ton press, and a manual press, oven, and dry ice and access to a large assortment of pullers and adaptors here at work.

[jos]

hello,

Have a look at http://www.hoverland.it/

Under prodotti you find arrow engines.
There is an email adress and a phone number.
The guy is nice and has everything. He took over the business from Guido.

JOS

[jos]

Hello again,

In case you use your 20 ton press and the gearbox comes out to short, I have complete ones, but second hand.

JOS

[scottessex]

Thanks JOS, I will let you know. I wish my Italian was better, Thanks