Lost Tailpower - broken setsrews in tailgear

[Knud Pedersen DENMARK]

Yesterday I lost Tail power – because the small setscrew that tighten the “Front tail rotor gear”(0427-1) to the shaft, did brake.
The end of the set screw is gone, so that the gear can turn on the shaft.
The setscrews is secured with Loctite 243……..
This is the second time I’ve got this failure :-(
Now I have made two flate areas for the both setscrews…….maybe this will help…..

Have any others have this failure with the setsvrews on in the gears????

[DavidH]

http://www.ronlund.com/Merchant2/mer..._Code=MA0800-7

The input shaft already has a flat on it. Grinding another flat is not going to gain anything. The set screws must be loosening for some reason.

David

[misio]

With continuums problem like yours I will ask any fury owner in you gang to check this out. I have notes that over years I did develop bad habits working on my helis.

[DavidH]

Knud,
Just reread the first post again. Here is a quote from it.

The end of the set screw is gone, so that the gear can turn on the shaft.

Just curious. But do you happen to be using the dog earred set screws to hold the gears in place. This would be the set screw that has a blunt tip on it that is smaller diameter than the set screw and protrudes approx. 2mm.

I don't see how the tip could break off a set screw that is flat or blunt on the end.
If your using the dog earred set screws. They should only be used to hold the tail rotor hub on the output shaft. You should only use blunt tipped set screws to hold the gears to the shafts.

David

[Knud Pedersen DENMARK]

I took apart the “tail gear box” yesterday.
It was the Gear on the “tail rotor shaft” that did fail.
The screw was not tight anymore (it was glued with loctite 243)
The screws that was in the gear was not the “dog earred set screws” – but some steel screws with Flat ends.

I the change the Tail rotor shaft (because of slop between the shaft and the Tail hub), I noticed that this new Tail shaft did have a “Bigger” flat area than the old shaft…….

I have now assembled the gearbox again – but secured the screws with Loctite 273…..

Maybe this will hold.

David H: “A blunt tipped set screws”

Is that a totally flat ended screw or has it small notch on the end?

misio: With continuums problem like yours,,,,,

mmhhh - maybe the problem is not that big. The Fury has flown +700 flights, and I had have this problem (last time it was the other gear) two time........



ChopperKnud

[Wayne]

The gears you are running are very well tested, and while it is possible you may have had a set screw break, I have never heard of that. Did you properly clean the set screw before you loctited it? And did you tighten it properly? Too much torque and I have seen them break, (but you would have known that) and not enough and it will come loose.

I have run those gears for no kidding hundreds of gallons and never had one just come loose or break in flight.

Another thought, and I do this a lot since I have caught problems, is part of your pre-flight every day should be to grab the tail rotor and the main blades and give the tail rotor a twist to see how much play there is. You will get a feel for what is right after a few times, then if it suddenly loosens up you might detect it during your pre-flight.

Good Luck!

Wayne

[Laddy]

He says one set screw. What happened to having two on there? Gear is drilled and taped for two. Instructions show two.

[Knud Pedersen DENMARK]

Wayne; I think that I might had “fumled” a little with the grease, so that the thread might not have being clean enough……
I tighten them as much as I dare….without breaking the hexagon….

Don’t you use both screws in the gear?


I also do this precheck of the heli before every flight.
One of the check is to hold the front tailgear, and then turn the tailrotor to see if every thing is OK….but there is a lot of free play between the torque and the two Delrin-transmission-shaft, therefore I might have overlooked that the gear was loose…….

PS: I use setscrews that are totally flat on the end – is that correct?


ChopperKnud

[DavidH]

Yes you should use two set screws in each gear.

The set screws should have a flat or cupped tip.

David

[Wayne]

The set screws are flat on the end. The gears have two set screws in them, but frankly one will work fine if it is loctited in right and is torqued right, as long as it is on the flat part of the shaft.

good luck, let me know if you have any more questions.

Wayne