Broke Hawk drive-wire, Again!

[marked23]

I now feel as though I have earned the right to say that the Hawk Sport drive wire is junk.

I was in a hover, just a few feet off the ground. The wire broke. The heli spun. I was standing too close to try and save it... I had to dump it before it got to me. ...And dump it I did. Landing gear, blades, and everything attached to the boom.

This is the second time this has happened this summer.

I am never going to use the drive wire again. So what are my other options?

-Mark

[pepper]

sorry to hear about that!! convert it to the drive shaft..

pepper

[pepper]

this may help..

http://www.runryder.com/helicopter/t121002p1/?highlight=hawk+drive+tail

pepper

[Rodney]

Drive shaft is the way to go. Will never have problems again as long as you use loctite on the set screws that hold drive cups to shafts. They fly really well with shaft installed as well, when using 240 or 401 gyro.

[sreuss]

Mark,

What exactly failed on the wire drive?

I put about 100 flights on a Hawk III back in 2000, and was flying the FAI patterns with the wire drive. Although the drive didn't provide fast/clean start/stop piros, it was more than adequate for practising the maneuvers.

Cheers,
SteveR

[marked23]

The failure was that the wire broke. I've broken two. One broke at the point just barely inside the tail input shaft. The other broke at a point just barely outside the tail input shaft. The two breakpoints were mere millimeters apart.

The repeat location of the break makes me believe that the wire was whiping around back there. I had not glued my wire guide tube in place. It's cetainly possible that the guide tube slid forward and left the rear portion unsupported.

Another contributing factor is that I was using the wrong kind of lube for the tail gears. I was using a dry powder teflon lube. Upon examining the gears, it's clear that they were prematurely worn. I suspect that the gears may have been worn enough to allow the gears to jam against each other. If that happened, I can easily see the wire breaking.

A third contributing factor was the unbalanced tightening of the two set screws on the tail input shaft. I noticed that if you tighten one screw fully, and then the other, the wire is deflected to one side and you have a situation where the wire is not exiting exactly straight. With several trails, I was able to tighten the set screws equally and have the wire coming out of the tail input shaft visibly straight.
(I had not taken this care in the situations where I broke the wires. I remember that one was visibly deflected.)

Since I started this thread, I've been back in the air once... with the $54 torque tube mod. I crashed (pilot error this time). Since my torque tube damage was $45 worth, I decided to give the wire drive one more shot.

I've glued my guide tube in place and I'm now using Bullshot lube on the gears. The set screws are balanced such that the wire comes out straight. I'll probably get a chance to fly it this weekend. It took several weekends to break the others, so this experiment is likely to last the rest of the season.

-Mark

[ThBrtmn]

Mark...
Yes...please glue your guides in...this will help cause that thing will move. I do remember on RR a while back about the equally tightening the set screws being a problem for the break if you dont.
As Far as lube.... I went to Home Depot and got a can of White lithium grease(which will probably last me the rest of my life) and that will lube it pretty good. I dont have the exact # of flights that I had on my hawk but it was about 10 to 15 gallons worth. I never had a break. Here is Clintstone doing some small 3D stuff with my wire drive in. I now have a torque tube.
http://www.augustoheli.com/videos/videoarchive/Miscellaneous/Clintstone_BartsHawk%20Sport.wmv.zip

[WillJames]

Cool video work Bart!! That Haws flys great!!

[SteveH]

Marked23,

Here is a copy of a post I put up on "the other site" about the problem with the drive wire breaking. The is the cause and soution to your problem if you want to stay with the stock drive wire system.

The most important thing to making the wire drive live a long life is to properly align it during installation. By alignment I mean to check the runout of the wire in the tail rotor box input shaft after tightening the set screws. If there is any runout after tightening the set screws, go back and adjust the two screws until it runs true with no "wobble" at the joint between the wire and the input shaft.

If this is done properly, the wire drive gives little or no troubles, and if it is not done properly, I guarantee you it will break as well as cause vibration problems.

Sorry I haven't been around here much lately, but I'll try to do better.

[marked23]

I got a chance to fly yesterday. It seemed to work ok. I did have a bit of a scare though. I did a slow pirouet in forward flight and I got to see the wind-up that everybody talks about. The tail did complete the piro, but not without complaining. It was a violent, jerky piro and you could hear the heli complaining... "Voop, Voop, Voop!" it said as it spun once around... three sharp hesitations... like a three point piro, but not intended.

After that, I calmed down my flying quite a bit. I wasn't >trying< to break it. Just straight, long figure eights. It was good to go home with an un-crashed heli.

-Mark

[marked23]

... duplicate post