SonexBuilders.net

Hi,

Overtime a few hard landings have resulted in the main gear on my Onex taildragger deforming. It's enough that my right wing tip is now 3 inches lower than the left.
Does anyone have any advice on rebending the Onex one piece main gear?




Thanks,
Wayne

I bent the left leg of my Onex gear in a hard landing. The bend was more than you have in yours so I had to deal with it. I removed the gear and found a hydraulic press. It would be very difficult to rebend the gear without removing it from the aircraft. The forces required to straighten the gear are certainly sufficient to damage the fuselage if the fix is attempted with the gear in place. Using wood and padded blocking I was able to bend it back into the original shape. This is an iterative process due to springback so it took several attempts to get the gear leg back to the same on each side. There is obviously an amount of bend that is not fixable without weakening the gear. I checked mine for cracks or other signs of permanent failure and found none. The gear was re-installed and the aircraft now sits even. I will closely monitor the wing tip heights to detect any sign of future gear leg weakening. Should that occur the gear will be replaced.

Many years ago the tailspring on my Sonerai broke (a com prob then) in half after landing resulting in a ground loop. The wheel pants disintegrated and the main gear splayed out. With the gear still on the fuselage I tied a chain come-along between the two axle points and cranked it in. I was 25 and broke so it was good enough. Today I'd probably replace the gear.

Interestingly, a friend took the broken tail spring to work, cut the failed ends off, and put them under a high powered microscope...you could count the successive breaks across the diameter leading to the failure.

peter

vhhomer wrote:I removed the gear and found a hydraulic press.

Do you have a picture of the hydraulic press, or even better a picture of the press being used to straigthen out your gear.

Thanks, a picture is worth a thousand words and it will help out many OneX pilots.

vhhomer wrote:It would be very difficult to rebend the gear without removing it from the aircraft. The forces required to straighten the gear are certainly sufficient to damage the fuselage if the fix is attempted with the gear in place.

Thanks for the response. I had considered trying to straighten the gear while in place, but I'll take your advice and remove it from the airplane. I have access to a large hydraulic press at my place of work but since this is an iterative process, and my airplane is 135 miles from my office, I'm wondering if I should get myself a Harbor Freight press to do it at the hangar? How exactly did you set up the gear in the press to straighten it? I'm scratching my head a bit on this one.

Thanks,
Wayne

I used a 20 ton Harbor Freight press. Unfortunately, I don't have any photos of the process. Be sure to pad the gear to avoid denting it where it contact steel in the press. I made a tracing of the bent gear or some plotter paper and compared the gear to it as I went through the straightening process. You can layout the position the bent leg needs to in up at on the paper. As far as the set up I used some hardwood blocks and positioned the gear crossways in the press. Take little bites at it and continually compare the gear to the pattern you have made. Also, carefully measure the angle between the leg diagonal and the vertical part where the wheel attaches to get the camber back in line if it has bent. The wheel mount pad also needs to be checked for twist. This can make setting the toe-in difficult. Mine seemed to be OK.

When you re-install the gear do a complete check on symmetry, toe-in, camber and, of course, are the wings now level.

I'm sure there's a metallurgist out there who can advise as to how much bend can be safely straightened. I would be interested to hear from him/her.

vhhomer wrote:I used a 20 ton Harbor Freight press....

Thanks for the explanation, I feel a little more confident about taking this on now.

I contacted Sonex and they said the gear is cold bent and should not be heated.
They also sent the below diagram showing the main gear geometry.

The MLG may not have been tempered correctly. This is the solution:
http://www.okeefeaero.com/

When I had my Onex, I replaced my main gear by a custom gear from Grove. I shipped the original gear to them. Grove questioned the design of the original gear, the alloy used and the temper of the alloy. Grove chose to use 7075 alloy (don’t remember the temper) for the gear and it was slightly beefed up. They should have the design handy and might be able to replicate it easily if anyone is interested. IF I remember correctly, Sonex told me that the gear out of specs should not be bent back and should be replaced. They also told me that the design was fine and that people just landing the Onex too hard For the gear.....