A slant has developed

[Battson]

I've noticed that my plane has developed a slant, and I haven't been able to determine why (yet).

It was sitting level to start with, as far as I can tell. Now (220hrs later) the starboard wing tip is about 2"-4" lower than the port wing tip, on average. It is easy enough to see if you're looking closely, so I presume it's a new development.

I have checked the tires and the pressure is equal, I've tried increasing the pressure one or two psi on the low side to no avail (14psi base pressure). Fuel load I have discounted, it's not caused by lop-sided tanks.

My worst fear is that something has bent / distorted, but that is totally unfounded at this stage. I have theorised that the MLG oleo springs could be relaxing unevenly, or that one tire is slightly smaller than the other.

Has anyone else seen this?
Any thoughts on the probable cause?

It's a pretty minor thing, I agree. But it's been bugging me.

[Battson]

And to confirm it, one MLG spring is now approximately 1.5" shorter than the other, with equal weight applied to each. This surprises me.
Possibly a defective spring, developing a memory?
I believe that is possible if they aren't heat treated correctly?

[whee]

That's what I figured it would be but I didn't say anything because of my lack of BH experience. Luscombes lean when their oleo spring gets soft. Incorrect heat treatment would be my bet.

[S Lathrop]

Sounds like the issue is a spring yielding. This happens when a spring is compressed beyond a certain percentage of its length. This indicates to me there might be a QC issue with the spring manufacturer or the damping designed into the system may not be up to snuff. In any case the fix should not be difficult.

[Mark Goldberg]

I waited to respond to your post Jonathan until I had a chance to talk with Bob Barrows. He thinks you probably hit hard on one side more than the other and you might have put a set into the spring. You are an engineer and can probably do the calculation of how much spring set it would take to make the 1.5" at the wingtip. Bob thought somewhere between 1/16" & 1/8" difference in the heavy springs would give you what you are seeing.

Bob suggested you also look at the top of the shock struts and see whether both have the same length of tube sticking out above the bronze top cap. If you really want to take things apart you can check and see if that one spring has taken a set compared to the other. Bob suggested you just adjust it out with the rod end bearing. One to two turns should do it.

Now this is assuming you haven't bent anything. The spring taking a set is the most likely culprit. I replaced my two springs when my BH had about 500 hours, and both had taken about 1/8" set. Bob says that if it did take a 1/8" set, it probably will not take any more set and be stable there. Mark

[Battson]

Hi Mark,

I guess the wing is about 4" low, but I measured that one "bit above the bronze cap" is about 1"-1.5" shorter than the other. It depends how the plane is sitting.

The 'slantiness' has come on slowly over the last couple of months. At first it was barely noticeable, but recently it's become quite noticeable.

I am planning to change all my gear bolts at the next 100hr inspection (the 300hr), just to see how they are doing. I guess I should plan to replace both springs at that stage.

Jonathan