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

[ThreeD]

Jonathan

how did you resolve this?

I now have 60hrs on the plane and was working on the baffles to modify the cooling for cylinder Number 5

when I hangared the plane on sunday I had not noted a “slant but it is certainly there now

the plane has only 60 hrs on it and certainly has not had any “significantly hard landings but the right wing tip is about 5” lower than the left inside the hangar

I am going to go fuel up tonight after work in anticipation of flying on the weekend to test the mod for my baffles and will see if the slant resolves itself with some movement

currently the daytime temperatures here are in the 40 degree Celcius range so I need every ounce of cooling I can squeeze through the fins

Yours is the only report I have seen regarding a bearhawk sitting with a slant and am curious if you found what was wrong and how you resolved it

I assume it was simply to replace the springs?
Daniel Dagasso

[Nev]

Daniel, I've seen this too, though possibly for a different reason, but not consistently. So just to add another data point, any slight "slant" (when parked on level ground) caused by say a little more fuel weight in one tank or a mid-match in oleo spring settings can amplify over a few hours if the fuel selector is in BOTH and as fuel transfers to the low tank. Not to say it's the only cause. However if troubleshooting, put the fuel selector into another position to prevent transfer of fuel and eliminate that as a possibility.

On my aircraft, I typically lose air very slowly (about 1 PSI per week) from the left tire, which causes a slow fuel transfer to the left tank, which exacerbates any slant to the left. It's a double whammy because as one wing gets heavier, the other wing gets lighter, and the lower the wing, obviously the quicker the transfer.

It annoyed the crap out of me for months. Solution (in my case) ? I don't worry about it anymore .

[jaredyates]

303AP does this too, the right wheel leaks a little air very slowly. I need to add another squirt before we pack up to maybe fly it to Oshkosh in another day or two.

[ThreeD]

Daniel, I've seen this too, though possibly for a different reason, but not consistently. So just to add another data point, any slight "slant" (when parked on level ground) caused by say a little more fuel weight in one tank or a mid-match in oleo spring settings can amplify over a few hours if the fuel selector is in BOTH and as fuel transfers to the low tank. Not to say it's the only cause. However if troubleshooting, put the fuel selector into another position to prevent transfer of fuel and eliminate that as a possibility.

On my aircraft, I typically lose air very slowly (about 1 PSI per week) from the left tire, which causes a slow fuel transfer to the left tank, which exacerbates any slant to the left. It's a double whammy because as one wing gets heavier, the other wing gets lighter, and the lower the wing, obviously the quicker the transfer.

It annoyed the crap out of me for months. Solution (in my case) ? I don't worry about it anymore .

Nev and Jared

thank you, I think you were right on the money with what happened, I had the right tyre at 11.5 psi and the left at 13, and the fuel selector was on both so the right side tanks were full and the left were not, I am building my knowledge base

thanks for your patience

[Battson]

Jonathan

how did you resolve this?

Yours is the only report I have seen regarding a bearhawk sitting with a slant and am curious if you found what was wrong and how you resolved it

I assume it was simply to replace the springs?
Daniel Dagasso

Hi Daniel,

I think it was the springs "relaxing" ever so slightly, as you suggest. I know of several others who have had the same issue and changed their springs to address it, including Patrols and 4-Places.

In our case, I can't recall ever doing anything about it - except having spare springs on hand in case it got worse, and monitoring the situation.

Eventually it seems to have evened itself out again. The problem went away on its own.