Heat-Induced Control Blockage

[rwanttaja]

Seattle has a very temperate clime... temperatures almost never get above 100 degrees F, and almost never drop below 0 F.

Until this year, the record for the number days per year above 90 degrees was *three*.

This year is different. We're up to about seven.

Today was one of them...about 95 degrees, absolutely beautiful day to fly an open cockpit airplane. I took Moonraker up, flew around for about 40 minutes, then came back and landed. As I rolled out, I decided I wanted more. But the fuel was a tad low, so I pulled up to the pumps to get it filled.

After a bit, I fired up and taxied out to the runway. Start pre-takeoff checks....

Hmmmm. The ailerons are sticking. They'd go to the right just fine, then come to neutral and lock. A bit more pressure and it'd clear....

But, shoot, somethings wrong. I taxied back to the hangar and shut down. After pulling out my ear plugs, I wiggled the stick back and forth. There was a distinct "Thud" when the stick went left of neutral, synchronized with the sticking. Following my ears, it seemed to be coming from the aileron itself.

I climbed out and took a closer look. The inboard aft edge of the aileron was striking the end corner of the aileron notch in the wing. I could work things by hand, and actually feel the surfaces rub across each other.

No other sign of issues...no buckled ribs, no wrinkled fabric.

The only thing I could think of was the heat, and the fact that the airplane sat out in it, stationary, for about 30 minutes.

I pushed it back into the hangar. Five minutes later, the interference was gone, and there was a gap about the thickness of a business card where the pieces had been striking, before.

Pretty amazing.

I'm going to try to shave off in the inboard side of the aileron to get a bit more clearance... just taking off the paint might be enough.


Ron Wanttaja

[wallda]

Very interesting discovery. Glad you caught it.

[Marc Zeitlin]

I climbed out and took a closer look. The inboard aft edge of the aileron was striking the end corner of the aileron notch in the wing. I could work things by hand, and actually feel the surfaces rub across each other... I pushed it back into the hangar. Five minutes later, the interference was gone, and there was a gap about the thickness of a business card where the pieces had been striking, before.

On VE's, Long-EZ's and COZY's, there is a requirement (in the plans) to have at least 0.060" to 0.100" of clearance between any control surfaces and the parts of the wing/canard/winglet next to them. When I do Condition Inspections, I find that this is a common error that many builders make - not leaving near enough clearance on control surfaces (including mass balance horns). Usually for aesthetic reasons. While I'll sometimes let it go if the clearance is just slightly less than 0.060", I ALWAYS tell the owner that it needs to be opened up to eliminate the chance for binding, and if there's only a paper's width of clearance (or even a credit card's width), I'll tell the owner that the plane's not leaving the shop until it's fixed by one of us.

On these canard planes, this binding and lockup will usually occur (for aileron cove clearance issues) during a high G maneuver. There have been instances of binding/lockup in flight and the way to stop the binding is to unload the wing/canard by pushing the stick.

Definitely something about which to be aware, and definitely a safety issue.

[rwanttaja]

Thanks, Marc, interesting insights.

I'm just amazed it took ~35 years for the right conditions to exist for this to happen. Talking about it in the Fly Baby community, several mentioned that they included extra margins around the ailerons to ensure this never happens to them. It just semi-freaks me out in that this happened just with the airplane sitting quietly on the ground....

Ron Wanttaja

[Frank Giger]

Or, you could be like us in Alabama and build the wings, including fitting the ailerons, in 105 degrees with 85% humidity.

[Neil]

I would have to ask if you have aluminum trailing edges. The heat expansion of the aluminum would be the culprit here as the wood probably would not expand the same way. I would agree that the gap was too small anyway.

[rwanttaja]

I would have to ask if you have aluminum trailing edges. The heat expansion of the aluminum would be the culprit here as the wood probably would not expand the same way.

My plane appears to have been built totally stock, and the plans call for either steel or aluminum trailing edges. So you're probably right.

Ron Wanttaja