Hawker wing oscillation

TFaudree_ERAU said:
Oh come on now. The newer 800XPs and higher are actually 370-410 airplanes. You're only doing .74-.76, but you're still up there...

Regarding the issue at hand; from what I've heard, it's an aileron rigging problem. Cable tensions get slack, and with the reduced pressure over the tips of the ailerons due to winglet design, you get the flutter.
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Yeah, I was just gonna say that looks like aileron flutter. You can actually see the last 3rd of the wing twisting! *SHUDDER*
 
inigo88 said:
Flutter is no joke....
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Have you ever seen the videos on Youtube of the Cirrus pilot instructor who mounts his GoPro (or similar) camera to the top of the rudder?

Found one of them...



It's difficult to tell, but it looks like it's installed behind the counterweight and possibly behind the attachment point.
 
TwoTwoLeft said:
It's difficult to tell, but it looks like it's installed behind the counterweight and possibly behind the attachment point.
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:aghast:

That is an amazingly dumb thing to do. I mean, I know there's nothing in the PTS that talks about hinge moments and flutterLCO (I think) … I guess they just assumed people would know to not change the weighting and aerodynamic forces on a control surface using a GoPro and some gaffer's tape.
 
AIN Article from 2007 on API Winglets:
http://www.ainonline.com/aviation-news/2007-11-14/winglets-give-hawker-800-boost-range

Installation of the composite blended winglets requires removal of a section of the Hawker’s prominent aileron horn balance and the addition of leading-edge weights for aileron balance. Certification is expected next summer. Installed price is expected to cost about $350,000, significantly less than the $520,000 price for the GII winglet installation.
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Well there's yer problem!

AIN Article from May, 2013:
http://www.ainonline.com/aviation-n...in-advises-fl340-limit-api-wingletted-hawkers

In a Service Bulletin issued May 3, winglet manufacturer Aviation Partners (API) instructed operators with winglet-equipped 800-series Hawkers modified by STC#ST01411SE to reduce maximum permissible altitude to 34,000 feet. “Several instances of aileron/wing oscillations have been reported on the Hawker 800 [series],” the company said. “Aviation Partners and the FAA consider this Service Bulletin to be a safety-related limitation until a design change to preclude the oscillations is developed and FAA approved.”
Aviation Partners COO Hank Thompson said that after meeting with the FAA to discuss these incidents, “We did a great deal of analysis using finite element modeling, refining it and putting different models on the aircraft until we were able to get a model that agreed with what was being reported in flight.” It found that rebalancing the ailerons to a new tolerance forward of the hinge line fixes the problem.
The company tested “every scenario and potential model,” he said, “and every one of them dampened out with our solution.” Aviation Partners will flight-test the solution and then submit documents to the FAA, after which operators will be able to rebalance their ailerons and remove the 34,000-foot restriction. This should be ready next month, Thompson said. The FAA will be issuing an Airworthiness Directive that mirrors the company’s Service Bulletin, he said.
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Aren't they supposed to do the Finite Element Modelling before they get the STC? I'm curious why it didn't catch this the first time around.
 
Pilot Fighter said:
.... or we could hope that mods are well designed and adequately tested.

Have there been other incidents reported?
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I'm sure they weren't an overnight development done in a garage.

From what I've read elsewhere, there have been two incidents. After each incident, the cable rigging/tension was checked and brought back into spec, and it didn't happen again.

I'd say it's not a winglet issue so much as it is an underlying airframe maintenance issue.

I'm thinking this is going to be like the gear shimmy; happens to a few planes, they check the shims, and it never happens again. But you will hear about it for evermore...
 
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So, if you were to encounter something like this, what would your response be as captain?

I would assume slow airspeed to reduce load and hope for a speed that doesn't induce/maintain the flutter and descend to thicker air... but I'm just guessing.
 
rframe said:
So, if you were to encounter something like this, what would your response be as captain?

I would assume slow airspeed to reduce load and hope for a speed that doesn't induce/maintain the flutter and descend to thicker air... but I'm just guessing.
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The original sb did say to slow below m.70 to stop the oscillations. In the 3+ years of our installation there hasn't been any problems in many flight environments.
 
Slowing down causes the vibration to stop. Seems to take a certain Mach number and some light turbulence to set things off. Balancing and tensioning the aileron cables towards the tight side of the adjustment range solves the issue. Interestingly, there was a SB for reconfiguring and adding some VGs issued in 2010 for this same issue so it's been known for some time.

The story I've heard is that an operator encountered an aileron buzz/flutter problem and didn't buy off on APIs recommendations to solve the issue. Instead they went to the FAA. Subsequently, the current SB was issued.

Nothing like riding out weather that you could top because you're complying with a SB. Hopefully an AD with a terminating action will be issued soon.
 
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