Surviving Flutter - Slow Down

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pelmet
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Surviving Flutter - Slow Down

Post by pelmet » Sun Dec 08, 2019 9:42 pm

https://www.youtube.com/watch?v=2wOiGS9RODY

The pilot does give his experience of the first indication of flutter. Maybe each case is different and based on how quickly it happened, it is unlikely that most of us would recognize it and react before it got significantly worse. But if a flight control has just been replaced or painted, perhaps one should be alert for something like this and what actions were taken in this case.

Slow down now.
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PilotDAR
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Re: Surviving Flutter - Slow Down

Post by PilotDAR » Sun Dec 08, 2019 9:54 pm

Yes, any flight control surface work justifies extra attention, balancing is very important.

Also important is freeplay in trim tabs. The Reno accident with the Mustang is a case study in this. I was asked to test fly a Navajo some time ago, which was to include a dive test to 110% of Vne. I did my walkaround, wiggling anything which moved. I found that the elevator trim tab had about 1/4 inch of freeplay. I required that it be either made better, or that I be shown that Piper said that amount of freeplay was okay. After a fuss, the actuator was replaced, and the freeplay near zero. The dive went fine. I think that Cessna allows maximum 3/16" tab freeplay for many of their aircraft, and I go by that, if there is no other data. It's in the fine print, but it's worth looking up if there is doubt about the condition of the control.

This is the video which gives me the willies:

https://www.youtube.com/watch?v=TfL6iyeH8OA

You can even see the side of the fuselage oil canning ahead of the tail!
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jakeandelwood
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Re: Surviving Flutter - Slow Down

Post by jakeandelwood » Mon Dec 09, 2019 1:10 am

https://youtu.be/XggxeuFDaDU

Of course there is the famous Tacoma Narrows bridge collapse that was destroyed by flutter.
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goingnowherefast
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Re: Surviving Flutter - Slow Down

Post by goingnowherefast » Mon Dec 09, 2019 5:56 am

Flutter can go from 0 to gone in less than a second. The examples in this thread are the good ones where we know what happened. Flutter can also be set off in unexpected situations. Maybe you flew 20kts over the limit yesterday and were fine. Well today the temperature is different, your in a different plane of the same model, different altitude. Maybe yesterday was dead smooth, and today you hit a near imperceptible bump, somebody taps the controls, autopilot makes a small correction.

Flutter accidents are often like the Comet crashes were initially. Airplane falls out of the sky in pieces and nobody knows why.
Respect those airframe speed limitations like your life depends on it. Some day it might.
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AirFrame
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Re: Surviving Flutter - Slow Down

Post by AirFrame » Mon Dec 09, 2019 7:37 am

PilotDAR wrote:
Sun Dec 08, 2019 9:54 pm
The Reno accident with the Mustang is a case study in this.
Well, only sort of. The failure was in the trim-tab actuator that couldn't handle the loads associated with racing. The stock configuration on a Mustang is for there to be two tabs, one on each side, and they share the load. Ghost, like most of the racing mustangs, had one trim tab fixed and the other one took all the load. The actuator gave out. Only then did the trim tab flutter and depart.
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