Suspected tail-flutter downs Otter (DHC-3T) • US Sep. '22

[Garfly]

 

 

 

[mkennard]

"This video is private". Can't watch it

[tillmanr]

Same for me.

[Garfly]

Sorry, it must have been taken down for some reason.

It was a regular Blancolirio video.  It will probably re-emerge.

Here is Kathryn's Report of the same incident:

 

 

http://www.kathrynsreport.com/2022/09/de-havilland-canada-dhc-3t-turbine.html

 

 

And here is one pertinent comment from the Blancolirio video:

Mark P

2 hours ago

Good video! As a young design engineer working at a major aircraft manufacturer, I had a friend ( older and more experience than me) who was in charge of the flutter model wind tunnel testing of the YC-15. One day he stopped by my desk and suggested I follow him to go watch a video of one of their tests. As I watched the video, they incrementally increased the wind speed while sending the horizontal stabilizer a "pulse" (literally pull a string that was attached to it) simulating a gust or other similar disturbance. Finally at one critical speed, the tail failed almost instantly. I couldn't actually see the flutter because it happened so quickly. When he re-ran the video in slow motion, we saw the pulse deflect the stab upward, and then it cycled down and up for about 2 or 3 diverging cycles, and then failed completely. Absolutely NO chance for pilot intervention. The results of this test had already resulted in design changes to stiffen the tail, so the first vehicle rolled out with the stronger tail already in place. That moment was one that will remain in memory and it gave me great respect for flutter for the remainder of my 43 year design career.

 

Edited October 13, 2022 by Garfly

[Garfly]

 

 

FAA Emergency AD:

https://drs.faa.gov/browse/excelExternalWindow/DRSDOCID139391948320221005002535.0001

 

EXCERPT [click for full rez] :

 

 

FAA Under Scrutiny for Timing of DHC-3 AD

Transport Canada issued a similar airworthiness directive more than four years ago.

https://www.flyingmag.com/faa-under-scrutiny-for-timing-of-dhc-3-ad/

 

 

 

Edited October 13, 2022 by Garfly

[facthunter]

Flutter is bad news. Most times it happens quickly and nothing can be done. Nev

[Garfly]

Here is the re-posting of the original video by Blancolirio:

 

 

[facthunter]

Salt environment and vibration. Aluminium doesn't like it. The Otter dates back to the 50's.  Nev

[Student Pilot]

Otter is a good machine, designed with the 1340 radial. The turbine pulls harder and flys faster than the radial ever did, this creates problems the designers didn't allow for.

[APenNameAndThatA]

16 minutes ago, Student Pilot said:

Otter is a good machine, designed with the 1340 radial. The turbine pulls harder and flys faster than the radial ever did, this creates problems the designers didn't allow for.

Flutter occurs because of excessive airspeed (actual airspeed, not indicated airspeed). I could not work out how an established, old, slow design could get flutter. Looks like I just found out. 

[Thruster88]

Flutter also occurs when things get loose, working rivets, cracked parts or worn control rods etc.

The Vne on the turbine conversion DHC-3 was reduced from 180? to about 140knots because of earlier issues. The accident aircraft was not speeding.

[facthunter]

Some of that Maintenance is terrible  The structure has to remain firm and connections playless. Propwash causes vibrations too.. Do they use BETA? Nev

[Student Pilot]

13 hours ago, facthunter said:

Some of that Maintenance is terrible  The structure has to remain firm and connections playless. Propwash causes vibrations too.. Do they use BETA? Nev

Depends on the engine fitted, Pratts yes, Garret not as much but still yes.

[Student Pilot]

14 hours ago, Thruster88 said:

Flutter also occurs when things get loose, working rivets, cracked parts or worn control rods etc.

The Vne on the turbine conversion DHC-3 was reduced from 180? to about 140knots because of earlier issues. The accident aircraft was not speeding.

Having a lower VNE doesn't mean they will stick to it. The Drom conversions in Oz had a low VNE anyway but didn't stop people from flying around way beyond VNE. 

[facthunter]

  Obviously they don't know the meaning of NEVER exceed.. I do and it might be one of the reasons I'm still here.. Nev

[Student Pilot]

I am always wary towards VNE.....

[facthunter]

Anyhow bad Maintenance throws the book figure away. it's always  LOWER than the original published one. Nev

[Garfly]

Today's update:

 

 

[Garfly]

On 14/10/2022 at 5:48 PM, Thruster88 said:

Flutter also occurs when things get loose, working rivets, cracked parts or worn control rods etc.

The Vne on the turbine conversion DHC-3 was reduced from 180? to about 140knots because of earlier issues. The accident aircraft was not speeding.

Looks like our Thruster88 might have been barking up the right tree! 

Edited October 25, 2022 by Garfly

[facthunter]

They had no hope at all. That clip is inadequate as a lock feature. This all operates in a salt and ice environment. Be alert to any resistance or change of feel in any trim or control.   Nev

[Thruster88]

Having an external wire clip securing the vital clamp nut seems less than ideal.  

[facthunter]

They have specified a mandatory inspection for the clip installation but it's still a lousy arrangement. No clip was found at the accident site. Nev