Possible Trim Tab Flutter at 135kt

[Roger Lee]

I talked to FD. Until this gets resolved stay away from those speeds. No more taking flights just to look. It doesn't look present at normal flying speeds under 120 knots. Do the few things I suggested. Especially look at the trim tab rods and ends.

[FlyingMonkey]

I just got off the phone with Tom at Flight Design.  I'm working directly with them at this point and am confident we'll figure out what's happening.  I've removed the video at this time while we troubleshoot to find the true cause of the issue.   

[FlyingMonkey]

I talked to FD. Until this gets resolved stay away from those speeds. No more taking flights just to look. It doesn't look present at normal flying speeds under 120 knots. Do the few things I suggested. Especially look at the trim tab rods and ends.

 

Tom and I agreed that 115 knots is a prudent maximum speed for now.  There will be no more "test flights".  

 

I looked at the rod ends today and they all *appear* tight.  There is no side-to-side play in the upper rod ends, so they are attached tightly.  The check nuts are firmly up against the rods.  The lower rod ends are more problematic; everything looks tight, but there's no way to get a finger or wrench in there to check for sure.

 

Tom gave me some more items to take pictures of, so we're actively investigating.

[ralarcon]

Tom and I agreed that 115 knots is a prudent maximum speed for now.  There will be no more "test flights".  

 

I looked at the rod ends today and they all *appear* tight.  There is no side-to-side play in the upper rod ends, so they are attached tightly.  The check nuts are firmly up against the rods.  The lower rod ends are more problematic; everything looks tight, but there's no way to get a finger or wrench in there to check for sure.

 

Tom gave me some more items to take pictures of, so we're actively investigating.

Good, I hope it gets resolved quickly. Good luck !

 

Cheers

[chanik]

One more point, Roger may have forgotten, but when I just got my plane and took it to him, my trim tab was all dimpled skin and weird looking like some people have seen with the 'skin cancer' on the bottom strake, etc. My plane was outside the SB mod serial numbers, but still, on closer inspection, Roger saw that the trim tab was of the faulty type, without the inset balance weights. So you may have the fluttery sort of trim tab.

[FlyingMonkey]

One more point, Roger may have forgotten, but when I just got my plane and took it to him, my trim tab was all dimpled skin and weird looking like some people have seen with the 'skin cancer' on the bottom strake, etc. My plane was outside the SB mod serial numbers, but still, on closer inspection, Roger saw that the trim tab was of the faulty type, without the inset balance weights. So you may have the fluttery sort of trim tab.

 

Thanks.  The balance weights is one of the areas we're checking.  My anti-servo tab looks hard and straight, and the attach brackets for the counterweights are visible, but we'll see.

[gbigs]

Tom and I agreed that 115 knots is a prudent maximum speed for now.  There will be no more "test flights".  

 

I looked at the rod ends today and they all *appear* tight.  There is no side-to-side play in the upper rod ends, so they are attached tightly.  The check nuts are firmly up against the rods.  The lower rod ends are more problematic; everything looks tight, but there's no way to get a finger or wrench in there to check for sure.

 

Tom gave me some more items to take pictures of, so we're actively investigating.

 

So FD told you to SLOW down and quit toying with your plane, right?  You may also want to ask FD what the IAS speeds are for your plane since the SW POH lists all speeds in CAS.  You were also assuming some dangerous IAS numbers that are not listed in your POH.

[FlyingMonkey]

So FD told you to SLOW down and quit toying with your plane, right?  You may also want to ask FD what the IAS speeds are for your plane since the SW POH lists all speeds in CAS.  You were also assuming some dangerous IAS numbers that are not listed in your POH.

 

Oh please, STFU already.  This is *NOT* a case of a pilot (me) "toying" with his airplane.  It's a case of the airplane entering into potentially hazardous mode at well below the speed where this should be expected to occur.  I am not the first owner to experience this, in fact I had a phone conversation with another owner who experienced this exact phenomenon at identical speeds and worked with FD to correct the situation.  

 

I'm not going to share the details of the conversation that Tom Peghiny and I had about this, but he in no way indicated he thought this was a result of pilot error or "toying" with anything.  We mutually agreed that until we get to the bottom of this that a 115kt limit on the airframe is wise.

 

Do you limit your CTLS in flight to 115 KIAS?  Why not?  STOP TOYING WITH YOUR AIRPLANE!!!

 

EDIT:  I ran my numbers through a calculator to find CAS at 135kt at the conditions I was flying in.  the number I came up with was 136.87kt.  So CAS is 1.87kt different from IAS in that circumstance.  So burgers do you expect aerodynamic flutter to occur at ~137kt CAS in an airplane with a Vne of 145kt CAS? 

[Brucegoose]

So FD told you to SLOW down and quit toying with your plane, right?  You may also want to ask FD what the IAS speeds are for your plane since the SW POH lists all speeds in CAS.  You were also assuming some dangerous IAS numbers that are not listed in your POH.

 The SB from FD when it first came out was reducing the VNE to 121kts.

The POH lists all speeds in CAS which is "calculated"  So up at 3000ft one should reduce the Vne by 3kts for every 1000ft above MSL to be safe. In this case MrMorden would have been 1kt off Vne.(CAS)  I'm generally up at 7000ft and experienced flutter at about 140 indicated so I was way through. Urrrgh!  I felt it in my feet and it felt as if the motor was moving up and down by a foot. scary!!! but I survived to tell the story and just ask please for all to fully understand Vne and why the POH is shown in CAS.

Safe flying!

Bruce

[FastEddieB]

Andy,

 

One concern is that you may have a progressive situation.

 

That's assuming your plane used to not have any flutter, and now it does at a certain speed.

 

If something is loosening up or otherwise changing or weakening, you might start finding the flutter at slower and slower speeds.

 

Just be very, very careful if you choose to fly the plane. And ask yourself what The Most Conservative Action would be.

[Ed Cesnalis]

...  airplane with a Vne of 145kt CAS? 

 

You have to assume the Vne is TAS not CAS.  You don't know the reason for Vne but flutter is a likely reason.  Flutter is a function of TAS not CAS.

[FlyingMonkey]

Andy,

 

One concern is that you may have a progressive situation.

 

That's assuming your plane used to not have any flutter, and now it does at a certain speed.

 

If something is loosening up or otherwise changing or weakening, you might start finding the flutter at slower and slower speeds.

 

Just be very, very careful if you choose to fly the plane. And ask yourself what The Most Conservative Action would be.

 

Agreed, it could be a situation that is getting worse.  But I don't know that until recently I had ever been at those speeds before, so it might just be a situation that has been in place since I got bought the airplane.  No way to know really.  

 

I'm encouraged by my detailed inspection of the stabilator yesterday.  There is no play fore/aft or up/down in the stabilator pivot, and no cracks in the gelcoat that could indicate structural damage.  I pulled the bolus tape off of the stabilator/tab gap and checked there for damage, and found none.  The edge surfaces are clean and intact and the hinges look normal.

 

I did not really want to get an OK to fly from FD to fly around as if nothing happened, but more so that I could make a few flights if I wanted to, and to be able to transport the aircraft elsewhere for repairs or service to correct the problem if necessary.

[FlyingMonkey]

You have to assume the Vne is TAS not CAS.  You don't know the reason for Vne but flutter is a likely reason.  Flutter is a function of TAS not CAS.

 

Fair enough.  IIRC the TAS on the flight in question was about 143kt at maximum.  That would be close to Vne, but not there yet.  The airframe should be stable to Vne at the very least, and good engineering design practice should ensure no flutter up to Vne + 10% or  159.5kt TAS.  Since the CTSW using identical airframes is certified in other countries with Vne up to 160kt, I assume there should normally be no flutter to some airspeed value north of 160kt TAS.

 

I am confident that the flight in question at no time should have had an airspeed value sufficient to induce flutter of any surface in normal circumstances.

[Anticept]

I believe FD tested the airframes to 160 kts or so. They stopped the test because it satisfied the engineering requirements, and no damage was found.

[FlyingMonkey]

I believe FD tested the airframes to 160 kts or so. They stopped the test because it satisfied the engineering requirements, and no damage was found.

 

That seems likely.  No need to test far beyond the expected flight speeds.  Nobody really knows what loads many airframes will take, just because nobody has taken them that far.  Not to mention that every airframe is a little different.

[FastEddieB]

Agreed, it could be a situation that is getting worse.  But I don't know that until recently I had ever been at those speeds before, so it might just be a situation that has been in place since I got bought the airplane.  No way to know really.  

 

I'm encouraged by my detailed inspection of the stabilator yesterday.  There is no play fore/aft or up/down in the stabilator pivot, and no cracks in the gelcoat that could indicate structural damage.  I pulled the bolus tape off of the stabilator/tab gap and checked there for damage, and found none.  The edge surfaces are clean and intact and the hinges look normal.

 

I did not really want to get an OK to fly from FD to fly around as if nothing happened, but more so that I could make a few flights if I wanted to, and to be able to transport the aircraft elsewhere for repairs or service to correct the problem if necessary.

 

OK.

 

Let me know if I can be of any assistance.

[FlyingMonkey]

OK.

 

Let me know if I can be of any assistance.

 

Thanks Eddie!

[Roger Lee]

Hi Andy,

 

Do you have both top and bottom trim tab gaps taped? Can you find out who did the stab stiffening mod, they may not have balanced the unit when done. This may be a procedure you'll have to do to check the system.

[FlyingMonkey]

The top was taped, the bottom was not.  I know you recommend taping both, It came that way and I just have not gotten around to taping the bottom.  The dealer that sold the plane was Airtime Aviation in Tulsa, and the previous owner's mechanic was Ed Babovec, so I assume one of those two did the work.  Don't have any idea if things were balanced afterwards.  I will look in the log and see if there is a notation on that.

[Tom Baker]

Hi Andy,

 

Do you have both top and bottom trim tab gaps taped? Can you find out who did the stab stiffening mod, they may not have balanced the unit when done. This may be a procedure you'll have to do to check the system.

Roger, his serial number doesn't fall into the group that required stiffening. It should have the early mod of the composite angle at the trim tab horn attachment.

[Roger Lee]

The bulletin was not 100% on exact numbers. I think it even sad that. You have to look to make sure if you are on the cusp at the beginning or end of the numbers.

 

My money lies on a worn part or an unbalanced part whether the mod was done or not.

[FlyingMonkey]

The bulletin was not 100% on exact numbers. I think it even sad that. You have to look to make sure if you are on the cusp at the beginning or end of the numbers.

 

My money lies on a worn part or an unbalanced part whether the mod was done or not.

 

That seems to be where FD is going with it...they want pics inside the stab/tab gap to see the areas where the balance weights pass through.  I'm guessing that will tell them which stab design I have and if it's been properly updated if required.

[GlennM]

I believe FD tested the airframes to 160 kts or so. They stopped the test because it satisfied the engineering requirements, and no damage was found.

They flight tested the stabilator stiffening mod to 180kts.

[FlyingMonkey]

They flight tested the stabilator stiffening mod to 180kts.

 

Wow.

[FlyingMonkey]

Turns out that even though I'm outside the serial number range for the SB, my airplane needs the stabilator stiffening mod performed on it.  When I bought the airplane I asked about that SB and was told it was checked, but I guess "caveat emptor" is the moral here.

 

Tom Peghiny has really worked fast on this, and I'm working with the factory now to work out the logistics on getting this work done.  The Stab is going to come off the airplane and ship to FD USA to have their tech perform the work.