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Possible Trim Tab Flutter at 135kt


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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.

I have a nice crate for shipping the stab. You can have it if you want. You just need to figure out how to get it there. When I shipped the stabilators that I had done I used Fed Ex Ground.

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I have a nice crate for shipping the stab. You can have it if you want. You just need to figure out how to get it there. When I shipped the stabilators that I had done I used Fed Ex Ground.

 

I believe Tom said they would ship me an appropriate packing box and arrange a pickup.  I'll let you know if that changes, thanks!

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That's great Andy.

Hope you get it all taken care of and back in the air soon.

 

I hope they give us a detailed diagnosis of the problem and the remedy.

To say the least, this is very interesting.

 

Bill, I think their diagnosis would be "check to see if your aircraft needs the SB that has been in place for a few years now done"...   ;)

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There is no doubt, FD was quick on the draw here.  Tom has been extremely responsive and very good to deal with.  I've always been impressed with FD's customer service, and this confirms it.

 

Of course, I haven't got the quote yet for the modifications.  The number at the bottom of that sheet might color my impressions.    :lol:

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There is no doubt, FD was quick on the draw here.  Tom has been extremely responsive and very good to deal with.  I've always been impressed with FD's customer service, and this confirms it.

 

Of course, I haven't got the quote yet for the modifications.  The number at the bottom of that sheet might color my impressions.    :lol:

If this is a manufacturing defect , shouldn't this be covered repair ?

 

Cheers

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If this is a manufacturing defect , shouldn't this be covered repair ?

 

Cheers

 

It's actually a SB, which are usually paid for my owners.  Tom said he was going to work with me to make it as cost effective as possible.  That's about all you can ask for.

 

HOWEVER, I just had another conversation with Tom.  After the German techs reviewed my imagery, they said I *do* have the triangular reinforcements at the stab trailing edge designed to stiffen that area and prevent vibration of the anti-servo tab.  It does *not* have some additional stiffening around the counterweight areas, but that should not be part of this problem.  So we are going to hold off on sending any parts back for now; I'm going to try to get with my A&P this weekend and go through the entire trim system, stem to stern, and look for any play/slop/looseness/slack in any of the components.

 

Others have had good results getting any play out, so that is a good place to start. 

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Andy,

Are all the control surfaces balanced pretty well, do you know for sure?

A glider of the same design as mine experienced flutter over the Sierras. Upon inspection, it was found that there was an exorbitant amount of Bondo or the equivalent put on to smooth out a rough surface. Ufda!

Keep us posted on your findings.

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It's actually a SB, which are usually paid for my owners.  Tom said he was going to work with me to make it as cost effective as possible.  That's about all you can ask for.

 

HOWEVER, I just had another conversation with Tom.  After the German techs reviewed my imagery, they said I *do* have the triangular reinforcements at the stab trailing edge designed to stiffen that area and prevent vibration of the anti-servo tab.  It does *not* have some additional stiffening around the counterweight areas, but that should not be part of this problem.  So we are going to hold off on sending any parts back for now; I'm going to try to get with my A&P this weekend and go through the entire trim system, stem to stern, and look for any play/slop/looseness/slack in any of the components.

 

Others have had good results getting any play out, so that is a good place to start. 

If that is the case I would give Tad a call, Randy Wildman at Wild Air. They can fill you in on the repairs and modifications they did on my aircraft.

 

Cheers

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If that is the case I would give Tad a call, Randy Wildman at Wild Air. They can fill you in on the repairs and modifications they did on my aircraft.

 

Cheers

I think that I know the mod Tad did on your airplane, and I don't recall seeing or hearing of this being a problem with the CTSW.

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I just got the word back from Tom, they do want to see the Stabilator, as well as the pivoting attach bracket (so they can re-balance after the work).  The quote the gave me is very reasonable.  They are planning to replace the trim tab hinges (in case any play in them is contributing) and do the rest of the trailing edge reinforcements that my stab doesn't have done yet.

 

However, the shipping costs involved are pretty high.  They have a special crate to pack the stab into, and for them to get it to me, then ship the stab both ways, then ship the crate back to them, comes to $1000.  This is using a freight company, does anybody know of a cheaper way to (safely) get this done?

 

It's almost tempting to drive the darned thing up to CT myself and wait while they do the work...probably not any cheaper, but at least I get a vacation out of it and can see some old friends (I grew up in CT)!

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Why drive?  Looks like it's only a 4-5hr flight so you'd only burn around 50 gallons roundtrip.  Drop off the plan and fly commercial roundtrip from FD US to NC for $3-$400.  Assume 50/50 split on Avgas/Mogas and you'd only spend around $150 in fuel.  Total out of pocket is around $550 on the top-side.  Inclement weather in the NE can be a problem so you might get stuck with $150 change fee but you're still below a $1000 and you get some cross-country flying in.  

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Dave, I considered that. But flying to the NE in February with no flight experience in real winter weather seems like a marginal idea. Add in the potential weather delays (I work a regular job), and the logistics get steep pretty quickly. It's a lot of work to "maybe" save $500.

 

I will probably end up eating the freight charges, but I am interested in options.

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If you can find someone who has an account shipping will likely be less. On an other site for a different airplane that I visit someone needed to ship a set of wing struts to a company for inspection and repair. By having the company they were shipping to arrange the shipping they saved 80%. If you know anyone with a business that ships freight regularly see if they can get you a quote. When I shipped mine I did it through an account from someone I know.

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  • 1 month later...

UPDATE:

 

I have been talking this issue out with Tom Peghiny quite a bit.  FD USA has been really great in taking this issue seriously and working through a solution with me.

 

The Stabilator and trim tab assembly, as well as the pivot bracket and all associated hardware are going back to FD.  They are going to inspect everything for wear and make sure there is not some hidden problem in any of hardware and attach points.  

 

Assuming no other problem is found, FD is planning to reinforce the trailing edge of the stab in accordance with the later versions of construction.  Mine already has one set of reinforcements, so they are probably just going to have to apply the second set which reinforces the areas around the counterweight positions.  They are also going to replace the top hinges to eliminate any play that might be present there.  The idea is to stiffen everything up so that the long-span trim tab is no longer free to move at all in a "twisting" moment.  The stab setup will also be rebalanced at the factory.

 

My limited understanding of aerodynamic flutter is that two forces are required for it to present itself, a linear force (in this case, the air moving over the stab/trim tab) and a rotational or "twisting force" (I'm guessing this is the rotational force from the prop pushing up on one side of the stab and down on the other side).  The stiffening should dampen or disallow completely the rotational component, eliminating the possibility of flutter (at least below Vne speeds).

 

I'm satisfied with this solution, and I think it will be effective.  And again, FD USA has been very responsive and helpful on this, much more so that would be strictly required by a manufacturer on an out-of-warranty product.  I can't say enough good things about the customer service I've received from Tom, Mat, Dave and the whole crew at FD USA.

 

BTW, if anybody from FD is reading this, feel free to correct me if I have any of the particulars wrong on the work being performed, the theory of how it should correct things, or anything else I may have botched in this explanation.  :)

 

Andy

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Glider can have flutter. There are you tube videos of it. A glider of my model developed high speed flutter that involves an unbalanced elevator (the home builder used too much bondo to smooth out the skin :-) ). That may challenge the theory of prop wash.

Not at all. A twisting moment is required, and propwash is only one way that can happen. In my case it seems the most likely source. Obviously in a glider that would not be the case. :)

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