Jump to content

Possible Trim Tab Flutter at 135kt


Recommended Posts

  • Replies 141
  • Created
  • Last Reply

Top Posters In This Topic

38 minutes ago, robthart said:

All this is pretty scary stuff, but a question... I'm a senior citizen who's been flying a long time, the last 10 years in a CTLS. I usually flight plan for 116 knots, rarely exceed it, the fastest I've ever been in those ten years was 130 knots with a VERY strong tail wind. If you have no desire to break boundaries, or go through mountain wave effect, do I need to worry about stabilator flutter in our CT?

In a typical LSA the only time you will ever see 130 knots TAS is in some kind of dive ... ( not to be confused with ground speed which sometimes can go all the way up to 150 knots or so, depending on winds  ) 

Link to comment
Share on other sites

27 minutes ago, sandpiper said:

Skunkworks - does your plane have SB-ATSM-CTSW-07 complied with? This is for stabilizer rear wall stiffening. Should have been done 2009 or later if your aircraft was affected.

His airplane is outside the serial number range, but there have been a few others outside the range that have had issues.

Link to comment
Share on other sites

10 hours ago, sandpiper said:

Skunkworks - does your plane have SB-ATSM-CTSW-07 complied with? This is for stabilizer rear wall stiffening. Should have been done 2009 or later if your aircraft was affected.

My Stab has the stiffeners at the hinge points mentioned in this SB. There is no log in the books about this being completed so I can only assume it came from the factory with the updated stab. This would also confirm since my SN is well outside the range listed in the SB.

Link to comment
Share on other sites

After some discussion with FDUSA, there appears to be more than just a reinforcement on the hinge tabs. There is some additional modification that is done to the holes in the rear spar where the tab counterweights pass through.  So looking at just the hinge reinforcements(which my AC has) does not mean you have the most upgraded stab.

image.png.8a25aede4d7e90389106ff95a6eb7d2c.png

Does anyone have any pictures of the modified rear spar?

Additionally, Does anyone have a copy of the service instruction for this SB?     SI-ASTM-CTSW-04?

image.png.f9819c478099c505e4431a20ea11ece5.png

 

 

Link to comment
Share on other sites

16 hours ago, dabaero said:

Skunkworks85,

  If the stabilator on your aircraft still has cutouts at the balance weights for the trim tab SI-ASTM-CTSW-04 rev. 00 dated 30 Nov. 2009 should be reviewed for compliance.

Let me know if you need the SI.

V/R,

DabAero

If you have a copy of the SI I would love to see it.

 

Link to comment
Share on other sites

  • 2 months later...

Update, 

We made the decision that even though my plane is outside of the effective serial numbers, I decided to complete SI-ASTM-CTSW-04 . My stabilator had all items listed in the service instructions except for the "big ribs" below

image.png.431d9c0e0e7123a8baccd2986155a630.png

 

The plane went to Tom Baker for the annual conditional inspection and that is when the job was completed, We also opted to replace all the hinges, as well as all rod ends on the trim tab and the cable.

FD USA had to make the ribs, and took 2 weeks to receive.

 

Here is the Stabilator with the ribs epoxied in. 

62185.thumb.jpeg.cfc43ffa33910ac968484f53cc32bf72.jpeg

 

Tom did an excellent job on the repair.

I have since had the plane up to 137 KIAS without any indication of flutter, This did fix the issue.

 

Keep in mind, that just because you plane does not fall into a specific serial range you are not affected. Lesson learned I guess.

 

 

Link to comment
Share on other sites

Stinker,

I see 4 epoxy repair areas with what look like curved inserts in the trailing edge spar. But you say you didn't get the "big ribs" in the kit photo. Did you have to make them? Were there holes in the trailing edge spar at these locations before the repair or did you have to cut the spar away in these areas? If it had holes, that's not much of a spar.

I see 10 "small ribs" in the kit photo but I see what looks like 14 braces between the trailing edge spar and the lower skin. Did you make the extras?

Thanks,

Mike Koerner

Link to comment
Share on other sites

On 3/5/2020 at 12:45 AM, Mike Koerner said:

Stinker,

I see 4 epoxy repair areas with what look like curved inserts in the trailing edge spar. But you say you didn't get the "big ribs" in the kit photo. Did you have to make them? Were there holes in the trailing edge spar at these locations before the repair or did you have to cut the spar away in these areas? If it had holes, that's not much of a spar.

I see 10 "small ribs" in the kit photo but I see what looks like 14 braces between the trailing edge spar and the lower skin. Did you make the extras?

Thanks,

Mike Koerner

Mike, his airplane came from the factory with the small ribs installed, but like the older airplanes there were just cut outs for the trim tab counterweights. There was an extra layer of composite around the opening. The big ribs were supplied from flight design for the repair. They either have the mold to make them in house or have someone make them locally. They are just a formed single ply of fiberglass. The big rib essentially creates a full length spar without cutouts while still retaining clearance for the counterweights. The cut out openings did have to be enlarged for installation of the rib.

Link to comment
Share on other sites

My 2006 CTSW is  s/n 08-06-02 which has the full length trim tab.  I experienced the trim tab flutter even though the stabilator reinforcement had been done.  Same situation as others.  130 kts under full throttle while descending.  I believe that the basic problem is that the trim tab is not fully balanced.  The counter weights move the tab closer to a "zeroed" center of gravity but they fall short of fully "zeroing" this out.  I solved my problem by tightening all pivots, rod end fasteners, etc. that are connected to or involve the trim tab.   Went to 135 kts. with no flutter exhibited after inspection/tightening.

Link to comment
Share on other sites

Haha Tom.  Good catch.  Yup, let's try 06-08-02.  It seems that those CT's that exhibit a flutter respond favorably to tightening of components.  At least my CT did.  Reading about the pros & cons of bolus tape on the trim tab I'm wondering if the method of installation of the bottom and top bolus tapes might lessen the flutter tendency?  What if the top and bottom tapes are installed with the trim tab at a "neutral" position during tape installation?  The tape would now be stretched during trim travel and act as an additional spring in the system.  This may help to incrementally raise the speed where flutter occurs.  This depends on the tape remaining attached to the surfaces which may not occur during the stretching of it but think 2" wide bolus may stay attached.  I see on my CT where I probably didn't reflex the trim tab fully during tape installation and the tape shows stretching but it still adheres to the surfaces.  Didn't notice any problems in flight controls.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...