Rudder skin Repair

[Grant_Waite]

I recently removed the inoperative AeroTrim rudder trim, from my 77J and I’m now left with a square hole in the skin of the rudder. My plane is currently at the shop for other work and the mechanic is unsure what’s the best or legal way to repair the hole. Looking at the service manual the material on the rudder skin is 2024 T3 Clad 0.20thickness. Could a simple rectangular patch with blind rivets not be an acceptable method? The rudder trim servo was exactly that and probably lesser quality of material. I don’t see a need to have the whole rudder reskinned or even worse replaced. I did fly with the patch covered with hvac tape and it did just fine. 

 

 

[EricJ]

I'd put a square patch over the same spot with a logbook entry stating it covered the hole from the trim system deletion.  Proper treatment and priming/painting of the patch should be included in that.

 

[N201MKTurbo]

I would check the rudder balance after removing the servo. You should be fine with the cover patch.

[Red Leader]

Why cannot you just reinstall the cover without the associated hardware? That would effectively cover the hole and keep it legal.

[N201MKTurbo]

1 minute ago, Red Leader said:

Why cannot you just reinstall the cover without the associated hardware? That would effectively cover the hole and keep it legal.

That’s fine, but if you remove weight from the rudder, you should check the balance. The balance procedure is in the service manual.

[MB65E]

337 Is required as any repair to a flight control is a Major repair. As well as one for removing the STC’d.

I don’t think the SRM has any repairs to Flight controls allowed. 
 

I would look for a new rudder or leave it alone. 

-Matt

[Grant_Waite]

6 hours ago, N201MKTurbo said:

I would check the rudder balance after removing the servo. You should be fine with the cover patch.

Yeah that’s the plan as well. It could be what’s causing my plane to not fly straight but it did that before the rim was removed so I’m not sure. 

[N201MKTurbo]

The rudder balance has nothing to do with your plane flying straight. That is a rigging issue. Rudder balance has to do with flutter margins. Which won’t have any effect on flying qualities until it starts happening.

[A64Pilot]

6 hours ago, Grant_Waite said:

Yeah that’s the plan as well. It could be what’s causing my plane to not fly straight but it did that before the rim was removed so I’m not sure. 

First in my opinion a patch would be fine, but be sure the “square” has very rounded corners.

Secondly the Rudder MUST be removed and rebalanced after all the work was accomplished to include paint, it is VERY much a safety issue, improperly balanced you can very easily get flutter that can very quickly literally rip the flight control off and of course cause a fatal crash, balance should not affect trim. Personally I’d put the patch on with a bead of fuel tank sealer, among other things this will prevent water intrusion and corrosion. If you ever fly again with an unbalanced flight control, do so slowly, flutter is very much aggravated or caused by speed. The purpose of balancing a flight control is flutter prevention.

Then as has been noted one 337 for the modification / Repair and another for the removal of the STC. Although I think they could be combined.

The first is required as it is a Major, the second because your changing type design, yes returning it to original, but it’s still a change.

That cover was put on poorly and poorly designed in my opinion, first there was no edge distance on at least one rivet and I would have put a doubler in with nut plates and made the cover removable myself.

[A64Pilot]

1 hour ago, N201MKTurbo said:

The rudder balance has nothing to do with your plane flying straight. That is a rigging issue. Rudder balance has to do with flutter margins. Which won’t have any effect on flying qualities until it starts happening.

When I was a Test Pilot, flutter was one of the very few things that scared me, a good friend of mine (Dr Ralph Kimberlin) who literally wrote the book on small aircraft test flying  and my Civilian Test Pilot mentor when he was flight testing the Aero Commander 112 got flutter that caused the aircraft to disintegrate, he got out, the flutter Engineer did not. There is a story why the Engineer was onboard of course, because that was uncommon and honestly he shouldn’t have been.

Ralph passed away last Nov. https://www.fit.edu/faculty-profiles/k/kimberlin-ralph/

https://asn.flightsafety.org/wikibase/2731

People think, if I get into flutter I’ll just slow down, maybe, maybe not.

North American Rockwell recreated the incident in NASA’s wind tunnel, time from flutter initiation to complete disintegration of the entire empennage was less than 1 sec.

This aircraft had been dove to Vd several times with small issues occurring, what was different in this dive was Ralph had trimmed the elevator full nose down to keep from having to push so hard down, as is common on many aircraft only one elevator had a trim tab, this caused enough unbalance to trip flutter once it was initiated with a control doublet, a control doublet inputs forces very similar to turbulence and “excites” a flight control.

Edited yesterday at 01:30 PM by A64Pilot

[A64Pilot]

10 hours ago, Red Leader said:

Why cannot you just reinstall the cover without the associated hardware? That would effectively cover the hole and keep it legal.

The cover does not conform to the original rudder skin aerodynamically because of the bump, to prevent having to reskin or replace the rudder etc. it’s best to return the rudder as close as possible to original, then it’s possible that bump could cause trim issues that are normally overcome by the trim tab of course, but the tab has been removed.

I’m not saying it would of course just that it could

I bet if you lined up 5 FAA inspectors, at least 1 would say the skin would have to be replaced, 2 would say a patch is fine and the rest would want additional data as in a DER or similar. But if say in a ramp check or something a 337 would satisfy all of them, a log book entry maybe not.

Edited yesterday at 02:06 PM by A64Pilot

[Slick Nick]

For all the work involved, why not just replace the rudder? BAS has a bunch, you'd just need to have it repainted, which you'd need to do to your stock rudder anyways.

[EricJ]

FWIW, your A&P will determine whether 337(s) need to be filed.   I know of no regulatory requirement to file a 337 for this repair.   There does not seem to be agreement among the relevant masses that a 337 is required to remove an STC, if this was installed with one, but you do hear that opinion a lot.    Some argue that the original, pre-STC configuration is already approved, so if removing an STC restores it to an approved state, that's...already approved.   I don't think many people file a 337 to remove a Brackett air filter (which requires a 337 on many airplanes).    The other side of that is that the TC is altered by the 337 and altering it back requires another 337, for the record keeping if nothing else.   I don't know of any clear regulatory guidance either way, just opinion.

YMMV, your A&P/IA's opinion is the one that counts.

[varlajo]

Speed tape!! 

[A64Pilot]

20 hours ago, EricJ said:

FWIW, your A&P will determine whether 337(s) need to be filed.   I know of no regulatory requirement to file a 337 for this repair.   There does not seem to be agreement among the relevant masses that a 337 is required to remove an STC, if this was installed with one, but you do hear that opinion a lot.    Some argue that the original, pre-STC configuration is already approved, so if removing an STC restores it to an approved state, that's...already approved.   I don't think many people file a 337 to remove a Brackett air filter (which requires a 337 on many airplanes).    The other side of that is that the TC is altered by the 337 and altering it back requires another 337, for the record keeping if nothing else.   I don't know of any clear regulatory guidance either way, just opinion.

YMMV, your A&P/IA's opinion is the one that counts.

A 337 should be filed for removal of an STC, an STC of course changes the Type Certificate, often that’s not a small thing, some are just silly though like sun visor STC’s.

The reason is to keep the records correct

They very often aren’t, for that reason it’s not uncommon at all for older aircraft to have several comm and Nav radios installed, Marker beacons, DME’s etc when you get the CD from the FAA, yet when you look at the panel the DME, ADF, and most of the listed radios aren’t there of course. Many IA’s that are on the ball so to speak will file a “correct the record 337” listing the items removed and what’s currently in the aircraft just to correct the paperwork on the aircraft they maintain.

Do incorrect records render an aircraft unairworthy? Most would say not, but it does bring into question just how correct are the other records of the aircraft, it’s just an indicator that I look at when doing a pre-buy, it won’t stop me from buying, but correct records do go in the buy column in my decision.

Edited 7 hours ago by A64Pilot

[MikeOH]

I don't know about others' aircraft but the 337s for mine indicate not only the new equipment being installed, but what is being removed.  It's not like separate 337s are being filed for the removal of old stuff.