Modified flight controls

[Tom Downey]

I asked this on serveral message boards and will here.

If your aircraft came from the factory with a rudder covered with ceconite and dope, as per the AC43,13-2b, such as the Maule/ Av-Husky/ & supercub, and you as an owner wanted to place a 24 inch vinyl decal across the rudder and vertical fin splitting 2/3s of the decal on the fin, and 1/3rd on the rudder would that be a modification of the skin?

Is that rudder skin modified because the manufacturers install procedures do not include the sticker?

If you were inspecting a C-175 with a GO-300-D engine, where would you find the inservice limits for the drive gear backlash?

If the Prop tip could be moved 1 inch with out restriction like in loose, would that be too much?

What would you use to tell the owner that their engine is not airworthy? It says right here------.(where) and you are over that.

I'll be dipped if I know.

[GAHorn]

Gee, Tom,...as experienced/proficient as YOU are ...these HAVE to be trick questions!!
If you want an opinion:
The decal is classified as a "decorative coating" in my opinion...except the only problem being whether 1) the rudder is balanced and 2) if the decal is a replacement or a new installation. (The latter makes it a major alteration IAW FAR 43, Appdx A, (a)(1) and the former removes it from qualification under(c)(9).
Less sure about the GO-300-D. (I thought the C-175 only came with the GO-300-A, C, or E engines. But, if the installation of a "D" engine is an approved one, I'd guess the best source for such technical info would be the GO-300 Overhaul manual or TCM.)
Prop tip: Is that still on the GO-300? Is the movement a cumulative 1" of movement from Prop-shaft looseness (should be checked seperately) and prop blade/hub looseness? (The McCauley C20 series of constant speed props, such as those used on the C-175-C/GO-300-E combination has a AD note regarding truncating the threads where the blade screws into the ferrules. If the blades have not been properly truncated they can fracture and cause a loose blade (as can any of the more common causes such as cracked hubs, cracked/loose ferrules, etc. etc. Last I knew such blades have to be sent to either Canada or Germany to be truncated as those were the only two shop locations still performing that work.) The prop blade being loose in the hub would be a separate issue/measurement, of course. 1" of movement sounds like cause for investigation to me if it's an easy movement to make. A prop shop or McCauley should be able to assist on this. (It may be possible that such movement is not disqualifying especially on a static constant-speed prop....the blades do tighten up under centrifugal force.)
I don't know if you can force an owner to ground their airplane (or even it it's ethical to attempt to do so.) Of course, as the A&P/IA you can refuse to sign it off if you don't feel it's airworthy and the owner won't submit it to the prop shop and a qualified engine shop for inspection to prove otherwise. (In fact, without the pertinent current maintenance manuals and specifications I wouldn't think it appropriate for an ill-equipped inspector to accept the inspection work or to declare it airworthy.) Just my own opinion, which with 2 cents still won't buy anything.

[Bruce Fenstermacher]

George you may not know this but on a fabric covered aircraft the covering process now includes the "decorative coating" and it all must be approved. At one time not to long ago this was not the case where the approved process stopped at the silver coat.

Never thought about it but Tom might be on to something with the decal. Your point about balance controls is also good.

[Tom Downey]

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Gee, Tom,...as experienced/proficient as YOU are ...these HAVE to be trick questions!!

These are NOT trick questions. I was asked and did not know the answers.

The decal is classified as a "decorative coating" in my opinion...except the only problem being whether 1) the rudder is balanced and 2) if the decal is a replacement or a new installation. (The latter makes it a major alteration IAW FAR 43, Appdx A, (a)(1) and the former removes it from qualification under(c)(9).

The rudder on a Aviat Husky is factory Ceconite with Dope.

This owner placed a large vinyl decal on the vertical fin and allowed it to protrude over on to the rudder about 1/3rd to 2/3rds.

I agree with you that this is a modification. Just as Bruce says it is not an approved finish as per factory installation.

All fabric finish systems are now treated as a "system" from start to finish by the manufacturers procedures manual.

Stits (poly fiber) Has thier own installation manual that is explicit on what products are to be used. and if you finish with some thing else you have an illegal covering.

Air-Tech is the same.

The C-175 I have in shop now has the GO-300-D with fixed pitch Mc Cauley you can ROTATE the prop about 1" with out feeling any rotation of the crank shaft. (think back lash) the Overhaul manual will give me the overhaul limits both the service limits and new limits. But I would be required to remove and disassemble the gear box the mike out the parts, I do not want to do that, It's a tools and manual thing.

[GAHorn]

Aha! Backlash! (not as I previously thought)
I don't know that there's a spec for that at the prop tip, but every 175 I've ever seen had a certain amount of that backlash, and it was more than one might first suppose. If the gearbox isn't excessively noisy and not making metal, I'd probably let it go. (That opinion still won't buy anything.)
In any case, surely there's a spec for backlash at the output shaft in the manual. (Try contacting Cory Thompson, TCM field rep. in Colorado Sprgs. He's a walking encyclopedia.) I'm on a trip to PHX and won't be at my resource materials until I return next week. Sorry.

[Bruce Fenstermacher]

The decal is classified as a "decorative coating" in my opinion...except the only problem being whether 1) the rudder is balanced and .....

Tom how could you balance a rudder? I understand the part of the rudder forward of the hinge line helps but gravity and or weight wouldn't. The decal wouldn't change the aerodynamics (and balance effects) of the rudder unless it was used to seal the hinge line.

All fabric finish systems are now treated as a "system" from start to finish by the manufacturers procedures manual.

Stits (poly fiber) Has thier own installation manual that is explicit on what products are to be used. and if you finish with some thing else you have an illegal covering.

Air-Tech is the same.

Ceconite also has a manual and proceedures through the color coat. There know we've covered all the fabrics and paint systems a '48 170 owner might use. If you want to use a car finish you may have to find Grade A cotton. Don't think the procedures have changed for that.

[GAHorn]

What about the airplane that was finished with Stits and painted with Imron...BEFORE the process was re-specified as a "system"? Is the aircraft now unairworthy? Hmmm.

[Tom Downey]

Yes, these proceses were there for many years. no one ever made much fuss over them until resently.

[jon s blocker]

Bruce,
The rudder is actually balanced with weight, it is placed on pivots, and using a specific formula, balanced to within a certain envelope given by the manufacturer. When a rudder is recovered it is critical to get the correct balance, just like the ailerons, flaps, and elevators. paint can make a huge difference in the balance of the rudder. Depending on the size, make up, and placement of a decal, it just might put it out of the envelope of balance.
Jon

[punkin170b]

Sorry to be diversionary (word?)... The "big sticker" on the Husky wouldn't be a Tasmanian Devil would it? If so, I know who the owner is... hehehe.
Matt

[Bruce Fenstermacher]

George
Aircraft that were covered before the change are grandfathered sort of speak for the life of the covering as that process was approved at the time. In fact it is the aircraft that where pianted with Imron and other car finishes that brought on the change. These finishes where generally not flexable enough over time and eventually cracked. The cracking could cause a failure of Ceconite/Polyfiber (polyester) covering due to UV.
Cotton fabric had a life of around 10 years so this was less of a problem because the covering was replaced more often. Polyester covering, if installed correctly and reasonable care is taken, has an indefenite life span. That is why it is more important today than in the past to treat the substructure of fabric covered aircraft before recovering.

I know all of this first hand because my "other" aircraft is a Clipped Wing Cub that I'm right in the middle of recovering. In fact as soon as I stop typing I'm going to the garage to finish rib stitching the second wing.

Jon
I understand how to balance a control surface, and under stand how it would work on an aileron or elevator as they are generally parallel to the earth and gravitational force. A rudder on the other hand is perpendicular to gravitational force. So how would weight effect it? I just don't see it.

[jon s blocker]

Bruce,
Not being a rocket scientist (grin), I don't know exactly how the weight effects the balance of the rudder. I do believe that the rudder is effected about as much as the other surfaces though. I believe that lift , and drag , as well as gravity effect all of the surfaces equally, and once you are "at speed", air moving over the surface of the aileron and elevators pretty much nuetralize the effect of gravity on the surface, thus making the balance of all the surfaces about equal in that respect. At that point the rudder, elevators, flaps, and ailerons don't care if they are horizontal or perpendicular. I hope the way I explained that makes sense. I do know that an out of balance surface can cause flutter, which can be a real problem. Jon

[GAHorn]

Generically speaking, one balances a rudder just like one balances an elevator.....by doing so in the horizontal position.
Although we "weigh" the counter-balance weights...the real thing we are doing is equalling out the MASS of the rudder fore/aft of the hinge-line to discourage flutter at critical speeds (usually at/above redline but hot always.) So IF your aircraft has a balanced rudder...that's how it's usually done.

[Tom Downey]

Generically speaking, one balances a rudder just like one balances an elevator.....by doing so in the horizontal position.
Although we "weigh" the counter-balance weights...the real thing we are doing is equalling out the MASS of the rudder fore/aft of the hinge-line to discourage flutter at critical speeds (usually at/above redline but hot always.) So IF your aircraft has a balanced rudder...that's how it's usually done.
_________________
'53 B-model N146YS SN:25713

Rudders on the Supercub/Av-Husky/Fairchild are not balanced.

see my web page (rudder) to see typical construction.

http://www.fairchildnc19143restoration.com

The issue of the decal is of the finish being part of the approved covering system.

[Tom Downey]

George
""Aircraft that were covered before the change are grandfathered sort of speak for the life of the covering as that process was approved at the time.""

This is a false concept, the Ceconite procedures manual has never allowed auto finishes.

""In fact it is the aircraft that were pianted with Imron and other car finishes that brought on the change. These finishes where generally not flexable enough over time and eventually cracked.""

This is true, Air-Tech is the only system formulated start to finish as a fabric paint. Randolph and several others have met the testing requirements as aircraft finishes. IMRON has not.

""The cracking could cause a failure of Ceconite/Polyfiber (polyester) covering due to UV. ""

There is no failure criteria for Polyester fabrics, The Maul tester is for COTTON only. (read the directions) Ceconite/Polyester will not rot in direct sun light. It is the paint system that fails. Cracking which allows the rain/water to enter the aircraft and attack/corrode steel tubes and any thing else it can destroy.

""Cotton fabric had a life of around 10 years so this was less of a problem because the covering was replaced more often. Polyester covering, if installed correctly and reasonable care is taken, has an indefenite life span. That is why it is more important today than in the past to treat the substructure of fabric covered aircraft before recovering.""

Polyester never fails, it is the paint that fails, any dope or paint system that is applied to Polyester must be forced through the fabric and allowed to link over on the interior surface it is this layer that fails. The tiny pillars of paint that are between the threads of the fabric will brake due to flexing and age, and allow the exterior paint layers to peel off.

""I know all of this first hand because my "other" aircraft is a Clipped Wing Cub that I'm right in the middle of recovering. In fact as soon as I stop typing I'm going to the garage to finish rib stitching the second wing.""

I wish you luck, I have 2 wings to recover on the F-24

Jon
I understand how to balance a control surface, and under stand how it would work on an aileron or elevator as they are generally parallel to the earth and gravitational force. A rudder on the other hand is perpendicular to gravitational force. So how would weight effect it? I just don't see it.

The rudders on the C-170 are weighted, to mass balance the rudder horizontally. but most fabric aircraft are not, they just have a dynamic balance of a portion of the rudder / and elevators forward of the hinge line.