3DPlanes
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Why Fabric Control Surfaces?

Wed Nov 01, 2006 11:38 am

At the local airshow last weekend, there was a two-seat Yak 7. In doing a walk-around, I noticed it had fabric covered control surfaces. I know that many metal planes had fabric covered controls - from a search, I found that even the fairly modern Do-228 has them.

My question is why?

Reducing mass way out on the moment arms would make for better maneuverability... But there can't be that much difference, can there? Initially, I thought it might be to allow faster repairs of battle damage, but using that logic the whole plane should use fabric - unless the controls are bullet magnets...

Anyone got the answer?
"Simplicate and add lightness." - Ed Heinemann
 
474218
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RE: Why Fabric Control Surfaces?

Wed Nov 01, 2006 11:50 am

Cheap, light weight (easier to balance) and since they are non-structural fabric covering was the an excellent choice. Remember, at one time the entire aircraft was fabric covered.
 
Bobster2
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RE: Why Fabric Control Surfaces?

Wed Nov 01, 2006 12:30 pm

Fabric control surfaces provide more than a double weight savings, because the required balance weight is also reduced. The balance weight is heavier than the control surface since it's closer to the hinge.

[Edited 2006-11-01 04:35:07]
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N231YE
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RE: Why Fabric Control Surfaces?

Wed Nov 01, 2006 1:30 pm

I know WWII aircraft such as the Vought F4U Corsair had fabric control surfaces...they were designed that way to be lighter on the controls.
 
2H4
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RE: Why Fabric Control Surfaces?

Wed Nov 01, 2006 1:37 pm



So let's say I owned a fabric 140, or maybe a Citabria, and it needs all new fabric. What do people typically spend to completely re-cover fabric planes of this size? I realize the cost depends on myriad factors, but I'm just wondering what an average total price would be.



2H4


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HAWK21M
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RE: Why Fabric Control Surfaces?

Wed Nov 01, 2006 6:02 pm

Weight Saving = $$$ Saving.
regds
MEL
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vzlet
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RE: Why Fabric Control Surfaces?

Thu Nov 02, 2006 12:00 am

Quoting 2H4 (Reply 4):
just wondering what an average total price would be

From a 1998 Sport Aviation article.

"All of the materials to cover a J-3 Cub size airplane will cost around $2,500 to $3,000 regardless of the covering process. If someone gives you a quote much lower than that they are not including everything that you need. You will spend that much money when all is said and done. Look at it this way, you are going to save approximately $10,000 in labor costs by covering the airplane yourself. Yes, that’s correct, the price charged by most professionals to cover an airplane will range between $8,000-$12,000."
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timz
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RE: Why Fabric Control Surfaces?

Thu Nov 02, 2006 9:12 am

Nowadays fans don't realize how many airliners had fabric rudders back then-- all the DC-4/DC-6/DC-7 series, all Constellations-- but maybe not Viscount/Britannia?
 
2H4
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RE: Why Fabric Control Surfaces?

Thu Nov 02, 2006 9:15 am




Quoting Vzlet (Reply 6):

Thanks, Vzlet. I didn't realize labor costs were so high...



2H4


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KELPkid
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RE: Why Fabric Control Surfaces?

Thu Nov 02, 2006 9:47 am

On WWII birds, in many cases wood and fabric control surfaces were done in an effort to spare valuable war material (like metals).
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Starlionblue
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RE: Why Fabric Control Surfaces?

Thu Nov 02, 2006 9:48 am

Quoting KELPkid (Reply 9):
On WWII birds, in many cases wood and fabric control surfaces were done in an effort to spare valuable war material (like metals).

Indeed. It also made repairs easier since they could be done in the field.
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vzlet
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RE: Why Fabric Control Surfaces?

Thu Nov 02, 2006 10:50 am

I'm under the impression that fabric (or other lightweight material) is used primarily for the anti-flutter balance-related reason that Bobster2 mentioned. On the T-34, for example, all control surfaces except the trim/servo tabs are magnesium. If (and I'm assuming here) magnesium is not only more expensive than aluminum, but more difficult to repair, what reason sways the cost/benefit equation in its favor?

That said, the T-34 stabilizers (horizontal and vertical--did you know that they're interchangeable?) are also magnesium. That would save weight compared to aluminum, but obviously isn't for a flutter-related reason.

(And this post ends up being more contributory than conclusive! Any expert opinion out there?)
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L-188
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RE: Why Fabric Control Surfaces?

Thu Nov 02, 2006 12:33 pm

Quoting Vzlet (Reply 11):
I'm under the impression that fabric (or other lightweight material) is used primarily for the anti-flutter balance-related reason that Bobster2 mentioned.

That's my understanding of the situation, in fact I want to say that their are several examples of aircraft that where designed with metal control surfaces, experienced flutter during flight test and where reworked with fabric for the production models. The Corsair AFAIK was one of these aircraft.

I also think that is how the A4 Skyhawk ended up with it's distinctive external rib rudder.
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3DPlanes
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RE: Why Fabric Control Surfaces?

Fri Nov 03, 2006 8:59 am

Thanks for the replies, guys. I hadn't thought about flutter and the counter-balance...

And, L-188, you are correct, the A-4 got the unique rudder after encountering flutter during testing. They simply remade it with the skin in the middle and the ribs on the outside. Heinemann said the fix worked and they were moving so fast that they never did go back and find the reason for the flutter...
"Simplicate and add lightness." - Ed Heinemann
 
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HAWK21M
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RE: Why Fabric Control Surfaces?

Sun Nov 05, 2006 2:26 am

I remember the Piper PA18 used to have warm Linseed oil poured into the Metal Frames prior to Fabric coating as a Corrosion preventive measure.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
KELPkid
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RE: Why Fabric Control Surfaces?

Sun Nov 05, 2006 4:14 pm

Quoting HAWK21M (Reply 14):
I remember the Piper PA18 used to have warm Linseed oil poured into the Metal Frames prior to Fabric coating as a Corrosion preventive measure.
regds
MEL

As I recall, this is how just about all American planes with metal frames and fabric covering were constructed.
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Buzz
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RE: Why Fabric Control Surfaces?

Sun Nov 05, 2006 11:02 pm

Hi KELPKid, Buzz here... across the river from you. I'm fond of the "new" polyester fabrics, last a lot longer than the Grade A cotton and they're relatively easy to repair (glue on, dope on), and it's about twice as strong as cotton.

On a lot of the fabric covered surfaces, the side loads aren't very high. So fabric covered surfaces are sufficiently strong and a maybe equally light, but more durable (hailstorm? ) and easy to repair. But the skill to do fabric is sort of vanishing.

To cover an entire Champ, or Cub it's now about $4000 of materials: polyester fabric and dopes, fabric tapes, rib stitching or screws. It it somewhat time consuming, but not worse than putting aluminum skin on an RV wing. Need to spray things, that causes some problems.

T-34 magnesium controls: Mag is quite prone to corrosion... I don't like it. It's lighter. But metal control surface panels tend to be thin, easy to damage. So your repair needs to be light... yet strong.

Hey KELPKid, we ought to go Champ flying... if the rain lets up and a few grass airstrips dry out.
 
erj-145mech
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RE: Why Fabric Control Surfaces?

Mon Nov 06, 2006 7:06 am

During WWII there were two fighters built with metal covered control surfaces, one was pre war designed and built.

They were the P-38 and the P-47.

Control surfaces have to be light enough to be able to balance, we're already talked about that.

When most of these airplanes were designed, metallurgy wasn't to the point where it is today and the metal was too thick to be practical to keep from cracking when extruded thin enough for control surfaces.

Today, sheet aluminum is available in thicknesses as thin as .016", and still be crack resistant.
 
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Jetlagged
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RE: Why Fabric Control Surfaces?

Mon Nov 06, 2006 6:51 pm

Quoting Erj-145mech (Reply 17):
During WWII there were two fighters built with metal covered control surfaces, one was pre war designed and built.

They were the P-38 and the P-47.

Just two? These were not the only WWII fighters with metal skinned control surfaces. For example: later model Spitfires, FW-190, etc. I'm not sure but I would assume the P-51 also had metal covered control surfaces.

Quoting N231YE (Reply 3):
I know WWII aircraft such as the Vought F4U Corsair had fabric control surfaces...they were designed that way to be lighter on the controls.

Fabric covering does not necessarily make the controls feel lighter, even though the control surface itself is lighter. Control feel is governed by hinge moments, mechanical advantage, etc. Fabric covered controls are less well sealed so much less effective at high speed, requiring higher deflections and so greater forces. Early Spitfires had fabric covered ailerons. At high speeds these became less effective and so actually increased control forces. Metal covered ailerons were then fitted, which increased aileron effectiveness and reduced control forces at high speeds.
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