Fabric Covered Control Surfaces

[silence]

It looks like many planes of WW2 had fabric-covered control surfaces, even when the rest of the plane was all-metal. Why do this and not make the control surfaces metal also?

I also read that wooed propellers such as that on the Doras were fabric-covered. Again, why?

 

[swampyankee]

Fabric is light, and it makes it easier to balance the control surfaces. For the propellers, it's probably because the fabric will protect the surface from damage.

 

[FLYBOYJ]

The lighter the control surface you have, the lighter the control surface counter balance you need to prevent flutter. As faster aircrft were produced, fabic control surfaces would "balloon" under certain conditions.

The fabric covering of props was introduced to help prevent blade errosion from dust, flying grit and rain etc. It also keeps moisture from delaminating the prop.

 

[mike siggins]

an oldtimer told me that the metal control surface could jam from bullet damage where the bullet would pass threw the fabric and keep going

 

[FLYBOYJ]

an oldtimer told me that the metal control surface could jam from bullet damage where the bullet would pass threw the fabric and keep going

Far stretched comment, LOL! Where will it jam? Fabric surfaces have similar if not the same moving parts as a metal surface.

 

[davebender]

20mm mine shell will explode and rip fabric to shreds. Tough on aluminum too but I would expect metal to be more resistant to shrapnel and blast damage.

 

[Civettone]

I am not sure a 20mm shell would explode when it hits fabric ...



Kris

 

[bobbysocks]

I am not sure a 20mm shell would explode when it hits fabric ...



Kris

thats one for mythbusters to check out... good question.

 

[FLYBOYJ]

I don't know how much pressure would set off an exploding shell but I can tell you that fabric on WW2 aircraft control surfaces is pretty thick and taunt, I have data in some old text books and manuals indicating how strong fabric should be on higher speed aircraft.

 

[bobbysocks]

i just recovered an elevator with some top of the line stuff. its is tight and thick as a drum head. i imagine i could poke a hole in it with a pencil where as i could never get through a piece of .020 ac grade aluminum. then again ww2 stuff might have been way heavier and stiffer. idk, i guess a lot would depend on how sensitive the detonators were on 20mm rounds. FlyboyJ...they test fabric with a poke test....what is the weight or measure they use to fail the fabric?

 

[Jabberwocky]

Control surfaces of WW2 fighters could be fabric (cotton, linen and occassionally canvas), wood, aluminium alloy, or even other metals like steel. Doped, stiffened fabric had been the traditional material of choice for ailerons and rudders and it was used on the majority of WW2 fighters.

Problems came at high speed, when the airflow caused the aileron fabric to bloom/distort off the frame. Spitfire, F4U, P-47 and 109 pilots all reported this problem.

I know the Spitfire transitioned to metal ailerons in 1941, resulting in both an increased peak rate of roll (from about 75 deg sec to about 90 deg sec peak) and a generally higher rate of roll above 220-240 mph. Several other fighters (P-47 for sure) transitioned to metal skinned ailerons through the war.

 

[gumbyk]

i just recovered an elevator with some top of the line stuff. its is tight and thick as a drum head. i imagine i could poke a hole in it with a pencil where as i could never get through a piece of .020 ac grade aluminum. then again ww2 stuff might have been way heavier and stiffer. idk, i guess a lot would depend on how sensitive the detonators were on 20mm rounds. FlyboyJ...they test fabric with a poke test....what is the weight or measure they use to fail the fabric?

The shear strength characteristics of modern fabrics is quite different to cotton/linen that would have been used in WW2. This is why the FAA AC 43-13 (the universal repair info) states that 'mechanical devices are not applicable to to glass fiber fabric that will easily shear and indicate a very low reading regardless of the true breaking strength'

 

[nuuumannn]

Irish linen was the predominant fabric used in aircraft construction, or mandapolam. These days, Ceconite is the preferred material and it is still used in modern aircraft to cover litening holes in control surfaces. I remember balancing flight controls of C-130s, P-3s and things and fitting pre-cut patches over the litening holes.

 

[FLYBOYJ]

i just recovered an elevator with some top of the line stuff. its is tight and thick as a drum head. i imagine i could poke a hole in it with a pencil where as i could never get through a piece of .020 ac grade aluminum. then again ww2 stuff might have been way heavier and stiffer. idk, i guess a lot would depend on how sensitive the detonators were on 20mm rounds. FlyboyJ...they test fabric with a poke test....what is the weight or measure they use to fail the fabric?

Two tests are generally done, a punch and pull test.

Here's some good bathroom reading, I don't feel like typing, just had my third beer tonight...

http://www.faa.gov/regulations_poli...raft/amt_airframe_handbook/media/ama_Ch03.pdf

Control surfaces of WW2 fighters could be fabric (cotton, linen and occassionally canvas), wood, aluminium alloy, or even other metals like steel. Doped, stiffened fabric had been the traditional material of choice for ailerons and rudders and it was used on the majority of WW2 fighters.

Canvas was not a "normal" covering. It's too heavy

 

[bobbysocks]

nice...thanks.

 

[nuuumannn]

I don't feel like typing, just had my third beer tonight...

Surprised you're on the computer at all, Joe! That's a dedicated mod, does it whilst settling in with a brew!

 

[N4521U]

Not sure about WWII.

I wrangeled myself into the Wood Fabric and Dope section of the A&P school years ago when the A&P school was doing the museum non-airworthy aircraft control surfaces for school projects. I was doing sign painting for the museum and they got me into the class, unofficially, so I know "just enough to be dangerous".

We used seconite and Irish linnen thread for stitching, and patching cuts and tears. Every rib is stitched with a prescribed spacing, leading edge to trailing edge of wing, or control surface. Where prop wash and air speeds are faster over the fabric surface, the stitching spacing is at least halved. A strip of fabric about 2" wide, with the edges and ends "pinked" are "doped" over the stitching of ribs and patches. The leading edges of wings and control surfaces are "padded" with cotton before covering. The whole of the perimeter of the wing or control surface has a "second covering" of a pinked tape doped over the doped wing cover. The stitching and knotting and spacing requirements are very precise.

It's a blast to do. Something anyone interested in aircraft should have the chance to try.

 

[Dash119]

It looks like many planes of WW2 had fabric-covered control surfaces, even when the rest of the plane was all-metal. Why do this and not make the control surfaces metal also?

I know this is an old thread, but were there any planes in WWII that did not have at least one fabric-covered control surface? I can't think of any...

 

[Dash119]

Sorry, the question should have appeared outside the quote;

I know this is an old thread, but were there any planes in WWII that did not have at least one fabric-covered control surface? I can't think of any...

 

[BobB]

The replies have already veered off at tangents from the original question so I'll add this story. The C-130 had lots of Grade A cotton patches in various places including over the cutouts in the wing root fairings to reach the life raft release handles. In the 1980's someone decided that the cotton should be updated to Ceconite so the Engineering Design Standard for the patches was revised to show that you should buy Ceconite. An old timer objected that the Ceconite would be too tough to punch through with your fist to get to the life raft release handles. A test specimen was made by doping Ceconite over the top of an open paint can. Someone stepped forward and said "I can punch through that! I've trained in karate!" He punched it and his fist bounced off. He punched again, same result. He went into a frenzy of punching and finally broke through. My boss pointed out that if you were on top of a C-130 ditched in the ocean with waves washing over the wing, even a karate expert might have difficulty in getting to the life raft release handles. A lightweight fabric was specified for that location with all the other lightening holes etc getting the Ceconite.