Fabric control surfaces

[17f]

Can anybody explain the process of covering fabric control surfaces and what type of material is used? My dad posed the question today and i have to admit, i never thought about it. His best idea was using damp fabric and heating it after application to shrink it. I would think that would be a nice way to start some corrosion. Thanks - Chris

[Kyleb]

Basically, you drape loose fabric over the surface. Then you pull most of the wrinkles out and glue the fabric down at the edges. Generally, you need at least a 1" glue line. Repeat the process on the other side of the surface.

If you are using today's dacron fabrics, you use a calibrated iron at specific temperatures to shrink the fabric taught. After that, you mechanically attach the fabric to the intermediate structure using rib stitches, screws, or other appropriate means.

Once that process is finished, you apply reinforcing tape across all of the fasteners, across any seams, and around the perimeter of the assembly. You also reinforce other points like inspection holes, airframe protrustions, etc.

Then you prime and paint the fabric.

That's a generic description. Each covering system (and there are 4 or 5 I can think of) is slightly different and requires different glues, primers, and procedures.

Stewart Systems (one of the covering systems) has quite a few videos on Youtube if you're interested in the details of how to apply their product(s).

[shrike]

Old-school would be cotton (or linen for older-school) sewn to shape, misted with water (not much) to start the tautening and attached mechanically - sewn, screwed, clipped what have you. Then multiple coats of nitrate or butyrate dope are applied. The dope, like lacquer, shrinks as it dries tightening the fabric as if goes.
Doped cotton can have a life as short as six months, or several years depending on the color. Yellow is one the short lived ones, which is why the USAAF switched to silver on training aircraft. Modern synthetic coverings can have lives of decades.

[John Dupre]

I remember being taught that with original fabrics, cotton or linen. After the misting a few coats of a taughtening dope were used and afterward none taughtening dope was used. It is possible to warp and even break structure under the fabric if too much taughtening dope is used or if too high a heat is applied to the modern synthetic fabrics. Years ago one of the alphabet groups offered a J-3 Cub as a prize and you could see that the wing tip bows were warped from the fabric being too tight.

[Enemy Ace]

Kind of off topic but IMHO anyone using old style linen and dope is guilty of criminal negligence. The old linen and dope are incredibly flammable and that's very dangerous. the ceconite/ poly fiber type systems are so much better.
If the airplane is a flyer that goes double.

[17f]

So in an over-simplified way it works just like the balsa wood and tissue paper kits I built as a kid.

So, a follow-up question: How did they maintain the fabric control surfaces of WWII aircraft? Provided an aircraft stayed in theater long enough and didn`t have the fabric turned to swiss cheese by flak, did they just swap surfaces with a second set so that the airplane could stay mission ready?

[Kyleb]

So in an over-simplified way it works just like the balsa wood and tissue paper kits I built as a kid.

So, a follow-up question: How did they maintain the fabric control surfaces of WWII aircraft? Provided an aircraft stayed in theater long enough and didn`t have the fabric turned to swiss cheese by flak, did they just swap surfaces with a second set so that the airplane could stay mission ready?

Possibly. But field repairs on cotton/dope could be made very quickly. Dope dries fast and they weren't interested in cosmetics. Patching could be done in a matter of a few hours, and I'd bet a total surface recover of something like an aileron would only take a day or two at worst.

[jaybird]

Well, not a warbird...but the process is the process. (Polyfiber in this case)

[Dan Jones]

Kind of off topic but IMHO anyone using old style linen and dope is guilty of criminal negligence. The old linen and dope are incredibly flammable and that's very dangerous. the ceconite/ poly fiber type systems are so much better.
If the airplane is a flyer that goes double.

Not hardly. The flammability issue principally came from the use of entirely nitrate dopes throughout, but they are still used as the initial chemical coating on the synthetic fabrics because the less flammable butyrate dopes won't stick to the synthetic fabric but will stick to the nitrate dope initial coat. Whether one uses cotton, linen, or Dacron as the covering medium makes no significant difference to the flammability issue.

[ZRX61]

Doped cotton can have a life as short as six months, or several years depending on the color. Yellow is one the short lived ones, which is why the USAAF switched to silver on training aircraft. Modern synthetic coverings can have lives of decades.

I can never understand why museums with static aircraft would ever specify Irish linen instead of ceconite etc. I understand they want to "preserve the past" but when the aircraft is painted & parked for decades why the heck they would go with a system that won't last & anyone looking at the aircraft from 20ft away won't be any the wiser about what fabric was used... Wright Patterson being the culprit here....

[shrike]

Doped cotton can have a life as short as six months, or several years depending on the color. Yellow is one the short lived ones, which is why the USAAF switched to silver on training aircraft. Modern synthetic coverings can have lives of decades.

I can never understand why museums with static aircraft would ever specify Irish linen instead of ceconite etc. I understand they want to "preserve the past" but when the aircraft is painted & parked for decades why the heck they would go with a system that won't last & anyone looking at the aircraft from 20ft away won't be any the wiser about what fabric was used... Wright Patterson being the culprit here....

It depends on the presentation. Ceconite tends to be very white, and synthetic covering materials are coloured to show coverage (PolyFiber is pink unless you special order clear). If you are going to do a final opaque finish, then I agree with you, if it's a Bleriot, or Wright or anything originally finished in clear doped linen, than thats' impossible to duplicate.

[The Inspector]

Fabric covered control surfaces remained in production up to at least the end of the DC-7 and CONNIES. In a combat zone, fabric damage repairs could be made in hours in a forward combat area by a semi trained individual with a pair of scissors and a pot of dope and some fabric where a metal repair would require air driven tools and lots of support equipment plus the surface might need rebalancing (ask anyone who's painted a BONANZA).
UVA and UVB have always been the enemy of any covering besides metal. and are still a threat to CFRP airframes which is why you won't see any bare surfaces except metal leading edges on the 787.
Don't want to stir any bad memories, but did you ever know anyone who built a BEDE BD-4? (not the mini, the one that looked like the crate a CESSNA 177 was shipped in) The design was very clever as the wing panels were nested interlocking fiberglass panels that you just pulled out like a window drape then epoxied to the wings structures. Pretty clever but some who built them and left them tied down outside discovered that after a few seasons, you could rest your hand on the wing surface and with very little effort press out a section of very fragile and brittle fiberglass, and of course by then old Jim was no where to be found

[Dan Jones]

If you go to http://www.ceconite.com there is an excellent series of articles written by Ron Alexander, who has likely forgotten more about working with fabric than many of us know. The processes for working with cotton, linen, Polyfiber, Stewart, etc, vary, but this will give you a decent introduction to fabric work. The biggest killer of any type of fabric is ultraviolet light, and the purpose of the silver coats of dope is to block that light from being able to get at the fabric. Any properly finished fabric covered airplane, regardless of it's final finish color, should be entirely silver underneath. I would hazard a guess that the reason why the USAAF and USN switched from yellow trainers to just silver trainers was more along the lines of the benefits of the higher visibility coloring didn't justify the extra time, effort and expense, especially during wartime.

[17f]

Awesome photos jaybird. Neat to see the process from start to finish.

[JDK]

It's a good question! As has been touched on, just about anyone can repair a fabric ding; in fact bullet holes were easier to patch in fabric than metal, as demonstrated by Hurricane vs Spitfire repairs, the Hurricane having a fabric covered fuselage, and early examples fabric covered wings.

And as a friend of mind discovered, T-shirt material will serve when the right fabric is not available.

The use of modern synthetics for fabricing is more popular in the new world, while, IIRC, many restorers in the UK particularly go for the more authentic natural fabric, in restorations striving for 100% originality. What dopes they use, I don't know, but I'm amused by the suggestion that they must be negligent - the absence of such charges will, presumably, relate to modern dopes.

I can never understand why museums with static aircraft would ever specify Irish linen instead of ceconite etc. I understand they want to "preserve the past" but when the aircraft is painted & parked for decades why the heck they would go with a system that won't last & anyone looking at the aircraft from 20ft away won't be any the wiser about what fabric was used... Wright Patterson being the culprit here....

Substituting a non-period material goes against one of the most basic museum tenets, and compromises the worth of the aircraft as an historical document for future researchers - such as 22nd century warbird operators...

Which is one reason why so many museums mandate minimising UV - and incidentally frustrating the photographers among us with the 'mood lighting'.

Regards,