Sport Pilot Talk

mcjon77 · Joined: 20 Aug 2007 Posts: 27 Location: Chicago

Hi guys,

What are the benefits and drawbacks to modern tube & fabric as opposed to metal for aircraft today. The only thing I have heard is that metal is more durable and fabric must be replaced every 20 years. How easily damaged is the fabric covering on an aircraft? I've never even touched a tube and fabric aircraft, so I have no idea if it is hardened with some kind of laminate or feels like the fabric on a kit stretched on its frame.

Thanks,

Jon

CharlieTango · Posted: Mon May 12, 2008 11:57 am Post subject:

the fabric is both easily damaged and repaired.

we tend to be careful with our aircraft and therefore damage is generally avoided.

tube and fabric are inexpensive and lighter weight and should lead to lesser expensive designs.

charlie has lots of experience and will likely tell you that if cared for modern fabrics have good lifespans.

Cub flyer · Joined: 10 Sep 2006 Posts: 333

Guess that's my cue.

From what I have seen most fabric systems work well if the instructions are followed. Problems come from using auto paints, brittle urethanes and mixing processes.

I have used the classic Randolph dope with great success. It is fairly cheap, easy to use and easy to repair.

Drawbacks are it needs waxing to keep from getting chalky, is not as fire proof as Stits process (Polyfiber) but close. topcoat finish can crack if impacted when cold. Dope will continue to shrink with age. I have seen many 30 year old dope cover jobs doing ok. Dope can be easily repainted.

Polyfiber can also crack but usually will not peel. Polyfiber is all the same base chemical (vinyl process) and can be repaired easily. Is self extinguishing. Will not shrink with age. Poly tone finish can be easily repainted.
We have used Poly fiber the most during the last 10 years

Urethane finishes are the big thing right now. Watch for airplanes finished with one process and then top coated with another. It violates most STC's.

The Airtech finish is fairly new. I have tried it and went back to another type. It worked ok but was more fussy of pinholes, paint settling, glue lines and other stuff. Not bad but just different. the gloss is really good. How it holds up we'll see. Not sure how hard it would be to repaint. Repairs were ok on our test parts.

My next one to try is the Stewart system. Some of it is water thinned and the sample I have has survived our destruction test well.

Fabric is not easily damaged in normal use. I will bend the airplanes structure before puncturing the fabric if hit with a large blunt object. Sharp objects will of course tear it but most sticks and light brush just slide by. You could not punch your hand through a good fabric job.

Also repairs can be made to tubing with an internal splice. the area recovered and no visible evidence.

Modern paints, primers, and tube oils are very good. Tig welding has worked well for us so far. Rust is easy to prevent with a little care. Most airplanes with rust problems were a. covered years ago and the tubing paint is 50 year old original stuff, b. painted with incompatible paint, c. powder coated tubes, d. repaired and improperly painted.

Old enamel, zinc chromate, lacquer don't hold up to the modern MEK thinned glues. causing problems later.

I have seen many crash results and would choose a tubing airplane every time. That is why most crop dusters have steel tube frames.

Outside storage the urethane finishes will hold up longer but when they go it's time to recover. The soft dope and polytone finishes will last about 12 years outside and can be rejuvenated and resprayed easily to last another 12. Usually the primer / paint on the tubing breaks down before the fabric ever goes bad. or the airplane just gets ratty looking.

for a good test remove an inspection panel, shine a bright light on the outside and see if it shows inside. If it does there was not enough silver.

This works on all but the airtech finish which uses a UV inhibitor in the paint.

Inside storage there is no lifetime depending on care.

There is no reason after a rebuild a tubing airplane cannot look just like new inside and out. Hard to do that with a metal one.

Lots of supercubs working all over alaska that have never seen a hangar since new in the 50's and 60's. All the beavers have a tube frame cockpit section with a lot nearing 15,000 hours of very hard use.

Cub flyer · Joined: 10 Sep 2006 Posts: 333

Piper used to paint their tubing with a blend of paint ends from Randolph.

Yep. Painted the frames with toxic waste. It held up for many years.

Old man Piper was the master of cheap airplane construction.

mcjon77 · Joined: 20 Aug 2007 Posts: 27 Location: Chicago

Thanks for the info, guys.

I'm looking at high-wing taildragger kits right now and the metal ones, while looking more durable, have longer build times, are more expensive, less aestheticlly pleasing, and have worse performance numbers. I'm trying to find out if there is any other benefit to metal, other than being able to leave the plane outside.

Cub flyer · Joined: 10 Sep 2006 Posts: 333

There is a difference in a glued on and heat shrunk fabric and tube airplane like a Cub or a pulled on sailcloth covered aluminum tube airplane like the X-air or Rans.

The aluminum tube airplanes usually flex more and have a lot more fasteners. Weight is about the same for the same size airplane between steel tube frame and aluminum tube with steel reinforcements due to the number of fasteners.

The aluminum tube frame has a lot more points to wear, vibrate, loosen if the airplane is going to be used hard for training or other.

I had good luck with the sailcloth dacron sprayed with a Stits UV blocking clear coat.

They offer a mylar which is really not mylar. And now there is a white material on the X air SLSA that is some kind of PVC I believe.

Not sure how it holds up but it really builds fast with these systems.

Also easy to change later if you want a different color or to repair.

The wing rib attachment schemes are kind of odd on most sail cloth airplanes. I hated the batten system on the X air. Not sure how the Ikarus does their wings but the photos look nice.