Fabric Covered Dreams
Veeduber
While explaining how it is possible to build a safe, reliable airplane for very
little money I described covering the wings with polyester fabric shrunk tight
with a clothes iron and sealed with urethane varnish into which you've mixed
some powdered aluminum.
Boy did I catch hell :-) (The original message, posted a couple of years ago,
was titled ‘Flying on the Cheap.' It has since been reposted widely and has
generated a lot of email.)
About 90% of the messages were negative, in whole or in part. The wholly
negative responses, which made up a good three-quarters of the Negative Crowd,
insisted it simply could NOT or SHOULD not be done. A fair number implied I
was running some sort of scam. A larger number simply thought I was stupid :-)
The remaining quarter of the Negative Crowd were convinced the prospect was
flawed in a particular detail, such as using garden tractor wheels for your
landing gear or carving your own prop. That simply was not done. And since
that part of the idea was impossible, the whole idea was impossible.
Well... okay. Thank you for your opinion.
For all you OTHER yahoos with a yen to fly, the original message is valid.
Indeed, in telling you how you can fly on the cheap I've done little more than
read a page from the history of American aviation, describing wooden wings and
fuselages of welded steel tubing. But time marches on and some of the things I
said, such as using fabric from your local fabric store and picking up a packet
of powdered aluminum from your local paint store, are no longer correct, at
least in detail.
The truth is, powdered aluminum is still available. But not from your local
paint store, as it was here in Vista, California (and I assume everywhere else)
at least until 1975 or thereabouts, when I last bought some. Nowadays powdered
aluminum is considered a PYROTECHNIC, probably because it is one of the
components in thermite. All that means is that you must register with a
supplier of pyrotechnic chemicals and buy the stuff from him. The internet can
provide you with the addresses of several who sell to the public... once you
fill out their forms.
Or you can buy powdered aluminum PASTE from someone like Wag-Aero or Aircraft
Spruce.
In a similar vein some of you have discovered that heat-shrinkable polyester
fabric is no longer available from most local yardage stores. I didn't know
that and apologize for sending you on a snipe hunt. Let's see what we can do
about it.
Using the internet I tracked down four varieties of 100% Polyester fabric and
bought sample quantities of each. Then I tested them.
But the first step was to establish a standard.
Out in the shop there's some boxes of scrap fabric, remnants of Covering Jobs
Past. The certified stuff is in one box, generic stuff in another. Along with
rat turds and lotsa other crud the box of uncertified, generic 100% Polyester
fabric scraps yielded up a piece about two feet wide by 66" long. Filthy of
course, but you can wash it, which is what I did. Cold water. Not a lot of
soap. Two rinse cycles. Air dry.
After being washed the dacron fabric came out wrinkled like a piece of aluminum
foil that had been wadded up then flattened out. Looks like hell but looks can
be deceiving. I made up some test frames, gave them a seal coat of varnish and
glued the Standard fabric to a frame.
As soon as that stuff even SAW the iron, the wrinkles vanished. A little more
heat and it shrunk up so tight it threatened to warp the frame. Given a coat
of Home Depot dope, it got even tighter and when cured, sounded like an Inuit
drum. Bottom line: This is good stuff for covering a simple airplane. (The
fabric is probably from Aircraft Spruce, catalog number 09-00300. Three ounces
per square yard [or thereabouts], 66" wide and probably about four bucks per
linear yard at today's prices.)
So there was my Standard, against which I could compare my Internet Fabric
Store Wing Covering Fabric.
The first test was to cut a 2x10 inch strip of fabric and iron it, first on the
‘low' setting, then on ‘high.' Only one of the samples shrunk and then
only by 2% or so. The next step was to attach the samples to frames to see if
I could produce a drum-taut surface. The results were... marginal. The fabric
that did heat-shrink came out pretty good but the others took a couple of coats
of nitrate dope to tighten up and didn't have that resonant drum-like BONK when
tapped. (If it don't BONK, don't fly it.)
One of the fabrics I tested was unbleached 100% cotton muslin. I included it
in the tests because a couple of you don't live in Detroit. Or even in the
USA.
After being tacked to a frame (the other samples were attached with contact
cement) the cotton tightened up beautifully with water and gave me a good drum
sound after two coats of dope. But it wasn't as smooth as Grade A cotton,
weighed about 6.5 ounces per square yard going in and one hell of a lot more
after it soaked up two coats of dope. That wouldn't be so bad if we were
talking Pietenpol's and Model A Fords swinging an eighty-inch prop. But we're
talking single-place, VW-power and a twenty-four foot wing span. And cheap.
The biggest part of the secret to flying on the cheap is to keep things LIGHT.
In some parts of the world unbleached cotton muslin may be your only option.
It'll work but it's going to run about four times heavier than dacron, so plan
accordingly.
The polyester fabric that DID shrink and DID play the drums was ‘Poly Suit
Lining' material from fabric.com. Ninety-five cents a yard. Width is about
45" and the weight something under two ounces per square yard. No, you can't
buy none because you apparently already HAVE, you rascals! After the tests,
which I've been sharing with the guys who are actually building the Practice
Wing, I tried to order some more... and was told they were sold out.
So what's the bottom line? I think you should buy the good stuff; save
yourself some headaches. (A suggestion I've voiced before.) But yeah, if you
know what you're doing and if you want to invest some time in testing fabrics
that are locally available, you can probably find something suitable for
covering a light airplane. The Dream stays alive but the path is a bit
steeper.
- - - - - - - - - - -
After receiving the fabric via UPS, cutting the first test-strips and
discovering they did NOT shrink, I devoted some time to trying to find out why,
since I'd been able to buy heat-shrinkable polyester from local stores in the
past. (I've already mentioned part of this in an earlier post; what you see
here has to do with the fabric I got via the Internet.)
Now this was kinda funny so bear with me.
After a bit of effort (quite a bit, in one case) I managed to reach humans at
the places from which I'd ordered fabric. But any mention of having the stuff
SHRINK produced Instant Denials. Not OUR fabric! No way, Jose! ALL of our
polyester fabrics are PRE-SHRUNK...
It took a while to get across to them that I wasn't angry, didn't want my money
back and wasn't accusing them of anything. At least, for two of them. One
lady remained convinced I was trying to lodge a complaint and insisted I do so
in writing. Ah well... But with the other two, the penny finally dropped and
here's what I was told. Heat-shrinkable polyester fabric WAS fairly common at
one time... but no one has made anything like that for at least ten years.
(Now here's the funny part :-)
...but if I DID receive some non-preshrunk fabric, and if it was one of their
Clearance Sale Items (which the Suit Lining Material happened to be) then I had
no recourse because somewhere in the fine print on their web site was some
legalese boilerplate bullshit stating that all such sales were final.
So, no, heat-shrinkable polyester fabric is not commonly available. And if it
was, they'd never admit it :-)
- - - - - - - - - -
So... whatcha gonna do? One option is to do what I did: Buy samples and test
them. And there's a bit of a tale here, too, because heat-shrinking isn't the
only way to tighten fabric. As I mentioned above, the sample of unbleached
(and I assume un-Mercerized) cotton that I tested shrinks like a cheap wool
suit, very similar to the way Grade A Cotton aircraft fabric shrinks. Just
sponge on warm water and let the stuff dry. My particular sample of unbleached
muslin had quite a bit of sizing and would not accept a LIGHT sponging of
water. But after adding one drop of liquid detergent to a gallon of warm water
(i.e., as a wetting agent) and scrubbing it onto the framed fabric with a
sponge, it soaked it right up. And as it dried, it shrank.
- - - - - - - - - - -
If you are very careful to apply your fabric with no wrinkles at all, you can
get a usable surface by shrinking it with dope or some form of sizing. The
Colditz Glider was covered with cotton bed-ticking, carefully sewn and tacked
to the airframe. It was then made taut by coating it with a starchy sizing the
prisoners produced from some kind of cereal; oatmeal or millet or something
like that. This is similar to what happens with common wall-paper paste (which
is basically wheat flour). Boiled to release its gluten and applied wet, the
stuff shrinks as it dries.
I don't expect anyone to paint their airplane with library paste. What I want
to get across here is the process of applying some form of coating or sizing
that shrinks as it dries. And the best example of that is aircraft dope.
But here again, the success of this procedure will depend largely on your
experience. And if you haven't used dope you should do some experiments to
teach yourself how. Which leads to the next part of this story :-)
- - - - - - - - - - -
After sticking the fabric to the frames and seeing the stuff remain as limp as
Odie's tongue I grabbed a can of dope and... I grabbed the NEXT can of dope
and...
I didn't have any dope. I had several cans that USED to contain dope. Now
they contained a cellulose potato chip.
Dope is cellulose nitrate lacquer. It isn't very expensive and it's fairly
common although if you want it to say ‘Aircraft Dope!' on the can you'll
probably have to order it from an aircraft supplier and pay a premium to boot.
I used to buy it at the same paint store where I used to buy powdered aluminum
:-) The paint store is no longer in business, thanks to Home Depot so that's
where I went. Sure enough, tucked away on a shelf in the paint department were
several gallon cans labeled ‘CLEAR CELLULOSE NITRATE LACQUER.' I bought a
can. (So who uses dope besides airplane builders? Luthiers, for one. Sandy
Eggo county, especially up here in the northern part, is over-run with
luthiers. You rarely see them but at night when the moon comes out, you can
hear them, playing out there in the hills.)
The stuff from Home Depot looks and smells like real dope but doesn't tighten
up as much, although more so than ‘non-tautening' aircraft dope. It worked
well enough for the tests. If I couldn't get anything better I'd be willing to
fly with it. But I don't think you should; not unless you've got a lot of
experience with fabric & dope (in which case you probably wouldn't be reading
this :-) The experience-factor is fairly critical here because the first coat
of dope is the one that does most of the tautening and you need to apply it
properly, which means encapsulating the fibers when you're working with
polyester and that calls a fairly thick viscosity. But with cotton (or other
absorbent fiber) you want to saturating fabric, which calls for a fairly thin
viscosity. The tricky bit here is the ‘fairly thick' vs ‘fairly thin'
because there really isn't that much difference between them. To adjust the
viscosity you pour some dope into a can and leave it set to thicken (i.e.,
increase the viscosity) or add thinner to reduce the viscosity. Temperature is
also a factor as is the orientation of the work. Some experiments will show
you which direction you need to go... but only for that particular set of
prevailing conditions. Fortunately, when covering just one airplane, the tail
feathers usually provide enough experience to let you do a good job on the
wings.
- - - - - - - - - - - - - - -
I've mentioned test frames a couple of times and can see the question marks
slowly rising over several heads, so...
Home Depot sells what they call "1x2 Whitewood." That's Yuppie-speak for
Western Hemlock furring strips, 3/4" thick, inch and a half wide by eight feet
long. Price varies according season, store and availability. I've bought them
for as little as thirty-nine cents and as much as $1.49. I tend to keep eight
or ten lengths on-hand. Like most of Home Depot's wood it's mostly crap but
now that they driven all the real lumber yards out of business, for lots of
folks they're the only source of lumber.
So go buy yourself some of that 1x2 whitewood crap. We're going to make some
fabric frames.
A fabric frame is just an open box over which we stretch a piece of aircraft
fabric in order to teach the newbies how to tack, glue, stitch and dope. Back
in the Good Ol' Days, whenever that was, we'd use an old drawer or a lug-box.
The size isn't especially important but for polyester the frame should large
enough to accept a standard clothes iron, which is what we use to shrink
polyester fabric.
Never built a fabric frame? See the drawings - FABRIC01 thru FABRIC03 (These
are in the ‘Files' section of the Fly5kfiles mailing list over on Yahoo.)
Keep in mind that our goal here is to work with FABRIC rather than the frame.
Don't go overboard on the thing. Chop the furring strip into lengths, start a
4d nail on each end, smear on a dob of Gorilla Glue and nail that puppy
together. Then hang it up and do another. Make three or four of them.
Then leave them alone for at least 24 hours.
- - - - - - - - - -
Looks like hell, don't they? :-)
Don't worry about it. In fact, there is an extremely valuable lesson in those
awful looking fabric frames. Follow me through here and see if you can pick it
up.
Got your angle-head grinder? Install a flat flapper-type sanding disk. Coarse
is good. Fire it up and get rid of all the glue squeeze-out. Keep the sander
flat; don't gouge the wood.
See how those corners are mis-aligned? Make them line up. Go on; use the
flapper wheel to even out the high side, taper it back a couple of inches.
Yeah, it's a mess. DON'T WORRY ABOUT IT. (You gotta trust me here.) Chamfer
all the edges. Just knock them down, mebbe a sixteenth of an inch. Use nice,
even motions with the angle-head grinder, almost no pressure at all; let the
flapper wheel do the work. If you spend more than a minute per frame, you're
missing the point.
Got them all cleaned up? Then take your powered sanding block, clip on a sheet
of #80 grit and get rid of the sanding marks from the flapper wheel. Smooth
things up.
Get a rag, dip it in some mineral spirits and wipe down the frames. This will
pick up most of the sanding dust.
Open up a can of VARNISH. Spar varnish is good but so is urethane. If you're
an aircraft type you know that nitrate dope will also serve to seal the wood,
which is what we're doing. But I'd rather you use varnish.
Lay on a full, wet coat of varnish then hang the frames up and use the brush to
smooth out any drips. If you don't have someplace to hang them, figure that
out before you make them.
Now go do something else. Allow the varnished frames to cure for at least 24
hours.
- - - - - - - - - - -
The varnished frames will come out rough as a cob. If we wanted a dense, shiny
finish we'd go after that rough surface with some #120 grit, knock it down and
lay on a second coat.
But in this particular case the one thing we DON'T want is a dense, shiny
finish. We want that rough-but-sealed finish because we're going to lay down a
layer of contact cement. And contact cement works best when the surface has
some tooth. Which is also true in the case of real airplanes and real fabric
cement. That was #1 in the Valuable Lesson Dept. #2 is the fact that you can
do the same thing with an airplane.
We always try to do the best we can but being human and building just one
airplane, sometimes things don't come out perfect.
Valuable Lesson #2 is the fact that most of the time, things don't HAVE to be
perfect to work perfectly well and this is especially true when doing fabric
work.
Does the fabric lay smooth? Try it out and see. Just stretch a piece of
fabric over the frame and look for irregularities. Sharp corners that have
escaped your notice for months are suddenly evident. So smooth them off.
Ditto for unexpected low spots, except you fill them; just glue on a filler and
sand it flush. Awkward angles that threaten to leave a puckered corner? Glue
in a block of balsa and convert the empty corner to a smoothly faired surface.
So long as such irregularities are neither frequent, abrupt nor large, they
will have no effect on how well your airplane performs. Resolving minor
problems of this sort is one of the realities of fabric work
- - - - - - - - - - - -
I used contact cement to attach the fabric to the frames. Regular fabric
cement (FabTac, et al) will work at least as well and costs about the same. I
used two coats of cement on the wood, allowing the first to dry before applying
the second. The fabric was applied while the second coat was still wet. A
third coat was applied OVER the fabric and squeegee'd through the weave with my
thumb. The goal is to encapsulate the fibers of the fabric with the cement.
Nothing bonds very well to polyester so we force the cement THROUGH the fabric
and allow it to bond TO ITSELF. There are a host of variations on this theme;
for a wing I would use a different method. Experiment; find a method that best
suits your situation.
Shrinking was done with a clothes iron reserved for that purpose and already
described in earlier posts. I did all the shrinking on the ‘high' setting...
then realized you wouldn't have any idea whathell I was talking about. Dug out
a thermometer that read to 400 degrees and measured the iron. The second mark
on my masking-tape dial produced a consistent 350 degrees Fahrenheit.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - -
In closing, allow me to offer a word of explanation about ‘Building on the
Cheap' and other messages some folks have found so disturbing.
My dad was an aircraft mechanic. I used to help him. The first time I can
recall helping him, I was about seven years old. I stood on a lug crate to
push needles back at him through the wing of an airplane. Such chores were
kinda interesting for the first five minutes after which I'd hear the Call of
the Wild and he'd usually let me go. But most times it was kind of neat to
just hang out with my dad, and between the two of us, me poking and him
pulling-through and tying-off, we'd do a whole wing.
Other times it was driving rivets. Or helping him sand. Or helping him paint;
masking off the NC numbers on the left while he did the right. Pulling wire.
Making up fittings. Polishing plexiglas... scrubbing the grime off the belly
of the Cub... It never seemed like work.
My dad never ‘taught' me to work on airplanes, as in Major Instruction, with
quotation marks and so on. He'd ask me to ‘give him a hand.' Nothing
complex; nothing I couldn't understand. Always demonstrated rather than being
told or ‘taught.' Always one small step at a time; ‘Do it Right, we won't
have to do it Over,' a shared joke always spoken with a smile because that was
one of my grandfather's favorite expressions. Waxing the thread, spinning two
thin threads across my thigh to make a thick thread, cleaning the oil off the
needles before and replacing it after, laying on dope or glue or cleaning
brushes or... No ‘teaching' at all. About twenty years of it off and on,
from the time I was a child until his death when I was in my mid-thirties.
You'll probably find this funny but somewhere in the back of my adult mind was
the notion that EVERYONE who flew planes or worked on them or wanted to BUILD
one, knew all that stuff that I'd learned without ever being taught. Like the
fact it's a Seine Knot (except we called it a Net Knot), tied flat instead of
with your toes holding the mesh, your netting bobbin flashing in and out, fast
as you could, as automatic as a woman knitting while rocking the baby and
carrying on a conversation at the same time. When (and where) I grew up, every
boy knew how to make nets. Not just for catching minnows but for basketball
hoops and summer-time hammocks and string-bags for your mom and all sorts of
other things. Common Knowledge; the stuff that never needs to be mentioned
because it's something EVERYONE knows. Like dope and fabric and welding and
woodwork and engines and...
Turns out, everyone don't. Which is probably why I see a simple, reliable
airplane as something everyone can build, and inexpensively, too... where
others see it as a Certified, Type Certificated, Approved Aviation-Quality
Bureaucratic Impossibility. And they're right. Absolutely. Because if
they're positive they can't build an airplane, they won't even try.
-R.S.Hoover
Jim Austin
Jim Austin
Veeduber wrote:
(Interesting reading, as usual)
Wright1902Glider
fun I had covering the wings of my Wright machine. Cotton muslin WITHOUT any
dope or shrinking... just streched tight with very sore fingers.
I did a considerable amount of fabric testing over the last year looking for a
suitable substitute for the infamous "Pride of the West." I made a similar
fabric frame to test that the fabric would NOT shrink and distort my unbraced
wings. (The fabric iteslf provides the lateral bracing.) I even developed a
vacuum testing device which measured fabric porisity in Hg. Alas, I ended up
going with a custom-milled cotton from WW1 Originals. Very pricey, but very
very acurate.
Harry
Robert Little
"Veeduber" <veed...@aol.com> wrote in message
news:20030811175032...@mb-m21.aol.com...
Morgans
"Robert Little" <razo...@tcac.net> wrote in message
news:vjio9tt...@corp.supernews.com...
Have you never heard of trimming, Robert?:
What a pain in the a**!
--
Jim in NC--
Barnyard BOb --
Yep...
This one is trophy size to the point
that I'd wonder about Robert and
anything he touches, including,,,,
RAZORBACK FABRICS, INC.
Barnyard BOb --
Corrie
> >Have you never heard of trimming, Robert?:
> that I'd wonder about Robert and
> anything he touches, including,,,,
> RAZORBACK FABRICS, INC.
Look on the bright side. You order a yard and he sends you the whole bolt....
Corrie, perennial optimist