Thursday, March 29, 2007

AV - Sewing

It's an ‘Upholstery Needle,' okay? Yeah, you can call it a 'Rib Stitching Needle' if you want. But expect the price to double (or more). Sometimes it's called a 'Quilting Needle,' 'Button Needle,' ‘Cushion Needle’ or just the generic 'Long Upholstery Needle' but whatever it's called, you need at least one and more is generally better.

Usta cost about fifty cents for a 10-inch upholstery needle (circa 1955) and anyone who worked on airplanes of that era was bound to accumulate a few. They end up down in the corner of your Covering Kit, sharp ends stuck in a cork. Along with your sail-palm, lump of bees wax, pinking shears and other stuff unique to dressing naked airframes.

My dad had about a dozen rib stitching needles in a piece of tubing in one of his tool boxes when he passed away and they fell to me, my younger brother being strictly a rotary-wing sorta guy. But a few years later when my brother died I found an assortment of needles in his kit, including a couple of long ones, proving that even the sling-wingers did a bit of sewing now & then.

Some guys who write to me about Flying on the Cheap can't get real steel needles. Sometimes it's because they simply aren't available and sometimes it's because they're too expensive. That’s because a lotta guys who write to me do so from foreign countries. They've got the same yen to fly as anybody else but Lord, the troubles they run into. One fellow has to ride his bike five kilometers each way to gain access to the internet, then has to pay a fee. It's even worse when they live in a village away from a city of any size. That makes their chances of finding a 10" Upholstery Needle somewhere between slim and none.

Ali went so far as to heat a bed spring, straighten it out and forge an eye on one end. After doing so he asked if a needle having a diameter of 1.5mm and a length of 23cm would be suitable, to which I replied: "Oh my yes!" although forging a dozen needles might leave you sleeping on the ground, which is why I advised him to use bamboo. (Being a grass rather than a wood, bamboo has a perfectly linear grain, meaning it splits evenly.) Thin knitting needles are another alternative but like upholstery needles, they seldom stray far from town.

The bamboo needles Ali made were about twelve inches long with a diameter of 3.7mm (about 0.145"). It took several messages to work-out their fabrication and additional exchanges to discuss the size of the hole, which caused him a lot of worry. After doing one-half of the elevator, which needed only a short needle but was something he could do without assistance, Ali saw that the size of the hole was of no consequence since it was completely covered by the finishing tapes.

Patel's problem was similar in that he could not find 'suitable string.' ('Thread' lead to some confusion during our electronic communictions, as did 'cord' but 'string' served well enough.) But he did have access to 100% polyester 'string' having a strength of 'approximately 3 kilograms in five trials' and wondered if he could spin several strands together, which lead to another affirmative from me and an interesting exchange in the principle of rope-making, since you can't simply spin the strands together. Fortunately, Patel grasped the principle at once since he also has a strong interest in Robotics (or at least, in small gear trains) and owns a hand-powered drill of which he is justifiably proud, along with a real carpenter's brace. The result was an unlimited supply of rib-lacing cord having a breaking strain of about 20 kilograms, more than enough to satisfy the strictest of CAA inspectors.

American homebuilders have it pretty easy, being able to buy suitable needles and string :-) But if you'd care to see how others have done it, a shish-kabob skewer makes a good rib stitching needle. (Ed.Note: See the photo above.) Simply sand the dull end to a thickness of about 1/16th of an inch and use a small drill bit to connect a series of holes to form the eye. Sanding and a bit of varnish will make it smooth enough for several wings- worth of rib-stitches.

Sharpen a nail or wire to make the initial hole in the doped fabric; bamboo must be re-sharpened too frequently to make it practical for punching its own holes. Don't worry about the size of the hole, it will vanish when you apply the finishing tapes.

And it doesn't absolutely have to be a Seine Knot. A plain old- fashioned Square Knot does just fine, assuming you're willing to tie-off each stitch. All of which goes to show that man really can fly... with a bit of help from his friends.


PS -- A regular 13-gauge, 10" upholstery needle has a diameter of 0.0975" And yes, it can make its own hole :-)

PPS -- You can whip two strands of waxed thread together without causing any problems. But if you want more, it's best to spin them together in the manner used to make a rope. You can find examples of how to do this on the Internet.


- On Mar 19, 5:53 pm, " jls" wrote:

> I like that flat thread from Stits, with the wax on it.


It's actually 'lacing tape,' originally used for lacing together looms of wiring. We usta call it 'Collins 12-cord' after the Collins Radio Company, who would sell us rolls of it. Do a Google for 'dacron lacing tape,' you'll run into it. You want the white stuff with the 50- pound rating; usta come in 500 yd spools, pre-waxed & mildew-proofed and was delightfully inexpensive. Trouble is, it isn't STC'd for all fabric-covered aircraft... unless it is part of an STC'd package from one of the covering suppliers, who will very kindly re-spool you a quarter of a spool for about ten times the price... like what happens when an upholstery needle gets turned into a rib-stitchin’ needle :-)


(Ed.Note: The yellow twine in the photo is to illustrate the size of the eye. The twine, which has a breaking strain of about 70 lbs, is nylon and not really suitable for rib stitching, except in an emergency... such as being poor :-)