Whittle Your Own Airplane

Fellow came by the shop to borrow a Dutch Oven. He works at one of the local
colleges and is a Boat Person rather than a Plane Person. Boat People usually
takes their kitchen with him when they travel but he's taking a bunch of
college kids over to Death Valley to count pup fish and the best the college
could do for chow and equipment was a couple of Sierra cups and some outdated
MRE's.

I've known this guy maybe twenty years, figure it's safe to loan him a Dutch
Oven. He's built a couple of boats, knows about wood. I helped him rig an
aluminum mast, ‘way back when sometime. He knows I fiddle with airplanes but
thought they were always aluminum.

"I thought you only worked in aluminum,' he said. We were out behind the shop.
Perplexed look on his face, inspecting an aileron that seemed to be growing
plumes of wood shavings where the ribs attached to the spar. I found the Dutch
Oven, not too rusty considering it hadn't been used in a year or more. Took it
in the shop to clean it up. He wasn't leaving til the next day; there would be
time to season the oven before he left.

I've been making some tail feathers. One set is all corners, simple and quick
to build. The other is all curves. I had a bundle of pine strips, one inch
wide but barely an eighth of an inch thick. When he arrived I'd been scarfing
them into ten-foot strips. Being a Boat Person he knows about scarfing.

"What slope is that?"

I didn't know. I finished cleaning up the Dutch Oven, went in the house for
some bacon grease, rubbed it down good. You can use vegetable oil if you want.
When I came back out to the shop he'd found a yo-yo and was measuring the
scarfs.

"That's about sixteen to one," he sounded surprised. Boat people tend to use
steep scarfs; eight to one; even six

Best I could do was shrug. I honestly had no idea what the slope was, told him
so. For the second time.

"How can you be sure they'll match if you don't even know what slope you're
using?"

He sounded kind of stern. I just looked at him. College teacher. Boat
person. He'd figure it out. I waited, kept looking at him.

"Oh!" You could almost see the light bulb go on over his head.

(So long as you cut all of your scarfs using the same set-up, they'll match.
It doesn't really matter what the angle is.)

The big disk sander was still set up for scarfing. I'd clamped a piece of 2x4
to the table, cocked it around so it formed a very flat angle relative to the
disk then simply shoved the strips into the gap like sharpening a pencil. Full
depth, the disk cut a taper about two inches long. The strips are about a
sixty-fourth shy of an eighth, which was how the set-up came out. I found
some scrap, squared them on the bandsaw, let him scarf them then put them
together to see how they fit. Nice.

Scarf joint is a special case of end-grain gluing. For full strength across
the joint you need a lot of surface which dictates a nice flat angle.
Producing that angle by sanding presents you with something of a problem.. You
need to get the sanding residue out of the fibers. I coat it with glue then
scrape it off with a single edged razor blade, then apply fresh glue. Seems to
work okay, which is good because most of the strips had three splices – four
pieces of wood. That's the reality of Building On The Cheap, using whatever
wood is locally available.

I showed him a couple that were already glued, showing off a bit by tying one
in a knot. They were glued with an epoxy because it's less viscous than most
of my other glues and epoxy doesn't need a lot of pressure to make a good
joint. To turn short strips into long ones, I taped them to a work bench.
There was a small strip of waxed paper under the glued area but the alignment
was strictly by eye, sighting down the strip until they aligned then holding it
in place by taping it to the bench. This leaves the scarf free to lift up,
apply the glue and check the wet-out. Then another piece of waxed paper went
over the top followed by a steel plate to provide some weight. Clean-up is
with a razor after which one edge gets trued up. They aren't perfectly
straight but for making bows, they don't have to be. All you need is one edge
that is reasonably true. That will be the down-edge when I laminate the curve,
which should take about fourteen of the strips and about two dozen sewer-pipe
clamps, plus a couple of real clamps to secure the laminated bow to the blocks
that make up the curves. Once the bow is cured it will be carved to its final
shape. Any irregularities in the strips will vanish during the carving.

Out back of the shop I dug around, found the trivet and some fire irons, showed
him a Squaw Wood kit and explained how to use it, loaned him a pair of heavy
leather gloves. He kept looking at the aileron with its little tufts of wood
shavings fluttering in the breeze.

I explained that they were errors. Those particular blocks had shown a gap
when fitted in place. I didn't want to make up new blocks so I installed them
square then filled the gap with wood shavings coated with glue on both sides.
Once the glue is cured I'll sand off the curls. I also pointed out an error he
hadn't seen, where the disk sander got away from me and gouged a rib.

"How did you keep it in place?" he asked, which was a good question. The rib
is curved and less than a quarter of an inch thick.

"Clothes pins. Put some waxed paper over the glue." If I couldn't grab it
with clothes pins I'd of had to use rubber bands or something like that. Once
the glue had cured I sanded the patch smooth.

"Does it effect the strength?"

"Not there. This all gets covered with cloth; it has to be smooth. Worse case
load is a few pounds per inch of rib."

He had his nose right down into the thing now looking at the filleted joints
and the scarfed doublers. And the struts.

"Are those what I think they are?" he pointed to a strut.

"Are you thinking bamboo?"

"Actually, I was thinking shish-ka-bob."

"You sound like my wife. No, those are Aviation Certified bamboo struts."

He gave me a look. I gave him a look. We both grinned.

All loaded up, he started his engine then ran the window down. "I hadn't
really thought about wood in the way you're using it there. What's the
trade-off compared to using aluiminum?" We've talked airplanes before. He's
dead set against composites, having developed a major reaction to resin. And
he's not much of a hand with metal. But he likes wood.

"Go play with your pup fish," I told him. "Give me a call when you get back."
He didn't look too happy with that. "It's not a trivial subject. The biggest
airplane ever built was made out of wood."

"The Spruce Goose! Up in Long Beach, by the Queen Mary." He'd just remembered
it was made of wood. His eyes didn't spin around like pin-wheels but they were
jumping around a lot. You could almost hear the ideas bumping into each other.

"Up in Oregon, now. And it's mostly birch." I thumped the roof of his car to
let him know he could take it away. "Call me. I'll show you how to rivet then
show you how to make a proper glue joint. Once you understand the procedures
you'll see most of the trade-offs yourself."

"You know, glue provides a continuous bond where rivets only fasten things
together like sewing. Or nails. Or..."

Back in the shop the air compressor cycled on, reminding me I had things to do.
But I'd lit his fire and he was enjoying the glow. You could hear the whirr
of his gears. Any minute now I expected to see smoke coming out his ears. I
thumped the roof again, harder. "Pup fish. Go count some."

He drove off and I went back to work. That aileron really did look like hell.
I found the drill motor and knocked the curls off the thing. If the professor
builds an airplane I have a hunch it won't need any gap-fillers.

Cleaning up the aileron, I got to thinking about what he said, about never
having thought of wood as an aviation material. Without really meaning to, we
fall prey to our prejudices. But given just a glimpse of wood's versatility
the professor immediately began to see it's advantages. I wonder how many of
us don a pair of blinders when we look at airplanes?

According to data from the Census of 2000 the median income in the United
States was $27,800. With approximately 135 million wage earners that means
about 67 million of them are earning LESS than twenty-seven eight. During that
same period one of the so-called Leaders of Sport Aviation referred to a
$20,000 airplane kit as "inexpensive" and a $25,000 Lycoming as "affordable."

Kind of makes you wonder who he's talking about. Certainly not any of the
sixty-seven million poor *******s pulling down that median wage. Or less.
Median means middle, you know. ‘Average' is what the bean counters like to
talk about. Average wage, you get to include Billy Gates, the head of the
Stock Exchange, those Enron execs and all of our millionaire Congressmen.
Average income in America is pretty high. But if you plan the future of
American aviation on the Average Income you've just guaranteed the end of
General Aviation as we know it. Come to think of it, I've got a hunch someone
already has.

Wood isn't very expensive. Yet. While we're all sitting around with our thumb
up our ass waiting for the bean counters to deliver another unworkable
bureaucratic solution to our steadily dwindling numbers, maybe we should be
teaching folks how to whittle their own airplanes.

-R.S.Hoover