Monday, May 04, 2009

Follow-Up from the Scottsboro Fly-In

My buddy Scott now lives Down Yonder in New Zealand. As expected, he provided some useful insights into my questions and comments about the items I photographed on Saturday. And so, without further ado, here's Scott:

G’day Bart –

I sure hope you took the opportunity to visit the Unclaimed Luggage Center on your trip to Scottsboro. If not, you’ll just have to go again.

Along with future visits to fly-ins, you might want to visit a skydiving operation. You’ll know within a couple of minutes if you’ll want to jump, but I still wouldn’t do it on that trip. You could, however, ask if they offer something we used to call “observer lifts.” That’s where you get to sit in the plane with the jumpers, but get to ride back down to earth, not fall down. They won’t charge you double what they charge the jumpers just because you’re getting a round trip, although they might joke about it. In fact, the charge is usually less.

Also, make sure you get a ride in a Stearman or other open-cockpit airplane. They’re fewer and fewer of them as time goes on. You haven’t really been flying until you’ve done this.

Unfortunately your captions don’t line up with the photos, so here are my comments as best I can guess to where you meant to place the captions.

  • The loud end of a PT-17 Stearman "Kaydet" trainer aircraft. I’m assuming that’s the pic that includes the kid in the red shirt. Stearman, yes. Kaydet, no. Only because it’s wearing Navy paint. In another photo you see the model name N2S-3, a Navy designation, on the vertical fin. Above the number 68 note a red filler cap, which is for the oil reservoir. Forward of that is a beveled sort of pipe-y appendage, and just below it is a black T-handle. To start the engine, you stuck a crank into the hole shielded by the beveled pipe. You cranked with great vigor and a very heavy inertial wheel began to turn. Once the inertial wheel was spinning fast enough (you knew this from the pitch of the whine), you removed the crank handle and then pulled the T-handle which would then transfer the energy to the crankshaft turning the engine over. Russian aircraft use compressed air to do the same thing. You use a hand pump to fill an air bottle, then pull a handle in the cockpit. Note how many layers of wood are glue-laminated to make the prop. If it were a solid piece of wood it would warp as temperature and humidity changed. Also note that it’s legal to tape over stone chips and similar dings. If a bigger chunk is taken out of the prop, it’ll vibrate. It’s uncomfortable for the pilot and crew, and it’s bad for the engine. At that point the prop is removed from the aircraft and balanced. Balancing consists of taking a similar-weight chunk of wood out of the prop’s heavy side, taping over the new ding, and away you go. The cost is a couple hundred instead of thousands.
  • The wings are covered with canvas. Fabric, yes. Canvas, no. It’s too heavy. It used to be linen, but it rarely lasted >5 years. In the 1930s it was replaced with a synthetic fabric called ceconite, which is still in use today. It’s got a life of 25-30 years, even when the plane is parked out in the sun. To apply the cover, fabric is stretched over the fuselage/wing/control surface ribs as tightly as possible, then dope was applied to shrink it. The first dope was nitrile, which when placed over linen made almost the same thing as gun cotton. Not exactly what you want stretched over wooden ribs and spars with a fire-belching engine and an air-breathing fuel tank close by. Nitrile was replaced with something called butyrate, which also is still in use today. Butyrate is not flammable, is available in different colors, and can also be painted. To paint nitrile you had to varnish it first. To me that’s a fire hazard on top of a fire hazard on top of something flammable next to something else very flammable, all in close proximity to a flame producer. And that’s before you put guns on the aircraft. Next time you walk around a DC-3 tap your fingers on the wings (metal), then on the ailerons (fabric). You’ll note the difference right away. Most of the new Light Sport Aircraft (LSAs) are fabric-covered, at least partially, as well.
  • Anyone want to take a guess at the structure on the left? Tornado siren? The wind sock showed almost no wind. That’s the rotating beacon; it indicates the airport to night-flyers. It shows green on one side and white on the other. Green-white indicates a civilian airport. Green and a quick double-white flash indicates a military airfield. Green-yellow-white indicates a heliport. You’ll often see this one atop a hospital.
  • …what's this horn-shaped protuberance on the port side? On older aircraft, directional gyros, turn-and-bank-indicators, and artificial horizons were powered by air, which was generated by vacuum. That’s the vacuum horn, which you will note is always placed where it can pick up prop blast. On middle-age aircraft there’s an electric vacuum pump, and the horn is the standby source of vacuum pressure. The last thing you need while making a descending turn through a raincloud on a night approach is to lose your artificial horizon.

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