September 4, 2013
My son, Ian, is working on a 7th grade science project, and is studying what wing position works best for maximum glide — that is, for a balsa wood glider launched from our roof. His standard is a swept-wing design, but we’re expecting that his straight wing, either the high or low version, will make the farthest penetration into our persnickety neighbor’s front lawn.
All aircraft have a center of pressure, also called center of lift, which is normally at a fixed location (except, I assume, in a swing wing like the F-14 or Tornado). They also have a center of gravity, which is where the aircraft’s weight balances fore-and-aft. The CG depends on the distribution of fuel, baggage, etc., and is moveable. Normally, the center of gravity is placed forward of the center of pressure, which creates a corresponding down force exerted by the tail assembly, and which results in an inherently stable aircraft.
This we learned from a King Schools video on You Tube (pretty basic, as befitting Ian’s two-time liberal arts major dad):
In a straight-wing design, this is easier to visualize. We’ve been balancing his gliders on our fingertips, and we’re adding pennies (chosen because of their standard, verifiable weights) to the nose to move the CG. His straight-wing gliders all balance backward at the wing tips, but if we add nose weight such that they’re slightly nose-heavy, we wanted to know if the down force of the tail would keep them flying straight without stalling. I think (and I’m no aeronautical engineer) that if the gliders balance perfectly fore-and-aft when held lightly at the wing tips, the centers of pressure and gravity would be in essentially the same position, and hence, the gliders will nose up, since the normal down force of the tail created by having the center of gravity forward of the center of pressure would be minimal, or missing.
But, what will happen with the swept -wing version? Since the wingtips of a swept-wing design are quite a bit aft of the roots, Ian’s swept-wing model (unlike his straight-wing models) acts nose-heavy if balanced at the wingtips, but very similar to the straight-wing designs — tail heavy — if balanced at the wing roots. Will we have to add even more weight to the nose to counteract the extra weight of the swept wings behind the CG?
Next step: three more designs–one high-wing, one low-wing, and one high-wing with dihedral (wings bent slightly upward at the roots.)
Edwards AFB has nothing on us. A wobbly step ladder to the roof and a few free hours after school are all we need. (And even Mommy approves.) Stay tuned for our flight test data.
January 28, 2013
Time was when almost every boy knew how to carefully lower a bubble canopy to a P-51 Mustang, eyeball a fuselage to make sure the wings were straight on a P-47, or perhaps line up the Luftwaffe cross on the wings of a Ju-88. All done with glue-smeared and paint-stained fingertips. Today, plastic models have given way to Xboxes and PlayStations.
I’ve collected models since childhood. They spent decades stored in cardboard boxes, following me from move to move. Once we settled back in Florida, I finally unpacked them and carefully shelved the kits above my father’s old worktable, where he had once built museum-quality ship models that were auctioned at Sotheby’s. My airplanes were never gallery-worthy, but they were still a pleasant reminder of my youth.
Years ago, when I began working for Air & Space as an editor, I found those old plastic models served me in another way. Spend hours of frustration painting cockpit details or studying the various struts of a Rube Goldberg F4F Wildcat landing gear trying to get it to a) not collapse, and b) not make the model tilt drunkenly to one side, and you find you can start to recognize aircraft simply by a propeller spinner, a gear door, or a wing — a skill that became valuable when editing photo captions, for instance. A chin turret on a B-17? It’s obviously a “G” model. A two-door nose gear on an F-16? Why, that’s the prototype YF-16 and not a production “A” model.
It warmed my heart when my then-nine-year-old son Ian caught the bug and started building kits from my dusty collection. First an F4U Corsair, then the inevitable P-51. And, without prompting, the day came when he wanted help hanging the planes from his bedroom ceiling — something I, and most of my friends, had done 30-odd years earlier, but few kids do today. Pretty soon a de Havilland Mosquito had joined the formation behind a Martin B-26, while a North American T-28, Republic P-47D, and Lockheed P-38J flew a combat air patrol over his bunk bed. Now age 11, his skills have improved, and he’s currently working on a Douglas SBD Dauntless — a kit I also built when I was his age — that features a retractable landing gear, dive flaps, and a droppable bomb.
The English company Airfix began producing plastic kits in 1947, but it was its 1953 Supermarine Spitfire that is perhaps best known, and beloved, by aircraft modelers. Check out this excerpt from the first episode of the BBC series James May’s Toy Stories, in which the host enlists a crew of kids to build a full-scale Spitfire model, molded in the form of the Airfix kit:
American companies like Lindberg, Revell, and Monogram were staples of my own childhood air force, later to be joined by the excellent kits of Japanese companies like Hasegawa and Tamiya. The earliest plastic kits were rudimentary, with sometimes questionable proportions and ridiculous steam locomotive-appropriate rivets festooning fuselages and wings. But they were only a few bucks, well within a typical suburban allowance. Todays airplane modelers are typically my age, and the high-end kits are bought with twenties. Inside, they’re nearly perfect technical representations, with recessed panel lines and laser-etched metal accessories for fine details, like the thin metal frame of a Head Up Display. Some, especially large-scale warbirds, like the latest 1/32 scale jets, can run hundreds of dollars.
As of tonight, the Dauntless is painted, and has done some practice bombing runs in the living room. Soon, it’ll take its place hanging in formation, rolling in on an imaginary Japanese destroyer sailing the carpet below.