A Guillow Jetfire, it was called – and at 69 cents, was about the only aeroplane I could afford at the time. I got it from a bin by the cash register at All Aircraft Parts. It was an attempt to cause my son’s childhood to resemble my own before he got too big to be influenced.

Peter Garrison

I MUST HAVE OWNED, flown and wrecked dozens of these things as a boy: there was a comfortable familiarity about the balsa wings that slip into the slot in the fuselage, the spring-steel nose weight, the profile of the helmeted pilot limned in seeping red on the canopy that breaks off every time I handle the aeroplane clumsily. Things haven’t changed much. You still slide the wing backward to dive and forward to crash.

Balsa models — I believe they cost 10 cents, or at most a quarter, in the early 1950s — taught me almost everything I know about aeronautics.

As I fooled with this new one, I realised how hard and tedious it can be to put into words the basic facts about flight that the model teaches.

                                    ‘the balsa gliders whispered it to me.’

The directions emphasised certain transient and exciting states. By moving the wing forward you could make the aeroplane loop. It finished its loop gracelessly, entering a too-steep climb with insufficient momentum, stalling and diving into the floor.

A less ambitious approach pleased me more. The first project was to find the “best” wing position—the one at which the aeroplane would perform a flat, slow, gentle glide, terminating in a smooth landing. If the wing was too far forward, the flight was scalloped, a series of slow swoops and stalls; if it was too far aft, the glide was steady but too steep and fast, and the aeroplane hit the ground chin-first. But there was an ideal position, almost all the way forward, that yielded a gentle, steady descent in a level attitude. When I was a kid flying these things, nobody ever told me that the best glide speed was relatively low; but the balsa gliders whispered it to me.

In these experiments, launch speed was important. If you tossed the aeroplane too vigorously for its trim setting, it entered a series of oscillations that wouldn’t damp out before it landed. It needed to be launched at as close to the trimmed speed and attitude as possible.

You noticed right away that the farther aft you put the wing, the more steadily the aeroplane maintained its pitch attitude. You might have inferred from this that the aeroplane got steadier as it got faster, but that would be wrong. What was misleading was the Ptolemaic view that the cockpit was the centre of the aeroplane’s universe; really it was the wing about which everything, including the pilot, revolved. (At least this was true in pitch; the wing was comparatively indifferent to yaw.)

When you moved the wing aft what you were really doing was moving the rest of the aeroplane forward. The steadiness you noticed when the wing was aft was that mysterious imp called “static longitudinal stability,” which, as pilots are always warned, decreases as the CG moves aft. If you put a paper clip on the trailing edge of the horizontal tail, you could easily see the consequence of too far aft a CG location. The transition from stability to instability was quite distinct, corresponding to a rearward adjustment of a mere eighth of an inch in the location of the paper clip.

To see a more dramatic demonstration of the meaning of longitudinal stability, you could remove the horizontal tail altogether. Taking away the vertical tail produced an expected result, but an interesting one to observe. The flight began normally; we are used to looking for anomalies in pitch behaviour, and there were none. But 10 feet or so along its trajectory the aeroplane began to yaw. The yaw being unopposed, a huge excursion quickly developed, the upwind wing rose, and the aeroplane departed in a spinlike manoeuvre whose ultimate outcome eluded me: the floor intervened.

The reason for that roll-off was the same as the reason why you can make the aeroplane turn by skewing the wing in the fuselage. The vertical tail aligns the fuselage with the direction of flight. The wing has some dihedral; consequently a section along the line of flight has a higher angle of attack on the leading wing than on the trailing one, and the aeroplane rolls toward the trailing wing.

To test the explanation, I put the wing in upside down and skewed it. Now, sure enough, the aeroplane rolled toward the leading wing. It also looked wonderfully like a MiG-15 as it flew away from me. Unskew the wing and there remained another consequence of inverting the dihedral. The lateral stability was diminished: the aeroplane was more prone to deviate from a straight track. But the effect was subtle; I had to make several flights to confirm it. And that tells you something else: that dihedral effect was comparatively weak.

Since inverting the wing didn’t seem to harm the flying qualities of the aeroplane, I wondered why I shouldn’t just leave the wing alone and invert the whole aeroplane. I tried it. The aeroplane plunged vertically into the floor. The missing element was the decalage: the difference in incidence between the wing and the horizontal tail. Upside down, the aeroplane was trimmed for an inverted dive. If you could change the effective incidence of the horizontal tail, say by taping little strips of business card to the trailing edges and bending them downward (with respect to the upright aeroplane), the aeroplane might fly reasonably well upside down.

One of the astonishing things about the configuration, in fact, was its robustness; it seemed to fly fairly well almost no matter what I did to it. The tail surfaces were swept back; turn them around, and you detect no change at all. If the wing had no dihedral, skewing it would make no difference. In fact, a skewed-wing airliner has been proposed, and a manned miniature of it test-flown. And of course the wing had no aerofoil section, nor even any camber. So much, it would seem, for all those textbook explanations about air going a longer distance over the top.

                                    ‘The missing element was the decalage’

The neatest thing about the balsa model was that it could be made to fly backwards. The only changes necessary were to remove the vertical tail entirely, and to remove the nose weight and put it, or some other weight such as a large paper clip, at the tip of the tail. The reversed aeroplane flew quite beautifully, being only slightly deficient in directional stability. This I corrected by cutting a shallow slot in the top of what used to be the nose and slipping the vertical tail into it.

If I inverted the wing of the backward-flying aeroplane, I found that it behaved just as it did while flying forward: it deviated gently from a straight path. It also responded similarly to fore-and-aft shifts of the fuselage along the wing: too far aft a CG location produced an early stall. But the backwards aeroplane stalled less sharply; rather than pitch down and dive for the floor, it dipped gently and parachuted downward while gathering speed. I suppose the reason for this behaviour was that it was the nose surface, and not the wing, that was actually stalling. Inverting the backwards aeroplane produced the predictable result: a dive into the floor. Again, a higher incidence on the fore wing than on the rear was needed to trim the aeroplane for level flight.

I find it at once surprising and poignant that the remarkably simple, sturdy combination of elements that we know as an aeroplane should have eluded human efforts for so long. It seems as though virtually any combination of the four pieces in the Guillow Jetfire’s plastic package produces a flying machine. If I could have appeared in the court of the Emperor of China with this thing a millennium or two ago, I would have been reckoned a great sorcerer.

As it was, I had a hard time impressing my six-year-old with it — once I stopped playing with it long enough to give it to him.

The AD-1 skew wing airliner study with its wing at a moderate angle.

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