Personally I liked the bi-plane version over the jet but let’s get to the question.
The main wing of the balsa wood glider (BWG) had two settings. You could slide the wings forward or back to achieve different flight patterns. One position (I don’t remember which) would make the BWG loop and the other position (if the gods were smiling that day) would make the glider fly level.
Why?
You didn’t change the pitch of the wings just their relative position on the fuselage. How does that affect the lift the wings provide?
It changes the relation of the center of lift, and the center of mass.
In the forward (looping) position, the lift occurs at a point ahead of the center of mass, causing the nose to rise. At the back position, the two points coincide, and the glider is balanced. At least, that’s my scientific wild-ass guess.
It changes the center of gravity of the glider so this changes the angle of attack of the wings. Think about it. Shift the wings forward, the glider becomes tail heavy and the glider will climb or loop. Shift them to the back and the glider becomes nose heavy and dives. Move the wings so that it is balanced perfectly and the plane ill fly just right (think of Goldilocks and the Three Bears). The same principle applies when designing a real airplane and even when loading passengers, fuel, and cargo.
I’d guess the “loop” postion was the front one. Moving the center of lift in front of the center of gravity makes for a tail-heavy plane.
When launching the glider, the steering impulse will attempt to lift the nose, at least until it hits vertical - then I suppose momentum carries it round.
Just waiting for the pilots to arrive and prove me wrong…
S. Norman
Post-preview: DAMN, you guys are quick. Yeah, what the others said.
If you move the wings foward shouldn’t the nose be heavy? After all, you shift the weight of the wings to the front so the back end gets lighter.
I was thinking some more about this and it seems that the wings provide the same ammount of lift (which was the idea that was bugging me) but the lift is applied differently in the different configurations.
Now I have to go out and find one of these so I can see what position does what.
The absolute position of the center of gravity on the airplane does not determine it’s natural pitch tendency. The position of the center of gravity relative to the center of lift determines the pitch tendency. Moving the wings forward will shift the center of gravity forward, but it will shift the center of lift forward by a greater degree. This is because the wings represent only some of the aircraft’s weight, but produce all of the aircraft’s lift. The relative movement of the center of gravity will be aft, causing the aircraft to pitch up.