How to infiniglide

[numerobis]

We've all seen those crazy infinigliders that reach solar escape velocity below 10 km on Kerbin -- but that's like building a nuclear bomb. I'd like to understand infiniglide well enough to harness its power in a controlled manner, like a nuclear power plant. In other words, build a spacecraft with a lab module; take off from Kerbin; use rockets to get me to Eve; land on Eve; then take off again; return to Kerbin; land.

What I've worked out so far is why you get forward thrust from lifting surfaces:

1. The lift of a control surface is a vector perpendicular to the surface velocity. If you're climbing, you get parasitic drag. If you're falling, you get parasitic thrust.
   
2. When you use a control surface, with respect to calculating the lift vector for that control surface, you're bending the velocity vector rather than bending the control surface.
   
3. Bend it enough, and the velocity vector will look like you're falling, so you get parasitic thrust, even though actually you're climbing.
   

So, an example. Say you're flying level (i.e. prograde is tangent to the surface) at an angle of attack of +5 degrees. KSP lift is perpendicular to the prograde direction, so the lift vector is straight up. Its magnitude is related to sin(angle of attack), but the direction isn't.

Now hit 'q' to roll counterclockwise. Fairly quickly your ailerons will tilt by 20 degrees. Visually, your left aileron tilts up so that it's now at an angle of attack of -15 degrees, whereas your right aileron tips down to be at +25 degrees. If that's what happened internally, lift would still be straight up, and there would be no infiniglide. But that's not how KSP works: by bending the velocity vector, it bends the direction of lift.

The left aileron tilts prograde down 20 degrees, and computes its lift. The lift vector is 20 degrees off vertical towards the back, so we get parasitic drag of sin(20 degrees). The magnitude takes into account a 15 degree AoA.

The right aileron tilts prograde up 20 degrees, and computes its lift. The lift vector is 20 degrees off vertical towards the front, so we get parasitic drag of sin(-20 degrees), or in other words, we get thrust. The magnitude takes into account a 25 degree AoA.

The parasitic components of the two lift direction vectors are the same size, but sin(25) is bigger than sin(15): the right aileron gets more lift force overall, which means we get more thrust than drag. Infiniglide! And a yaw moment.

OK, so that's the theory of it all -- now, I need help putting it in practice. Two main issues: how to control my direction when infinigliding; and how to turn off that fake thrust and manage to land. Any ideas from the peanut gallery?

Edited January 17, 2014 by numerobis