[gurps] vehicle challenge

[Anthony Jackson]

Onno Meyer wrote:

> Wrong is such a harsh word. Simplified is more like it. 

Wrong is the correct word. VE2 has two major problems with aircraft 
performance:
1) It totally ignores induced drag, which is very important at low 
speeds, since it varies as 1/v^2.
2) For propellers, thrust at any given power actually varies 
substantially with speed (this is less true with jets).

Equivalent errors with ground vehicles are:
1) realistic power requirements are on the order of W*V + A*V^3, not W*V^2
2) acceleration is not a constant; it drops with velocity.