Its a lot like the Heli but I see one major difference. The air can't be deflected into the ground so I would think the normal force increases (car pushes on the earth more) when the prop runs-up. It could be verified by placing the car on a bathroom scale. I would also think the reason the car creeps forward a bit is because the deflector bent under the force of the prop blast lending a very slight horizontal component to the deflected thrust (sorta F cos89.5). If that joint is stiffened up the car shouldn't want to creep anymore. Neat vid!