Friction and thrust

[SteveJanesch]

I've been keeping up with "Propulsion that does not involve driving wheels" (and even contributed to derailing it), and have had this going through my head the last day or so:

Part 1: Friction
Assume the robot, battery, bumpers, and trailer tongue weight add up to 150 lb. With a coefficient of friction of 0.08 (on the high end of experimental data), the lateral force available for acceleration can be as high as 12 pounds. That's just the normal force (due to the total weight on the robot wheels) times the coefficient of friction, independent of wheel configuration.

Part 2: Thrust
(My apologies in advance for using non-standard terms for this, it's not really my field. Feel free to provide the correct syntax.)
I looked up equations for thrust (on wiki) of a driven fluid, which is the product of the mass flow and the velocity of the fluid. Using a value for air density of 0.075 lb/ft^3 and a flow rate of 60 ft^3/min or 1ft^3/s gives a mass flow of 0.075 lb(mass)/s. Forcing this through a nozzle at 100 ft/s, you'll get a thrust of 7.5 lb. Based on what teams did last year, this seems like it might be possible with a scavenged shop vac or leaf blower impeller.

Is that thrust calculation right, or even in the ball park? Could a jet-assist directed laterally really give a 60% or greater boost to the drive train?

- Steve