In this video (http://www.youtube.com/watch?v=5CcgmpBGSCI&feature=related), the vehicle is pushed by a tail-wind until approximately 25-30mph, where we see the chase-truck with anenometer achieve a "head wind" due to its velocity rather than a tail wind.This happens at 1:30 into the video. The propeller acts as a sail that interfaces with a direct drive gear to turn the wheels.
One small correction (that doesn't change your point). The wind in that run was averaging about 18mph, not the 25-30mph that you state. For safety reasons, we never ran the Blackbird in winds above 20mph.
After this point, the vehicle IS TRAVELING INTO A NET HEADWIND, and accelerating into it. That is, by definition, moving upwind.
Your chosen definition of ‘moving upwind’ would be an uncommon one. In absence of the term “relative”, the essentially universal definition of 'upwind' and 'downwind' relates to the *true wind* -- or the wind over the ground. For all other applications the term "relative" is usually added.
Example 1: For obvious reasons, airplanes in proper flight *never* have a relative tailwind, but rather always have relative wind coming from the nose of the craft – they can’t fly otherwise. This does not preclude them from flying downwind and pilots refer to this regularly as in "we'll be making good time on this flight because we’ll be flying downwind", or "we'll get to the gate early because we'll have a tailwind with us all the way".
Example 2: If the wind is blowing to the south at 30mph and I get in my car and head directly south at 60mph, I certainly have a *relative* headwind, but few will buy your argument that I’m no longer going downwind and am now “by definition, moving upwind”. In common terms, having a relative headind doesn't mean I'm still not going downwind if I'm traveling in the direction of the true wind.
As such, the wheels are not driving the propeller. Drag from rolling friction and aerodynamic friction would bring it to a stop, with a headwind.
As it turns out, you are simply wrong on this point – unless one slams the brakes on very quickly (slowing the vehicle faster than the spinning propeller wants to slow down), the wheels *always* drive the propeller and the propeller never once even *tries* to drive the wheels forwards. Even if it wanted to at some point, there is a large ratchet installed on the prop shaft that precludes the prop from ever making that happen. You’ll need to work on your understanding and theory in this case.
I am a bit surprised that the propeller, when faced with resistance from a net headwind, did not cause the entire vehicle to pull a "wheelie." How much did you have to weight the nose to avoid that, or was that even a consideration?
Once again you’ve come to an incorrect conclusion. As all speeds (including above wind speed), the entire load on the pylon structure is to the front – levering the front wheel *down*, not up. The propeller is generating thrust to push the vehicle forwards and this thrust vector at the top of the pylon is pointed in the direction of travel.
JB
