Posted: Mar 05, 2011 10:04 am
Onyx8 wrote:
In the video quite a deal is made when the ribbons fluttering from the mast start being blown to the rear of the craft,
You mean this at about 3:00 ?
[youtube]http://www.youtube.com/watch?v=EEuAqq8FINw[/youtube]
Onyx8 wrote:it also would seem that it would mean that the wind is now acting to slow the craft down.
The apparent wind at the chassis is creating drag that acts to slow the craft. The apparent wind at the rotating airfoils is creating lift that acts to accelerate the craft.
Onyx8 wrote:
Or has the pitch on the propellor changed to now provide forward force to the cart even though the wind is now from the front?
No, on this early prototype the blade pitch was fixed. You don't need to change the pitch, to accelerate past windspeed. Just like you don't need to change the sail setting on an ice boat, to accelerate past downwind VMG = windspeed on a downwind tack.
Onyx8 wrote:
Variable pitch propellors are non-trivial things, you notice if you happen to build one.
They later implemented variable pitch to optimize acceleration. But it works without it, just very slowly at the start as you see in the video.