I will leave y'all with one more thing this evening: a great article by Kimball Livingston -- an editor at Sail Magazine:
http://kimballlivingston.com/?p=3971
JB
http://kimballlivingston.com/?p=3971
JB
Ross, last night I started going through the thread from front to rear and answering questions that were asked -- no need to get all snippy as I can't answer all questions at once.Thanks to all of the links and the lack of answers to questions concerning distance of a sustained speed I know how it works.
See:The blades change pitch to decrease drag and convert rotational energy to drive the wheels.... making it go faster than the wind.
You are correct that drag and other losses increase witih speed -- the energy comes from the wind to overcome these losses.It can't go indefinately. Drag (parasitic and induced) will increase as its speed increases. Energy must come from somewhere to overcome this drag.
Yes it does -- that's what brakes do.Notice it slows down at end of video.
There's no difference in the ultimate top speed based on the variable pitch -- the prop is optmized for high end and that's as good as it can do. The variable pitch was added so we could accelerate faster and in a shorter space.the fixed blade was "only" able to acheive ~2.5 times the true wind speed from what I could tell, the later variable pitch prop was able to hit a sustained 3.5 times true wind!
You've nailed it druid. If you do the energy calcs (happy to run through them if anyone wants to follow along) you easily see that the power available at the wheels is greater than is needed by the propeller *when there is a true tailwind*. Just as you say, the energy needed is reduced by 10mph through the air because of the wind while the energy available to the wheels isn't reduced by the same 10mph.... , in zero wind, this arrangement would slow down and stop due to under 100% efficiency. BUT, we have the energy of the wind behind us. So, if the car is going, say, 30mph, it only needs the energy to go 20mph if there is 10 mph wind behind it.
It's all a great theory, but there is no "derailleur style transmission" on the vehicle Ross.The vehicle weighs 600 pounds. It is in that mass that energy is stored during acceleration by the wind and extracted for driving the variable pitch prop by means of the chain and derailleur style transmission.
The only limitation on distance is wind and terrain. (we have generally been terrain limited in our testing as we need a couple miles for top speed runup, timing and runout.Through what distance was this speed sustained? And is there limitation on distance?
Bill, you've nailed it 100%.I think this will help.
Forget the sled and all its mechanisms. Consider just the prop for right now. Think of a section of the prop as a boat so that all your old calculations for true and apparent wind remain the same except you substitute the speed of the prop (pick a diameter the prop has "twist" just like a mainsail and for the same reasons) for the speed of the boat.
So the prop is on a "broad reach" (RE the true wind) and all the vectors work out nicely.
Now insert the machine that just takes that power and turns it 90 degrees and applies it efficiently to the ground.
Ingenious, dare I say insanely ingenious.
Sometimes it takes genius to see the blindingly obvious.
Correct -- the sails of the vehicle are constrained to one long continuous broad reach. Absolutely no more complicated than that.I got it backward (typical) the wheels drive the prop.
But the concept is still the same the prop is on a broad reach no matter how "fast" the sled is going and so can pull the sled along.