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
DDW Faster Than The Wind
- Thread starter Maine Sail
- Start date
way to go ,congratulations!!!! Facts always trump ideals in the real world ideals have to conform to the facts.
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 speed curve is going to be bell shaped and depending upon the top speed the slope will be somewhat steep and the peak will be sharp or if they are more conservative the slope will be flatter and the peak will more resemble a plateau. Without the secondary drive from wheels to prop and with the ability to feather the prop the vehicle would coast for a considerable distance. Much of that inertia is converted to speed by the prop.
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.
I not avoiding anyone's questions and I'll get to yours.
Oh, and no you don't know how it works -- you demonstrated that in your next post.
Thanks
JB
See:
http://forums.sbo.sailboatowners.com/showpost.php?p=738380&postcount=58
You are correct that drag and other losses increase witih speed -- the energy comes from the wind to overcome these losses.
Yes it does -- that's what brakes do.
Depending on the wind strength, it can take near a mile for it to get up to speed. We have to have it very high geared to go fast and we aren't allowed by NALSA rules to have any gear shifting capabilities -- thus we have to start out in high gear. Once we get up to top speed (often 50mph and above) you eat up a dry lakebed very fast.
JB
Amazing!!!
While I get it, I still have trouble believing it.
I guess it is no more "insane" than being able to sail into the wind.
While I get it, I still have trouble believing it.
I guess it is no more "insane" than being able to sail into the wind.
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.
One of our primary and close by testing runways was only 3/4 of a mile long and without the variable pitch system the low speed acceleration was just to lazy to get above windspeed in that length.
The increase in speed between the Ivanpah tests (~2.5x) and El Mirage (~3.5x) was due to a stronger transmission and aerodynamic reduction efforts (fairings, etc.)
You can see the difference in configuration and acceleration when comparing these two videos:
http://www.youtube.com/watch?v=EEuAqq8FINw (no VP, no fairings)
http://www.youtube.com/watch?v=5CcgmpBGSCI (VP and fairings)
JB
Saw this link posted on the trailer sailor forum..
http://karmatics.com/dwfttw
If you raced the blackbird with the Nalsa boats, maybe it would be about class 5 (they would probably total up the area of your prop blades). In a traditional upwind/downwind race, something like these http://sports.groups.yahoo.com/group/wingboats/ would probably be considerably faster on the race course - but way slower directly downwind (if the effects of momentum are removed).
http://karmatics.com/dwfttw
If you raced the blackbird with the Nalsa boats, maybe it would be about class 5 (they would probably total up the area of your prop blades). In a traditional upwind/downwind race, something like these http://sports.groups.yahoo.com/group/wingboats/ would probably be considerably faster on the race course - but way slower directly downwind (if the effects of momentum are removed).
Sailing applications
The sled has a 1:1 (no slipage) connection to the ground through the wheels. I'm thinking that while that may not be compleatly necessary it is VERY important to extracting the energy while going DDW.
So since my water prop slips I'm thinking that this is going to be rather difficult to produce a working modle for sailboats.
Perhaps we could do it by sailing "dead down current"????
The sled has a 1:1 (no slipage) connection to the ground through the wheels. I'm thinking that while that may not be compleatly necessary it is VERY important to extracting the energy while going DDW.
So since my water prop slips I'm thinking that this is going to be rather difficult to produce a working modle for sailboats.
Perhaps we could do it by sailing "dead down current"????
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.
If there is zero true wind, the calcs will show that the vehicle will not move or simply roll to a stop of pushed and released.
The energy input *IS* this true tailwind.
JB
It's all a great theory, but there is no "derailleur style transmission" on the vehicle Ross.
As I have said *repeatedly*, the ratio is fixed between the prop shaft and the wheel shaft and that any shifting capabilities was and is against NALSA rules (www.nalsa.org). Their inspection of the vehicle before each run was to ensure that this and many other rules were met.
Here is a photo taken by the Editor of Sail Magazine (from his above linked article) showing the gear cluster and NO derailleur. By disconnecting the chain and adding/subtracting links, one could change gears by hand between runs if one chose to, but not during a run in any way.
http://kimballlivingston.com/wp-content/uploads/2010/08/machining.jpg
JB
Curious, JB, Would having closing spoilers in the vertical support help with acceleration from a stop? Hinge both port and stbd vertical surfaces of the pylon at max chord and have them open at the trailing edge for start and close at around 0 relative?? Like a BIG joker valve
Then by trial and error and some calculation optimum gear ratios and propeller pitch are found. I salute you for an ingenious design. Once the vehicle has passed the wind and is facing a head wind of its own making the benefit of the tail wind is reduced dynamic drag on that run. Speed over the ground will usually be different than air speed.
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.
Here are the NALSA rules that we were bound by for ratification:
http://www.nalsa.org./BlackBirdDDWSR/NALSA%20REGULATIONS%20FOR%20SPEED%20RECORD%20ATTEMPTS%20%20Rev%203.pdf
I'll summarize the more important rules:
A: The wind can switch no more than 10 degrees off of DDW course during a run or the run is invalidated. (for our record run, we managed a nice stable run with less than 5 degrees of wind switching and yes, we had to throw a lot of runs out because as we alll know, wind moves around).
B: No stored energy -- the vehicle must be *incapable* of using said stored energy for acceleration
C: The timed portion of the course is 10 seconds, and during that 10 seconds the vehicle must be accelerating. In other words, the vehicle must exit the course faster than it entered the course.
D: The 10 second average of the speed through the course much be higher than an peak gust measured during the run.
Notes:
The combination of "B" and "C" fulfills the "steady state" requirements of the record. If no stored energy can be released for acceleration (rule A) and still the vehicle accelerates (rule B), then that acceleration came only from the power of the wind. And clearly since the vehicle can accelerate to a faster speed from only wind power it can obviously maintain the entry speed from only wind power (the definition of steady state).
Rule "D" ensures that gusts are not being used to power the vehicle while measuring against the lulls. In other words, we not only had to beat the wind that was powering us to be ratified, we had beat the fastest gust recorded during the run (we did this with ease).
JB
For those with sailboats
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.
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.
Proof I'm not a genus
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.
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.
Bill, you've nailed it 100%.
People say "it has absolutely nothing to do with sailing", but they are dead wrong -- it's *exactly* like sailing once you wrap your head around it.
Adjusting the gearing between the wheels and the prop is identical to a change in 'boat' heading and adjusting the pitch is identical to 'setting and trimming the sail'.
JB
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.
On a boat, the keel provides this contraint and on this vehicle it is the gearing that provides the constraining force to keep the sail on the reach.
JB