ETNZ To Attempt Wind Powered Land Speed Word Record
- Thread starter Stingray~
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- #483
The point made about the perfect height of the outrigger being barely above the surface to maintain perfect balance but without the extra wheel's drag was cool too.
Not surprised. It is the same in any proa. Some of the speed increase also comes from the improved CLR/CE balance, where the steering wheel load is reduced due to less rounding up resistance.
Keeping it there for long enough periods of time for max speeds is the big challenge. On a straight track, you lose the ability to round/feather up into the wind to reduce heeling moment and maintain best VMG. Wing trimming needs to be precisely controllable and instantly responsive. Get it wrong and you really do come down with a bang, even on water. Don’t ask me how I know….
Ashby is pretty much the best around at understanding, anticipating and controlling foils, if anyone can do it, he can.
The_Alchemist
Super Anarchist
I rewatched a few of the interviews and speed runs of GreenBird. Richard Jenkins talked about how difficult it was to get everything tuned exactly right and get the exact wind/weather conditions.
As you mentioned, it is a matter of keeping things balanced long enough to gain enough speed. GreenBird was as light as possible at about 600 kg (steel only used in the bearings/wheels). Greenbird reach 120 miles/hr on numerous occasions while testing on a runway tarmacs before the runs on natural surfaces. NZ plans to add up to a ton of weight on the outrigger wheel to keep it down. I can't help but question the weight of the NZ racer. The weight doesn't affect the max speed, but it does affect the acceleration and how long the pilot has to keep everything in balance to reach that top speed. So if the NZ raver is 2 to 3 times heavier than GreenBird, the acceleration is 1/2 to 1/3 slower and the time to reach the finial speed will be 2 to 3 times longer. So the pilot has to hold it steady and in balance 2 to 3 times longer than Richard Jenkins did and they will have to travel at least 2 to 3 times the distance.
Here is a speed chart of the greenbird record:
Some note from a Wired article (https://www.wired.com/2008/08/wind-powered-ra/)
- 110 deg from the nose is the fastest point of sail. This is actually about the same for all sailboats, independent of speed.
- depending on the surface traction, we can achieve ratios of up to 5 times the true wind speed (on tarmac, 3-4 times on dirt/salt), meaning an apparent wind angle of around 12 deg to the nose. The angle of the wing is then at about 3-5 deg (to leeward) of the apparent wind (7-9 deg from the vehicle track).
ChairborneRanger
Member
I've heard elsewhere that while Greenbird, as a completed land yacht, was approx 600kg, It was actually running a lot more weight for the record and was capable of being loaded up as needed. I think I remember it being 1,800kg, but not sure. Has anyone else heard, seen, or read the same?
The counter to that argument is that weight gives inertia to keep speed up through the lulls and gives you more speed before you fly the ama regardless. The slower acceleration/deceleration (especially roll speed) buys you a little more time in terms of foil control as well.
Hopefully we shall soon find out….. if the weather behaves.
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The_Alchemist
Super Anarchist
I have not seen anything talking about using that much weight ballast. All of the reports that I read say he was very concerned about making it as light as possible. This article talks about the downward force transfer:
Greenbird only weighs 600kg but at high speeds it is transferring up to one tonne of side force into the ground
Record-breaking wind-powered car gives a glimpse of the future | Engineer Live
Just as the Formula 1 technologies of today filter down into the production cars of tomorrow, so Richard Jenkins, the designer of the wind-powered Greenbird, believes the technologies behind his record-breaking vehicle could herald a new era of environmentally-friendly transportation
www.engineerlive.com
It was a revolutionary change from his earlier WingJet design:
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1000kg side force x heeling arm (HA) has to be balanced by 600 kg x righting arm (RA).
Where: HA is the vertical distance from ground to wing CE, RA is the horizontal distance from leeward wheel base axis to the CG of the whole vehicle.
If HA was (say) 3 metres, the heeling moment is 3000 kgm. It needs to be balanced by (say) at least 600 kg x 5 metres RA.
The weight of the leeward pod and rig effectively produces no righting moment, it all has to come from the windward connective strut and ama pod. In static condition, the weight is shared proportionally between the two pods, but when the ama pod is flying, it static weight contribution is transferred to leeward, increasing wheel traction with no overall increase in weight.
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ChairborneRanger
Member
It must be BAU for the water to pool in that corner then, as the thicker water, must deposit more salt, and this has been repeating for hundreds of years, so maybe this pooling is nature's final stage before a big dry out.
- Thread starter
- #494
You’re suggesting the saltier the water the faster it will dry? Cool.
I hope the salt makes for a better surface too.
The_Alchemist
Super Anarchist
Salt water evaporates much slower than fresh water. The salt acts as a humectant and holds onto the water longer.
Also, water levels itself out and only collects in portions of the lake that are lower than the dry sections. The leveling of the water makes these dry lake beds so flat and desirable for these speed records. Wind is not what caused the water to collect in that portion of the lake.
The water is 70-80 mm deeper than it was in the first video, not a positive sign. The weather forecast has a 60% chance of another 0.1 inch of rain on Thursday/Friday. The highs are in the 60’sF with lows in the 40’sF (highs about 15C and lows in the 7-9C range).
It looks like the water will be in that section of the lake for a long time.
ChairborneRanger
Member
No, I was suggesting it must be normal for the water to pool in that corner, that area of the lake has much thicker salt than the rest of the lake, so it must frequently have more water sitting and drying there than other areas. Nothing to do with dry time.
shebeen
Super Anarchist
well it's september now. let's see.
ChairborneRanger
Member
Clouds gives his weather update on the "dry" lake.
The_Alchemist
Super Anarchist
Nice to get an update, but why doesn't Clouds just check the historical rain patterns in the area. The "special El Nino" did drop a massive amount of rain, but there is no need to wonder why it is still raining in June, July, August and September! It is the wettest season of the year!
Here is the information that is posted directly on the DLRA website (they race there every year and should know the patterns):
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Rainfall at Lake Gairdner
Historically Lake Gairdner recieves it's lowest rainfall in. March, followed by April, Feburary, and NovemberThe highest rainfall is typically during June, July August, and September.
In February and March there is historically less than 2 days of rainfall greater than 1mm with the average rainfall for these months being just 10mm.
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