Yup - that's because it makes sense to use the average. As many have noted, there's simply no basis for using RMS when it comes to wind direction.
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Merged DDWFTTW in a “Real” Wind
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Yup - that's because it makes sense to use the average. As many have noted, there's simply no basis for using RMS when it comes to wind direction.
It is the standard procedure. NIST for example. Bluff denial won't work away from the forum.
You have direct contradiction from many other sporting and sailing bodies who do use RMS. You will need to explain that away.
A new experience for you Spork. Someone is checking your work.
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What rules are we talking about?
It does not matter what the rules say. Their validity is are being questioned. You would need external support against the resources that say they are not valid.
NALSA established a very carefully considered list of rules one must follow to make an attempt for this record category. I'm pretty sure you can find them on their site at NALSA.org
The rules NALSA wrote for the record, those, and the official reports, can be found here:
http://www.nalsa.org/DownWind.html
Yes, using a rigid mechanical analogy with no slip is one way to understand the theoretical limit.
In terms of an actual fluid propeller that is geared to the wheels, the theoretical limit for groundspeed is where the propeller creates zero axial force.
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That's for wind SPEED, because there is a quadratic relationship between wind speed and drag force.
Name them, and where they ever use RMS for wind direction.
Do those two give the same answer? Or is the first just an approximation?
I guess I'm asking, if the propeller blades are twisted the same amount in both cases, does the propeller provide zero thrust in air at the same speed that it would advance along my rigid cylinder?
Forgive my ignorance about rms and its relevance in this debate:
The humber angle, if I get it, is that all variations from ddw add to the available power, and that the ones to the right don't cancel out the ones to the left, as an averaging might tend to do?
Some ways back, I thought I heard mentioned that the cart actually does better ddw than with the variations. Is that correct?
Has the cart been experimented in various non ddw conditions? Would it go faster at 40 degrees off, for instance? Or is it actually designed to maximise at ddw?
Lastly, wouldn't the constant direction of the tread mill answer these questions?
Have they, at least for non-humbers? I realize their are a few (maybe 2) objecting to the TM's equivilance.
I'm also confused about the speed of ice sail crafts. The cart makes use of tire traction and friction; the ice carts do the opposite. Have ice carts never managed ddwfttw? What about with mildly deviant wind direction?
These are primitive questions, but there's no way I have time to slog through this entire thread, much less the debates on other forums. I'd sure like to understand more better.
The humber angle, if I get it, is that all variations from ddw add to the available power, and that the ones to the right don't cancel out the ones to the left, as an averaging might tend to do?
Some ways back, I thought I heard mentioned that the cart actually does better ddw than with the variations. Is that correct?
Has the cart been experimented in various non ddw conditions? Would it go faster at 40 degrees off, for instance? Or is it actually designed to maximise at ddw?
Lastly, wouldn't the constant direction of the tread mill answer these questions?
Have they, at least for non-humbers? I realize their are a few (maybe 2) objecting to the TM's equivilance.
I'm also confused about the speed of ice sail crafts. The cart makes use of tire traction and friction; the ice carts do the opposite. Have ice carts never managed ddwfttw? What about with mildly deviant wind direction?
These are primitive questions, but there's no way I have time to slog through this entire thread, much less the debates on other forums. I'd sure like to understand more better.
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Not in general, because for your propeller-in-cylinder-analogy only the blade tip matters, which doesn't have to be representative for the rest of the blade. Usually a screw that goes trough a massive block is used to explain propeller pitch.
About this RMS business: If the point of the rule is to rule out the mode of operation of a regular land yacht, I guess the important question is, how does the thrust of a regular land yacht depend on the difference between its direction of travel and the direction of the wind? Is the thrust linear or quadratic in that difference?
In any case, the 10 degree limit is somewhat arbitrary anyway, no? So, where does that leave us?
In any case, the 10 degree limit is somewhat arbitrary anyway, no? So, where does that leave us?
I see. Sort of.
Are propeller blades generally shaped so that they could be screwed into a block with deep threads without getting stuck? Or is there some reason to vary the twist along the length of the blades in a different way than that?
To first order the twist is designed to give "true pitch". This would allow it to thread its way through a block of jello. But in reality you want to reduce the angle of attack toward the tips to give you the optimal load profile (for maximum efficiency). You can see the same thing on a glider wing for example. You add "washout" to the tips to reduce the wing loading there. The object is to get an elliptical load profile.
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RMS is only a red herring that humber and Harold seem to care about.
I don't have the data, but I do believe they did some tests that showed the cart does worse at an angle.
The treadmill only shows that the cart can go faster than the wind directly downwind. It does not show how much faster it can go. The carts can get nowhere near their maximum speed on a treadmill, they demonstrate that seemingly impossible transition from below the speed of the wind to above the speed of the wind.
Lastly, on a velocity made good course, or an average course that is directly downwind, an iceboat can easily get over three times the speed of the wind directly downwind. But they do that by jibing back and forth with the wind. If you had two iceboats working together with a fishing line between them you could have an object at the midpoint that went directly downwind faster than the wind.
The twist of the propeller means that the prop has variable pitch , because og the increasing velocity away from the root.
A screw has a constant pitch, so won't get stuck, but prop would. Saying the prop can move through jelly, is saying that a screw can turn in air.
As for the wing and gliders, it's also a good idea limit the force applied to the end of a lever connected to a lightweight airframe.
A) No it isn't
B) RMS is not dependent upon a quadratic relationship of the variable.
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humber, the pitch of a screw seems to be constant since you only see a very short section of a blade. In other words, humber wrong, try again.
...and I need not point out how astonishingly wrong he is on props.
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humber? Wrong about anything to do with aerodynamics? I'm shocked
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