I don't understand how this car works.

@georgeob1,

Quote:

The only forces acting on the vehicle are
(1) the wheel friction which will tend to slow the vehicke down;

Would you mind defining "wheel friction".

Is this the crr (rolling resistance) of the tire against the ground?
Is this the air friction on the rotating wheel?
(to be fair, I assume you've at least include both of the above)
Something more?

I'm sure you'll again consider the above "pedantic", but for Christ's sake you make a definitive and blanket statement : "The only forces acting on the vehicle are " and then just want us to accept that at TRUTH without allowing someone to question your definitions.

JB

0 Replies

@georgeob1,

I believe I stated my hypothetical (and illustratative) case clearly enough. Here it is again;

georgeob1 wrote:

Let's imagine our vehicle (with a fixed mechanical connection between propeller and wheels, and a non steerable fixed pitch propeller) is on level ground with a tail wind and travelling at exactly the speed of the wind. In that situation there is zero relative motion between the surrounding airstream and the vehicle. The only forces acting on the vehicle are
(1) the wheel friction which will tend to slow the vehicle down;
(2) The thrust of the rotating propeller which will push it forward
(3) The drag force on the propeller blades which creates a torsional moment tending to slow the propeller and the wheels down.

Thus the vehicle can accelerate to a speed greater than the wind speed (i.e. experience a relative wind from ahead) only if the thrust of the rotating propeller exceeds the combination of wheel friction and propeller blade drag.

It is conceivable that this may occur with a very light vehicle with very low wheel friction and a very efficient propeller with a very high lift/grag ratio for its propeller blades.

However if the vehicle goes any faster it will begin to experience bulk air drag which will quickly eliminate any net forward thrust.

How much faster than the wing speed (in percent) is it claimed this thing can go?

I don't think "wheel friction" is an obscure or ambiguous term. But to avoid further argument let's just agree I am referring to the work done, kinetic energy lost, and forces involved with with respect to mechanical frictional losses due to the rotating mechanical components of the wheels and propeller mechanism and the wheels & the ground.

I believe "thrust of the rotating propeller is clear enough as well. However, to be sure, I mean the forward propulsive force, parallel to the vehicle's velocity vector, generated by the lift on the rotating propellers.

"Drag force on the propeller blades" is used in the normal aerodynamic sense with respect to the rotating airfoils of the propeller.. it is the retarding force parallel to the plane of rotation (relative to the moving vehicle) of the propeller.

Now, will you please answer the question? By how much (what %) does the vehicle exceed the wind speed? What is the maximum steady speed the vehicle can maintain relative to the trailing wind?

2 Replies

Theoretical limit based on no drag, no slip (air is incompressible and inviscid (I think that's the right word?)) screw speed ratio (I think the TAD team calls it "advance ratio") of prop vs wheels:

http://a.imageshack.us/img696/3659/ddwfttw.png

The purple line is the windspeed minus the advance rate of the screw (prop), or vice versa. Its slope is (1-advanceRatio) and it crosses the ordinate at -Windspeed, so the equation of the line is

(Windspeed-Screwspeed) = (1-advanceRatio) * Wheelspeed - Windspeed

I did something screwy with the sign there, obviously, so it might be (Screwspeed-Windspeed).

and the theoretical (as in no drag, no slip) limit to the Wheelspeed of the cart is where the purple line hits the abscissa i.e. Windspeed / (1-advanceRatio). That is where the prop is cutting through the air at zero angle of attack so thrust is zero.

The advance ratio is the ratio of the rates of the prop-through-air and wheel-over-ground motions. The ratio is fixed by the gearing, prop pitch, prop diameter, and wheel diameter (did I forget anything?) . The rate prop-through-air motion is the prop moving through the air in a no slip environment e.g. at zero angle of attack. The wheel-over-ground motion is the wheels moving over the ground.

Am I missing anything?

1 Reply

@sirclicksalot,

Quote:

Theoretical limit based on no drag, no slip (air is incompressible and inviscid (I think that's the right word?)) screw speed ratio (I think the TAD team calls it "advance ratio") of prop vs wheels ...

I think the actual as-build (geometric) advance ratio may be closer to, or even greater than, one to account for slip.

Also, I didn't mean to imply the Blackbird advance ratio is 0.75 or any fixed value. The spreadsheet is meant as a idealization and/or characterization of what is going on by imagining what happens with no slip i.e. the prop-air interface is like soft butter yet drag free i.e. L/D = infinity.

0 Replies

@georgeob1,

Your question has been answered many, many times now, but I guess we'll do it again.

As it relates to the vehicle in the OP, we'd be silly to claim anything other than what it has done and been reported on this thread many times

NALSA collected data from various sensors showing speed well over 3x the speed of the wind (that would be 200+% in the format you requested).

Due to averaging and other rules (that we agree with), the NALSA record will likely be in the high 2xs rather than in the 3xs however.

In it's current configuration, the vehicle was limited by transmission strength (chain breakage, etc) at the wind strength it was optimized for. Could it achieve more? -- we believe so, but don't necessarily "claim" so.

On another note -- subsonic, there is no theoretical limitation to the multiple of wind speed this design can achieve.

As all this has been reported over and over and over, I hardly see how we've given you any new info, but whatever.

JB

2 Replies

@ThinAirDesigns,

Would you care to give a link to this claims of yours?????????

I am sure you would have such a link if true.

1 Reply

If there is any real money betting that happens here.... please please please don't leave me out.

(I would be happy to give 20:1 odds for any amount of money... and I will raise the odds to double whatever spork is offering Wink

)

0 Replies

@ThinAirDesigns,

ThinAirDesigns wrote:

On another note -- subsonic, there is no theoretical limitation to the multiple of wind speed this design can achieve.

JB

Perhaps so, but not with a fixed pitch propeller.

1 Reply

@ThinAirDesigns,

Quote:

On another note -- subsonic, there is no theoretical limitation to the multiple of wind speed this design can achieve.

How in the hell can any sane mind read that and not know this is complete nonsense?

Free energy to go over 600 mph is now being claims!

Six mph wind and 600 mph wind car!!!!

Yes anything over one wind speed is equally silly in fact but one hundred wind speed just underline the gross silliness of these people.

If NALSA does end up supporting the claim of two or three time wind speed I would love to take the blackbird apart milligram by milligram.

Yes, I know that is not going to happen and we will have a few years of one wind car after another not being able to reach more then 1x and hearing from the blackbird supporters how they just are not getting the cars right.

2 Replies

@georgeob1,

Me:

Quote:

On another note -- subsonic, there is no theoretical limitation to the multiple of wind speed this design can achieve.

georgeob1:

Quote:

Perhaps so, but not with a fixed pitch propeller.

Another false statement.

JB

0 Replies

@georgeob1,

Quote:

I don't think "wheel friction" is an obscure or ambiguous term. But to avoid further argument let's just agree I am referring to the work done, kinetic energy lost, and forces involved with with respect to mechanical frictional losses due to the rotating mechanical components of the wheels and propeller mechanism and the wheels & the ground.

Just as a note: It's pretty freakin' funny that you would think it normal and typical reference that all those losses that you list would be commonly included in the (itself unusual)term "wheel friction".

Losses in the "propeller mechanism" included in "wheel friction" ??? WTF sort of world do you live in where you think that I would automatically know you included propeller mechanism losses in "wheel friction"?

JB

0 Replies

@BillRM,

Quote:

Would you care to give a link to this claims of yours?????????

I am sure you would have such a link if true.

Bill, I'm truly unsure what you're asking for. A variety of claims have been made -- tell me which one you want a link to.

JB

1 Reply

@BillRM,

Me:

Quote:

On another note -- subsonic, there is no theoretical limitation to the multiple of wind speed this design can achieve.

BillRM

Quote:

Six mph wind and 600 mph wind car!!!!

You do know the meaning of the word "theoretical" don't you Bill? LOL

JB

2 Replies

@ThinAirDesigns,

ThinAirDesigns wrote:

You do know the meaning of the word "theoretical" don't you Bill? LOL

JB

Well you didn't define it other than subsonic. Clearly you are ignoring viscosity, Reynolds number effects, including turbulence, and even some basic Bernouli effects, including flow separation and stalling propeller blades.

What is the "theoretical" limit with a fixed pitch propeller blade?

2 Replies

@BillRM,

Quote:

If NALSA does end up supporting the claim of two or three time wind speed I would love to take the blackbird apart milligram by milligram.

You wouldn't love it enough to do it that's for sure. How do I know this? -- here's how ... you won't, in spite of the fact that I'm going to invite you to.

Just moments ago I received a copy of the comprehensive three page report from the El Mirage attending NALSA Observers to the full NALSA BOD. This report contains all relevent details and data of the test and recommends that the NALSA BOD ratify a record of 2.8x the speed of the wind.

Considering the particularly careful way that this feat was documented (way above NALSA requirements) and considering that we have data showing even faster runs but WE chose to submit this lower one for it's exceptional defensibility, there is no reason to believe that the BOD will not ratify and every reason to believe that they will. Remember, a large percentage of their BOD members have already seen the Blackbird in action at over 2x at the Ivanpah test.

(No, I won't release any NALSA document I've been CC'd on. The Observers Report will be public once the BOD ratifies the record and will appear on the NALSA website. You get it from them, not from me -- that way you know it's real)

So, with that in mind -- I'd like to personally invite you to show up at our shop and disassemble the Blackbird and stare at every component to your hearts content.

But you won't.

JB

1 Reply

@georgeob1,

Quote:

What is the "theoretical" limit with a fixed pitch propeller blade?

The same as with a variable pitch prop.

JB

0 Replies

@georgeob1,

Me:

Quote:

You do know the meaning of the word "theoretical" don't you Bill? LOL

Georgeob1:

Quote:

Well you didn't define it other than subsonic

I didn't attempt to define the word "theoretical" at all. It has a very clear and established definition already -- look it up.

JB

1 Reply

@ThinAirDesigns,

You are wrong on several points, including the limits with fixed and variable pitch propellers. An airfoil won't produce lift if it is stalled.

3 Replies

>>"Spork you poor baby as you know experts in physics one with Noble prizes are stating the same thing I had been IE this is a free energy device that can not work."

@BillRM: Not so fast monkey-boy. Both of your heros have backed away from thier claim that DDWFTTW is impossible. Kammen even claims that he never made such a claim. Fortunately I have quotes from an email showing he did originally agree with your point of view. But as I said, you're becoming a very rare specimen.

>>"Yes Spork I can see why you would wish to run away from that fact."

I'm the one that keeps bringing these idiots up! How am I running away from this prime entertainment!?

>>"If I am wrong and this craft work then some of the best minds on earth are also wrong".

It's tough to tell whether Kammen is mentally challenged in a broad way, but he sure as hell seems to be weak technically and in terms of academic honesty. The notion that Rhett Allain possesses one of the "best minds on earth" is even more laughable than most of the spewage you've offered so far. Unlike Kammen, Allain publishes a blog so we can see day-to-day just how poor an understanding he has for basic physics.

>>"Could be but I am still betting it is far more likely then not that this is a hoax."

Wrong. You're not betting. I offered a bet. You won't even respond. Hell, you don't even want to discuss the actual mechanism or mathematics of operation. You just want to stand in the middle of the road flapping your arms about and yelling "HOAX". That's why I'm offering you the bet that you choose too ignore. Fortunately, everyone else knows exactly how to interpret that.

>>"If you wish me to believed in something like the Blackbird you need to bring a mountain of proof that could not be fake in any way or in any manner."

If you understood the most basic math and physics all it should take is a half a sheet of very simple equations. The mountain of evidence:
- is already huge
- continues to grow
- Will NEVER be good enough for you.

>>"I would like some group that could not be involved in any possible hoax to build a similar craft and get similar results."

Think about what you're asking. There's no reason for anyone that understand the thing to go and build one - they already get it. If ANYONE BUT YOU builds it and it works, you'll claim it's a hoax. No one will do your homework for you. If you want to see one built by someone you trust, I assure you it'll have to be YOU.

So, did you want to take the bet? Perhaps you'd like to make a counter offer?

0 Replies

@ThinAirDesigns,

That Dr. Kammen had now seen the light and had released a public statement to that effect.

1 Reply

I don't understand how this car works.

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