Merged DDWFTTW in a “Real” Wind

[CORed]

Let's knock this "retreating prop" argument over. All points of the prop are symmetrical about the hub. All points on the prop, move the same distance forwards as the hub. There is at no time any motion other than that.
Think of the prop as a solid disk and it becomes obvious that must be the case.

[qimg]http://www.internationalskeptics.com/forums/attachment.php?attachmentid=22072&stc=1&d=1304642842[/qimg]

Once again, by ignoring the angle of attack, and thinking of the propeller as a solid disk, even though it isn't one, humber "proves" that propellers don't work. The Wright brothers, and all those planes we were led to believe flew in WWII, clearly fraudulent. That wind you think you feel when you turn on a fan, all in your imagination. Brilliant!

 

[windgrins]

Yep, Llyracist is correct!

I suspect you could get a very small amount of thrust at high angles. But it depends on whether that particular airfoil becomes stalled before reaching that angle. If you look at the very broad rounded inlets for Hiller's hovering platform you can get the idea of a foil that is capable of doing that. The fairings we used for our pylons were only designed to reduce drag, so I suppose it's likely that they will stall before reaching such an angle to produce any forward thrust. Perhaps I'll check the polars. If nothing else it will give humber something to make fun of without having a clue what he's talking about.



The keel on your sailboat only has to provide a reasonable lift/drag ratio. It certainly doesn't have to be able to produce a lift vector whose "forward" component exceeds the drag vector's "aft" component. That's a sort of arbitrary requirement, but one that's probably not often achieved with any typical airfoil.

Yep, As stated in my new quote. Llyricist is right. I stand corrected. There's no help at all from the pylons for Humber.

WindGrins

 

[humber]

I suspect you could get a very small amount of thrust at high angles. But it depends on whether that particular airfoil becomes stalled before reaching that angle. If you look at the very broad rounded inlets for Hiller's hovering platform you can get the idea of a foil that is capable of doing that. The fairings we used for our pylons were only designed to reduce drag, so I suppose it's likely that they will stall before reaching such an angle to produce any forward thrust. Perhaps I'll check the polars. If nothing else it will give humber something to make fun of without having a clue what he's talking about.



The keel on your sailboat only has to provide a reasonable lift/drag ratio. It certainly doesn't have to be able to produce a lift vector whose "forward" component exceeds the drag vector's "aft" component. That's a sort of arbitrary requirement, but one that's probably not often achieved with any typical airfoil.

Just carry on, eh? That won't work away from the forum, and your lack of cogent response, and obvious deception, will be bought to NALSA's attention.
Simple tricks, where you use Dr Hepperle's programme to "design" a prop, apply to the engine-driven case, which is of course the basis of the progamme and all supporting theory.

But even then, you managed to show that your submission calculation will fail your own claim. That too, will be brought to NALSA's attention.

 

[humber]

Yep, As stated in my new quote. Llyricist is right. I stand corrected. There's no help at all from the pylons for Humber.

WindGrins

Spork should hope there is, and a chorus of approval from Carteers carries no more weight, than one opinion.

 

[humber]

Once again, by ignoring the angle of attack, and thinking of the propeller as a solid disk, even though it isn't one, humber "proves" that propellers don't work.

All points within the solid disk move forwards with the hub, at the same speed as the hub. Carving that into another shape, be it a cone or a prop, does not change that, and Dr Hepperle, screws your claim too.
And what has the Wright Brothers' science, go to do with the cart? Always something other than the cart, because it would be a bad idea, so there are no references in any text book to support it.

 

[69dodge]

Here is the data for the nominal prop design.

Thanks.

Now I think I need to learn more about propellers to make sense of it.

But I do see airspeed, RPM, thrust, and torque, which is what I'm mainly interested in. And the figures for various advance ratios let me calculate thrust and torque for different airspeeds and RPMs?

What about the wheel diameter and gear ratio of the Blackbird? How far does the BB move forward for every revolution of the propeller?

r(ft) chord(ft) incidence(deg) yle(ft) yte(ft)
0.57500 0.18983 80.12490 -0.04746 0.14237
...
7.92500 0.15414 20.56549 -0.03853 0.11560

This describes the shape of the propeller, correct?

 

[spork]

Now I think I need to learn more about propellers to make sense of it.

No problem. I'll be happy to answer questions.

the figures for various advance ratios let me calculate thrust and torque for different airspeeds and RPMs?

Yes. An advance ratio of zero would nominally put you in the static thrust condition. For our cart this would correspond to moving downwind at wind speed. From the definitions at the bottom you can work out the torque and thrust for any given RPM and airspeed.

What about the wheel diameter and gear ratio of the Blackbird? How far does the BB move forward for every revolution of the propeller?

I suspect JB has those numbers closer at hand than I do. If he doesn't post them I'll look for them.

This describes the shape of the propeller, correct?

Yes, r is the radius to a given point of the prop, measured from the prop-shaft. Chord is obviously the chord of the prop at that radius, and incidence is the angle the chord line at that radius would make with a horizontal surface if the prop were sitting on that horizontal surface (prop shaft being vertical).

I think Yte an Yle are the distances from the horizontal surface to the leading and trailing edges at the given radius. But that info is redundant, so I ignored it.

 

[ThinAirDesigns]

What about the wheel diameter and gear ratio of the Blackbird? How far does the BB move forward for every revolution of the propeller?

Wheel diameter = 27"
Drive axle sprocket 23t
Prop shaft sprocket 60t

JB

 

[humber]

No problem. I'll be happy to answer questions.
Yes. An advance ratio of zero would nominally put you in the static thrust condition. For our cart this would correspond to moving downwind at wind speed. From the definitions at the bottom you can work out the torque and thrust for any given RPM and airspeed.
I suspect JB has those numbers closer at hand than I do. If he doesn't post them I'll look for them.
This describes the shape of the propeller, correct?
Yes, r is the radius to a given point of the prop, measured from the prop-shaft. Chord is obviously the chord of the prop at that radius, and incidence is the angle the chord line at that radius would make with a horizontal surface if the prop were sitting on that horizontal surface (prop shaft being vertical).
I think Yte an Yle are the distances from the horizontal surface to the leading and trailing edges at the given radius. But that info is redundant, so I ignored it.

For a prop with a 2.8HP motor and running at 120rpm. Where is your data for the cart from the starting state? And where does that power come from above windspeed, when there is no tailwind, but a headwind?

And how do you counter Dr Hepperle's contradiction to the screwing prop claim, and specific mention of that the HIS programme is not valid for high states of disk loading such as in the static case? I have posts where I brought that to your attention ( independently of the programme), well before the trial. No reply will not look good when presented to NALSA.

 

[humber]

Wheel diameter = 27"
Drive axle sprocket 23t
Prop shaft sprocket 60t

JB

That's 85rpm at 18mph, not 120rpm.

And 18mph is not a random figure, but the speed of the cart above WS, when the record 28mph was claimed. Thanks for the data.

 

[Subduction Zone]

humber, even when the cart is going above the speed of the wind the wind is still blowing. You seem to think that the cart is even more powerful than anyone else believes it is.

 

[Llyricist]

That's 85rpm at 18mph, not 120rpm.

And 18mph is not a random figure, but the speed of the cart above WS, when the record 28mph was claimed. Thanks for the data.

And at 28 mph the rpm is 133

 

[humber]

Here is the data for the nominal prop design.
If need be I can look up the polars for the symmetrical airfoils we used on the pylons. I'm pretty sure they will produce a net drag in their longitudinal configuration at any reasonable angle to the wind (say up to humber's magical 40 degrees?).

Can you produce that, please?

According to JB;
Wheel diameter = 27"
Drive axle sprocket 23t
Prop shaft sprocket 60t

That's 85rpm at 18mph, not 120rpm, so the at the record speed of 28mph, that would be 132rpm. Is that correct?

And the weight of the cart. It is given as 650lb, but you mentioned a while ago that it was 450lb.
Do you have the precise weight of the cart (that known to NALSA) and the weight you allowed for the pilot?

 

[humber]

And at 28 mph the rpm is 133

Yes I know, so the figures do not represent the cart at record speed. I suppose the numbers will have to be reworked to reflect the claim. Does Javaprop accept negative values for the airspeed?

 

[ThinAirDesigns]

And the weight of the cart. It is given as 650lb, but you mentioned a while ago that it was 450lb.

450 - empty
650 - with pilot

JB

 

[Llyricist]

I just ran the numbers through my cartcalc spread sheet + Macro that utilizes the generic prop formula for thrust.

I get equilibrium power for 28 mph in a 10 mph wind of 3.58 HP at the prop shaft, torque of 153 ft lbs, rpm of 133.63 and thrust of 66.43 lb.

Not too far off, but some of the parameters are still guesses.

I'm using a crr of .0055, which is what wiki says for BMX tires. A Cd of .24 and area of 5 sq meters for drag. 92% efficiency for the drive train. And 89% efficiency for the prop while the formula says 92% is max theoretical at that speed and power.

 

[ThinAirDesigns]

I get equilibrium power for 28 mph in a 10 mph wind of 3.58 HP at the prop shaft, torque of 153 ft lbs, rpm of 133.63 and thrust of 66.43 lb.

What do you get for 56mph in a 16mph wind?

JB

 

[humber]

450 - empty
650 - with pilot

JB

And they are the numbers known and checked by NALSA?

What are the prop figures for 132rpm, please?

 

[CORed]

All points within the solid disk move forwards with the hub, at the same speed as the hub. Carving that into another shape, be it a cone or a prop, does not change that, and Dr Hepperle, screws your claim too.
And what has the Wright Brothers' science, go to do with the cart? Always something other than the cart, because it would be a bad idea, so there are no references in any text book to support it.

Well, it involves relative motion, which you have repeatedly demonstrated that you don't understand.

 

[humber]

I just ran the numbers through my cartcalc spread sheet + Macro that utilizes the generic prop formula for thrust.

I get equilibrium power for 28 mph in a 10 mph wind of 3.58 HP at the prop shaft, torque of 153 ft lbs, rpm of 133.63 and thrust of 66.43 lb.

Not too far off, but some of the parameters are still guesses.

I'm using a crr of .0055, which is what wiki says for BMX tires. A Cd of .24 and area of 5 sq meters for drag. 92% efficiency for the drive train. And 89% efficiency for the prop while the formula says 92% is max theoretical at that speed and power.

Does Javaprop accept negative values for the airspeed? That must be the case when above WS.