Merged DDWFTTW in a “Real” Wind

[Jack by the hedge]

But you think there is some magical way of getting more power.

Yeah. The magical power of the wind moving over the land.

Let's say the geared gizmo is driven by a sail. The power available to that sail is dependent upon the wind speed and sail area, but the gears have no influence upon that. It won't go any faster because you tried to "fool" it.

Nobody but you thinks anyone has claimed gears multiply power. I think we all appreciate they only trade torque for speed. The BB's power source is not a gearbox.

 

[Modified]

The headwind against the cart's body opposes the cart. That is accepted.
If a panel were fitted over the venturi, I would expect that to be a drag force too, so why does it suddenly drive the cart, because it hits the rotor instead? Voodoo.

Lets use your same argument for an iceboat outracing the wind: The headwind against an iceboat's opposes the boat. That is accepted. If a panel were set horizontal on the boat, I would expect that to be a drag force too, so why does it suddenly drive the boat, because it hits the sail instead? Voodoo.

 

[humber]

Ah. So, the cart only behaves in the way you describe when it is broken. OK. So it doesn't do that in normal operation - during the record-setting run, for example? Got it.

The record breaker is indeed, a record breaker.
Forces act to oppose or add, so both can exist at the same time.
You can work a car against its brakes. It still works, but not as well as if you took your foot off the brake. Similarly, the prop still turns, but not so well as if the force of tailwind were not opposing the force from the wheel.

That's right. It tries to oppose the rotation of the prop. Exactly as I tried to explain to you in this very thread.

Like when it accelerates when it shouldn't. The Chief's own hand says that the says the performance of the cart would suffer if not DDW.
The data says that a 25 degree shift in the wind, does not bother it, and accelerates just as well. It not a matter if you agreeing with my explanation or not, but that your explanation does not agree with the recorded facts.

 

[humber]

Lets use your same argument for an iceboat outracing the wind: The headwind against an iceboat's opposes the boat. That is accepted. If a panel were set horizontal on the boat, I would expect that to be a drag force too, so why does it suddenly drive the boat, because it hits the sail instead? Voodoo.

The headwind does oppose the ftw iceboat, but it tacks the wind to gain the power to overcome that. ddw carts see nothing but the opposing headwind.

 

[humber]

All very good 'n' all, but the chart says the cart does just as well when 25 degrees off the wind. And that contradicts the claim that it is, and it's "theoretical" explanation.

However, the acceleration can be related to the changing wind, and that explains all without any contradictions. NASAS Steve Smith says that the changing wind could do the trick, so I say it does.

 

[Jack by the hedge]

The headwind does oppose the ftw iceboat, but it tacks the wind to gain the power to overcome that. ddw carts see nothing but the opposing headwind.

The cart's propeller is mechanically equivalent to the iceboat's sail. Just as shown in that video you can't bear to look at.

 

[jduffy77]

Like when it accelerates when it shouldn't. The Chief's own hand says that the says the performance of the cart would suffer if not DDW.
The data says that a 25 degree shift in the wind, does not bother it, and accelerates just as well. It not a matter if you agreeing with my explanation or not, but that your explanation does not agree with the recorded facts.

Careful Humber, you are lying again. Twice.

 

[I Ratant]

...
The salient point is that the propeller is driven faster than it would turn if it were freewheeling in the wind.

...

.
It's actually the drag of a non-motored prop being used here.
Backwards, but the same thing.
A true freewheeling prop is de-coupled from the motor, and will spin at a speed commensurate with the pitch of the prop at the time, and speed of the plane.
The usual response to a failed motor without the ability to de-couple the prop is to feather prop so it can't rotate.
A windmilling/connected prop can damage the bearings it rides in, and break off the front of the motor; the prop frequently then flies into the fuselage of the plane, bad things tend to worsen their situations.
Few airplanes have the capability to de-couple the prop.. the larger turbo-prop motors will cause the propellor to disconnect from the gear box that drives it, when the motor fails, and the propellor can't be feathered.
The prop will then freewheel at some speed; on the P3 Orions this speed is quite high, and I've heard it said the decoupled prop sounds like a giant siren.
If the prop can't be feathered and couldn't be separated from the motor gear box, the drag it puts -into- the airframe can be more than the flight control system of the plane can correct, and the plane can yaw uncontrollably towards the windmilling but coupled prop.
The DDW carts merely use this windmilling force. The coupling from the wheels which drive the cart acts as the connection from the wheels (the motor) up to the speed the propellor begins to lose thrust due to the combination of the ground speed and the windspeed, achieving the windmilling rpm.
That speed will be a function of the propellor pitch.

 

[Jack by the hedge]

NASAS Steve Smith says that the changing wind could do the trick, so I say it does.

So you simply accept, on authority, an explanation which merely remarks on a possible power source but does not explain in any way how that source could be exploited by the actual design. Oh, yeah, that must be it. <shrug>

Wow. Maybe people should have made less effort to try to explain.

 

[jduffy77]

.
It's actually the drag of a non-motored prop being used here.
Backwards, but the same thing.
A true freewheeling prop is de-coupled from the motor, and will spin at a speed commensurate with the pitch of the prop at the time, and speed of the plane.
The usual response to a failed motor without the ability to de-couple the prop is to feather prop so it can't rotate.
A windmilling/connected prop can damage the bearings it rides in, and break off the front of the motor; the prop frequently then flies into the fuselage of the plane, bad things tend to worsen their situations.
Few airplanes have the capability to de-couple the prop.. the larger turbo-prop motors will cause the propellor to disconnect from the gear box that drives it, when the motor fails, and the propellor can't be feathered.
The prop will then freewheel at some speed; on the P3 Orions this speed is quite high, and I've heard it said the decoupled prop sounds like a giant siren.
If the prop can't be feathered and couldn't be separated from the motor gear box, the drag it puts -into- the airframe can be more than the flight control system of the plane can correct, and the plane can yaw uncontrollably towards the windmilling but coupled prop.
The DDW carts merely use this windmilling force. The coupling from the wheels which drive the cart acts as the connection from the wheels (the motor) up to the speed the propellor begins to lose thrust due to the combination of the ground speed and the windspeed, achieving the windmilling rpm.
That speed will be a function of the propellor pitch.

This is not the same scenario at all. The windmilling prop is being turned by the wind and does not produce thrust. It is a drag which is why the plane can yaw towards it. If it is still connected to the engine more torque required so more drag. In the case of the cart it is being spun by the wheels. Without the ground to leverage the wheels the cart would not work.

 

[Llyricist]

So you simply accept, on authority, an explanation which merely remarks on a possible power source but does not explain in any way how that source could be exploited by the actual design. Oh, yeah, that must be it. <shrug>

Wow. Maybe people should have made less effort to try to explain.

In the interest of, well, honesty, Here's the whole paragraph he's quote mining:

One other possibility is worth discussing — that it could be the time-variation of the wind direction, rather than simply the fact that the wind is not DDW. There are examples of similar effects in nature that would give some reason to consider this. For example, what is called “dynamic soaring” -- the maneuvering in a wind gradient field (regions where there is a consistent pattern of different wind speed) that allows birds (and gliders) to soar by extracting energy out of the wind gradient field. This is the life-blood of the albatross, and to some extent, the frigate bird. The world record for a radio-controlled glider in dynamic soaring is something close to 400 mph! In the case of the DWFTTW cart, it might be possible to extract a very slight amount of extra energy from the time variation of the wind – I will at least give it additional thought. But it is certainly not the dominant effect, which is much more simple and, (dare I say...) obvious.

 

[Llyricist]

Humber want math? I'll go ahead and do what I haven't seen anyone else do, and do the math for an equilibrium state.

A BB like cart is traveling at 14 m/s with a wind of 5 m/s, giving a w/s multiple of 2.8. At slightly higher speeds than the record.

A 9 m/s relative headwind will produce 85.33 newtons of drag force given a cross sectional area of 7 m² (No, the prop disk doesn't count) and a Cd of .25.

An additional 15.9 Newtons of Rolling resistance wirh a crr of .0055 and weight of 295 Kg.

Giving a total retarding force of 101.23 Newtons before taking any power to turn the prop.

I'll retard the wheels with an extra force of 532.857 Newtons, giving a total retarding force of 634.1 Newtons.

At 14 m/s, this gives 7,460 Watts of power (Power = Force * Speed) at the axle. About 10 HP for us laymen in the US.

The twisted chain may be more efficient, but I'll say it is 90%, giving 6,714 Watts available at the prop shaft.

Using a good propeller with an efficiency of 85%, will give an effective power to the air of 5,706.9 Watts.

A propeller doing work at a rate of 5,706.9 Watts will produce 634.1 Newtons of thrust at 9m/s.

Where have I seen that number before? Oh yeah, that is the total retarding force, giving an equilibrium speed of 14 m/s with a 5 m/s wind.

In the FOR of the cart, In 1 second the ground does 7,682.7 J of work on the cart (Rolling Resistance + Power extraction), while the prop does 5,706.9 J of work on the air, and the cart body does an additional 768 Joules of work on the air.

That's 7,682.7 J in, and 6,474.9 J out. Work out is less than work in. No magic energy, just heat loss and scattered air from the prop.

As an aside, that 532.857 Newtons of force on the wheels translates to 130 Ft lbs of torque on the axle. Which, through the 22:60 gearing, becomes 355 ft lbs of torque on the prop shaft. That's at ~31 MPH. Which jives pretty closely with JB's estimate of 6-800 ft lbs at 50-55 MPH.

 

[humber]

So you simply accept, on authority, an explanation which merely remarks on a possible power source but does not explain in any way how that source could be exploited by the actual design. Oh, yeah, that must be it. <shrug>

Wow. Maybe people should have made less effort to try to explain.

Well, I don't need too, and Spork won't let me see the data, so that going to be hard to do.
But, I don't have to worry about that, because your explanation contradicts the recorded fact, but mine doesn't.

I mentioned that a closed venturi port would be like the same thing attached to the chassis, and so a source of drag.

That's a problem for the tacking prop idea. If prop blade is seen as being "angled to the wind", the only difference is that the drag is divided into lateral and longitudinal forces. Meaning it will be pushed back, but perhaps at an angle.

 

[recursive prophet]

There's been an endless amount of discussion about humber's interpretation of the NALSA data. I am curious about what the Carteers believe-based on that data-was the overall average direction of the wind wrt the cart during the record run at El Mirage?

 

[I Ratant]

This is not the same scenario at all. The windmilling prop is being turned by the wind and does not produce thrust. It is a drag which is why the plane can yaw towards it. If it is still connected to the engine more torque required so more drag. In the case of the cart it is being spun by the wheels. Without the ground to leverage the wheels the cart would not work.

.
It's the exact same situation, with the motive power (forward airspeed for the airplane affecting the propellor rotation) and the ground speed of the cart driving the propellor.
The wheels/ground interaction are the motor for the cart. It's forward airspeed for the plane.
The speed of the cart on the ground drives the wheels which drives the prop which is on the cart that Jack built.

 

[D'rok]

.
It's the exact same situation, with the motive power (forward airspeed for the airplane affecting the propellor rotation) and the ground speed of the cart driving the propellor.
The wheels/ground interaction are the motor for the cart. It's forward airspeed for the plane.
The speed of the cart on the ground drives the wheels which drives the prop which is on the cart that Jack built.

Unless I am misunderstanding the terms you are using, the cart's prop does not windmill.

ETA: Referring to this:

If the prop can't be feathered and couldn't be separated from the motor gear box, the drag it puts -into- the airframe can be more than the flight control system of the plane can correct, and the plane can yaw uncontrollably towards the windmilling but coupled prop.
The DDW carts merely use this windmilling force. The coupling from the wheels which drive the cart acts as the connection from the wheels (the motor) up to the speed the propellor begins to lose thrust due to the combination of the ground speed and the windspeed, achieving the windmilling rpm.

That does not describe the cart.

 

[jduffy77]

.
It's the exact same situation, with the motive power (forward airspeed for the airplane affecting the propellor rotation) and the ground speed of the cart driving the propellor.
The wheels/ground interaction are the motor for the cart. It's forward airspeed for the plane.
The speed of the cart on the ground drives the wheels which drives the prop which is on the cart that Jack built.

You can either join Humber and keep making statements which you don't understand or learn something. Your choice. How can a dead engine be a motor for anything? The windmilling prop is not producing thrust. It is producing negative thrust.

 

[jduffy77]

There's been an endless amount of discussion about humber's interpretation of the NALSA data. I am curious about what the Carteers believe-based on that data-was the overall average direction of the wind wrt the cart during the record run at El Mirage?

It is not up for debate or a matter of beliefs. It is part of the report. The average was just under 5 degrees. The cart performed best when it was just about 0 degrees and then slowed at the end.

 

[Christian Klippel]

Other than being of no more importance than the number of angels a pinhead can handle, going downwind faster or slower than the wind has no practical use, with such cumbersome machinery.
Henry Ford's first production vehicle that problem, with the added ability to go crosswind, and even gasp! upwind, with no configuration changes, just point and go.
And the "down chain crawler"... really...

Your illustration is wrong. It really moves from left to right, and not right to left as you state in that illustration.

Just take a yoyo and test for yourself.

Greetings,

Chris

 

[humber]

It is not up for debate or a matter of beliefs. It is part of the report. The average was just under 5 degrees. The cart performed best when it was just about 0 degrees and then slowed at the end.

Just because NALSA say so, does not improve upon the fact that their ideas contradicts their own data. The wind changes from ddw by 25 degrees, but the cart still accelerates.

There is a problem with their reasoning.

"One of the reviewers of this report pointed out that the true wind speed (black line in separation graph) was 4-5 mph faster a few seconds before the measurement period(MP) than the speeds during the period yet it continued to accelerate in the lighter winds present in the MP . This brings up the question if there is some way the energy associated with the higher wind can provide acceleration during the measurement period. The observers see no meaningful way this could happen without using stored energy. Blackbird
has no such capability. "

The wind speed falls, but the cart continues to accelerate. That is unexpected. But, they think that only the release of stored momentum could be responsible for that, but end by saying the BB does not have any, so they leave it at that. Well not quite

" In effect the higher wind speed before the measurement period got the craft close to its equilibrium speed more quickly but it would have gotten there if the wind had stayed at exactly 10 mph for the entire run."

Voodoo. "Equilibrium Speed". They are suggesting that the cart can accelerate in the slower wind, by the "memory" of the higher wind that preceded it

They thought of witchcraft, and the possibility of stored energy, but not that the changing wind may be the source of the wonder.

The fact is that it does accelerate in changing wind, which contradicts Spork's and their claims, that the cart is best ddw. That is, it is WORSE when not ddw, but in fact it isn't.