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ThinAirDesigns
New Member
13 Posts |
 Posted - 08/03/2010 : 13:30:29 [Permalink]
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Dave W
| what would happen if, say, the driver was capable of turning the cart directly upwind without losing more than, oh, 25% of the forward speed? |
Likely nothing more dramatic than than the prop slowing down until full stop and then reverse.
| Really, I'm just wondering if the lack of theoretical problems could someday result in a practical vehicle that'd work better than sticking a wind turbine generator on the roof of an all-electric car. |
I would not count on that being particularly practical. There just isn't enough room for rotor on a street vehicle and then you have to drag it around even during the times that the wind is not favorable (which is a LOT of the time).
| Well, towards that practicality question: how much of a difference in performance of your actual BUFC does the mass of the driver make? |
In our case the driver is a third of the total mass. This makes a very measureable different in accelertation, but very little difference in top speed.
JB
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Dave W.
Info Junkie
USA
26020 Posts |
Posted - 08/03/2010 : 14:39:11 [Permalink]
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Originally posted by ThinAirDesigns
I would not count on that being particularly practical. There just isn't enough room for rotor on a street vehicle... |
You're ruining my dreams of a day when interstate trucks go by with no more than a "whoosh-whoosh-whoosh" sound.| ...and then you have to drag it around even during the times that the wind is not favorable (which is a LOT of the time). |
Well, we're talking about the rotatable prop with continuously pitchable blades, here.
Hey, we could even add a "bridge detector" which would lower the whole propeller mast out of harm's way. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 08/03/2010 : 19:56:40 [Permalink]
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Originally posted by ThinAirDesigns
I have to admit that I simply do not understand the way this car operates. Smarter people than myself are trying to explain it, but for me to no avail. But, unless someone convinces me otherwise, I will simply accept that this thing works as advertised.
Apparently you folks did some pretty fine engineering. Congrats!
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Thanks Halfmooner.
If you are willing to put up with me for a few posts I might be able to walk you through some of the basic principles involved and make the lightbulb go on.
I understand though it you don't have the time or are otherwise uninterested.
JB
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Oh, please try, thanks! It's not time I'm lacking, but comprehension. |
“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 08/03/2010 : 21:15:39 [Permalink]
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Originally posted by Dave W.
Originally posted by ThinAirDesigns
If you are willing to put up with me for a few posts I might be able to walk you through some of the basic principles involved and make the lightbulb go on. |
Forget about whether HalfMooner would put up with it, I will happily put up with it, and I've got more clout another here than he.
In other words: please!
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"Clout. I haz it." |
“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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bngbuck
SFN Addict
USA
2437 Posts |
Posted - 08/04/2010 : 00:26:14 [Permalink]
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ThinAirDesigns.....
Last off-topic question, I promise.
Re: the hypothetical aircraft landing on a moving treadmill:
Reverse the treadmill to run 100 mph in the same direction as the plane is landing. What happens now when the wheels of the aircraft touch down on the moving treadmill?
Although the first hypothetical was quite easy for me to visualize, and my view was precisely as you described; somehow the second seems more difficult. I see a conflicted situation with the aircraft's wheels wanting to turn counter-clockwise upon landing: but the force of the treadmill attempting to turn the wheels clockwise. Would the two opposing forces cancel each other and leave the wheels still (non-rotating) even though the airplane is now traveling 200 mph forward on the treadmill. Or is it? What would happen? Does the landing event affect the expected LDA this time?
Thank you so much for your indulgence. |
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Dave W.
Info Junkie
USA
26020 Posts |
Posted - 08/04/2010 : 05:06:53 [Permalink]
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Originally posted by bngbuck
Reverse the treadmill to run 100 mph in the same direction as the plane is landing. What happens now when the wheels of the aircraft touch down on the moving treadmill?
...
Would the two opposing forces cancel each other and leave the wheels still (non-rotating) even though the airplane is now traveling 200 mph forward on the treadmill. |
Why would the airplane suddenly gain 100 MPH on contact with the treadmill? |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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ThinAirDesigns
New Member
13 Posts |
Posted - 08/04/2010 : 06:17:36 [Permalink]
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bngbuck:
| Reverse the treadmill to run 100 mph in the same direction as the plane is landing. What happens now when the wheels of the aircraft touch down on the moving treadmill? |
They don't spin at all (on initial touchdown)
| I see a conflicted situation with the aircraft's wheels wanting to turn counter-clockwise upon landing: but the force of the treadmill attempting to turn the wheels clockwise. Would the two opposing forces cancel each other and leave the wheels still (non-rotating) even though the airplane is now traveling 200 mph forward on the treadmill. |
There is no conflict and as Dave point out, the plane isn't going 200mph. (the plane and the belt are both traveling in the same direction at the same speed at the time the plane touches down)
| Does the landing event affect the expected LDA this time? |
Yes, there are minor effects -- in this case the LDA would be ever so slightly longer again because of the belt influence on the air.
JB |
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ThinAirDesigns
New Member
13 Posts |
Posted - 08/04/2010 : 08:50:49 [Permalink]
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halfmooner:
Oh, please try, thanks! It's not time I'm lacking, but comprehension.
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Ok, as thought exercises, here are the simplest forms of DDWFTTW that I can think of:
A: Imagine a telephone pole with a pivot at the bottom (the pivot allows the pole to fall directly upwind or downwind).
B: Place a sail halfway up the the telephone pole and then wait for the wind to blow.
C: When the wind pushes on the sail, the top of the pole will move twice as far as the sail and if you happen to be polesitting, you are (for a brief time) moving DDWFTTW powered by the wind.
If you want to extend this theory to a continuous application, imagine that the pole becomes the spoke on a bicycle tire.
A: Each spoke of the bike tire has a retractable sail installed at the point halfway between the rim and the hub.
B: This retractable sail is only extended when the spoke rotates to a point near the bottom of the wheel as it spins and retracts at all the other times around the loop.
C: When the wind blows, these sails on the lower spokes push the wheel downwind, but exactly as the top of the telephone pole moved faster than the sail, now so does the top of the spoke (which is the hub of the wheel).
D: you've now just created the simplest form of continuous DDWFTTW that I can think of -- a wheel that roll twice the speed of the wind powered only by the wind.
If you have any doubts as to the bicycle wheel idea, simply grab any bike and push forwards on the low spokes with your finger at the halfway point between the rim and the hub -- you'll see that the bike moves forward at twice the speed your finger moves.
JB
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| Edited by - ThinAirDesigns on 08/04/2010 11:13:09 |
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Robb
SFN Regular
USA
1223 Posts |
Posted - 08/04/2010 : 11:40:18 [Permalink]
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Originally posted by bngbuck
ThinAirDesigns.....
Last off-topic question, I promise.
Re: the hypothetical aircraft landing on a moving treadmill:
Reverse the treadmill to run 100 mph in the same direction as the plane is landing. What happens now when the wheels of the aircraft touch down on the moving treadmill?
Although the first hypothetical was quite easy for me to visualize, and my view was precisely as you described; somehow the second seems more difficult. I see a conflicted situation with the aircraft's wheels wanting to turn counter-clockwise upon landing: but the force of the treadmill attempting to turn the wheels clockwise. Would the two opposing forces cancel each other and leave the wheels still (non-rotating) even though the airplane is now traveling 200 mph forward on the treadmill. Or is it? What would happen? Does the landing event affect the expected LDA this time?
Thank you so much for your indulgence.
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Mythbusters did something like this. http://mythbustersresults.com/episode97 |
Government is not reason; it is not eloquent; it is force. Like fire, it is a dangerous servant and a fearful master. - George Washington |
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Robb
SFN Regular
USA
1223 Posts |
Posted - 08/04/2010 : 11:44:29 [Permalink]
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Originally posted by ThinAirDesigns
halfmooner:
Oh, please try, thanks! It's not time I'm lacking, but comprehension.
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Ok, as thought exercises, here are the simplest forms of DDWFTTW that I can think of:
A: Imagine a telephone pole with a pivot at the bottom (the pivot allows the pole to fall directly upwind or downwind).
B: Place a sail halfway up the the telephone pole and then wait for the wind to blow.
C: When the wind pushes on the sail, the top of the pole will move twice as far as the sail and if you happen to be polesitting, you are (for a brief time) moving DDWFTTW powered by the wind.
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Thanks, this makes alot of sense. I have to think about how it applies to the car though. |
Government is not reason; it is not eloquent; it is force. Like fire, it is a dangerous servant and a fearful master. - George Washington |
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bngbuck
SFN Addict
USA
2437 Posts |
Posted - 08/04/2010 : 13:21:05 [Permalink]
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Dave and ThinAir.....
Dave
Why would the airplane suddenly gain 100 MPH on contact with the treadmill? |
After a really serious attempt to visualize the concept, I now understand that, at touchdown, the plane would be immobilized at a single point on the treadmill, wheels stationary, traveling at 100 MPH on the treadmill toward the point where the treadmill belt reverses on its pulley wheel.
The ETA would be the distance between the point the treadmill passed when the aircraft touched down and the point to which the treadmill carried it when the treadmill stopped turning (assuming the treadmill power is turned off when the plane touches down and shuts down its engine.) The plane comes to rest when it's inertial energy is exhausted on a normal run-out on the now-stationary conveyer (very long) belt.
Would you both say this is correct or not? Damned if I know!
Now assume a extraordinarily long belt (miles) running at the speed of the plane 's full power in the opposite direction of the plane's landing direction and the plane touches down under full power (power landing) and does not throttle down.
Conveyor belt continues to turn under full power. The airplane's wheels are turning twice as fast as normal, but plane and belt are both going 100 MPH (or better, normal airspeed of the plane) in opposite directions so plane is going 200 MPH or more relative to the belt, 100 or more MPH relative to the ground (or air) - or not? Maybe it is stationary relative to the ground or air? At this point I've confused myself inexcuseably.
What does happen?
Does the plane land, take off, or stand stationary on the treadmill (as a car does on a dynamometer?) And if it is stationary, what happens to it's inertia when it instantly goes from flying to standing still. (I can't really believe this happens)
Postscript
I am in no way attempting a "gotcha" here, I just don't clearly understand it. TAD's explanation of his propeller/sail car makes perfect sense to me, and between him and Dave I am gaining an understanding of this old Internet and Mythbusters' chestnut.
I apologize to SS for what was not intended as a hijack of this thread but is turning out that way, and perhaps it would be appropriate if a moderator moved it to a new thread if anyone is interested enough (besides me) in it.
There is commentary on this hypothetical on the Internet as to a plane taking off from a treadmill, but I have not found much on a plane landing on a treadmill.
There's gotta be some way we can trash a 747! (Empty of passengers and flown by wire, of course) |
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Dave W.
Info Junkie
USA
26020 Posts |
Posted - 08/04/2010 : 14:42:08 [Permalink]
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Originally posted by bngbuck
The ETA would be the distance between the point the treadmill passed when the aircraft touched down and the point to which the treadmill carried it when the treadmill stopped turning (assuming the treadmill power is turned off when the plane touches down and shuts down its engine.) The plane comes to rest when it's inertial energy is exhausted on a normal run-out on the now-stationary conveyer (very long) belt.
Would you both say this is correct or not? Damned if I know! |
I'd say that it assumes that the plane requires the use of brakes on its wheels in order to stop. Assume, instead, a jet-powered plane that can vector its thrust in any direction with equal efficiency.
So it comes in for a landing at 100 MPH on the treadmill that's moving at 100 MPH in the same direction. The wheels touch down without rotating, since the speeds are identical. Now, without using brakes, the plane vectors its thrust forward to slow down. The wheels begin to turn backwards as the plane slows relative to the treadmill. When the plane reaches 0 MPH, its wheels are doing 100 MPH backwards.
OR assume that the plane can only slow down with its brakes. It touches down at zero relative speed to the treadmill, and the pilot essentially sets the parking brake. Assuming tires with enough friction, the plane has effectively glued itself to the treadmill, and so will slow down at the same rate as the treadmill (whatever rate - deceleration - that is).Now assume a extraordinarily long belt (miles) running at the speed of the plane 's full power in the opposite direction of the plane's landing direction and the plane touches down under full power (power landing) and does not throttle down.
Conveyor belt continues to turn under full power. The airplane's wheels are turning twice as fast as normal, but plane and belt are both going 100 MPH (or better, normal airspeed of the plane) in opposite directions so plane is going 200 MPH or more relative to the belt, 100 or more MPH relative to the ground (or air) - or not? Maybe it is stationary relative to the ground or air? At this point I've confused myself inexcuseably.
What does happen? |
The plane's ground-speed doesn't change due to its making contact with the treadmill in any of these scenarios. The wheels are free-spinning (and for the sake of this discussion, ride on friction-free bearings), and so do nothing more than keep the body of the plane at a non-zero altitude (in other words, they prevent belly-flops).| Does the plane land, take off, or stand stationary on the treadmill (as a car does on a dynamometer?) And if it is stationary, what happens to it's inertia when it instantly goes from flying to standing still. (I can't really believe this happens) |
No, that doesn't happen. The plane lands, and the pilot has to keep forcing it down because it's still going through the air at "full power." If it were going at just below stall speed, it'd land and stay landed (but still doing just-less-than-stall speed relative to the ground). |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 08/04/2010 : 20:45:25 [Permalink]
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Originally posted by ThinAirDesigns
halfmooner:
Oh, please try, thanks! It's not time I'm lacking, but comprehension.
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Ok, as thought exercises, here are the simplest forms of DDWFTTW that I can think of:
A: Imagine a telephone pole with a pivot at the bottom (the pivot allows the pole to fall directly upwind or downwind).
B: Place a sail halfway up the the telephone pole and then wait for the wind to blow.
C: When the wind pushes on the sail, the top of the pole will move twice as far as the sail and if you happen to be polesitting, you are (for a brief time) moving DDWFTTW powered by the wind.
If you want to extend this theory to a continuous application, imagine that the pole becomes the spoke on a bicycle tire.
A: Each spoke of the bike tire has a retractable sail installed at the point halfway between the rim and the hub.
B: This retractable sail is only extended when the spoke rotates to a point near the bottom of the wheel as it spins and retracts at all the other times around the loop.
C: When the wind blows, these sails on the lower spokes push the wheel downwind, but exactly as the top of the telephone pole moved faster than the sail, now so does the top of the spoke (which is the hub of the wheel).
D: you've now just created the simplest form of continuous DDWFTTW that I can think of -- a wheel that roll twice the speed of the wind powered only by the wind.
If you have any doubts as to the bicycle wheel idea, simply grab any bike and push forwards on the low spokes with your finger at the halfway point between the rim and the hub -- you'll see that the bike moves forward at twice the speed your finger moves.
JB |
Thank you so much. Amazingly, I understood that perfectly. |
“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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sailingsoul
SFN Addict
2830 Posts |
Posted - 06/08/2013 : 16:02:39 [Permalink]
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That piece of history was just sold on Ebay today.
Item condition:
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“This vehicle is used (and wasn't all that pretty even when it was new). Low miles :)”
Ended:
Jun 08, 2013 13:00:25 PDT
Winning bid:
US $5,120.00
[ 65 bids ]
Shipping:
Free Local Pickup
Item location:
Mountain View, California, United States
Seller:
dnrsw |
It went for $5,120.00 usd
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There are only two types of religious people, the deceivers and the deceived. SS |
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sailingsoul
SFN Addict
2830 Posts |
Posted - 06/08/2013 : 16:12:19 [Permalink]
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Originally posted by sailingsoul
That piece of history was just sold on Ebay today.
Item condition:
--
“This vehicle is used (and wasn't all that pretty even when it was new). Low miles :)”
Ended:
Jun 08, 2013 13:00:25 PDT
Winning bid:
US $5,120.00
[ 65 bids ]
Shipping:
Free Local Pickup
Item location:
Mountain View, California, United States
Seller:
dnrsw |
It went for $5,120.00 usd
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Edit to add sale link; Link I quoted the link because I know ebay won't keep the expired ad active for very long after the sale closes, so view it while you can. It will go away. |
There are only two types of religious people, the deceivers and the deceived. SS |
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A most counter-intuitive feat!
