Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 18-07-2021, 20:10   #31
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 4,790
Images: 7
Re: Novel Propeller propulsion, going faster downwind than the wind

That must be the same wind which is going to allow us to shut down all the nuclear and coal fired power plants and give us reliable 24/7/365 electrical power from wind generators. Damn, that's a relief I thought renewables was all smoke and mirrors.
__________________
Satiriker ist verboten, la conformitť est obligatoire
RaymondR is online now   Reply With Quote
Old 18-07-2021, 22:25   #32
Registered User

Join Date: Feb 2010
Location: Australia
Posts: 830
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by waterman46 View Post
I'm sure it is tempting to think that once the vehicle reaches a speed equal to true wind DDW, and apparent wind is then zero, that the wheels, being in contact with the ground, can somehow extract power from that motion that can spin the propeller and draw the vehicle forward. As I understand it, this is your argument and there seem to be many who tend to agree with this.


However it is not possible. To generate forward thrust, the prop would need to extract power from the wheels. When you extract power from a moving object, that object has to slow down. This is extremely basic physics and I am ashamed to think that some Professor of Physics graduated from a UC engineering school who doesn't know this fact.

Besides, when switching from speed less than true wind to an imaginary speed greater than true wind, will require a reversal of pitch of the propeller. Did any of the video's mention a reversible pitch prop?


So, did you actually watch the video with the inventor (not the driver) explaining his side of the story? It was very entertaining, neither the inventor nor the owner wanted to drive the damned thing.
Your view on this is what cost the professor 10 large.
skipperpete is offline   Reply With Quote
Old 19-07-2021, 01:03   #33
Senior Cruiser
 
Dave_S's Avatar

Cruisers Forum Supporter

Join Date: Jun 2016
Location: Brisbane Australia
Boat: Schionning Waterline 1480
Posts: 1,653
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by waterman46 View Post
I'm sure it is tempting to think that once the vehicle reaches a speed equal to true wind DDW, and apparent wind is then zero, that the wheels, being in contact with the ground, can somehow extract power from that motion that can spin the propeller and draw the vehicle forward. As I understand it, this is your argument and there seem to be many who tend to agree with this.


However it is not possible. To generate forward thrust, the prop would need to extract power from the wheels. When you extract power from a moving object, that object has to slow down. This is extremely basic physics and I am ashamed to think that some Professor of Physics graduated from a UC engineering school who doesn't know this fact.

Besides, when switching from speed less than true wind to an imaginary speed greater than true wind, will require a reversal of pitch of the propeller. Did any of the video's mention a reversible pitch prop?

I'm sure it is tempting to think that once the vehicle reaches a speed equal to true wind DDW, and apparent wind is then zero, that the wheels, being in contact with the ground, can somehow extract power from that motion that can spin the propeller and draw the vehicle forward. As I understand it, this is your argument and there seem to be many who tend to agree with this.


However it is not possible. To generate forward thrust, the prop would need to extract power from the wheels. When you extract power from a moving object, that object has to slow down. This is extremely basic physics and I am ashamed to think that some Professor of Physics graduated from a UC engineering school who doesn't know this fact.

Besides, when switching from speed less than true wind to an imaginary speed greater than true wind, will require a reversal of pitch of the propeller. Did any of the video's mention a reversible pitch prop?
I'm beyond my pay grade but this is how I see it.

I think you are thinking that the propeller sees a reduction in effect as the vehicle approaches wind speed like a sail would.

If when stationary the vehicle has 10N of force applied by TW and the propeller blades have 10N applied by TW the assembly has 20N of force applied to the vehicle.

Point the vehicle DDW and release the brake. The 20N is sufficient force to move the assembly DDW. The grounded wheel rotates and through a drive drives the propeller in such a way to make more thrust than the losses felt through changes to AW. The thrust is working to move air in the apposing direction to the TW.

Because the propeller is overdriven it is increasing drag/thrust at a greater rate than the reduction of drag felt by the vehicle.
  • The vehicle feels a 1:1 reduction in ground speed/AW, decreasing as vehicle speed increases.
  • The propeller is driven by the wheels in such a way that it increases force at 3:1, ground speed/thrust (I made up 3:1, I don't know what the magic number is)
  • At wind speed the vehicle sees no apparent wind but the propeller is now generating 30N of force, a total of 30N. 50% up from 20N when the vehicle is at rest.
  • So at wind speed the propeller is producing more thrust than at rest. Each new speed is just a sum of forces which progress unaffected if it matches wind speed or not.
  • It makes no or little difference if the thrust from the propeller is apposing or running with the apparent wind it is just a differential in flow like drag.
__________________
Regards
Dave
Dave_S is offline   Reply With Quote
Old 19-07-2021, 01:43   #34
Registered User

Join Date: Mar 2016
Location: Portsmouth, VA
Boat: Morgan 382
Posts: 377
Re: Novel Propeller propulsion, going faster downwind than the wind

I keep reading explanations of this, and it is surprising that the professor didn't understand it, and why so many people can't seem to grasp a simple idea.

Wind velocity isn't the factor that determines how fast a vehicle can go DDW. It's the force the wind imparts on a vehicle. So you have a vehicle, and a drag device. You make the drag device larger, and the vehicle goes faster, until wind velocity is reached. But you can keep making the drag device larger, to capture more energy. If the drag device is large enough that it could push a vehicle twice the mass of the actual vehicle to the velocity of the wind, there is a lot of extra power to capture, and the drag on the vehicle from turning wheels and mechanics will not slow it down. Then you need to convert that extra energy into velocity to keep going faster.

The wheels are not converting forward motion of the vehicle into energy to move the vehicle. If that were happening, that conversion would slow the vehicle. They are capturing that extra energy from a drag device capably of pushing more massive vehicle, allowing the rotating propeller to convert extra unused energy into velocity.
__________________
-Warren
wholybee is offline   Reply With Quote
Old 19-07-2021, 15:22   #35
Registered User

Join Date: Feb 2015
Location: Somewhere warm
Boat: Morgan 462
Posts: 1,676
Re: Novel Propeller propulsion, going faster downwind than the wind

I now understand that the prop pitch vs. rotation is configured to provide thrust when moving forward and rotated by connection to the wheels. I had assumed the configuration was to extract power as a wind turbine at vehicle speeds less than true wind.
Conservation of energy arguments are easier for me to understand. I like Wholybees explanation that a large and well designed propeller does the job of converting excess energy into increasing velocity. In effect it creates a more optimum gear ratio to favor velocity over power - the sail is 1:1, but the propeller can be designed to provide a more optimum gear ratio of the system to increase velocity by using excess energy. The excess energy is provided by the velocity gradient between ground and true wind and is always present and can be cleverly used even when the vehicle travels faster than the wind.
__________________
No shirt, no shoes, no problem!
waterman46 is offline   Reply With Quote
Old 23-07-2021, 06:38   #36
Registered User

Join Date: Feb 2020
Location: Lymington UK
Boat: UFO27 Holman & Pye 8.2m
Posts: 198
Re: Novel Propeller propulsion, going faster downwind than the wind

This short film may be of interest

John
johnn33 is offline   Reply With Quote
Old 23-07-2021, 06:44   #37
Registered User

Join Date: Feb 2020
Location: Lymington UK
Boat: UFO27 Holman & Pye 8.2m
Posts: 198
Re: Novel Propeller propulsion, going faster downwind than the wind

and a little more about Lord Brabazon's Redwing dinghy with an autogyro
AUTOGIRO BOATS - History 1870-1933
John
johnn33 is offline   Reply With Quote
Old 23-07-2021, 06:46   #38
Registered User

Join Date: Feb 2020
Location: Lymington UK
Boat: UFO27 Holman & Pye 8.2m
Posts: 198
Re: Novel Propeller propulsion, going faster downwind than the wind

and again

Rotary Sailing Homepage
John
johnn33 is offline   Reply With Quote
Old 23-07-2021, 09:17   #39
Registered User

Join Date: Sep 2019
Posts: 57
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by wholybee View Post
The wheels are not converting forward motion of the vehicle into energy to move the vehicle. If that were happening, that conversion would slow the vehicle. They are capturing that extra energy from a drag device capably of pushing more massive vehicle, allowing the rotating propeller to convert extra unused energy into velocity.
I donít think this is a correct explanation. When you get to the wind speed going DDW, the apparent wind is zero and there is no energy from the drag device (sail). The claim appears to be that you would then take some of the kinetic energy from the moving vehicle to increase itís kinetic energy. Thatís seems like a clear violation of energy conservation (1st law of thermodynamics) and why I think most people with a physics background are skeptical if this.
Chris31415 is offline   Reply With Quote
Old 23-07-2021, 12:21   #40
Registered User

Join Date: Nov 2019
Posts: 58
Re: Novel Propeller propulsion, going faster downwind than the wind

Soooo...

I had a multi-week argument about this in the comments section of the original video. I was taking the position that this vehicle (blackbird) was not possible.

However...

There have been multiple papers on this subject showing that it is theoretically possible. It was a question on one of the science decathlons.

My argument hinged on the fact that at some point the car without a propeller will reach energy equilibrium - the drag and friction forces would exactly equal the energy being input to the system by the wind. If we then require more energy by making the wheels turn a prop, that removes energy from the vehicle, thereby slowing it down.

But I was wrong. Oh, and yes, I used to teach physics, though I'm by no means a PhD in physics!

Not sure if anyone wants the pages of math, but it comes down to work equations. The prop is doing almost the same work as the wheels (assuming perfect bearings and stuff for a moment). However, since the wind is moving with the vehicle, the prop is covering less "distance" relative to the wind than the wheels are doing relative to the ground. Since Work = force x distance and Work remains the same for both objects (prop and wheel) and distance decreases for the prop, the prop must, to keep things balanced, be exerting more _force_ on the air mass, which is related to thrust, of course. Thus, the prop is able to accelerate the vehicle past wind speed.

The increase in that force has to be only _slightly_ more than all the frictions and aerodynamic drags on the vehicle in order for the vehicle to continue to accelerate. The inventors claim a factor of 1.1 for their vehicle which is, apparently, enough. it also took a lot of careful tuning of the pitch of the prop blades.


This is a completely different effect than a sailboat sailing DDW, which is relying purely on flat-plate drag for its drive and it can not exceed the wind speed.


Also, due to slippage of the paddlewheel in the fluid, which takes even more energy away from the system, I doubt that a sailboat using these principles actually can exceed wind speed even with a similar set up - paddlewheels are just too inefficient for this. Maybe if you were floating in liquid mercury or something it might work, though I have my doubts about that. I also think that the wind turbine powered vessel that was quoted is a fish of a different mother as I believe the wind turbine drives the water prop rather than the other way around, and so it's not applicable to the discussion.

I have yet to study the math for the opposite direction - direct upwind - for the vehicle, but the claim is that it can work in that regime as well.
CyKlop is offline   Reply With Quote
Old 23-07-2021, 13:00   #41
Registered User

Join Date: Sep 2019
Posts: 57
Re: Novel Propeller propulsion, going faster downwind than the wind

So Iím in my frictionless vehicle traveling down wind at the speed of the wind. I have not connected the turbine to the wheels yet. You are saying that when I connect them I will get some energy that will cause my vehicle to speed up (accelerate).

Where is the energy coming from that speeds up the vehicle?
Chris31415 is offline   Reply With Quote
Old 23-07-2021, 13:27   #42
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jun 2018
Location: Rock Hall, MD
Boat: Catalina 25
Posts: 318
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by Chris31415 View Post
So Iím in my frictionless vehicle traveling down wind at the speed of the wind. I have not connected the turbine to the wheels yet. You are saying that when I connect them I will get some energy that will cause my vehicle to speed up (accelerate).

Where is the energy coming from that speeds up the vehicle?
The push prop is slowing down the air behind the car. The air in the wake of the car has less kinetic energy, as that energy was transferred to the car.
JoeRobertJr is offline   Reply With Quote
Old 23-07-2021, 13:30   #43
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 31,280
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by TrentePieds View Post
When I wuz a lad, way, WAAAAY before telly, let alone "social media" and YouTube, you often heard it said "It was in the paper - it MUST be true!"

Plus Áa change, plus c'est pareil

TP

Before telly? But Zworykin was broadcasting in New York in 1939. You were a lad in 1939?
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 23-07-2021, 13:30   #44
Registered User

Join Date: Jun 2021
Posts: 92
Re: Novel Propeller propulsion, going faster downwind than the wind

Your sail is a propeller of sorts. It why racing hulls can go three times wind speed
EngineerRetired is offline   Reply With Quote
Old 23-07-2021, 14:08   #45
Moderator

Join Date: Jun 2015
Posts: 4,429
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote: "You were a lad in 1939?"

Ooh, ahr! I wuz indeed. And by 1940 MySaintedMother had conniptions cuz I was wading out to a fisherman's skiff lying on the hook off our home. Next time you come northbound through the Lillebślt look to starbord. You may still see our house at the place called Strib, now a suburb of Middelfart :-)

My first exposure to telly was a physics class in about 1953 when we were drug off to witness a special demonstration of it. Cameras in one room at the art galley in my home town. Receiver in the very next room. Wildly exciting! Telly came to Canada that same year, if I recall, and I was not long after it. Two stations via "rabbit ears": Channel 2, CBC Vancouver and channel 12, KVOS Bellingham (WA). Ch 2 "Juliette", Ch 12 Tennessee Ernie Ford. Each as bad as the other :-)!

But that was all way, way before your time:-)!

Cheers

TP
TrentePieds is offline   Reply With Quote
Reply

Tags
propeller, propulsion, rope, wind

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Faster winds and faster currents disputin Weather | Gear, Reports and Resources 16 16-03-2020 17:46
Vestas Sailrocket 2 - Faster and Faster We Go SV Bacchus General Sailing Forum 2 13-09-2018 13:25
New tech shows its possible to go faster than the wind, dead downwind foolishsailor Deck hardware: Rigging, Sails & Hoisting 3 28-09-2012 17:04
Faster than Wind Agility Multihull Sailboats 0 08-05-2009 06:41

Advertise Here


All times are GMT -7. The time now is 00:54.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.