The Wind Powered Sail-less Boat

soon as you two are done with all the hugs and kisses

 

JB
Another way of considering the turbine is that it reduces the speed of the airflow through the disc. A propeller accelerates it.

There is an elegant little Java Applet called JavaProp that you can run on any computer that enables you to do a prop design. You do need to establish the design conditions and this involves iteration with the wheel powered prop.

Lets say the vehicle has a design speed 7m/s in 5m/s wind. That means far field airflow is 2m/s relative to the prop. We will say the vehicle requires 20N to drive it at 7m/s on the road and 2m/s through the air. This gives power out of 140W. As a first guess lets say overall efficiency is 60% so power input is 233W.

So wheel drag for power input is 233/7 = 33N. Total vehicle drag is thus 53N.

I have attached the JavaProp design for this condition with a 4.5m prop. Here is a link to the applet.
http://colaco.freeshell.org/mhepperle/javaprop/jp_applet.htm
You will see it is possible to get something around 65% efficiency under this condition but it will need 5 blades with about 300mm chord. You can see the prop requires input of 162W to generate that thrust so there is 71W left to overcome the mechanical losses in the drive train and wheel slip.

The efficiency improves as it picks up speed but you need the grunt to get it through the low airflow condition.

If I was making a vehicle I would set up the weight distribution so almost the entire weight is on the driving wheels. This will tend to reduce wheel slip. A pushing prop is self stabilising so having a rear mounted prop is likely to be the best. The steering wheel would be well in front so any moment from the prop thrust does not reduce the wheel load too much. A wheelbase of say 5m would be reasonable. You may need a jockey wheel to stop the thing from tipping when at rest as it will tend to flip backwards if the ballance is set up for best performance.

If you go up to a 6m prop then you only need two blades with average chord around 400mm.

I imagine the required prop size is bigger than you expected. I might be a bit conservative with the vehicle drag but it is roughly 1% of likely vehicle weight which is not much.

Rick W.

 

The ball's been in your court Boston -- I nicely asked a couple questions and am simply awaiting your response.

One more bit ... I tend to respond to critics who wish to have serious conversations. Unless they entertain me I tend to ignore those who just want to be condescending smart-a888es. That's my three catagories and my two responses -- you're free to pick where you fall.

JB

 

Some thoughts about practical design for the "ride-upon" device

JB

The model cart is great, but I wondered if it would have been more stable the other way round, that is, with the prop at the front and the double wheels at the back, this would have put the small stabilising wheel at the front.

This is rather like the difference between the old "taildragger" planes and a modern nosewheel job which, as we all know, is more stable on the ground. In the big version the small wheel would be used for steering - front wheel steering being more user-friendly than rear wheel steering.

Secondly, isn't the size of the prop dependent upon the gearing? Cannot the prop be made smaller with using higher speed with the same result as a larger slower moving version?

I don't believe the "certainty" of mathematics as Rick does, and I really think maths doesn't come out with much honour in this discussion so far, since so many of the detractors have used maths or pseudo maths to prove "impossibility". (However, I know it does have its place, if sensibily applied)

I don't necessarily expect specific answers to my ideas, but just thought I would put them on record!

 

There are many aspects to vehicle dynamics, but to tell you the truth the form of the small cart was determined by availability of parts and nothing more. A really bright guy by the name of Mark C put the first rough version together and it worked quite well as it sat. We just then polished it.

The design form that appears most likely to be built currently will have two wheels in the rear and one in the front (much like what Rick describes earlier). Again, this form isn't driven by any particular vehicle dynamics, but rather by transmission parameters.

You are correct, a small prop can be used -- however the larger the prop the more efficient and within reason this makes it more likely we will be able to achieve our goals.

I do believe in the certainty of math done right. However as my partner likes to say ... "if your going to use math as a proof, you better be darn sure you carried the two". I tend to be better with the conceptual and build portions of these problems and rely less on the math. I do respect those like Drela and others who do have the education to use math to accurately predict the world around them. I love math and take every chance I can to learn more.

I will say this about math ... since a DDWFTTW device can be easily built and tested with positive results upon demand, when I see math that says it can't be done I don't even scan for errors -- it's just bad math.

Happy to chat. I respect people who go out and build stuff for proof as you have.

Best wishes.

JB

 

on maths

Mathematics could be described as the logical analysis of 'quantity'. In order for maths to be valid it must be followed rigorously, mathematically, at all steps along the way from initial assumptions to final conclusion.

The initial assumptions must be so simple as to be self evident. (at uni i had to mathematically prove, amongst other things, that 1+0 = 1) From there one can go on proving in small steps which are logically indestructible (that is why proof is important) all the way to what a lot of times ends up being previously unknown, or seemingly impossible conclusions.

There is also another aspect to maths in the applied field which is the 'art' of recognising what is crucial and what is a complicating distraction within a given set of full equations and hence be able to reduce a problem to its fundamental characteristics and be able to solve it analytically.
Nowadays, with mega computers which are able to numerically solve analytically unsolvable problems, it has become possible to find approximations to the full set of equations for many different problems. This kind of 'brute force' approach is very usefull but one cannot deny the subtle ingenuity of the sophisticated analytical methods....

My point is that maths will give absolute results (but one has to observe very closely the method that was used and the approximations that crept in along the path) . When maths is used to disprove an observable phenomenon it is actually mathematically provable that the 'proof' is flawed.

 

hey Thin Air no worries
just joking around
although there was some pretty heated exchanges in the past
as far as Im concerned its all in good fun
my theory is Im just an innocent bystander on this one as I believe the concept was proven flawed from the start
if you read back you will see that the answer to the question you pose is yes
so feel free to continue although Im likely to keep to myself on this one
short any new earth shattering principals of physics
which is about what it would take to accomplish the stated goal
I just dont believe in it

I would in my defense however state that there are a number of rather unconventional beliefs in physics that I do hold regardless of there being a minority opinion
for instance variable light speed theory and faster than light travel
the theory of causality bla bla bla

I might also point out that despite Ricks frustrations with me
in regards to DDWFTTW the ball is definitely not in my court
I never bought it in the first place and so Im not exactly sure how it ended up my responsibility to prove or disprove it
I abdicated from that game about the instant the idea was raised

I think Rick was just frustrated that his baby didnt work out
I can understand as Ive tried a few things myself that proved themselves unworthy and its never a pleasant realization

I would point out that the premise of the original math offered was

now if this is DDW then assuming 7m/s from a 5m/s wind is not the best place to begin
seems like somewhere there's an imagined few m/s that never really existed and thus working backwards from there you get nothing but fictitious numbers
this among other basic flaws has been Ricks nemesis from the word go

better place to start might be from a place of known physics and then extrapolate the unknown
rather than start from a place of unknown and extrapolate backwards into the void
if you know what I mean

have fun guys
B

ps

Ill take smart *** skeptic any day
its more fun

speaking of fun I thought #256 was kinda funny
certainly didnt mean it to be taken to heart
grain of salt folks
its what makes us all able to shake and hoist a few in the end
at least thats always my intention
best
B

 

JB,
I've been away from this discussion for a while, but I just wanted to let you know that I do believe that DDWFTTW is possible. It is certainly counter-intuitive, and my math skills aren't up to a useful level here.

The problem I had with your videos is that you never bothered to try explaining the math/physics that make it work. Yes, you can show people that it works, but if you don't explain how, then they will remain skeptical. (Maybe you've done that, but I haven't seen it.)

I've seen most of your videos, plus video of at least one boat doing it, so I know it works.

To me, the biggest problem is explaining what happens to get from slower-than-windspeed to faster-than-windspeed -- crossing the zero-relative-velocity barrier. I suspect that what's missing may be that the prop is pushing hard enough before that condition is reached.

As to the person who believes that direct upwind travel can't be done: once you've gotten DDWFTTW, you are effectively going upwind anyway -- you do one, you've done both.

Anyway, this is fun stuff, and I'm glad to see it start up again.

 

Curtis
The idea of "crossing zero-relative-velocity" is not something the propeller contends with. Once the vehicle starts to move forward under the pressure of the wind behind, the prop must turn because the wheels are geared to overcome its resistance. It is now turning in the forward direction and the near-field air flow is already moving backwards relative to the blades. There is a point where the near-field airflow begins to reverse relative to the far-field in an absolute sense but at this stage the near-field airflow is a well established rearwards airflow at the prop. So even at very low forward speed the airflow through the blades of the prop will be going backwards relative to the blades. By the time the vehicle reaches wind speed the propeller is moving the air backwards at quite a rate. It just needs to be large enough to generate the required thrust to keep accelerating.

The upwind case is completely different to the downwind case because you now have a turbine taking power from the air and delivering it to the wheels. The gear ratio is the opposite way around whereby the turbine can overcome the wheels the vehicle moves against the wind.

I gave you the math for a road vehicle above. All the numbers are based on achievable design.

I doubt that you have seen a DDWFTTW boat. Maybe a turbine boat going directly upwind or the same boat going downwind slower than the wind. A boat able to achieve DDWFTTW needs a ginormous prop. It needs to operate on a huge area of air to achieve even modest thrust at the slow relative air speed.

In thinking about the DDWFTTW it is best to think of airflow in the immediate vicinity of the blades rather than the airflow some distance away. Stand behind a static plane some time while it is testing brakes and you soon relise the nearfield airflow can be dramatically higher than the farfield flow. It can quite easily be in the reverse direction relative to the ground.

Rick W

 

JB and Rick

could we see a quantified mathematical analysis of the near air mass influenced by the prop its resistance and interaction with ambient air and prop
its energy potential its energy requirements and its mass reaction density and area
also please combine that with the same type of analysis in regards to the resistance of the wheels and its gearing systems its energy expenditures and sources
also please draw a mathematical model of the drag from this carriage including how this system "produces" energy that is then transferred to the prop which then produces thrust and more importantly
were this energy comes from
I believe there was the offer of any level of physics or maybe it was complexity involved ( #246 I think it was )
I would like to take you up on that offer

skeptics are us
have a fantastic holidays one and all
best
B

the average straight gear looses 1% to friction per each
bevel gears loose more
the average chain gear between 5~15% like in a bicycle
the average aero-prop is about 80% efficient and so looses ~20% percent of its energy to resistance and far more the slower the air speed
the average wheel has about 5~8% drag although its been a long time since I took automotive engineering and Im not really looking any of this up
wind resistance rises exponentially so the lower the speed the less air resistance depending on conditions and direction of wind
IE the slower you go the better you are in terms of wind resistance on they system but the faster you go the more efficient your prop becomes
this circumstance leads to a classic tug of war between interactive forces resulting in a the possibility of a computational energy requirement
that computation of energy requirements is what Im after here
thank you for offering
B


just a few points that need to all jive in the end

 

<<<<<<<the average chain gear between 5~15% like in a bicycle>>>>>

please tell us where you' re getting this numbers.
I am a long time cycling enthusiast and from what i've read over the years the chain drive in a bicycle is a lot more efficient than that.

 

I ripped it out of my ***

I'm sure you can find it down to say 2~3 on a high end bike
certainly no less than ~2

 

Actually the best figures are at around 1.5 %. Chain drives are some of the most efficient transmission systems around, rivalled only by well engineered belt drives. In a not so good quality setup count on 3 or 4 % loss. Of course with worn, dirty, rusty or in other wise poor state of repair the losses climb very rapidly.

I think that for the purposes of this discussion it is fair to assume the better numbers available as we are not talking about a system cobbled together out of hardware found at the dump..

It is always appreciated when numbers are given with a certain amount of forethought instead of snatched out of guess land - or lower..

 

If you wish an exchange with me (and it's fine if you don't), the balls is in your court as I stated, because I have nicely asked you to answer one or two questions so I know where you stand.

With those questions still unanswered I'll assume you aren't looking for any discourse with me.

JB

 

Boston, the ball is still in your court when it comes you our exchange. See previous post above.

JB