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Annoying brain teaser #1

spork

Veteran

Mountain View, CA

Can you make a vehicle that goes directly downwind, powered only by the wind, faster than the wind (no collecting and storing energy)?

03-16-2006 Over year old.
HOMEPAGE  
MAVRICK

Veteran

Northwest Georgia

yes

03-16-2006 Over year old.
kokamo

Senior Heliman

Liberty Hill Tx

The idea is that you have is more than likely a hot watertank/windturbine/cold water tank "sandwich" set up on a trailer towed by an electric vehicle. The wind turns the turbine and a water vortex in the lower tank which adds to the rotation equilibrium. The vortex converts the heat stored in the upper tank to energy and pumps cooled water up to be reheated. The system generates sufficient power to drive the vehicle and dump unused power into heating the water in the top tank by an electric element. Solar and ambient air conditions adds to heating the water and the vehicle's slipstream adds to the turbine. An air condensation system incorporated replaces any water lost by evaporation. The whole system burns no fuel whatsoever and simply runs on the energy contained in the environment. This is my assumption of what you may be talking about.

Or......possibly a kite?

Joe

03-16-2006 Over year old.
spork

Veteran

Mountain View, CA

Wow, I wasn't able to follow that. What happens when the vehicle is going downwind at exactly the speed of the wind? Seems it wouldn't see any wind going over the turbine.

03-16-2006 Over year old.
HOMEPAGE  
GimbalFan

rrProfessor

Big Coppitt Key, FL

Not possible, however sailboats and windsurfers regularly go faster with a crosswind than the wind itself is blowing, even with the friction of the water on the hull. And your heli will go faster flying level with full collective (nose down just enough to keep from climbing) than it will if you're at full collective with the nose pointing straight down (still flying horizontally). Of course you gotta be up pretty high to get to full speed before dropping to the ground, but it's true.

Go figure.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

03-16-2006 Over year old.
spork

Veteran

Mountain View, CA

Not possible, however sailboats and windsurfers regularly go faster with a crosswind than the wind itself is blowing
As an avid kitesurfer I know this to be true. So to take that a step further, can such a vessel sail a downwind tack (say 45 degrees off the wind) such that his downwind velocity component is faster than the wind (in essence outrunning the wind)?

RC

03-16-2006 Over year old.
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zoom boy

Key Veteran

N.E. Lincolnshire UK

How about a glider, they are powered by thermals (which could be looked at as a vertical wind) then if the glider dives it can go downwind (talking about normal horizontal wind) faster than the windspeed because of the speed it gained in the dive.

03-16-2006 Over year old.
Mark C

Key Veteran

Houston, TX - USA

Can you make a vehicle that goes directly downwind, powered only by the wind, faster than the wind (no collecting and storing energy)?
My problem here is the wording. Either you are going downwind (with the wind at your back) or you are going faster than the wind (the wind in your face) take your pick. Can't do both sorry.

So what is it? Is the wind in your face or hitting your back?

Mark C.

03-16-2006 Over year old.
Pistol_Pete

rrProfessor

Seffner, FL

Spork...

Absolutely...

http://www.nalsa.org/

scroll down until you see "speed trial" I believe the first one is for 2001.

Regardless of the wording.

~~Enjoying the hobby one flight at a time~~

03-16-2006 Over year old.
HOMEPAGE  
Mark C

Key Veteran

Houston, TX - USA

Pisto_Pete

Agreed. If you disreagard the wording then certainly there you have it! Those guys are running those speeds crosswind or at steep angles to the wind.

They look like a blast! I would love to have one! Not too many places here in Houston you could play with one though.

Mark C.

03-16-2006 Over year old.
zoom boy

Key Veteran

N.E. Lincolnshire UK

If the glider answer isnt correct, then surely what about any vehicle where the wind is to your back, and the wind dies down, for a short time it will still have its momentum, so it will be now travelling faster than the wind in the direction of the wind until its speed drops off

03-16-2006 Over year old.
Pistol_Pete

rrProfessor

Seffner, FL

Ditto here Mark...instead I go sailing at sea...sailor at heart and plenty of salt water here. As a matter of fact tonight is full moon racing night...thrilling!

I intentionally gave up the wording despite my background. I have seen threads where a simple question such as blade balancing was taken way out of place. Then there was the precession one.... Not interested in a battle of the wits. I do respect those that acquired the knowledge but some just like to show off with I know more than you so bow before me attitude.

KISS works for me. Not looking to reinvent the heli...its just works. I just feel sorry for those that come in here seeking simple answers based on our personal experiences. Something we all have here regardless of education and how fat your wallet is.

Just living life to my fullest capacity instead of wasting time arguing...its an age thing.

EDITED:
Can't have a full scale one but have an R/C on the building table. Debating whether to go with a simple sail or a wing type.

~~Enjoying the hobby one flight at a time~~

03-16-2006 Over year old.
HOMEPAGE  
Mark C

Key Veteran

Houston, TX - USA

Cool Pistol_Pete!

I gotta agree. I even jumped in on the precession thread and gave it my best shot at explaining it to the guy (since that is what he originally asked for) but as the thread went on I realized I was wasting my breath and gave it up.
Can't have a full scale one but have an R/C on the building table. Debating whether to go with a simple sail or a wing type
I thought about doing the same and was thinking about putting a gyro on the tip over axis to keep it from blowing over.

Be sure to post photos up when you get it done!

Mark C.

03-16-2006 Over year old.
Pistol_Pete

rrProfessor

Seffner, FL

I realized I was wasting my breath
Instead you could have designed a sail car by now

I did not think of using a gyro but sounds interesting.

Using a thin and light pvc body and a breakaway aluminum axle for rear wheels. Only needs two servos, one for steering forward wheel and the other for sail. The size of project dictates size of servos as well their cost. The larger the sail the higher the torque needed.

Hopefully I can complete it within the next two weeks among all my other projects. My main problem is coming up with an excuse of why the sail looks exactly like the silk shirt mother in law gave me Unfortunately its not white.

Will post photos when completed...thats a given.

~~Enjoying the hobby one flight at a time~~

03-16-2006 Over year old.
HOMEPAGE  
bagobitz

Veteran

saddleworth,lancs,UK

P. P. BLEACH !
downwind...when you reach windspeed, you are in still air....if conserved energy allowed you to accellerate , you would have a headwind,which would slow you down , pdq.
Kokamo's idea was pretty ingenious,but would need a lot of stored energy to pass through the transitional head/tail wind phase.
as already posted, offwind is another story altogether,also,the headwind component increases with speed,unless you bear away....but the hypothesis was a fixed downwind course.
I was in on the early "C" class Catamaran wing-mast development...literally a vertical aerofoil about 25' tall,with the ability to be turned about it's axis....the boat sailed upwind without a stitch of sail up!

03-16-2006 Over year old.
spork

Veteran

Mountain View, CA

How about a glider, they are powered by thermals..."
Nope. I also fly sail-planes and hang gliders. As you correctly point out they aren't going directly downwind because of the vertical component. I'm looking for something that goes *directly* downwind, powered only by the wind, but "outruns" the wind. Steady state. No storing energy.
My problem here is the wording. Either you are going downwind (with the wind at your back) or you are going faster than the wind (the wind in your face) take your pick. Can't do both sorry.

So what is it? Is the wind in your face or hitting your back?
Mark, I followed your posts on the precession thread, and then checked out some of your other posts. I have great respect for you intellect and your sense of humor. I'll try to clarify the wording. I'm speaking of wind in the typical sense. Air moving relative to the ground. I'm not speaking of the relative wind that you would feel in the face once you begin going faster than the wind, downwind.
...what about any vehicle where the wind is to your back, and the wind dies down, for a short time it will still have its momentum, so it will be now travelling faster than the wind in the direction of the wind until its speed drops off
I like it, but it's not what I'm looking for. I'm imagining a steady-state solution, where you can beat the wind downwind as long as it blows.
Not interested in a battle of the wits. I do respect those that acquired the knowledge but some just like to show off with I know more than you so bow before me attitude.
Bear in mind - the title of this thread is "annoying brain teaser". I hope no one is looking at it as a "battle of wits". I enjoy the crap out of these things. This thread is for others that do too.
I even jumped in on the precession thread and gave it my best shot at explaining it to the guy (since that is what he originally asked for) but as the thread went on I realized I was wasting my breath and gave it up.
I gotta agree with you there. I did the same thing. That's when I searched back and saw an explanation you already posted that I think was very simiilar to mine. It seems he wasn't really looking for an answer. For the record, neither am I. It's a brain teaser (of sorts). I wouldn't ask it if I didn't already know the answer. But it's not a trick question.


That being said, I'll post the answer(s) if you like.

RC

03-16-2006 Over year old.
HOMEPAGE  
GimbalFan

rrProfessor

Big Coppitt Key, FL

Any movement with the wind directly at one's back cannot possibly be any faster than the wind itself.

With any degree of angle other than direct though (disregarding the effect of hull or wheelbearing friction at those low angles), the vehicle should be able to move faster than the wind, up to a point that the angle differential is somewhat greater than 90 degrees forward of the 'stern.' I imagine that the ratio can continue to be greater than 1/1 well past that 90 degree mark. Sailors?

An interesting sidebar to the initial question might be: What angle to the wind results in the greatest vehicle/wind speed differential, and is that angle the same for landsailers as for boats?

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

03-16-2006 Over year old.
Topher

Veteran

Rochester, Michigan

Could this be a solar wind?

03-16-2006 Over year old.
HOMEPAGE  
bagobitz

Veteran

saddleworth,lancs,UK

An interesting sidebar to the initial question might be: What angle to the wind results in the greatest vehicle/wind speed differential, and is that angle the same for landsailers as for boats?
Gimbal, about 10 years since I last sailed, so the theory's a bit rusty.
assume you start with the wind at90* to direction of travel..(a Reach in sailing terms) as the boat accellerates,it introduces a headwind component...(imagine it moving at that sped in stillair)
so now your APPARENT wind is forward of the beam..the sails are actually airfoils and have to be trimmed to keep a laminar flow..the foresail in conventional"yacht" rigs,PULLS the boat along and funnels the air over the front surface of the mainsail,which,again,PULLS the boat along
when the boat is moving, as above, you can "bear away"and bring the TRUE wind towards the rear..but with the headwind component,the APPARENT wind can be kept on the beam.....the aerodynamic "pull" also explains how a boat sails AGAINST a headwind, albeit at a maximum45* off the eye

It's a bit like slow-motion, 2d, planking in very thick air, really Oh, yea, the crashes tend to be a bit more survivable!

03-16-2006 Over year old.
GimbalFan

rrProfessor

Big Coppitt Key, FL

I'm seriously tempted to pick up one of those 1m RC sailboats to fool around with between trips to the airfield.

Anything that involves fluid dynamics really tweaks my knobs.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

03-17-2006 Over year old.
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