will it take off?

   / will it take off? #901  
I watched a fellow running on a treadmill once. Aside from getting real sweaty and inhaling huge lung fulls of air he just could not seem to go anywhere. No doubt his cardiovascular system was thanking him!:D

Musta been the shoes he was wearing wouldnt let him get ahead. But maybe as his boss was into fitness he was getting ahead!:D :D
 
   / will it take off? #902  
SPYDERLK said:
Pat, I must admit I am a bit baffled

Wheels store energy both translationaly and rotationally. In the case of wheels, the conveyor manipulates the plane by thrusting the contact patch on the wheels. Acceleration of this contact patch is resisted by the mass of the wheels factored against their moment of inertia. In our case the acceleration is rearward in order to cancel the planes thrust via the connection at the axle. In a perfect sense, relying only on accelerating rotational mass for the counterthrust, the wheels are storing energy at the same rate as the engine is putting it out. The energy doesnt come from the engine - it comes from the conveyor resisting the thrust of the engine. The energy stored [HP x T] is available to be fed back to the plane if the conveyor is slowed at a rate that prevents a peel out.

++++++++++++++++++++++++++++++++

With skis, as with wheels, the thrust of the plane can only be countered up to the point at which they slip. With skis on hardpack Im guessing that dynanic slip occurs at a force of about 0.01 to 0.02 of the weight the ski supports. With tires on pavement this value is static since the tire doesnt have to slip to move, and is usually high within the 0.5 to 1.0 range - enuf to counter the thrust of most planes. We are talking a multiple of 50 over the skis. It doesnt seem like ski drag would ever increase to the point of balancing a thrust-to-supported-weight ratio of anywhere near what even a normal plane has. While acceleration of the conveyor has no effect, since with skis there is nothing for the acceleration to work against because of slippage, the speed of the conveyor may. Thats where I have a problem. The quandary of low drag at high enuf speed being power, but having no apparent ability to cancel thrust in excess of said drag. I would really love to have this "click".
larry

Larry, I am pretty much "with you" on the above down to the ++++ including having the rapidly spinning wheels help accelerate the plane if the conveyor slowed down.

Where we part company (in our analysis) is at your statement, "With skis, as with wheels, the thrust of the plane can only be countered up to the point at which they slip."

I don't agree with yor statement as applied to the case of wheels or skis.

The conveyor would have to speed up dramatically after the tires began to slip in order for the slipping tires to create the lateral force required to equal the prop's thrust where in reality a blowout would soon follow from overheating, wearing right through the tire to the metal wheel, and such minor difficulties but for our theoretical idealized case we will assume the tires to be pretty magic too.

It takes more energy (per unit time or looked at another way a greater distance) to slide skis rapidly than to slide them slowly. Even if the coefficient of friction DID NOT CHANGE with speed (which it surely will in our high speed sceanario approaching relativistic speeds) the lateral force applied to the skis by the weight on the skis, the coefficient of friction, and the distance traveled per unit time, increases with speed. In the case where we have a magic conveyor, the conveyor runs up to the speed required to produce the lateral force equal to thrust.

In your rocket example which I DID NOT EXAMINE REALLY CLOSELY, I suspect that on close examination you will find that the equivalent HP of the rocket thrust does not change over time. The rocket will accelerate at a non linear rate with static thrust due to the rocket's mass being reduced at the rate of mass ejection out the nozzle. Simply firing a rocket engine for an extended time is NOT a way to make it more powerful. (Now for a probably unneeded caveat: the above rocket talk assumes non-relativistic, i.e. Newtonian physics.)

Too bad it doesn't work like that. It would be sort of a reverse reciprocity effect where the slower you expend a rockets fuel the more work you get done. Applying the argument of reductio ad absurdum, we see then that as the rate of burn approaches zero the ultimate work done approaches infinity so if you would only be willing to start a long time in advance, accelerating very slowly, you would ultimately approach the speed of light with the rocket.

If you disagree with the above rocket science conclusion then it is incumbent on you to find a flaw in either the logic or the premises or both. I think the logic is pretty air tight and the premises are yours. I guess maybe NASA hasn't overlooked a great boon to rocket science and you and I will not be going to Sweden to collect lots of $ for this idea.

Dang, and we could have just gone hog wild at Harbor Freight, bought all the cheese we wanted, and upgraded our movie channels on Dish.

Side note: I went to HF yesterday with a friend to get a particular tool. We came home with a few hundred bucks worth of treasures but not the tool for which we ostensibly went. It is internet only now and the lightweight version solld in the store did not blow my kilts up.

Pat
 
   / will it take off? #903  
Pat -- let me rephrase my question in a non-theological way.

Imagine our plane is equipped with only one wheel. The wheel is essentially spherical and rotates on an axis perpendicular to the fuselage, as a normal wheel would. Now, as the plane and conveyor undergo their relative motions, the wheel rotates at some decent amount of rpm on this axis which is also perpendicular to the motion of the conveyor. Once this rotation is taking place, can the plane and wheel be made to rotate on a vertical axis passing through the equator of the wheel, perpendicular to axis of rotation of the wheel and also perpendicular to the conveyor?

That's all I'm asking -- in your retired professional opinion, can a rapidly rotating massive body simultaneously rotate on two perpendicular axes?
i.e. can you make a big gyro flip rapidly end over end while it's spinning?

My understanding of rotational inertia says it can't happen regardless of what the conveyor is doing.
 
   / will it take off? #904  
Talking about rockets, if a rocket was launched in a 100mph down draft could it lift off,
 
   / will it take off? #905  
Egon said:


They may be cremated!:D :D :D Or the body may be lost to some sort of mishap and never be recovered!:D :D :D

Don't say cremated....that involves a conveyer you know. :D
 
   / will it take off? #906  
RobS said:
Ah, but this is the debatable point in the excercize. One could argue that there is some resistance in the wheels that will counteract the prop thrust. While unlikely, the possiblility is certainly there.

Maybe they just left the parking brake on. :D
 
   / will it take off? #907  
daTeacha said:
The waves in the air resulting from the falling of an object are just waves until a brain interprets them as sound.

So a deaf scientist can argue there is no such thing as sound? So a dogs whistle really doesn't make any sound(because I can't hear it), just a quoincidence that dogs come a running.

Why will sound waves produced by sound break a glass...in a room full of deaf people.

Thunder will break a window if the town is empty.

If I hold my nose does that mean there is no smell? (Hang around after some bean chili. :D)

I can't see air...so is it really there?

If I close my eyes does that mean there no light? Infra red light is just a lie?

Velvet feels the same as concrete if I never touch it?

And I guess a bear doesn't crap in the woods...as long as I don't see, feel, touch, smell it. :D

And if the trees were cut down...I could see the forest. :D

Heck maybe red is really blue and blue is really yellow. and yellow is really red, heck they are just names we gave them.

:D:D:D
 
   / will it take off? #908  
RobJ said:
So a deaf scientist can argue there is no such thing as sound? So a dogs whistle really doesn't make any sound(because I can't hear it), just a quoincidence that dogs come a running.

Why will sound waves produced by sound break a glass...in a room full of deaf people.

Thunder will break a window if the town is empty.

If I hold my nose does that mean there is no smell? (Hang around after some bean chili. :D)

I can't see air...so is it really there?

If I close my eyes does that mean there no light? Infra red light is just a lie?

Velvet feels the same as concrete if I never touch it?

And I guess a bear doesn't crap in the woods...as long as I don't see, feel, touch, smell it. :D

And if the trees were cut down...I could see the forest. :D

Heck maybe red is really blue and blue is really yellow. and yellow is really red, heck they are just names we gave them.

:D:D:D

To him there isn't, but I said "a" brain without specifying human.

Yes there is since the dog's brain can hear it.

Because the glass vibrates sympathetically with the correct frequency, resonates if the shape of the glass is correct, and the motion of the molecules of silicon dioxide vibrate enough to separate from one another, causing the glass to lose its structural integrity and fall apart.

Thunder is a very seriously large wave of alternating high and low pressure. If the window is large enough the difference in pressure inside to outside during the passage of the wave causes the window to bow in and out, ulitimately breaking the glass the same as if you pushed on it hard enough.

You "smell" things because molecules of that substance are landing on your olfactory organ (buried deep in your nasal passages) and causing nerve messages to pass to the olfactory center of your brain. "Smell" is simply molecules in your nose -- remember that next time you clean out the barn.

Yes, but you can't visually prove it unless you have a lot of it to look through.
"Light" is a term used to describe a certain portion of the electromagnetic spectrum. Originally it was reserved for that portion to which nerves in the human eye are sensitive, but we now of other organisms that can sense in a similar manner other frequencies, and therefore use the term to refer to those, too. Your microwave works with the same stuff, travelling at the same speed, but with a different wavelength. So does your car radio, non-cable TV, cell phone, speed radar, etc. The proper term to cover all of it would be electromagnetic radiation.

Neither one feels like anything to you if your brain gets no information about it.

Yeah, but not the one that used to be standing in front of you.

Absolutely right. We have no definitive proof that what I think of as red your brain might not call blue if we could get the same thing going on in both of them. We were both trained early on that the wavelengths that cause that particular activity in our brain were called "red" so that's what we call it.

Rattlesnakes can sense infrared with special organs, the eyes of a bee are sensitive to ultraviolet. A brain interprets those wavelengths in a manner akin to our vision, so we call them "light". Dogs ears and those of bats for that matter, are sensitive to wavelengths that are far above ours, but those are "sounds" since some brain hears them. Whales use frequencies far below those which the human ear responds to, but those are also "sounds" since a brain interprets them as such.


If you want something to puzzle over, explain how to describe a color such as yellow to a person who has been blind since birth, a sound to a person who has been deaf since birth.

It all goes back to the old saying about beauty being in the eye of the beholder but the "eye" is actually the brain's interpretation of the message sent to it by the eye. That's why some of us like red tractors, some green, some blue and some orange. :)
 
   / will it take off? #909  
daTeacha said:
That's why some of us like red tractors, some green, some blue and some orange. :)

Rich...I was just funning around man. :D

BTW, maybe your red tractor is really orange, and green is really blue. How do ya describe a MF to a blind person?

OK STOP!!!! I'm just kidding!! :D:D

But now what causes the glass to vibrate? Not sound waves...but goober waves!!! :D:D:D Sorry going back to work now...
 
   / will it take off? #910  
RobJ said:
but goober waves!!!


Goober waves??? There was this scientist who would be interested in your brain. His name was George Washington Carver. He did lots of things with goobers. ;) ;)


Oh, and daTeacha... rigidity in space, if memory serves...

Here is a plagiarized bit on gyroscopes. I shamelessly copied it from a web site AND made minor edits.

gyroscope (jī`rəskōp'), symmetrical mass, usually a wheel, mounted so that it can spin about an axis in any direction. When spinning, the gyroscope has special properties. Many spinning objects exhibit some of these properties; the rotation of the earth about its axis gives it the properties of a huge gyroscope. Once a gyroscope starts to spin, it will resist changes in the orientation of its spin axis. For example, a spinning top resists toppling over(usually, with most tops), thus keeping its spin axis vertical. If a torque or twisting force, is applied to the spin axis, the axis will not turn in the direction of the torque, but will instead move in a direction perpendicular to it. This motion is called precession. The wobbling motion of a spinning top is a simple example of precession. (why the blurb on gyros did not mention nutation is beyond me, it should) The torque that causes the wobbling is the weight of the top acting about its tapering point. The modern gyroscope was developed in the first half of the 19th cent. by the French physicist Jean B. L. Foucault, and its first notable use was in a visual demonstration of the earth's rotation. In the second half of the 19th cent., with the invention of the electrically driven rotor, its uses multiplied. It became possible to rotate the gyroscope's wheel at desired speeds without interfering with the precession. Large gyroscopes are used in ship stabilizers to counteract rolling. The gyroscope is the nucleus of most automatic steering systems, such as those used in airplanes, missiles, and torpedoes. It is also used in the gyrocompass, a directional instrument used on ships. Unaffected by magnetic variations, its spinning axis, when brought in line with the north-south axis of the earth, provides an accurate line of reference for navigation.

All this said (above), I have a top that has axial symetry and when given a good spin by thumb and forefinger applied to a little knob on top and set on a smooth surface it spins nicely for a bit and then becomes unstable and flops over on its side and then transitions upright and continues to spin but upside down on the little knob used to impart the spin. Drove some of my physics profs batty while they contemplated the little "dime store" novelty that seemed to easily violate the principal of gyroscopic action, rigidity in space.

There were no hidden weights, the plastic was the same thickness top and bottom (top and bottom were of contrasting colors to better illustrate that it flipped upside down and were glued together along the "equator."

Pat
 
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