Pitchless prop

[Wufnu]

Do they make a prop without pitch, airfoil only? I was just wondering if it would ever work. You could have fairly large propellers going at insane RPM to provide lots of pull with zero thrust.

[Jeffery]

. to provide lots of pull with zero thrust.

Sort of an oxymoron, is it not??

[Wufnu]

No. Thrust is the propellor pulling the plane via pushing air, much like a paddleboat. A pitchless propellor would pull without thrust, like a wing in Bernoulli's equation.

Ever taken one of those giant foam gliders from Walmart and spun while holding one of the wings? It really pulls up hard, but doesn't blow air down. Lift, via differing pressures due to varied velocities. It's what makes planes fly :(

[flatfour]

http://www.amasci.com/wing/airfoil.html

[Bill Mixon]

I guess this would depend on the airfoil, but for the most part 0 AOA will equal little thrust / pull or whatever you want to call it. You need some pitch, or you'll never fly and airplane because you will not have the speed you need.

[Wufnu]

I imagined something along those lines, as the blades would pass through the air so quickly that the variations in pressure would be minimal. Perhaps a little bit of pitch, like a rl heli, would be a solution. Mainly, I'm curious how much power you can get out of a small motor spinning a big prop, ungeared.

Thinking now, if there was something to it it would be done already I'm sure.

[Cas123]

And how would you counter act the torque this large diameter prop would have. The plane would do as much rotating as the prop.
Ron...

[Wufnu]

http://amasci.com/wing/airgif2.html

"In the lefthand diagram, the air approaches the wing horizontally and also leaves the wing horizontally. This violates Newton's laws, since by F=ma there cannot be a lifting force unless air is accelerated downwards. The wing must deflect the horizontally-moving air downwards, as shown in the righthand diagram."

I would have to disagree. Pressure in a fluid, as we all know, has force in all directions (otherwise it wouldn't be pressure). The air IS accelerating, it's accelerating upwards (via lowerpressure caused by increase in wind velocity) and the plane is accelerating downwards. All air is in a state of upwards acceleration due to pressure, because otherwise air would always be falling downwards due to gravity. They balance each other out. Action, reaction.


Second picture, "Pulsed smoke streams illustrate that the parcels of air which are divided by the leading edge DO NOT recombine at the trailing edge. Therefor the "wing shape" explanation of lifting force falls apart." Look at that picture. Count the rows of smoke before and after it meets the airfoil, THEN look at the trailing edge of the airfoil. What do you see? Heck, measure the space between the two smoke trails that the airfoil passed through. How much as the smoke displaced, around 10-15%? Here's a better way to measure it. Create a vertical line (perpendicular to as many smoke trails as possible) and make that your Y axis. Now, measure the length of the line that goes over the top and then the line that goes under the airfoil. One's longer than the other, and since that happens over the same amount of time, the velocity of one has increased.

Picture three, "The real reason for the rapid flow of air above the wing is never explained in "Bernoulli"-based textbooks." That's an outright lie. The entire principle that the professor lables as the real reason planes fly is a paddle. When the boats moving, ever held a paddle over the edge? It goes up, it's true. The good professor just said that it wasn't because of a lowerpressure on one side. Here's why the smoke that went over the top got faster: as the smoke travels around the wing, it MUST speed up therefor lowering the pressure. The increased velocity on the bottom is equally matched by the compression of the air, thereby retaining its initial pressure. The air that goes over the wing speeds up, and is then sucked by the lowerpressure created by the void left as the wing passes through the air. P1 + 1/2 p(1)v(1)^2 + k(1) = P2 + 1/2 p(2)v(2)^2 + k(2)!! That's Bernoulli, sounds pretty explained to me.

I think he got off on the wrong start when he seperated angle of attack and the bernoulli principle. They're both one and the same.

I'm not entirely sure what the professor is trying to prove here, but he's doing it with faux science and I resent it. It takes me a few minutes to explain why his "facts" are wrong, he obviously didn't put much time into it. I'll even requote some of the more amusing ones.

"In the lefthand diagram, the air approaches the wing horizontally and also leaves the wing horizontally. This violates Newton's laws, since by F=ma there cannot be a lifting force unless air is accelerated downwards." In his hours spent studying a picture, he didn't take the time to learn the physics of acceleration. He can't SEE the acceleration, therefor it doesn't exist.

"Pulsed smoke streams illustrate that the parcels of air which are divided by the leading edge DO NOT recombine at the trailing edge." Yes it does. My eyes are fine. While the exact molecules might not meet up, when the plane is gone that airspace will return to complete force balance. It's inevitable.

"In the past I've spent time as an embedded designer and software engineer, consulted on textbooks, lectured about electricity education, designed science projects for kids, and built physics exhibits while at the Museum of Science in Boston." Perhaps he should take a fluid mechanics course :( I'm all for new ideas and theories, but his entire article is a hall of smoke and mirrors caused by assumptions and lack of understanding. He even says it's impossible to create lift just because the smoke isn't pointed downwards after it passes the trailling edge; 100% not true. Angle of attack is important to lift? Of course it is. A bernoulli based airfoil can't create lift without forcing air downwards? Folly.

Edit: Removed a mistake on my part. Sorry :)

[Wufnu]

I don't know Cas. I'm not sure how much moment it would create, but I imagine if it airfoil is designed right it would be minimal. I would be more concerned with the gyroscopic effect, although I don't know if such a small mass would create one that would be noticeable on a small model.

[Cas123]

I think the losses of spinning a large pitchless prop at high speed would end up being greater than spinning a smaller piched prop more slowly.
Remember at max level flying speed if the prop size and pitch is carefully selected, pitch is almost cancelled by the plane's forward movement through the air, resulting in almost no effective pitch. A pitchless prop would stop providing forward motion as soon as the plane started moving.
A planes wings work because it moves along the horizontal plane. look at how much power and extra speed is required to make a plane climb in level flight without using the elevator to create some wing pitch.

Wings on aircraft do have pitch I believe, its called angle of attack. correct me if I'm wrong.
Ron....

[Wufnu]

Angle of attack is right on.

"Remember at max level flying speed if the prop size and pitch is carefully selected, pitch is almost cancelled by the plane's forward movement through the air, resulting in almost no effective pitch."

I didn't think about that, good call. I figured it would be a silly notion, but since I couldn't think of a reason why not, I figured I would ask. Thanks for a reason not to, hehe.

[Cas123]

Hey, Remember some " silly notions " turn out to be great Ideas, but you will never know until you think them through and debate them. "Silly" is when you can't be bothered to check them out.
Cheers, Ron...

[vintage1]

I think a course in high school physics is advised.

And a dictionary :D)

[Cas123]

Couldn't agree more vintage1, but who has the time. I'd rather be flying my planes. They seem to stay up there so why worry. :p

Ron...

[Wufnu]

Did I make that many spelling errors? :( I didn't even look.

[henke]

Hi

some one mentioned angle of attack...

even with no angle of attack the foil makes the air go down or (back if a prop) resulting in a force in the opposite direction...

I agree with those who think a plane flies by thronging air down... with use of aoa, not very much by the common explained curved foil which creates underpressure... where inverted flying or knifedge would be inpossible ;)

/Henke

[Wufnu]

"where inverted flying or knifedge would be inpossible"

Not with a large enough aoa. Enough aoa and power, and anything will fly inverted. Aoa is the greater force, but not the only force, and certainly isn't "why airplanes fly."

Found a nice picture of net forces to perhaps explain what I'm trying to say.

http://static.howstuffworks.com/gif/airplane-pressure.gif

[tim hooper]

And a dictionary :D)

Glass houses, Vintage............

tim
:p

[Wufnu]

Ok, I'm not as smart as I thought I was. I was wrong about the equal time. There's more to it than I was thought, and the equal-time longer distance method doesn't stop in high school (belive me, it goes way up). Alot of my points still stand, and some of the things the article said is not only wrong, but silly. Either way, I'll go on a wiser man and attribute this one to too much vinegar and "the folly of youth." :)

As a lesson in humility, I'll leave the rest of my mistakes up there.

[Aio_1]

........ Aoa is the greater force, but not the only force, and certainly isn't "why airplanes fly.".....

Firstly,

Angle of attack is not a force!!!!


Secondly,

AoA is usually defined by the angle to the ambient airflow of a line drawn from the furthest forward point of the airfoil to the furthest rearward point. This is really just an arbitrary datum. You could call this the geometric AoA.

Zero lift AoA is defined as the AoA at which the airfoil does not provide lift. Zero lift AoA is the same as Zero geometric AoA for symetrical airfoils but not for cambered airfoils. The angle of the airfoil to the airflow is fundamental to the production of lift.


Back to your original question:

In the case of a prop AoA varies along the length of the blade and at different rotational and forward speeds. However, essentially the AoA of any part of the blade is a function of pitch.
A 'pitchless propellor' will produce static thrust only if you're measuring pitch based on geometric AoA. ('Lift' and 'thrust' are just names for forces. The lift from a wing is the same as the thrust from a prop!) If you define 'pitchless' as the zero thrust case then obviously a pitchless prop provides zero thrust.

If you define 'pitchless' as zero geometric mean AoA then you could produce some thrust but only at VERY low speeds so that it would only be suitable for helicopters.

Aidan

[Wufnu]

"Angle of attack is not a force!!!!"

Whoops, just slap a "cause of" there before those forces I mentioned.

[Jeffery]

No. Thrust is the propellor pulling the plane via pushing air, much like a paddleboat. A pitchless propellor would pull without thrust, like a wing in Bernoulli's equation.

Ever taken one of those giant foam gliders from Walmart and spun while holding one of the wings? It really pulls up hard, but doesn't blow air down. Lift, via differing pressures due to varied velocities. It's what makes planes fly :(

Ahhhh.... When I was leaning about "what makes planes fly", all they mentioned was: Lift, weight, thrust, and drag. They never mentioned pull.

Do a Google search for: "Lift, weight, thrust, drag ". Lots and lots of places discuss these, the 4 basic aerodynamic forces. Ad "pull" to the search and see where you get.

Just giving you a bit of a hard time, I sorta have an inkling about "what makes planes fly".

[vintage1]

Did I make that many spelling errors? :( I didn't even look.

Not spelling errors. Errors of usage. If you want to use a term in a definite technical sense, its a good idea tioo use it in - er - a definite technical sense.

I.e. one dows not normally measure the power of the white house in kilowatts, or the thrust of Geroge Bush in ounces, but when talking technical rather than just dirty, it helps to use them in the strict sense that engienners do.

Otherwise what comes out is not a technical discussion, but something more akin to Modern Art.

I.e. very interesting, if you can relate to it, and something that looks like a pile of dog poo if you can't.

:D

[Wufnu]

Jeff, only reason I wanted to seperate them as what was I was invisioning was a spinning piece of plastic without any moving air.

As long as people may have had some idea of what I was trying to say, I'm too tired to care :( If they didn't, I'd be happy to explain it later if I can remember what I was thinking at the time.

[Cas123]

Talking about angle of attack, Isnt that the principle kites use? They don't seem to have much of a airfoil shape.
Ron...

[Hasher66]

Wufnu hit it right on the head.

This is the basic reason that all airfoils work, even flat sheets. Flat sheets can function just like regular airfoils, (flat sheets are in fact airfoils with zero camber), because of angle of attack. Flat sheets are fairly inefficient as lifting surfaces at low speed, because the high angle of attack required to make them function as an airfoil, creates a lot of drag. At higher speeds, they work a bit better, because the angle of attack is much less, and the profile drag of a flat sheet can be very low, at low angles of attack, (F-104 Starfighter has nearly flat airfoil).

As a thought experiment, picture two air molecules approaching the leading edge of an airfoil. One molecule travels under the wing, and the other travels over. The one moving under the wing takes exactly the same amount of time to traverse the chord of the wing, as the molecule above the wing. Since the molecule on the top of the wing is traveling a farther distance, (travelling along a curved line, vs going in a straight line), the molecule above the wing must have traveled along the chord at a higher velocity. This higher velocity results in lower pressure above the wing, thus the pressure differential causes the wing to move upward.

This works really well, if the flow around the airfoil is laminar. Eventually, the airflow will become turbulent and separate from the airfoil at some point past the peak of the airfoil. The longer the airflow stays attached to the wing, (i.e. closer to the trailing edge), the more efficient that airfoil will be in it's lifting and drag performance. When a flat sheet is given an angle of attack, it effectively creates an airfoil shape, (as seen by the airstream). It can be pretty inefficent, because the airflow becomes turbulent very quickly past the leading edge. It works, it's just not very efficient.

For 3D planes, there probably is a component of "thrust vectoring" that the wing is providing, which is deflecting the airflow from the prop downward, and giving the plane upward movement as a reaction to that impinging airflow. This probably has some positive lifting affect, but this is really more like the effect of a control surface.

I know this would be more clear with a drawing, so if anyone is really interested, I'll put one together.

I'd like to put in my 2 cents with respect to that "professor" who espoused his theory on why airfoils work: He's an idiot, or a nut job.

Chris

[Wufnu]

"As a thought experiment, picture two air molecules approaching the leading edge of an airfoil. One molecule travels under the wing, and the other travels over. The one moving under the wing takes exactly the same amount of time to traverse the chord of the wing, as the molecule above the wing."

That's, actually, not true. That's what started my foot on the path to my mouth :(

[Cas123]

I presume you're refering to post No#8 Chris. In which case I must admit its a bit offbeat. I'm no Aerodynamicist but in laymans terms, an ideal airfoil creates lift by increasing the distance the air must travel along the top of the airfoil compared to the air travelling under the airfoil therefore thinning it out, hence lower pressure. the pressure on the bottom of the wing does not change much at all except for an increase under the leading edge. An important factor being that there must be minimal or no separation of air from the wing surface.

A flat lifting surface uses AOA, causing compression of air under the wing by deflection, and lowered pressure on the top surface by air being diverted by the leading edge from reaching there. The diverted air contributing to the under surface compression. this causes separation of air from the top surface resulting in turbulance and drag on the top of the wing.

Have I got it right or can someone shoot me down in flames. :o
Ron...

[Wufnu]

Kinda of, but not really. In all honesty, the best explanations I have found were at howstuffworks.com Read their tutorials, and the "other peoples webpages." Just be careful about what you take to heart, you might find someone like that first article :(

[DaveA]

Chris,

On a well-designed airfoil, when two molecules of air start over the top and under the bottom together, the one over the top gets to the back of the wing considerabley BEFORE the one under the bottom. I did not believe this until I was given a wind tunnel demo of it by a friend who is an aero engineer. He pointed out that if you do the calculation of the pressure difference with Bernoulli's equation assuming that the air over the top and under the bottom arrived at the TE together, a Cessna 172 wing would produce about 20 pounds of lift, no where near enough to fly! This phenomenon has been well-known to aerodynamicists for 70 or 80 years, so it is very puzzling why the old "air over the top has to go farther to get to the back at the same time" explanation has persisted so long.

- - Dave

[RonD]

I presume you're refering to post No#8 Chris. In which case I must admit its a bit offbeat. I'm no Aerodynamicist but in laymans terms, an ideal airfoil creates lift by increasing the distance the air must travel along the top of the airfoil compared to the air travelling under the airfoil therefore thinning it out, hence lower pressure. the pressure on the bottom of the wing does not change much at all except for an increase under the leading edge. An important factor being that there must be minimal or no separation of air from the wing surface.

A flat lifting surface uses AOA, causing compression of air under the wing by deflection, and lowered pressure on the top surface by air being diverted by the leading edge from reaching there. The diverted air contributing to the under surface compression. this causes separation of air from the top surface resulting in turbulance and drag on the top of the wing.

Have I got it right or can someone shoot me down in flames. :o
Ron...


Actually the professor is right! The problem is that you have been told the bernoulli lie for so long/so many times that you finally believe it!

[Fred Bronk]

Moving this over to Modeling Science.

This has little to do with power systems now it is purely theotical now.

Remember guys, what happens on paper has proed to be wrong many times in pratice.

FB

[steve lewin]

In my view one would have to be excessively simpleminded to imagine that any single theory can explain the whole of the complexity of lift. Bernoulli's theory works brilliantly to explain flow in venturis, which is what Bernoulli proposed it for. However a wing is not a venturi. Coanda adds some interesting insights too. All of it can also be explained by the sensible application of Newton's rather basic laws.

If you just want to understand why planes don't fall to the ground and when they're likely to, stalls etc, you can use any explanation that appeals to you. Most of the simplified ones being discussed are not for airfoil designers they're for pilots. OTOH if you need to calculate exactly how much lift will be produced by an airfoil of a defined shape in a particular attitude it's going to get a lot more complicated yet.

Steve

[Purdue Aero Man]

Lift is a function of three things in a typical airfoil: 1) AoA, 2) Camber, and 3) thickness. By the method of superposition, you can get a fairly accurate estimate of the airfoils lift characteristics. By taking out the pitch of the propeller, i.e. the AoA, you can still get a propeller that works, but since the camber of the blade would be very large, the propeller would likely be very sensitive to to the angle of attack the blade was seeing. Turbine blades in jet engines are a good example of very low AoA, highly cambered airfoils. Compressor blades are even more sensitive to the AoA than are turbine blades, because of the adverse pressure gradient and the possibility of massive flow separation and possible surge. BTW, good discussion guys. Funny to see that the old "air on the upper surface is moving faster to make it to the end at the same time" theory is still being propogated out there. Cheers.

[vintage1]

In my view one would have to be excessively simpleminded to imagine that any single theory can explain the whole of the complexity of lift. Bernoulli's theory works brilliantly to explain flow in venturis, which is what Bernoulli proposed it for. However a wing is not a venturi. Coanda adds some interesting insights too. All of it can also be explained by the sensible application of Newton's rather basic laws.

If you just want to understand why planes don't fall to the ground and when they're likely to, stalls etc, you can use any explanation that appeals to you. Most of the simplified ones being discussed are not for airfoil designers they're for pilots. OTOH if you need to calculate exactly how much lift will be produced by an airfoil of a defined shape in a particular attitude it's going to get a lot more complicated yet.

Steve


What is also not appreciated, is that two theories can be in fact saying exactly the same thing.

For example you can describe a sine wave by the actual formula of amplitude=A sin w, where w is the angular frequency, or you can say it is simply A (2 pi w) where it is represented by a single amplitude and frequency.

To convert one way of looking into another you use a transform - in that case the Fourier transform.

Bernoulli and Newton etc. etc. actually are TRANFORMS of each other..that is they each say the correct thing, but in two different ways.

Neither is absolutrely correct because they treat air as in incompressible liquid, and therefore incapable of vortex generation etc etc. So both are approximately correct for lamminar airflow - what you nearly get over a very smooth glider wing operating efficiently. True totally laminar airflow implies zero drag wings, from memory. The fact that they aren't zero drag shows you its only approimately true, right off.


If you plug in 'real' air the equations move to the nearly insoluble. I had a discussion with one of the techies at an F1 racing team. The best computers they have can still not reliably model airflow over the whole car - it simply takes too long to get the accuracy needed. They can get a better estimate faster using a model in a wind tunnel, but even that doesn't tell the whole story - because once out on the track with bumps in the road and crosswinds, the slipperiest shape can suddenly stall and give high drag under non-ideal conditions. Remember those Le mans cars taking off ?

None of this invalidates basic theory. Its just that simplified forms of it have limited applicability. By its very nature turbulent flow is chaotic and cannot be exactly modelled by simple linear equations. Otherwise we would have perfect weather forecasting by now. :D

It has been a general principle of engineering that the best way to proceed is to find things that are relatively reliable and simple to model, and build machines that use the materials around in the areas in which they behave themselves reasonably well.

Aircraft based on (modified=fudged) laminar flow theory work quite well and accord with a hodge podge of theories close enough to work...until you get near the stall, or the speed of sound. At that point the approximations inherent in laminar flow or adaptations of it become so serious that all bets are off.

This, however, does not excuse the sort of dialectic that goes 'OK these theories are all junk, therefore any crackpot theory is equally good' which I have seen time and time again.

That is tantamount to saying 'if a piece of fishing line streches 1mm with 1lb hanging on it, but breaks when I hang a ton on it, the elastic theory is proved to be wrong, and therefore I will propose a theory of infinite extensibility of fishing lines' and expect to be taken seriously. Elastic theory is NOT wrong, just LIMITED. It happens to be approximately correct for a certain class of solids undergoing small strains. If you go down to the atomic level and look at molecular bindings etc etc, you can get a much more complete, but much less USEFUL theory.

Aerodynamics - you have a choice. Use a simple theory inside known limits of applicability, or a hugely complex one that ultimately tracks the path of every air molecule from infinitely far away to infinitely past your model, and, uses a computer approximately as large as the known universe. In fact there is a school of thought that says its EXACTLY as large as the known universe, and the unknown bits of it as well...

And then you get into the whole philosophy of information theory, the computability of functions, the validity of reductionism in real world situations etc etc etc. You know, the sort of stuff the swots did after you left college and keeps them in PHD theses forever :D

Or you can use some fudged approximation in between. Which is basically what most of real world aerodynamicists do.

Plough through enough of it and the message is clear. Nothing can be proven to be correct in absolute terms (Godel incompleteness theorem, Heisenberg uncertainty principle, noty to mention Schroedingers dear old cat etc. etc.), there is no formula that we CAN come up with that COULD explain everything and allow everything to be predicted. The only final answer to anything is to run it on the biggest computer we have, for as long as possible, and see what happens. Its called Living In the Real World :D

Even if we decide that e.g. quantum physics describes the real world exactly , there is still a problem in that quantum physics is non linear - and leads to chaotic solutions. Therefore the computing power needed to accurately predict outcomes is infinite, in the limit. And, in the limit, switching the computer on affects the way the experiment goes......(e.g. butterfly effect)

Sorry to rant on. But having spent most of my life struggling to work out how to find out what is true and what is not, and coming up with the answer 'no one knows, but at least some people take understanding the limits of knowledge and theory seriously and really get to grips with it'. I do get a little grumpy when someone comes along and says they have heard about a 400% efficient motor or whatever, or some other perpetual motion machine.

Maxwell invented one a century or two ago. Its called Maxwell's Demon. It would generate infinite energy. Trouble is, no one knows how to make it.

By definition, a pitchless prop is an oxymoron. It does nothing. It doesn't propel. At best it may be low drag, at the worst, it just makes a lot of noise stirs the air up and wastes power.

sigh. I think its past my bedtime. I have a library of science fiction and fantasy, that doesn't pretend to have ANYTHING to do with the real world......I think I'll go read some...

:cool:

[Purdue Aero Man]

By definition, a pitchless prop is an oxymoron. It does nothing. It doesn't propel. At best it may be low drag, at the worst, it just makes a lot of noise stirs the air up and wastes power.


Not true. The prop would produce power because you are only getting rid of the component of lift associated with the AoA. I agree that it may not be a great idea for producing thrust, but so long as the airfoil of the prop had a positive Cl_alpha=0 , the prop would work.

Also, laminar flow does not imply no drag. There is still the drag associated with skin friction because of the viscosity.

[steve lewin]

Once more we have confusion over terminology. People keep using the single term "pitch" to mean completely different things. Certainly a propeller with a cambered blade section and no pitch ANGLE might produce some thrust in exactly the same way as a cambered wing section with no AoA relative to the chord line will.

OTOH the other definition of pitch as used by prop manufacturers is "A theoretical number that describes how far the propeller would move forward with a single rotation if there were no slippage". E.g. a 10 x 6 (pitch) prop would move 6 inches per revolution. By simple definition a 10 x 0 (zero pitch or pitchless) prop will not move forward and will produce no thrust. This effectively implies having the blade airfoil positioned at the zero lift angle (usually a negative pitch ANGLE).

But so what ?

Steve

[vintage1]

Not true. The prop would produce power because you are only getting rid of the component of lift associated with the AoA. I agree that it may not be a great idea for producing thrust, but so long as the airfoil of the prop had a positive Cl_alpha=0 , the prop would work.

Also, laminar flow does not imply no drag. There is still the drag associated with skin friction because of the viscosity.


Again that's a matter of definition. Whether you define 'pitch' as 'zero geometric angle of attack' or 'having such an angle of attack that zero lift is produced'

I think tho, that on the second point, again its a matter of definition. True laminar flow doesn't happen with viscous liquids. IIRC. Its a LONG time since those dull fluid dynamics lectures...

The whole point is that the Bernoulli/Newtonian analysis is approximate only.

As soon as you put in real liquid properties, you get vortices, and vortices contain energy, and that energy is lost by the 'perfect' wing/prop blade and becomes drag.

If the air was perfectly still before the airfoil came along, and perfectly still after it went, then you would have dragless flight.

[vintage1]

Actually, gong back to waht teh OP was trying I *think* to drive at, in theory a very large prop with a very ine pitch COULD generate huge thrust.

But it would lose it as soon as any motion was put in the picture.

If you gear an IPS motor down enough it will lift a ton. It may take all day to lift it an inch, but lift it, it will....

...and thats the point. Engineering physics teaches you that power is force times speed. You can devise mechanisms that will trade one off for the other, and a large fine pitched prop geared down is just such a mechanism, but you can't break the more fundamental rules of power/energy conservation.

Yet people talk about thrust as if it were a measure of power. Its not. You need to bring the pitch speed into the mixture. THEN you have a measure of how good your power train really is.