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Propeller torque & engine torque

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Propeller torque & engine torque

Old 30th Mar 2012, 15:28
  #61 (permalink)  
 
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The document that oggers posted does not relate to what I was talking about.
In that case I'm not sure what you think you're talking about but it certainly relates to the power induced by the rotor of a helicopter in the hover. Induced power and THP - two names, same concept. Not that the name is important seeing as you already asserted that there was no power at the rotor, only thrust:

The engine will definitely be creating lots of BHP(SHP) and burning lots of fuel to produce the thrust that is keeping the helicopter in the hover - but I believe THP will be zero...the "power (lift)" you mention is BHP(SHP)
And the essay I cited in my last post definitely states that power is induced by a prop. Which didn't come as much of a surprise to me

italia: you must try to remain calm.

Now, do I take it from the last post that you now acknowledge there is induced power, and that you get this at the prop in the static thrust scenario? Because you said 'if the aircraft doesn't move no work is done. No work is no THP' Is it just that you didn't think to mention induced power in any of the many pages you have devoted to this so far?

Last edited by oggers; 30th Mar 2012 at 15:42.
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Old 30th Mar 2012, 15:39
  #62 (permalink)  
 
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Hi italia458,

(1) THP = SHP * p.e. (from NAVAVSCOLSCOM-SG-111 page 4)
The speed of the aircraft (to be specific it would be the TAS of the aircraft) is included in the THP equation.
There is no mention of TAS in equation (1)

The reason it is falling does NOT prove that it is in an accelerating frame of reference.
Correct - but I said "... the "free fall" flight of a golf ball shows you that you are in an accelerating frame of reference."
The ball is in "free fall" during it's flight, the ball is in an inertial frame of reference - not you.

What you feel when turning in the airplane is the centrifugal force which is a pseudo force. It is only there because YOU are in an accelerating reference frame.
Just like gravity.

I sincerely hope that you do not confuse your students with the theory of General Relativity, whilst explaining what a simple balanced turn is all about.
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Old 30th Mar 2012, 15:41
  #63 (permalink)  
 
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italia: you must try to remain calm.
I know... sorry. It gets frustrating having to consistently repeat myself, especially when the recipients will not accept the way things really are.

Feynman sums up what I think about this: you don't WANT to believe what the truth actually is and you won't accept it. It makes much more sense to you to say that THP won't equal zero in a hover and so you will fight everything that says otherwise, disregarding the way it actually is!

You don't like it? Go somewhere else! by Richard Feynman, the QED Lecture at University of Auckland - YouTube
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Old 30th Mar 2012, 15:44
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I edited my last post - just so you know.
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Old 30th Mar 2012, 15:53
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rudderrudderrat:

There is no mention of TAS in equation (1)
You're going to have to actually listen to what I say. What is the equation for THP? You'll find that TAS is in that equation.

... the ball is in an inertial frame of reference - not you.
As I've said before, being on the earth puts you in an accelerating reference frame (non-inertial reference frame). However, you can analyze a number of phenomena by treating it as an inertial reference frame. Some of these include your golf ball example and an aircraft in flight. Go take a physics course.

I sincerely hope that you do not confuse your students with the theory of General Relativity, whilst explaining what a simple balanced turn is all about.
I don't think you understand the difference between proving and explaining. I do not start by proving what frame of reference we're in and then proving all the forces and so on. You would need to be enrolled in an advanced physics course to begin down that path.

I start by explaining the forces in a turn by drawing something like this: http://selair.selkirk.ca/Training/Ae...es/lf-turn.gif

This picture is wrong: http://www.aero-mechanic.com/wp-cont...09/08/4-28.jpg

It shows the forces from an inertial reference frame and a non-inertial reference frame. As I've shown before, if the forces are equal, there is no acceleration. So how does the aircraft turn if the forces are actually balanced, like shown in the second picture?

I usually don't mention how forces in a turn are sometimes depicted incorrectly. But I have the knowledge to be able to answer questions regarding the forces in a turn if the student asks.

Last edited by italia458; 30th Mar 2012 at 16:03. Reason: Grammar
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Old 30th Mar 2012, 15:58
  #66 (permalink)  
 
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oggers:

Is it just that you didn't think to mention induced power in any of the many pages you have devoted to this so far?
Is this a guilt trip now? We were never talking about induced power. Don't blame me for your inadequacies in understanding material. I kept it pretty simple I thought - obviously not. I never said that the propeller wasn't doing any work. You adamantly said that I was wrong about THP being zero when the aircraft is at rest and so this whole discussion has been regarding THP. You were the one to mention induced power and I immediately agreed with it. What else do you want, oggers?
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Old 30th Mar 2012, 16:21
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As the others said, Brakehorse power and shaft power.


You just have to remember that it is not measured at the propeller. It is measured between the motor and the reduction gear box.
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Old 30th Mar 2012, 16:45
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@ italia458,

You're going to have to actually listen to what I say. What is the equation for THP? You'll find that TAS is in that equation.
I'm listening - but it only seems to be one way at the moment.

Please explain why you believe THP = SHP * p.e. (from NAVAVSCOLSCOM-SG-111 page 4) is NOT correct.

You repeatedly insist the formula for Engine + Prop + Airframe with regards to Aircraft performance as being the only correct version.

So, standing on the earth we consider that to be an inertial reference frame.
As I've said before, being on the earth puts you in an accelerating reference frame (non-inertial reference frame).
Where do you actually stand on this?

edit
So how does the aircraft turn if the forces are actually balanced, like shown in the second picture?
By a combination of elevator and rudder.

The "centrifugal force" (A) is what you feel (like the force of gravity).
The centripetal acceleration is the reason for (A).
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Old 30th Mar 2012, 17:03
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Please explain why you believe THP = SHP * p.e. (from NAVAVSCOLSCOM-SG-111 page 4) is NOT correct.
When did I say that equation wasn't correct? I don't think you realize that the equation in that form is very basic. The terms THP, SHP and p.e. all expand to include a heck of a lot of variables. Like I said before, a physics class would benefit your understanding.

You repeatedly insist the formula for Engine + Prop + Airframe with regards to Aircraft performance as being the only correct version.
No. I. Do. Not! I've only disagreed with everyone incorrect interpretation of what THP is.

Believe what you would like. I think I've had enough with this thread.

Where do you actually stand on this?
When standing on the earth you are technically in an accelerating (rotating) reference frame; which is a special case of a non-inertial reference frame. However, some phenomena can be explained easier from the perspective of an inertial reference frame. I'm pretty sure I said virtually the same thing in a previous post.
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Old 30th Mar 2012, 17:06
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By a combination of elevator and rudder.
I do not care what you're doing with the elevator and rudder. If the forces are balanced, the aircraft WILL NOT turn. End of story.
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Old 30th Mar 2012, 17:59
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rudderrudderrat:

It would be good to read this.

Inertial frames

In a location such as a steadily moving railway carriage, a dropped ball (as seen by an observer in the carriage) would behave as it would if it were dropped in a stationary carriage. The ball would simply descend vertically. It is possible to ignore the motion of the carriage by defining it as an inertial frame. In a moving but non-accelerating frame, the ball behaves normally because the train and its contents continue to move at a constant velocity. Before being dropped, the ball was traveling with the train at the same speed, and the ball's inertia ensured that it continued to move in the same speed and direction as the train, even while dropping. Note that, here, it is inertia which ensured that, not its mass.

In an inertial frame all the observers in uniform (non-accelerating) motion will observe the same laws of physics. However observers in another inertial frame can make a simple, and intuitively obvious, transformation (the Galilean transformation), to convert their observations. Thus, an observer from outside the moving train could deduce that the dropped ball within the carriage fell vertically downwards.

However, in frames which are experiencing acceleration (non-inertial frames), objects appear to be affected by fictitious forces. For example, if the railway carriage were accelerating, the ball would not fall vertically within the carriage but would appear to an observer to be deflected because the carriage and the ball would not be traveling at the same speed while the ball was falling. Other examples of fictitious forces occur in rotating frames such as the earth. For example, a missile at the North Pole could be aimed directly at a location and fired southwards. An observer would see it apparently deflected away from its target by a force (the Coriolis force) but in reality the southerly target has moved because earth has rotated while the missile is in flight. Because the earth is rotating, a useful inertial frame of reference is defined by the stars, which only move imperceptibly during most observations.The law of inertia is also known as Isaac Newton's first law of motion.

In summary, the principle of inertia is intimately linked with the principles of conservation of energy and conservation of momentum.
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Old 30th Mar 2012, 18:07
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Read this: http://en.wikipedia.org/wiki/Work_(physics).
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Old 30th Mar 2012, 18:44
  #73 (permalink)  
 
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italia458

It would be good to read this.
Yes - I'm very familiar with that - it formed part of my Space, Time and Cosmology Open University course.
And your point?

Like I said before, a physics class would benefit your understanding.
My 1960s University degree involved plenty of Maths and Physics.

Thank you for confirming that I completely wasted my time discussing anything with you.

Last edited by rudderrudderrat; 30th Mar 2012 at 22:47. Reason: spelling
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Old 30th Mar 2012, 20:29
  #74 (permalink)  
 
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Italia: I’ve been reviewing the thread and would like to respond to some of your previous comments in light of recent developments:

“We were never talking about induced power. Don't blame me for your inadequacies in understanding material. I kept it pretty simple I thought - obviously not. I never said that the propeller wasn't doing any work.”
I’d like to give you the benefit of the doubt but I’m afraid the suggestion that you were sitting on this knowledge about induced power (just when the aircraft was still, obviously, the rest of the time you call it THP) doesn’t quite dovetail with a lot of what you have written:

“It might be good to specify that the "power (lift)" you mention is BHP(SHP) as we've been talking about THP…

The engine is using a ton of energy (fuel) to create that force (thrust)... but since the thrust isn't moving the aircraft, the thrust isn't doing any work. Therefore, there is zero Thrust Horsepower…

When you're talking about Total Rotor Thrust, that's just thrust..

That force (Total Rotor Thrust) comes from the power of the engine (BHP or SHP)…

I believe that when the helicopter is in a fixed position over the ground the THP will be zero. The engine will definitely be creating lots of BHP(SHP) and burning lots of fuel to produce the thrust that is keeping the helicopter in the hover - but I believe THP will be zero. Work will be done to lift the helicopter off the ground into the hover position which will obviously make a certain amount of THP.”
etc etc. Would've been so much easier just to mention induced power.

“Can you provide evidence that my point is different than what is said in the references I provided?”
Yes. That navy reference you keep using states clearly at the top that it is predicated on the assumption of “equilibrium flight”. That doesn’t include sitting on the ground. For that you need the alternative method of calculating power output from the book and the essay I linked to.

“But the 'Navy stuff' clearly showed that you were in fact creating zero THP when the aircraft was stationary!”
Forgive me for labouring the point as you do seem to rely on that equation, but it assumes equilibrium flight as stated clearly at the top of your reference document. An aircraft on the ground is not in equilibrium flight.

“THP has its own equation - if you want to see if there is THP in a situation, you need to use it. As stated numerous times, if the flight velocity is zero, there is zero THP - that is what the equation says, not me.”
And so.

OTOH, a helicopter in the hover [where you insist there is no THP] is in equilibrium flight. The aircraft itself is not moving but there is a velocity which is the induced airflow. You have acknowledged that there is thrust. Therefore you can apply the formula – weight x [velocity of induced air flow]. The result is THP. It has to be because it’s the power associated with the thrust. Although you insist there is no THP for a helo in the hover.

The same could be said for an aircraft in equilibrium flight into a strong headwind such that groundspeed was zero. You have been very clear:

“I have been very clear in describing that if the 'vehicle' is not moving, then the THP is zero... THP is related to the distance that the aircraft moves with reference to the earth.”
I'd suggest the THP is exactly the same into wind as it would be downwind and the earth has nowt to do with it.

And I really like what you did here:

“There is no need to complicate this with special or general relativity…”
Followed a few hours later by:

“General relativity deals with the theory of gravitation. I will try to explain a little bit about what's going on below.”
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Old 30th Mar 2012, 23:01
  #75 (permalink)  
 
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oggers:

I’d like to give you the benefit of the doubt but I’m afraid the suggestion that you were sitting on this knowledge about induced power (just when the aircraft was still, obviously, the rest of the time you call it THP) doesn’t quite dovetail with a lot of what you have written:
I don't care what you think. I was not sitting on that information. 'Induced power' had not entered my mine ONCE while in this discussion. Would it have been easier to mention induced power, you ask? No, induced power is how efficient thrust is made. It is not about THP. I do believe it adds another perspective to everything and it's great you introduced it but to accuse me of 'holding out' info is a bunch of bullocks.

Yes. That navy reference you keep using states clearly at the top that it is predicated on the assumption of “equilibrium flight”. That doesn’t include sitting on the ground. For that you need the alternative method of calculating power output from the book and the essay I linked to.
They stated those at the beginning so that they wouldn't have to keep repeating all the different conditions for every specific thing they talk about. It does not affect THP actually. For THP, it doesn't matter and here's why. THP has to do with thrust and velocity. That is it. There is no lift equation in there, lift was not mentioned once, weight was not mentioned once, for all intents and purposes, that aircraft can be assumed to be no different in this condition than in "equilibrium flight". If the TAS of the aircraft is zero, there is zero THP.

And no, it's not just an alternative method of calculating power output. It's a different way. They aren't the same, oggers! I've already proved that with the difference in words and, more importantly, with the difference in equations!

Forgive me for labouring the point as you do seem to rely on that equation, but it assumes equilibrium flight as stated clearly at the top of your reference document. An aircraft on the ground is not in equilibrium flight.
See above.

OTOH, a helicopter in the hover [where you insist there is no THP] is in equilibrium flight. The aircraft itself is not moving but there is a velocity which is the induced airflow. You have acknowledged that there is thrust. Therefore you can apply the formula – weight x [velocity of induced air flow]. The result is THP. It has to be because it’s the power associated with the thrust. Although you insist there is no THP for a helo in the hover.
As stated a number of times, THP = thrust x flight velocity (which is TAS) and it is NOT induced velocity!! You're mixing up all the equations and calling them all the same.

I'd suggest the THP is exactly the same into wind as it would be downwind and the earth has nowt to do with it.
You found a legitimate error, finally, so I would congratulate you for it, but I find it hard to do that because you didn't even realize that it was an error!

In the quote you used, I said THP is relative to the distance the aircraft moves with reference to the earth. That's incorrect. It's TAS, which is flight velocity and explicitly states as so in the Aerodynamics for Naval Aviators text. I made a mistake.

I'd suggest the THP is exactly the same into wind as it would be downwind and the earth has nowt to do with it.
That's how I knew you didn't know it was an error. You just happened to think and suggest something that was actually turned out to be true but, again, with no proof. If you really did know I had made a mistake you'd jump over the opportunity to prove me wrong, something you've been trying really hard to do this whole thread! You could have posted this picture that I've used a few times: http://i.imgur.com/NXLV3.png, and tell me that it's flight velocity and not relative to the ground!

But I really don't care if you knew or not. I'm glad that you did point my mistake out to me. I'm just mentioning this because of you consistently trying to prove me wrong and then accuse me of holding out info. It's just a way of keeping track of what is going on. It's also to prevent you in the end saying "I knew it was wrong...".

Regarding my two, seemingly, different comments separated by a few posts: 1) There is no need to complicate the THP with special or general relativity. That's why I said that! 2) We started getting into more complex examples actually dealing with relativity and not THP anymore, so that's why I said that second comment. Without the context I've provided here, it does seem I'm a bit off my rocker... but I think that's what you were trying to show! Nice try

Now, getting back to this induced power and induced velocity stuff. Reference this propulsive efficiency equation: http://i.imgur.com/NXLV3.png

I just realized that the bottom part is actually the formula for the 'induced power' that you provided. In the AfNA document they call it input power. On top is the output power and in this case, it's THP. I think that blows your whole "induced power = THP" out of the water!... again!

Check this out: http://i.imgur.com/1Ev3y.png

That's from the Wikipedia page on Disc loading. You'll notice that they're calculating the power required to hover - which is what you've been trying to figure out all this time. Just like we've been discussing, Power = thrust x velocity. However, in this case, the velocity part is "induced velocity". If you read the AfNA document I posted, immediately before the propulsive equation part they talk about induced velocity. It is 1/2 the total velocity change of the air, and it is measured at the propeller. Since the helicopter is in the hover, the flight velocity is zero so you can take that term out of the induced power equation and you are left with: Induced power = thrust x induced velocity. And that's exactly what the Wikipedia page shows.

I hope now you can see more clearly what THP is and that THP is not induced power.

Not being sarcastic at all, I have to say thanks for introducing the talk about induced power. It's added more clarity regarding all of this for me.
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Old 30th Mar 2012, 23:36
  #76 (permalink)  
 
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oggers:

You accusing me of holding out info and trying to guilt trip me has been bugging me. I shared all the resources I was using throughout this discussion. You and everyone else had access to them on here. I posted the whole AfNA document section on the propellers where it talks about induced power. The reason I hadn't picked up on this earlier and put the two together is because I hadn't read the article word for word and analyzed it. I also hadn't come across the article which you posted about Figure of Merit. Once you did post that, I picked up on it right away and I think it actually backfired on you! It added more evidence to the fact that you don't know what you're talking about. I highlighted that in my last post.

But I should ask the same of you: Have you been holding out this information knowingly as I constantly repeat myself in post after post, trying to explain THP? Have you been sitting on this information? Why didn't you speak up earlier about it? What proves that you haven't just been trolling the whole time, like someone else has mentioned in this thread, and knew all along about this?

I'm not responsible to teach you everything about aerodynamics. You need to take responsibility for your learning. You can't blame me for you not thinking about the efficiency of the prop in creating the thrust. I mentioned that there were other efficiencies that can be analyzed and I agreed that the propeller is doing work on the air. Did I really have to tell you that if anything is doing work, there is a way to analyze the efficiency of the object doing the work? I'm not responsible to think of everything for you.

You finally discovered something that would add to the discussion and then you blame me for not telling you earlier. You really are a piece of work.

Last edited by italia458; 31st Mar 2012 at 02:31. Reason: Added a paragraph.
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Old 31st Mar 2012, 09:09
  #77 (permalink)  
 
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In the quote you used, I said THP is relative to the distance the aircraft moves with reference to the earth. That's incorrect. It's TAS, which is flight velocity and explicitly states as so in the Aerodynamics for Naval Aviators text. I made a mistake.
That's right. You did make a mistake. But not just in that quote (which was actually two quotes anyway). No. You reiterated it across 4 pages:

I have been very clear in describing that if the 'vehicle' is not moving...

.....the distance that the aircraft moves with reference to the earth...”

...when the helicopter is in a fixed position over the ground...

...if the aircraft isn't moving, it isn't covering distance and so the work = zero. When work = zero, Power also = zero.
etc etc.

Who are you trying to kid? You made it central to what you've been prattling on about. Now finally you've dropped it.

You accusing me of holding out info and trying to guilt trip me has been bugging me
Well, maybe it will help if you go back and read between the lines. I wasn't really accusing you of holding out info. I was suggesting that it hadn't occured to you.

But let's just be clear about one thing. After 4 pages you have now done a ma-housiv u-turn and decided that the aircraft can stay still after all and still output power from the prop.

Last edited by oggers; 31st Mar 2012 at 09:16. Reason: added a cry baby emoticon
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Old 31st Mar 2012, 09:13
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blackhand:

The best thread hijack for 2012
Gets my vote
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Old 31st Mar 2012, 10:14
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Flat Rated

Aerbat77. The Allison is not flat-rated and to clarify my comment on reaching the limiting T.I.T I was simply saying that, especially on the T56A-11 it was common to reach max permissable T.I.T before achieving limiting torque.
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Old 31st Mar 2012, 13:52
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oggers:

We had never talked about a wind before and I had assumed that there would be no wind. Therefore, with no wind, TAS is the same as GS.

You hold onto it as if you 'won' or something. If you really were thinking about wind before, you would have made a comment about it the first time I mentioned a position relative to the ground. You also forgot to highlight the times when I referred to the same speed as "TAS". Of course you wouldn't want to provide an unbiased view because that would mean you don't really have a point in this case. I think its quite obvious to everyone that neither of us was thinking about wind.

I should also point out that out of the 4 quotes you posted, only 2 actually relate to what you were talking about. #2 and #3 mention earth or the ground. But #1 and #4 only mention motion.

You never addressed the recent 'issues' I brought up in my last 2 posts about what you said about induced power. It seems as though you actually can't admit being wrong at all. You would never be a good scientist or engineer.

I think the original point of discussion between us was if the aircraft velocity was zero, I said there would be zero THP and you obviously did not agree because you said this:

Not that myth again. It's disappointing to have to point out to one who calls himself an instructor that in your 'brakes on' scenario the aircraft is still producing 200 THP as well as 200 BHP because it is accelerating a mass of air rearwards in a futile attempt to turn the earth and the atmosphere in opposite directions. Come on italia, pull your socks up. These are fundamentals that instructors should have a grip on.
So, has this discussion changed your answer now, or do you still believe that the THP will equal the BHP because it's 'accelerating a mass of air rearwards'? After this discussion it's quite obvious that I have a better 'grip' on the fundamentals of aerodynamics than you do!

EDIT:
After 4 pages you have now done a ma-housiv u-turn and decided that the aircraft can stay still after all and still output power from the prop.
Where did I say that the prop does not do work on the air when the aircraft is not moving? I never said that! So, to put it bluntly, you are lying.

Last edited by italia458; 31st Mar 2012 at 15:02.
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