Propeller torque & engine torque
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Hi italia458,
That's odd because the relationship "THP = SHP * p.e." is from NAVAVSCOLSCOM-SG-111 page 4 and the equation tells me that I am developing THP if I am converting SHP using a propeller which has an efficiency >0. There is no mention of aircraft speed.
Your formula involving aircraft speed is good for explaining climb performance etc. but is not exclusive to explaining THP.
I disagree - standing on earth is not an inertial frame of reference. Your observation of the "free fall" flight of a golf ball shows you that you are in an accelerating frame of reference.
A "balanced turn" can simply be measured using a spirit level. The bubble has to be in an accelerating reference frame (that's gravity to those of us who haven't studied general relativity) else it wouldn't "float" to the top.
As stated numerous times, if the flight velocity is zero, there is zero THP - that is what the equation says, not me.
Your formula involving aircraft speed is good for explaining climb performance etc. but is not exclusive to explaining THP.
So, standing on the earth we consider that to be an inertial reference frame.
A "balanced turn" can simply be measured using a spirit level. The bubble has to be in an accelerating reference frame (that's gravity to those of us who haven't studied general relativity) else it wouldn't "float" to the top.
Last edited by rudderrudderrat; 30th Mar 2012 at 14:28. Reason: spelling
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italia:
The power that comes from the engine goes through the prop. Rudderrudderrat is correct about propeller efficiency not being zero. If it was zero there would be no thrust.
You can't work out the prop efficiency in the static thrust scenario using the formula you keep giving for propulsive efficiency. I have found an essay by a prop designer that explains why:
Theoretical Prop Efficiency
"This equation [propulsive efficiency] is very useful for many cases, but you should see a problem in that as your velocity goes to zero, no matter how much thrust you're producing, your efficiency goes to zero. So how do you know how good your prop is doing at low speeds or statically? Well, there's another term that can be used, Figure of Merit, which is Induced Power divided by Power Available, or how much of your power is going into accelerating the air..."
Induced power is the same as thrust horsepower.
Regarding your parcel of air explanation: as discussed, yes, it requires power to move air. That power comes from the engine. That power is called BHP or SHP. It is not called THP.
You can't work out the prop efficiency in the static thrust scenario using the formula you keep giving for propulsive efficiency. I have found an essay by a prop designer that explains why:
Theoretical Prop Efficiency
"This equation [propulsive efficiency] is very useful for many cases, but you should see a problem in that as your velocity goes to zero, no matter how much thrust you're producing, your efficiency goes to zero. So how do you know how good your prop is doing at low speeds or statically? Well, there's another term that can be used, Figure of Merit, which is Induced Power divided by Power Available, or how much of your power is going into accelerating the air..."
Induced power is the same as thrust horsepower.
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That's odd because the relationship "THP = SHP * p.e." is from NAVAVSCOLSCOM-SG-111 page 4 and the equation tells me that I am developing THP if I am converting SHP using a propeller which has an efficiency >0. There is no mention of aircraft speed.
The speed of the aircraft (to be specific it would be the TAS of the aircraft) is included in the THP equation. It also shows that when at a TAS of 0, the THP is equal to zero.
I already explained this earlier and I used that exactly picture in post #9.
Your formula involving aircraft speed is good for explaining climb performance etc. but is not exclusive to explaining THP.
As for everyone here: Stop saying what you 'think' is happening and stating it as a fact. If you are going to 'prove' something, please include evidence that proves that point, as I have done. If you have evidence that proves that what I'm saying isn't correct, I'm more than willing to listen. However, none of you are providing evidence that proves that Wikipedia, the U.S. Navy and William Kershner are all wrong. The document that oggers posted does not relate to what I was talking about. I have not read the document in its entirety, but I will eventually as it looks like a fantastic explanation about helicopter aerodynamics.
I disagree - standing on earth is not an inertial frame of reference. Your observation of the free flight of a golf ball shows you that you are in an accelerating frame of reference.
2) A reference frame is (courtesy of Wikipedia): "a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer. It may also refer to both an observational reference frame and an attached coordinate system as a unit." In the case of what we're talking about, it is both an observational reference frame and an attached coordinate system as a unit.
3) In an inertial reference frame, an object can be at rest with zero forces acting on it or at rest with all forces acting on it, balanced. An object can also be in motion with all forces either zero or balanced. An object can also be accelerating in an inertial reference frame due to an imbalance of force.
4) Your golf ball explanation doesn't prove what you're saying. The reason it is falling does NOT prove that it is in an accelerating frame of reference. It shows that there is a force imbalance which is causing the acceleration. Assume that the atmosphere is a vacuum. The wall will be 'fired' up and then will come down. The reason it comes back down to earth is because the force of gravity on the ball is not being opposed! It is accelerating back down to the earth. This is a basic problem that is easily analyzed in an inertial reference frame in ab initio physics courses. You're unnecessarily complicating the problem by analyzing it from a non-inertial reference frame.
5) Just like the golf ball phenomenon can be explained in an inertial reference frame, so too can an aircraft in flight. And that's how it has been done for ages!! If there wasn't lift, the gravity acting on the aircraft would accelerate it back to earth.
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oggers:
I don't disagree with anything he said! I hope you realize that he also agreed with what I said!
Like he says, you don't know how good your prop is doing at making thrust by analyzing THP. And he's saying that "Figure of Merit" will show you how efficiently the propeller makes thrust. That has nothing to do with THP!
So how does this 'prove' me wrong?
NO. IT. IS. NOT!
THP = Thrust x aircraft velocity
Induced power = Thrust x (aircraft velocity + induced velocity at the propeller)
I just taught my nephew the other day (who is 5 years old) that if a word isn't spelled the same, it's not the same! He seemed to understand that right away.
This equation [propulsive efficiency] is very useful for many cases, but you should see a problem in that as your velocity goes to zero, no matter how much thrust you're producing, your efficiency goes to zero. So how do you know how good your prop is doing at low speeds or statically? Well, there's another term that can be used, Figure of Merit, which is Induced Power divided by Power Available, or how much of your power is going into accelerating the air...
Like he says, you don't know how good your prop is doing at making thrust by analyzing THP. And he's saying that "Figure of Merit" will show you how efficiently the propeller makes thrust. That has nothing to do with THP!
So how does this 'prove' me wrong?
Induced power is the same as thrust horsepower.
THP = Thrust x aircraft velocity
Induced power = Thrust x (aircraft velocity + induced velocity at the propeller)
I just taught my nephew the other day (who is 5 years old) that if a word isn't spelled the same, it's not the same! He seemed to understand that right away.
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The document that oggers posted does not relate to what I was talking about.
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)
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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Hi italia458,
(1) THP = SHP * p.e. (from NAVAVSCOLSCOM-SG-111 page 4)
There is no mention of TAS in equation (1)
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.
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.
(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.
The reason it is falling does NOT prove that it is 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.
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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italia: you must try to remain calm.
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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rudderrudderrat:
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.
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 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.
There is no mention of TAS in equation (1)
... the ball is in an inertial frame of reference - not you.
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 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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oggers:
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?
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?
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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.
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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@ italia458,
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.
Where do you actually stand on this?
edit
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).
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.
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).
As I've said before, being on the earth puts you in an accelerating reference frame (non-inertial reference frame).
edit
So how does the aircraft turn if the forces are actually balanced, like shown in the second picture?
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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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.
Believe what you would like. I think I've had enough with this thread.
Where do you actually stand on this?
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By a combination of elevator and rudder.
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rudderrudderrat:
It would be good to read this.
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.
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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italia458
Yes - I'm very familiar with that - it formed part of my Space, Time and Cosmology Open University course.
And your point?
My 1960s University degree involved plenty of Maths and Physics.
Thank you for confirming that I completely wasted my time discussing anything with you.
It would be good to read this.
And your point?
Like I said before, a physics class would benefit your understanding.
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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Italia: I’ve been reviewing the thread and would like to respond to some of your previous comments in light of recent developments:
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:
etc etc. Would've been so much easier just to mention induced power.
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.
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.
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'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:
Followed a few hours later by:
“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.”
“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.”
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.”
“Can you provide evidence that my point is different than what is said in the references I provided?”
“But the 'Navy stuff' clearly showed that you were in fact creating zero THP when the aircraft was stationary!”
“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.”
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.”
And I really like what you did here:
“There is no need to complicate this with special or general relativity…”
“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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oggers:
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.
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!
See above.
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.
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.
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.
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:
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.
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.
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.
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.
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.
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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Hi guys,
Just a very quick question, what is the relationship between the propeller torque and the engine torque? Are they actually referring to the same rotational force but only different in teminology?
Hope you could shed me some lights.
Just a very quick question, what is the relationship between the propeller torque and the engine torque? Are they actually referring to the same rotational force but only different in teminology?
Hope you could shed me some lights.
To this
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
The best thread hijack for 2012
