Explaining in the simplest manner the power curve.
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tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
I would love to. Know of any resources?
True, that is an assumption. Can you name some general aviation airplanes where this is not true? How about some civilian transports?
Even if it were not the case for one of the above airplanes, I strongly suspect that any different behavior is coming from computers, rather than fundamental aerodynamics, because keeping a constant AOA is pretty much the definition of a trim system.
I think that it's an exaggeration to say that I "proclaimed an inviolable rule". Many rules can be thrown out the window when you have a FBW aircraft, or vectored thrust, etc.
The context of the discussion here was clearly "normal" aircraft...general aviation stuff and the typical jet transport. Anything more exotic than that should be discussed as interesting exceptions, rather than simply saying that the rules are incorrect.
I would love to. Know of any resources?
True, that is an assumption. Can you name some general aviation airplanes where this is not true? How about some civilian transports?
Even if it were not the case for one of the above airplanes, I strongly suspect that any different behavior is coming from computers, rather than fundamental aerodynamics, because keeping a constant AOA is pretty much the definition of a trim system.
I think that it's an exaggeration to say that I "proclaimed an inviolable rule". Many rules can be thrown out the window when you have a FBW aircraft, or vectored thrust, etc.
The context of the discussion here was clearly "normal" aircraft...general aviation stuff and the typical jet transport. Anything more exotic than that should be discussed as interesting exceptions, rather than simply saying that the rules are incorrect.
MDPilot
Well-Known Member
Re: Explaining in the simplest mannar the power curve.
Many of your "Core concepts" are the direct result of propwash of a single engine over tail surfaces of a GA aircraft. Your rules DO NOT generally apply to any other type of aircraft, especially high speed jet aircraft.
How about the sailplane?
Many of your "Core concepts" are the direct result of propwash of a single engine over tail surfaces of a GA aircraft. Your rules DO NOT generally apply to any other type of aircraft, especially high speed jet aircraft.
How about the sailplane?
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
In steady flight, a sailplane is always descending in the body of air in which it flies. If that body of air is rising, then the sailplane may rise in relation to the earth, assuming that the air is rising faster than the plane is descending. Pulling back on the yoke may convert a descent into a cilmb if the resulting higher AOA moves it closer to the point of minimum power required. The aircraft's descent rate is at a minimum at the minimum power required airspeed, which is theoretically at .76 of Vldmax.
Now, the airplane has a velocity which can be converted into altitude on a temporary basis. By zooming, in other words. This is a simply conversion of kinetic energy into potential energy. Still, the energy height of the aircraft will remain constant.
Power and thrust curve analysis do not take into account zooms or any kind of accelerated flight.
In steady flight, a sailplane is always descending in the body of air in which it flies. If that body of air is rising, then the sailplane may rise in relation to the earth, assuming that the air is rising faster than the plane is descending. Pulling back on the yoke may convert a descent into a cilmb if the resulting higher AOA moves it closer to the point of minimum power required. The aircraft's descent rate is at a minimum at the minimum power required airspeed, which is theoretically at .76 of Vldmax.
Now, the airplane has a velocity which can be converted into altitude on a temporary basis. By zooming, in other words. This is a simply conversion of kinetic energy into potential energy. Still, the energy height of the aircraft will remain constant.
Power and thrust curve analysis do not take into account zooms or any kind of accelerated flight.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
Absolutely not. None of the core concepts are the result of propwash. That is a secondary effect that will vary from airplane to airplane, or be non-existent.
Absolutely not. None of the core concepts are the result of propwash. That is a secondary effect that will vary from airplane to airplane, or be non-existent.
MDPilot
Well-Known Member
Re: Explaining in the simplest mannar the power curve.
We are not talking about changes in energy levels, that's another discussion, you specifically said CONTROL of aircraft. In this case, (as well as the general case) pitch controlls climb and descend. Thrust, or in the case of the sailplane more or less drag, controlls airspeed.
This is quite a true statement.
We are not talking about changes in energy levels, that's another discussion, you specifically said CONTROL of aircraft. In this case, (as well as the general case) pitch controlls climb and descend. Thrust, or in the case of the sailplane more or less drag, controlls airspeed.
This is quite a true statement.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
In this case, the quantity of excess power is controlling climb/descent rate. Changing airspeed is one way to change the quantity of excess power.
No. Any airspeed up to Vne is available to a glider, the quantity of drag merely determines the angle of descent at that airspeed.
In this case, the quantity of excess power is controlling climb/descent rate. Changing airspeed is one way to change the quantity of excess power.
No. Any airspeed up to Vne is available to a glider, the quantity of drag merely determines the angle of descent at that airspeed.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
MDPilot:
Throughout this entire discussion, you have asked a dozen questions which I have answered, but you have answered none of mine. Moreover, you have demonstrated understandings that are typical of a random pilot without any formal aerodynamic training and are certainly contrary to the most elementary aerodynamics textbooks. I have a hard time believing that you have the credentials you claim.
MDPilot:
Throughout this entire discussion, you have asked a dozen questions which I have answered, but you have answered none of mine. Moreover, you have demonstrated understandings that are typical of a random pilot without any formal aerodynamic training and are certainly contrary to the most elementary aerodynamics textbooks. I have a hard time believing that you have the credentials you claim.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
I have a better idea: Why don't we each compare what we're saying to a standard aerodynamics textbook?
In fact, I have one sitting in front of me, written by a Professor of Aeronautical Engineering at the US Air Force Academy, Thomas R. Yechout. Perhaps you have it? It says "Based on a 15-year successful approach to teaching airfcraft flight mechanics at the US Air Force Academy."
I'm interested in how you can explain even the simplest of aerodynamic formulas, such as ROC = (Power Available - Power Required)/Weight, or Sin(Climb Angle) = (Thrust Available - Thrust Required) / Weight. (pages 108 and 109).
You've made a lot of indefensible statements, including such absurdities as my core concepts are due to "prop wash" that I'd like to see you defend them. So far, you haven't defended any of the statements you've made and now you want to bail.
I have a better idea: Why don't we each compare what we're saying to a standard aerodynamics textbook?
In fact, I have one sitting in front of me, written by a Professor of Aeronautical Engineering at the US Air Force Academy, Thomas R. Yechout. Perhaps you have it? It says "Based on a 15-year successful approach to teaching airfcraft flight mechanics at the US Air Force Academy."
I'm interested in how you can explain even the simplest of aerodynamic formulas, such as ROC = (Power Available - Power Required)/Weight, or Sin(Climb Angle) = (Thrust Available - Thrust Required) / Weight. (pages 108 and 109).
You've made a lot of indefensible statements, including such absurdities as my core concepts are due to "prop wash" that I'd like to see you defend them. So far, you haven't defended any of the statements you've made and now you want to bail.
MDPilot
Well-Known Member
Re: Explaining in the simplest mannar the power curve.
Open your mind and listen for a minute. What you are looking at here is climb performance and capabilities. What you are NOT looking at is CONTROL of that climb capability.. CONTROL, CONTROL, CONTROL.
Granted, if you cob the power on an aircraft trimmed for a certain airspeed, it will start climbing at that airspeed sooner or later. It will enter a phugoid to settle at a climb rate and eventually a new cruise altitude as well. But you are not CONTROLLING this aircraft. You are letting it fly itself and meander its own way through the sky. We have been discussing CONTROLLED flight where the aircraft resopnds to pilot control inputs. Actually the threads author and I (and several other posters)have been discussing CONTROL. You have apparantly been letting uncontrolled model aircraft fly through the sky to crash somewhere.
Now if you want to discuss something other that how to CONTROL an aircraft, (energy maneuvering, V/G diagrams, whatever) feel free. But start your own topic.
Now, I have to go fly a trip, so I won't be discussing this further right now.
Open your mind and listen for a minute. What you are looking at here is climb performance and capabilities. What you are NOT looking at is CONTROL of that climb capability.. CONTROL, CONTROL, CONTROL.
Granted, if you cob the power on an aircraft trimmed for a certain airspeed, it will start climbing at that airspeed sooner or later. It will enter a phugoid to settle at a climb rate and eventually a new cruise altitude as well. But you are not CONTROLLING this aircraft. You are letting it fly itself and meander its own way through the sky. We have been discussing CONTROLLED flight where the aircraft resopnds to pilot control inputs. Actually the threads author and I (and several other posters)have been discussing CONTROL. You have apparantly been letting uncontrolled model aircraft fly through the sky to crash somewhere.
Now if you want to discuss something other that how to CONTROL an aircraft, (energy maneuvering, V/G diagrams, whatever) feel free. But start your own topic.
Now, I have to go fly a trip, so I won't be discussing this further right now.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
Ah, so you're changing the meaning of the word "control" in the discussion. And no, I don't think that's the meaning that you started with, but it is a way to keep from retracting your original statements. (Look up the "No True Scotsman Fallacy)
Your above paragraph does seem to acknowledge that excess power (or thrust) determines (that better?) the resulting climb rate (or angle) of the aircraft.
And yes, there would be a phugoid with a power advancement, but if the power application is smooth, very slight. The phugoid is well-damped. You will get a phugoid with a rapid AOA change as well.
So, we're making progress. Now let's take a look at the control of airspeed:
in unaccelerated flight, L = W (approximately), so we can say
Solving for the equilibrium velocity, we get
I don't see thrust or power anywhere in that formula.
Ah, a straw man.
Actually, the OP wanted to know "why", not how, and he hasn't posted since the original question.
Straw man again.
Ah, so you're changing the meaning of the word "control" in the discussion. And no, I don't think that's the meaning that you started with, but it is a way to keep from retracting your original statements. (Look up the "No True Scotsman Fallacy)
Your above paragraph does seem to acknowledge that excess power (or thrust) determines (that better?) the resulting climb rate (or angle) of the aircraft.
And yes, there would be a phugoid with a power advancement, but if the power application is smooth, very slight. The phugoid is well-damped. You will get a phugoid with a rapid AOA change as well.
So, we're making progress. Now let's take a look at the control of airspeed:
L = ClqS = Cl * 1/2*Rho*V^2 * S
in unaccelerated flight, L = W (approximately), so we can say
W = Cl * 1/2*Rho*V^2 * S
Solving for the equilibrium velocity, we get
V = Sqrt(2*W/(Cl*Rho*S)
Now, of the variables on the right, the only one under control of the pilot is Cl, the lift coefficient. This is determined by the AOA, which is controlled by the elevator.I don't see thrust or power anywhere in that formula.
Ah, a straw man.
Actually, the OP wanted to know "why", not how, and he hasn't posted since the original question.
Straw man again.
tgrayson
New Member
B767Driver
New Member
Re: Explaining in the simplest mannar the power curve.
Tgrayson,
A question for you. How do you teach your instrument students to track an ILS glideslope?
Tgrayson,
A question for you. How do you teach your instrument students to track an ILS glideslope?
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
The normal way. Small changes in airspeed will result in rate of descent changes. In other words, elevator.
Still, rate of descent is controlled by excess power. When you make AOA changes, you slide the aircraft back and forth along the power required curve. You create different amounts of excess power by changing your power requirements, rather than your power available.
This only works on the front side of the power curve. If I'm on the backside of the power curve and below glideslope, when I pull back on the yoke, I will get further below the glideslope (except for a brief balloon as I convert kinetic energy into potential energy.) This is one of the considerations behind choosing our approach speed. When you're on the steep part of the power required curve, small AOA changes result in large power requirement changes.
When I start out teaching an instrument student, I go through power and thrust curves in order to show how things work.
The normal way. Small changes in airspeed will result in rate of descent changes. In other words, elevator.
Still, rate of descent is controlled by excess power. When you make AOA changes, you slide the aircraft back and forth along the power required curve. You create different amounts of excess power by changing your power requirements, rather than your power available.
This only works on the front side of the power curve. If I'm on the backside of the power curve and below glideslope, when I pull back on the yoke, I will get further below the glideslope (except for a brief balloon as I convert kinetic energy into potential energy.) This is one of the considerations behind choosing our approach speed. When you're on the steep part of the power required curve, small AOA changes result in large power requirement changes.
When I start out teaching an instrument student, I go through power and thrust curves in order to show how things work.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
Sorry about ignoring this...there were other fires to fight.
You ask a difficult question. To me the big issue is not to dumb something down such that the concepts transferred will interfere with future learning. Leaving something out is ok, but conveying something grossly incorrect is not.
Part of the problem is that understanding the implications of some facts takes a lot of effort. Some people do not make that effort, insteading choosing a more intuitive, but wrong model, and then turn around and teach it to others. Suddenly students are hearing two different points of view. Which do they believe? They're going to believe the more intutive concept.
If, instead, they heard the same facts from everyone, they'd be more likely to learn it correctly, since they had no easy alternatives to choose from.
A great deal of the effort I have expended is to learn enough so that I could evaluate the things that I've heard and throw out the garbage. If there were no garbage to hear, then this amount of effort would never have been needed.
So, in an ideal world, you don't really need a lot of theoretical knowledge to "teach it right the first time", but in order to sort the wheat from the chaff, you do.
That's why I'm extremely frustrated with this thread. The debate confuses people and they don't know whom to believe, so they will most likely accept whichever concept they find more intutive, or keep their original opinions.
Sorry about ignoring this...there were other fires to fight.
You ask a difficult question. To me the big issue is not to dumb something down such that the concepts transferred will interfere with future learning. Leaving something out is ok, but conveying something grossly incorrect is not.
Part of the problem is that understanding the implications of some facts takes a lot of effort. Some people do not make that effort, insteading choosing a more intuitive, but wrong model, and then turn around and teach it to others. Suddenly students are hearing two different points of view. Which do they believe? They're going to believe the more intutive concept.
If, instead, they heard the same facts from everyone, they'd be more likely to learn it correctly, since they had no easy alternatives to choose from.
A great deal of the effort I have expended is to learn enough so that I could evaluate the things that I've heard and throw out the garbage. If there were no garbage to hear, then this amount of effort would never have been needed.
So, in an ideal world, you don't really need a lot of theoretical knowledge to "teach it right the first time", but in order to sort the wheat from the chaff, you do.
That's why I'm extremely frustrated with this thread. The debate confuses people and they don't know whom to believe, so they will most likely accept whichever concept they find more intutive, or keep their original opinions.
B767Driver
New Member
Re: Explaining in the simplest mannar the power curve.
I only like half of this. I'm glad to see you teach pitch for the glideslope, but I don't like the airspeed part at all. The ILS approach, the last 1000' anyway, is a constant IAS maneuver. The PTS only allow -5/+10kts IAS during the final approach segment. To suggest to a pilot that he/she should vary the rate of descent by making changes in airspeed is not appropriate, IMO. This will lead to IAS variations that will flirt with the boundaries of the PTS...and an approach that may never become stable as the power "shucks and jives" trying to keep the IAS as designated for the approach.
To track a constant descent gradient (an ILS glideslope), a change in rate of descent and groundspeed go hand in hand. So I don't disagree that a change in airspeed results in a change in descent rate. However, that is groundspeed dependent...and we're trying to maintain a constant IAS.
I'd rather see a presentation that states that the elevator controls the rate of descent that may vary due to changing groundspeeds on the approach. This allows us to counter a glideslope deviation with pitch controlling the descent rate...and then simulataneously making a small power input to nail the IAS.
The rate of descent (vsi) = descent gradient X the groundspeed.
So the formula works for your description. However, in practical flying, the IAS should never change on an ILS approach and rate of descent should be directly controlled by the elevator to correct for glideslope deviations caused by changes in groundspeed, turbulence, etc. This now leaves slight power changes to keep the airspeed within tolerances.
If we teach to vary the airspeed first...we're moving off of a target that should be fixed. This in turn will lead to out of IAS tolerances and unstable approaches.
I only like half of this. I'm glad to see you teach pitch for the glideslope, but I don't like the airspeed part at all. The ILS approach, the last 1000' anyway, is a constant IAS maneuver. The PTS only allow -5/+10kts IAS during the final approach segment. To suggest to a pilot that he/she should vary the rate of descent by making changes in airspeed is not appropriate, IMO. This will lead to IAS variations that will flirt with the boundaries of the PTS...and an approach that may never become stable as the power "shucks and jives" trying to keep the IAS as designated for the approach.
To track a constant descent gradient (an ILS glideslope), a change in rate of descent and groundspeed go hand in hand. So I don't disagree that a change in airspeed results in a change in descent rate. However, that is groundspeed dependent...and we're trying to maintain a constant IAS.
I'd rather see a presentation that states that the elevator controls the rate of descent that may vary due to changing groundspeeds on the approach. This allows us to counter a glideslope deviation with pitch controlling the descent rate...and then simulataneously making a small power input to nail the IAS.
The rate of descent (vsi) = descent gradient X the groundspeed.
So the formula works for your description. However, in practical flying, the IAS should never change on an ILS approach and rate of descent should be directly controlled by the elevator to correct for glideslope deviations caused by changes in groundspeed, turbulence, etc. This now leaves slight power changes to keep the airspeed within tolerances.
If we teach to vary the airspeed first...we're moving off of a target that should be fixed. This in turn will lead to out of IAS tolerances and unstable approaches.