When on final approach and at slow airspeeds you pitch for airspeed and power for altitude. However, at higher airspeeds (such as cruise) you pitch for altitude and power for airspeed. At what point does this change over?? Is the changing point the best glide speed, having to do with region of reverse command???
Pitch for a/s, power for altitude/vice versa
- Thread starter pkrgod
- Start date
B767Driver
New Member
In a jet, you plan to stay at the optimum altitude for as long as possible then make the descent at idle power. This will improve fuel efficiency by 1) staying at a fuel efficient altitude longer, 2) maintaining a high TAS at the higher altitude reducing flying time and 3) making an idle descent. So in most cases you will pitch for airspeed as the power will be at idle.
In a piston powered airplane...an idle descent is not always practical due to shock cooling, but the philosophy is the same.
In the ATC system...most of the time you are assigned a speed. Outside of level flight...the speed is maintained by pitch...the climb or descent varied by changing the power.
The one exception...is on an ILS approach. Here the pilot should pitch for glideslope guidance and adjust power for airspeed. This will allow for the most accurate and direct guidance on the approach.
In a piston powered airplane...an idle descent is not always practical due to shock cooling, but the philosophy is the same.
In the ATC system...most of the time you are assigned a speed. Outside of level flight...the speed is maintained by pitch...the climb or descent varied by changing the power.
The one exception...is on an ILS approach. Here the pilot should pitch for glideslope guidance and adjust power for airspeed. This will allow for the most accurate and direct guidance on the approach.
Grabo172
Well-Known Member
pkrgod said:
It's the same at any flight regime, just the midset is different.
Pitch always controls airspeed and Power always controls altitude.
In cruise it just seems different because you set a power level for cruise then use the yoke to maintaing level flight and you take whatever airspeed you get.
If you wanted an exact airspeed you then have to pitch for that airspeed then use power to maintain level flight.
At approach, you set up an airspeed with pitch (remember your CFI always telling you to not let the plane descend until the proper airpeed is reached after the initail power reduction?) then adjust power to get the proper approach path.
If you want some great reading and expianation on this, pick up a copy of Stick and Rudder. It is a great book!
Grabo172 said:
Hmm...In cruise dont you pitch for your altitude by bringing the nose to the horizon for straight and level flight, then reduce the power as airspeed builds. Then you set the power for cruise, but you can do more or less power if you want a faster or slower airspeed, but you are still going to be pitching for your level flight.
Grabo172
Well-Known Member
pkrgod said:
You are actually pitching for the airspeed, you're just doing it after the power change.
Think about it this way, if you are in level flight and add power, what happens? You climb, because the pitch is set for a certain airspeed, and power now exceeds that which is needed for level flight. In order to actually speed up, you have to pitch down (push the yoke forward) (lower the AOA) to get back to level flight at that new power setting...
Make sense?
USMCmech
Well-Known Member
"At what point does this change over?"
Never,
They are always interconected, adjust one you have to adjust the other.
One thing that helped me to understand the relationship between pitch, power, airspeed and altitude was realizing that there are two wings on every airplane. (actually there are at least 4, but I'll keep this simple)
The first is the one we all know and love which creates lift. The second is the important one, it is much smaller, was flipped upside down, place all the way in the back and called the elevator. It creates lift in a downward direction called downforce.
The same rules for creating lift that apply to the wing also apply to the elevator. Airspeed plus AOA equals more lift (or downfroce in this case).
Since the elevator is located in the back any change in the downfroce affects the pitch of the nose up or down.
Well duh you say we all know this, now comes the point of my post
When you change any one thing affecting the downforce of the elevator, the airplane will try to reballance the forces acting on it.
If you reduce power, the airspeed drops, the lift created by the wing drops, the downforce created by the tail drops, therefor the nose lowers.
Then the airspeed builds up, the lift created by the wing builds, the downforce created by the tail builds, and the nose comes back up. This tiem it is slightly lower than it was at the higher power setting and you are descending slightly faster at a steeper pitch.
Reverse the entire scenerio if you add power. What is actually happening is that you are changing the pitch of the airplane, but you are doing it with the throttle.
In cruise you use excess power to accelrate to a higher airspeed. More airspeed = more lift and more downforce = nose wants to pitch up. Therfore you must reduce the downforce produced by the tail by reduceing the AOA. You do this initially by pushing forward on the yoke, then adjusting the trim tab untill that AOA stays there with out you constantly pushing forward.
Never,
They are always interconected, adjust one you have to adjust the other.
One thing that helped me to understand the relationship between pitch, power, airspeed and altitude was realizing that there are two wings on every airplane. (actually there are at least 4, but I'll keep this simple)
The first is the one we all know and love which creates lift. The second is the important one, it is much smaller, was flipped upside down, place all the way in the back and called the elevator. It creates lift in a downward direction called downforce.
The same rules for creating lift that apply to the wing also apply to the elevator. Airspeed plus AOA equals more lift (or downfroce in this case).
Since the elevator is located in the back any change in the downfroce affects the pitch of the nose up or down.
Well duh you say we all know this, now comes the point of my post
When you change any one thing affecting the downforce of the elevator, the airplane will try to reballance the forces acting on it.
If you reduce power, the airspeed drops, the lift created by the wing drops, the downforce created by the tail drops, therefor the nose lowers.
Then the airspeed builds up, the lift created by the wing builds, the downforce created by the tail builds, and the nose comes back up. This tiem it is slightly lower than it was at the higher power setting and you are descending slightly faster at a steeper pitch.
Reverse the entire scenerio if you add power. What is actually happening is that you are changing the pitch of the airplane, but you are doing it with the throttle.
In cruise you use excess power to accelrate to a higher airspeed. More airspeed = more lift and more downforce = nose wants to pitch up. Therfore you must reduce the downforce produced by the tail by reduceing the AOA. You do this initially by pushing forward on the yoke, then adjusting the trim tab untill that AOA stays there with out you constantly pushing forward.
MidlifeFlyer
Well-Known Member
Thank you.USMCmech said:
This huge pitch v power controversy is a lot of nonsense over what is nothing more than a teaching technique. I teach pitch for airspeed at the primary level because I think it's the most effective way to move the new pilot from the 2-D world of driving to the 3D world of flying (especially on short final) where everyhting is ultimately based on the simple "pitch + power = performance" equation. But other CFIs have just as much success teaching it the other way.
Beyond that, it's a combination of convenience and efficiency and what you were taught. For example more than one pilot pitches for altitude on an ILS and then switches to pitch for airspeed on short final, without even thinking about it.
B767Driver
New Member
pkrgod said:
Pkrgod,
You are exactly right.
Maybe we can make this more simple.
In a climb or descent...adjust the power. Typically full power in a climb or idle or some low power setting for the descent. Then adjust pitch to maintain airspeed.
In level flight...adjust pitch to maintain altitude. Then adjust power for the desired airspeed. Remember slow flight? Maintian 3000' and 90kias. Now 80kias. Now 70 kias. How do you obtain each new airspeed? By adjusting power.
There is no "crossover point". So you may be thinking too much "outside the box" on that.
seagull
Well-Known Member
The quote below, is, of course, correct.
The MD11 autopilot clarifies the "controversy" on which to use when fairly nicely. If power is at a limit, either a climb power setting or idle, it annunciates that it is controlling the speed by "pitch", all other times it is speed on "thrust". Consequently, it is usually speed on thrust. Just like the other more advanced aircraft, you need to look at what the aircraft is on if you are going to handfly with just part of the automation (i.e., the autothrottles), because if you are speed on pitch, the autothrottles are not going to be helping you much. If you have the autopilot off with a/t on, you need to make sure you're speed on thrust. The airplane still prevents any major goof ups by automatic high and low speed protection features, so the autothrottles will react if you get real slow or fast, but that would be considered poor technique!
The MD11 autopilot clarifies the "controversy" on which to use when fairly nicely. If power is at a limit, either a climb power setting or idle, it annunciates that it is controlling the speed by "pitch", all other times it is speed on "thrust". Consequently, it is usually speed on thrust. Just like the other more advanced aircraft, you need to look at what the aircraft is on if you are going to handfly with just part of the automation (i.e., the autothrottles), because if you are speed on pitch, the autothrottles are not going to be helping you much. If you have the autopilot off with a/t on, you need to make sure you're speed on thrust. The airplane still prevents any major goof ups by automatic high and low speed protection features, so the autothrottles will react if you get real slow or fast, but that would be considered poor technique!
MidlifeFlyer said:
jrh
Well-Known Member
Oh my, I could go on for WAY too long about this issue...but I can't stop myself...
Almost best glide speed. A little less than best glide speed, actually. However, that is coincidental, not because the two airspeeds are actually related.
This can be sort of complicated, but I'll try to explain it as best as possible.
Have you seen a "total drag curve" that comes from adding the induced drag and parasite drag curves together? It is sort of a lopsided "U" shape, or curved "checkmark" shape for most aircraft. Most private pilot textbooks should show one of these graphs somewhere inside.
The total drag curve is important because it directly corresponds to how much power is needed to maintain level, unaccelerated flight at a given airspeed. The reason for this is the basic equation that thrust must equal drag in unaccelerated flight. Have excess thrust? You'll climb. Have a lack of thrust? You'll descend. Give it just enough thrust to equal a point on the curve and you will be able to maintain level flight at that corresponding airspeed on the curve. Understand this principle and you've got a big part of the problem out of the way.
You were close by saying the transitional airspeed is best glide, but not quite. Best glide speed is derived from placing a tangential line against the underside of the curve and drawing it back to the origin of the graph (0 airspeed, 0 drag). The airspeed where the tangential line touches the drag curve is the point at which you will glide the furthest distance, assuming there is no headwind or tailwind. A headwind or tailwind shifts things a bit, but I won't get into that.
The very lowest point on the curve, where there is the least drag (at an airspeed slightly slower than best glide) is the point at which you get into the region of reverse command and need to start pitching for airspeed and powering for altitude.
Think about this in the real world. You're flying level at a given altitude. You reduce the power a little. The airplane begins to slow down. You pitch up a little to maintain altitude. Everything stabilizes. You're now flying level at a slower speed. You reduce the power a little more and everything repeats itself. Picture yourself incrementally sliding down that total drag curve (which could also be called the curve of power needed to maintain level flight). You can keep maintaining altitude with different power settings, but you will get slower and slower.
Sooner or later you will reach the bottom of that total drag curve. When that happens, you are entering the region of reverse command. Think about it. At that speed, if you back the power off you will start to slow down and sink. In response, you pitch up. But what does pitching up give you now? Less airspeed and therefore more drag, because you're adding induced drag on this side of the curve. More drag means a higher sink rate, not climbing like you want to do. So you start adding power. You can maintain altitude again. But if you pitch up, all you're doing is adding drag. In response, if you want to maintain altitude, you have to add power. What is this? Slow flight. Now look at the total drag curve again. It shows this requirement to add power at slower speeds, because you can see the drag rising again as you slow down.
Is this making sense?
Ok, now on to my point about flying approaches. Pitch for your aiming point, use power for airspeed. Just drive the plane down final like a car. How do you control a car? Point it where you want to go, then step on the gas to control how fast you get there. Same deal with a plane. If your aiming point stays at the same point in the windshield, you will eventually go straight to that point. Changing the power only changes how fast you get there.
That being said, here's a fine point I think a lot of people miss: If you change the power, you will need a small corresponding change in pitch in order to hold your point stationary in the windshield--that is because of that first principle I talked about, how excess power equals climb rate and lack of power equals descent rate.
For instance, reduce the power and leave the pitch the same. The plane will slow down and begin sinking at a faster rate of descent. This will steepen the approach path and consequently make the aiming point rise in the windshield. To hold the point in the same spot, you have to raise the nose to adjust the flight path (this also changes the angle of attack, but I don't want to get into that). The aircraft will slow down, but the way you got there was by reducing power, not because of pitching up. Pitching up and slowing down was the necessary consequence of reducing power.
Why does it matter? First of all, I don't know of any aircraft that fly final approaches significantly deep into the region of reverse command. To put that in perspective, a C-152 would have to come down final at about 50 knots or less in order to be on the "backside of the power curve." If you're on the front side of the curve, you need to use power for airspeed and pitch for altitude like you would in cruise.
I also say to fly this way mainly because it makes for more stabilized, precise approaches. Pitching for airspeed and using power for altitude will get you on the ground, but you might end up doing vertical S's down final because of it, unless you're perfectly stabilized early on.
As for all the comments about airliners...I don't know what to say. I've never flown one. I don't know the best way to fly approaches in them. But remember, you're not in an airliner. Fly the plane you are flying now, not what you used to fly, and not what you're going to fly.
I wish I had a white board and could go crazy drawing graphs and diagrams in person for you. This all makes a lot more sense when you see it visually.
Oh well. Hope this helps. Sorry for the long post. I get a little too excited about aerodynamics.
I don't like pitching for airspeed any time during approach, but I'll get to that in a minute...pkrgod said:
pkrgod said:
Almost best glide speed. A little less than best glide speed, actually. However, that is coincidental, not because the two airspeeds are actually related.
This can be sort of complicated, but I'll try to explain it as best as possible.
Have you seen a "total drag curve" that comes from adding the induced drag and parasite drag curves together? It is sort of a lopsided "U" shape, or curved "checkmark" shape for most aircraft. Most private pilot textbooks should show one of these graphs somewhere inside.
The total drag curve is important because it directly corresponds to how much power is needed to maintain level, unaccelerated flight at a given airspeed. The reason for this is the basic equation that thrust must equal drag in unaccelerated flight. Have excess thrust? You'll climb. Have a lack of thrust? You'll descend. Give it just enough thrust to equal a point on the curve and you will be able to maintain level flight at that corresponding airspeed on the curve. Understand this principle and you've got a big part of the problem out of the way.
You were close by saying the transitional airspeed is best glide, but not quite. Best glide speed is derived from placing a tangential line against the underside of the curve and drawing it back to the origin of the graph (0 airspeed, 0 drag). The airspeed where the tangential line touches the drag curve is the point at which you will glide the furthest distance, assuming there is no headwind or tailwind. A headwind or tailwind shifts things a bit, but I won't get into that.
The very lowest point on the curve, where there is the least drag (at an airspeed slightly slower than best glide) is the point at which you get into the region of reverse command and need to start pitching for airspeed and powering for altitude.
Think about this in the real world. You're flying level at a given altitude. You reduce the power a little. The airplane begins to slow down. You pitch up a little to maintain altitude. Everything stabilizes. You're now flying level at a slower speed. You reduce the power a little more and everything repeats itself. Picture yourself incrementally sliding down that total drag curve (which could also be called the curve of power needed to maintain level flight). You can keep maintaining altitude with different power settings, but you will get slower and slower.
Sooner or later you will reach the bottom of that total drag curve. When that happens, you are entering the region of reverse command. Think about it. At that speed, if you back the power off you will start to slow down and sink. In response, you pitch up. But what does pitching up give you now? Less airspeed and therefore more drag, because you're adding induced drag on this side of the curve. More drag means a higher sink rate, not climbing like you want to do. So you start adding power. You can maintain altitude again. But if you pitch up, all you're doing is adding drag. In response, if you want to maintain altitude, you have to add power. What is this? Slow flight. Now look at the total drag curve again. It shows this requirement to add power at slower speeds, because you can see the drag rising again as you slow down.
Is this making sense?
Ok, now on to my point about flying approaches. Pitch for your aiming point, use power for airspeed. Just drive the plane down final like a car. How do you control a car? Point it where you want to go, then step on the gas to control how fast you get there. Same deal with a plane. If your aiming point stays at the same point in the windshield, you will eventually go straight to that point. Changing the power only changes how fast you get there.
That being said, here's a fine point I think a lot of people miss: If you change the power, you will need a small corresponding change in pitch in order to hold your point stationary in the windshield--that is because of that first principle I talked about, how excess power equals climb rate and lack of power equals descent rate.
For instance, reduce the power and leave the pitch the same. The plane will slow down and begin sinking at a faster rate of descent. This will steepen the approach path and consequently make the aiming point rise in the windshield. To hold the point in the same spot, you have to raise the nose to adjust the flight path (this also changes the angle of attack, but I don't want to get into that). The aircraft will slow down, but the way you got there was by reducing power, not because of pitching up. Pitching up and slowing down was the necessary consequence of reducing power.
Why does it matter? First of all, I don't know of any aircraft that fly final approaches significantly deep into the region of reverse command. To put that in perspective, a C-152 would have to come down final at about 50 knots or less in order to be on the "backside of the power curve." If you're on the front side of the curve, you need to use power for airspeed and pitch for altitude like you would in cruise.
I also say to fly this way mainly because it makes for more stabilized, precise approaches. Pitching for airspeed and using power for altitude will get you on the ground, but you might end up doing vertical S's down final because of it, unless you're perfectly stabilized early on.
As for all the comments about airliners...I don't know what to say. I've never flown one. I don't know the best way to fly approaches in them. But remember, you're not in an airliner. Fly the plane you are flying now, not what you used to fly, and not what you're going to fly.
I wish I had a white board and could go crazy drawing graphs and diagrams in person for you. This all makes a lot more sense when you see it visually.
Oh well. Hope this helps. Sorry for the long post. I get a little too excited about aerodynamics.
MidlifeFlyer
Well-Known Member
Only if you realy suck as a pilot.jrh said:
Must be tough to be a "true believer" about nonsense.
B767Driver
New Member
jrh said:
Completely disagree on your technique. I find the speed on pitch method of flying final approach to permit a more stabilized approach. Configure the airplane and trim for final approach speed. Now slight pitch changes will very accurately maintain speed without a need to retrim the airplane. Very slight power adjustments will correct for approach variances.
If you make frequent power changes (the shuck and jive method) to control airspeed... 1) It will take awhile for the airspeed indicator to catch up with power change. The lag in indication results in less direct control of the target airspeed. 2. Every time a power change is made...the airplane will need to be retrimmed. 3. Pitching immediately for path will cause the airspeed to vary from the target... if the speed increases substantially...it is very difficult to recover unless the power is drastically reduced, thus hastening an unstablized approach.
An airliner flies the same way as a C152. When ready for descent from traffic pattern altitude...I trim and configure for final approach...reduce the power for an approximation of that required for the approach...then pitch to maintain target airspeed. If I find myself high...the first thing I'll do is reduce power...then maintain a pitch attitude that will keep me on the target airspeed and follow the airspeed to the proper approach profile. Once re-established on the profile...add power...adjust pitch to maintain airspeed.
In every airplane I've flown...to make a good landing...requires precise airspeed control on final and into the flare. I've found this best done using the speed on pitch method...using power to adjust for the proper approach path.
The only exception would be on an ILS approach. Due to the sensitivity of the glideslope...I find it best to pitch for the path...and adjust power for airspeed.
jrh
Well-Known Member
Midlife--I don't understand your position. First you say:
Then, to the "other way" that I teach, you say:
Maybe I misunderstood you, but it looks like one minute you look at "pitch for altitude, power for airspeed" as a valid alternative way to look at things, then the next minute you call it "nonsense."
I've read from several reputable authors, been taught by multiple CFIs, and been told in no uncertain terms by two designated examiners that a pilot should always pitch for their point, then use power to control airspeed during approach.
Let me explain myself further in another post...
MidlifeFlyer said:
Then, to the "other way" that I teach, you say:
MidlifeFlyer said:
Maybe I misunderstood you, but it looks like one minute you look at "pitch for altitude, power for airspeed" as a valid alternative way to look at things, then the next minute you call it "nonsense."
I've read from several reputable authors, been taught by multiple CFIs, and been told in no uncertain terms by two designated examiners that a pilot should always pitch for their point, then use power to control airspeed during approach.
Let me explain myself further in another post...
jrh
Well-Known Member
Ok, I'm with you on this idea. The key words are "slight" and "very slight" here. We both agree that pitch, power, altitude, and airspeed are all continuously intertwined. The difference is more in the way we visualize the approach. As long as the control inputs are very slight, nothing goes wrong with either method.B767Driver said:
B767Driver said:
I know and have seen exactly what you're saying. Isn't this also considered a pilot "getting out of phase" with an aircraft? The pilot is overcorrecting for variances that are fairly slight. The problems you describe won't happen if the pilot makes subtle control inputs and is patient with the aircraft.
The key to making the "pitch for your point, power for airspeed" method work is to make sure you don't overcorrect. But not overcorrecting applies to almost every operation in every phase of flight. The same could be said for pitching for airspeed and using power for altitude.
Here's the way I teach the approach on final: You should already be reasonably close to aimed at your point and reasonably trimmed out and stabilized on whatever airspeed you want. If you don't have those things going for you already, you have more to worry about outside of the scope of this discussion.
If the aiming point begins to slide under the nose, in other words, you are getting high, that means you need to lower the nose. But what happens if you lower the nose and leave the power the same? You will begin to increase airspeed. To keep the airspeed from increasing, you need to decrease the power simultaneously as you lower the nose. How much to lower the nose, and how much to decrease power? I don't know...do it by feel and experience.
The same thing applies to any phase of flight on the front side of the power curve. If you want to maintain a given airspeed, whenever the pitch is changed, the power must be changed also. And if the power is changed, the pitch must be changed. The two go hand in hand. They can't be seperated.
For me, teaching the "pitch for point, power for airspeed" method makes the most sense. It seems intuitive, at least for me. I give people a base line power setting to use initially, then encourage them to either leave the power where it is at, or make slight reductions. The throttle jockeying that you talk about is definitely inappropriate.
The reason I made my comment about vertical S's on final is because I've seen pilots get ridiculously out of touch with the aircraft while trying to use pitch for airspeed and power for altitude. They come in high and fast, so what do they do to reduce speed? Pitch up. And where does that take them? Up even higher, so they chop the power. Then, because they chop the power and they have the pitch too high, all of their airspeed decays. In order to regain airspeed, they lower the nose. However, because they're so high from their first excursion of pitching up, they lower the nose too far in an effort to dive for the runway. The diving causes their airspeed to increase again, but because they have no power left to reduce, they have to either accept the gain in airspeed and come screaming into the flare, or pitch up and start the cycle all over again.
I think either method works if the pilot has a feel for the plane, thinks ahead, and makes simultaneous pitch/power adjustments. You could also say that neither method works if the pilot gets out of phase with the aircraft.
Does this make the "pitch for point, power for airspeed" method any more acceptable? Or do you still consider it poor technique?
MidlifeFlyer
Well-Known Member
It sounds like I may have misunderstood you, in which case I apologize.jrh said:
In the part I quoted, you seem to say that if you don't do it your way, you will end up doing vertical Ses. That sure sounded like "=this= is the only right way. If you do it the other way you are wrong."
But I guess I was mistaken about that. Sorry.
Blah, blah, blah...
I say potato, you say..."I do it this way...yadda yadda yadda". To answer your question, take a look at the typical power curve for piston powered aircraft (don't know how to post links to pictures...sorry).
When looking at graphical representation of the airspeed/power required relationships you will notice that a given power setting will result in two airspeeds (pitch attitudes) that will achieve straight and level flight (angle of attacks if you want to get critical, but we are talking straight and level, so pitch angle works o.k.). The top (or bottom, depending on how you graph it) of the parabola is L/D max, so I guess the anwer to your question is right there at an airspeed equal to L/D max is where the "change over" occurs.
Meaning at an airspeed slower than this, you will need more power to increase altitude, and an airspeed faster than this you can pull back and the houses get smaller. -Yes I know you will get slower doing this, but we are simply talking the relationship between airspeed and power setting.
It is more efficient to cruise on the faster side of this curve, however it is tough to flare if you are flying faster than L/D max.
pkrgod said:
I say potato, you say..."I do it this way...yadda yadda yadda". To answer your question, take a look at the typical power curve for piston powered aircraft (don't know how to post links to pictures...sorry).
When looking at graphical representation of the airspeed/power required relationships you will notice that a given power setting will result in two airspeeds (pitch attitudes) that will achieve straight and level flight (angle of attacks if you want to get critical, but we are talking straight and level, so pitch angle works o.k.). The top (or bottom, depending on how you graph it) of the parabola is L/D max, so I guess the anwer to your question is right there at an airspeed equal to L/D max is where the "change over" occurs.
Meaning at an airspeed slower than this, you will need more power to increase altitude, and an airspeed faster than this you can pull back and the houses get smaller. -Yes I know you will get slower doing this, but we are simply talking the relationship between airspeed and power setting.
It is more efficient to cruise on the faster side of this curve, however it is tough to flare if you are flying faster than L/D max
.