Explaining in the simplest manner the power curve.
- Thread starter CaptainChris87
- Start date
B767Driver
New Member
Re: Explaining in the simplest mannar the power curve.
This is something you mentioned earlier, and we may not have the same understanding of the "backside of the power curve". My understanding is that it is the region where drag increases exponentially due to an increase in induced drag. So, it requires more power to maintain altitude the slower you go.
However, power available still exceeds power required and the airplane is free to climb and descend as excess power will still exceed the weight plus drag component of the airplane. At the extreme lower end of the power curve, I agree with you, power available will be less than required....and at this time...the airplane will only have one option...to descend...regardless of elevator inputs. However, at many points on the backside of the power curve, the airplane is maneuverable in a climb or descent as long as enough power is added and available.
This is something you mentioned earlier, and we may not have the same understanding of the "backside of the power curve". My understanding is that it is the region where drag increases exponentially due to an increase in induced drag. So, it requires more power to maintain altitude the slower you go.
However, power available still exceeds power required and the airplane is free to climb and descend as excess power will still exceed the weight plus drag component of the airplane. At the extreme lower end of the power curve, I agree with you, power available will be less than required....and at this time...the airplane will only have one option...to descend...regardless of elevator inputs. However, at many points on the backside of the power curve, the airplane is maneuverable in a climb or descent as long as enough power is added and available.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
I left out part of the explanation to address your exact question. You asked about staying on the glideslope, rather than airspeed.
My training goals are always zero deviation. Perfect airspeed, perfect localizer, perfect glideslope. I never *intentionally* accept a deviation. That said, some of the GA training materials find small airspeed variations perfectly acceptable. One of the most commonly used is by Peter Dogan, the Instrument Flight Training Manual. He recommends accepting small deviations, making power changes only when they become close to PTS limits. Generally, absent sharp wind gradients, this is possible to do, well within PTS limts.
Still, I disagree with him.
Let me step back and go over what's happening when you try to maintain proper airspeed too.
If you're below glideslope, you need to increase your excess power in order to return and stay on the glideslope. You can do this by decreasing your drag by pulling back on the yoke slightly, or you can increase your power setting.
Using the yoke is preferable, because it's quicker. However, pulling back on the yoke results in a reduction in airspeed, eventually. Adding power would fix the problem, without changing the airspeed, but it's slow.
The best technique is a combination of both. Pull back on the yoke and add a touch of power. As the power kicks in, the yoke is returned to the original position. We think about this as "pitching for glideslope and powering for airspeed", but the aerodynamics is the reverse.
The reason I originally said "airspeed reductions" to remain on glideslope, I was merely explaining why it worked, not making a recommendation.
I left out part of the explanation to address your exact question. You asked about staying on the glideslope, rather than airspeed.
My training goals are always zero deviation. Perfect airspeed, perfect localizer, perfect glideslope. I never *intentionally* accept a deviation. That said, some of the GA training materials find small airspeed variations perfectly acceptable. One of the most commonly used is by Peter Dogan, the Instrument Flight Training Manual. He recommends accepting small deviations, making power changes only when they become close to PTS limits. Generally, absent sharp wind gradients, this is possible to do, well within PTS limts.
Still, I disagree with him.
Let me step back and go over what's happening when you try to maintain proper airspeed too.
If you're below glideslope, you need to increase your excess power in order to return and stay on the glideslope. You can do this by decreasing your drag by pulling back on the yoke slightly, or you can increase your power setting.
Using the yoke is preferable, because it's quicker. However, pulling back on the yoke results in a reduction in airspeed, eventually. Adding power would fix the problem, without changing the airspeed, but it's slow.
The best technique is a combination of both. Pull back on the yoke and add a touch of power. As the power kicks in, the yoke is returned to the original position. We think about this as "pitching for glideslope and powering for airspeed", but the aerodynamics is the reverse.
The reason I originally said "airspeed reductions" to remain on glideslope, I was merely explaining why it worked, not making a recommendation.
PositionAndHold
Well-Known Member
The point of the whole article was for the "typical pilot", not designed for an aero engineering class.
I think TG it irks you more then any thing that we as pilots still manage to fly with out the knowledge you have in regards to aerodynamics. I do not need that level of understanding to ba a safe pilot nor do I want it. I am sorry if I am just a "typical pilot", but if you were my instructor and made me study the areo stuff till I understood it like you, I would find a new instructor. I think every pilot would benifit more from some tail wheel time and aerobatic training, then from that level of aerodynamic understanding. But it won't happen, and they will still be safe pilots.
You are waaaaaaay smarter then me, I realize that. But I think you need to realx a bit and focus on the bigger picture, of creating a safe pilot.
We fly airplanes not design them.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
Well, yes. But to say "it requires more power to maintain altitude the slower you go. " is the same thing as saying "if you increase your AOA, your power required goes up, rather than down." These are synonymous interpretations. I can explain further if necessary. I may need to draw a chart.
Being on the backside of the power curve does not mean that the aircraft cannot climb, it has to do with what happens when you make an AOA change. Normally, on the front side of the curve, if you pull back on the yoke, you will climb. If you pull back further, you rate of climb will increase. Up to a point. There is an airspeed below which when you increase your AOA, you climb rate will go down. This is normally not what you want (region of reverse command). If you pull back further, your climb rate will further decrease. Eventually, you may end up in a descent, if you don't stall first.
When you are on the glideslope, if you got behind the power curve and got low, pulling back on the yoke would increase your descent rate. Yes, increasing your power would fix this, but then you're not pitching for altitude, you're powering. That's what I mean when pitching for descent rate doesn't work behind the power curve. BTW, generally you're not behind the power curve on an instrument approach...you'd have to screw up big time.
Well, yes. But to say "it requires more power to maintain altitude the slower you go. " is the same thing as saying "if you increase your AOA, your power required goes up, rather than down." These are synonymous interpretations. I can explain further if necessary. I may need to draw a chart.
Being on the backside of the power curve does not mean that the aircraft cannot climb, it has to do with what happens when you make an AOA change. Normally, on the front side of the curve, if you pull back on the yoke, you will climb. If you pull back further, you rate of climb will increase. Up to a point. There is an airspeed below which when you increase your AOA, you climb rate will go down. This is normally not what you want (region of reverse command). If you pull back further, your climb rate will further decrease. Eventually, you may end up in a descent, if you don't stall first.
When you are on the glideslope, if you got behind the power curve and got low, pulling back on the yoke would increase your descent rate. Yes, increasing your power would fix this, but then you're not pitching for altitude, you're powering. That's what I mean when pitching for descent rate doesn't work behind the power curve. BTW, generally you're not behind the power curve on an instrument approach...you'd have to screw up big time.
tgrayson
New Member
And I wouldn't blame you.
The level of discussion here isn't what a private pilot needs to know. These are discussions intended to decide what to *teach*.
When I quiz a private student, and I say "What controls airspeed?", I want to hear "elevator", or "yoke", or "angle of attack". When I ask "What makes an airplane climb?", I want to hear "Power!" or "Thrust!" When I ask "What do flaps do?", I want to hear "Lower your stall speed." I don't expect that a private student can explain why these things are true.
Trust me, even getting CFI students to be able to discuss these things knowledgeably is very, very difficult.
B767Driver
New Member
Re: Explaining in the simplest mannar the power curve.
I pretty much agree with all of your clarifications.
The above still bothers me. You've escalated your power available...and now the pitch control still works like it always has, albeit less crisp in handling, where a change in pitch attitude will result in a corresponding change in climb/descent rate, and aircraft control will ultimately work just like the front side of the power curve up to where Pr > Pa.
I pretty much agree with all of your clarifications.
The above still bothers me. You've escalated your power available...and now the pitch control still works like it always has, albeit less crisp in handling, where a change in pitch attitude will result in a corresponding change in climb/descent rate, and aircraft control will ultimately work just like the front side of the power curve up to where Pr > Pa.
PositionAndHold
Well-Known Member
And I wouldn't blame you.
The level of discussion here isn't what a private pilot needs to know. These are discussions intended to decide what to *teach*.
When I quiz a private student, and I say "What controls airspeed?", I want to hear "elevator", or "yoke", or "angle of attack". When I ask "What makes an airplane climb?", I want to hear "Power!" or "Thrust!" When I ask "What do flaps do?", I want to hear "Lower your stall speed." I don't expect that a private student can explain why these things are true.
Trust me, even getting CFI students to be able to discuss these things knowledgeably is very, very difficult.
So what your saying is you "dumb it down" (your words not mine) for the typical pilot. Isn't this what you were mad at the article for? What I have been saying is he did a good job of "dumbing it down" for us typical pilots.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
Not quite....the *shape* of the power required curve has not changed, only the difference between required and available. It's the "U" shape of the required curve that causes the problem
If you are on the left side of the "U", then increasing your AOA will make your climb rate worse, no matter what it was to begin with. If you're climbing as a result of increased power, then pulling back on the yoke will reduce that climb rate. To climb better, you would have to push the yoke forward to increase your airspeed.
We see this when teaching student pilots all the time. The student pilot will get low and slow in short final. If the instructor must take control, it's full power and push on the yoke. Without the push, the airspeed will never come up and you may mush into the ground.
Not quite....the *shape* of the power required curve has not changed, only the difference between required and available. It's the "U" shape of the required curve that causes the problem
If you are on the left side of the "U", then increasing your AOA will make your climb rate worse, no matter what it was to begin with. If you're climbing as a result of increased power, then pulling back on the yoke will reduce that climb rate. To climb better, you would have to push the yoke forward to increase your airspeed.
We see this when teaching student pilots all the time. The student pilot will get low and slow in short final. If the instructor must take control, it's full power and push on the yoke. Without the push, the airspeed will never come up and you may mush into the ground.
tgrayson
New Member
Not dumbed down, because those things are the truth. There may be an element of rote memorization to it. Still, my first few flight hours are spent showing the student that the yoke controls airspeed. I even show him that the throttle alone will make the airplane go slower as it pitches up after full throttle application.
Will he understand all the nuances? No, probably not. But he is well prepared for future growth.
My own instructor as a private taught me that power controls altitude, but I didn't understand at the time; he probably didn't either. But I eventually understood; had he taught me incorrectly, it would have been far more difficult.
B767Driver
New Member
Re: Explaining in the simplest mannar the power curve.
I'll buy that. At first I thought you were saying that you could not climb on the backside. But I'll agree that you cannot increase your climb rate on the back side.
I'll buy that. At first I thought you were saying that you could not climb on the backside. But I'll agree that you cannot increase your climb rate on the back side.
tgrayson
New Member
Re: Explaining in the simplest mannar the power curve.
Thank you. Maybe I made one sale today.
I don't know if this is still true of modern delta wings, but I understand in days gone by, a number of them crashed on the approach because they got so far behind the drag curve that they simply didn't have enough thrust to overcome the drag. While it seems startling that an airplane could get so dragged up, this is easer on a delta wing because of the low aspect ratio. Not only is the induced drag very high, the stalling AOA is also very high, in the 30 degree range, so it can climb quite a ways up the drag curve.
Thank you. Maybe I made one sale today.
I don't know if this is still true of modern delta wings, but I understand in days gone by, a number of them crashed on the approach because they got so far behind the drag curve that they simply didn't have enough thrust to overcome the drag. While it seems startling that an airplane could get so dragged up, this is easer on a delta wing because of the low aspect ratio. Not only is the induced drag very high, the stalling AOA is also very high, in the 30 degree range, so it can climb quite a ways up the drag curve.
seagull
Well-Known Member
seagull
Well-Known Member
Thanks. I think most of the guys I know were there well after you.