Region of reverse command

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Confusednewbiepilot

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Confusednewbiepilot
Hey flyers,

As per my name, I am 7 lessons into my PPL. I suppose I will be posting here a lot.

My question is regarding the region of reverse command and what it pertains to.

I understand that the roles reverse and that pitch is for altitude and power is for airspeed.

Is this only the case during low air speed? When getting set up for slow-flight or power-off stalls, I seem to take forever to get configured and I am fighting with the airspeed and altitude once those flaps come down.

Do I need to pitch for altitude and power for air speed when getting configured for slow flight and power-off stalls?

Secondly, does trim also hold altitude as well as airspeed?

When I change altitude, my airspeed also changes (for example, I find it difficult to maintain 74 knots when putting full power in to climb)

Please don’t laugh… thank you
 
Ugh,and hoooo boy! It sounds like you might have an air force guy or airline pilot for an instructor, or that your instructor was taught in that methodology of pitch for altitude and power for airspeed. That can work, but it's not the easiest way to teach a primary student and it IS confusing.

You're probably going to read several different theories here, and there are valid reasons behind them more than likely but right now, you need to realize that there ARE different categories of aircraft that are flown differently. You don't need to worry about all of them, or aircraft that you aren't currently flying.

More than likely, you are flying a standard, light, civilian aircraft powered by a single piston engine with relatively low energy. This aircraft is a whole lot closer to a glider than it is to a jet.

Now, imagine yourself in an aircraft without an engine - a glider or sailplane. You don't have an engine to speed up, there is only one way to increase your airspeed - point the nose down. Pulling the nose up will result in slower speeds or a stall, which you don't want. What you want is to establish a steady airspeed. In the glider, the way to achieve this is to fly the same pitch in a steady descent.

If you are in your light trainer, and you fly up to about 3000-4000' AGL, pull the power back to nearly idle, don't touch it, and play with your pitch a little for 500-1000 feet. If you pull up, you WILL slow down. If you pitch down, you WILL speed up. Learn to look outside the plane and pitch the cowling in front of you relative to the horizon for the speed you want, and trim the controls so you can take your hands off and it maintains that pitch.

When you add power back in to the mix, you use various settings for things like cruise flight (relatively high settings) and lower or nearly idle settings when descending or landing - and it will behave closer to a glider in a descent unless you are doing a lot of throttle jockeying, which is not helpful and definitely destabilizes you.

Trim holds PITCH. It's making the elevator want to ride in a certain location for a given airflow.

Power can be used to adjust airspeed, for sure, and both pitch and power must be used together, but it's easiest to think of your plane as a glider with the ability to use the power to to slow the rate of descent for a given pitch. It's actually easier in light planes to use pitch for airspeed and power for rate of descent when you are landing.

It SOUNDS like you may be keeping your eyes inside the cockpit and looking at the instruments too much as well. If you are chasing needles you are going to be behind what is happening outside. Try looking outside a LOT more.

Where are you training??? This is stuff a student show know by like lesson 2-3.
 
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Confusednewbiepilot said:
I understand that the roles reverse and that pitch is for altitude and power is for airspeed.
Click to expand...
I'll just take this one. If you are close to stalling, raising pitch could stall the wing. Adding power could result in a climb or slower descent. That's the opposite of what you wrote.
 
Thrust required for level flight is equal to the amount of total drag produced. Due to total drag being the sum of induced drag and parasite drag, the total drag is high both at low speed and at high speed. There is a speed in the middle where drag as at a minimum.

The minimum drag speed is a relatively low airspeed, and 99% of the time we are flying faster than this speed. We are typically only slower than this speed for a very brief period just after liftoff and just before landing, or when it is practiced deliberately during slow-flight.

Screenshot 2023-07-29 at 11.40.43 PM.png

As the aircraft slows down below the speed for minimum drag, drag increases, requiring more thrust. The slower you go the more thrust (and power) you need. Raising the nose below this speed will result in an airspeed reduction, and, after the aircraft stabilizes at the new speed, may result in a descent if power is not increased. This is why it is often called "the region of reverse command" — the pilot pitched up but now the aircraft is descending.

Slow flight is usually performed as follows: Starting at cruise speed, we reduce power to a predetermined setting (in accordance with experience and practice) and maintain altitude with pitch. We add flaps and continue maintaining altitude with pitch. We add trim so we don't have to fight the elevator. As the airspeed gets close to stall speed, we will be in the low-speed, high drag region of the graph above and power has to be added aggressively to maintain altitude at the slower speed. Small deviations from the desired altitude or airspeed should be corrected with both pitch and power coordinated together.
 
When you are cruising around, moving the yoke back with result in a climb at a rather quick rate. Airspeed will bleed off initially at a slow rate.

If you are slow, behind the power curve, pulling the yoke back with not give you that positive climb you previously experienced. You will see a marginal climb (if any at all) and a large loss in your airspeed. The thing to do here is to increase power setting for more altitude while carefully adjusting pitch to give you the airspeed desired.
 
In regards of to slow flight practice, we used to set the power to 1500 rpm, progressively increase flaps, hold altitude with pitch/trim, then when the airspeed bleeds down to desired number set the lower to approx 2000 rpm. Adjust pitch and power as required to hold the altitude.

When you do your slow flight turns, only bank the plane 5-10 degrees max. Larger banks will reduce the vertical component of lift and make it difficult for you to hold altitude. Small banks are just fine because the slower airspeed has a tighter turn radius, and also it isn’t a race to make that turn.

Once configured, to descend just reduce your power setting. To climb, add power. Pitch for the airspeed you desire. Flight the instinct to make big pitch changes to climb/descent as that will mess up your airspeed.
 
I never liked the "this control does this and that control does that and never do the two meet" concept.

Like the ailerons and rudder, pitch and power need to be coordinated. You can pitch and climb, but at a slower speed. Or you can add power and climb at the same airspeed. Or you can add pitch and power and climb at a higher rate, at an intermediate airspeed.

They work together.

To enter slow flight, reduce the power, and increase pitch to hold altitude as you slow down. You can reduce power to idle to slow down the quickest, then when you get to the desired speed, add power to hold that speed.
 
It's good to understand the theory behind what's happening, but it's most important to understand how to control things with out doing an engineering analysis for each perturbation.

Being slow at this stuff is fine, get it out of your head that you need to get configured and flying a regimen in a small amount of time. At this point you are learning, take as long as you need. With experience you'll get quicker, but you should never rush doing this stuff.

When I trained for ppl, slow flight was done by slowing until the stall horn was blaring and the wing was starting to buffet. You maintained this speed with pitch. The drill was to fly straight and level for a bit, then turn 90 degrees one way, then 90 the other, both to headings. Then maintain the heading. The take away was feeling how sloppy the controls got, how easy it was to stall, especially in the turns, that you needed power to maintain altitude, that finesse made life a lot easier. And most importantly, staying coordinated was critical to keeping bad things from happening. It sounds like a lot, but it's really pretty easy.

Now when I do it for recurrent training, you just have to hit an airspeed, which is pretty slow, but you are not hanging at the edge of stall, so it's even easier, but the lesson is the same.

I had to do this on my checkride. The examiner asked for it, it was a real bumpy, gusty day. I got configured, had the stall warning blaring, then bam, a gust hit us and the nose dropped, full stall. So I did a recovery, got back to altitude, the examiner was just looking at me. When I was level, back at altitude, I thought I had busted the check ride. I told him "I stalled the airplane, that wasn't supposed to happen, can I try it again?" He smiled a little and said "sure". I got my PPL that day.

You're 7 lessons in, study hard, listen to your instructor, you'll be fine.


Edit: Oh, and ask your instructor to demonstrate being in the region of reverse command. Not a big deal, you just don't want to stay there low to the ground.
 
This is REALLY a deep and fundamental concept, that won’t make sense until it does.

Also keep in mind, your body and brain can assimilate it before your conscious brain does. You probably don’t have a good physical (as in physics) understanding of what happens when you shoot a free throw or park a car, yet you can. So….

One concept I teach EARLY is the fundamental difference between flying and nearly all the other hand eye coordination things you do (think sports), and that is flying is ANYTHING but muscle memory, it’s visual memory. You teach your brain to do WHAT EVER is necessary to make the proper sight picture for the maneuver. Sometimes you push, other times you pull. Doesn’t matter, make the sight picture correct, make the power setting correct, you WILL get predictable results. This is known as “power plus pitch equals performance”. Period.

Apply this to slow flight, your brain will assimilate all the rest in time, and rapidly enough to be efficient.

Next comes “PAT”: power attitude trim.

I frequently won’t allow students to use trim until certain concepts are assimilated. Once it’s assimilated, we can discuss WHY. Once in a while I get a student that MUST understand the why BEFORE the what, frankly, I’m that way…
 
Pinecone said:
I never liked the "this control does this and that control does that and never do the two meet" concept.

Like the ailerons and rudder, pitch and power need to be coordinated. You can pitch and climb, but at a slower speed. Or you can add power and climb at the same airspeed. Or you can add pitch and power and climb at a higher rate, at an intermediate airspeed.

They work together.

To enter slow flight, reduce the power, and increase pitch to hold altitude as you slow down. You can reduce power to idle to slow down the quickest, then when you get to the desired speed, add power to hold that speed.
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This is a pretty good explanation.

The only things the pilot is directly controlling are power, elevator, ailerons, trim and rudder. Airspeed, climb rates etc.. are outcomes, and they are much more interelated and cannot be attributed to a single control input. You could think of it is as a sequence of events, one leading to another. The pilot has to respond to each outcome with an action, resulting in a feedback loop until airplane reaches the desired stable condition. For example, in cruise flight, power increase (pilot) -> pitch increase ->vertical speed positive/airspeed increase -> trim down (pilot) -> pitch decrease -> vertical speed zero/airspeed increase. In slow flight regime, power increase -> pitch increase -> vertical speed negative/airspeed decrease -> trim down (pilot) -> pitch decrease -> vertical speed zero/airspeed increase. You can do a similar flow chart for flap extension, power changes etc.. It is useful to do this on the ground as an exercise and then experiment with it in the air.
 
Confusednewbiepilot said:
My question is regarding the region of reverse command and what it pertains to.

I understand that the roles reverse and that pitch is for altitude and power is for airspeed.
Click to expand...
No, you don't understand. There is no "region of reverse command.".

Power controls rate of climb at a constant airspeed, pitch (or more properly, angle of attack) controls airspeed.

If you try to adjust your speed by adjusting power, you have to also adjust pitch, since it's pitch that controls airspeed. If you're holding a constant airspeed and want to climb, got have to add power; raise the nose without adding power and you'll slow down.

If you're flying very slow and try to climb by increasing pitch, you may stall, or if not, the drag increases rapidly (because you're in that region of the drag curve), speed drops more, you pitch up even more to maintain altitude, drag increases even more, so the plane slows down even more, etc... until you stall (or add power, which you should have done in the first place).
 
Dana said:
No, you don't understand. There is no "region of reverse command.".

Power controls rate of climb at a constant airspeed, pitch (or more properly, angle of attack) controls airspeed.

If you try to adjust your speed by adjusting power, you have to also adjust pitch, since it's pitch that controls airspeed. If you're holding a constant airspeed and want to climb, got have to add power; raise the nose without adding power and you'll slow down.

If you're flying very slow and try to climb by increasing pitch, you may stall, or if not, the drag increases rapidly (because you're in that region of the drag curve), speed drops more, you pitch up even more to maintain altitude, drag increases even more, so the plane slows down even more, etc... until you stall (or add power, which you should have done in the first place).
Click to expand...


So, I'm not an instructor, but IMO where the "region of reverse command" can get you in trouble is on take off. You lift off, and pitch the nose too high. I've done this a couple of times in my flying, during training with an instructor and usually while flustered. The last time was a few years ago during instrument training, I took off, there were two instructors in the airplane, and I pitched up too high. Not sure why I did it, but I recognized it immediately. The symptoms were simple, it was an SR-22, the nose was high, the airplane was at the top of ground effect, it wouldn't accelerate and wasn't climbing. The solution is equally simple, although not intuitive if you don't understand what is happening. You simply lower the nose to the proper attitude, the airplane will accelerate and begin climbing. Where pilots get themselves in trouble is they realize they are not climbing and pull the nose further up, to disastrous results.

The instructor in the right seat was my primary instrument instructor, he knew me, and generally doesn't help out unless I really f up, which hasn't happened in a long, long time. The instructor in the back seat was his protege. During the lesson debrief the back seat instructor asked me what happened during the take off. While I was doing it, I had said out loud, "crap, I'm behind the power curve, lowering the nose." I told the instructor I over rotated, we weren't going to climb like that, so I fixed it.
 
understand what is actually meant by “region of reverse command.” It’s not about changing how you control the airplane, it’s simply a reversal of the power requirements that we normally think appropriate. From the Pilot’s Handbook of Aeronautical Knowledge:

Flight in the region of normal command means that while holding a constant altitude, a higher airspeed requires a higher power setting and a lower airspeed requires a lower power setting….

Flight in the region of reverse command means flight in which a higher airspeed requires a lower power setting and a lower airspeed requires a higher power setting to hold altitude.
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Another way to explain L/D max, the top of that curve, the crossover point if you will, is: if you push forward you go down, if you pull back, you go down. Once you understand why, you’re well on your way.
 
Dana said:
No, you don't understand. There is no "region of reverse command.".

Power controls rate of climb at a constant airspeed, pitch (or more properly, angle of attack) controls airspeed.

If you try to adjust your speed by adjusting power, you have to also adjust pitch, since it's pitch that controls airspeed. If you're holding a constant airspeed and want to climb, got have to add power; raise the nose without adding power and you'll slow down.

If you're flying very slow and try to climb by increasing pitch, you may stall, or if not, the drag increases rapidly (because you're in that region of the drag curve), speed drops more, you pitch up even more to maintain altitude, drag increases even more, so the plane slows down even more, etc... until you stall (or add power, which you should have done in the first place).
Click to expand...

At cruise speed, increasing pitch results in a climb and a slower airspeed.
At slow speeds (below the best glide speed for range), increasing pitch results in a descent and a slower airspeed.
You can call it by a different name, but "region of reverse command" is just one way of referring to a flight regime where induced drag is higher than parasite drag.
 
Most of us know it as the back side of the power curve, and it’s important since it’s used every time we land. Other than when demonstrating slow flight, there’s not any use for it outside of the pattern.

Wait for it…. Somebody’ll tell me I’m wrong.
 
Thank you all kindly for your input. I’m just going to have to do some trial and error. I suppose.
 
PaulS said:
It's good to understand the theory behind what's happening, but it's most important to understand how to control things with out doing an engineering analysis for each perturbation.

Being slow at this stuff is fine, get it out of your head that you need to get configured and flying a regimen in a small amount of time. At this point you are learning, take as long as you need. With experience you'll get quicker, but you should never rush doing this stuff.

When I trained for ppl, slow flight was done by slowing until the stall horn was blaring and the wing was starting to buffet. You maintained this speed with pitch. The drill was to fly straight and level for a bit, then turn 90 degrees one way, then 90 the other, both to headings. Then maintain the heading. The take away was feeling how sloppy the controls got, how easy it was to stall, especially in the turns, that you needed power to maintain altitude, that finesse made life a lot easier. And most importantly, staying coordinated was critical to keeping bad things from happening. It sounds like a lot, but it's really pretty easy.

Now when I do it for recurrent training, you just have to hit an airspeed, which is pretty slow, but you are not hanging at the edge of stall, so it's even easier, but the lesson is the same.

I had to do this on my checkride. The examiner asked for it, it was a real bumpy, gusty day. I got configured, had the stall warning blaring, then bam, a gust hit us and the nose dropped, full stall. So I did a recovery, got back to altitude, the examiner was just looking at me. When I was level, back at altitude, I thought I had busted the check ride. I told him "I stalled the airplane, that wasn't supposed to happen, can I try it again?" He smiled a little and said "sure". I got my PPL that day.

You're 7 lessons in, study hard, listen to your instructor, you'll be fine.


Edit: Oh, and ask your instructor to demonstrate being in the region of reverse command. Not a big deal, you just don't want to stay there low to the ground.
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Thank you so much
 
Stewartb said:
Most of us know it as the back side of the power curve, and it’s important since it’s used every time we land. Other than when demonstrating slow flight, there’s not any use for it outside of the pattern.

Wait for it…. Somebody’ll tell me I’m wrong.
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Nope, you right. :)

An interesting demonstration is to settle down on any particular airspeed and hold the stick out yoke rigid, then change the power setting. After a few oscillations the plane will settle down at the same airspeed or close to it.

The above demonstration may or may not work with a trim setting as the trim tab authority is itself affected by the airflow from prop wash.
 
So, I'm not an instructor, but IMO where the "region of reverse command" can get you in trouble is on take off. You lift off, and pitch the nose too high. I've done this a couple of times in my flying, during training with an instructor and usually while flustered. The last time was a few years ago during instrument training, I took off, there were two instructors in the airplane, and I pitched up too high. Not sure why I did it, but I recognized it immediately. The symptoms were simple, it was an SR-22, the nose was high, the airplane was at the top of ground effect, it wouldn't accelerate and wasn't climbing. The solution is equally simple, although not intuitive if you don't understand what is happening. You simply lower the nose to the proper attitude, the airplane will accelerate and begin climbing. Where pilots get themselves in trouble is they realize they are not climbing and pull the nose further up, to disastrous results.
PaulS said:
The instructor in the right seat was my primary instrument instructor, he knew me, and generally doesn't help out unless I really f up, which hasn't happened in a long, long time. The instructor in the back seat was his protege. During the lesson debrief the back seat instructor asked me what happened during the take off. While I was doing it, I had said out loud, "crap, I'm behind the power curve, lowering the nose." I told the instructor I over rotated, we weren't going to climb like that, so I fixed it.
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Actually being in the region of reverse command gets you into trouble when low and slow with full flaps / gear extended during landing. Taking off isn’t that much of a factor.
 
Clip4 said:
Actually being in the region of reverse command gets you into trouble when low and slow with full flaps / gear extended during landing. Taking off isn’t that much of a factor.
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Not normally, but imagine high gross weight at high DA when flown by a pilot who is used to sea-level performance. Or accidentally taking off with flaps or too much nose-up trim.
 
Clip4 said:
So, I'm not an instructor, but IMO where the "region of reverse command" can get you in trouble is on take off. You lift off, and pitch the nose too high. I've done this a couple of times in my flying, during training with an instructor and usually while flustered. The last time was a few years ago during instrument training, I took off, there were two instructors in the airplane, and I pitched up too high. Not sure why I did it, but I recognized it immediately. The symptoms were simple, it was an SR-22, the nose was high, the airplane was at the top of ground effect, it wouldn't accelerate and wasn't climbing. The solution is equally simple, although not intuitive if you don't understand what is happening. You simply lower the nose to the proper attitude, the airplane will accelerate and begin climbing. Where pilots get themselves in trouble is they realize they are not climbing and pull the nose further up, to disastrous results.

Actually being in the region of reverse command gets you into trouble when low and slow with full flaps / gear extended during landing. Taking off isn’t that much of a factor.
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MANY mishap reports disagree.

Most times with high density altitude and near gross weight.
 
Taxi onto the runway. Push the yoke forward, when you hit Vr, push in the throttle and climb.
 
RyanShort1 said:
Ugh,and hoooo boy! It sounds like you might have an air force guy or airline pilot for an instructor, or that your instructor was taught in that methodology of pitch for altitude and power for airspeed. That can work, but it's not the easiest way to teach a primary student and it IS confusing.

You're probably going to read several different theories here, and there are valid reasons behind them more than likely but right now, you need to realize that there ARE different categories of aircraft that are flown differently. You don't need to worry about all of them, or aircraft that you aren't currently flying.

More than likely, you are flying a standard, light, civilian aircraft powered by a single piston engine with relatively low energy. This aircraft is a whole lot closer to a glider than it is to a jet.

Now, imagine yourself in an aircraft without an engine - a glider or sailplane. You don't have an engine to speed up, there is only one way to increase your airspeed - point the nose down. Pulling the nose up will result in slower speeds or a stall, which you don't want. What you want is to establish a steady airspeed. In the glider, the way to achieve this is to fly the same pitch in a steady descent.

If you are in your light trainer, and you fly up to about 3000-4000' AGL, pull the power back to nearly idle, don't touch it, and play with your pitch a little for 500-1000 feet. If you pull up, you WILL slow down. If you pitch down, you WILL speed up. Learn to look outside the plane and pitch the cowling in front of you relative to the horizon for the speed you want, and trim the controls so you can take your hands off and it maintains that pitch.

When you add power back in to the mix, you use various settings for things like cruise flight (relatively high settings) and lower or nearly idle settings when descending or landing - and it will behave closer to a glider in a descent unless you are doing a lot of throttle jockeying, which is not helpful and definitely destabilizes you.

Trim holds PITCH. It's making the elevator want to ride in a certain location for a given airflow.

Power can be used to adjust airspeed, for sure, and both pitch and power must be used together, but it's easiest to think of your plane as a glider with the ability to use the power to to slow the rate of descent for a given pitch. It's actually easier in light planes to use pitch for airspeed and power for rate of descent when you are landing.

It SOUNDS like you may be keeping your eyes inside the cockpit and looking at the instruments too much as well. If you are chasing needles you are going to be behind what is happening outside. Try looking outside a LOT more.

Where are you training??? This is stuff a student show know by like lesson 2-3.
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I'm an instructor and this is the best explanation I've ever heard for this concept. Thank you and I'm stealing this :).
 
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Confusednewbiepilot said:
... My question is regarding the region of reverse command and what it pertains to. ...
Click to expand...
Simple answer to a simple question, similar to what @dmspilot said:

At normal flight speeds, going faster takes more power and going slower takes less. We're familiar with this, it's intuitive and how cars work. Yet if you fly slow enough, the reverse happens: going slower takes more power, going faster takes less. This is because in slow flight induced drag is the dominant form of drag and it increases even more the slower you go. Drag increasing as you go slower has no analog with cars and is counterintuitive for new pilots.

So if you are in the region of reverse command and you add power, it only points the nose up even higher and makes you fly even slower. To get back to normal flight you must push the nose down. More precisely, add power while pushing to prevent the nose from rising. Doing this, you can increase airspeed and smoothly transition back to normal flight without losing altitude.

PS: in slow flight, it's helpful to maintain coordination by feel rather than by the ball. This is because the ball has a small lag/latency so if you are chasing the ball you are always behind the airplane. In slow flight, don't think "step on the ball" but instead, "step on the high wing" and use the rudder to keep wings level.
 
MRC01 said:
Simple answer to a simple question, similar to what @dmspilot said:

So if you are in the region of reverse command and you add power, it only points the nose up even higher and makes you fly even slower. To get back to normal flight you must push the nose down. More precisely, add power while pushing to prevent the nose from rising. Doing this, you can increase airspeed and smoothly transition back to normal flight without losing altitude.
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This is generally, mostly true, but it may also be aircraft specific and related to the engine's location to the aircraft's CG and it's thrust line. Adding power doesn't always bring the nose up. For instance, in a light sport pusher, adding power can push the nose down. Regardless, look outside and maintain the pitch you want visually when making changes.
 
RyanShort1 said:
This is generally, mostly true, but it may also be aircraft specific and related to the engine's location to the aircraft's CG and it's thrust line. Adding power doesn't always bring the nose up. For instance, in a light sport pusher, adding power can push the nose down. Regardless, look outside and maintain the pitch you want visually when making changes.
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Agreed. My over-simplification is targeted at the OP, a student pilot flying a 152/172 airplane.

PS: this pitch up force in slow flight when power is applied, also happens with go-arounds, so learning to use whatever stick/yoke pressure is needed to maintain pitch attitude when applying power, is so important. Those forces may be large, you (the pilot) can't be shy about it.
 
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MauleSkinner said:
It’s not about changing how you control the airplane, it’s simply a reversal of the power requirements that we normally think appropriate.
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Well, yes and no. Training addresses this as part of teaching the slow flight maneuver, and in essence demonstrates the two sides of the power curve more than demonstrating control reversal.

But try looking at it this way.....

Suppose we are in level cruise at a high power setting. (I'm going to ignore flaps and some secondary effects.) Now suppose we do not touch the throttle at all, but we pull back on the yoke a bit and pitch up. The plane will begin to climb and vertical speed will increase (airspeed decreases). Pull back a bit more and vertical speed increases more. Continue doing this and vertical speed continues to increase until airspeed falls to Vy. Now continue pulling back on the yoke and as airspeed falls below Vy, the vertical speed will decrease. Continue pulling the yoke back and vertical speed will continue to decrease until it reaches zero and we're once again in level flight but at a much slower airspeed.

Throughout this, we have not touched the throttle and we've only moved the yoke in the same direction, back. Yet the effect of the elevator control has reversed. Initially it increased the climb rate, then below Vy it decreased the climb rate until we were climbing no more.

A similar thing happens in a power-off glide. From level flight, pull the power to idle and leave it there, and the plane will begin to descend at whatever airspeed it was trimmed at. Pull back on the yoke a bit, and the plane will glide farther (airspeed slows). Pull back more, and the plane will glide even farther, until airspeed falls to glide speed, Vg. Continue pulling back and the glide gets shorter again as speed slows below Vg. Again, the effect of the elevator control has reversed.

This is important to understand during landing. We don't do slow flight every time we go up, but we certainly land. When we're on final with power at or near idle and we're slowing to approach airspeed, our airspeed is typically well below Vg and Vy and the effect of the elevator control is reversed.

So, if it looks like we're going to be short of our touchdown point, we can pitch down slightly, causing us to speed up and thereby moving the airspeed in the direction of Vg, lengthening the glide. Conversely, if we're going long, we can pull up slightly and shorten the glide. (I'm talking minor adjustments here as we continue to slow down to the approach speed; larger adjustments are done with the throttle.)

This creates an illusion that can confuse students. We want the touchdown point to be stationary on the windscreen. If it's moving upward, we're going to be short. The natural tendency is to pull back on the yoke, which will temporarily move the point downward on the windscreen due to the pitching movement but will also cause us to land even shorter due to the airspeed decreasing further away from Vg. Instead, pushing down on the yoke will lengthen the approach by increasing the airspeed closer to Vg.

Sorry for the length of the post. It's a bit complex to explain, and that's probably why it isn't presented to students this way.
 
Half Fast said:
Suppose we are in level cruise at a high power setting. (I'm going to ignore flaps and some secondary effects.) Now suppose we do not touch the throttle at all, but we pull back on the yoke a bit and pitch up. The plane will begin to climb and vertical speed will increase (airspeed decreases). Pull back a bit more and vertical speed increases more. Continue doing this and vertical speed continues to increase until airspeed falls to Vy. Now continue pulling back on the yoke and as airspeed falls below Vy, the vertical speed will decrease. Continue pulling the yoke back and vertical speed will continue to decrease until it reaches zero and we're once again in level flight but at a much slower airspeed.
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I don’t think this is an accurate description, because until you get to the extreme of impending stall, the vertical speed would show an initial increase regardless of which side of the power curve you’re on.

As the FAA states, it is really only about the power requirements for level flight on the back of the power curve instead of the front. The additional description may enhance an individual’s understanding, but unless it’s severely restricted that additional description could be inaccurate.

now, if you extrapolated it into power requirements for a steady state climb or descent, I wouldn’t argue against that, but “pull(ing) back on the yoke“ destabilizes the airplane, and the description fails to be accurate until the airplane resumes unaccelerated flight.
 
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MauleSkinner said:
I don’t think this is an accurate description, because until you get to the extreme of impending stall, the vertical speed would show an initial increase regardless of which side of the power curve you’re on.
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Go try it. You might see a brief transient as airspeed until airspeed has had a chance to bleed a bit, but I'm talking about steady-state. The vertical speed will move together with the airspeed. Above Vy, vertical speed goes up as soon as airspeed goes down. Below Vy, vertical speed goes down as soon as airspeed goes down. Vertical speed peaks at Vy; in fact, that's the definition.
 
Half Fast said:
Go try it. You might see a brief transient as airspeed until airspeed has had a chance to bleed a bit, but I'm talking about steady-state. The vertical speed will move together with the airspeed. Above Vy, vertical speed goes up as soon as airspeed goes down. Below Vy, vertical speed goes down as soon as airspeed goes down. Vertical speed peaks at Vy; in fact, that's the definition.
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show me that definition in any official documentation.

yes, you’re talking about steady state, but the words you’re using include the non-steady state, and saying “pull back to go down faster” will Probably do more to confuse most people than anything else. its still a power requirement…in the region of reverse command, it takes more power to either fly level or climb/descend at a given rate the slower you are.
 
The term "region of reverse command" seems ambiguous. I've heard this region described as below the speed of minimum power, and as below the speed of minimum thrust/drag. They aren't the same since the speed of minimum power is slower than the speed of minimum drag (Vldmax).

In the airplanes I've flown, on short final the approach speed is between Vx and Vldmax. You're near the top end of the region of reverse command as defined by thrust/drag, and above the region of reverse command as defined by power.
 
MRC01 said:
The term "region of reverse command" seems ambiguous. I've heard this region described as below the speed of minimum power, and as below the speed of minimum thrust/drag. They aren't the same since the speed of minimum power is slower than the speed of minimum drag (Vldmax).
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which is why I try to use the official FAA definition instead of something heavily paraphrased.
 
MauleSkinner said:
its still a power requirement…in the region of reverse command, it takes more power to either fly level or climb/descend at a given rate the slower you are.
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Nope. That's one effect, but "reverse command" can be seen at constant power.

Consider the circumstance where you're climbing at Vy at max power. Say your climb rate is 1000 fpm. There are two airspeeds where climb will be reduced to 750 fpm (for example), one slower than Vy and one faster than Vy. Pull back on the yoke to get to one, push forward to get to the other, without changing power setting.

It doesn't matter whether you go slower than Vy or faster than Vy, either way you get less climb. The elevator effect on climb is opposite above and below Vy; it's "reversed."
 
I think you're both right in the specific points you're making.
 
I wrote:
Half Fast said:
Vertical speed peaks at Vy; in fact, that's the definition.
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Then you wrote:
MauleSkinner said:
show me that definition in any official documentation.
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Per the FAA:
V Y is the airspeed for best rate of climb, which produces the greatest amount of altitude gain over the shortest period of time. ​

Sure sounds like peak vertical speed to me! Altitude gain per time is vertical speed, and the point where it's greatest is its peak.
 
Salty said:
I think you're both right in the specific points you're making.
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Agreed. It's merely two ways of describing the same phenomenon.

IMHO, an explanation of how a flight control works the opposite in one region from the other region makes clear how command is "reversed."
 
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