Slow Flight Question (back side of power curve)

[Strega]

With all the discussion about stick and rudder skills in the asiana thread.. I thought I would ask a simple question in the flight training forum..

If you are in slow flight, what happens if you pull back on the controls and leave the power/thrust where it was?

Im curious to hear what peoples responses are..

[PilotDAR]

Well, you could be in slow flight climbing, level or descending.

If you pull, you'll pitch up accordingly. This pitch up is presuming that you do not pitch so far as to stall the plane, and thus you can maintain the commanded pitch attitude.

However, the drag will increase, and thrust remain constant, so the speed will decrease. If there was a positive rate of climb, it will be less so. Otherwise you will descend in that attitude.

[200hr Wonder]

In slow flight your pitch angle controls airspeed and your power setting controls climb/descent rate.

[akoch]

slow flight or not, pulling the elevator changes the angle of attack

[photofly]

With all the discussion about stick and rudder skills in the asiana thread.. I thought I would ask a simple question in the flight training forum..

If you are in slow flight, what happens if you pull back on the controls and leave the power/thrust where it was?

Im curious to hear what peoples responses are..

Does anyone know what the "speed for maximum endurance" is for a 777 in the landing configuration?

[Strega]

The whole point of my question is when you pull back (at constant power) in slow flight.. you will actually go down, not up....

[Beefitarian]

Maybe.

[trey kule]

It depends on
1. The type of aircraft to an extent
2..Where you are in the slow flight envelope
3. How hard you pull back.

Generally, if you are in the slow flight envelope and pull back slowly (1 kt/sec deacceleration) you will not go up or down initially, but will slow down, and to maintain level flight or the flight path you will have to continue pulling back , which will slow you down more, and this will continue on until you reach the critical angle of attack...At that point any pitch up will cause the aircraft to descend. (assuming no change in power)

Now, if you just are on the top edge of the slow flight envelope, and pull back quickly, you may get what amounts to a ballistic climb for a short period, and then the above paragraph will come into play.

I realize that Tc wants the stall warning horm to be honking to demonstrate slow flight..That is the edge of the slow flight envelope..some instructors do not understand that, and as aresult slow flight is not taught as it should be.
The danger with slow flight is if you inadvertently slip into slow flight say on an approach, your descent rate will increase which will cause you to be low. Pull up to get back on the glidepath...slower speed...even higher descent rate...I am sure you get the idea.. It is this trap that pilots fall into.
To get out of slow flight, particularily near the bottom end you must reduce the angle of attack, and that might cause a significant loss of altitude before the situation corrects itself.

hope this helps.

[PilotDAR]

I realize that Tc wants the stall warning horm to be honking to demonstrate slow flight.

Well, though it might happen concurrently, not necessarily. The stall warning horn indicates exactly that - warning. It is required to actuate at least 5 knots before the stall, but not more than 10 knots before. The stall warning can also sound at speeds well above the slow flight regime, if G loading is involved.

Therefore one could be in the beginnings of the slow flight regime without a stall warning. Bear i mind that it is also a requirement that the aircraft be controllable, with normal use of the controls, up to the point of the stall. Therefore, as long as the pilot maintains good control of the aircraft at those slower speeds, the biggest hazard of slow flight should be overheating the engine.

Some aircraft can be flown in full power slow flight, with no climb or descent, at an indicated airspeed much slower than the power off stall speed. A Robertson STOL Cessna 206 can be flown at speeds slower than the "first" stall speed, though not in complete control, and with some pitch bobbing. Thus, the stall speed is defined as the faster speed in that range.

[photofly]

you may get what amounts to a ballistic climb for a short period

9 feet of altitude per kt per 100 kts.

[trey kule]

Pdar..
When I was ranting sometime ago that students did not understand slow flight, someone pointed out the flight test standard guide thingie or whatever its called. Take a few moments and see what it wants for a slow flight demonstration. Instructors teach to the test...accidents happen because pilots slip into slow flight close to the ground and because the stall horn is not indicating dont realize the effects including higher sink rates as you pull back.
I am very aware the stall warning systems, where installed are just that, though I have been surprised in the past that some (including TC inspectors) dont.
In any event, I was trying to make my post fairly general in nature so as not to confuse the OP that the exceptions are the rule.

[PilotDAR]

Yeah Trey, I know that you know, everyone else should.

For those lesser experienced pilots reading this, there is not excuse for not feeling confident flying into the slow flight regime, 3 or 4 knots into the stall warning, and holding the plane there through gentle well coodinated turns. Of course, this should be practiced at altitude. If you can't do this with confidence, you would benefit from some competent training. It is the development of precise handling skills which most benefits from this practice.

So why should pilots practice slow flight? You never use it? Well, every proper tricycle landing, and arguably every takeoff, should take you through this regime at least a little, and those are the times when controlling the plane precisely is most important. It is generally agreed that good tricycle landings may include the stall warning horn sounding (I certainly offer a "good job" to new pilots when I hear it during a good landing). If you are doing soft field takeoff and landings, you should be well into flying behind the power curve. Ground affect may have helped you, but you still did it.

The skill to fly in the slow flight regime is kinda like four wheel drive. You never use it to get in, but it can be really great to have if you need to get out! I used to set up, and then demonstrate STOL kit modified Cessnas. The owner would come back some time later, and say: "This STOL kit doesn't really make a difference". My first question to that owner would be: "Have you flown at less than 60 knots? Invariably - "no". We would fly.

I did over do it once. I did the demo, including really soft field work on the grass runway. At the end of the flight, the owner just walked away without a word. "That was a bit rude...." I thought to myself. Later the boss came to me and said, "Hey, go easy on them, you literally scared that fellow speachless - in his own plane!"

Just always remember that if you loose the engine, while in slow flight, lowering the nose a lot, right away is you're only chance of survival. So either be close enough to the ground that you can safely settle on ( the soft field technique) or high enough that you have room to fall first. Slow flight a hundred or so feet up, is a very bad idea - you will not get to the ground without damaging the plane - or worse....

[trey kule]

Good points.

I did not express my concern well. My concern is that pilots, particularily student pilots do not think they are in slow flight unless they are getting a stall warning indication. It can lead to problems.
The natural tendency on an approach when they get a bit low is to raise the nose to get the sight picture back to normal..not lower it or add power. The result is they slip farther back on the curve, the descent rate actully increases.........., they pull back....and by the time they get a warning they are to slow and to low...it is not a good place to be.

Slow fight, in a typical trainer can be easily demonstrated, and , I believe is an actual exercise.
To many graphs and formulas, when, as you mention.....gotta put the nose down. As an aside. I have noticed during IF training, the missed approach is pitch, power....not sure I like that sequence...same with the APT sequence for initiating a climb.

Time to let some others get in on the discussion

[crazy_aviator]

Over a few beer I tried to explain to a BE-18 float pilot ( I was an inferior beaver pilot at the time ) about the existance of the venerable "back side of the power curve" He was totally unconvinced that, as you increase power, you can actually fly a slower indicated airspeed. Oh well, not all students are taught equally.

[Shiny Side Up]

So why should pilots practice slow flight? You never use it? Well, every proper tricycle landing, and arguably every takeoff, should take you through this regime at least a little, and those are the times when controlling the plane precisely is most important. It is generally agreed that good tricycle landings may include the stall warning horn sounding (I certainly offer a "good job" to new pilots when I hear it during a good landing). If you are doing soft field takeoff and landings, you should be well into flying behind the power curve. Ground affect may have helped you, but you still did it.

This is a point that's frequently missed by new instructors - that maneuvering in slow flight happens in every flight, and thus the importance of being proficient at it, it has direct application to take off and landing. When I interview new hires this is usually the PGI I have them do, and so far its about 50/50 the instructors who get this and the ones who don't. The ones who don't often have it presented as a beast of its own, some arcane thing you must merely do to get past the flight test. You also then see many PTRs where a grand total of maybe 5 minutes of slow flight was worked on before hours and hours of circuits commenced. One leads to the other.

[Colonel Sanders]

5 minutes of slow flight

As usual, SSU nailed it. Like anything else, you
can't get good at slow flight unless you practice
it, with the stall warning horn wailing away, and
the occasional wing drop.

Slow flight is really important. Any @sshole can
fly fast - and usually does. But when someone
says, "I have trouble with my landings", it really
isn't his landings that he needs to work on.

You will be in slow flight before you touch down
during every landing, and you will be in slow flight
after every takeoff. It is of the utmost importance
that you are able to maneuver the aircraft precisely
during that slow flight.

Like SSU, I am mystified by people who ignore slow
flight, and go 'round and 'round, struggling with their
circuit work.

I have dark suspicions that flight instructors don't like
(and often outright fear) slow flight and stalls.

You probably don't want to know one of my many
techniques for dealing with slower traffic ahead of me
on downwind ... I like to hang it on the prop at full
power. Maybe flip on the smoke

Not recommended for flight instructors with marginal
aircraft handling skills, of course!

[frog]

To answer the initial question : stall !

[avinstructor]

This is a great thread - I've seen a lot of misunderstanding from many of my colleagues about slow flight and its a bit scary to see the results.

The one that drives me nuts is the typical answer to "how do you know you are in slow flight". Most students will say: "slow airspeed, stall horn, nose-high attitude, and high power setting." I don't get this ... Why are people being taught that to be in slow flight you have to been in a nose-high attitude and have a high power setting? What about a slow-flight descent? I know of one TC inspector that failed an initial class 4 candidate because she said that you could be in slow flight on approach ... His response was that you needed a nose-high attitude and high power setting to be in slow flight! Am I missing something?

[photofly]

It comes from mixing up "slow flight" and Exercise 11.

In demonstrating Exercise 11, how do you know you've arrived in the slow flight regime? Because you're maintaining level flight with low airspeed, high power setting, etc etc.

[Shiny Side Up]

I know of one TC inspector that failed an initial class 4 candidate because she said that you could be in slow flight on approach ... His response was that you needed a nose-high attitude and high power setting to be in slow flight! Am I missing something?

This sounds a bit like a story that got muddled in the telling since there are two parts here. Technically you shouldn't be in slow flight on a normal approach, but rather transition to it and through it during the round out/flare portion. Approaches on the back side of the power curve I wouldn't reccomend for your average PPL student. If the instructor candidate during their PGI gave the strong impression that it would be "OK" to be on the back side of the curve during a typical approach, I could see the reason for failing them. As per the second part, it would be more accurate to say You need a relatively nose high attitude and a relatively higher power setting to be in slow flight relative being the operative bit. I would maybe fault the examiner for not being specific enough. To clarify, when you're descending in slow flight, you're going to have a more nose up attitude than a fronst side descent, possibly combined with a higher than usual power setting compared to a front side descent, though the second bit not necessarily since its possible to be on the back side of the curve in a power off descent - gliding like a brick so to speak.

As an aside, I personally hate the phrase "area of reverse command" that appears in the FTM and much of the rest of the material. Its misleading and causes too much confusion.

[iflyforpie]

As an aside, I personally hate the phrase "area of reverse command" that appears in the FTM and much of the rest of the material. Its misleading and causes too much confusion.

Yes, it is terrible.

I struggled a lot with landings and the slow flight aspect thereof because of a lot of what I am reading here. Very few people have said that if you pull the stick back in slow flight, the plane will climb or reduce its decent rate.

The increased drag and the reduction of airspeed only comes after the increase in coefficient of lift... so unless you are at the stall, the plane will rise with the nose going up every single time. This is the bane of student pilots who over flare and then balloon, and the taildragger pilots who wheel land too hard and then bounce back into the air. That's about when the drag and lower airspeed kicks in and you need power or a robust landing gear.

[avinstructor]

I know of one TC inspector that failed an initial class 4 candidate because she said that you could be in slow flight on approach ... His response was that you needed a nose-high attitude and high power setting to be in slow flight! Am I missing something?

This sounds a bit like a story that got muddled in the telling since there are two parts here. Technically you shouldn't be in slow flight on a normal approach, but rather transition to it and through it during the round out/flare portion. Approaches on the back side of the power curve I wouldn't reccomend for your average PPL student. If the instructor candidate during their PGI gave the strong impression that it would be "OK" to be on the back side of the curve during a typical approach, I could see the reason for failing them. As per the second part, it would be more accurate to say You need a relatively nose high attitude and a relatively higher power setting to be in slow flight relative being the operative bit. I would maybe fault the examiner for not being specific enough. To clarify, when you're descending in slow flight, you're going to have a more nose up attitude than a fronst side descent, possibly combined with a higher than usual power setting compared to a front side descent, though the second bit not necessarily since its possible to be on the back side of the curve in a power off descent - gliding like a brick so to speak.

As an aside, I personally hate the phrase "area of reverse command" that appears in the FTM and much of the rest of the material. Its misleading and causes too much confusion.

I see what your saying ... Having not been in the briefing I can't know for sure exactly what was said, but I think the jist was that it was possible, not advised or normal, but possible to be in slow flight on the approach - I haven't run the numbers but I think a vRef approach at 1.1 VSO would qualify as being in slow flight. I know of a couple of specialty aviation groups that use 1.1 VSO when approaching some very difficult short landing strips overseas - definitely not for the PPL student. Knowing the student that failed that class 4 ride that is probably what she was thinking when she said that it was possible to be in slow flight during the approach ... I can see why an inspector would see that as not being necessary in a PPL PGI, but I also don't think she should have failed for it.

As for the part about needing a relatively higher nose attitude I agree, and thanks for helping me clarify it in my head. I also assume that students get stuck with the "nose-high attitude and high power setting" thing because they are taught slow flight only in relation to the flight test in which you are required to maintain a selected altitude - in that case you will of course be nose-high with lots of power. Does this make sense?

[white_knuckle_flyer]

As a newbie, let me chime in here that I have never really appreciated the need for learning slow flight other than it allowed for certain skills and/or discussions surrounding power, stalling, aileron control, rudder effectiveness, etc. In other words, as a thing unto itself, it seemed unnecessary. As the colonel mentioned, I can appreciate that you pass through the slow flight envelope during every t/o and landing, but that is a far cry from lingering at the edge of a stall with the horn blaring away.

Is it just a stepping off point for the instructor ? Would it make more sense to practice recovering from hearing the stall horn during an over-zealous takeoff angle or an unnecessarily slow downwind ? Too dangerous ?

[Shiny Side Up]

I can appreciate that you pass through the slow flight envelope during every t/o and landing, but that is a far cry from lingering at the edge of a stall with the horn blaring away.

The point of the lesson is that its not a far cry from it. You're not just blasting through the slow flight on a headlong impact to the ground, on the flare to landing you're doing the same motion you need to do when you transition into slow flight. It might be said that in addition to handling the airplane in slow flight, its also important to practice the transition to it - the operative part to being able to land the airplane is keep straight while you're doing it.

I should note that the horn, or stall warning indicator, is really just a distraction during this process. When you want to be in slow flight, its really irrelevant. Case in point, I did a check out for a fellow with a M-7 a while ago. He had a really hard time with the idea that the stall warning didn't mean instant death was shortly going to follow. Had a hard time with landing, keeping way too much energy way too late in the approach, did a lot of floating down the runway, that was until we got him away from that habit, then we got to do what the Maule does best.... I digress.

edit: Part of the fix for that was to go do some more slow flight practice.

This point here though, also shows that its not just instructors who are to blame for slow flight not getting all the attention it needs.

Would it make more sense to practice recovering from hearing the stall horn during an over-zealous takeoff angle or an unnecessarily slow downwind ?

Students also want to hurry to the circuit, and instructors too often want to oblige them. To be honest, your average new student frequently asumes that flight training works like so.

1) Learn what the stick does, push forward, cows get big, pull back, cows get small (1 hour)
2) Start practicing landings. (40hours)
3) Stuff like nav and instruments (the rest)
4) Test and done!

Its the instructor's job to convince them otherwise, of course if the only thing the instructor knows about slow flight is that its required on the test, well then...

I struggled a lot with landings

I think I had a good instructor because I did have a good concept of slow flight from the start. That said, I still sucked at landings for a long time because I'm slow and clumsy. I've never had problems being straight on landing though.

[Big Pistons Forever]

A couple of thoughts.

1) There is no reason for a low time pilot to be in the slow flight regime. New pilots should recognize the symptoms of slow flight early and take effective correcting actions. For your average spam can you won't stall unless you go through slow flight first. Recognizing the entry into slow flight is an essential precursor to avoiding inadvertent stalls

2) Don't forget that slow flight doesn't just occur in level flight, the way it is typically demonstrated in flight training. It can also occur in climbing and descending flight. The latter is important because getting too slow on approach is how, in the real world, an unrecognized transition into the slow flight regime will bite you in the ass. I just finished a PPL in a Nanchsng CJ 6 and this was a great airplane for demonstrating this. Get into descending slow flight with the gear and flap down and not even full power will arrest the descent.

3) Revovery from a badly bounced landing can require a near perfect slow flight recovery manoever but this aspect of "slow flight" doesn't seem to get the emphasis it IMO, deserves.