Ball centered during engine outs?

[de facto]

..And yep I've certainly shot well-deserved flack directly at those AI Tooloose frogs after a
certain double-failure event where they replied to my Co who reported to same that it was
l'impossible ...and that I must be to blame!

Frogs versus Rednecks Part 1

[john_tullamarine]

My understanding is that bank also takes part in easing off rudder's drag thus improving performance

Bank influences sideslip .. which influences yawing moments ... which influences how much work the poor old rudder has to do ie very effective for influencing real world Vmca.

However, too much of a good (sideslip) thing is not so good .... so be careful not to be too cavalier with bank angle ...

[doubleu-anker]

Feno

Fair question.

Spoilers, kill (spoil) lift not to mention the increased drag. I prefer to have all the lift at my disposal.

If the control column is too far off centre, you are in a cross control scenario, especially on an aircraft with no spoilers. Lets go back to basics here. Do you pick up a stalled wing with ailerons, or rudder? Give me the rudder every time.

[Feno]

Agreed.

More bank applied results in less yaw needed from the flight mechanics point of view, the automatic consequence of which being a reduced rudder drag.

Surely the 5 deg mark is a good one not too exceed though.


Hello doubleu anker

Point taken regarding the lift disruption.
However I'm not sure I'm with you about the cross control scenario thing though. In the context of a flame out, pilot's inputs on both bank and yaw axis are towards the live engine aren't they. Then how would the "cross" notion apply here ?
Cheers

[Microburst2002]

Quote:
I deemed the twins as more dangerous that singles in approach, landing and take off phases
Tell that to Boeing who are designing a bigger 777. They need your sage advice.

I can give sage advice.

"read carefully" is one of my favourites

[john_tullamarine]

More bank applied results in less yaw needed from the flight mechanics point of view, the automatic consequence of which being a reduced rudder drag.

I think that you might be missing the point. Bank directly affects slip angles which affects yawing moments (something about further effect of controls, as I recall ? - bank with aileron and you see the nose turn to the low side - severe adverse yaw cases notwithstanding). By picking up some useful yawing moment associated with the bank angle, you are reducing the proportion of the total yawing moment which needs to be found via the rudder input. This lets you put some more rudder in to reduce the Vmca a bit further which is the aim of the exercise.

Conversely, find yourself back around the real world Vmca on the day (and we're talking only a few knots) AND you don't put the bank in, then you might get a surprise from the aircraft's response ....

Surely the 5 deg mark is a good one not to exceed though.

For sure, this is a certification limit to put a fence around the OEM innovation paddock. However, it is a Vmca thing, not a performance consideration.

[Uplinker]

Slasher, sorry, you caught me in a bad mood and your post seemed to be dissing Airbus.

I apologise and have removed the unneccessary words from my post.

[tommoutrie]

Quote "Do you pick up a stalled wing with ailerons, or rudder? Give me the rudder every time."

I would "pick up a wing" by reducing the angle of attack so that its flying again. I hope you would too. Does anyone still think that an inadvertent wing drop or incipient spin is best dealt with using a boot full of rudder? Stick forward, unstall the wing..

[john_tullamarine]

Do you pick up a stalled wing with ailerons, or rudder

One of those FT versus operations OWT conflicts.

Suggest you search for some of John Farley's wise words on stalling.

Aim should be

(a) prevent yaw with careful rudder input. Stall plus lots of rudder is a pretty standard spin entry .... if the wing is dropping and you put in lots of top rudder ... chances are that over it goes - very quickly - the other way.

(b) more recent aircraft should have no significant problem with aileron input

but, as tommoutrie observes, if it's stalled, first unload to unstall then worry about getting back to level flight. If you happen to be close to the ground at the time you may well be out of ideas and height simultaneously but that's another story.

[italia458]

John T,

This would keep a yaw string (if installed) right down the centerline of the aircraft.

don't think so ...

If the airplane is in the attitude for "zero sideslip" I do believe the string would go straight back... am I missing something?

tommoutrie,

Quote "Do you pick up a stalled wing with ailerons, or rudder? Give me the rudder every time."

I would "pick up a wing" by reducing the angle of attack so that its flying again. I hope you would too. Does anyone still think that an inadvertent wing drop or incipient spin is best dealt with using a boot full of rudder? Stick forward, unstall the wing..

Yes! I do this every time I hear an instructor teach that you should slam rudder in to make sure the nose doesn't move a hair off your heading when you stall. As soon as the wing is flying again you can use aileron and rudder to put the airplane into a coordinated roll to wings level. I wrote an article about this exact issue in stall recovery awhile ago.

[john_tullamarine]

If the airplane is in the attitude for "zero sideslip" I do believe the string would go straight back...

I'd go along with that ..


am I missing something?

yes -


His view is that during initial ME training, the ball was kept half out and a bank of 5 degrees towards the good engine was needed.

noted and quite appropriate for speeds around Vmca


This would keep a yaw string (if installed) right down the centerline of the aircraft.

unfortunately, no - the previous description does not define nil slip. With 5 degrees bank, you would expect there to be some slip into the live engine and the yaw string to be off centre to the dead engine.


every time I hear an instructor teach that you should slam rudder in to make sure the nose doesn't move a hair off your heading when you stall

putting the colourful use of "slam" to one side, the technique should be to use rudder to the extent necessary to maintain a constant heading. All part of the desirable aim to minimise the likelihood of a departure.

[italia458]

John T,

Ah yes, I did miss that!

putting the colourful use of "slam" to one side, the technique should be to use rudder to the extent necessary to maintain a constant heading. All part of the desirable aim to minimise the likelihood of a departure.

I understand the philosophy behind keeping a constant heading to be that it will significantly lessen the likelihood of entering a spin - do you agree? Shouldn't the main focus of stall recover be just that - stall recovery? The primary pitch control is the elevator and should be used to decrease the pitch of the airplane so that it begins flying again.

It seems that instructors (with good intentions) end up putting so much emphasis on using the rudders in the stall instead of ailerons that the student ends up coming out of the lesson with the idea stuck in his/her head that for a stall "use the rudder and not ailerons!", instead of, "decrease pitch to recover!".

For example, lets say the airplane enters a stall and gets a wing drop of 45 degrees bank to the left. What happens when the pilot pitches down to reduce the angle of attack? The elevator, now acting 50% as pitch control and 50% as directional control, will cause the airplane to decrease its angle of attack AND decrease the directional deviation (yawing moment) from its heading. What happens when the pilot decides to instinctively fight the wing drop by adding rudder? It's also at 45 degrees and so it acts like the elevator does - in this case, it does help reduce the yawing moment but it also pitches the nose of the airplane up! Pitching up in a stall is definitely not a good idea.

Then there are the instructors who don't just say to use rudder to control the heading deviation but say to "pick up the wing" using the rudder. That puts the airplane into a slip initially (hardly the maneuver you'd like to do when you're trying to get maximum performance out of your wing), which slowly transitions to a skid as the airplane rolls towards level which is, again, not a good idea when you're at such a low speed.

Here are some quotes from an article I wrote:

During this training, the student will need to be taught a recovery procedure that will produce a combined high rate of success and a minimum loss of altitude, if it is initiated at the point of stall. “In arriving at an optimum procedure for use by the operational pilot, the test pilot must not only consider the effectiveness of the technique (in terms of altitude loss or manoeuvrability regained) but must also consider the simplicity of the technique.” [2] That quote is from the U.S. Naval Test Pilot School Flight Test Manual for Fixed Wing Stability and Control. Keeping a simple recovery procedure is important to keep the pilot focused on reducing the angle of attack, the only reaction that will unstall the wings. That is especially important when flying during a critical phase of flight, i.e.: take-off or landing, where it is easier to become distracted and where, unfortunately, most of the stall/spin accidents occur. I believe that the four-step procedure listed above will produce a combined high rate of success and a minimum loss of altitude.

The four-step procedure:

1. Reduce pitch
2. Power full
3. Coordinated roll to wings level
4. Pitch for VY

In summary, applying opposite rudder is not conducive to carrying out an effective and safe recovery from a stall. Here are a couple quotes from FAA documents on the stall recovery procedure: “Straight and level flight should be established with full coordinated use of the controls.” [3], “...straight-and-level flight should be regained with coordinated use of all controls.” [4] These two paragraphs from the FAA Airplane Flying Handbook, under the heading “Use of Aileron/Rudder in Stall Recovery”, summarize it well: “When the airplane is in a stalled condition, the wingtips continue to provide some degree of lift, and the ailerons still have some control effect. During recovery from a stall, the return of lift begins at the tips and progresses toward the roots. Thus, the ailerons can be used to level the wings.”, “Even though excessive aileron pressure may have been applied, a spin will not occur if directional (yaw) control is maintained by timely application of coordinated rudder pressure. Therefore, it is important that the rudder be used properly during both the entry and the recovery from a stall. The primary use of the rudder in stall recoveries is to counteract any tendency of the aircraft to yaw or slip. The correct recovery technique would be to decrease the pitch attitude by applying forward-elevator pressure to break the stall, advancing the throttle to increase airspeed, and simultaneously maintaining directional control with coordinated use of the aileron and rudder.” [4]

If the FAA, and others, support teaching stall recovery using the elevator first in the stall recovery to reduce the angle of attack and then use coordinated aileron and rudder to roll level, where are these instructors getting the idea that you should use uncoordinated rudder in the stall recovery?

Here is a Transport Canada AC regarding stall training and checking: Advisory Circulars - Transport Canada

It's a bit off topic but I encountered pilots who believed that an "approach to stall" exercise should be done with zero altitude loss because, in their words, "you weren't stalled". Nowhere in the flight test guide, or anywhere else, does it say that one of the aims of the exercise is zero altitude loss. Some (read: most) DFTEs were/are also under the impression that zero altitude loss was/is required to get a mark of 4 on the flight test. That's clearly not what Transport Canada wants but showing the document to these pilots didn't change their minds.

[john_tullamarine]

do you agree?

Absolutely, the aim is to minimise departure risk during the exercise


The primary pitch control is the elevator and should be used to decrease the pitch of the airplane so that it begins flying again.

Concur. However, it doesn't assist the goal if the aircraft departs controlled flight. The stall needs to be well-controlled consistent with the aeroplane's characteristics.


emphasis on using the rudders in the stall instead of ailerons

That is an historical hangover from earlier aeroplanes for which aileron input complicated stall behaviour. More recent aeroplanes should be reasonably well behaved. Rudder has the potential for surprises so needs to be used in a very constrained manner entering the stall regime.


"decrease pitch to recover!"

it might be preferable to emphasise unloading to reduce alpha with the aim of unstalling .. the recovery, say, to straight and level flight occurs post unstall.


The elevator, now acting 50% as pitch control and 50% as directional control

that's a little in the way of innovative thought. If one is looking at body axes, I would have expected the elevator to produce pitching moment only ?


AND decrease the directional deviation (yawing moment) from its heading.

can you walk us through just how this occurs ? Sometimes I'm a tad slow picking up the details ...


What happens when the pilot decides to instinctively fight the wing drop by adding rudder? ... but it also pitches the nose of the airplane up!

again, might I ask for some further clarification of the mechanics involved ?


The four-step procedure:

1. Reduce pitch
2. Power full
3. Coordinated roll to wings level
4. Pitch for VY

while the semantics may vary from source to source, presuming there is no departure other than the stall and recognising that AFM/POH guidance is prescriptive I might prefer to see something along the lines of

- manual flight - reduce pitch - control yaw
- reduce thrust if/as necessary
- unstall
- simultaneously increase thrust while returning to the desired flight path using co-ordinated control inputs.

Increasing thrust significantly while stalled (ie high alpha) may result in significant and undesirable nose up pitching moments, especially for larger engines. Pitching motion potentially may give rise to undesired yawing moments.

As to target speed, that would depend on circumstances and priorities on the occasion.


Straight and level flight should be established with full coordinated use of the controls

one presumes that we are referring to post unstall ?

some of the quotes are a bit generalised but well-intentioned.


where are these instructors getting the idea that you should use uncoordinated rudder in the stall recovery?

Probably part historical hangover from a bygone era mixed with a very sensible concern for the typical low level stall event scenario. However, it should be a matter of minimising overall risk .. and, below whatever height might be appropriate for the Type involved, it just might not be possible to recover successfully .. hence the real importance of being very aware of exposure to stall risk situations.


an "approach to stall" exercise should be done with zero altitude loss because, in their words, "you weren't stalled".

In earlier days, it was expected that pilots would be highly attuned to prestall warnings and would be able to recover post warning prior to entry into the stall environment. For many aircraft this was quite feasible with little or no height loss .. indeed, for some of the larger turboprops at low to mid weights, the exercise involved power up and climbing out of the prestall situation ..


Nowhere ... does it say that one of the aims of the exercise is zero altitude loss

The sensible test program addresses a wide range of stall situations and should cover role related considerations.

The line pilot is far more interested in the real world operational imperatives of

(a) not hitting the hard bits

(b) getting back to where the aeroplane was intended to be

These differences result in differing emphases.

At least, in recent times, we have been seeing a pronounced move away from the minimum height loss philosophy.

[italia458]

John T,

I should point out that the 4-step recovery procedure I stated was written for an audience of students flying Cessna trainers. The stalls I was talking about were level, 1G stalls that may or may not produce a wing drop. It does apply, in general, to other airplanes but there are other factors - that you've mentioned - that would need to be considered.

it might be preferable to emphasise unloading to reduce alpha with the aim of unstalling .. the recovery, say, to straight and level flight occurs post unstall.

Yes, "unloading" would be a more correct term for all airplanes.

that's a little in the way of innovative thought. If one is looking at body axes, I would have expected the elevator to produce pitching moment only ?

The flight controls always control the airplane relative to its axes but bear with me as I try to explain what I was meaning.

In most planes (except model airplanes and very high-powered aerobatic airplanes) the engine power is insufficient to 'pull' a plane out of a stall. I've seen model airplanes stall, with power at idle, at around 30-50 degrees nose up and as soon as the airplane stalls and the nose starts dropping, the operator slams full throttle and the engine literally pulls the airplane out of the stall and puts it into a vertical climb! Now that's a good power-to-weight ratio! Since virtually all airplanes don't have that capability, there needs to be another way to accelerate the airplane back to normal flying speed - this is assuming a 1G stall condition where the airplane is slightly below stall speed by the time the pilot starts recovery.

The answer is: gravity! The nose must go down because the airplane is going down. If the airplane stalls and starts descending from level flight, the airplane will go deeper into the stall if the attitude is not lowered. Since the airplane is descending, movement of the nose away from the ground is not conducive to stall recovery. The aircraft's bank is really not a factor in this.

You're 100% correct that rudder only ever yaws the airplane and elevator only ever pitches the airplane - I could probably write that paragraph better. However, considering a 45 degree bank to the left, applying right rudder would yaw the airplane to the right, which in this case, would raise the nose of the airplane away from the ground. If you were to use elevator instead - you will point the nose towards the ground, and since the airplane is traveling towards the ground, that will automatically decrease the angle of attack. There really isn't much 'load' on the wings at all at this point - gravity is pulling the airplane down and the aerodynamic forces aren't enough to oppose it. If you're at the critical angle of attack, you can unload the wing by either reducing angle of attack or increasing angle of attack - the former is usually more preferable!

AND decrease the directional deviation (yawing moment) from its heading.

can you walk us through just how this occurs ? Sometimes I'm a tad slow picking up the details ...

When the airplane is at the stall and there is a wing drop, the longitudinal axis usually gets tilted off the heading in the direction of the roll. This is due to the airplane not only rolling but 'falling' towards that side due to the sudden decrease in required lift on that side. So when the airplane has 'wing-dropped' to a 45 degree angle of bank, the longitudinal axis would be pointing 10-15 degrees (maybe more, maybe less) off the heading that the stall was initiated on. By pitching down, while at 45 degrees of bank, you will move the longitudinal axis back towards the initial heading.

Increasing thrust significantly while stalled (ie high alpha) may result in significant and undesirable nose up pitching moments, especially for larger engines. Pitching motion potentially may give rise to undesired yawing moments.

You do bring up a good point! Every airplane will be different and I think the specifics of each should be addressed when training to fly that specific airplane.

As to target speed, that would depend on circumstances and priorities on the occasion.

Definitely.

Straight and level flight should be established with full coordinated use of the controls

one presumes that we are referring to post unstall ?

Yes.

In earlier days, it was expected that pilots would be highly attuned to prestall warnings and would be able to recover post warning prior to entry into the stall environment. For many aircraft this was quite feasible with little or no height loss .. indeed, for some of the larger turboprops at low to mid weights, the exercise involved power up and climbing out of the prestall situation ..

I know that there are lots of airplanes that can not only not lose altitude, but can start a climb in a few seconds after power is applied. I don't think a lot of these people realize that the conditions in which you're getting a pilot to recover with zero altitude loss is completely different from what that pilot would encounter in an operational environment. If a pilot has gotten so slow that he hears a stall warning I think it'd be safe to say that he/she has less than the required situational awareness for that phase of flight. In pretty much every case, the pilot wasn't expecting the stall warning to come on - if they had expected it, they would have taken action to fix the low speed situation.

So in one case (training flight) you have a pilot who's purposefully slowing to the stall warning with the express purpose of applying maximum power at the instant the stall warning goes off and then carefully flying the airplane to maintain altitude - that's a precision flying maneuver. In the other case, you've got a pilot who's lost situational awareness, is startled/surprised when the stall warning does come on, and by the time they initiate a recovery action the airplane could very well be well into the stall. Adding power at that point would not be ideal because if there is any sort of differential thrust created you risk flipping over. Looking at the height at which the airplane stalled in the majority of stall-accidents you should be able to see that zero altitude loss isn't/should be a priority!

The line pilot is far more interested in the real world operational imperatives of

(a) not hitting the hard bits

(b) getting back to where the aeroplane was intended to be

I agree with that. But it's becoming apparent these days that pilots don't have the skills and/or training to achieve their operational goals of not destroying an airplane!

At least, in recent times, we have been seeing a pronounced move away from the minimum height loss philosophy.

I'm glad to see that but it seems it's going to take awhile for everyone to get the memo.

[john_tullamarine]

Hopefully further debate will follow on your points of interest as the matters are of importance. However, I also think that you might read up on some basic undergraduate flight mechanics text material as your thoughts are somewhat unconventional and, just possibly, not compatible with conventional engineering assessment.


I should point out that the 4-step recovery procedure I stated was written for an audience of students flying Cessna trainers ...

That's understood. However, the philosophical problem is that what is trained and studied at the start forms the basis of actions in high stress situations later in a pilot's career - especially if subsequent training paradigms are a bit light on, as may be the case in some segments of the Industry. It is preferable, while training to the requirements of specific Types, to make sure that the underlying explanations are not over-simplified to the point of being unhelpful and, perhaps, counterproductive.


movement of the nose away from the ground is not conducive to stall recovery.

Probably preferable to concentrate on the interaction of the aeroplane and the surrounding air flow rather than wherever the ground might be .. other than if ground contact is an imminent risk, we probably can afford not to worry unduly about where the ground might be whilst endeavouring to get the aeroplane back into controlled flight ?


considering a 45 degree bank to the left, applying right rudder would yaw the airplane to the right,

Depends on what degree of control you might have in the particular circumstances. However, presuming that the input produces yaw .. that produces slip and too much slip may precipitate a significant departure. Probably not a good technique as a general consideration ?


which in this case, would raise the nose of the airplane away from the ground

If the former problem occurs, the nose might rapidly point more directly towards the ground. Just what aerodynamic benefit arises from having the nose point away from the ground ?


If you were to use elevator instead - you will point the nose towards the ground,

While that may be an effect, it also will have the primary, and desirable, effect of reducing alpha. How is the ground relevant to the aerodynamic concerns ?


and since the airplane is traveling towards the ground, that will automatically decrease the angle of attack.

That probably will be the consequence. However, one needs to be considerate of the particular Type's pitching moment characteristic - some aeroplanes have nasty spots where the elevator's capability to produce pitching motions is compromised greatly.

Again we should be thinking about the airflow, not the ground. The latter is only of interest were we at risk of hitting it ...


If you're at the critical angle of attack, you can unload the wing by ... increasing angle of attack

Perhaps you can provide further amplification on this suggestion ?


When the airplane is at the stall and there is a wing drop, the longitudinal axis usually gets tilted off the heading in the direction of the roll.

Typical behaviour - further effects of controls stuff from basic training.


By pitching down, while at 45 degrees of bank, you will move the longitudinal axis back towards the initial heading.

And the effect of that might be ?

[italia458]

John T,

It is preferable, while training to the requirements of specific Types, to make sure that the underlying explanations are not over-simplified to the point of being unhelpful and, perhaps, counterproductive.

I agree.

Probably preferable to concentrate on the interaction of the aeroplane and the surrounding air flow rather than wherever the ground might be .. other than if ground contact is an imminent risk, we probably can afford not to worry unduly about where the ground might be whilst endeavouring to get the aeroplane back into controlled flight ?

Agreed. I was talking about a specific scenario where the airplane was in a basic 1G stall. If the airplane starts descending towards the ground, the nose needs to be lowered so as to reduce the angle of attack.

I understand the descriptions I was using sound 'unconventional'. I wouldn't teach someone to recover from a stall by talking about the ground and not about the aerodynamic aspects such as angle of attack, etc.

Depends on what degree of control you might have in the particular circumstances. However, presuming that the input produces yaw .. that produces slip and too much slip may precipitate a significant departure. Probably not a good technique as a general consideration ?

Exactly! And that's what I'm trying to convey - that using rudder in that situation isn't conducive to efficient stall recovery.

If the former problem occurs, the nose might rapidly point more directly towards the ground. Just what aerodynamic benefit arises from having the nose point away from the ground ?

No benefit! I'm not sure if you misunderstood what I wrote or not. I think we're thinking similarly - I'm just approaching it from a different angle.

If you were to use elevator instead - you will point the nose towards the ground,

While that may be an effect, it also will have the primary, and desirable, effect of reducing alpha. How is the ground relevant to the aerodynamic concerns ?

Yes. I've always been teaching that if you're in a stall you need to reduce alpha, and that the primary method of doing that is by pitching down.

What I was meaning with regard to the ground in this case is that your velocity vector is pointing towards the ground, so pointing the nose towards the ground (towards the direction that you're going) will reduce the angle of attack.

Maybe I just had a weird way of saying it - I wanted to point out that putting in 'top-rudder' at the point of stall in an effort to stop a wing drop produces undesired effects.

However, one needs to be considerate of the particular Type's pitching moment characteristic - some aeroplanes have nasty spots where the elevator's capability to produce pitching motions is compromised greatly.

Agreed. That would be discussed in that type's training then.

If you're at the critical angle of attack, you can unload the wing by ... increasing angle of attack

Perhaps you can provide further amplification on this suggestion ?

I don't suggest this as being something I would teach as part of stall training but what happens to the coefficient of lift when you're at the critical angle of attack and reduce alpha? It decreases. What happens when you increase alpha? It decreases. I was specifically talking about the wing loading when the airplane is significantly past the critical angle of attack (stalled). Obviously increasing alpha beyond the stall is the opposite of what should be taught in stall recovery.

By pitching down, while at 45 degrees of bank, you will move the longitudinal axis back towards the initial heading.

And the effect of that might be ?

Nothing really gained in my opinion. But for the pilots who are anal about heading control in stalls I thought it might make them see things differently - the same ones that practice the 'falling leaf' stall and think it's doing good for the student. I don't quite share their philosophy.

[bubbers44]

Using a few degrees bank into the operating engine is good. Once single engine climb speed and clean center the ball. One of our very good pilots at our airline was taking off with the FO flying in a B727 and just before V1 the #3 reverser deployed half way because of a failure and the FO continued. The captain took over and used the 5 degree bank procedure barely climbing at 500 fpm. No reverser lights were on but he found by reducing power on #3 engine his climb improved. He was able to return and land and found the right side of the clam shell reverser had broken and went into reverse.

This is a fine example of how automation would have doomed them but basic piloting skills worked. He was in my era of pilots that made it work no matter what.

[bubbers44]

Us old guys just would love you to have the same basics that we did. We are not better than you by any means. We just had different training. We went from J3's to Cessnas to Piper to Lear Jets to Boeings, to MD80's to biplanes and sailplanes effortlessly because they all flew the same. Some of the planes didn't even have a battery installed. Tailwheels were normal and aerobatic flight was effortless. Beach18's with round motors were what we got our multiengine rating in. Then we got to haul freight at night single pilot IFR and loved it. I guess we were the lucky ones. We loved what we did and grew up during the perfect time to fly.

[Slasher]

You hit the nail on the head bubbers - I have a PA18 to remind me I'm not an Airbus
robot - and a couple of hours throwing a DH82 around the sky once a year brings me
back as to why I wanted to fly to begin with.