Zero sideslip: Engine failure on multi engine airplane

Great post 99000. I agree with you entirely regarding scenario #2.

Also, you make a point I hadn't considered -- the accelerated flow over the right wing and not the left in the left engine failed case. This can be offset by right aileron. After all, when the plane is in a constant, coordinated bank to the right the wings are producing the same amount of lift. If not the bank angle would change, rolling toward the wing producing less lift. But this is new information I had not considered. Thanks.

As far as your first paragraph, the wings level, string centered, ball centered is not the scenario I am considering. I don't know where the ball would be with the string centered. In the scenario I am considering the wings are level and the string is straight. The ball goes wherever it wants. The pilot ignores it and keeps the string straight. This isn't shown in the AFM.
 
Roberto152 said:
As far as your first paragraph, the wings level, string centered, ball centered is not the scenario I am considering. I don't know where the ball would be with the string centered. In the scenario I am considering the wings are level and the string is straight. The ball goes wherever it wants. The pilot ignores it and keeps the string straight. This isn't shown in the AFM.
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In order to keep the string straight you have to use less rudder than is required to maintain level flight. The rudder input to keep the string straight is less than the rudder input required to put the left wing far enough ahead of the right wing to generate enough lift to compensate for the decreased lift from the inoperative engine.

The reason the Airplane Flying Handbook doesn't show wings level with yaw string straight is simple. Using only enough rudder to center the yaw string puts the plane into a situation where as speed decays and aileron effectiveness is reduced you will reach a point, Vmc, where the ailerons cannot compensate for the extra lift from the right wing and the right wing will rise up and flip the plane into a left hand spin. Or in other words if you fly engine out, wings level, and yaw string straight, you're gonna have a bad time.
 
I think I found the answer. Thanks to everyone who took the time to think about this problem. I found the following link, written it seems by the USAF:

www.dtic.mil/dtic/tr/fulltext/u2/a319982.pdf

It explains that for a given bank angle there is exactly one rudder position that will lead to straight flight (not necessarily coordinated, but straight). I haven't gone through their moment and force equations yet, but no doubt they will prove my thoughts wrong and that the zero side slip for straight flight does occur with a small bank. It certainly was not intuitive for me but I am glad to not only have found the truth, but WHY it is the case. No doubt many students may ask you the same questions I did -- I believe this article will explain (and prove mathematically) why, and in a way that is irrefutable. Our tax dollars at work??

As a result of their analysis it appears that the case I was advocating, left engine failed, wings level, yaw string straight, would cause a coordinated turn to the left. So turning an aircraft is possible with no horizontal component of lift. I thought before I read the article that was not possible, and it led to my erroneous conclusion.

Many thanks,
Roberto
 
Roberto152 said:
I think I found the answer. Thanks to everyone who took the time to think about this problem. I found the following link, written it seems by the USAF:

www.dtic.mil/dtic/tr/fulltext/u2/a319982.pdf

It explains that for a given bank angle there is exactly one rudder position that will lead to straight flight (not necessarily coordinated, but straight). I haven't gone through their moment and force equations yet, but no doubt they will prove my thoughts wrong and that the zero side slip for straight flight does occur with a small bank. It certainly was not intuitive for me but I am glad to not only have found the truth, but WHY it is the case. No doubt many students may ask you the same questions I did -- I believe this article will explain (and prove mathematically) why, and in a way that is irrefutable. Our tax dollars at work??

As a result of their analysis it appears that the case I was advocating, left engine failed, wings level, yaw string straight, would cause a coordinated turn to the left. So turning an aircraft is possible with no horizontal component of lift. I thought before I read the article that was not possible, and it led to my erroneous conclusion.

Many thanks,
Roberto
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You're getting too wrapped up in the concept of coordinated flight. Zero sideslip is uncoordinated in that your "good engine buttcheek" will be heavier. The bank is to create a horizontal component of lift to counter the horizontal lift in the opposite direction created by the deflected rudder. It was explained to me once this way:

Imagine two line guys pushing an airplane down an icy ramp. The guy pushing the right wing slips and falls, so the plane starts turning right. By the time he scrambles back up, he's behind the airplane, so he pushes the tail of the aircraft to the right to turn the nose back to the left. Now the plane is pointed in the right direction again, but sliding to the right, because of the guy pushing the tail right...

Now, let's take that same airplane airborne. The guy pushing the left wing becomes thrust from the left engine, and the guy pushing the tail right to counter the yaw of the dead right engine is the rudder. To counter (or zero out) the created sideslip we bank to the left a little to create a leftwards horizontal component of lift.

If a multi-engine aircraft is flying with one engine inop, the ball and the yaw string will never agree. **NOTE** The boundary layer air over the windscreen most likely will be turbulent enough that you won't be able to see the effects of zero sideslip. I tried it back in the day as a MEI once or twice, and it was very hard to see.
 
Roberto152 said:
Yes, me too, during climb out after a V1 cut when airspeed is slow and Vmc is a factor. And I'm glad I never lost one for real, but in the box I have never flown, and have never seen anyone else fly around dumping fuel while holding bank into the good side. Or being vectored around for a 3 engine approach. It is always wings level once sufficient speed is established (unless of course a turn is desired.)
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Don't confuse a Part 25 airplane with a Part 23. You will get hurt.

Don't confuse a straight wing airplane with a swept wing airplane. You will get hurt.

Don't use techniques that will cause more drag than necessary when trying to put altitude between you and the dirt.

Like others, I've watched the end result of this and friends burn in the wreck.
 
Polar742,
Your adumbrations of my doom are noted. Nonetheless, they are totally irrelevant to the subject of this thread.

I began this thread because I thought the idea of banking into the good engine to maintain straight flight with zero side slip to be wrong. It seemed that flying wings level with a straight yaw string would accomplish this. After reading the USAF training manual listed above (Chapter 11 and Chapter 4) I am now convinced I was wrong and that the traditional position I challenged is the correct one. I freely, happily, and readily admit I am wrong and am glad to have found the truth. The truth is summarized in the equations of motion discussed in Chapter 11.

Interestingly enough, virtually everyone who responded agreed with the "conventional wisdom" but no one could prove it. Instructors should be able to prove concepts to students, not simply say, "DON'T CHALLENGE WELL ESTABLISHED PRINCIPLES". Students deserve the truth, and the truth is what I was looking for. Now I can prove this "well established principle".

By the way, the equations apply equally well to Part 23 and Part 25 airplanes. Wing sweep is not a factor in bank angle for zero side slip with an engine failure.

Weight, or more accurately, the inverse of weight, does have a very large effect on bank angle required for zero side slip. W^-1 is proportional to the SIN(bank angle) for zero side slip with an engine out. Perhaps this is why when I used to fly the 747-200 (as it appears you do or did) the wings "appeared level" while, in fact, they may have been ever so slightly banked with aircraft weight of 800,000 lbs plus. The amount of this bank was so close to zero it was imperceptible -- at least to me. Maybe you could see it.

As far as keeping altitude between myself and the dirt as you say, in the very post of mine you quoted I agreed that banking a few degrees into the good side is perfectly legitimate and a good idea in first segment climb, even second segment in order to keep Vmc in check.
 
Roberto152 said:
Polar742,
Your adumbrations of my doom are noted. Nonetheless, they are totally irrelevant to the subject of this thread.

I began this thread because I thought the idea of banking into the good engine to maintain straight flight with zero side slip to be wrong. It seemed that flying wings level with a straight yaw string would accomplish this. After reading the USAF training manual listed above (Chapter 11 and Chapter 4) I am now convinced I was wrong and that the traditional position I challenged is the correct one. I freely, happily, and readily admit I am wrong and am glad to have found the truth. The truth is summarized in the equations of motion discussed in Chapter 11.

Interestingly enough, virtually everyone who responded agreed with the "conventional wisdom" but no one could prove it. Instructors should be able to prove concepts to students, not simply say, "DON'T CHALLENGE WELL ESTABLISHED PRINCIPLES". Students deserve the truth, and the truth is what I was looking for. Now I can prove this "well established principle".

By the way, the equations apply equally well to Part 23 and Part 25 airplanes. Wing sweep is not a factor in bank angle for zero side slip with an engine failure.

Weight, or more accurately, the inverse of weight, does have a very large effect on bank angle required for zero side slip. W^-1 is proportional to the SIN(bank angle) for zero side slip with an engine out. Perhaps this is why when I used to fly the 747-200 (as it appears you do or did) the wings "appeared level" while, in fact, they may have been ever so slightly banked with aircraft weight of 800,000 lbs plus. The amount of this bank was so close to zero it was imperceptible -- at least to me. Maybe you could see it.

As far as keeping altitude between myself and the dirt as you say, in the very post of mine you quoted I agreed that banking a few degrees into the good side is perfectly legitimate and a good idea in first segment climb, even second segment in order to keep Vmc in check.
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My post wasn't directed to you per se.

The only thing I'll comment on is your comment on the whale. I have yet to find anyone teach anything except wings level after an engine failure on takeoff.

Maybe it's just my company. Or the guys from Evergreen and Kalitta that ended up here.
 
Polar742 said:
My post wasn't directed to you per se.

The only thing I'll comment on is your comment on the whale. I have yet to find anyone teach anything except wings level after an engine failure on takeoff.
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Roll spoiler deployment at an inopportune time may have bad results.
 
Autothrust Blue said:
Roll spoiler deployment at an inopportune time may have bad results.
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Not so much that. More engine pod on the runway.

I'd have to check with @Jimflyfast or @seagull to be positive why, but all the guidance I recall Boeing providing is to start with approximately neutral aileron and add as necessary to keep the winds level as spoilers extended well slightly increase ground roll.

IOW, I know of no maximum aileron input limitation during takeoff runs.
 
Polar742 said:
Not so much that. More engine pod on the runway.

I'd have to check with @Jimflyfast or @seagull to be positive why, but all the guidance I recall Boeing providing is to start with approximately neutral aileron and add as necessary to keep the winds level as spoilers extended well slightly increase ground roll.

IOW, I know of no maximum aileron input limitation during takeoff runs.
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Would you get a flipping mohito and check out the local scene?
 
If I remember correctly, a pod strike won't happen until 7 degrees bank (tail strikes at 11 degrees pitch up). I believe the outboard spoilers begin to deploy at a certain amount of aileron deflection which would allow for "small" aileron inputs for a small bank angle. I know "small" isn't scientific. IMO the heavy weight V1 cuts were easier because the airplane was more stable. There was also more time before acceleration height.

No offense Polar with my previous post. I am very sorry about your friends. They weren't the Kalitta guys out of Columbia were they? They flew like heroes, never giving up, even down to 1 engine. Bad fuel.
 
Roberto152 said:
So put a yaw string on the airplane and when the engine fails simply keep the wings level and keep the yaw string straight[..] What's the problem with this?
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The yaw string indication depends on it's location.If you turn and the string is not in CG (though you keep it perfectly centered) but located on a canopy ahead of CG you will produce a skidding turn(as indicated by the ball).Skid enough an she will snap and tuck under.
 
Don't know if it's been mentioned, but think of the rudder as a vertical wing. When you press a lot of rudder to keep the nose straight with the wings level, the rudder is "lifting", like a wing with lots of down elevator, towards the (left-if your holding lots of right rudder), so...while the nose is pointed to a consttant heading, and the wings are level, the left pull of the rudder is making the airplane track in a left linear line so that the fuselage drag is greater than if you bank right so that the horizontal component of lift to the right compensates for the drag to the left. Now the airplane is tracking a straight line the same as the heading. Decreased drag- lower Vmc.
 
Roberto152 said:
As far as your first paragraph, the wings level, string centered, ball centered is not the scenario I am considering. I don't know where the ball would be with the string centered. In the scenario I am considering the wings are level and the string is straight. The ball goes wherever it wants. The pilot ignores it and keeps the string straight. This isn't shown in the AFM.
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The yaw string and the ball do not work the same way. The ball gets kicked around by gravity and inertia and the yaw string gets moved by the relative wind. If you're flying single engine with the wings level, you're flying crooked and the yaw string will not be centered.
 
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