Ball centered during engine outs?
 

A colleague and I were discussing where to place the "ball" during engine outs on airliners. I've always taught and was taught to keep the ball centered. 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. This would keep a yaw string (if installed) right down the centerline of the aircraft. His thinking is that airliners are no different.

Now I'm no aerodynamic genius so I thought I'd consult this forum. Does this apply to jet airliners?

You bet it does... moderate sideslip towards the live engine is never a bad thing and on some older types it was absolutely necessary to maintain directional control at low speed. As AAIB noted in report on British Airtours B707 crash at Prestwick in 1977, aeroplane's certified Vmca with 5° bank was 119 kt but when bank was reduced to zero, Vmca jumped to 160 kt.

On single aisle Airbus I never gave much thought to how much slip is needed; as soon as engine failure was detected, skypointer index on AH turns blue, indicating it's representing single engine sideslip target. One just centered it and had optimal sideslip.

B737 FCTM barely mentions it, but yes, the ball is slightly out of center toward the "good" engine. More time is given to making sure the rudder is trimmed so the yoke is level in straight flight.

SF340 I flew for years, it was centered with the Y/D engaged, but that was a turboprop. Still an airliner, but not swept to turbojet, of course.

Not sure of the origin of these notes, but they provide some background.
Asymmetric Flight.

I've always taught and was taught to keep the ball centered.

you can do that wings level - has both advantages and disadvantages. Important thing is what is most critical at the time in the circumstances ?

In addition, systems limitations may have an input - eg some ADIs don't like sustained small bank angles.

the ball was kept half out and a bank of 5 degrees towards the good engine was needed.

appropriate for OEI back around Vmca

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

don't think so ...

His thinking is that airliners are no different.

just bigger and (usually) noisier. Jet versus prop has some effects due to prop wash

No ball in the 737s i fly but when i had one flying props:E i was taught and agreed to keep the ball slightly off the middle(half ball deflection) during engine out after take off.

In flight school long time ago, they used to calibrate how much out of center you should put the ball. They used a string to visualize the one engine out zero slip angle, then they made a mark in the instrument.

they used to calibrate how much out of center you should put the ball

one needs to be a bit careful. Three situations for which one should cater ..

(a) back around Vmca, nil slip is not the aim - control is. Unless the POH says different, you want 5 degree bank to the operating engine(s). Vmca is strongly dependent on bank angle

(b) once you have things sorted out and a decent speed for climb (somewhere near blue line, perhaps), then performance becomes critical. Something approximating nil slip will be optimal. As a general guide, looking for 2-3 degrees bank to the operating engine(s)

(c) cruise (and for those aircraft with ADIs not liking small bank angles). The performance benefit of a small bank angle is not warranted so we generally tolerate some extra drag and go for wings level. For awkward ADI aircraft, wings level is used for performance climb as well. Consider that the performance delta is not all that great so pilot workload comes into the equation as well.

"Raise the dead and let the ball fall."
Works every time.

very true. Control comes always first.

The marking in the ball indicator was not to be used below the red line, if I recall correctly. Or perhaps it was the blue line.

Upon engine failure, control was primary and performance secondary. If performance was too bad and speed was near red line... Retarding the live and putting the airplane back on the runway was the thing to do. We never used limiting runways, of course, but those Senecas would not make anywhere near the performance on the POH charts.

I deemed the twins as more dangerous that singles in approach, landing and take off phases. In the cruise, though, is better to have two.

Or perhaps it was the blue line.

hopefully.

If performance was too bad and speed was near red line

if you have the latter then expect the former ...

Another consideration is control drag.

On Airbus, the 'slip' indicator changes with an engine out to indicate when one is flying at minimum control drag - i.e. no spoilers out and ailerons neutral. Having centered the 'engine-out slip indicator' you will be flying at minimum control drag, but will have about 5 degrees bank towards the live engine, as mentioned above.

Before this subject degrades to Airbuses -

5* towards live engine, approx half ball deflection, dead engine feathered, Vy, gear up.
Since there's no guaranteed perf for twins under 5700kg (except 1% at 5000ft ISA gear
up, eng feathered,Vy, max cont) which means the inevitable prang will be about a mile
further along than had the feather and gear etc not been taken care of). (Reference -
Gove prang C402 circa late 70s).

Same with jets except you DO have a guaranteed perf in the 2nd seg with bits hanging
out. In the 737 it was still half ball deflection IIRC till end of 4th segment.


..I understand John the Wombat was a real handful
with a No 1 cut at VMCG - including full left aileron!

The original post did refer to airliners.

According to Boeing on the 747-400.

"If the engine failure occurs at or after liftoff apply rudder and aileron to control heading and keep the wings level. In flight, correct rudder input approximately centers the control wheel. To center the control wheel, rudder is required in the direction that the control wheel is displaced. This approximates a minimum drag configuration."

Actually, the 727 manual says pretty much the same thing resulting in the ball being slightly out of center.

Bit concerned about the preoccupation with 5° bank ...

(a) around Vmca 5° is the way to go. Unless the POH/AFM says different, presume that book Vmca was determined with 5° bank. As speed increases, the bank can be relaxed.

(b) blue line will give you best climb at around 2-3°

(c) if you prefer 5° at higher speed, then consider that climb performance will be not all that much different to wings level .. so why bother with the effort to keep on a higher workload bank angle ?

I understand John the Wombat was a real handful

Had its moments ... Avalon for local with the usual howling westerly. Off to the south with full aileron into wind, fail #4 and if one were slow to reverse the aileron into the operating engines .. it all got very interesting ... very quickly.

But empty .. did she lift up her skirts and go ... MTOW a bit of a dog.

Hey Slasher, that is unnecessary. I didn't design the things, I just fly them. Thread starter asked about JET AIRLINERS, not turboprops.


U

KIS. Don't complicate the issue!!

My first consideration is to have the control column centered. That way you wont have any spoilers sticking up on the wing, at the very time you dont need it. How do you centralise the control column? "kick it level" E.G., if the wheel/column is to the left of centre, left rudder is needed. Boot it, then hold it. Give it time to settle but dont juggle the rudders. Don't even need a ball, as it will be very close to centre.

This worked for me, on light piston twins to heavy 4 engined jets.

A fixed wing aircraft, is just that. Just another aircraft. The basics are the same, whatever the power plant, when ever they are situated, swept or straight wing.

"If it ain't Boeing, I'm not going"

Uplinker stop being so touchy mate and RTFP - I said BEFORE it degrades to Airbus. I
wasn't directing it at you.

..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! http://serve.mysmiley.net/mad/mad.gif

Tell that to Boeing who are designing a bigger 777. They need your sage advice.:D

doubleu-anker
 

hello,

I take it that you consider spoilers' drag as systematically being greater than rudders' no matter the deflection magnitude of said rudders you may need to center the column ?

Never had a flame out in real life, but surely my type's sim (ATR) wouldn't let you control it with the sole rudder's help, at least in the recovery phase.

The 5 deg bank being part of Vmca certification aren't there by chance.
My understanding is that bank also takes part in easing off rudder's drag thus improving performance.

The 707 example brought up in a preceding post tells pretty much what's happening: 40 knots Vmca degradation for 5 deg bank variation towards a level wing situation.

That's why a conservative approach like the one you propose sounds a bit odd to me, no disrespect to your experience.