Single engine twins

[Bear Cub]

I've just been sifting through some stuff on multi engine aircraft flying.

If I understand it correctly, when you lose an engine in an N registered aircraft you MUST bank 5 degrees toward the live engine, but if you have an engine failure in a G registered aircraft you hold wings level.

What have I missed here? How does the aircraft know what registration it has?

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[TWINCOMM]

BearCub

Not quite sure where the registration issue came from, but all my M/E books suggest that up to 5 deg bank towards the live engine may be necessary to achieve balanced flight.

I belive it's A/C specific, but if you are doing any sort of IFR procedures, the zero bank will always be better because it does not cause the ADF needle to dip.

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TwinComm

[BlueLine]

The primary objective in applying 5 degrees of bank towards the live engine is to lower critical speeds (VMC). The aircraft can be controlled at a lower speed when 5 degrees of bank is applied as demonstrated in Ex Assy 2.

If the aircraft is flown wings level and the ball central with one engine inoperative, there will be a sideslip towards the dead engine. Balanced flight can be achieved by applying 5 degrees of bank towards the live engine, but now the ball will now be offset towards the live engine.

Pre-Flight Briefing Manual - Multi-Engine Course by Mike Woodgate is a worthwhile reference.

[2R]

Banking into the live engine create's "Zero sideslip" .Anything you can do to reduce drag will increase performance.
Quote from AC 61-21A P237 FAA Flight Training Hanbook
"Flight tests have also shown that the high drag caused by the wings level,ball centered configuration can reduce single engine climb performance by as much as 300 FPM,which is just about all that is available at sea level in a non turbocharged light twin."
Banking at least 5 degree's into the good engine ensures that the airplane will be controllable at any speed above the certificated Vmc,that the airplane will be in a minimum drag configuration for best climb performance,and that the stall charecteristics will not be degraded.Engine out-out flight with the ball centered is NEVER correct.

[Bear Cub]

2R...you have answered TwinComms question with regard to the registration issue.

It seems that the FAA are of the opinion that flying on one engine with the ball centred is NEVER correct - but the CAA seem to suggest it is, sometimes.

Any other arguments from people - especially one who will admit to being a multi engine instructor or examiner in the UK?

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[BlueLine]

Bear Cub

When flying a twin on one engine there are basically 3 methods of preventing the yaw.
The 1st method uses aileron but no rudder and has no great merit.
The second method is to prevent yaw with rudder by centering the slip ball and rolling the wings level.
The third method is to apply 5 degrees of bank towards the live engine and use less rudder to fly straight.
Each method has its advantages and disadvantages. Clearly, if you have just taken off performance is your main concern so 5 degrees of bank towards the live engine will give you the most efficient configuration and best rate of climb. If you are instrument flying in the cruise, where performance is no longer a major issue, you may find it less disorientating to fly wings level with the ball centered and accept a little more drag and some sideslip.

The only difinitave publication issued by the CAA is CAP 528 Commercial Flight Instructors Manual. Part 3 Ex 23 includes teaching the use of 5 degrees of bank towards the live engine.

It is not uncommon for different techniques to be used in different countries. The whole purpopse of conducting asymmetric training is to present the student pilot with all of the problems and the solutions.

There are many different ways of doing things in aviation, they are not all correct neither are they all wrong. As a pilot you should know the relative merits of each and use your judgement to apply them in an appropriate manner.

[This message has been edited by BlueLine (edited 17 July 2000).]

[Bear Cub]

Thanks for that, Blue Line.

I was made particularly curious by the FAA (and King video) phrase that flying "wings level with the ball in the middle is NEVER correct".

The emphasis of NEVER was theirs, not mine.

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[A and C]

Part of the multi trainning should show you just what 5 degrees of bank can do for you,see it in the air and what blue line has writen will be forever etched in your brain ,that extra performance that 5 degrees gives you may one day save your skin.

[Oleo]

FWIW I am an MEI, and have been thru the systems in both the US and UK. I thought it was very strange in the UK when they insisted on no bank. It has been demonstrated that bank from 3-5 deg decreases Vmca and increases performance. I have no idea why it is not taught in the UK. Surely the ultimate reference has to be the aeroplane manual. Duh - why would we not want that performance??

If you rely solely on rudder to keep straight you are presenting a larger side surface of the aeroplane into the airflow and hence creating more drag. This drag can be reduced by using a modicum of bank into the live engine thereby relieving the job of the rudder a little and presenting a more normal streamlined shape.

Perhaps someone from the CAA or an examiner would care to illuminate something the rest of us poor sods are missing...

[This message has been edited by Oleo (edited 19 July 2000).]

[Bear Cub]

This is getting harder...promise me that somebody has made a typo here...BlueLine says bank toward the LIVE engine, Oleo says bank toward the DEAD engine - and the CAA seem to say "wings level, ball in the middle".

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[A and C]

Its 5 degrees into the LIVE engine that gives the best performance increase i think that the CAA only recomend wings level for aproaches when perpormance is not critical.
Part of the multi engine trainning will show you this as you should look at the Vmca with and without the bank into the live engine also try it into the dead engine and see the performance fall and Vmca rise (do this all at least 3000ft above the ground with an instructor)

[Oleo]

Whoops Bear Cub (and everyone else)...it was late when I was typing that!! Yes LIVE!!!

[Bear Cub]

Oh well...got it now, Oleo - at least it shows that I am listening to what you say.

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[watford]

Vmca (Minimum Control Speed in the Air) is unaffected by bank, or anything else come to that, it is an absolute figure for each aircraft and can be found in the Flight Manual/POH/etc. It is defined in BCARs as:

The minimum speed at which, if sudden and complete failure of the critical power unit occurs during the take-off climb out, it is possible to regain control and thereafter maintain straight, steady flight at the same speed. The change of heading should not exceed 20 degrees and the final angle of bank should not exceed 5 degrees.

What the officer meant to say was that Critical Speed is decreased if bank is applied towards the live engine. It is theoretically possible to overcome all asymmetric forces if sufficient bank is applied, removing the need for any rudder. However, this technique would cause more problems than it would solve and the generally accepted angle of bank to be applied is 5 degrees.

The problem is that the aircraft is not easy to fly accurately at 5 degrees angle of bank without constant reference to the AI, and one certainly does not want to be glued to the instruments at this critical stage of flight. Neither is it easy to keep in balance, since the slip indicator will not be central and balance will have to be judged by reference to yaw in relation to an external visual reference or the turn co-ordinator/compass. For these reasons, it is recommended that, where performance is not critical, the aircraft is flown wings level with the slip indicator central.

The pilot who understands the problem will be capable of adjusting his handling of the aircraft in response to the conditions pertaining at the time, he/she may need bank towards the live engine, he/she may not. With the greatest respect to the FAA and Mr. King, to say that flying "wings level with the ball in the middle is NEVER correct" is something of a cop-out and avoids the pilot having to think for him/herself. It would be more accurate to say that flying with 5 degrees of bank to the live engine and the aircraft not yawing is never wrong.

The measure of a good pilot is one who can think for him/herself and make valid decisions based on a thorough understanding of the principles involved, not simply reacting in a fixed way only because the King video said so.

Nobody will fail a JAA skill test for flying an asymmetric aircraft wings level with the ball in the centre (if performance is not a consideration). However if, in making an unnecessary attempt to fly with 5 degrees of bank to the live, he/she allows the aircraft to drift off the required heading, a fail will surely result.

[2R]

The purpose of training is to provide the correct conditioned response to any situation.
Do not forget to fly the airplane. :)

[Bear Cub]

2R, is your posting a suggestion that you have "changed your behaviour as a result of experience" (American definition of "learning")?

Further up the page you finish your message with "Engine out-out flight with the ball centered is NEVER correct."

You now seem to agree with Watford.

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[dragchute]

Watford,

Above, you said: "Vmca (Minimum Control Speed in the Air) is unaffected by bank, or anything else come to that, it is an absolute figure for each aircraft and can be found in the Flight Manual/POH/etc." This statement is not quite correct.

Vmca is in fact affected by bank angle and a number of other factors including CG, weight, power output, windmilling propeller etc. Vmca is related to controllability rather than performance. Banking ‘five degrees towards the live' results in a ‘slip' causing the relative airflow to pass over the fin at a greater angle of attack. This results in improved control effectiveness. (A lower speed for the same rudder deflection). Vmca will therefore be lower with bank than with wings level.

During certification under FAR 23 the FAA stipulate as an option, a maximum bank angle of five degrees. Obviously the manufacturer will accept this parameter to enhance his product.

Bank angle will also improve performance quite markedly. An early experience with a 400 series Cessna almost resulted in my demise following an EFATO on an obstacle cluttered flight path. My training had been along the lines of wings level, ball centred and I was not impressed with the climb performance. A later endorsement introduced the bank technique and I regret not being told of it earlier. However, many Australian training manuals were of British origin and made little point of the subtleties contained in Section 3 of American POHs.

Interestingly, whilst five degrees assists with control, about half that angle provides optimum performance (Vyse/Vxse). The shallower bank angle reduces slip or skid and minimises form drag.

I look for maximum use of the trim controls thereby easing the workload in achieving optimum bank angles. I have also found that some turbine aircraft with more sophisticated yaw dampers may be more accurately controlled by disengaging the yaw damper and re-engaging with the required rudder input.

Regards



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dragchute
email: [email protected]

[watford]

Sorry, dragchute, but you are falling into the same trap of confusing Vmca with Critical Speed. All of what you say is correct when applied to Critical Speed, Vmca is declared by the manufacturer as a result of certification flight testing and refers to the speed at the moment of engine failurebelow which it will be impossible to control the aircraft.

[DesiPilot]

One thing I noticed that helped me achieve "Zero Side Slip" was the use of yaw string. Apparently it is a common practice in the multi training in Comair Aviation Academy. You keep the string alligned with the longitudinal axis and your longitudinal axis is allingned with the relative wind hence giving you the so called zero side slip.
Watford I dont agree with you that bank angle has nothing to do with Vmc. In the book Aerodynamics for Naval Aviator it says that for each degree of bank angle towards the good engine your Vmc reduces by approximately 3 kts.
Now considering this the manufacturer could bank as much as they want so that they can publish lower Vmc, because of this reason FAA came out with certain conditions that manufacturers has to follow to establish Vmc. In my school I was taught that with an acronym MULTICGBREST
Max take off power
Max gross weight
Unfavorable Center of Gravity
Landing gear retracted
Take off configuration (cowl flaps open and trimmed for take off)
Inoperative engine wind-milling
Critical engine inoperative
Ground effect (out of ground effect)
Bank 5 degrees toward good engine (for standardisation purposes)
Rudder pressure not to exceed 150 lbs. (for standardisation purposes)
Exceptional pilot skills
Standard day (for standardisation purposes)
Twenty degree recovery. (for standardisation purposes)

I may be wrong here, but right after introducing asymmetric performance to students, we demonstrate Vyse (drag) demo and I make the students write down the different performance under different drag settings and its a real eye opener for a student to see that you get the best performance with flaps up, gear up, props feathered and upto 5 degrees of bank angle towards the good engine.
CAA says when the performance is not required you could maintain wings level. Yes I agree in the ideal world that would be great, but I personally any day will take more performance by banking into good engine and reduce the power hence further reducing my Vmca.
But than again I guess its the matter of your personal opinion, after all when engine quits on you, you are the Pilot in Command.

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My mascot is a bumblebee. Because of its tiny wings and heavy body, aerodynamically the bumblebee shouldn't be able to fly. But the bumblebee doesn't know that, so it flies anyway.

[This message has been edited by DesiPilot (edited 21 July 2000).]

[A and C]

Watford the term "critical speed" has now been superseded in the syllabus by "minimum control speed" the same thing but very eazy to get mixed up with Vmca ,but thats the way the CAA want us to teach it.

[Bear Cub]

I'm getting the vibe - from the two postings - that watford agrees with the 5 degrees stuff IF PERFORMANCE IS CRITICAL - but suggests that if not (say descending on an instrument approach at a high enough IAS - where downward movement is to be encouraged) it is better to be wings level.

I don't think anybody is arguing that it should be wings level ALL THE TIME.

Curious to hear some definitions of "Vmca", "Crtical Speed" and "Minimum Control Speed"

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[watford]

A and C - Not quite. What used to be referred to as Vmca by the British Civil Airworthiness Requirements (BCARS) has, under JARs become Vmc (Minimum Control Speed). The definition in JAR 23.149 is similarto, if a little shorter than the definition in FAR 23.149 and is as follows:

JAR 23.149 - Minimum control speed
Date: March 11, 1994


(a) VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the aeroplane, with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank not more than 5°. The method used to simulate critical engine failure must represent the most critical mode of powerplant failure with respect to controllability expected in service.

(b) VMC for take-off must not exceed 1.2 VS1, (where VS1 is determined at the maximum take-off weight) and must be determined with the most unfavourable weight and centre of gravity position and with the aeroplane airborne and the ground effect negligible, for the take-off configuration(s) with -

(1) Maximum available take-off power initially on each engine;

(2) The aeroplane trimmed for take-off;

(3) Flaps in the take-off position(s);

(4) Landing gear retracted; and

(5) All propeller controls in the recommended take-off position throughout.

(c) For all aeroplanes except reciprocating engine-powered aeroplanes of 2730 kg (6000 lb) or less maximum weight, the requirements of sub-paragraph (a) must also be met for the landing configuration with -

(1) Maximum available take-off power initially on each engine;

(2) The aeroplane trimmed for and approach with all engines operating at VREF at an approach gradient equal to the steepest used in the landing distance demonstration of JAR 23.75;

(3) Flaps in the landing position;

(4) Landing gear extended; and

(5) All propeller controls throughout in the position recommended for approach with all engines operating.

(d) At VMC, the rudder pedal force required to maintain control must not exceed 667.5 N (150 lb) and it must not be necessary to reduce power of the operative engine. During the manoeuvre the aeroplane must not assume any dangerous attitude and it must be possible to prevent a heading change of more than 20°.


You will note that there are no variables involved - flap setting, power, propeller controls, etc. are all fixed resulting in a single speed being declared for each aeroplane.

Critical speed, on the other hand, is defined as "The lowest possible speed on a multi-engined aircraft at which, at a constant power setting and aircraft configuration, the pilot is able to maintain a constant heading after failure of one or more engines on one side" The Critical Speed (but not the Minimum Control Speed) can be affected by many things including, for example, the thrust from the live engine, the position of the centre of gravity, asymmetric drag, the aircraft configuration (flaps, slats, gear, etc.), slipstream, asymmetric blade effect, turbulence, altitude, temperature, rudder trim position and the strength and skill of the pilot.

The Minimum Control Speed for the PA34, for example, is quoted in the POH as 68 knots. The Critical Speed, however, can be anywhere between about 70 knots in the worst configuration (wings level, windmilling propeller, full rudder trim applied, aft centre of gravity, etc) and something less than the stalling speed in the best configuration.

Thus there is a significant difference between Vmc/Vmca (fixed) and Critical Speed (variable).

[dragchute]

Watford,

I am not really confusing Critical Speed with Vmca as Critical Speed is not in our vocabulary in Australia. Our teaching techniques seem to follow a different tack to the UK. Vmc as defined by FAR 23.149 forms the basis of ‘control' discussion and understanding. But when expanding on that principle the various factors and considerations impacting on Vmc are dealt with. Particularly since during the Air Exercise, the minimum speed at which control is maintained will not necessarily coincide exactly with the red radial. Your methods on the other hand seem to be rather pedantic in teaching Vmc coincides exactly with the red radial and any variation is another speed termed ‘Critical Speed' which may be any speed. I probably prefer the Australian approach.

But my main concern in any initial or subsequent endorsement session revolves around the wings level -v- five degree bank towards the live engine. A point raised in the initial post above by Bear Cub (G and N registrations). In any situation where altitude is a priority then the bank technique is imperative to achieve both performance and a margin of control. In cruise it may be optional, and irrelevant in descent. An engine failure during a descending turn may require momentarily levelling the wings and centring the ball to identify the failed engine. However the student must be able to demonstrate satisfactory control with bank to meet the handling criteria of the endorsement.

Regards,

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dragchute
email: [email protected]