Boeing 777 - Automatic takeoff?
 

I was discussing this at last nights bbq+beer with an aviation professional. Is it true that the Boeing 777 can perform a fully automatic takeoff? That is, with centerline guidance commands?

Regards,

Martin

Errr...the answer's NO!!

Your 'aviation professional' might have had one too many lagers.

:} :} :}

all the boeings do fully automatic takeoffs in 45 knot crosswinds, just set power and sit on your hands, feet across lap, and allow it to takeoff:} ...i'm just playing !!!

however i have heard of a piper cub taking off from a GA ramp due to engine running on a snowy surface and flying around till fuel exhaustion and crashing intact ... true story afaik:O

Certainly not fully automated, however, like most things regarding the B777 there is still a high degree of automation.

When Phil Condit was leader of the 777 design team he said: "the pilot must be able to control the aircraft with his feet on the the floor, not with the rudder pedals - no rudder application should be neccessary, and he can maintain stability with just the yoke."

To achieve this the aircraft has a wheel-rudder cross-tie and a Thrust Assymetry Compensator (TAC). The wheel-rudder cross-tie moves the rudder (up to 8 degrees of deflection) in response to control wheel inputs. The TAC on the other hand, applies up to 10degrees of rudder deflection when the thrust from one engine exceeds the other by 10 percent.

When Phil Condit was leader of the 777 design team he said: "the pilot must be able to control the aircraft with his feet on the the floor, not with the rudder pedals - no rudder application should be neccessary, and he can maintain stability with just the yoke." (Quote)

Forgive me for being naive, but.... why? Whats he got against rudder pedals?!

If you have seen the doco produced about the development of the 777 (5 hours, was shown as a series a number of years ago) the original engineering philosophy was to DESIGN an aircraft which did not require pilot input. This design was then downgraded for the production aircraft because of certification restrictions and perceived passenger resistance. The flight control system is not capable of auto takeoffs, but how much modification would be required only the engineers would know. 200 ft min for the autopilot is only a cert restriction. I know in the sim, the autopilot does a wondeful job after you have set the attitude on rotate, makes no difference 1 or 2 engines.
while not cert to, it handles the yaw just fine, TAC on or off.
I would think that AB, being more inclined to push the boundries of auto flight, will be the first.

Probably
 

Probably the capability exists but the interlocks would prevent it. The active part is, of course, the roll out function of the autoland which uses the localiser to steer down the runway initially on rudder, then NW Steering so this would have to be reversed for a start. But to take off you would need the system to go straight onto elevators or horizontal stab trim for pitch control and roll control for wings level. I would think that probably has been incoprorated but downgraded/locked out. I think the A320 has it but also inhibited.

A little off the main-stream topic, but whilst there are some people on-line who are familiar with Phil Condit's design philosophy, and TAC in particular, can anyone provide an answer to the following?

I'm a practicing B777 pilot (practice makes perfect), and never really sure of the intent of the small residual slip (or is it skid?) when TAC operates the rudder following engine failure. I have been told that a small amount of slip/skid was deliberately left for pilot input (seems strange to me), but also told that the small residual slip allows for the optimum rudder input / slip for minimum drag and optimum performance.

My own experience is that if you try to 'rudder out' the small residual slip, the aircraft flys terribly, other B777 pilots and my students during conversions agree, it's better to not touch the rudders.

So which is it - Correct it, or leave it alone?

Regards,

Old Smokey

No idea if this is true, but I was told that the TAC as originally designed was so good that there was no noticeable yaw after an engine failure. During initial certification the TAC had to be "de-tuned" to allow some yaw in order to: a) make it obvious an engine had failed, and b) allow easier identification of the failed engine.

As I said, that's what I was told...

I agree with Smokey. With an engine out the airplane flies a lot better with a tiny bit of sideslip and little bit of bank than it does with wings level & ball centered. Dunno why it should be, though

For any aeroplane on asyemetric thrust, the true zero sideslip (and thus minimum drag) condition in straight flight is achieved with a small amount of bank towords the live engine.

What I don't know is how the slip indicator works (the little rectangle under the bank pointer)

Does it indicate true sideslip under aysemetric thrust (and would therefore be centered with the correct small bank angle)? or does it simply replicate the traditional slip ball (and would therefore be displaced toword the lower wing)?

The little bank and side slip is min drag. The bank means less rudder and the resulting sideways moment is being compensated for by the side ways component of lift. Any more bank, and you risk the spoilers at the low speeds. The side slip ensures the aluminium tracks in a straight line.
I would imagine the drag curve has a relativly sharp bottom due to increased form drag from the dead engine and induced from the rudder, so any change to the config is putting you towards the back of the curve ( If only slightly), so a reduction in performance and "feel".

I think a potential sourse of confusion here is exactly what we mean by "sideslip" under aysemetric thrust.

Traditionally sideslip was indicated by a ball in a curved tube which in straight line flight indicates the direction of gravity. This we might call "indicated sideslip"

True sideslip is the direction of the airflow relative to the fuselage centerline. It could theoretically be measured by a vane or, in an aeroplane with a one piece windscreen, by a piece of string in the center of the windscreen like glider pilots use.

Under symetric thrust, indicated sidslip is the same as true sideslip.
Under aysemetric thust however true and indicated sideslip are not the same.

Any true sideslip is a source of drag due to the fuselage being not aligned with the airflow. For min drag therefore we want to find the zero true sideslip condition. At zero true sideslip there will be an indicated sideslip towords the live engine.

I suspect that the little rectangle under the bank pointer shows indicated sideslip, not true sideslip.

(a) the ball has naught to do with sideslip .. symmetric or asymmetric .. or, indeed, gliding ... (other than incidentally ..)

(b) after the failure has been sorted out, there is a lateral force (due to the rudder angle) .. which causes a lateral acceleration and velocity to balance out the unbalanced force .. hence, a resulting sideslip angle

(c) a touch of bank the other way (2-3 deg) cancels out the sideslip in (b)

Try a few searches as this topic has been done to death in the past ..

This one is a good place to start ... be aware that Milt is a retired, very experienced test pilot and is stirring the pot masterfully in this thread ... he sucked me in well and truly for a while until I twigged to his gameplan. Amongst his acknowledged skills is included telling wonderfully entertaining tales over dinner with a wine or two ..

And another one .. which includes a piccy of the Concorde slip indicator. Bellerophon was a Concorde pilot in the heady days when the bird ruled the skies.

.. and there are a few more threads around worth a revisit, I'm sure.

OK, I shall avoid being drawn further into a topic that has already been done to death.

I agree that the ball might best be called a balance indicator, but most people call it a slip ball.

The little rectangle under the bank pointer is called Slip / Skid indication in the FCOM, but I suspect it isnt.

"With an engine out the airplane flies a lot better with a tiny bit of sideslip and little bit of bank than it does with wings level & ball centered. Dunno why it should be, though"

Thanks Rivet & Singleseat. What i actually meant to put across was that on the 777, this is tendancy to fly wing down is much more pronounced than on other Transport Category twins such as A310 & 737. Perhaps it has got something to do with thrust-weight ratio vs relative size of the rudder too. If one were to compare the wings level engine out behaviour on all three of the said airplanes, one would find that on the 777 you'd need an awful lot more rudder than on the 737 or A310.

Going back to topic, some 3 years ago I came across a notam that left me wondering. It stated aproximately "localizer not usable for take-off".

Any clues?

Para-Visual Display
 

That will be for take-off using a Para-Visual Display (PVD).

System provides a visual indication of displacement from the centreline using the localizer signal. Uses indicater stripes that move in the direction that the aircraft is required to move.

Same system is used on roll out from an auto land if ILS not cleared for automatic roll out.

System needs to be switched on, ILS manually tuned (for take off), have a valid front cse signal present, aircraft heading to be within 45 degrees of front cse, auto pilot OFF and aircraft on the ground.

cool! i never really knew that the 777 was THAT advanced TAC my first time hearing of it amazing...I just love Mr. Boeing's Ladies :)

Getting back on topic!

L1011 AP was capable of Auto Take Off but un-certified.