Heavy jet operation re: V2

[backin5]

Any heavy jet pilots out there, any thoughts?... I'm trying to et my head around the complexities of V-speeds!!

If after normal rotation on a normal (4 engine) heavy weight take off the aircraft has not reached V2 would you maintain a slightly lower nose attitude to increase speed to V2, or continue rotation and fly below V2 and count on acceleration in the climb?

Would you consider increasing thrust if it were available?
Is flying below V2 on initial climb out unsafe?

Could you assume that the aircraft loading data was probably incorrect and that the aircraft was actually heavier than what the figures had been calculated for?

Does this kind of underperformance occur regularly?

Thanks.

[Basil]

Slightly lower nose attitude to accellerate to V2 or V2 +10kn. If that doesn't work then it's time to use up some of that engine life that engineers keep going on about (only joking, F.E.s)

If the aircraft has all engines running and does not achieve V2 following a normal rotation then something's wrong: windshear, heavier than planned, power down, gear left down :O

Yes, it's unsafe inasmuch as flight tested margins are being eroded and, in the event of an engine failure, you could lose further speed and be in a high drag situation, closer to Vs, stall in a turn and also be approaching Vmcg :ooh:

I've usually found that sort of thing's caused by windshear or to a lesser extent immediately after take-off, temperature inversion which tends to get you a little later (another good reason to achieve V2 +10)

Not regularly but at max RTOW it requires a bit of attention but then so do lightweight departures zooming (good tabloid term) up to/through initial cleared altitude.

The standard phrase for drawing other crewmembers attention to any of the foregoing is: "What the F V K K 's up wi' this thing!"

[411A]

This was more of a problem with the old straight-pipe (non-fan) powered heavy jet aircraft, ie: 707-321 (Pratt&Whitney JT4A) or Conway powered machines.
After rolling 11,500 feet on a 12,000 foot runway, then climbing at V2/400 fpm, one began to wonder....where is 'd thrust?

All the while hoping one didn't flame out.:ooh:

With fan powered aircraft, much better runway performance is the norm....usually:oh:

[backin5]

Thanks so much guys, I really appreciate the "heads up".

In regard to legalities... is V2 the actual REQUIRED min. climb speed? ie. 1.15VS? (I can't remember the actual figure), or is it regarded as generally acceptable to operate below V2 if the aircraft requires a 12.5 degree nose-up pitch attitude for the initial climb-out?

What I'm getting at is: If the aircraft operating manual states a 12.5 deg pitch angle for initial climb, would you maintain this pitch angle to get away from the ground even if the aircraft is operating below V2?
Or would it be acceptable/ preferable to, say, fly 10 deg nose-up pitch attitude and fly V2?

Thanks again for your help, it's really appreciated!

[Hawker-rider]

Allright,

when an airplane's engine flames out for whatever reason and continues the take-off, after rotation, passing through 35feet the speed at that moment is called V2 or takeoffsafety speed.

So if you use standard practices as far as rotation etc is concerned you will reach V2 right after rotation. at least the certificated V2 speed. So going below V2 is basically only possible to do when you use practices that are non standard and not approved.

Offcourse there is such a thing a an "optimized V2" which is approx 1.5Vs as opposed to the normal certificated V2 which is 1.2Vs

Remember V2 doesn't have anything to do with the speeds Vx and Vy

[backin5]

...woops, I just realised how dumb I just sounded!

I understand the definition (I think), but what I really want to know is how an experienced pilot would fly a take-off if the aircraft is not performing as well as it should for whatever reason...

Is it more important to climb out at V2, but with a lower nose attitude, or would you climb out at the ops manual specified nose up attitude but fly below V2?

Is V2 a legal requirement purely for performance calculations (ie for RTOW & CL Grad calculations), or a real flying performance speed?

Thanks, any help??!!!

[Hawker-rider]

edited the post, because the comments I was referring too have been removed, so my post wasn't making sense anymore

[FE Hoppy]

Vmu is above Vr.
vr is the speed at which the pilot initiates rotation. It may not be less than V1 or 1.05Vmca

Vmu it the speed at or above which the aircraft can safely lift of the ground and continue the take off with out hazard.

V2 is the speed atained at 35feet OEI when the aircraft is rotated at vr
it is selected to be
=>1.1vmca
=>1.2vs(1.13vs-1g)
=>vr
Yes you will be at v2 at 35 feet because your take off was planned that way. if you are limited then the screen height will be at the end of toda if not it will be somewhere before.

You must rotate the aircraft as per the SOP otherwise you copramise the height atte end of toda. If the speeds don't match then the take off calc was wrong.http://www.flightcrewinfo.com/vspeed.JPG

[Hawker-rider]

???

The airplane I currently fly has a Vmu below the rotationspeed per the flight manual.

I agree with you that the Vmu ( is a fixed speed) is higher then the LOWEST POSSIBLE Vr, but that that low of a Vr is not used in operational speeds, because of the tailstrike that occurs. Therefore the Vr in the books, for a balanced field length or whatever isn't necessarily lower then Vmu.

Back to your main question though.

Mostly you rotate initially to the pitch attitude that is taught, and proven in operation. Then you expect to get a certain acceleration from that, both engines you will accelerate through V2, and then gradually increase your pitch attitude ( or not) to climbout etc. So if for some reason the speed doesn't increase as anticipated, (or over rotated) I'd slowly decrease the pitch attitude to get the speed increase. ( or should I say instead of decrease the pitch>>> less-increase the pitch because you don't want to "level off")

so speed first, then altitude will come!

[sepolnad]

b5, there are different ways to deal with it.
During a situation like an engine failure before reaching V2, but without any other complication like a secondary system failure, for example, pilots must follow the recommended SOP for their airplane. Usually they must rotate at Vr with a continuous motion. Target pitch attitude have to be established, adjusting initial climb attitude to maintain a minimum of V2 and positive rate of climb. IAS can increase (considering landing gear retracted) if the pilot flies below initial target pitch attitude, but lower than certain limits a zero climb rate or even an undesirable downward movement can occur. Performance analyses normally consider a situation where the airplane will pass the opposite runway threshold at 35ft and V2, at least. Increasing thrust on remaining engine(s) is an option, but usually limited to go around thrust.
… But now if the situation is beyond a routine emergency drill, it’s hard to say the best option to follow. Reduce pitch attitude? Well, as previously mentioned, the airplane can stop climbing and climb performance can be severely affected. Increase thrust? Yes, but not above engine limits unless in case of impending airplane stall or a possible ground contact. V2 is always a guarantee of safety (observing some conditions, like bank angle limits, for instance) and flying below it means a speed close to VMCA or even below it… and it’s not really a good deal.
Could you assume that the aircraft loading data was probably incorrect and that the aircraft was actually heavier than what the figures had been calculated for?
I’m sure there’s no time to confirm it… at least when someone is fighting to survive during an E/O with a poor airplane performance.

[backin5]

Thanks to all for extremely thought-provoking discussion!

I'm still not sure that I know what is correct in the situation, but as most things in this business go, do the right thing on the day and be hailed a hero, make the other choice and it's all down to Pilot Error again.

I hope this discussion is not considered over, because if anybody feels like adding, expanding, contradicting or clarifying further it will all be very much appreciated!

Thank you!

[411A]

backin5,

Large aircraft performance has changed a lot over the years.

With the old 4-engine piston types, runway requirements were calculated with a 50 foot screen height, and the liftoff speed was to be no less than V2.
In normal line flying, the aircraft was not rotated until V2 was acheived. There was no separate Vr, under CAR4b for piston types.
With most early turbopropeller types, this was also the case.

When jet transports came along, the regulations were re-written to allow for a 35 foot screen height, and due to aerodynamic design, a Vr was established, so as to reach no less than V2 at the lowered screen height.

I can tell you from personal experience flying some of these early aircraft (especially the non-fan powered B707-321) at heavy weights, it was common practice to begin rotation at Vr very slowly, as these aircraft did not perform well in the climb with the normal rates of rotation used today with more modern types.

Suspect many younger guys today, if they had one of these older types strapped to their behind, at MTOW, would have eyes the size of dinner plates at the lack of acheivable climb performance...and this was with all engines operating.
Very long takeoff runs were required, followed by a surprisingly shallow climb.
Personally believe that the lowered screen height was selected, so that these types could be certificated in the first place.:ooh:

[FE Hoppy]

Just another thought for your non-normal op.
what is your aircrafts sop for windshear.
probably max power(however its defined by your company), wings level and fly to the stick shaker. If the world turns to poo this is probaly your best bet.

[LOMCEVAK]

V2 is actually the minimum speed at which, with one engine inoperative, a specified gross gradient can be achieved (3% for 4-engined aircraft, 2.7% for 3-engined and 2.4% for 2-engined), subject to it being not less than the factors that FE Hoppy states above.

However, there is one other consideration that must be taken into account; Vr must be not less than Vmcg. Therefore, if Vr is determined by Vmcg then V2 may become purely the speed which is attained at screen height following rotation at the specified rate; this applies especially at low TOW. This needs to be remembered in older aircraft where flap retraction speeds are sometimes based on V2 (747-200 for example). This procedure is to give a margin above the stall. However, if V2 is determined by Vr equalling Vmcg then the flap retraction speeds will be greater than is needed for stall margin.

I know that much of this reply is a little off the original question but it is important to realise that if you are below V2 then your climb gradient will be reduced.

[backin5]

From my understanding, V2 is also a margin above Vmca, so if V2 were say, 150kts, then flying 145kt means you are eroding your protections for engine failure - would probably need a lot more rudder, and some bank and have to get the nose down in a bit of a hurry.
...and if your perf fig's were indeed under-calculated, you might actually be a lot closer to Vmca and Vs than what you think...?

[Crossunder]

There's a difference between minimum V2 (V2min) - and actual V2 being used for climbout:

From JAR 25, Section 1:

[(b) V2MIN, in terms of calibrated airspeed,
may not be less than –
(1) 1·13 VSR for –
(i) Two-engined and threeengined
turbo-propeller powered
aeroplanes; and
(ii) Turbojet powered aeroplanes
without provisions for obtaining a
significant reduction in the one-engine inoperative
power-on stall speed;]
[(2) 1·08 VSR for –
(i) Turbo-propeller powered
aeroplanes with more than three engines;
and
(ii) Turbojet powered aeroplanes
with provisions for obtaining a significant
reduction in the one-engine-inoperative
power-on stall speed: and
(3) 1·10 times VMC established under
JAR 25.149.]
(c) V2, in terms of calibrated airspeed, must
be selected by the applicant to provide at least the
gradient of climb required by JAR 25.121(b) but
may not be less than –
[(1) V2MIN;
(2) VR plus the speed increment
attained (in accordance with JAR 25.111(c)(2))
before reaching a height of 35 ft above the
take-off surface; and
(3) A speed that provides the
manoeuvring capability specified in JAR
15.143(g).]