rossyboy
Posts: 68
Joined: Wed Oct 27, 2004 11:08 pm

Speed On Departure

Sun Mar 13, 2005 5:02 am

Hi everyone.
I was just wondering as to if it was normal operation for the pilot to reduce the aircraft's speed after take-off. I would assume they would, since if they didn't do anything then the aircraft would overspeed, the turns would be too wide e.t.c. Any pilots out there who know if this is true?

Many thanks!
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FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Speed On Departure

Sun Mar 13, 2005 5:09 am

No, you don't reduce speed. You just stop accelerating.  Wink

There's a precalculated speed which is optimal for the early phase of the climbout. You let the aircraft accelerate through V1, lift the nose at Vr, or the rotation speed, and about the time you are climbing you should reach this predetermined speed, V2 or frequently V2 + 10 for some added margin.

You then adjust your pitch attitude to keep this speed.

At a predetermined altitude you lower the nose and again begin accelerating, thus enabling you to retract the flaps and get to the optimal climbout speed and configuration.

There are complexities along the way, but I hope this answered your question. If not, just ask again! It was a good question.

Regards,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
undehoulli
Posts: 80
Joined: Sun Jan 16, 2005 10:04 am

RE: Speed On Departure

Sun Mar 13, 2005 10:32 am

At ExpressJet here is the procedure (if I remember correctly).

Normall callouts on takeoff are made: "set thrust, thrust set, 80 kts, etc...).

At V1 the captain removes his or her right hand from the thrust levers. At Vr the aircraft rotates (it's pretty close to V1, sometimes the same speed too). V2 is the speed the aircraft initially accelerates to, and is trimmed for V2 in the event of an engine failure, but the pilots want V2+15 for that margin FredT mentioned.

Every runway has an acceleration height that's been published in the runway analysis charts book carried on board. If the aircraft has not reached V2+15 and is at acceleration height, the aircraft must level off and accelerate to V2+15. If it is at V2+15 before acceleration height, great. I believe this is the speed that the flaps are retracted too.

The next speed is Vfs (final segment speed). At this speed the pilot flying calls for the PNF to "set climb" (the engine thrust rating), then to set the vertical speed mode (FLC or 200 kts, depending on the airspace and departure direction), and perform the after takeoff checks (engine bleeds open, shut the APU down). FLC will climb the aircraft at 240 kts until 10,000 feet, and I believe this is the normal speed to climb out at.

The power is reduced after takeoff, but the aircraft doesn't slow down, it speeds up and just like FredT said, it stops accelerating.

[Edited 2005-03-13 02:34:50]
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PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Speed On Departure

Sun Mar 13, 2005 11:31 am

On the 744, at Vr you rotate to anywhere from 12-15 degrees and your target speed is V2+10. Depending on the noise profile, at either 1000' AGL or 3000' AGL you lower the nose to about 9 degrees, although the FMS/PFD take care of the actual pitch via the pitch command bar, and begin accelerating to retract the flaps.

Once the flaps are up, you will be somewhere around V2+100, so a heavyweight takeoff you could be around 287Kias and begin your climb out at that speed.

The thrust requirements are all handled by the autothrottles based on what the pilots enter into the FMC. But climb thrust is set at either 1500' in the event of cleaning up at 3000 or at flaps 5 when cleaning up at 1000'.

At some locations in the world, there is no 250 below 10,000 restriction. In this case, you'd accelerate right to 340 kias for your climb. You'd climb at 340 Kias until intercepting your climb Mach, usually around ,852 or so.
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