novice
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Boeing Rate Of Climb?

Tue Oct 09, 2012 9:29 pm

General
At VR the aircraft should be smoothly rotated to a body angle of 15 degrees in accordance with the recommended Boeing rate of 3 degrees per second.

I understand that the 15 degrees must be measured from the horizon though what does the 3 degrees per second be measured from and what does it mean?
 
Fabo
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RE: Boeing Rate Of Climb?

Tue Oct 09, 2012 9:32 pm

3 degrees per second means that you should take 5 seconds of smooth transition to 15 degrees of pitch.
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tdscanuck
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RE: Boeing Rate Of Climb?

Wed Oct 10, 2012 12:51 am

Quoting Novice (Thread starter):
I understand that the 15 degrees must be measured from the horizon

It's from *horizontal*, not the horizon. If you're anywhere with terrain features, 15 degrees above horizontal will be less than 15 degrees above the horizon.

Tom.
 
Yukon880
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RE: Boeing Rate Of Climb?

Wed Oct 10, 2012 1:00 am

Quoting tdscanuck (Reply 2):
It's from *horizontal*, not the horizon. If you're anywhere with terrain features, 15 degrees above horizontal will be less than 15 degrees above the horizon

Not if you're rotating off the last half of Runway 33 at ANC.
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Jetlagged
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RE: Boeing Rate Of Climb?

Wed Oct 10, 2012 12:36 pm

Quoting Novice (Thread starter):
I understand that the 15 degrees must be measured from the horizon though what does the 3 degrees per second be measured from and what does it mean?

Pitch angle and rate are as indicated by the pitch scale on the PFD. There is no pitch rate indication, but to achieve 15 deg at 3 deg/sec will take 5 seconds. The pitch target is displayed on the PFD and the pilot will aim to get there smoothly in about 5 seconds. The exact pitch rate doesn't matter, the point is to achieve a steady and consistent pitch rate. Too fast or erratic and you risk a tail strike. Too slow and you may compromise terrain clearance and will be accelerating rapidly through V2.

The pitch target isn't always 15 deg though. It depends on the aircraft type and the takeoff conditions.
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RE: Boeing Rate Of Climb?

Wed Oct 10, 2012 6:33 pm

Quoting Jetlagged (Reply 4):
The pitch target isn't always 15 deg though. It depends on the aircraft type and the takeoff conditions.

Bingo. It was routine on the 757 to end up at 20 degrees nose up when somewhat light. On a very heavy 737-800 you'll be going to about 13.
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tb727
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RE: Boeing Rate Of Climb?

Wed Oct 10, 2012 6:52 pm

Quoting Jetlagged (Reply 4):
The pitch target isn't always 15 deg though. It depends on the aircraft type and the takeoff conditions.

And on the 727, we have a target pitch for 3 engines and 2 engines figured for every takeoff. Depending on weight and takeoff flap config it can vary from 7 to 22 degrees for 2 and 3 engine. Our rotation is a little slower at 2-3 degrees per second then after liftoff you just pitch for V2+10 to 1000', target is a just kind of a guide to get you close to it.
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novice
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RE: Boeing Rate Of Climb?

Mon Oct 15, 2012 6:45 pm

Quoting tdscanuck (Reply 2):
Quoting tdscanuck (Reply 2):
It's from *horizontal*, not the horizon. If you're anywhere with terrain features, 15 degrees above horizontal will be less than 15 degrees above the horizon.

Just to make this clear then, the horizon is where the earth and sky met therefore where the top of the terrain and the sky met. So for instance going by that definition if there where a mountain in front of the runway, the horizon viewed by the pilot on the runway would be a much higher angle/degrees than the 15 degrees measured from the horizontal?

Also is horizontal measured from the longitudinal axises of the plane?
 
thegeek
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RE: Boeing Rate Of Climb?

Tue Oct 16, 2012 1:02 am

Why is this done so quickly? Gives that uncomfortable moment when you are pushing into your seat just as you take off.
 
tdscanuck
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RE: Boeing Rate Of Climb?

Tue Oct 16, 2012 3:26 am

Quoting Novice (Reply 7):
Just to make this clear then, the horizon is where the earth and sky met therefore where the top of the terrain and the sky met.

Yes.

Quoting Novice (Reply 7):
So for instance going by that definition if there where a mountain in front of the runway, the horizon viewed by the pilot on the runway would be a much higher angle/degrees than the 15 degrees measured from the horizontal?

Whether it's higher than 15 degrees depends on the terrain. But yes, the horizon (where the earth meets the sky) would be at a higher angle than horizontal. As a result, 15 degrees above horizontal would be less than 15 degrees above the horizon.

Quoting Novice (Reply 7):
Also is horizontal measured from the longitudinal axises of the plane?

Horizontal is defined relative to the geoid (approximately mean sea level). The pitch angle is measured between horizontal and, usually, the plane's longitudinal axis. There are a couple of instances in flight dynamics when you measure relative to the flight path and/or the stability axes (which generally aren't the same as the longitudinal axis) but those aren't presented to the pilot.

Quoting thegeek (Reply 8):
Why is this done so quickly?

3 degrees per second isn't quick...it would take 2 minutes to go through a full revolution at that rate. Put another way, it's half the speed that a sweep second hand moves.

Quoting thegeek (Reply 8):
Gives that uncomfortable moment when you are pushing into your seat just as you take off.

That's not caused directly by the rotation rate...the normal acceleration just due to pitch rate is pretty small. The vast majority of the normal acceleration bump at rotation is caused by the AoA increase of the wing increasing lift and accelerating the aircraft upwards.

Tom.
 
thegeek
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RE: Boeing Rate Of Climb?

Tue Oct 16, 2012 4:12 am

Quoting tdscanuck (Reply 9):
The vast majority of the normal acceleration bump at rotation is caused by the AoA increase

Am I missing something? AoA increase = rotation rate given a level trajectory on the runway.
 
BMI727
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RE: Boeing Rate Of Climb?

Tue Oct 16, 2012 6:06 am

Quoting thegeek (Reply 10):
Am I missing something?

The distinction between forces. What Tom is saying, I think, is that the normal force you feel is less the centripetal force from the pitch rate and more due to the wings producing progressively more lift as alpha increases.
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tdscanuck
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RE: Boeing Rate Of Climb?

Tue Oct 16, 2012 2:34 pm

Quoting thegeek (Reply 10):
Quoting tdscanuck (Reply 9):
The vast majority of the normal acceleration bump at rotation is caused by the AoA increase

Am I missing something? AoA increase = rotation rate given a level trajectory on the runway.

Yes. The point is that the vertical force you feel isn't the centripedal force due to rotation rate, it's force due to vertical acceleration from lift. Changing rotation rate won't make much change to the vertical acceleration you feel (it will change how fast that force comes on, i.e. the third derivative or jitter).

Quoting BMI727 (Reply 11):
The distinction between forces. What Tom is saying, I think, is that the normal force you feel is less the centripetal force from the pitch rate and more due to the wings producing progressively more lift as alpha increases.

Exactly. Centripedal force due to pitch rate is very small compared to vertical acceleration due to lift.

Tom.
 
Fabo
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RE: Boeing Rate Of Climb?

Tue Oct 16, 2012 8:20 pm

Quoting tdscanuck (Reply 12):
Exactly. Centripedal force due to pitch rate is very small compared to vertical acceleration due to lift.

It is even negative in aft section of the aircraft and you still feel the acceleration in the vertical.
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thegeek
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RE: Boeing Rate Of Climb?

Wed Oct 17, 2012 12:03 am

My point was that isn't the peak AoA higher than it would be with a slower rotation rate, perhaps starting earlier?

I wasn't referring to the centripetal acceleration.
 
tdscanuck
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RE: Boeing Rate Of Climb?

Wed Oct 17, 2012 2:28 am

Quoting thegeek (Reply 14):

My point was that isn't the peak AoA higher than it would be with a slower rotation rate, perhaps starting earlier?

Maybe, but given that there's not much lag between AoA, lift increase, and vertical acceleration change and that the pitch rate is pretty slow, I can't see it being very significant. The angle you rotate to is going to make a lot more difference than the rate you rotate at.

Tom.

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