B737 performance question
B737 performance question
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I can only answer with this, it's not going to answer your question fully, but i hope it helps, (Unless you already knew this)
As temperature increases, the air becomes less dense, thus needing a higher speed to get of the ground.
It works the other way around in cold temperatures.
Temperature decreases, Air Density increases, Lower T/O Speed.
As temperature increases, the air becomes less dense, thus needing a higher speed to get of the ground.
It works the other way around in cold temperatures.
Temperature decreases, Air Density increases, Lower T/O Speed.
Last edited by The90sAME; 6th Oct 2012 at 11:34.
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Im not 100% Sure, you'd need to wait for some a little more clued up than i am on this, im a 'Heavy' engineer, if it involves avionics or working these things out, count me out aha.
But racking my brains, not 100% if this is entirely correct, but your V speeds, even though shown on your IAS speed tape, theyre still calculated with; weights, temperature and flap settings.
But racking my brains, not 100% if this is entirely correct, but your V speeds, even though shown on your IAS speed tape, theyre still calculated with; weights, temperature and flap settings.
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B737 Performance question
With credit to M. Hulshof Boeing 737 Performance Reference Handbook (FAA Edition) Page A-6
V1...A lower density altitude(higher OAT or lower PA) results in less life force which must be counteracted by a higher speed.For the continued takeoff this implies a higher V1, but this will be restricted by the ability to stop in the aborted takeoff case.
VR...A lower density altitude(higher OAT or lower PA) results in less lift force which must be counteracted by a higher speed, therefore VR needs to be increased.
V2...A higher OAT or higher PA result in LESS thrust, hence less acceleration capability. To keep the T/O Distance Required within the T/O Distance Available, V2 must be lowered. In the combined effect in ISA(higher PA with lower OAT and vice versa), the influence of PA is much more significant than the influence of OAT.
Again, not pitching this book, but more information than a body should know(both FAA and ICAO versions)
Cheers
Vark
V1...A lower density altitude(higher OAT or lower PA) results in less life force which must be counteracted by a higher speed.For the continued takeoff this implies a higher V1, but this will be restricted by the ability to stop in the aborted takeoff case.
VR...A lower density altitude(higher OAT or lower PA) results in less lift force which must be counteracted by a higher speed, therefore VR needs to be increased.
V2...A higher OAT or higher PA result in LESS thrust, hence less acceleration capability. To keep the T/O Distance Required within the T/O Distance Available, V2 must be lowered. In the combined effect in ISA(higher PA with lower OAT and vice versa), the influence of PA is much more significant than the influence of OAT.
Again, not pitching this book, but more information than a body should know(both FAA and ICAO versions)
Cheers
Vark
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Just to confirm, when you go in the N1 limit page during the setup on the ground, the values of N1 are adjusted according to temperature right?
Does the N1 increase with PA and/or temp increasing to compensate the thrust decrease at a given N1?
On a standard day, 0 ft AMSL, 15°C, how much thrust would one get in pushing the thrust lever until the far forward end
.
Finally, why is the temp entered by the crew and not measured by the aircraft?
Seriously the latest fmcs do have the function of oat auto selection.
Last edited by de facto; 10th Oct 2012 at 05:15.
A lower density altitude(higher OAT or lower PA)
While we're on the subject, can anyone tell me why when the actual OAT goes up the FMC calculated N1 for take-off goes up, even when using assumed temp for take-off? Isn't the N1 then based on the assumed temperature, so why does a change in the actual OAT have any effect?
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Quote:
A lower density altitude(higher OAT or lower PA)
Last time I checked, a higher OAT resulted in a higher DA
A lower density altitude(higher OAT or lower PA)
Last time I checked, a higher OAT resulted in a higher DA
Higher than 0c ,DA/MDA are not changed(not increased).
De facto,
I meant Density Altitude, not Decision Altitude, as referred to in the quote.
I meant Density Altitude, not Decision Altitude, as referred to in the quote.
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I meant Density Altitude, not Decision Altitude, as referred to in the quote.
Now, just to get back to my second question. When you push forward the thrust levers to the far end, it will give you 27,300 at MSL...what's the commanding/limiting parameter by the EEC in that case: N1 max, N2 max, EGT? Would it be the same in EEC alternate mode?
Last edited by de facto; 11th Oct 2012 at 11:50.
