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Macgyver
4th Sep 2007, 22:39
Hey guys,

Here is a question that I don't quite understand the answer:

How can the climb limited take off weight be increased:
a) reduce V2
b) reduce V1
c) reduce Vr
d) Reduce flap angle and increase V2

The answer given is d), but I do not understand the reasoning behind it. Any help is appreciated.

Thanks.

john_tullamarine
4th Sep 2007, 22:54
Like most such questions, it is a case of trying to make generalisations into specifics ..

Underlying constraint is that we are looking at WAT-limited conditions.

(a) generally not relevant as "normal" V2 is a minimum. If the original V2 is for an overspeed schedule .. to improve climb weight ... reducing it is not the way to go ..

(b) V1 generally not relevant to after takeoff considerations

(c) similar to (b)

(d) generally, climb performance improves at lower flap settings provided that a suitable speed can be used. It is very common for a heavy aircraft to have AFM TO schedules for multiple flap settings. Provided that the runway etc permits the higher speed schedule, the usual outcome is a higher RTOW for the lower flap setting

This sort of question is trying to check whether the candidate has a bit of an idea of what is what ... rather than a detailed understanding.

Keith.Williams.
5th Sep 2007, 12:23
Assuming that this is a JAR ATPL question then the logic that the examiner is looking for is as follows:

FLAP SETTING
The Climb Limited Take-Off Mass (WAT Limit) is the maximum mass at which the aircraft can achieve the minimum legal climb gradient.

So to increase WAT Limit we must increase the climb gradient that can be achieved at any given mass.

Climb gradient at any given mass is maximum with zero flap.

So reducing flap angle will increase climb gradient and increase WAT Limit.


INCREASED V2
Climb angle is maximum when flying at VX and for jets VX is VMD.

VMD is greater than V2, so if we increase V2 we will be climbing at a speed that is closer to VX.

So if we increase V2 such that it is closer to VX we will achieve a greater climb gradient at any given mass.

This will increase our WAT Limit.


You should be able to demonstrate these effects by using the various graphs at fig 4.4, fig 4.5 and fig 4.15 and fig 4.16 in the CAP 698.