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Use of flaps during approach and landing phase of a flight

Posted on 2013-06-30
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I wanted to check the following question that I got wrong. My understanding of the use of flaps is that on approach the descent angle is steeper (improving forward vision), the stall speed is reduced and a slower groundspeed (decrease in aircraft momentum) which will shorten the landing run compared to a clean configuration.

"Why is full flap selected during the approach and landing phase of a flight?"

A- the safe flying speed is increased and a flatter approach path is achieved which improves forward vision.

B-the approach speed is reduced and a steeper approach path flown which improves vision.

C-the approach speed is reduced and a flatter approach path flown which improves vision.

I picked answer B but the book has answer C. I have attached the extract of the explanation from the book(EPP14C).

I would agree that for "take off" that the use of flaps helps reduce the ground run getting the aircraft into the air sooner(take off at lower IAS) than a clean configuration and the use of flaps for take off provide a flatter angle (reduce the initial angle of climb).

Any thoughts would be appreciated.

Cheers,

Ross
image.jpg
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Question by:ross13
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aadih earned 668 total points
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I believe you are correct, in general:

"During the landing phase, flaps contribute to a steeper descent angle by increasing the parasite drag produced by the wing. A slower approach speed and a shorter landing distance (as a consequence of reduced stall speed and increased aerodynamic braking) is also achieved by an appropriate deflection of wing flaps."

[Note: It also depends on the airplane model. On some airplanes, flaps cause a decrease in aircraft pitch angle which improves the pilot's view of the runway over the nose of the aircraft during landing (book answer). So, it depends on airplane, flap type, and location of the wing.]
flaps.jpg
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Expert Comment

by:ozo
ID: 39288276
Are you confusing the pitch angle of the aircraft with the angle of the approach path?
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by:TommySzalapski
TommySzalapski earned 664 total points
ID: 39288385
I would say the answers are worded poorly
flatter approach path flown which improves vision
It is not the flatter approach path which improves vision, it is the flatter pitch altitude that improves vision (as the book states in the image).

Using the flaps does both flatten approach path and improve vision but the flatter approach path does not directly improve the vision as C implies (although they are related). C is still the most accurate since B says "steeper approach path" which is wrong.

The flaps increase the lift generated which is what makes the approach path flatter. The flaps also allow the pitch to be flatter (the nose doesn't point up as high) so the vision is improved.
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by:ozo
ozo earned 668 total points
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flaps increase the lift
they also increase drag, which would tend to steepen the glide slope angle, so pilots often compensate by increasing thrust.
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