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Effect to pitch when extending flaps
03-02-2011, 06:37 PM
Post: #1
2 school of thought here:

1. With flaps extended, the C of P will move rearwards, therefore aircraft will pitch nose down.

2. With flaps extended, more lift will be generated by the wings, therefore aircraft will pitch nose up.

Both examples above are talking about early stages of flaps (lift flaps)
Both also true, so can we say it depends on aircraft?
Some aircraft will pitch up, some pitch down, depends whether C of P movement or lift generated is greater?
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03-03-2011, 08:15 PM
Post: #2
from my understanding and what I have been taught~

With flaps extended your aircraft will pitch UP because of sudden increase of lift.
When you pitch up your speed will decrease so in order to get your desired speed you push the control column forward thats why the nose of the aircraft pitches down.

correct me if im wrong.. xD

"Learn from mistake" is totally not suitable for a pilot. You might be don't have chance to fly again after you did a mistake. You can only learn from people's mistake.
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03-03-2011, 09:09 PM
Post: #3
From what I know earlier,
1) C of P will move rearwards as flaps are extended (this is for sure)! note : pitch down moment are due to movement of C of P.
2) But, when flaps are extended, move lift are generated, AOA increases, pitch up moment will be created.

Practically, we use FACT no.2 when operating an aircraft (which means pitch up moment will be created with extended flaps).. I was puzzled by this question for quite some time too, and was left unsolved. When you think about it, C of P move rearwards will of course creates pitch down moment.. anyone got better idea?
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03-04-2011, 06:29 PM
Post: #4
In theory flaps extend, C of P moves rearward, C of P being aft of CG, effect is aircraft nose down.

In practice, aircraft will pitch nose up because a lot of lift is generated by flaps. Maybe this lift generated overcomes the aft C of P movement, that's why nose in the end will pitch up? The greater force will win?

Same thing with effect of using ailerons only to bank. Aircraft will bank, sideslip results, airflow against keel surface of fuselage yaws aircraft in same direction of bank.
BUT when learning about turns, airfract is said to yaw in opposite direction of bank due to aileron adverse yaw!
Contradicting, but maybe end product is which force is stronger???

Any other thoughts?

Thoery of flight is ever controversial...
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03-04-2011, 07:20 PM
Post: #5
Taken from Ace the technical pilot interview

"The direction and degree of the chance in pitch depend on the relative original position of the CP and CG"

Basically lift created by increase in wing area lead to pitch up moment if the CP is in front of CG
If movement of CP behind CG leads to nose down pitch

"Normally, the increased lift created by extending the wing chord line when flaps are extended is dominant and will cause a nose-up pitching tendency because the CP normally remains in front of the CG"

As u said earlier, its true depending on aircraft type
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03-04-2011, 08:01 PM
Post: #6
szech Wrote:Taken from Ace the technical pilot interview

"The direction and degree of the chance in pitch depend on the relative original position of the CP and CG"

Basically lift created by increase in wing area lead to pitch up moment if the CP is in front of CG
If movement of CP behind CG leads to nose down pitch

"Normally, the increased lift created by extending the wing chord line when flaps are extended is dominant and will cause a nose-up pitching tendency because the CP normally remains in front of the CG"

As u said earlier, its true depending on aircraft type
That should clear our doubts!
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03-05-2011, 09:53 PM
Post: #7
C of P is normally in front of CG?

I thought C of P is normally slightly behind CG, the reason being to get the 'coupling' effect of lift vs weight, so that if lift is less than weight, with weight (CG) being in front of lift line, aircraft will nose down.
Aircraft designed such a way so that nose will always have a tendency to pitch down.
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03-08-2011, 05:32 PM
Post: #8
nobody has mentioned which flap are we talking about?

leading edge flap or trailing edge flap? :neutral: :neutral: :neutral:

there are differences between the both.

extending either one will alter the Center of Pressure in a different way.

“A friend cannot be considered a friend until he is tested in three occasions: in time of need, behind your back, and after your death.”
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03-08-2011, 05:58 PM
Post: #9
mosumo,
There are not many aircrafts installed with a leading edge flaps. It is safe to assumed that we're taking about the trailing edge flaps in general and of course the leading edge devices that works together. Further more, you can't deploy leading edge devices(slats or flaps) independent of their trailing edge devices counterparts... :^^:
There are exceptions but lets not get into it..

Real planes have propellers!
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03-08-2011, 06:09 PM
Post: #10
My mistake, yes I was talking about t/e flaps.
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