Fly Lah!

torx wrote: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..

Yes torq. that's true and i understand what you mean.

sometimes when talking about theory of flights there are many versions of them, which could be found from many books from different authors from different backgrounds and experiences and this sometimes could be quite tricky for some to digest.

As for my understanding,,i believe;

1. Extending the trailing edge flap will bring the C of P backward. this can be explained thru a diagram presents the airfoil camber being altered. With flap extended, 2/3 from the trailing edge, the camber is very pronounce that the total pressure is considered to act within this range. (c of p)

2. That moved C of P will cause a down pitch moment...making a possible relevant visual approach for a pilot.

3. I have no idea how the c of p will be brought forward when flap is extended, understanding all the necessary terminologies of an airfoil wont satisfy me on this phenomenon.

4. If you are a pilot then you know better. Even if you are a 'simulator pilot'... you will understand that the C of P moves backward/aft when the flap is extended.

5. to make it more understandable, (assuming an aircraft is flying)...you reduce the airspeed,,,in order to maintain a height you must increase lift. then you increase the angle of attack (AOA).... OR.... you extend the flap. here is the trick... if the C of P moves forward when flap is extended, you will increase the AOA further (pitch up) following the increased of angle of attack. does that make sense?? for me NO.

mosumo wrote:5. to make it more understandable, (assuming an aircraft is flying)...you reduce the airspeed,,,in order to maintain a height you must increase lift. then you increase the angle of attack (AOA).... OR.... you extend the flap. here is the trick... if the C of P moves forward when flap is extended, you will increase the AOA further (pitch up) following the increased of angle of attack. does that make sense?? for me NO.

I thought C of P always moves aft with flaps extended?

Shumway wrote:
I thought C of P always moves aft with flaps extended?

yes definitely that's what i mean

Ok, after much reading from different sources & sleepless nights, I wish to conclude as follows:

Effect to pitch when operating flaps vary from aircraft type, end of story.

For Part 66 AML, try giving that answer to the DCA's surveyor or in Part 66, the Assessor. Acceptable?

extending flaps for sure pitch up la. For those still in flying school, try extending the flaps during training flight and look at the pitch of your aircraft after extending the flaps. With pitch up attitude comes decrease in speed, so as to get your desired airspeed back your immediate reaction is to lower the pitch of your aircraft.

Guys i think u are confusing urselves with the movement of the Centre of pressure of the wing ( u are considering only an airfoil, not the whole aircraft) and pitch stability of the aircraft ( which includes the tailplane). The centre of pressure of the main wing moves towards the leading edge as lift is increased. The tailpane produces a downward pitch moment (due it's setting angle) to provide a nose down pitch moment when the aircraft pitches up. Consider the fact Moment= length * force. The cog of the aricraft is pretty close to the mainwing, but further from the tail plane. Hope it helps. A diagram will be much more useful to make the point