Exact location of the center of gravity and CL in some fighters

[Gaston]

Thanks guys. What I am looking for is the range of distances between the center of gravity and the center of lift.

I know on the P-38 CoG can vary between 20-30% of wing chord. I would assume then 25 %...

If I could know the precise location at say, "Normal Take Off", or even just determine the "middle" of the available range of CoGs, then with the location of the center of lift I could work out a distance, or an average distance, between the two.

Also, it should be noted, if that is possible, that I would prefer to know the location of the center of of lift of the main wings alone, in isolation of the overall lift center of the aircraft as a whole, and compare the location of that to the "Normal Take Off" center of gravity of the whole aircraft, if that makes sense...

I don't even know if the CoL of the main wings is ever determined separately of the CoL of the whole airframe...

Gaston

[Art-J]

I'm not sure what you mean by "determined separately". Computed during design phase or checked when the prototype is already built?
I recall that during my flight mechanics classes in university, in static pitch computations phase, we were indeed starting with aero characteristics of the wing alone (center of lift included) to compute the pitch moment of the complete wing, then added the moment caused by the fuselage and/or nacelles (based on RAE ESDU reports, we've been told that typical fuselage usually moves CoL of the whole airframe by 2 to 5%), then added vertical stabilizer to it (ESDU report again).

For the wing computations we were using the CoL position given for 2D airfoil only, we did it just for the sake of simplyfying the task - not so much of an error if you have a rectangular wing anyway. I suppose things get a bit more complicated when you have a trapezoidal or eliptical wing, but I really don't know how strongly such a wing planform affects the position of the CoL for the airfoil.

Cheers.

[Gaston]

Thanks Art-J!

I would be curious to know this, since you seem to know: I know that for stability reasons the center of drag should be behind the center of gravity: That is pretty much a given.

What I am curious about is whether the center of lift is always behind the center of gravity, or if it does make sense that it would be ahead of the CG if we take into consideration the center of lift of the wings in isolation of the rest of the airframe?

Another issue I would like to know about: Is the wing's center of lift generally considered as moving forward at all when the angle of attack of the wings is increased?

Basically I am looking at stability issues vs thrust location.

Gaston

P.S. (As an aside, one other thing I would be curious about is if there are any pusher prop-only monoplane aircrafts with unswept wing leading edges?

Of the top of my head, I can only come up with pusher-prop monoplane types that have a lot of leading edge sweep.)

G.

[TheGrunch]

There are several pusher-prop monoplanes with little leading edge sweep, but they are typically more modern aircraft, for example the Piaggio 180 and the NAL Saras. I haven't seen any that have NO leading edge sweep at all, though. Even that UAV thing has a bit of sweep.

EDIT: Have a look at this thing.

[Xilon_x]

you loock this manual for Weighing the Aircraft and Determining
the Empty Weight Center of Gravity.

WHEIGHT and BALANCE HANDBOOK.
http://www.faa.gov/library/manuals/a...-H-8083-1A.pdf

[Gaston]

Thanks The Grunch!

That certainly helped to clarify the conventional configuration: The tailplanes have a downward lift to counter-act the CG being ahead of the Center of Lift:

http://en.wikipedia.org/wiki/Piaggio_P.180_Avanti

"The arrangement of the wing surfaces allows all three to provide lift, as opposed to a conventional configuration, where the horizontal stabilizer creates a downward force to counteract the nose-down moment generated by the center of gravity being forward of the center of lift."

The other aircraft you mentionned is still in trials or pre-production, so the Piaggo is most interesting...

Thanks to everyone who answered.

Gaston