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

Hello.

I would like to know the if the exact location of the center of gravity, and of the center of lift, of the various late WWII fighter types is available on reliable plans.

I'm sure game designers must have these location points established somewhere... I would like the source material to be established as well.

I would look more specifically for the Spitfire Mk IX, Me-109G, FW-190A, P-51D and P-47D.

Gaston

The position of the CG will vary with fuel load etc. As for the 'centre of lift', do you mean the centre of pressure (which varies with angle of attack with a cambered airfoil), or the aerodynamic centre? The two terms aren't interchangeable.

In any case, if you want the 'exact location', you'd have to specify in relation to what - I suspect you would most likely want it as a percentage of mean aerodynamic chord, but even this is a little hard to define precisely.

Broadly speaking, the further forward the CG is relative to the aerodynamic centre, the more longitudinally statically stable, and less manoeuvrable a plane becomes, but this isn't enough on its own to make any definitive statements about the relative performance of aircraft.

Well Gaston,

For Andy's answer one can see that this is not a light subject. Be it percentage from Mean Aerodynamic Chord or inches from Datum, the numbers won't help much per se.

Taking this part as a premise, I'd infer that you'd like to know if the Flight Model of those planes are based on real data, plans and so, instead of a concoction from designers. Am I correct to assume that?

If so, would a piece of info, in the manual or whatever, in the lines of...

Cliffs of Dover: planes recreated digitally from official plans and realistically simulated.

... meet what you are needing?

I adopting this line, because more than once I witnessed people, IRL conversations, asking similar questions.

té mais
tityus

Each individual airplane would have it's own unique charting for weight and balance recorded. And this record would be updated regularly with every modification such as equipment added or removed to include paint. At least in peace time.

What your really looking for is the operating limits, what is the maximum aft and forward limits for that type, at fully armed and fueled combat loads to stripped and empty. The reason they do it with full and empty is your limits are usually dependent upon weight. As you lose weight via fuel burn and weapons release, your overall allowable forward and aft CG limitations can and usually do shift.

So it's not a simple subject and the behavior is very much dynamic with conditions of flight.

My guess is that he is asking for the aerodynamic center. Since he also asks about the CG, and would make it look like he is trying to work something about aircraft stability, and the aerodynamic center is the point used for that.

Noh idea, but a flight manual should give you the minimum and maximum positions of the CG, since them are operational limits of the aircraft that should not be exceeded otherwise there are could be stability problems in some flight situations.
I doubt there are plans with the aerodynamic center stablished.

These are both variable locations depending on many factors that change dynamically in flight. There is a "range" inside which these values occur for each aircraft, however but I'm not sure what you're looking for.

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

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.

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.