C.G. and Speration point

[earl1937]

  Here is a question which applies to these aircraft in the game: As you burn fuel, your C.G. does what and how does that effect the separation point on the wings?

[PJ_Godzilla]

That would vary by aircraft and the tank from which you're burning your fuel.

As for the separation point, I assume you're talking about the max alpha, which inheres to the section. While cg may tend to affect alpha, it doesn't affect the section properties, afaik.

[earl1937]

That would vary by aircraft and the tank from which you're burning your fuel.

As for the separation point, I assume you're talking about the max alpha, which inheres to the section. While cg may tend to affect alpha, it doesn't affect the section properties, afaik.

Generally speaking about WW2 era aircraft, as you burn fuel, your CG moves towards the rear and the separation point of lift and drag on the wing to the rear because of the slight change in AOA. The only exception to this is the "ponie", which, when you burn fuselage tank first, as you should, it will move forward,(the CG) and then as you burn wing tanks, it will move rearward again. At least that is what my engineering buddies toward me, back when "dirt" was invented! LOL

[PJ_Godzilla]

Generally speaking about WW2 era aircraft, as you burn fuel, your CG moves towards the rear and the separation point of lift and drag on the wing to the rear because of the slight change in AOA. The only exception to this is the "ponie", which, when you burn fuselage tank first, as you should, it will move forward,(the CG) and then as you burn wing tanks, it will move rearward again. At least that is what my engineering buddies toward me, back when "dirt" was invented! LOL

I was wondering if you were talking about the max alpha or the chordwise location of the separation point. Sounds like you meant the latter. If so, then no, my recollection is, as the AoA increases, the separation point will actually move forward. This will continue until you reach a critical angle, after which, the flow will become almost completely separated and lift will decrease dramatically.

As for the fuel distribution, I'm used to flying 109s. The tank is behind and the cg moves forward, IIRC. The Pony, also IIRC, is as you state - marginally stable at full fuel, more stable as you burn off the tank.

Mind, I'm going back some years as well. aero engin school for me was back in the 80's.

[GhostCDB]

 

[guncrasher]

just curios does unleaded fuel weight less than leaded?




semp

[earl1937]

just curios does unleaded fuel weight less than leaded?




semp

No! That has no bearing on computing weight and balance for flight!

[Ramon]

Ze Zeparation point iz always near ze bullet holes.

[1stpar3]

Ze Zeparation point iz always near ze bullet holes.

I agree with that   That's my usual experience anyway! Its the last thing I see actually!

[FLS]

PJ is correct. The center of pressure moves forward on the wing when you increase AOA within normal flight conditions.

[PJ_Godzilla]

Thank you, FLS, not for confirming this relatively basic point, but for not ridiculing the whole dialog.

Man, I was feeling kind of embarassed there for a while. I mean, fun's fun and all but the OP was genuinely curious and we are trying to bring others into the game.

Those young hooligans <shaking bony gnarled old fist in the air>... Alles gut, I guess.

[FLS]

I believe Earl was teaching via Socratic method. He's shared with us that he flew B-29s and has flown P-51s. He has extensive practical knowledge.

[PJ_Godzilla]

Aka, the method of elenchus... That said, I just learned something, so I guess it's working.

So, where are you going with this, Earl?

[Groth]

 Earl...and Puma44...were there when some smarty mixed dirt w/water..and made mud....
                                   JGroth
                                         PS..I wasn't there till week or two after..when some smarty found hitting two rocks together made sparks..no, wasn't me, but I still have scars.

[Puma44]

just curios does unleaded fuel weight less than leaded?




semp

Depends on the temperature.  

JG, I've see the mud on the back of your neck.