advanced aerodynamic question

[Bernoulli]

Why does stall speed increase with a forward CG? Does it have to do with the horizontal stab stalling?

 

[banned username 2]

Sort of...

With a forward CG the horizontal stab needs to create a greater down force, further increasing the amount of lift the wing needs to develop.

In VERY simplified terms, the wing needs to develop enough lift to overcome weight + the total downforce of the horizontal stab. If the CG is forward, the stab needs to create more downforce, thus increasing total lift required (almost like increasing your weight).

You will need a higher angle of attack to maintain the lift for a given speed (as opposed to the lower angle of attack required for a lighter and/or further aft CG aircraft). Since you will need a higher angle of attack for a given weight, you will be closer to the stall angle of attack. As you slow, you will hit the stall angle at a higher airspeed.

Hope this clears it up, this is hard to explain without pictures.

 

[CLCAP]

CG is always (at least unless you're flying fly by wire planes - and most often even then) a bit forward of your center of lift.

The more forward your CG is - the bigger the arm (and thus momentum) between the two. = The wing has to produce more lift to offset the nose down force created by the CG.

That it does through flying at higher angle of attack at a given speed to maintain a given flight condition (i e constant altitude).

Since you always stall at a certain angle of attack - you actually have "less" degrees availible between your current aoa and your critical aoa when the cg is forward.

This also to an extent explains why Va is higher at a higher weight.

I think what falcon capt said holds true to an extent - not sure though because that would mean that canard airplanes actually work "backwards" in this regard - Anyone ever flown a canard and cares to comment?

 

[Bernoulli]

Hey Thanks for the info... that helps clear up that question for me

 

[Mickey]

Falcon Capt is right on the money. Very well said.

CLCAP....you are right on your first statement if you change it to," the CG is usually forward of the COL." The rest is pretty much incorrect.

A canard aircraft is efficient because both horizontal surfaces are lifting devices thus the CG and the COL is in between the wing and the canard. A standard aircraft has the main wing as a lifting device and the horizontal stabilizer as a pulling down device to offset the CG being forward of the COL, thus requiring the main wing to lift the weight of the aircraft plus the weight being pulled down by the horizintal stabilizer.

Trivia question. Is the Avanti a Canard?

Take care everyone.