A320 full back stick

[Ellsworth]

Can anyone clarify this for me?

-IN NORMAL LAW
Valpha max = the top of the red stripe on speed tape, and it corresponds to the maximum pitch attainable in normal law with full back stick. It is therefore target speed during GPWS Pull-up maneuver.

Green dot speed = Best L/D ratio (ie BEST ANGLE of Climb Vx). Shows only in Clean Config.

Now, in cruise, obviously the Green Dot is well above the Valpha Max speed. They are two separate speeds. Which would mean if you pulled the stick fully back, the aircraft will NOT give you Vx. Is that Correct?

Then howcome in GPWS Pull-up warning (in which you want Vx, not Vy), the procedure is TOGA, stick fully back and let the speed drop all the way to Valpha max? Isn't that giving you less-than-maximum climb angle?

Thanks in advance

[zonnair]

The moment you pull back, the speed decrease towards ValphaMAX. This will give you shortly a lot of V/S.

[mcdhu]

I've seen greater than 10,000 fpm up during a correctly flown EGPWS manoeuvre - in the sim of course (A320).

mcdhu

[I-2021]

Ellsworth A320 full back stick
Which would mean if you pulled the stick fully back, the aircraft will NOT give you Vx. Is that Correct?

Correct. The result is to give you a coeficient of lift very close to the maximum one (top of the curve on the CL/AOA curve).

Then howcome in GPWS Pull-up warning (in which you want Vx, not Vy), the procedure is TOGA, stick fully back and let the speed drop all the way to Valpha max? Isn't that giving you less-than-maximum climb angle?

During such a situation your goal is to obtain maximum aerodynamic lift. What you do is changing your kinetic to potential energy up to the "alpha" max. By then you should be free from troubles coming from EGPWS terrain closure.

All the best

[Ellsworth]

Very clear and logical answers there guys, thank you!

[Clandestino]

Don't worry, neither Airbus that demands full back stick nor Boeing that asks for pull-up-until-stickshaker during GPWS escape maneuvers are wrong. Both techniques get you very near Vx.

Best L/D ratio (ie BEST ANGLE of Climb Vx)

...is very common misconception, stemming from mixing up power and thrust. Thrust for turbojets is fairly constant over the speed range, while for propeller aeroplanes, power is more-or-less constant, while the trust diminishes with speed. Power is thrust multiplied by speed, regardless of the propulsion. Vx is speed at which there is greatest thrust excess, while Vy is speed where there is the greatest power excess.

Setting the props (which, as we all know, are for boats) aside, the greatest excessive thrust for the jet is when the drag is minimal and that's below best L/D speed. Green dot will give you Vy, not Vx. Following approximations are good enough for everyday use:

Vx = min drag = maximum endurance
Vy = best L/D = maximum range

[foff]

-IN NORMAL LAW
Valpha max = the top of the red stripe on speed tape, and it corresponds to the maximum pitch attainable in normal law with full back stick. It is therefore target speed during GPWS Pull-up maneuver.

Green dot speed = Best L/D ratio (ie BEST ANGLE of Climb Vx). Shows only in Clean Config.

Both are wrong
V alpha max is the speed corresponding the highest permissible angle of attack. nothing to do with a pitch.
otherwise, GD is the best L/D ratio in one engine out condition