V Alpha prot A320

[Speedwinner]

Hello folks,

Could somebody explain me how the logic of the lower speed tape is? Sometimes we see only v alpha prot without the thin vls line. Than the vls line comes and disappears again. How is the logic at high altitude, turns and the v alpha prot abnormal? Coming from the 737 old one it's sometimes really hard to follow on that one!

Thanks!

[hph304]

PRO-SUP-10 Characteristic speeds:
VLS : Lowest Selectable Speed.
Represented by the top of an amber strip along the airspeed scale on the PFD.
Computed by the FAC based on FMS weight data, and on aerodynamic data as a backup,
and corresponds to 1.13 VS during takeoff or following a touch and go.
Becomes 1.23 VS, after retraction of one step of flaps.
Becomes 1.28 VS, when in clean configuration.
Note: If in CONF 0 VLS were 1.23 VS (instead of 1.28 VS), the alpha protection strip
would hit the VLS strip on the PFD.

The V Aplha prot is calculated using the AOA-vanes and depends on configuration.

[vilas]

Speedwinner
Vls is not g dependant it varies with weight. Valpha prot and Valpha max are current AOA measured by two active valid AOA probes and averaged. It is converted to speed and shown on PFD. They are load factor sensitive so vary with load factor. So when you bank or increase the load factor the alphaprot (at high altitude) may catch up to vls and cover the Vls. The difference between current speed and Valphaprot (or Valphamax) represents the actual margin between alpha prot and alpha max.

[penpen]

What my FCOM says about ALPHA PROT SPEED:

FCOM DSC-31-40 AIRSPEED
...corresponding to the angle of attack at which alpha protection becomes active (displayed when in Pitch normal law)

FCOM DSC 27-20-10 PITCH CONTROL - PROTECTIONS
Va Prot, Va Floor, Va Max vary according the weight and configuration
Below 200ft the AOA is also deactivated

http://www.a320quiz.com

[pilot-737]

Speedwinner
Vls is not g dependant it varies with weight

Vstall is g dependent (Basic PPL knowledge Pilot's Web The Aviators' Journal - Load Factor (http://www.pilotsweb.com/principle/load.htm) )

If Vls equals 1.13,1.23,1.28 Vstall, Is it possible to say that the Vls is NOT g dependent ?

[Escape Path]

Vstall is g dependent (Basic PPL knowledge Pilot's Web The Aviators' Journal - Load Factor (http://www.pilotsweb.com/principle/load.htm) )

If Vls equals 1.13,1.23,1.28 Vstall, Is it possible to say that the Vls is NOT g dependent ?
If I'm not mistaken, when talking about stall on Airbus FBW aircraft, Vstall is always referenced as Vs1g. That would make Vls not G-dependant

[vilas]

True! Airbus FBW speeds are referenced to Vs1g and not Vs.

[sonicbum]

pilot-737, next time you fly have look especially after takeoff at heavy weights, during turns the V alpha prot will increase sometimes hiding completely the vls which will only vary with the weight and/or aerodynamic configuration changes (speedbrakes, flaps).
It is very evident on a heavy 321 for example.