How is the load factor less than 1g at VSmin?

[IFLY_INDIGO]

Going through the A320 FCOM, I read airbus saying that ' for a conventional aircraft, the reference stall speed, VSmin, is based on a load factor that is less than 1g.' I am confused how is this possible? stalling speed is minimum flight speed and it would ensure sufficient lift for a given weight unless we are manoeuvring the aircraft. After the stall speed, yes, the load factor is less than 1, till the time stall recovery is made.

[vilas]

IFLY_INDIGO
At CLmax is Minimum speed at which load factor is one. Vs is slightly after that at which load factor is minus. That is reference speed for conventional aircraft.

[bubbers44]

The only way I can see stall being computed at less than 1g is in a steep climb or descent. A hammerhead stall maneuver isn't really a stall because the aoa is almost zero when your as drops to almost zero.

[FLEXPWR]

INDIGO,

As I read, stall by definition is a reduction of the lift generated by an airfoil. If you are loosing lift, technically you start going downhill, thus your load factor has to be less than 1G.

From this, can we say that the stall speed is the speed at which the aircraft is no longer able to maintain level flight for a set of fixed parameters?

In this case, there are two separate speeds we can look at: one is the stall speed (less lift, nose drop, less load factor), the other one, slightly higher (maybe just one knot or so), would be the minimum steady speed for level flight , i.e. no loss of lift at his point. That is before the aircraft stalls.

Does this make sense?

[Tourist]

Stall is not speed dependent, it is only AoA dependent.


Since this is the case, you can base a "reference stall speed" on any g you like. They happen to have chosen one that is less than one.


I assume they want a "stall speed" to refer to because speed is the closest/most useful allegory to AoA in the normal Airbus cockpit.


If you really wished, you could fly an Airbus at 10kts without stalling, or conversely, stall it at 200kts.


You could also stall it whilst climbing at 5000ft/min

[FLEXPWR]

Tourist, I am not sure to grasp your explanation, neither on the stall load factor, nor how it applies to Airbus.

Airbus had to redefine the stall speed characteristics as the FBW is based on constant G load (when no input is made on the joystick), thus the FBW is trying to maintain 1G in level flight, right to the point where lift is no longer available. Of course, in practice, the lay pilot may never see this, as Aplha Floor would kick in before that point is reached.

You mention "They happen to have chosen one that is less than one."

Who is they? I suspect "they" did not happen to chose, as you might suggest, arbitrarily, but "they" must have observed that as the lift first decreases (definition of stall), so is the load factor.

A perfect 1G stall is something that a computer can do. I don't think any pilot is able to maintain exactly 1G as the stall is initiated.

I'd be happy to see inputs from fellow pilots and their views on the stall applied to FBW aircraft.

[roulishollandais]

Descending a bit !

If the wing shape has no sudden nose-drop, Just let the plane descending ! the nose-up pull is limited by what they call "protection" ! They say lift is still enough...

Airbus had the idea to give that defiition of their fake "no-stall" (Re rudderruddererrat link in thread Habsheim post 269", and comments rudderruddererrat, Chris Scott and Haserlnuts39 posts 269-272).)
http://lessonslearned.faa.gov/Indian...0Condition.pdf

Doing that they sold both the idea that
1. we don't need to use an AoA sensor,
2. no use of inertial HUD,
3. having only the speed on the HSI, and
4. the biggest idea to sell ad libitum their aircrafts : "they do not stall". Now we know they are lyuing.

[de facto]

Hi there,


Reference of VS is for conventional aircraft and represents the speed when lift suddenly collapses(load factor<1).

The yanks use VS,so for example VREF is based on VS which cant be less than 1.3 VS.

Airbus and EASA use VSR (reference stall speed) which may be not less than VS1G (calibrated speed/aoa at which max lift coefficient is just before lifts start decreasing).

For example, vref cant be less than 1.23 VS1G for flaps used (1.23VSRO), VLS on airbus i think.
V2 minimum for example can not be less than 1.13 VSR ...

[Tourist]

"A perfect 1G stall is something that a computer can do."


I don't think the word stall means what you think it means.........

[john_tullamarine]

Comments -

(a) no specific background with Airbus certification

(b) speed reduction during the final approach to stall is quite slow

(c) low thrust = descent = reduced load factor

(d) stall definitions have varied over the years

(e) always one needs to check the frozen certification standard for a particular aircraft before throwing numbers into a discussion.

(f) current heavy rules for FAA can been reviewed here. One might note the requirement to correct for load factor.

[roulishollandais]

Where is it easy to find the"stall definition" used, the date of certification and modifiations, and additions, in the different ICAO countries?

[BARKINGMAD]

And I thought load factor referred to the ratio of bums on seats to the total of seats on a particular service?

Still learning after all these years........................

[FLEXPWR]

Let me rephrase:

A computer (FBW in this case) will try to maintain exactly 1G all the way to the collapse of lift. A pilot cannot possibly do such a thing with any precision with conventional flight controls flying manually.

Better?

[bubbers44]

If you can hold altitude plus or minus 10 ft like everybody I know you will hold 1 g to a stall.

[Tourist]

"A pilot cannot possibly do such a thing with any precision with conventional flight controls flying manually"






I would disagree. (where can I find a smiley that shows how appalled I am at such a statement...)


In fact, it borders on a definition of a pilot!


If you can't do that then in my opinion you should not call yourself a pilot.


When we used to carry out stall check test flights, we were required to fly maintaining level flight while reducing speed at 1kt/second and check that the buzzer, stickshake and stick push all operated at the correct speeds and time intervals. These would not work if we didn't hold altitude.




john


"(c) low thrust = descent = reduced load factor"


Am I misunderstanding you, or are you saying that a descent means less than one g?!?

[bubbers44]

Yes, a descent is less than 1g and as you approach a vertical descent which is common flying aerobatics you are at zero g loads. The hammerhead or wing over maneuver is in zero g during the top as you rudder over into a vertical dive and the aoa is also zero so no stall.

[Machinbird]

Let me really get people going.

If you define Nz as your g measurement, then when your aircraft is pitched up in level flight near stall speed, your z axis is inclined to the vertical, perhaps 15 degrees.

In that case, your Nz will be less than 1 in level flight (before you start falling out of the sky), probably somewhere around .96 g.
That force you feel on your back accounts for the rest of the gravitational field.

[HazelNuts39]

Originally Posted by Machinbird

If you define Nz as your g measurement, then when your aircraft is pitched up in level flight near stall speed, your z axis is inclined to the vertical, perhaps 15 degrees.

The applicable regulation defines Nzw as the acceleration measured normal to the flight path, i.e. vertical in level flight, whatever the pitch attitude. In certification flight test the airplane is decelerated 1 kt/second with idle thrust, i.e. on a slightly descending flight path at slightly less than 1 g. As the airplane approaches the stall speed, the Drag-to-Lift ratio increases so the flight path steepens slightly, curving downwards. For most swept-wing airplanes the minimum speed occurs after passing the point of maximum lift, because the airplane is still losing airspeed due to high drag while the flight path steepens further downwards.

[Meikleour]

Surely, with a lot of swept wing aircraft, the wing does not give up 100% of its lift at one exact speed but rather it progressively loses lift. This is different to the straight wing case when there is usually an abrupt stall "break" and pitch down.

Hence the aircraft is going downhill and progressively stalling the lower the speed? That is my understanding of why the g used is less than 1g.

Where is John Farley when you need him? !!

[Tourist]

I was misreading

I was reading load factor but thinking g experienced by the pilot rather than load factor ref the aircraft axis.