CONF iture;
Originally Posted by CONF iture
At FL350 ?
Never been there by chance but would be very surprised by such AoA figures ... !?
Originally Posted by PJ2
Quote:
For 212k kg, FL350 the pitch attitude at AlphaProt is almost 9deg
To me your CBT autoflight software is not really representative performance wise, a simulator would be a better reference.
I believe the numbers produced by HN39 for the AoA make more sense, I would be interested to know how he did estimate them ?
Well, I hesitated using the CBT for this very reason but did so because these speeds (but not the pitch although I have no basis to doubt it) were independently verified as accurate from book sources.
For clarity, the term "Angle of Incidence" is sometimes used instead of "Angle of Attack". I know also "incidence" means the angle at which the wing is mounted on the fuselage, (chord vs longitudinal axis).
Of course, pitch attitude and AoA are entirely independent of one another.
Recovery from the stall is part of the script for initial conversion. From simulator experience during initial training on the airplane the pitch attitudes described and on the CBT are in the ball park, perhaps higher.
(To get the simulator to actually stall, a failure has to occur so the airplane is in Alternate (or Direct) Law. It takes a great deal of back-stick pressure to get the airplane to stall. In my recollection it was very docile, at low altitude, (14,000ft AGL, anyway.)
We don't know what the AoA was during the exercise of course because there is no cockpit indication of such. Traditionally the industry has never used AoA because for any specific weight there is a direct, corresponding relationship between CAS and AoA regardless of altitude. "
For every air speed - as indicated on the Air Speed Indicator - there is a corresponding angle of attack at which level flight can be maintained (provided the weight of the aeroplane does not change)" - Kermode, Mechanics of Flight, 1962.
The actual VS is not displayed in the A330. AlphaMax is VS 1.0g and is slightly higher than VS, (explained below). VLS is 1.23 VS 1.0g for the approach phase. Vapp is VLS +5kts plus FMGC-added wind to maintain the energy of the aircraft in strong winds and/or shear conditions.
From actual experience with flight data, for Vref +5kts (which is "Vapp" in the A320), on approach we will typically see AoA's of 5 to 6deg with pitch attitudes of 2 to 3 degrees at 1.23VS 1.0g. So "6deg of AoA" is not close to the stall.
On my "guess" regarding the AoA, I thought of Davies' diagram, (Davies uses the term, "Angle of Incidence" or just plain "incidence"), in which the C/Lmax occurs at around 18deg AoA or incidence. Now I fully realize that Davies' work is dated and the diagram is (necessarily) generic but in the absence of solid information anywhere, I posited the notion that an AoA for a swept wing on a transport to stall would be around 14-18 degrees. It's not 6 or 7.
Originally Posted by CONF iture
Not on the 330 but from memory, the AoA will trigger the stall warning.
The following is from the FCOM regarding VS:
For a conventional aircraft, the reference stall speed, VSmin, is based on a load factor that is less than 1g. This gives a stall speed that is lower than the stall speed at 1g. All operating speeds are expressed as functions of this speed. (For example, VREF = 1.3 VSmin).
Because the aircraft has a low-speed protection feature (alpha limit) that the flight crew cannot override, the airworthiness authorities have reconsidered the definition of stall speed for this aircraft.
All the operating speeds must be referenced to a speed that can be demonstrated by flight test. This speed is designated VS1g.
Airworthiness authorities have agreed that a factor of 0.94 represents the relationship between VS1g for this aircraft and VSmin for conventional aircraft types. As a result the authorities allow this aircraft to use the following factors:
V2=1.2 * 0.94 VS1g = 1.13 VS1g
VREF=1.3 * 0.94 VS1g = 1.23 VS1g
These speeds are identical to those that the conventional 94% rule would have defined for this aircraft. The aircraft has exactly the same maneuver margin that a conventional aircraft would have at its reference speeds.
The AOM uses VS for VS1g.
So regarding AoA, this leaves us with an open question which may or may not be thread drift depending upon what the recorders have to say. If they are found...
As always I am happy to be corrected in any of this, with information or data that supports the opposite view. I'm posting for learning, not to be right or "win the debate".
PJ2