>>Don't get me wrong, I realize there is a zero chance that aoa's will be >>adopted in the fleet but that is largely because so many pilots don't >>fully understand aoa in the first place...and come to grief because of >>it.I love these debates as it gets me thinking about stuff I might not give much thought to.I don't believe that pilots don't understand it! It is simply the case that ADCs (Air Data Computers) completely remove the need for one (in most commercial a/c). ADCs turn a simple to read, hard to interpret guage into a command function - e.g. stick shakes...add power. Where ADCs are not present, then I would like to refer you to my comments on the CofA (Certificate of Airworthiness). What I do think is that it is a very difficult instrument to use properly and as the law of aircraft design states: if a system can be used incorrectly, then one day it will be! For example, peering at your AoA thinking "Its OK, 5 degrees before crit alpha" but failing to take account of the 20deg of flap currently deployed.For an average spamcan (read "a/c with no particular vices"), the one time that an AoA would be very very very useful is when your ASI fails - if you did your job properly in the first place you are in the realm of rollover lottery odds. However, the changes of relying on and misreading an AoA are very much higher.

re: if the stick shakes add powerIf we are talking about low speed stall where the AoA is too high, merely adding power might not do much. The first step is to lower pitch to reduce the AoA to startup the lift process again. As you drop the nose the aircraft will start to fly with all surfaces. Typically you may have to reduce power to avoid a power dive if you are already at a high airspeed. If recovery places you on a descent, then you slowly add power why raising the pitch to stabilize altitude to maintain a proper airspeed and altitude while reducing the AoA.Now for high performance Mach aircraft, you may also get a stick shake at the high speed Mach barrier at the other end of the speed range. Another story but the idea is that for some aircraft stick shake can indicate other situations, maybe exceeding Vne on a dive.

Details indeed!>>The first step is to lower pitch to reduce the AoA to startup the lift >>process again. As you drop the nose the aircraft will start to fly with >all surfaces.Stick-shakers are mandated to activate at least 5% above the calculated stall speed for the configuration, so in theory a stall recovery shouldn't ever happen. However, if it does go that far then with swept wing a/c (esp with T-tails), by the time you need to recover it will be very difficult to pitch nose down as the generic stall aerodynamic tendency is to pitch nose up. Depending on the a/c, dropping the gear and/or flaps can get the nose back down again. Power is essential but under-wing pods can again promote a nose up attitude if not checked. Stalling an airliner can be very bad news and has often been totally unrecoverable hence the almost universal need for a stick-shaker to attain a CofA.

However, if it does go>that far then with swept wing a/c (esp with T-tails), by the>time you need to recover it will be very difficult to pitch>nose down as the generic stall aerodynamic tendency is to>pitch nose up. I Believe you're talking about a "deep Stall"" On T-tail aircraft, with highly swept wings, theproblem comes about as a result of the configuration's geometry and canhappen at any CG. Examples of the HP Victor, HS Trident, BAC1-11 andTu-134 have all crashed from deep stall. The BAC1-11 and Tu-134 crashedon the same day. In all cases, they reached an angle of attack wherethey were stalled and in trim and lacked the control power to recover."(taken from a rec.aviation newsgroup post by David Lednicer).I remember when the 111 crashed this was pretty much an unknown phenomenon.Dave

>>I Believe you're talking about a "deep Stall"Yes I am and thanks for your information as I didn't know of any specific examples of the problem. We do digress, but indulge me and I shall waffle some more!I think the term "Deep Stall" is the specific effect of the swept wing/t-tail configuration. To be more accurate, it is the rearward swept wing configuration that causes the nose up on stall and the T-tail that makes it worse. The reason is that the tips stall first and as a result the centre of lift move along the wing to the root. The root of swept wing is ahead of the tip so the centre of lift moves forward too, pitching the a/c up.The specific problem with T-tails is that as the a/c pitches up, the elevators are blanked by the wings from the airflow and so there is now no way to control pitch. Hence the recommendation that flaps and/or gear be deployed to move the centr of lift back and cause much drag below the drag line levering the nose back down (there maybe other type specific procedures).There are problems with stadard stabiliser configurations too!! When the swept wing stalls, the root stalls last (as previously mentioned). This causes a massive downwash of air near the fuselage. This can cause a high pressure area over the tailplane pushing the tail down...and the nose up!! Although not as severe as a T-tail, elevator authority can still be greatly reduced.For this reason slots, slats, vortex generators (a saw tooth 2/3rds of the way along the wing), wing fences and other devices are often fitted to energise the air over the wing and/or reduce the amount of air travelling along the wing to the tip to reduce tip-stall.