Angle of Attack and its pratical use in airline jets..
Guest
Posts: n/a
Angle of Attack and its pratical use in airline jets..
It seems it would be more efficient to use angle of attack indicators (like the carrier Navy). Referencing V speeds for different weights would be eliminated and max a/c performance could be realized, for all phases of flight, even engine failures.
But, how is AOA used with take off decision speed? And, how is AOA used with high speed flight. AOA would be great for approach, but what about climb to the flight levels.
I may have answered my own question, somewhat, but I would like some in depth discussion.
But, how is AOA used with take off decision speed? And, how is AOA used with high speed flight. AOA would be great for approach, but what about climb to the flight levels.
I may have answered my own question, somewhat, but I would like some in depth discussion.
Guest
Posts: n/a
On the 737 we have pitch limit 'eyebrows' on the EADI when the flaps are down. This indicates the pitch angle corresponding to pre-stall buffet. As you pull g, the eyebrows move down (obviously) - it is very clever. The main use of these is during evasive manoeuvres when ground contact is imminent - Windshear / GPWS. The SOP is pitch to the PLI's (pitch limit indicators) and apply full thrust.
Very interesting point - the Navy use a 'dohnut' I believe which corresponds to 1.3Vs (or 0.6 of alpha max) for approach.
AoA has nothing to do with V1 as you are still on the ground at decision speed.
Very interesting point - the Navy use a 'dohnut' I believe which corresponds to 1.3Vs (or 0.6 of alpha max) for approach.
AoA has nothing to do with V1 as you are still on the ground at decision speed.
Guest
Posts: n/a
Guest
Posts: n/a
AOA is useless when not in flight -- ie no angle of attack to measure.
In flight, AOA is and instant source (regardless of weight) for determining:
1. Stall AOA - useful for stall recoveries and max performing the wing in the event of terrain closure or windshear escape.
2. Approach speed
3. Max ANGLE of climb (L/D max)or best holding speed
4. Best range AOA
There are several different types of AOA presentation, such as:
"Normalized" - where the max lift is calibrated as "1" on the gauge. In this case, the corresponding normal approach speed would be about ".6", and L/D max of about "3.2"
Or
"Raw units" calibrated in degrees of angle of attack. In the military aircraft I flew, approach speed was primarily referenced to AOA (in that case 7 units), with flaps down stall at about 16 units.
Many commercial airliners have the info avail but don't display it explicitly. For instance the newer 737s have a tiny little gauge in the CRT while the 767 has a "pitch limit indicator" on the attitude display when the flaps are down.
I like AOA raw presentations. You have to know what you're looking at, but once you do there is a wealth of information there. Depending on if the system display is independent of the CADC, it would be a good backup to total IAS indicator failure.
In flight, AOA is and instant source (regardless of weight) for determining:
1. Stall AOA - useful for stall recoveries and max performing the wing in the event of terrain closure or windshear escape.
2. Approach speed
3. Max ANGLE of climb (L/D max)or best holding speed
4. Best range AOA
There are several different types of AOA presentation, such as:
"Normalized" - where the max lift is calibrated as "1" on the gauge. In this case, the corresponding normal approach speed would be about ".6", and L/D max of about "3.2"
Or
"Raw units" calibrated in degrees of angle of attack. In the military aircraft I flew, approach speed was primarily referenced to AOA (in that case 7 units), with flaps down stall at about 16 units.
Many commercial airliners have the info avail but don't display it explicitly. For instance the newer 737s have a tiny little gauge in the CRT while the 767 has a "pitch limit indicator" on the attitude display when the flaps are down.
I like AOA raw presentations. You have to know what you're looking at, but once you do there is a wealth of information there. Depending on if the system display is independent of the CADC, it would be a good backup to total IAS indicator failure.
Guest
Posts: n/a
Hi folks
Just like to agree with what has been said above and add some emphasis perhaps
1 An angle of attack indication is the only way to go when you are interested in knowing what your current margin is from the stall. (which is why it is an AOA sensor that drives the shakers and pushers of this world)
2 AOA information on margin from the stall is correct regardless of weight, bank angle and power being used. (weight, bank angle and power are three biggies that for me make the concept of “the stalling speed” a pretty meaningless one)
3 As has been pointed out earlier, V data is essential for take off performance and asymmetric handling limits (as these are not determined by available wing lift considerations)
Regarding 2 above, one day I was the handling pilot on a CN235 after a long test flight of some seven hours (the aircraft does not have an autopilot). While the captain wrestled with weight calculations that involved US galls, kgs of this and lbs of that, we got ever closer to base. Starting finals I decelerated until the AOA indicator showed the normal approach value. (the aircraft was fitted as standard with a round instrumemt about 2/3 the diameter of the ASI to the left of the ASI - perfect)Then I looked at the speed - 132 kts - and flew that. Eventually the captain looked up from all the paperwork and said “124 kts”. I asked if he would mind checking that calculation. More head down. At a couple of miles he said “Sorry John that should have been 131 kts.” Glancing at the ASI he then asked, “How did you know?” To my undying shame (he was much younger than me – but a very sound aviator) I waggled the yoke a tad and commented “When you have been at it a while you get a feel for these things”
But then life is just too short to explain the advantages of AOA to everyone you meet.
JF
Just like to agree with what has been said above and add some emphasis perhaps
1 An angle of attack indication is the only way to go when you are interested in knowing what your current margin is from the stall. (which is why it is an AOA sensor that drives the shakers and pushers of this world)
2 AOA information on margin from the stall is correct regardless of weight, bank angle and power being used. (weight, bank angle and power are three biggies that for me make the concept of “the stalling speed” a pretty meaningless one)
3 As has been pointed out earlier, V data is essential for take off performance and asymmetric handling limits (as these are not determined by available wing lift considerations)
Regarding 2 above, one day I was the handling pilot on a CN235 after a long test flight of some seven hours (the aircraft does not have an autopilot). While the captain wrestled with weight calculations that involved US galls, kgs of this and lbs of that, we got ever closer to base. Starting finals I decelerated until the AOA indicator showed the normal approach value. (the aircraft was fitted as standard with a round instrumemt about 2/3 the diameter of the ASI to the left of the ASI - perfect)Then I looked at the speed - 132 kts - and flew that. Eventually the captain looked up from all the paperwork and said “124 kts”. I asked if he would mind checking that calculation. More head down. At a couple of miles he said “Sorry John that should have been 131 kts.” Glancing at the ASI he then asked, “How did you know?” To my undying shame (he was much younger than me – but a very sound aviator) I waggled the yoke a tad and commented “When you have been at it a while you get a feel for these things”
But then life is just too short to explain the advantages of AOA to everyone you meet.
JF
Guest
Posts: n/a
Guest
Posts: n/a
I you fly an aircraft with a HUD it usally has what some people call a "birdie" or flight path marker. It basically shows you where you are going relative to the ground. The cool thing about it is that the difference between the birdie and the pitch attitude is almost equal to your angle of attack. So by looking through your HUD you know where you are going and at the same time you know your angle of attack. You can fly an approach just by looking at these two symbols. Great stuff! Every aircraft should have a HUD!
Guest
Posts: n/a
I believe the Russians have used it for years in their commercial jets - usually raw AoA units combined with a "g" meter.
Again I`ve heard, that their military were so embarrassed by the number of departures at high AoA provoked during the Yom Kippur war (advisers operating Syrian and Egyptian equipment), that they made it a national doctrine to be aware of AoA.
GH
Again I`ve heard, that their military were so embarrassed by the number of departures at high AoA provoked during the Yom Kippur war (advisers operating Syrian and Egyptian equipment), that they made it a national doctrine to be aware of AoA.
GH
Guest
Posts: n/a
An angle of attack indicator is actually not a complicated instrument and is the MOST effective gauge of the efficiency of the airfoil for all those reasons above.
Wolfgang Langewiesche explains it rather well in his classic book "Stick and Rudder", first copyrighted in 1944.
Progress in aviation? Where?
Wolfgang Langewiesche explains it rather well in his classic book "Stick and Rudder", first copyrighted in 1944.
Progress in aviation? Where?
