747-400 Manoeuvre Margins And Manoeuvering Speeds
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747-400 Manoeuvre Margins And Manoeuvering Speeds
Recent discussions on another forum have raised a few questions (as well as highlighting my poor knowledge on the above subject 
)
On the 747-400, after every monthly FMC Nav Database update, I check the Manoeuvre/Maneuver Margin value on the PERF FACTORS page (ours is set to 1.30). As I understand it, the FMC uses this data for "flight envelope and bank limits calculations" and allows the FMC to draw little yellow "hockey sticks" on the Primary Flight Display above/below the Vmin/Vmax red bands on the airspeed tape.
http://members.ozemail.com.au/~b744e...vreMargins.gif
I had, until now, assumed that the yellow hockey sticks were related to Vmin and Vmax, but after discussions on the subject, now I'm not so sure. Speeds such "Va" and "Vb" have been mentioned, but what these are and how these relate Vmax and Vmin I don't exactly know (I haven't studied aerodynamics).
Q1. On the 747-400, the bottom segment/brick of the upper red band reflects "Vmax". This reflects either gear placard speed, flap placard speed or Vmo. The upper yellow hockey stick indicates "margin to buffet" (according to my text). Would Vmo and buffet be the same in straight and level cruise flight or do the two values have no direct relationship? What kind of buffet are they talking about here?
Q2. Regarding the lower hockey stick and the lower red band... My notes tell me that the top red brick of the lower red band is "Vss" (Stall Warning Management Card-calculated stick shaker speed) when the flaps are down... or, when the flaps are up, the greater of Vss or "Bbflo" ("FMC-calculated initial buffet speed"). What, exactly, is Vbflo. Is it Va (the speed at which, I am told, the aircraft is designed to stall to prevent damage to the wings when the aircraft is subjected to high g's during strong updrafts) or is it another buffet value, Vb, or something completely different?
Q3. When the aircraft banks, do the hockey sticks or the red bands change length or do they remain static. There are a lot of pitch-type inputs to the Stall Warning Management Cards, but there doesn't seem to be any roll inputs (Having said that, I realize that pitch does increase during turns, especially steep ones).
Thanks for any input.
Cheers.
Q.
) On the 747-400, after every monthly FMC Nav Database update, I check the Manoeuvre/Maneuver Margin value on the PERF FACTORS page (ours is set to 1.30). As I understand it, the FMC uses this data for "flight envelope and bank limits calculations" and allows the FMC to draw little yellow "hockey sticks" on the Primary Flight Display above/below the Vmin/Vmax red bands on the airspeed tape.
http://members.ozemail.com.au/~b744e...vreMargins.gif
I had, until now, assumed that the yellow hockey sticks were related to Vmin and Vmax, but after discussions on the subject, now I'm not so sure. Speeds such "Va" and "Vb" have been mentioned, but what these are and how these relate Vmax and Vmin I don't exactly know (I haven't studied aerodynamics).
Q1. On the 747-400, the bottom segment/brick of the upper red band reflects "Vmax". This reflects either gear placard speed, flap placard speed or Vmo. The upper yellow hockey stick indicates "margin to buffet" (according to my text). Would Vmo and buffet be the same in straight and level cruise flight or do the two values have no direct relationship? What kind of buffet are they talking about here?
Q2. Regarding the lower hockey stick and the lower red band... My notes tell me that the top red brick of the lower red band is "Vss" (Stall Warning Management Card-calculated stick shaker speed) when the flaps are down... or, when the flaps are up, the greater of Vss or "Bbflo" ("FMC-calculated initial buffet speed"). What, exactly, is Vbflo. Is it Va (the speed at which, I am told, the aircraft is designed to stall to prevent damage to the wings when the aircraft is subjected to high g's during strong updrafts) or is it another buffet value, Vb, or something completely different?
Q3. When the aircraft banks, do the hockey sticks or the red bands change length or do they remain static. There are a lot of pitch-type inputs to the Stall Warning Management Cards, but there doesn't seem to be any roll inputs (Having said that, I realize that pitch does increase during turns, especially steep ones).
Thanks for any input.
Cheers.
Q.
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G'day Qavion!
This subject is rather esoteric and highlights the shortcomings in our manuals.
As I undersatnd it, the 1.3g manouevre margin entered by the airline in the perf factors page affects the dispayed value of the hockey sticks as well as the 'max altitude' on VNAV pg.2.
What it means to us, in practice, is that if you fly at an IAS between the hockey sticks you can pull 1.3g without fear of buffeting. This equates to approx 40 degrees of bank in level flight.
At the high speed end this would be mach buffet, caused by the high angle of attack accelerating the airflow over the top of the wing to supersonic speed. In the early days of high speed research, this was known as a 'shock stall'.
At the low speed end this would be the more familiar pre-stall buffet, caused by the high angle of attack resulting in a break down of the laminar flow over the top of the wing.
The only time I've seen the upper hockey stick is when we've been fairly light and high (260 tonnes and FL410). Even then they only seem to project 2 to 3 knots below the upper red chequers, so it's not really a practical problem.
The lower red chequers certainly are sensitive to g loading as they are related to stall speed whereas the hockey sticks aren't because they are 'fixed' at 1.3 g.
If you fly at an IAS exactly at the top of the lower hockey stick and pull 1.3g, the lower red chequers will rise up and meet you. You will then experience buffet and the stick shaker will activate.
If, on the other hand, you fly at an IAS exactly at the bottom of the upper hockey stick and pull 1.3g, the upper red chequers will not move (they merely represent Vmo) but you would get mach buffet.
As you climb, the lower and upper hockey sticks (if displayed) will gradually come towards each other and the range of available speeds to fly at will be reduced (coffin corner). At the max altitude displayed on VNAV page 2, the two hockey sticks will meet and there will be only one speed to fly at! If you pull 1.3g you will get simultaneous mach buffet and pre-stall buffet/stick shaker. Ouch!
(Note that it is still perfectly proper to fly at this altitude, provided it is smooth and that you use normal bank angles of less than 40 degrees.)
Descending even a few hundred feet will cause the hockey sticks to separate significantly. This is due to the shape of the 'Cruise Altitude Limits' graph in the flight manual (page 16-12 in a certain airline's QRH). The weight lines have a rather flat top and so a small descent gives a large min/max speed difference.
Hope this answers your questions.
This subject is rather esoteric and highlights the shortcomings in our manuals.
As I undersatnd it, the 1.3g manouevre margin entered by the airline in the perf factors page affects the dispayed value of the hockey sticks as well as the 'max altitude' on VNAV pg.2.
What it means to us, in practice, is that if you fly at an IAS between the hockey sticks you can pull 1.3g without fear of buffeting. This equates to approx 40 degrees of bank in level flight.
At the high speed end this would be mach buffet, caused by the high angle of attack accelerating the airflow over the top of the wing to supersonic speed. In the early days of high speed research, this was known as a 'shock stall'.
At the low speed end this would be the more familiar pre-stall buffet, caused by the high angle of attack resulting in a break down of the laminar flow over the top of the wing.
The only time I've seen the upper hockey stick is when we've been fairly light and high (260 tonnes and FL410). Even then they only seem to project 2 to 3 knots below the upper red chequers, so it's not really a practical problem.
The lower red chequers certainly are sensitive to g loading as they are related to stall speed whereas the hockey sticks aren't because they are 'fixed' at 1.3 g.
If you fly at an IAS exactly at the top of the lower hockey stick and pull 1.3g, the lower red chequers will rise up and meet you. You will then experience buffet and the stick shaker will activate.
If, on the other hand, you fly at an IAS exactly at the bottom of the upper hockey stick and pull 1.3g, the upper red chequers will not move (they merely represent Vmo) but you would get mach buffet.
As you climb, the lower and upper hockey sticks (if displayed) will gradually come towards each other and the range of available speeds to fly at will be reduced (coffin corner). At the max altitude displayed on VNAV page 2, the two hockey sticks will meet and there will be only one speed to fly at! If you pull 1.3g you will get simultaneous mach buffet and pre-stall buffet/stick shaker. Ouch!
(Note that it is still perfectly proper to fly at this altitude, provided it is smooth and that you use normal bank angles of less than 40 degrees.)
Descending even a few hundred feet will cause the hockey sticks to separate significantly. This is due to the shape of the 'Cruise Altitude Limits' graph in the flight manual (page 16-12 in a certain airline's QRH). The weight lines have a rather flat top and so a small descent gives a large min/max speed difference.
Hope this answers your questions.
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"Hope this answers your questions."
It helps greatly, thanks Eckhard, but it may raise a few other questions, too
Some time ago, Boeing responded to an e-mail we sent to them regarding a problem we had with the hockey sticks rising above the flap markers on climb out, and they gave us the impression that the hockey sticks are simply added on top of the red chequers (and if, for some reason, the F/O's red chequers were higher than the Captain's, say, due to a right AOA vane problem, the (top of the) hockey stick would sit "x" knots above the highest red chequer..and the captain's hockey stick would extend to the same airspeed value as the F/O's hockey stick (even though the captain's red zone sat lower). If this were the case, I would have assumed that, during a high g turn, the hockey sticks also would have risen.
I'd love to be able to talk to the guys who actually design these things. It would certainly answer a lot of our questions.
Anyway, much the wiser (I think).
CJ.... I'll be looking for those pins tomorrow
Cheers.
Ian.
It helps greatly, thanks Eckhard, but it may raise a few other questions, too
Some time ago, Boeing responded to an e-mail we sent to them regarding a problem we had with the hockey sticks rising above the flap markers on climb out, and they gave us the impression that the hockey sticks are simply added on top of the red chequers (and if, for some reason, the F/O's red chequers were higher than the Captain's, say, due to a right AOA vane problem, the (top of the) hockey stick would sit "x" knots above the highest red chequer..and the captain's hockey stick would extend to the same airspeed value as the F/O's hockey stick (even though the captain's red zone sat lower). If this were the case, I would have assumed that, during a high g turn, the hockey sticks also would have risen.
I'd love to be able to talk to the guys who actually design these things. It would certainly answer a lot of our questions.
Anyway, much the wiser (I think).
CJ.... I'll be looking for those pins tomorrow
Cheers.
Ian.
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Posts: n/a
Hi Qavion,
I think that the Stall Warning Computer calculates the 1g stick shaker speed for the current weight / config and then derives a 1.3g stick shaker speed which is displayed as the top of the lower hockey stick. So it is correct to say that the top of the hockey stick sits x knots above the red chequers but only during 1g flight.
The anomaly you describe sounds like a problem with the flap position being incorrectly sensed. In our 'Flaps Drive' checklist (QRH 09-3) it says during the landing preparation:
'If the amber minimum manoeuvring speed band is above the flaps manoeuvring speed:
AUTOTHROTTLE...................................DISCONNECT
Use the displayed flaps manoeuvring speeds.
AIRSPEED LOW message is displayed.'
This seems to imply that with a flap problem the SWC may incorrectly calculate the hockey stick.
I should stress that I am not an engineer and have no documentary evidence to back up what I am saying. I am basing my opinions on what I have observed in flight and also during numerous Sim sessions. Unfortunately I won't be back in the 'box' until March at the earliest so I won't have an opportunity to play and check this out until then. (It's a bit difficult with passengers on board the aircraft!)
Merry Christmas!
I think that the Stall Warning Computer calculates the 1g stick shaker speed for the current weight / config and then derives a 1.3g stick shaker speed which is displayed as the top of the lower hockey stick. So it is correct to say that the top of the hockey stick sits x knots above the red chequers but only during 1g flight.
The anomaly you describe sounds like a problem with the flap position being incorrectly sensed. In our 'Flaps Drive' checklist (QRH 09-3) it says during the landing preparation:
'If the amber minimum manoeuvring speed band is above the flaps manoeuvring speed:
AUTOTHROTTLE...................................DISCONNECT
Use the displayed flaps manoeuvring speeds.
AIRSPEED LOW message is displayed.'
This seems to imply that with a flap problem the SWC may incorrectly calculate the hockey stick.
I should stress that I am not an engineer and have no documentary evidence to back up what I am saying. I am basing my opinions on what I have observed in flight and also during numerous Sim sessions. Unfortunately I won't be back in the 'box' until March at the earliest so I won't have an opportunity to play and check this out until then. (It's a bit difficult with passengers on board the aircraft!)
Merry Christmas!
