Gradient vs. Climb angle?
Joined: Dec 2005
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From: Canada
Or for 10%, 10 X .57 = 5.70 degrees. Correct answer is 5.71
To be exact, inv tan(gradient) = climb angle. Inv tan(.027) = 1.55 degrees
Joined: Jun 2004
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From: Australia
pstaney is right, but as most people are not usually very proficient with their .57 times table for mental arithmetic, multiplying by .6 does the trick, with just a small tad of conservatism for a climb (the opposite for a descent).
Very useful to fly a SID gradient accurately if you have Flight Path Angle (or Flight Path Vector) indication, and better yet if this angle is selectable as a Flight Director function. I use it all the time.
Regards,
Old Smokey
Very useful to fly a SID gradient accurately if you have Flight Path Angle (or Flight Path Vector) indication, and better yet if this angle is selectable as a Flight Director function. I use it all the time.
Regards,
Old Smokey
Joined: Dec 2005
Posts: 41
Likes: 0
From: Canada
I'm not familiar with flight path vector indication, but must work off the IRS? A quick ques on it's use as you describe....
Suppose on your 777 you have entered the SID required gradient, and come up with a required climb angle, and decide to fly this gradient. Eg 3.3% gradient gives 1.88 degrees climb angle. Will your flight path vector show 1.88 degrees in the AI?
Now you go from zero wind to a 30 knot tailwind. Does the flight path vector increase to a higher climb angle to ensure the 3.3% gradient?
Suppose on your 777 you have entered the SID required gradient, and come up with a required climb angle, and decide to fly this gradient. Eg 3.3% gradient gives 1.88 degrees climb angle. Will your flight path vector show 1.88 degrees in the AI?
Now you go from zero wind to a 30 knot tailwind. Does the flight path vector increase to a higher climb angle to ensure the 3.3% gradient?
Joined: Jun 2004
Posts: 1,843
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From: Australia
It depends upon whether the FPA is simply a read-out, or a selectable flight mode for the Flight Director Auto-Pilot.
If a display only, TAS and G/S variations will cause change in FPA. Simple pilot intervention is to alter pitch attitude as required to maintain the FPA (much as you would alter pitch attitude as required to maintain IAS).
If the FPA (or FPV) is a SELECTABLE flight mode, the F/D or A/P will maintain a constant FPA (very accurately, it's from the IRS) by varying pitch attitude to maintain as necessary.
"Now you go from zero wind to a 30 knot tailwind. Does the flight path vector increase to a higher climb angle to ensure the 3.3% gradient?" - FPA or FPV is climb angle, pitch and airspeed will vary as required to maintain the constant Climb Angle or FPA.
Caution is required as always, in climbing in any non-airspeed mode (e.g. V/S, FPA) to ensure that airspeed remains within acceptable limits. One SID that we fly on the B777 requires a 5% gradient (3.0°) to F/L 150, in this case, select the FPA at 3.0° (2.9° actually), set the required IAS to full climb speed (about 310 to 320 KIAS), and the AFCS maintains the FPA whilst the Auto-Throttle does it's best to maintain the 300 KIAS or so (which it cannot due to the steep angle, so full MCL is scheduled). The result is a climb in the vicinity of 260-270 KIAS (quite acceptable) whilst maintainiong the exact climb angle. In this way, you're getting the highest possible speed during climb (very desirable). If, as an alternative, V/S or FLCH at best gradient speed were used, climb angle would undoubtedly be higher than required, but the economics terrible (Climb economy depends heavily upon the highest possible speed right up to Cost Index Speed).
Did that help? or did it muddy the waters? I hope not!
Regards,
Old Smokey
If a display only, TAS and G/S variations will cause change in FPA. Simple pilot intervention is to alter pitch attitude as required to maintain the FPA (much as you would alter pitch attitude as required to maintain IAS).
If the FPA (or FPV) is a SELECTABLE flight mode, the F/D or A/P will maintain a constant FPA (very accurately, it's from the IRS) by varying pitch attitude to maintain as necessary.
"Now you go from zero wind to a 30 knot tailwind. Does the flight path vector increase to a higher climb angle to ensure the 3.3% gradient?" - FPA or FPV is climb angle, pitch and airspeed will vary as required to maintain the constant Climb Angle or FPA.
Caution is required as always, in climbing in any non-airspeed mode (e.g. V/S, FPA) to ensure that airspeed remains within acceptable limits. One SID that we fly on the B777 requires a 5% gradient (3.0°) to F/L 150, in this case, select the FPA at 3.0° (2.9° actually), set the required IAS to full climb speed (about 310 to 320 KIAS), and the AFCS maintains the FPA whilst the Auto-Throttle does it's best to maintain the 300 KIAS or so (which it cannot due to the steep angle, so full MCL is scheduled). The result is a climb in the vicinity of 260-270 KIAS (quite acceptable) whilst maintainiong the exact climb angle. In this way, you're getting the highest possible speed during climb (very desirable). If, as an alternative, V/S or FLCH at best gradient speed were used, climb angle would undoubtedly be higher than required, but the economics terrible (Climb economy depends heavily upon the highest possible speed right up to Cost Index Speed).
Did that help? or did it muddy the waters? I hope not!
Regards,
Old Smokey
