Best angle or best rate in departure?
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Best angle or best rate in departure?
Hi fellows,
Consider this case please:
Prior departure from an airport you receive this clearance from the ATC: "maintain runway heading until FL100 then turn left and proceed direct to XXXXX [to the first fix of route towards destination]".
The course to proceed to that fix is almost 180º of the runway heading, meaning while you fly keeping runway heading until FL100 you would be flying in the opposite direction to the destination.
There are no obstacles around the airport, and you want to use the less fuel for the trip.
What do think is the best course of action after cleaning the plane, to climb with best angle or with best rate of climb until reaching FL100 and turn to proceed to the destination?
Cheers!
Consider this case please:
Prior departure from an airport you receive this clearance from the ATC: "maintain runway heading until FL100 then turn left and proceed direct to XXXXX [to the first fix of route towards destination]".
The course to proceed to that fix is almost 180º of the runway heading, meaning while you fly keeping runway heading until FL100 you would be flying in the opposite direction to the destination.
There are no obstacles around the airport, and you want to use the less fuel for the trip.
What do think is the best course of action after cleaning the plane, to climb with best angle or with best rate of climb until reaching FL100 and turn to proceed to the destination?
Cheers!
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Actually, neither.
In a jet a big factor is turn radius, so keeping the speed back minimizes the time until enroute. It also, transiently, costs you initial ROC to achieve your Vx or Vy, and unless it's a high altitude you will probably reach it faster by staying back at Vcl.
If it is a low altitude, it may not even be worth cleaning up until in the turn.
In a jet a big factor is turn radius, so keeping the speed back minimizes the time until enroute. It also, transiently, costs you initial ROC to achieve your Vx or Vy, and unless it's a high altitude you will probably reach it faster by staying back at Vcl.
If it is a low altitude, it may not even be worth cleaning up until in the turn.
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Best rate or 250 KIAS.
Since there is a 250 KIAS speed limit below 10,000' in most areas, acceleration to a higher speed is not an option. So, climb rate lost during acceleration will likely not be a significant factor. Jet engines are much more fuel efficient at higher altitude, so getting to higher altitude as quickly as possible is the goal.
Since there is a 250 KIAS speed limit below 10,000' in most areas, acceleration to a higher speed is not an option. So, climb rate lost during acceleration will likely not be a significant factor. Jet engines are much more fuel efficient at higher altitude, so getting to higher altitude as quickly as possible is the goal.
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The course to proceed to that fix is almost 180º of the runway heading, meaning while you fly keeping runway heading until FL100 you would be flying in the opposite direction to the destination.
If turbulence then Max rate.
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Best angle = less distance away from the fix
On the other hand best rate = less time in high fuelflow altitudes but also you will have higher speed on the inbound leg to the enroutefix so timewise and fuelflow wise and with regards to earlier acquisation of fl100 hence an earlier turn back and a higher tas Vy sounds better.
I often think about this aswell. Can anyone help me get home earlier and save the enviroment (without changing career)
On the other hand best rate = less time in high fuelflow altitudes but also you will have higher speed on the inbound leg to the enroutefix so timewise and fuelflow wise and with regards to earlier acquisation of fl100 hence an earlier turn back and a higher tas Vy sounds better.
I often think about this aswell. Can anyone help me get home earlier and save the enviroment (without changing career)
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You will go 7.6 miles out on that runway hdg to FL100 or 6 miles at Vx
and 5.03 miles if you hold the stick back.
Look at Zurich SID, use the SID for a south Westerly en-route departure - I forgot the name now . . . but you`ll find it. Look at the route taking you over the town of Zurich yet not actually overhead the town due noise abate.
See the level you have to be at by 2.1 miles, some climb!................................ Added later Its a GERSA 1B
DP (SID) although not FL100 it is in the opposite direction with a neat turn left >180deg at about 9.5%.
and 5.03 miles if you hold the stick back.
Look at Zurich SID, use the SID for a south Westerly en-route departure - I forgot the name now . . . but you`ll find it. Look at the route taking you over the town of Zurich yet not actually overhead the town due noise abate.
See the level you have to be at by 2.1 miles, some climb!................................ Added later Its a GERSA 1B
DP (SID) although not FL100 it is in the opposite direction with a neat turn left >180deg at about 9.5%.
Last edited by Natstrackalpha; 30th Apr 2013 at 00:15.
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being a bit annoyed I entered the manuals (CRJ) and though being almost the same climbing at the max rate is the winner.
makes you reach 10000ft in about a minute less covering very short extra distance which is then gained being already accelerated - BUT radius of turn was not considered.
makes you reach 10000ft in about a minute less covering very short extra distance which is then gained being already accelerated - BUT radius of turn was not considered.
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I reckon staying at clean speed (Vx or close enough )until within about 60deg the direct heading will probably reduce cruise time by about a minute.
Last edited by Sciolistes; 30th Apr 2013 at 02:24.
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Never go fast the wrong way...
Personally, I would stay at F1 maneuvering speed until the turn was completed, then accelerate to the barber pole
Personally, I would stay at F1 maneuvering speed until the turn was completed, then accelerate to the barber pole
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Thank you guys for the replies.
Some days ago I was flying with a captain and we actually had this case. I was PF and he insisted in using Vx up to FL100 while I believed Vy would be a better option, although if it would had depended on me, I would had just set minimum clean speed and end of the story… As someone pointed out, this is totally a theoretical discussion, since obstacles or conflicting traffics were not involved.
Anyway, once brought the discussion to the cockpit I argued Vy would allow us to reach FL100 in less time so we could turn earlier towards our destination, resulting in less flight time, therefore less fuel. He would choose Vx based on a shorter distance would result in less fuel burnt.
The airplane was a B737, and Boeing doesn't provide as far as I know, a way to calculate fuel burn for Vx or Vy so I can't conclude which one is more fuel efficient. And I ignore if there is a way to calculate that regardless of the specific airplane, simply based on generic flight conditions information (speed, altitude, etc).
What I know is that on one hand Vx is Vmd for a jet, that is, the most economical speed for an aircraft, so flying constantly at Vx would result in the less fuel consumption. On the other hand Vy allows to be less time in low altitude, which for a jet results in a lower fuel consumption.
Now, which of these two factors is more dominant? I don't know…
Some days ago I was flying with a captain and we actually had this case. I was PF and he insisted in using Vx up to FL100 while I believed Vy would be a better option, although if it would had depended on me, I would had just set minimum clean speed and end of the story… As someone pointed out, this is totally a theoretical discussion, since obstacles or conflicting traffics were not involved.
Anyway, once brought the discussion to the cockpit I argued Vy would allow us to reach FL100 in less time so we could turn earlier towards our destination, resulting in less flight time, therefore less fuel. He would choose Vx based on a shorter distance would result in less fuel burnt.
The airplane was a B737, and Boeing doesn't provide as far as I know, a way to calculate fuel burn for Vx or Vy so I can't conclude which one is more fuel efficient. And I ignore if there is a way to calculate that regardless of the specific airplane, simply based on generic flight conditions information (speed, altitude, etc).
What I know is that on one hand Vx is Vmd for a jet, that is, the most economical speed for an aircraft, so flying constantly at Vx would result in the less fuel consumption. On the other hand Vy allows to be less time in low altitude, which for a jet results in a lower fuel consumption.
Now, which of these two factors is more dominant? I don't know…
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Teldorserious With pax I wouldn't stand it on it's tail. By myself I would peg the VSI if they tried to send me in the wrong direction for no reason.
