A320 Optimized V-speed
A320 Optimized V-speed
The Bumblebee
Joined: Jul 1999
Posts: 333
Likes: 1
From: Inside the shiny tube.
The RTOM/RTOW tables are produced using a performance optimisation procedure to give the best possible take-off mass. This procedure uses improved climb performance and its associated increase in speeds to increase take-off mass.
High Speeds - To increase maximum takeoff mass or flexible temperature, when climb, or medium to distant obstacle limited.
Low Speeds – To increase maximum take-off mass when field length limited, or close in obstacle limited. Or, when at maximum flexible temperature (TMAX FLEX), and increased speed does not give any benefit.
High Speeds - To increase maximum takeoff mass or flexible temperature, when climb, or medium to distant obstacle limited.
Low Speeds – To increase maximum take-off mass when field length limited, or close in obstacle limited. Or, when at maximum flexible temperature (TMAX FLEX), and increased speed does not give any benefit.
Joined: Dec 1999
Posts: 222
Likes: 0
From: Dubai, U.A.E.
Three V1's. Maximum, average and lowest possible V1. Optimized calculations takes a range of the above and does exactly that. It optimizes your speeds for the given conditions, weight, runway, obstacles, etc....
Joined: Apr 2004
Posts: 509
Likes: 3
From: United States of Europe
As above. Optimised V-speeds enable a higher RTOW/higher Flex temp.
Not true! Flex take-off's increase tripfuel. TOGA take-off requires least tripfuel. The reason we utilize Flex is to save on engine wear/maintenance cost only!
Regards
V2 optimised is for better climb in the second segment, saves fuel
Regards
Fleet Manager
Joined: Apr 2001
Aviation Qualifications: ATPL
Posts: 7,447
Likes: 310
From: various places .....
Some points to note.
(a) Airbus' optimised takeoff is similar in philosophy to Boeing's overspeed V2 takeoff
(b) minV2 schedule generally will give minimum runway distances. However, the climb gradient capability is nowhere near maximum. If you don't have any spare runway distance available, then that's the end of it and you're stuck with whatever RTOW you get from the analysis.
(c) the climb gradient capability graph is a bit like an upturned teacup .. as you increase speed a bit, the climb gradient improves. As the speed increases the rate of climb improvement falls off and somewhere around 20-30 kts is about as far as it is worth going.
(d) if you have some spare runway distance you can look at increasing the speeds to take advantage of the better climb gradient capability. This probably won't be of any use if you have close in critical obstacles (due to the extended TODR) but usually gives a better RTOW for nil or distant obstacles.
As always, one needs to look at ALL the relevant takeoff limits to end up with whatever speed schedule gives the best (optimised) RTOW.
Balanced Field Lengths were important decades ago when the calculations had to be done by hand .. the BFL calculations were somewhat simplified, quicker to do and, for most cases, gave adequate RTOW without going to the trouble of optimising for the last kilo. With the advent of cheap computing power, generally there is no reason not to optimise to your heart's content rather than just take the easy way out.
Caveat, some of the older aircraft AFMs only gave the option of BFL so there was no optimising option.
(a) Airbus' optimised takeoff is similar in philosophy to Boeing's overspeed V2 takeoff
(b) minV2 schedule generally will give minimum runway distances. However, the climb gradient capability is nowhere near maximum. If you don't have any spare runway distance available, then that's the end of it and you're stuck with whatever RTOW you get from the analysis.
(c) the climb gradient capability graph is a bit like an upturned teacup .. as you increase speed a bit, the climb gradient improves. As the speed increases the rate of climb improvement falls off and somewhere around 20-30 kts is about as far as it is worth going.
(d) if you have some spare runway distance you can look at increasing the speeds to take advantage of the better climb gradient capability. This probably won't be of any use if you have close in critical obstacles (due to the extended TODR) but usually gives a better RTOW for nil or distant obstacles.
As always, one needs to look at ALL the relevant takeoff limits to end up with whatever speed schedule gives the best (optimised) RTOW.
Balanced Field Lengths were important decades ago when the calculations had to be done by hand .. the BFL calculations were somewhat simplified, quicker to do and, for most cases, gave adequate RTOW without going to the trouble of optimising for the last kilo. With the advent of cheap computing power, generally there is no reason not to optimise to your heart's content rather than just take the easy way out.
Caveat, some of the older aircraft AFMs only gave the option of BFL so there was no optimising option.
