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StrIA 8th Nov 2016 13:12

Performance A320F
 
Why speeds are greater on FLEX, then on TOGA? (take off phase)

vilas 8th Nov 2016 15:59

Are you sure?

tubby linton 8th Nov 2016 17:14

Sample performance-
Conf 1+f IAE powered A321 TOW 80T
Toga V1 134 Vr146 V2 154 MRG 1152 Lim TOW Vmu
Flex 52 V 154 Vr 154 V2 156 MRG 1 Lim TOW-OBS

Cough 8th Nov 2016 17:39

When you flex, the performance computation will use the spare runway to achieve higher speed (think improved v2 climb) to get further reductions in flex temp.

When you use TOGA there isn't any point as there is ample performance for everyday use. Hence you simply get fast enough to takeoff and then do just that!

ps. Why your V1 is low on the TOGA case may be a company preference...

StrIA 8th Nov 2016 20:11

FLYSMART WITH AIRBUS (appstore)
For ex.
A321-211 TOW 78, wind-60/14,OAT-4,RWY-wet, CONF 2, AIRCOND-Off, A-ICE-Off
FLEX-52 153/161/161
TOGA 142/152/152

compressor stall 8th Nov 2016 22:40

As Vilas says, it's not the case that they are always greater.

Does your flysmart app have just the TOGA and max flex option? If so, then you might get that assumption.

But if your admin has it set up so that you can see all the flex variants, pick a runway at low weights and good conditions and run it.

For my local airport on a 2300m runway, I have the V1,Vr,V2 speeds at TOGA, F43,F45,F47,F49 and F51 all the same, and all VMCG limited.

Then F53 and F55 have same V1, but the Vr and V2 start to increase (Vmcg limited)

F57 and F59 have V1,Vr,V2 higher than Flex (Obstacle clearance limited).

Remember also that the Flysmart app chooses a V1 that gives the greatest margin (unlike the old LPC where you could pick a higher V1 and reduced margin, which was handy in some locations).

Lantirn 9th Nov 2016 17:18


Originally Posted by tubby linton (Post 9571592)
Sample performance-
Conf 1+f IAE powered A321 TOW 80T
Toga V1 134 Vr146 V2 154 MRG 1152 Lim TOW Vmu
Flex 52 V 154 Vr 154 V2 156 MRG 1 Lim TOW-OBS

Nice example.

In this airport with those conditions you became obstacle limited in this flex 52.
To clear those obstacles the speeds were increased to facilitate obstacle clearance probably for the second segment of the takeoff flight path.

Improved climb.

But you have to know the limited codes.

underfire 10th Nov 2016 22:31


A321-211 TOW 78, wind-60/14,OAT-4,RWY-wet, CONF 2, AIRCOND-Off, A-ICE-Off
Curious, OAT -4, RWY wet, and ice off?

Working on performance profiles for obstacles, I am curious as a guide, when you turn ice on.

FlightDetent 11th Nov 2016 00:28

SAT 10 or less, visible moisture.

Wet with -4 entirely possible on a sunny morning after treatment had been applied overnight. Not so uncommon in StrIAs are of operation with high pressure airmass, late February.

underfire 11th Nov 2016 05:37

ok, well, its November...

one could guess, or one could provide details on the assumptions.

Cheers


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