PPRuNe Forums - View Single Post - Airbus Approch Speed: VLS versus 'S' Speed
Old 8th Feb 2017, 13:32
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Citation2
 
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I am sorry Call it VREF or XYZ your margin to VS1g is shorter in final configuration than with Flaps 1 . Well initially just look at your PFD and watch how far is VLS with Flaps 1 and compare it to final configuration VLS.

Now let me Help you with this :

S : Equal to about 1.22 VS to 1.25 VS of CLEAN configuration

I would like to emphasize on "Clean " because it means that your margin to VS1G is based on a higher speed ( green dot ) and not actual configuration , hence greater margin to VS1G . That is why VLS is so low in Flaps 1 . Notice how VLS goes down when you select Flaps 1.

From Supplementary - Definition:
At Green dot speed VLS= 1,28 VS1G
S speed : 1,22 to 1,25 VS1g of CLEAN. Let's say an average of 1,23

So your margin to VS1G in S speed is 1,23X1.28=1,57 VS1g

Now let's compare this value to the tables available on Limitations :

For a weight of 60 T , VS1G is 120 kts in Flaps 1+F and 125 in Flaps 1
For a weight of 60 T , S speed is 185 kta

185/120=1,54

Close enough isn't it ? With the table I found a margin of 54% to VS1g and with the calculation I found 57% of margin to VS1g.

Let's say 55%. S speed is 55% greater than VS1g.

Now let's come back to final configuration . What is your actual margin to VS1g? 23% right? Vref= 1,23 VS1g

So where do you think you are closer to a stall ? You accept to fly with 23 % of margin to VS1g and not 55% , just because they call it VREF?
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