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160knots
1st Sep 2007, 15:26
Anybody know a rule of thumb to calculate V2 knowing the take off weight for the B737, A320 and B777?

Tail-take-off
1st Sep 2007, 15:39
Try looking it up in the QRH

160knots
2nd Sep 2007, 05:01
Why bother looking up a QRH if Rwy. Analysis charts are available. QRH might be suitable for Chopper Ops. but wouldn’t cater for obstacle clearance; unless you had the obstacles surveyed in the splay area and had the numbers in front of you. The reason for the question is to ensure that the V2 extracted from the tables is sensible. Even though the second pilot or Flight Engineer would be or should be checking the speeds.

Grow up lads.

RYR-738-JOCKEY
2nd Sep 2007, 13:29
Here's a thought. V2 is minimum 1,2 Vs, and minimum 1,1 Vmca. Assuming correct weigth is entered, you can read off Vs from the speed tape. 1,2 times that should give you a minimum V2. (Never actually done it myself)

stevehudd
2nd Sep 2007, 13:59
I thought V2 was just when you have a safe airspeed and climb, cant you just wait an extra 5 secs and say v2

AerocatS2A
2nd Sep 2007, 14:07
Why is the standard procedure where you read it off the approved documentation and crosscheck with the other pilot not good enough?

Does your company have a particularly convoluted way of aquiring the V2 speed or something? In ours we just go to the card for our weight and read off the relevent speeds. Sometimes one of us makes a blue and sets a bug to the wrong speed or calls out the wrong speed, the other pilot has always picked up the error.

AerocatS2A
2nd Sep 2007, 14:17
I thought V2 was just when you have a safe airspeed and climb, cant you just wait an extra 5 secs and say v2
It's not just any old safe airspeed. It is a minimum airspeed that, in the case of an engine failure at V1, is achieved by 35' after take-off and if maintained will allow for a climb that clears any obstacles in the take-off area. If you stray too far from it, obstacle clearance may not be guaranteed.

stevehudd
2nd Sep 2007, 18:31
I see, is it like the best angle of climb, ROC thinking, so if you have an engine faile 5 knots under V2 would that mean that you would puch the nose down a little to pick up speed or increase the throttle? :)

AerocatS2A
2nd Sep 2007, 19:46
Kind of but not really.

V2 is closely tied to the rotate speed. If you suffer an engine failure at V1 (which is at some point in the take-off roll and is the worst time to have an engine failure) and then rotate at the correct rotate speed, you will achieve V2 by 35'. The rotate speed is selected so that this will happen. All you then need to do is maintain V2 and you will have the required angle of climb to clear any obstacles.

The actual demonstrated aircraft performance during testing is assumed to be reduced by a certain amount on the basis that old aeroplanes don't perform as well as new ones and that not all pilots are test pilots.

V2 is not a best anything speed. It is neither best angle or best rate. If you were to have an engine failure at a speed slightly greater than V2 you would normally achieve a better climb angle by maintaining that higher speed (up to a point.)

londonmet
2nd Sep 2007, 21:30
Racking my brains I believe the point AEROCAT was referring to is V2 + 10.

I think!

stevehudd
2nd Sep 2007, 21:31
Thanks Aerocat, So you try to aim for this speed on an engine failure even if it's possible to apply full power on the 1 engine, Im guessing to not upset the yaw too much aswell

londonmet
2nd Sep 2007, 21:38
Stevehudd,

If you suffer an engine failure after V1 and -

Your speed is below V2 - aim for V2.

Your Speed is between V2 and V2 + 10 - hold that speed.

Your speed is above V2 + 10 - reduce to V2 + 10, clearly with the caveat of being safe.

stevehudd
2nd Sep 2007, 22:01
Thanks London Met aswell for your help:)

blackmail
2nd Sep 2007, 22:32
hello 160kts,

for b737-800ng take off with flaps 5: rule of thumb to X check v2 : take off weight in tons, add 80 = v2 in kts. eg : tow = 62ton + 80 = 142ktsV2.
kind regards,
bm:rolleyes:

Checkboard
2nd Sep 2007, 23:16
For the -300: http://www.b737.org.uk/vspeedcalc3.htm
For the -700/800: http://www.b737.org.uk/vspeedcalc2.htm
Full QRH speed tables are here: http://www.b737.org.uk/pilotnotes.htm

AerocatS2A
3rd Sep 2007, 01:49
Thanks Aerocat, So you try to aim for this speed on an engine failure even if it's possible to apply full power on the 1 engine, Im guessing to not upset the yaw too much aswell

Well, you have max power on the one engine and you maintain the speed by climbing. The higher your nose is, the slower you'll go.

Wizofoz
3rd Sep 2007, 02:20
Even though the second pilot or Flight Engineer would be or should be checking the speeds.


A320s, 737s and 777s don't HAVE flight engineers...

mustafagander
3rd Sep 2007, 04:59
Quoting stevehudd
Thanks Aerocat, So you try to aim for this speed on an engine failure even if it's possible to apply full power on the 1 engine, Im guessing to not upset the yaw too much aswell

V2 is not a speed we "try to aim for", it's a speed we MUST achieve or the performance calculations become worthless. In jets, V2 is almost invariably on the back side of the performance curves meaning that a small increase in speed will enhance performance, but any decrease will cost you your shirt, performance wise. Hence the concept of "overspeed" or "improved climb" T/O calculations.

Given that you are climbing away with 1 engine out, stable and making all required gradients I would highly recommend NOT increasing thrust if it is available. Derates and reduced thrust calculations are very conservative so you are safe to leave it as is. Now is NOT the time to perhaps destabilise an unfamiliar situation, not forgetting the Vmca in this configuration.

160knots
4th Sep 2007, 11:15
Wizofox, read the response. The crack about a Flight Engineer was in response to a poster who claims he was a FE and was being sarcastic in his reply. I am glad you know which aircraft in the past carried FE's your exceptional knowledge amazes me.

blacmail thanks for the info, thats the sort of thing I was looking for, now if someone can come up for a gross error check on the A320 and B777 it would be appreciated.