V2 + 5, why?
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V2 + 5, why?
Hi.
I am flying the ATR and we have a procedure that says we set the initial climb out speed to V2 + 5, but why?
Isn't V2 the t/o safety speed which insures the best climb performance in case we should loose an engine?
The only thing I could find which is coming close is either the noise abatemant procedures, but they state V2 + 10 or 20 or an increased V2 procedure but is that the answer to why ATR is saying V2+5?
I am flying the ATR and we have a procedure that says we set the initial climb out speed to V2 + 5, but why?
Isn't V2 the t/o safety speed which insures the best climb performance in case we should loose an engine?
The only thing I could find which is coming close is either the noise abatemant procedures, but they state V2 + 10 or 20 or an increased V2 procedure but is that the answer to why ATR is saying V2+5?
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Jets use V2+10
JIC,
If you lose an engine during initial climb, you then need to be at V2. You will probably lose a couple of knots as you respond to the failure, so on a normal departure you should climb out slightly faster than V2 (best engine-out speed).
Your climb performance with all engines at V2+5/10 is very close to what you get at V2. The performance loss at V2-5/10 is significantly less, especially if you are engine out.
Hope that helps.
Joe
If you lose an engine during initial climb, you then need to be at V2. You will probably lose a couple of knots as you respond to the failure, so on a normal departure you should climb out slightly faster than V2 (best engine-out speed).
Your climb performance with all engines at V2+5/10 is very close to what you get at V2. The performance loss at V2-5/10 is significantly less, especially if you are engine out.
Hope that helps.
Joe
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I've often wondered about this V2+5 thing as well. Why did the manufacturer not build this margin into Vtoss so that V2+5 is the FCOM V2 ? And why +5 anyway, as AB said, since +10 is even better ?
I am intrigued about what I don't know.
I am intrigued about what I don't know.
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If you have close look at it, V2+5 i very close to max excess thrust speed at single engine takeoff configuration. Max excess thrust=best climb gradient
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V2 is the speed you achieve at or prior to 35 ft height in a takeoff with one engine failed at V1 and using normal rate of rotation at Vr. With all engines operating it is inevitable to pick up more speed during rotation and transition to a steady climb attitude. In a jet you typically end up at V2+10 kt and it is recommended that you keep that speed even in the event of a later engine failure.
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Speaking as someone who has managed to fly all sorts of random speeds in the sim. following an engine failure, I can tell you for sure that it takes absolutely ages to get your speed above V2 if you let it fall below. Flying at precisely V2 is possible but V2 +5 just a little bit easier, with a buffer built in. But if you fly much faster than V2 +5 (or V2 +10 in my plane), your climb is adversely affected. So V2 +5 is a reasonable compromise.
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V2 is NOT the best ange of climb speed with single engine. Its a minimum safe speed and its equivalent to 1.2 VS. Best climb speed is usually a range of speeds above V2 and thats why its recommended you fly above V2.
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V2 could be any number of things depending on the operators need. Lot of aircraft with increased V2 schedules to give better climb performance.
The + 5 or whatever it might be on your type is a usable margin for operation and certification.
The + 5 or whatever it might be on your type is a usable margin for operation and certification.
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V2 is the greater of 1.1 VMCA or 1.2 VS.
JAR 25/CS 25 states words to the effect of "Close to but not below V2" for certification. I take that to mean that if you fly just 1 knot below V2 due to turbulence or a small handling error then you are outside the certified envelope of the aircraft. If it is a VMCA limit then it can be very difficult to handle.
The UK CAA tolerance limit for an EFATO in an LPC is V2-0/+10 knots.
So for all these reasons V2+5 is the ideal place to be!
JAR 25/CS 25 states words to the effect of "Close to but not below V2" for certification. I take that to mean that if you fly just 1 knot below V2 due to turbulence or a small handling error then you are outside the certified envelope of the aircraft. If it is a VMCA limit then it can be very difficult to handle.
The UK CAA tolerance limit for an EFATO in an LPC is V2-0/+10 knots.
So for all these reasons V2+5 is the ideal place to be!
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V2 could be any number of things
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Oldflyer... I just wanted to clarify that you're quoting references for Normal, Utility, Aerobatic and Commuter category airplanes in the US and Canada. For Transport category airplanes in US and Canada the regulations are slightly different: Part V - Airworthiness Manual Chapter 525 - Transport Category Aeroplanes - Transport Canada
If you feel like reading directly from the FARs, the reference is the same except no 5 in front, ie: 25.107.
Like some others have stated, V2 is NOT the same as VYSE. The 'safety' part in 'takeoff safety speed' relates to certain criteria that has to be met for the V2 speed. It does not mean that you will have the best performance at that speed while single engine. That is what VYSE is for - or VXSE.
If you feel like reading directly from the FARs, the reference is the same except no 5 in front, ie: 25.107.
Like some others have stated, V2 is NOT the same as VYSE. The 'safety' part in 'takeoff safety speed' relates to certain criteria that has to be met for the V2 speed. It does not mean that you will have the best performance at that speed while single engine. That is what VYSE is for - or VXSE.
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As some one brought up the rule book, a quick check shows that CS 25.143 defines the manoeuvre requirement for Take off all engines operating at V2 +xx as 40° before stall warning as apposed to 30° single engine at V2.
xx is the approved all engine climb speed.
So the addition 5 knots in the OP's question is to ensure the extra manoeuvre capability requirement.
as for what V2 is:
(b) V2MIN, in terms of calibrated airspeed, may not be less than –
(1) 1·13 VSR for –
(i) Two-engined and three-engined turbo-propeller powered aeroplanes; and
(ii) Turbojet powered aeroplanes without provisions for obtaining a significant reduction in the one-engine- inoperative power-on stall speed;
(2) 1·08 VSR for –
(i) Turbo-propeller
aeroplanes with more than three engines; and
(ii) Turbojet powered aeroplanes with provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed: and
(3) 1·10 times VMC established under CS 25.149.
(c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by CS 25.121(b) but may not be less than –
(1) V2MIN;
(2) VR plus the speed increment attained
(in accordance with CS 25.111(c)(2)) before reaching a height of 11 m (35 ft) above the take- off surface; and
(3) A speed that provides the manoeuvring capability specified in CS 25.143(h).
xx is the approved all engine climb speed.
So the addition 5 knots in the OP's question is to ensure the extra manoeuvre capability requirement.
as for what V2 is:
(b) V2MIN, in terms of calibrated airspeed, may not be less than –
(1) 1·13 VSR for –
(i) Two-engined and three-engined turbo-propeller powered aeroplanes; and
(ii) Turbojet powered aeroplanes without provisions for obtaining a significant reduction in the one-engine- inoperative power-on stall speed;
(2) 1·08 VSR for –
(i) Turbo-propeller
aeroplanes with more than three engines; and
(ii) Turbojet powered aeroplanes with provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed: and
(3) 1·10 times VMC established under CS 25.149.
(c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by CS 25.121(b) but may not be less than –
(1) V2MIN;
(2) VR plus the speed increment attained
(in accordance with CS 25.111(c)(2)) before reaching a height of 11 m (35 ft) above the take- off surface; and
(3) A speed that provides the manoeuvring capability specified in CS 25.143(h).
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Relevant information is also here:
AC No: 25.1329-1B - APPROVAL OF FLIGHT GUIDANCE SYSTEMS
Pages 71- 72:
a. Takeoff Mode.
(1) Vertical Guidance. In the Takeoff mode, the vertical element of the FGS
should provide vertical guidance to acquire and maintain a safe climb out speed after
initial rotation for takeoff.
(...)
(b) Pitch Attitude and Climb Speed/Normal Operation. The vertical axis
guidance of the takeoff system during normal operation should result in the appropriate
pitch attitude and climb speed for the airplane considering the following factors:
1 (...)
2 The system should provide commands that lead the airplane to
smoothly acquire a pitch attitude that results in capture and tracking of the all–engine
takeoff climb speed, V2 (takeoff safety speed) + X. X is the all-engine speed additive
from the AFM (normally 10 knots or higher). If pitch limited conditions are encountered,
a higher climb airspeed may be used to achieve the required takeoff path without
exceeding the pitch limit.
(c) Engine–Out Operation. For engine-out operation, the system should
provide commands that lead the airplane to smoothly acquire a pitch attitude that results
in capture and tracking of the following reference speeds:
1 V2, for engine failure at or below V2. This speed should be attained
by the time the airplane has reached 35 feet altitude.
2 Airspeed at engine failure for failures between V2 and V2 + X.
3 V2 + X, for failures at or above V2 + X. Alternatively, the airspeed
at engine failure may be used, provided it has been shown that the minimum takeoff
climb gradient can still be achieved at that speed.
AC No: 25.1329-1B - APPROVAL OF FLIGHT GUIDANCE SYSTEMS
Pages 71- 72:
a. Takeoff Mode.
(1) Vertical Guidance. In the Takeoff mode, the vertical element of the FGS
should provide vertical guidance to acquire and maintain a safe climb out speed after
initial rotation for takeoff.
(...)
(b) Pitch Attitude and Climb Speed/Normal Operation. The vertical axis
guidance of the takeoff system during normal operation should result in the appropriate
pitch attitude and climb speed for the airplane considering the following factors:
1 (...)
2 The system should provide commands that lead the airplane to
smoothly acquire a pitch attitude that results in capture and tracking of the all–engine
takeoff climb speed, V2 (takeoff safety speed) + X. X is the all-engine speed additive
from the AFM (normally 10 knots or higher). If pitch limited conditions are encountered,
a higher climb airspeed may be used to achieve the required takeoff path without
exceeding the pitch limit.
(c) Engine–Out Operation. For engine-out operation, the system should
provide commands that lead the airplane to smoothly acquire a pitch attitude that results
in capture and tracking of the following reference speeds:
1 V2, for engine failure at or below V2. This speed should be attained
by the time the airplane has reached 35 feet altitude.
2 Airspeed at engine failure for failures between V2 and V2 + X.
3 V2 + X, for failures at or above V2 + X. Alternatively, the airspeed
at engine failure may be used, provided it has been shown that the minimum takeoff
climb gradient can still be achieved at that speed.
Victor B1a
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Speeds.
In the early seventies I was taught by the RAF that 5 for the wife and 5 for the kids was a good option when one had spare tarmac.
It worked 'cos i'm writing here.
It worked 'cos i'm writing here.
If climbing at V2+5 and you lose one, by the time you say WTFWT?, get the rudder in and lower the nose, you'll be back at V2.
Last edited by Capn Bloggs; 12th May 2012 at 15:38.
In the early seventies I was taught by the RAF that 5 for the wife and 5 for the kids was a good option when one had spare tarmac.
Last edited by Right Way Up; 12th May 2012 at 16:03.
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Have a good read...
Have good read of "Getting to Grips with Aircraft Performance"....an Airbus
publication.
V2 is not the best angle of climb or best rate of climb or best anything. It is the minimum speed by which the aircraft will achieve the required (by certification requirements) climb performance with one engine inoperative.
Again, have a read of the Airbus pub. It's a long explanation of things, but it
pretty much tells you anything and everything you needed and wanted to know about aircraft performance.
Fly safe,
PantLoad
publication.
V2 is not the best angle of climb or best rate of climb or best anything. It is the minimum speed by which the aircraft will achieve the required (by certification requirements) climb performance with one engine inoperative.
Again, have a read of the Airbus pub. It's a long explanation of things, but it
pretty much tells you anything and everything you needed and wanted to know about aircraft performance.
Fly safe,
PantLoad
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JJIC,
Im flying the ATR as well and was in the sim few days ago.
We bug V2 but select V2+5 in the AFCS(ADU) because in case of engine failure you gain quite a lot by flying at V2 instead of 5 knots faster. On the older versions I would say you manage 500ft/mn instead of 200-300ft/mn
Im flying the ATR as well and was in the sim few days ago.
We bug V2 but select V2+5 in the AFCS(ADU) because in case of engine failure you gain quite a lot by flying at V2 instead of 5 knots faster. On the older versions I would say you manage 500ft/mn instead of 200-300ft/mn