V2 + 15, what is it, and what does it provide?
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V2 + 15, what is it, and what does it provide?
could anyone please tell me what the V2+15 speed is? what is so special with that speed? what does it give you?
thanks,
pt
thanks,
pt
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Maybe there's a reluctance to reply as it is so easy getting shot down here! Anyway I shall try.
V2 is the Take Off Safety Speed. When the aeroplane lifts off, it is fairly slow. Imagine an outboard (ie most unfavourable) engine failure. You counter this with opposite rudder. If you slow up, your rudder will eventually not be able to handle the asymmetric thrust, and you will unwillingly start turning towards the dead engine, and banking into it. This is the V2 speed. A speed of V2+15 gives you a margin so that should you lose an engine, you could still hold the heading- obviously the higher speed the better, but higher speed equates to less climb angle initially-at least it gives you a margin for handling an engine failure without having to push full rudder. There are other tricks you can pull at slow speed, sometimes you cannot hold a climb and the heading together,one has to go- imagine you are really heavy with an engine out. A little aileron towards the live engine side holding about 5 degrees bank away from the dead engine can give you a bit more control at very low speed with an engine out and full rudder desperately applied!.
Now watch out for me with one engine out, V2 -5, frantically pushing rudder pedal through floor, 5 degrees bank and being shot down in flames!
V2 is the Take Off Safety Speed. When the aeroplane lifts off, it is fairly slow. Imagine an outboard (ie most unfavourable) engine failure. You counter this with opposite rudder. If you slow up, your rudder will eventually not be able to handle the asymmetric thrust, and you will unwillingly start turning towards the dead engine, and banking into it. This is the V2 speed. A speed of V2+15 gives you a margin so that should you lose an engine, you could still hold the heading- obviously the higher speed the better, but higher speed equates to less climb angle initially-at least it gives you a margin for handling an engine failure without having to push full rudder. There are other tricks you can pull at slow speed, sometimes you cannot hold a climb and the heading together,one has to go- imagine you are really heavy with an engine out. A little aileron towards the live engine side holding about 5 degrees bank away from the dead engine can give you a bit more control at very low speed with an engine out and full rudder desperately applied!.
Now watch out for me with one engine out, V2 -5, frantically pushing rudder pedal through floor, 5 degrees bank and being shot down in flames!
Last edited by Rainboe; 23rd Sep 2005 at 18:37.
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V2 is the takeoff safety speed=1.2VS in takeoff config. or 1.1VMCA.
This speed is no performance speed only 20% margin to stall and 10% to VMCA.
The speed when you are unable to maintain heading is called VMCA and differs with powersetting and density altitude among other things.
Typically with V2 plus 15 you get a further margin and a speed closer to you best angle of climb.
Regards,
Bluesys....
This speed is no performance speed only 20% margin to stall and 10% to VMCA.
The speed when you are unable to maintain heading is called VMCA and differs with powersetting and density altitude among other things.
Typically with V2 plus 15 you get a further margin and a speed closer to you best angle of climb.
Regards,
Bluesys....
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'Handling the Big Jets' (or the 'Bible'). defines V2 as TOSS: "the lowest speed at which the aeroplane complies with those handling criteria associated with the climb after take-off following an engine failure." Now that doesn't in fact say an awful lot at first glance, but it does imply being able to keep in control following an engine failure. Vmca is exactly as you describe, but, it was not ever the figure you bear in mind in the event of engine failure. V2 is what you carry in your mind on take-off. So I don't disagree with you at all, but Vmca is not the whole story- it is maintaining heading control and climb and stall margin, and V2 is the more relevant figure. In accelerating to your V2 +15 speed, you flatten your climb to get a higher margin. On big Boeings, V2 is what you fly to, the flaps are retracted each stage according to the V2 baseline speed (set automatically on the FMS speed scale according to weight).
Generally V2 + 15 will give best ANGLE of climb in the take off configuration.
If you get the engine failure at V2 + 15 the advice is to maintain this speed since you get a better angle of climb. However if the engine fails before or maybe at V2 then you climb out at V2 as this is the minimum speed which gives a safe margin above the stall etc.
Hope this helps
If you get the engine failure at V2 + 15 the advice is to maintain this speed since you get a better angle of climb. However if the engine fails before or maybe at V2 then you climb out at V2 as this is the minimum speed which gives a safe margin above the stall etc.
Hope this helps
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V2
I hope i don't shoot myself in the foot, but here goes.
Quote: "V2- Take Off Safety Speed. The actual speed achieved at 35 ft above the runway surface, during takeoff with one engine inoperative."
V2 often equates to Vxse, best Angle of Climb Single Engine, but depends on the aircraft type. It is used for obstacle clearance. V2 + 15 normal equates to around Vyse, best Rate of Climb Single Engine, which is used to give a margin of safety and allow the aircraft to accelerate once obstacles are no longer an issue.
J
Quote: "V2- Take Off Safety Speed. The actual speed achieved at 35 ft above the runway surface, during takeoff with one engine inoperative."
V2 often equates to Vxse, best Angle of Climb Single Engine, but depends on the aircraft type. It is used for obstacle clearance. V2 + 15 normal equates to around Vyse, best Rate of Climb Single Engine, which is used to give a margin of safety and allow the aircraft to accelerate once obstacles are no longer an issue.
J
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Perhaps I might be permitted to put a different slant to the discussion...
(a) V2 (the basis for which will vary a little according to the certification) is the minimum speed scheduled for initial after takeoff climb having had a critical failure during the takeoff. This speed provides for WAT climb performance (or better), a modest margin above Vmca, and a modest margin above Vs. Rarely is the climb performance startling with any decent sort of RTOW.
(b) Some concerns with the takeoff might include ...
(i) the basic schedule considers a straight flight path. If the aircraft is required to turn (due obstacle avoidance in the escape path, SID, whatever) at V2, then the margins built into V2 will reduce due to the load factor increase associated with the increase in bank angle.
(ii) for a critical V2 climbing turn at 15 deg bank, this stall speed increase can be ignored .. however for larger bank angles, not so.
(iii) most operator SOPs will include a requirement to have a speed delta above V2 prior to executing a turn with bank angle above 15 deg and normally schedule some sort of data which is appropriate to the particular Type. From my observations, V2+15 often is prescribed as the minimum speed for an intentional AEO turn after takeoff to provide such a margin.
(iv) for AEO normal climb acceleration, a minimum passing target speed will be nominated for next flap selection and that may be relevant to V2+15 for a given Type.
(v) if a failure should occur shortly after takeoff, the AEO takeoff prior to failure will have seen AEO acceleration take the aircraft somewhat beyond the OEI V2 figure.
Recall that V2 is not associated with best rate of climb and that often an overspeed V2 or improved climb V2 schedule may be used to get a better climb performance. The actual speed for best OEI climb is significantly above V2 but the TODR penalties restrict the practical delta to something in the range of V2 to V2+25.
With this in mind it follows that, if the AEO takeoff has achieved V2+delta, it is better to hang onto that extra speed (and associated better performance) rather than slow back to V2 in the event of a failure (escape turn radius considerations permitting).
Although not directly related to the question, but relevant to the idea of slowing down to V2 after a failure, there was the very tragic crash (AA 191, DC-10-10, Chicago, 1979) in which an engine separation caused consequential LED damage. The damaged wing Vs was around V2+6 and the crew, in slowing towards V2 from above, found themselves in an asymmetric stall, uncommanded roll, crash scenario ... no criticism of the crew .. it was one of those days they just should not have got out of bed. However the accident does illustrate a danger of rote application of semi-automatic learned techniques.
(a) V2 (the basis for which will vary a little according to the certification) is the minimum speed scheduled for initial after takeoff climb having had a critical failure during the takeoff. This speed provides for WAT climb performance (or better), a modest margin above Vmca, and a modest margin above Vs. Rarely is the climb performance startling with any decent sort of RTOW.
(b) Some concerns with the takeoff might include ...
(i) the basic schedule considers a straight flight path. If the aircraft is required to turn (due obstacle avoidance in the escape path, SID, whatever) at V2, then the margins built into V2 will reduce due to the load factor increase associated with the increase in bank angle.
(ii) for a critical V2 climbing turn at 15 deg bank, this stall speed increase can be ignored .. however for larger bank angles, not so.
(iii) most operator SOPs will include a requirement to have a speed delta above V2 prior to executing a turn with bank angle above 15 deg and normally schedule some sort of data which is appropriate to the particular Type. From my observations, V2+15 often is prescribed as the minimum speed for an intentional AEO turn after takeoff to provide such a margin.
(iv) for AEO normal climb acceleration, a minimum passing target speed will be nominated for next flap selection and that may be relevant to V2+15 for a given Type.
(v) if a failure should occur shortly after takeoff, the AEO takeoff prior to failure will have seen AEO acceleration take the aircraft somewhat beyond the OEI V2 figure.
Recall that V2 is not associated with best rate of climb and that often an overspeed V2 or improved climb V2 schedule may be used to get a better climb performance. The actual speed for best OEI climb is significantly above V2 but the TODR penalties restrict the practical delta to something in the range of V2 to V2+25.
With this in mind it follows that, if the AEO takeoff has achieved V2+delta, it is better to hang onto that extra speed (and associated better performance) rather than slow back to V2 in the event of a failure (escape turn radius considerations permitting).
Although not directly related to the question, but relevant to the idea of slowing down to V2 after a failure, there was the very tragic crash (AA 191, DC-10-10, Chicago, 1979) in which an engine separation caused consequential LED damage. The damaged wing Vs was around V2+6 and the crew, in slowing towards V2 from above, found themselves in an asymmetric stall, uncommanded roll, crash scenario ... no criticism of the crew .. it was one of those days they just should not have got out of bed. However the accident does illustrate a danger of rote application of semi-automatic learned techniques.
Last edited by john_tullamarine; 23rd Sep 2005 at 23:14.
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stilton,
In times of old, V2 min was equal to 1.2 X Vs, somewhat below best gradient speed, and maintaining V2+10 APPROXIMATED best angle speed.
V2 min is now as low as 1.13 X Vs on newer aircraft, hence, if we wish to approximate the best angle of climb speed we'll need a little more than the earlier 10 knot additive, hence the change to the 15 knot additive.
A VERY SERIOUS CAVEAT - If the engine fails at or above V2+10 / V2+15, maintain V2+10 / V2+15 as appropriate. If the engine fails between V2 and V2+10 / V2+15, maintain the existing speed, don't accelerate. If the engine fails below V2, allow the aircraft to accelerate to V2 in the manner described in the AFM. Failure to observe any of these may result in impact with obstacles.
Regards,
Old Smokey
In times of old, V2 min was equal to 1.2 X Vs, somewhat below best gradient speed, and maintaining V2+10 APPROXIMATED best angle speed.
V2 min is now as low as 1.13 X Vs on newer aircraft, hence, if we wish to approximate the best angle of climb speed we'll need a little more than the earlier 10 knot additive, hence the change to the 15 knot additive.
A VERY SERIOUS CAVEAT - If the engine fails at or above V2+10 / V2+15, maintain V2+10 / V2+15 as appropriate. If the engine fails between V2 and V2+10 / V2+15, maintain the existing speed, don't accelerate. If the engine fails below V2, allow the aircraft to accelerate to V2 in the manner described in the AFM. Failure to observe any of these may result in impact with obstacles.
Regards,
Old Smokey
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Here's another 2 pennies...
V2+15 for a flap setting is usually very close to VREF for the next setting. I.e. V2+15 for flaps 5 is nearly the same as VREF flaps 15 (B734), which is the prescribed configuration for a single engine landing
I liked john's post, as well, since great importance to V2+15 is given for being the speed which gives you "full" 30 degrees bank load factor margin above the stall for T/O configuration. BTW, it's also the minimum speed to start raising the flaps upon acceleration.
V2+15 for a flap setting is usually very close to VREF for the next setting. I.e. V2+15 for flaps 5 is nearly the same as VREF flaps 15 (B734), which is the prescribed configuration for a single engine landing
I liked john's post, as well, since great importance to V2+15 is given for being the speed which gives you "full" 30 degrees bank load factor margin above the stall for T/O configuration. BTW, it's also the minimum speed to start raising the flaps upon acceleration.
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Depends on the aeroplane, Gufo...
Take the Lockheed TriStar as an example.
a) Min speed for 30 degree angle of bank, V2+10 in the takeoff configuration.
b) Let us suppose that, due to the field length, that a flaps 22 takeoff is required.
The AFM states...
When established in the climb, and the landing gear is retracted, select flaps 10 at V2+10.
Retract remaining flaps on schedule.
Now, to presume that a procedure on one aircraft naturally carries over to another, is many (most) times not correct.
a) Min speed for 30 degree angle of bank, V2+10 in the takeoff configuration.
b) Let us suppose that, due to the field length, that a flaps 22 takeoff is required.
The AFM states...
When established in the climb, and the landing gear is retracted, select flaps 10 at V2+10.
Retract remaining flaps on schedule.
Now, to presume that a procedure on one aircraft naturally carries over to another, is many (most) times not correct.
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Er.. can't really see the difference here.. You're stating the same I was, except the value is V2+10 instead of 15.
I put "B734" in parentheses because I supposed the values and flap settings might differ from type to type. But I reckon the concept is the same, which you've confirmed.
Cheerz
I put "B734" in parentheses because I supposed the values and flap settings might differ from type to type. But I reckon the concept is the same, which you've confirmed.
Cheerz
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On the B738, V2 is the minimum takeoff safety speed and provides at least 30° bank capability (15° + 15° overshoot) for all takeoff flaps. An airspeed bug (the white bug) is automatically set 15kts above command speed (V2). V2 +15 provides 40° bank capabilty (25° + 15° overshoot) for all takeoff flaps.
Just a bit of extra info
Just a bit of extra info
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And my two-penneth worth: V2+15 has probably been suggested as a "sensible" speed to fly following an engine failure, assuming at least this speed has been reached. It is, in many ways as much as a compromise as V2, but here's the rub. Allow the plane to decellerate to less than V2 and you'll have a real task on your hands getting the thing back to V2 in a reasonable time without undue loss of height.
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To my (very performance limited) knowledge...
For Performance A Aircraft ( for those unfamiliar, simply said your airliner)
V2= 1.2 Vs= 1.1 Vmca~(approximates) Vx
V2+15~(approximates) Vy
Where Vx is the Best ANGLE of climb
Vy is the Best RATE of climb
Vs is the Stall Speed for given flaps
Vmca is the Speed Minimum Control Ground ( min. rudder control speed)
We want to fly on jets on Vy because it gives us the least time to reach a certain altitude, thus more economical and above all, the safest thing to do in case of engine failure (think of your EFFRA, Engine Failure Flaps Retraction Altitude). If we would fly V2, this would give us a very slight margin to correct in case of engine failure, (10%),although with both engines working, V2 will protect us for all normal manoeuvres ( standard rate turns).
What Old Smokey wrote about which speeds to choose when the engine says kabooum is a very good thing by the way! thanx for that, never actually thought about it...
For Performance A Aircraft ( for those unfamiliar, simply said your airliner)
V2= 1.2 Vs= 1.1 Vmca~(approximates) Vx
V2+15~(approximates) Vy
Where Vx is the Best ANGLE of climb
Vy is the Best RATE of climb
Vs is the Stall Speed for given flaps
Vmca is the Speed Minimum Control Ground ( min. rudder control speed)
We want to fly on jets on Vy because it gives us the least time to reach a certain altitude, thus more economical and above all, the safest thing to do in case of engine failure (think of your EFFRA, Engine Failure Flaps Retraction Altitude). If we would fly V2, this would give us a very slight margin to correct in case of engine failure, (10%),although with both engines working, V2 will protect us for all normal manoeuvres ( standard rate turns).
What Old Smokey wrote about which speeds to choose when the engine says kabooum is a very good thing by the way! thanx for that, never actually thought about it...
