V2 and VYSE
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V2 and VYSE
Hi, hope someone can help me clarify something im having a bit of a brain freeze about and not had much luck researching.
Assume CS23/Perf B twin piston aircraft
V2 is the take off safety speed, to be flown in the event of an engine failure.
Vyse is the single engine best rate of climb speed.
What makes V2 not equal to Vyse?
Something in the back of the mind regarding V2 taking into account take off configuration which Vyse does not. If we say that the hypothetical aircraft does not in normal operations use any flap for take off, does this then equalise the speeds (after gear retraction anyway).
Having a complete brain freeze about this at the minute and appreciate any insight!
Assume CS23/Perf B twin piston aircraft
V2 is the take off safety speed, to be flown in the event of an engine failure.
Vyse is the single engine best rate of climb speed.
What makes V2 not equal to Vyse?
Something in the back of the mind regarding V2 taking into account take off configuration which Vyse does not. If we say that the hypothetical aircraft does not in normal operations use any flap for take off, does this then equalise the speeds (after gear retraction anyway).
Having a complete brain freeze about this at the minute and appreciate any insight!
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I thought V2 applied only to Perf Class A?
Take-off safety speed for a light twin is usually called VTOSS, and is all about controllability (margin over VS and VMCA).
VYSE is of course about performance, hence has nothing to do with controllability.
Take-off safety speed for a light twin is usually called VTOSS, and is all about controllability (margin over VS and VMCA).
VYSE is of course about performance, hence has nothing to do with controllability.
I believe it is all in the terminology used in the certification process and the expected flying techniques that will be applied.
V2 is in the take-off configuration , i.e. at whatever flap has been selected and at whatever weight, there will be a V2 speed. It will obviously vary through quite a range, depending on aircraft size and flap settings available for take-off. There may even be several V2 speeds for the one weight/flap configuration - from V2 min to a V2 max for so-called 'improved climb'.
Vyse - sometimes referred to as 'blue-line' speed - is quoted as just one speed, is often not variable with weight (though it could be, but certification may only require it for the gross weight case) and assumes that the aircraft has been cleaned up to flap zero.
From a pilot's perspective, experiencing an engine failure at V1, continuing through Vr to V2 should guarantee certificated performance (assuming correct handling, properly rigged airframe etc).
Suffering an engine failure in a light twin before Vyse has been reached guarantees nothing, hence often the advice to land ahead if an engine fails before reaching blue line.
V2 is in the take-off configuration , i.e. at whatever flap has been selected and at whatever weight, there will be a V2 speed. It will obviously vary through quite a range, depending on aircraft size and flap settings available for take-off. There may even be several V2 speeds for the one weight/flap configuration - from V2 min to a V2 max for so-called 'improved climb'.
Vyse - sometimes referred to as 'blue-line' speed - is quoted as just one speed, is often not variable with weight (though it could be, but certification may only require it for the gross weight case) and assumes that the aircraft has been cleaned up to flap zero.
From a pilot's perspective, experiencing an engine failure at V1, continuing through Vr to V2 should guarantee certificated performance (assuming correct handling, properly rigged airframe etc).
Suffering an engine failure in a light twin before Vyse has been reached guarantees nothing, hence often the advice to land ahead if an engine fails before reaching blue line.
Last edited by Mach E Avelli; 28th Jul 2013 at 07:43.
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Thank you both.
Oktas8, V2 is defined in CS23;
However I have only ever heard of people referring to TOSS on light twins.
Oktas8, V2 is defined in CS23;
The take-off safety speed, V2
, in
terms of calibrated airspeed, must be selected
for the aeroplane so as to
allow the gradient of
climb required in CS 23.67 (c) (1) and (c) (2)
but must not be less than 1·10 V
MC
or less than
1·20 V
SI
.
, in
terms of calibrated airspeed, must be selected
for the aeroplane so as to
allow the gradient of
climb required in CS 23.67 (c) (1) and (c) (2)
but must not be less than 1·10 V
MC
or less than
1·20 V
SI
.
Moderator
Common point of confusion.
(a) Part 25 Types have a much higher level of redundancy that applies to Part 23 .. across the board.
(b) For Part 25, providing that
(i) the conditions pertaining on the day reasonably approximate the certification presumptions .. and
(ii) the crew performs similarly .. and
(iiI) the ops eng folk have done their work competently
it is reasonable to presume that the aircraft will survive to fly another day.
(c) For Part 23, there is a range of certification performance criteria.
However, for the typical heavier light twin operation (at limiting weights) an engine failure during takeoff presents extremely significant problems .. until the aircraft is cleaned up and at a speed at or very close to Vyse the probability that the aircraft will live to fly another day is moot. It all depends very heavily on local terrain and pilot competence once the aircraft is in a configuration at least (maybe ?) able to climb.
In the case of lighter light twins ... all bets are off ... the power of prayer is said to be an important part of the pilot's toolkit in such circumstances.
(d) It doesn't matter too much what we call things but, generally, V2 is specified for Part 25 and Vtoss or something similar for Part 23
(e) for BOTH Parts 23 and 25 Vtoss/V2 is concerned with getting a reasonable field performance (while maintaining a margin above stall and Vmc), not optimum OEI climb performance.
For BOTH, the OEI best climb gradient speed will be significantly higher than Vtoss/V2, even if overspeed V2s are scheduled. This reflects the nature of the climb characteristic which is a bit like an upturned tea cup sticking up a little bit above going down conditions ...
- Part 25 sticks up a modest amount
- heavier Part 23 sticks up a tiny amount
- lighter Part 23 should not be presumed to offer any OEI climb performance of use.
Commuter Category is an in-between mongrel (I use the term in a breeding sense) having a modest OEI climb capability.
For more details, one needs to refer to the TCDS for any given Type and then do a bunch of Sherlocking to amass the set of relevant Design Standard documentation.
Even then, one cannot guarantee that one will have the complete and correct set of data due to backroom agreements and deals between the OEM and Regulator as part of the development of the agreed frozen design standard for the project.
[Such should be reflected in the TCDS but getting the data is not always straightforward .. however the TCDS records that there was an issue with a particular requirement so one is alerted to the situation that the published rules probably have been varied to some extent.]
(a) Part 25 Types have a much higher level of redundancy that applies to Part 23 .. across the board.
(b) For Part 25, providing that
(i) the conditions pertaining on the day reasonably approximate the certification presumptions .. and
(ii) the crew performs similarly .. and
(iiI) the ops eng folk have done their work competently
it is reasonable to presume that the aircraft will survive to fly another day.
(c) For Part 23, there is a range of certification performance criteria.
However, for the typical heavier light twin operation (at limiting weights) an engine failure during takeoff presents extremely significant problems .. until the aircraft is cleaned up and at a speed at or very close to Vyse the probability that the aircraft will live to fly another day is moot. It all depends very heavily on local terrain and pilot competence once the aircraft is in a configuration at least (maybe ?) able to climb.
In the case of lighter light twins ... all bets are off ... the power of prayer is said to be an important part of the pilot's toolkit in such circumstances.
(d) It doesn't matter too much what we call things but, generally, V2 is specified for Part 25 and Vtoss or something similar for Part 23
(e) for BOTH Parts 23 and 25 Vtoss/V2 is concerned with getting a reasonable field performance (while maintaining a margin above stall and Vmc), not optimum OEI climb performance.
For BOTH, the OEI best climb gradient speed will be significantly higher than Vtoss/V2, even if overspeed V2s are scheduled. This reflects the nature of the climb characteristic which is a bit like an upturned tea cup sticking up a little bit above going down conditions ...
- Part 25 sticks up a modest amount
- heavier Part 23 sticks up a tiny amount
- lighter Part 23 should not be presumed to offer any OEI climb performance of use.
Commuter Category is an in-between mongrel (I use the term in a breeding sense) having a modest OEI climb capability.
For more details, one needs to refer to the TCDS for any given Type and then do a bunch of Sherlocking to amass the set of relevant Design Standard documentation.
Even then, one cannot guarantee that one will have the complete and correct set of data due to backroom agreements and deals between the OEM and Regulator as part of the development of the agreed frozen design standard for the project.
[Such should be reflected in the TCDS but getting the data is not always straightforward .. however the TCDS records that there was an issue with a particular requirement so one is alerted to the situation that the published rules probably have been varied to some extent.]
