CS-25 V2min definition.

[FE Hoppy]

From CS-25:

(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 powered 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.

Does anyone have an example of a turbojet powered aeroplane with provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed?

If so, how does it do it?

[Keith.Williams.]

This was the subject of quite a bit of debate among the FTOs and CAA Examiners a few years ago.

When I asked the CAA Examiners the specific question " What does provisions for obtaining a significant reduction in the one-engine inoperative power-on stall speed actually mean?" their answer was ermmmmmmm................

[FE Hoppy]

We came to the same conclusion

[212man]

Antonov-74?

[Keith.Williams.]

212man

The crux of the matter is what constitutes a means of reducing ONE ENGINE INOPERATIVE stall speed.

Every large transport aeroplane that I can think of has flaps (and often slats) which reduce the stall speed. But this benefit is not limited to the ONE ENGINE INOPERATIVE situation.

If the regulation simply meant flaps and slats then which aeroplane would the higher 1.13 Vs limit apply to?

I am not very familiar with the Antonov 74. Does it have some kind of extra system which is intended specifically for the ONE ENGINE INOPERATIVE situation?

[212man]

Thanks Keith - yes I was aware it referred to the OEI case I'm not sure how the AN-74/72 series actually control the use of the coanda effect, but they use it (high wing with 'huge' over wing engines.) Whether it is permanent, or uses some form of nozel control, would be at the crux of this question, and indeed it may be a red herring (hence my use of ?)

[Mad (Flt) Scientist]

That wording is ancient - well, back to 1964 at least, the original FAR25 issue text.. The CAR4b text on the FAA website does NOT include equivalent wording, so it seems to originate about the time the FARs were first introduced.

certainly rules out the An74 though. I wonder if it's some kind of boundary layer blowing idea (such as Buccaneer or A-6) since that was in vogue briefly...

[212man]

This is what AC-25 7A says, and it supports the ideas that I and Mad Scientist put forward - I initially thought of the Buccaneer too, but couldn't think of any civil types that used boundary layer blowing. As you say, perhaps it was imagined it would come into vogue!

1.2 times VS for two-engine and three-engine turbopropeller and reciprocating engine-powered airplanes and for all turbojet airplanes that do not have provisions for obtaining significant reduction in the one-engine inoperative power-on stalling speed (i.e., boundary layer control, blown flaps,
etc.).

[FE Hoppy]

Cheers chaps. I was thinking about blown flaps and various config changes but couldn't imagine why you would do it after and engine failure when you've just lost half the donks rahther than all the time.

I also remember an old thread where the change in pitch attitude was used as an example but I remain a little sceptical about the maths.

[Mad (Flt) Scientist]

I think the assumption is that the blowing or whatever is on all the time; the "reduction" isn't between AEO power-on stall speed and OEI stall speed - it's between the power-off stall speed and the OEI power-on stall speed. The wording is a bit vague but I guess it's not been "tested" since we can't think of any examples which actually might have used that clause.