Vref = vs0 x1.3 vs vsr0 x 1.23

[buzzc152]

Hi all

As I understand it most modern large aeroplane (Cs25) vref is derived from 1.23 x a stall reference which is a little different from the old method of 1.3 vs0.

Perhaps someone can correct me if I'm wrong here but vsr0 is the fastest speed attained during testing at which a part of the wing starts to stall, corrected to 1g whilst vs0 is the slowest speed and will be below 1g.

Can soneone confirm if that's correct and maybe explain it all a bit more fully or even point me to a reference ? (I couldn't find it in CS25 certification specs). How long ago did this change take place ?

Many thanks.

[HazelNuts39]

buzz,

it is mostly correct, except where you write " t vsr0 is the fastest speed attained during testing at which a part of the wing starts to stall, corrected to 1g". Vsr0 is actually the slowest speed at which the airplane can attain 1g, i.e. have a lift equal to its weight at zero thrust and forward c.g.

[keith williams]

I don’t know about the FAA world, but in the JAA world it became an issue for ATPL/CPL examination purposes in about 2001/2002.

Prior to the introduction of Vsr the old Vs was actually defined as 94% of what common sense would tell us was the stalling speed. There is a thread somewhere in this forum discussing the subject.

Vsr was introduced to overcome some ambiguity regarding when exactly the stall warning system and stick pusher would activate. In effect the introduction of Vsr increased the stall speed from 94% to 100% of the minimum speed at which the wings began to stall in 1g flight.

Under the old system Vref was defined as 1.3 Vso. To avoid actually changing any of the speeds that were used in flight, the 1.3 was reduced to 1.23 to compensate for the increase from 94% to 100%.

So we have 1.3 x 94% = (approximately) 1.23 x 100%

The introduction of Vsr also changed many of the other numbers that students are required to remember (V2min etc).