wet correction

[westinghouse]

hi,

forgive me if this question has been asked before. im quite new to this forum.

for a wet runway we make corrections for v1/vR/V2.
is there any reason why we make the correction for V2?
after all at v2 we are airborne.

thanx

[Pugilistic Animus]

since V2 is a function of Vso or Vmc or as Mad Flight Scientist previously elucidated Vsro it can simplyb be said that....

Vr = the speed that allows V2 to be reached where appropriate [at the screen height].

therefore the Vr/V2 ratio becomes a composite function that has to remain tied together. v1 of course varies ASD

[leonel fonseca]

Aircraft performance may deteriorate significantly on contamined runway.reductions in runway/obstacle limited takeoff weight and revised takeoff speeds are necessary and performance is based on reversers operating and a 15ft.screen height at the end of the runway


rgds

[Old Smokey]

On the surface of it, V2 shouldn't change at all, but it does for some aircraft. Knowing which aircraft type that you fly would help a lot.

As Pugilistic Animus has pointed out correctly, the V1/Vr/V2 relationship should be preserved to ensure reaching the end of the TODA at screen height, correct, but, the rules have changed, no longer does the required relationship stand, as the normal V1/Vr/V2 relationship pertains to a 35 ft screen height, and not the less demanding 15 ft for Wet runway calculations. A new set of relationships come into play.

As the whole object of the Wet Runway exercise is to minimise V1 as far as possible (to ensure stopping in the degraded wet runway braking action), it stands to reason that we should reduce V2 as far as possible, V2 min is desirable, i.e. 1.2 Vs on older aircraft, and 1.13 Vs on newer aircraft. This V1/V2 Delta must be reduced as far as possible to ensure that the portion of the takeoff between the lower V1 and V2 is contained within the TODA.

Now, the importance of which aircraft type, or at least the operating policy of the operator, i.e. the performance schedule chosen from the manufacturer's options for standard (Dry Runway) operations.

Some aircraft operate with V2 min as standard, and keep the "Increased Speeds" or "Overspeed" V2 for special operations when Climb or Obstacle limited. The B777 is one such aircraft (as operated by yours truly). In this case, there will be no reduction in V2 evident from Wet Runway data.

Some aircraft operate with "Increased Speeds" V2 as standard, keeping V2 min in reserve for limiting runway lengths, or....wait for it.....Wet Runway operations. The DC9 (and possibly it's descendants) is one such aircraft. In this case, a reduced V2 will be evident when using Wet Runway data.

So, what is the aircraft type that you allude to?, and what is the "standard" speed schedule chosen for normal day to day operations, V2 min or "Increased Speeds" V2?

Regards,

Old Smokey

[Pugilistic Animus]

Old Smokey, thanks for the course correction. i'm glad the rules have changed, very fascinating indeed.