Who can educate me on wet vs dry V-speeds.

[ESzczesniak 128]

There have been a couple flights recently where I've forgotten to switch the runway condition on Takeoff Page 2 in the FMC from dry to wet until after the V-speeds were calculated. This allowed me to see how they all changed when selected wet and I've noticed that all V speeds (1, R and 2) all decreased when wet is selected.Now, I understand V1 decreasing. It is going to take long to stop in wet conditions and is obvious that you would need to initiate an RTO earlier.However, I always understand VR and in particular V2 to pertain to aerodynamic properties. Principally how heavy you are (i.e. how much lift you need) and how fast you need to be going to produce said lift. I haven't been able to see how the wheel/ground interface plays in to these (particularly V2). So....Can someone explain to me why VR and V2 depend on ground conditions? Specifically to either a wet or a dry runway?Eric Szczesniak

[FLEX1978 373]

Vr and V2 shouldn't be affected, at least on other types I know.Would be interested in hearing replys.Regards

[Jovabra 18]

It' all have to do with the braking action on a wet or dry runwayGraz Jack Broens

[FLEX1978 373]

How does VR the minimum single engine climb out speed get affected by the wet stopping distance?

[ZachLW 37]

Vr and V2 shouldn't be affected, at least on other types I know.Would be interested in hearing replys.Regards

Exactly. V1 should be the only effected speed when the runway is contaminated.

[Spook 96]

It' all have to do with the braking action on a wet or dry runwayGraz Jack Broens

Or put another way :If Vr @ 15000lbs is 150knots, why would a wet runway change -Vr- to a slower speed.

[ZachLW 37]

Or put another way :If Vr @ 15000lbs is 150knots, why would a wet runway change -Vr- to a slower speed.

I guess one way to put it is to keep the same accelerate/decelerate distance. You guys keep saying Vr changes. It does not.V1 (takeoff decision speed/reject or continue speed) is the only speed that changes to allow for the decreased braking action with a contaminated runway.

[FLEX1978 373]

Well I'm surprised I never picked on this and I guess it is why I wanted to hear some replys.I just did some calculations using the A330 FCOM and it seems that VR and V2 are affected by heavily contaminated runways, standard wet gave me the same v speeds.Still don't understand how VR is affected and I have been studying this for years.It would be good to get a definitive answer. Regards

[ZachLW 37]

Well I'm surprised I never picked on this and I guess it is why I wanted to hear some replys.I just did some calculations using the A330 FCOM and it seems that VR and V2 are affected by heavily contaminated runways, standard wet gave me the same v speeds.Still don't understand how VR is affected and I have been studying this for years.It would be good to get a definitive answer.Regards

Now you've piqued my interest... I have trouble believing a contaiminated runway will have any effect what so ever on aerodynamic performance. Your instance must be a special case involving something we're not thinking of.V1/Vr are not effected in the 737NG FCOM I have here. They must be taking something into account special to the 330...

[Flamin_Squirrel 71]

V1 < Vr < V2.Also, Vr > Vmcg. Not sure if it's applicable in this case, but a potential reason.

[ZachLW 37]

V1 < Vr < V2.Also, Vr > Vmcg. Not sure if it's applicable in this case, but a potential reason.

So maybe Vmcg comes into play here? Interesting.

[FLEX1978 373]

Zach, I just checked with my old man, he has flown 737 classic, 767, a330 340 744F and now 777.The reason is due to the screen height being reduced, VR is based on single engine acceleration from v1 to VR, if v1 changes so do the other v speeds.Screen height (obstacle clearance)Is 35ft dry, 15ft wetSo in basic terms you have reached VR at a different point on the runway therefore affecting you climb and obstacle clearance speed v2To be honest I should have known this..Regards

[ZachLW 37]

Zach, I just checked with my old man, he has flown 737 classic, 767, a330 340 744F and now 777.The reason is due to the screen height being reduced, VR is based on single engine acceleration from v1 to VR, if v1 changes so do the other v speeds.Screen height (obstacle clearance)Is 35ft dry, 15ft wetSo in basic terms you have reached VR at a different point on the runway therefore affecting you climb and obstacle clearance speed v2To be honest I should have known this..Regards

That makes sense. Thanks Rob!

[Flamin_Squirrel 71]

Zach, I just checked with my old man, he has flown 737 classic, 767, a330 340 744F and now 777.The reason is due to the screen height being reduced, VR is based on single engine acceleration from v1 to VR, if v1 changes so do the other v speeds.Screen height (obstacle clearance)Is 35ft dry, 15ft wetSo in basic terms you have reached VR at a different point on the runway therefore affecting you climb and obstacle clearance speed v2To be honest I should have known this..Regards

Ahha, learn something everyday, thanks!

[G550flyer 1,010]

That 15ft wet is more of a JAA thing. We have that issue with the G550 since it's data was based on JAA certification that also includes reverse thrust in takeoff computations. So in my ops I have to verify that my takeoff ground run will ensure that I am atleast 35ft(FAA) by departure end on a wet/contaminated runway.