twistedenginestarter
I should have clarified my statement, when you are doing a Derate takeoff you still have the choice of Min V1, Bal V1, Max V1. The actual speeds are different to the maximum rated speeds.
It is possible to have all three of these at the same speed as shown below.
Min V1 = 142.3 KIAS
Max V1 = 142.3 KIAS
Bal V1 = 142.3 KIAS V1MCG = 124.6 KIAS at 15.0 DEG C
VR = 149.6 KIAS VMCA = 116.9 KIAS at 15.0 DEG C
V2 = 157.9 KIAS
VS = 133.6 KCAS
These are for a B777-200, 7000 feet runway and 239872 kgs, GE90-90B.
However, if we start dealing with a runway length of 10,000 feet and a weight of 200,000 kgs which allows us to use a 20% Derate, the figures are a lot different
The lower that you derate the engine the lower the VMCG becomes, the V2 will still remain around the same at 1.2 Vs.
Takeoff Speeds B777-200, 200,000 kgs, 10,000 feet runway.
No Derate.
Min V1 = 125.3 KIAS V1MCG = 125.3 KIAS at 15.0 DEG C
Max V1 = 134.3 KIAS
Bal V1 = 126.1 KIAS
VR = 134.3 KIAS
V2 = 145.3 KIAS
VS = 121.1 KCAS
20% Derate.
Min V1 = 113.3 KIAS V1MCG = 113.3 KIAS at 15.0 DEG
Max V1 = 137.5 KIAS
Bal V1 = 134.0 KIAS
VR = 137.5 KIAS
V2 = 143.9 KIAS
VS = 121.1 KCAS
Look at the Bal V1 in relation to V1MCG and V2.
So getting back to your original point, yes it is possible to have the Min V1 / Bal V1 / Max V1 speeds the same, either at a Maximum Rated Thrust or a Derated Thrust.
That also applies if you use a maximum assumed temperature reduction (25%) on top of the 20% Derate.
Mutt
[This message has been edited by mutt (edited 30 September 2000).]
[This message has been edited by mutt (edited 03 October 2000).]