JT,
My question,
We currently operate a large trijet on ad hoc charter , this means often positioning empty . Short legs with very low weight take offs. The aeroplane goes like a screeming banshee when empty and the only way to keep thing sensible is to use a big de-rate.
However the MTOW tables we use for calcs although very good for NORMAL weights leave us with some odd speeds when very light.
e.g. xxx r/w 03 10000`+ ATOW 120tonnes
max derate uses an assumed temp of +54 and gives a max to of 209tonnes and the v speeds for this weight. We use these speeds but although they are safe, leave the aircraft on the runway for much longer than it should be.
The alternative is to use the speeds from our weight/flap tables for vr and v2 and as the vr speed is always less than v1 from the MTOW table, use v1/vr unity.
We do not use this method currently but are disscusing its merits as the aircraft is realy keen to fly 20 kts below the v1s we currently use.
This threatd has highlighted another consideration as the low weight vr speeds are always vmcg limited and the v2 speeds are often min v2 .
Any thoughts?