Fighter Top speed timeline

vanir said:

you're wrong.

do me a favour, check the altitudes on the Vmo of the lighter/heavier Spits, you'll find a disparity

altitude, not Vmax is affected. if you wanted to keep the same altitude...


edit. and fyi peoples, Vmax is on the airframe, not the condition.

Click to expand...

Forget about the comparisons of lighter versus heavier spits. Stick with 'same aircraft - different weight as only variable).

Dave is corect. For constant power and altitude, If you add weight to your airframe you have to adjust the attitude of the wing relative to free airsteam (increase relative AoA) to slightly increase the Cl (provide enough incremental lift to offset the incremental weight) to maintain same altitude with same power settings - or increase speed at the same AoA by virtue of increased power.

As Dave noted - at top design speed for max power, there is no more incremental power available to overcome the additional extra weight.

There will be a slight increase in Induced Drag as a result of the increased Cl. There will also be an increase in Parasite drag unless the aircraft wing incidence and optimal trim drag were optimal for that specific Gross weight - and most aircraft were not initially designed for maximum gross weight.

Net - add weight -----> increase drag, increase fuel consumption, slight decrease in top velocity attainable due to the increased drag...and a lower ceiling - all else being equal.

Forgot to mention the fact that if you are operating at ceiling for a design gross weight - then add weight - the incremental AoA to compensate will result in a stall at a lower altitude than the lighter version's ceiling.