backin5,
Large aircraft performance has changed a lot over the years.
With the old 4-engine piston types, runway requirements were calculated with a 50 foot screen height, and the liftoff speed was to be no
less than V2.
In normal line flying, the aircraft was not rotated until V2 was acheived. There was no separate Vr, under CAR4b for piston types.
With most early turbopropeller types, this was also the case.
When jet transports came along, the regulations were re-written to allow for a 35 foot screen height, and due to aerodynamic design, a Vr was established, so as to reach no
less than V2 at the lowered screen height.
I can tell you from personal experience flying some of these early aircraft (especially the non-fan powered B707-321) at heavy weights, it was common practice to begin rotation at Vr
very slowly, as these aircraft did
not perform well in the climb with the normal rates of rotation used today with more modern types.
Suspect many younger guys today, if they had one of these older types strapped to their behind, at MTOW, would have eyes the size of dinner plates at the lack of acheivable climb performance...and this was with all engines operating.
Very
long takeoff runs were required, followed by a surprisingly shallow climb.
Personally believe that the lowered screen height was selected, so that these types could be certificated in the first place.
