Originally Posted by
walbut
Sometime in the 1980's I attended a meeting at Boscombe Down to discuss heavy weight and single engined landing limitations for the UK Phantoms. Don Headley represented the BAE test pilots and I guess there were Flight test and Aerodynamics reps from BAe as well, but I can't remember who they were. My only reason for being chosen to attend was because, at the time, I understood the flight systems and the workings of the flap and BLC system and the associated 7th/12th stage bleed. It was intended to try and test various combinations of settings to allow approaches to be flown, potentially I think, even in reheat. I remember expressing some concern about some of the tests being proposed and Don Headley put me firmly back in my Flight Systems box. He pointed out that my concerns were based on the behaviour of the Buccaneer which could really bite if you reduced blowing pressures too far and in practice, the Phantom was much more benign. The main reason for the difference was that Phantom primarily 'blew' the leading edge of the wing and if blowing pressures were reduced, and the slits became unchoked, the aircraft would pitch nose down. Buccaneer on the other hand primarily blew the trailing edge of the wing and if BLC pressures fell too low, the aircraft pitched nose up which was the last thing you needed when low and slow and close to the ground.
Walbut
I agree with Don that the Phantom was less affected by low blow pressures than the Buccaneer, but the Bucc had much more extensive BLC. The slits were all along the top of the leading edge of the wings, along the front edge of the mainplane flaps and under the leading edge of the tailplane. Even at minimum blow pressure and at datum speed the stabilised rate of descent was very high. Unblown approaches (45-10-10) were 19 KIAS faster than blown approaches with 45-25-25.