F104- Boundary Layer Control

"Steve Mellenthin" wrote in message
...
The F-105 did not have BLC. The F-4 did, prior to the soft wing, for
both leading and trailing edge flaps. I don't recall any landing check
of engine indication for BLC proper operation. The BLC was checked by
the crewchief during preflight when flaps were lowered by his simply
running a hand along the area to feel the blowing. There was a warning
circuit for BLC duct pressure that illuminated a caution light on the
telelight panel in the event of a line rupture. That was very serious
emergency as the superheated air would quickly lead to structural
damage to the wing.

In later years some portion of the BLC was eliminated, but I don't
recall which parts. Maybe someone with some soft-wing experience can
recall.


Ed Rasimus

The BLC on the F-4 drew air from the 13th stage compressor. I seem to
recall
from my days as a propulsion engineer that the EGT rise for the BLC valve
open
was no more than 15 degrees. The valve istelf was connected to the flap
linkage When the flaps were lowered, a rod connected to flap structure
pulled
the BLC valve open. The circuitry that Ed refers to was on that linkage
iself.
When the flaps were down and the wheels were up the "Wheels" light
flashed
theoretically telling you to put your wheels down if you were going to fly
with
flaps down. If you had both wheels and flaps up, that supposedly meant
you had
a BLC valve stuck open and the possibility that Ed refered to, hot air
being
pumped to the flaps, existed and you needed to get the plane on the
gropund
ASAP as serious damage to things like hydraulic lines and electrcal
connections
would happen soon.

I saw one F-4D that had an actual BLC failure. The leading edge was
seriously
warped and the crew was luck to get the plane on the ground.

Most of the time the "Flashing Wheels Light" was a switch problem and was
a
real maintenance problem and a high manhour driver not to mention a strain
on
the runway rescue crews.

The BLC system was eventually capped off at the valve port on the engine
and
the planes flew without it. Made landinf speeds 10-15 knots higher, no
big
deal in the F-4.

In the early days of the F-4 in Europe, the F-4s sometimes refueled from
AFR
recip/jet KC-97 aircraft at 220 kts or so and half flaps. Never had the
opportunity to do but that flasing lights in the cockpit would have driven
me
nuts.

Steve

Excellent and informative answers guys, couldn't ask for more.

Thanks.

Scet