View Single Post
  #9  
Old August 14th 04, 01:28 PM
John Carrier
external usenet poster
 
Posts: n/a
Default

Generally, the sustained turn rate was around 14-15 degrees/second for
the F-4 hard-wing and about 12.5-13.5 for the F-105.


H'mm, those numbers seem kind of high for both, as far as sustained

capability
goes.

400 KTAS, turn rate in Deg./sec. (rounded off) = 19 (7g); 22 (8g).

500KTAS, turn rate in Deg./sec. (rounded off) = 15 (7g); 17 (8g); 20 (9g).

600KTAS, turn rate in Deg./sec. (rounded off) = 13(7g); 14 (8g); 16 (9g).


I'm missing something here. You say the numbers are high and then offer
higher numbers. Or are these just basic computations of turn rates w/o
regard to airframe factors?

Our thread has digressed slightly as we shifted the discussion from
instantaneous turn to sustained turn. The former is reached at the upper
left corner of the Vn diagram (curiously referred to as corner speed). The
latter is achieved at zero PsubS, typically at higher KIAS and influenced by
induced drag and (usually) transonic drag. To my knowledge no aircraft can
sustain a turn at corner speed at typical combat altitudes (but get a clean
F-16 low enough, hmm).

One source (Richardson/Spick) gives steady state turn radii and time to

make a
180 for the slat-wing and hard-wing, @ M0.6 and 0.9, 10kft. The slat-wing

has
the advantage, making a 180 in 15.53 sec. @ M0.6 (11.59 deg./sec.), and

13.96
sec. @ M0.9 (12.89 deg./sec.). The hard wing appears to be perhaps 10-20

deg.
or so behind. Assuming ISA, @10kft, Mach 1.0 is 638 knots. M0.6 and M0.9

= 383
and 574 KTAS respectively, so M0.6 is well under F-4 (hard) corner, M0.9 a

bit
over at that height -- assuming KIAS = KCAS, 420 KCAS = 490 KTAS @10kft.

OTOH
the Thuds 480 KCAS corner is slightly under M0.9; ca. 558 KTAS.

FWIW, the same source has a graph comparing the hard and slat-winged F-4's

Ps
capability @ M0.9 and10kft. The hard-wing has a Ps advantage at low g

(4.5g),
with the slat-wing advantaged at higher g, although the slats apparently

have a
lower max. g limit, +7 vs. +7.33g.


I had the opportunity to fly against both hard and soft wing F-4's as an
adversary on many occasions. The dynamics of ACM don't allow such fine
measurements. Subjectively, the slat generated significantly better turn
rates at the expense of energy addition rate and vertical performance.
IIRC, the VX-4 brief advertised around the order of 2 degrees/sec advantage
for the slat sustained and a 50 knot reduction in corner speed. One thing
stood out, it's buffet-free performance didn't give the pilot many cues as
to where his airspeed was headed ... easy to decell to a point where the
energy package was zip-point.

R / John