On Fri, 13 Aug 2004 23:08:33 GMT, Guy Alcala
wrote:
Ed Rasimus wrote:
Corner velocity, by definition, is the minimum speed at which you can
generate maximum allowable G-load. So, the corner for the F-4 relates
to 7.33+ G at most weights. We usually used 420 KIAS for the F-4
hard-wing. The max G, of course, could be considerably reduced based
on stores retained--even empty fuel tanks.
For the F-105, which had a max allowable G of 8.2, the speed was
higher--generally considered around 480 KIAS. But, the fact of the
matter was that drag rose so fast at high G that you couldn't sustain
for very long--airspeed bleed off put you below corner very rapidly.
(One reason why an F-105 driver only felt comfortable in the 540-600
KIAS region!).
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).
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.
Guy
Remember that fighter pilots generally don't have time (even in
today's computer laden techno-wonder aircraft) to go through that kind
of convolution of calculations.
For example, at 400 KIAS (not KTAS) you couldn't get 8G in an F-4.
Note that all of your start numbers are offered in "true" rather than
indicated airspeed. There are other issues, such as with the hard-wing
vs soft-wing question for the F-4--you'll get different performance
between the B, C, D, S, J, K, G, and E models depending upon things
like TISEO, slotted slabs, C/G etc.
Generally, you are correct that the hard-wing finishes the turn well
behind the LES bird, but in a lot of situations the hard-wing sustains
while the LES bird experiences rapid drag rise and airspeed bleed-off.
P-sub-s advantage, as you say, usually goes to the hard-wing. The LES
bird only wins in the knife fight.
Finally, my head hurts and I don't want to open the door to the
complexities of trying to calculate comparisons between KIAS, KTAS and
mach as related to turn rate.
Basic rule (kept simple for dumb fighter drivers) is that it takes
indicated airspeed to pull G. Mach don't make turn (and for that
generation super-sonic meant an incredible loss of G potential) and
true airspeed is only valuable for getting to the bar early. Indicated
(and it's close relative calibrated) is the only knots you need to
worry about when you want to max perform.
Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
"Phantom Flights, Bangkok Nights"
Both from Smithsonian Books
***
www.thunderchief.org