Peter Stickney wrote:

In article ,
Guy Alcala writes:
Peter Stickney wrote:

snip

"Quest for Performance", L.K. Loftin, NASA History Office, 1985,
available online, has a quite good explanation and analysis of the
directions that designing high performance airplanes took through the
first 80 or so years. The data tables list the following values for
the various airplanes.

Airplane: Aspect Ratio Wing Loading Cruise Speed L/Dmax
B-17G 7.58 38.7 182 12.7
B-24J 11.55 53.4 215 12.9
B-29 11.50 69.1 253 16.8

Altitudes in cases would be 25,000', (Critical Altitude for the
turbosupercharged engines, in each case) and all speeds are True
Airspeed.

Something appears seriously wrong with the B-17G cruise speed. At 25,000 feet, 182 TAS
works out to only 124 CAS, and we know the a/c normally cruised at 150-160 IAS (TAS about
215-240 at typical bombing altitudes) and climbed at about 130-140 IAS, vs. 160-180 IAS
cruise for the B-24. There's no way the position error is that high, and compressiblity
error is just 1-2% at that speed and altitude.

I just went and rechecked, and every source I have for the B-17G says
182 TAS @ 25,000, including Wagner, who gets his data from the
Aorcraft Characteristics Summaries.

From what I recall, Wagner shows the same 1,850 miles in 8.7 hours @ 25kft. for the B-17G that
Caidin gives, or an average of 212 mph. OTOH, AFAIR neither says that this was at Vbr.

My RAF Fortess II (B-17F) manual gives best cruise as 140 IAS, which
give a shade under 210 TAS at 25,000. This is backed up by the B-17F
Range Chart page that's posted on Zeno's Warbirds site.

Are we looking at the same chart?

http://www.zenoswarbirdvideos.com/Images/B-17/17TRC.gif


The G was, of
course, much dirtier, what with the chin turret, and, in the later
models, the bulged cheek gun windows & such. While 125 IAS seems a bit
on the low side, it wouldn't be impossible.

OTOH, the late Gs (maybe all? I forget) also had the fixed waist windows, partially
compensating. But they were unquestionably draggier than the Fs. Still, combat formation was
flown at 150-160 IAS in the G (the a/c on the inside of the turn might get down to 135-140).
And watching the B-17 Flight Operations video, it's stated that best range speed, at least at
10,000 feet on 91 octane fuel, is 150 IAS. A puzzlement. I can see them wanting to fly well
above stall and maybe somewhat above best range speed to allow for bumpy air in formation, but
the same video says to climb at 135 IAS, or 160 IAS when IFR. These are for the F model, so
maybe the G really is much less. But they flew them in combat at 150-160, as with the Fs. The
B-24 speeds seem a bit low as well, but a lot closer to actual combat usage.

Guy