In article , Guy Alcala
writes
Alan Minyard wrote:

On Tue, 9 Sep 2003 15:13:14 +0100, Dave Eadsforth
wrote:

In article , John Halliwell
writes
In article , Geoffrey Sinclair
writes
Apparently the outboard sections of the wing were watertight.
Interestingly
the Stirling's wing area was 1,460 square feet, Lancaster 1,297, later
Halifaxes 1,275, B-17 1,420, B-24 1,048 and B-29 1,736.

I'm not disputing the figures above, but I thought the B-24 had a larger
wing area than most contemporary bombers allowing it to fly higher?

Was it not the thick section Davis wing that gave it the improved lift?

Cheers,

Dave

The Davis wing was a high aspect ratio wing with a low angle of
attack.

I'll step with some trepidation into Pete's territory here as he explains this
stuff far better than I do, but we've been keeping him busy doing calcs. The
high
aspect ratio wing provides good L/D ratios, increasing range performance as
well
as
lift at low angles of attack. Here's how the a/c's aspect ratios stack up,
from
low to high:

Stirling 6.72:1;. B-17, 7.58:1; Halifax (early) 7.81:1; Lancaster 8.02:1;
Halifax
(late) 8.51:1; B-24, 11.55:1; B-29, 11.48:1.

As you can see, the B-24, designed a couple of years later than the British
heavies
and five years or so after the B-17, has a much higher aspect ratio wing, and
the
B-29 follows this practice. The wing area of the B-24 was considerably lower
than
the others, for low drag. Good altitude performance requires some combination
of
low wing-loading (high wing area for weight), engine thrust, and aspect ratio.

While the B-24 had good engine power at altitude and a high aspect ratio, it
also
had high wing-loading compared to its contemporaries (not the B-29). It had
better
altitude performance than the British a/c because of its engine supercharging,
not
its wings. The B-17, with similar supercharging as the B-24 had a higher
combat
and service ceiling, because although it had a moderate aspect ratio wing it
also
had far lower wing-loading, and was able to fly slower. The B-24 cruised
between
10-20 mph IAS faster than the B-17, but then it had to to be comfortable. The
crews hated having to fly in company with B-17s.

It's also easier to make lower aspect ratio wings of the same area stronger for
the
same weight, because the stresses can be spread over a longer (and thicker)
root,
which is one reason why a/c like the Stirling and B-17 have reputations for
being
able to take lots of wing damage and survive, and why a/c like the B-24 had
opposite reps. However, the lower aspect ratio wing requires more area to get
the
same lift at the same AoA, increasing drag.

Guy


Agree with all of the above analysis - and thanks for the useful summary
of aspect ratios; both the B-24 and the B-29 must have glided well...

To enlarge on my 'thick wing section' description, and working from
memory of a book read long ago (which can be fatal), I recall that Davis
conceived of a wing section that was based on a mathematically deformed
circle, which he believed would give a more laminar flow. The thicker,
'teardrop-shaped' aerofoil section that resulted was also very useful
structurally, given that he wanted to combine it with a high aspect
ratio wing.

Of course, any wing section inboard of the engines was going to have its
airflow messed up considerably by a few minor essentials; like engine
nacelles and de-icing boots etc etc, but the wing outboard of the
engines may have performed as Davis believed it should during cruise.

True that the high aspect ratio conferred most of the advantages of L/D
ratio, but perhaps Davis's ideas on the wing section itself should not
be forgotten.

Cheers,

Dave

--
Dave Eadsforth