In article ,
"Graham Salt" writes:

"Peter Stickney" wrote in message
...
In article ,
(JDupre5762) writes:
I have been wondering why were so few WW2 aircraft designs "stretched"
in order
to get more performance or payload? I know of the FW 190D which was
stretched
in the aft fuselage section in order to compensate for the installation
of Jumo
V 12 engine. Could other designs have benefitted from the technique of
stretching in one way or another? Was it not done because the designs
of the
era were not suited to it? In recent years even reworked C-47s have
been
stretched. Was there simply no perceived need to stretch a design?

For "stretch" it's rather hard to beat the Spitfire. I began the war
perfoeming at same level as its main competitors, and through
continual redesign and refinement was still in peak form when the war
ended.
Of course, installed power had more than doubled, the tail was
completely new, the feselage adn wing structure was completely redone,
they reshaped teh fuselage for a bubble canopy, and made a
fighter-bomber (And Carrier-borne Fighter-Bomber to boot) out of it.
Spits stayed in RAF and RN service well after the war. Not too half
bad.

I think that transports didn't get the same treatment for a number of
reasons. Most transport types didn't have options which afforded
greatly increased power, and the load carrying performance of
airplanes at that time was limited by available power more than
anything else - you'd run out of payload weight available before you
ran out of payload volume. Getting more payload required a whole new
airplane. The C-46 was considerable bigger than the C-47 it
supplanted.

That being said, I suppose you could make a case that DOuglas did
start a program of stretching transports with the DC-4-DC-6-DC-7
line.

I had originally thought of the Spitfire as a good example of stretching
when this question first came up. However, on reflection, there was very
little airframe stretch during the service life of this type which
contributed to its ability to maintain parity in air combat. Essentially
there were two major airframe changes (Mk.VIII and F.21), and two major
engine ones (2-stage supercharging in Merlin 60's, and introduction of the
Griffon). The basic Mk.I led to the Mk.II, Mk.V, and ultimately the Mk.IX.
The Mk.IX was essentially an interim type allowing use of the series 60
Merlin engine before the definitive Merlin powered Mk.VIII was ready. With
the introduction of the Griffon engine, the definitive Spitfire was to be
the F.21 (and followed by F.22, and F.24). Again, to facilitate early
introduction of the engine upgrade, an interim model was introduced, based
on the Mk.VIII, and called the Mk.XIV.

I have to disagree, a bit. (While the basic Spitfire Shape was
retained, the Griffon engined Spits were much different,
structurally. You couldn't make a Mk IX into a Mk XII with a
conversion kit. The wing structure also evolved quite a bit, as
well. (Wasn't the Mk VIII actually based on the Mk III, which was
to be a Merlin XX powered flavor that was abandined in favor of the Mk
V when it was decided that the 2-speed Merlins were better off being
put into Hurricanes? It's Rivet Counting, I know.)


But the most significant cause of the Spitfire's extended longevity was the
remarkable work of Ernest Hive's team at Derby in forcing more and more
power from the Merlin engine, and ultimately the successful installation of
the Griffon engine. Without the engineering brilliance of Rolls Royce, the
Spitfire, as a contemporary fighter, would have become obsolescent by
1941-42.

T'warnt so mach Hives as Stanley Hooker, and his almost mystical
ability to squeeze that last bit of efficiency out of a supercharger.
Not only did he develop teh improved blowers for teh XX adn 40 series
engines, but he came up with the 2-stage blower for the 60 Series and
up, which was what transformed the Merlin from a good engine to a
classic. Two stage blowers weren't new, by any means - the U.S. was
very fond of them in the turbosupercharged R1820s and R1830s used in
the B-17 and B-24, and the V1710 installations on the P-38 and the
prototype P-39. (It was deleted from teh P-39 because there wasn't
room for both the turbosupercharger and the requisite intercoolers,
and installed drag on a tiny airframe like an Airacobra went through
the roof.) and the mechanically driven second stages of the Wildcat's
R1830 and the Hellcat & Corsair's R2800s - but they tended to be
complicated and space-intensive, with teh auxiliarry stage blower
driven at its own optimum speed by a separate drive. Hooker figured
that if he sized things just right, he could have both blowers on the
same shaft, turning at the same speed, and have them match throught th
eperformace range of the engine. And he made it work, with nothing
more than slide rules and graph paper.
Before the 2 stage Merlin appeared, The folks planning Brit War
Production were getting ready to close down Merlin production in favor
of its intended followons - the Sabre and the Vulture. (The Griffon
was another Rolls private venture) It's a good thig that didn't
happen.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster