In article ,
"Graham Salt" writes:

"Peter Stickney" wrote in message
...
In article ,
"Graham Salt" writes:

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.)


Not sure what structural difference you are referring to, other than the
provision of a different engine. I disagree with your comments about the
Mk.XII. These were taken off the existing production lines, originally being
built as Mk.V / Mk.IX, and later as Mk.VIII airframes. Apart from
replacement of the tubular engine mounts with a girder mount to support the
new powerplant, there was no other change. The early Mk.XII's had fixed
tailwheels, the later ones retractable, indicating the airframes' original
provenance.This was of course a factory conversion, not a field one, but
nonetheless a simply solution to getting Griffon powered aircraft into the
line quickly. The Mk.XII was the only type to employ the single stage blower
Griffon.

Steel Longerons vs. Duralumin, for teh most part. That may sound
trivial, but it wasn't. (Among other things, the longerons had to be
hand-hammered into shape. This wasn't a big deal with the Dural
parts, but bashing the steel into shape was a wholly different matter.


With regard to wing structure evolution, this did not really occur until the
F.21 / 22 / 24 series.

The Mk.VIII was a consolidation of the improvements that were put into the
specialised Mk.VII high altitude fighter, although the pressurised cabin of
the latter was not required or retained.

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.

--

I know much credit has been given to Hooker for his work on supercharging
the Merlin, and this needs to be recognised. However, the point that I
wanted to make was that the Rolls Royce team under Hives was something
special, and so was his leadership. It wasn't just Hooker, but Cyril Lovesey
who also worked on supercharging. Hooker was an academic mathematician, and
what he did was remarkable. By his own admission, he was not an engineer
(see his biography "Not Much of an Engineer"), but Lovesey and Rubbra (who
managed the Merlin within Rolls Royce) were, and all formed an incredible
team, without which the Merlin as a power plant for contemporary fighters
was age limited.

No, it certainly wasn't just Hooker. And it wasn't strictly Rolls,
either. Many of the 60 series and later improvements came from
Packard, as well. There's plenty of credit to go around.

Hives deserves a tremendous amount of credit for his vision, and his
willingness to pursue officially unpopular directions. Hives was
willing to back the 2-stage Merlin, and adandon the Vulture. (One
wonders if he subscribed to the "Every ohter Rolls engine is good"
conundrum) and push the Griffon as well. Given the travails of the
Napier Sabre, that was wisdom indeed. (If it were a Curtiss-Wright
Vulture, they'd have stuck to it through the entire war.)
Hives was also the guy who got Rolls into the jet engine business, and
Rover out. This was vital to British jet development. The
Rover-Power Jets feuds had cost more than half a year in engine
development and production.

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