Re: Some Turbofan Questions

From:         GWilson404@aol.com
Date:         18 Aug 96 20:13:38 
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>>>I'm not sure about the Comet 4; they may have had Conways.
>>>
>>>No, they had Avons as well. Mk 117 (7,300lb st) for the series 2 Comets,
>>>Mark 502 (10,000lb st) for series 3 and Mark 524 (10,500lb st) for
>>>series 4. (I did check this time!)
>
>>My 1989 issue of "Jane's World Aircraft" lists the Nimrod (military
>>development of the Comet) as having Spey engines. Were the Nimrods
>>built with Speys, or was this a re-engining operation?

The Nimrod R1 and MR2 are equipped with the Spey 251 and 250 respectively.
These are the same actual engine and rated at 12000 lb (approx). The
different Mark number for the two engines stems from the need to manage the
engine maintenance. The R1 is a high altitude recce aircraft whereas the MR2
is an over the sea patrol aircraft. The inspection/overhaul period for the
250 engine modules is much lower due to the corrosive environment. It is
permissible to mix the modules from 250 and 251 in a rebuild, but once used
in a 250 the inspection/overhaul rules for the 250 must be applied even if
rebuilt into  a 251. So its preferable not to mix them.

All current Nimrods use the Spey 250/251 and were built that way.. Only one
Nimrod has flown with a different engine, and that is the avionic prototype
XV147 which was a converted Comet IV and retained its Avon Engines. This
airframe is currently at British Aerospace Warton and being used for cabin
and flight deck mockups for NIMROD 2000, coming into service in 2001. This
new Nimrod will be powered by a marinised variant of the BMW Rolls-Royce
BR710.

One Nimrod MR1 was re-engined and that was the aerodynamic prototype XV148
which was also converted from a Comet IV. All production Nimrods were new
build,

>The Nimrod, whilst based on the Comet is actually quite a bit bigger.
>It's certainly longer and also has a double-bubble fuselage, whilst
>the Comets' all had an oval one.  Apart from the need for a more modern
>power plant, the Nimrods also probably needed more power.

The fuselage length of the Nimrod is the same as the Comet IV. The circular
cross section fuselage had an unpressurised "pannier" grafted onto it to
contain a bomb bay and this gives it a double bubble cross section from the
outside. The higher MTOW demands higher  thrust engines.

Gerald Wilson