The Nimrod Review - Official Documents

The Nimrod Review
42
Addition of SCP duct to MR2 (c. 1979)
4.4
4.5
4.6
2 When 35 of the Nimrod MR1s were upgraded to MR2s (1975-1984), they were all fi tted with a Supplementary
Conditioning Pack (SCP) to supply extra cooling air to the aircraft’s upgraded electronic equipment. The SCP
increased the mass fl ow of conditioned air to the cabin by supplementing the original two conditioning packs
located in the wings. The SCP incorporates a pre-cooler in a fairing aft of the bomb bay and a tail pack in the
APU compartment, which includes a two-stage heat exchanger and a Cold Air Unit (CAU). Space did not allow
the SCP expansion bellows to be covered by the type of shrouds used on the Cross-Feed duct and so fl exible
muffs were used instead (see further below).
To power the SCP, it was decided to off-take bleed-air from the Cross-Feed duct and run the bleed-air aft to
the tail where the SCP was located. To do this, a fi ve-way junction was fi tted to the pre-existing Cross-Feed
duct, immediately below the entrance from the bomb bay to the starboard side No. 7 Tank Dry Bay. Adjacent
to this off-take, the new SCP bleed-air duct was routed through the very lowest section of the starboard No. 7
Tank Dry Bay and then aft (see below). With the air supply to the SCP switched on, hot, high-pressure air bled
from the Cross-Feed duct fed through the SCP duct to a combined Pressure Regulating and Shut-Off Valve
(PRSOV), which reduced the extracted bleed-air from up to 280psi (the maximum working pressure of the Cross
Feed duct) to approximately 56psi (the normal operating pressure of the SCP duct) and through a fl ow-limiting
venturi to the pre-cooler. Bleed-air for the SCP was routed along the outside of the starboard fuselage from the
PRSOV to the pre-cooler and along the outside of the port fuselage from the pre-cooler to the tail pack itself. 3
4 This combined duct now to be found in MR2s is referred to collectively in this Report as the “Cross-Feed/SCP
duct” (see Figure 4.2 – a cross section shown with the bomb bay doors open).
Figure 4.2: Nimrod MR2 Cross Feed Ducts
2 The RAF took delivery of 35 upgraded MR2s between 1978 and 1984. XV230 was one of those upgraded.
3 See also BOI paragraph 38 [2-27].
4 And the BOI.
Hot air from
starboard
engines
Original Cross-Feed Duct
SCP duct
Forward
Viewing Angle