Comet 4 - Sextant Mount
Smiths Periscopic Sextant Mount Mk. 1F
Previous screen shots showed the periscopic sextant mount fitted in a crew escape hatch. This was only on Comet 4B/4C. The earlier Comet 4 (and earlier) had no escape hatch — the crew had to make their way out of the crew door in the forward galley. The sextant mount was attached to a bowl-shaped reinforcement in the cockpit roof, slightly on the port side of the centre line. I've improved the modelled detail of the sextant mount itself, too, and added the bowden cable, electrical cables and p-clips.
The mount functioned as an air lock. The periscope tube had two grooves which engaged in the mount, giving an upper and lower position. In the lower stand-by position, the tip of the periscope remained inside the fuselage, but provided an air-tight seal. The lever on the left could then be pulled down, opening the shutter, and the periscope could be raised into the airstream. An interlock, via a bowden cable, prevented the lever from being pulled unless the periscope was in the mount. Similarly, the periscope could not be released from the mount unless the lever was up.
I've already simulated all that on the Comet 4C, which I'll update for the Comet 4.Fig. 1: Smiths Periscopic Sextant Mount Mk.1F right rear oblique view (headlining seam is along the aircraft centre line).Fig. 2: Smiths Periscopic Sextant Mount Mk.1F left front oblique view.