Warbirds in my Workshop

David Glen BSc (Hons) MSc, Model Maker, Journalist and Author

Formerly Spitfire in my Workshop

Pneumatics 2: some ancillaries

Tuesday, 22nd July, 2014

The arrangement of the pneumatic system varies in the Mk IX, dependent not least on the location of the air tanks. While relatively complex, much of it is hidden from view so can be ignored in a model. However, for my version I needed to include in the space behind frame 11 a significant cluster of pneumatic fittings and associated air-lines and T-unions, including the cup-shaped air filter and cube-like pressure maintaining valve, both of which are visible in the belly beneath the compressed air bottles. From my limited references, the arrangement of the remaining ancillaries is less clear. The partly visible magnetic and pressure reducing valves are bolted to a flanged mounting plate strapped to the back of frame 11. I took great pains to scale the plate from photographs, only to discover afterwards that I had a GA drawing showing not only the piece itself, but its full complement of kit. This is not the first time that this has happened, and it serves to illustrate the futility of accumulating reference material if it is not sorted and managed efficiently!  

Further forward, the big cylindrical flap operating ram is located on the port side close to the fuselage floor between frames nine and 10. Being just visible with the pilot’s seat in position, I included it – albeit as an afterthought – although I omitted its two flexible air hoses and their respective pressure inlets since these are arrayed on the inboard side and totally hidden beneath the seat. The ram casing was simple to turn in the lathe but the assembly was difficult to install, not least because the elevator control cables are in the way. At the forward end the stainless steel ram locates into the fork-end of a lever on the flap actuating shaft (installed last year). The other end bolts via a universal coupling to a heavy-duty bracket on the bottom of frame 10, and this is where the difficulty lay. I got there in the end, but not without a full day’s work, which included some significant ‘fudging’ and self-recrimination over the need to do things in a more considered sequence.

Back to Spitfire Mk IX Diary

The air filter ready to install and the Supermarine drawing from which it was made.
I have identified this as the pressure maintaining valve, although I hope someone will correct me if I am wrong. It is turned and milled from aluminium bar with brass and steel detail.
The installed parts and their pipe runs. The latter are made from various gauges of copper wire and the T-unions are turned from brass hexagon.
The mounting plate on the back of frame 11 is just visible.
The radiator door operating ram. What should be a universal coupling at the rear end is much simplified from the original, and the short length of aluminium tube is there only as a locating and attachment peg. It is completely hidden on installation.
Despite the compromises, the ram looks the part. It's a pity it will be barely visible when the pilot's seat is in position.
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