Knees up Mother Brown!

The Spitfire Chassis Control had, other than the name suggests, very little to do with it’s suspension. Instead it refers to the mechanism that activated the undercarriage. Perhaps the name was meant to convey its complexity, because complex it certainly is!

It is an array of hydraulic valves, pulleys and chains, which if by some stroke of dextrous genius the hapless pilot got right, would go clunking, whirring and rattling into place. Get it wrong and you would end up with a half retraction.

The manual describes the action required thus:

13. Undercarriage control.—The undercarriage selector lever (52) moves in a gated quadrant on the right-hand side of the cockpit. To raise the undercarriage the lever must be moved downwards and inwards to disengage it from the gate, and then moved forward smartly in one movement to the full extent of the quadrant.

When the undercarriage is locked up the lever will automatically spring into the forward gate.

Warning.—The lever must never be moved into either gate by hand as this will cut off the hydraulic pressure.

To lower the undercarriage the lever must be held forward for about two seconds, then pulled back in one movement to the full extent of the quadrant. When the undercarriage is locked down the lever will spring into the rear gate. An indicator in the quadrant shows DOWN, IDLE or UP depending on the position of the hydraulic valve. UP and DOWN should show only during the corresponding operation of the undercarriage and IDLE when the lever is in either gate. If, when the engine is not running, the indicator shows DOWN, it should return to IDLE when the engine is started; if it does not, probable failure of the hydraulic pump is indicated.

Our own design, which is progressing well, duplicates this action without the benefit of the hydraulics. We rely instead on a basic scissor spring action. It is set when the lever is moved downwards and inwards with a trigger plate. To move the lever inwards another spring (spring 2) needs to be compressed, as per the original mechanism. The lever is moved smartly forward, all in one movement, and then held in the foremost position for 8 seconds, the time in which the gear retracts. The lever is then released, causing it to snap outwards still under tension from spring 2. This activates the trigger release of spring 1 which snaps it back into the gate.

Quite simple. Heh heh…

You may of course elect to forego all that and do the build without the internals, having it operate simply as an up/down mechanism. But then, where’s the fun in that!

Chassis Control Progress

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