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148. Fuel Fitting Fitting

19/12/2014

I’ve been puzzling over how to fit the fuel system into the aircraft for a week or so.

The only drawings we have are for the Gnôme engine installation, and the carburetion seems to have been significantly different. The throttle lever was fitted on the right hand side of the cockpit above the top longitudinal, so that the lever would have stuck out above the cockpit coaming. The mixture was operated by a knob which you twisted underneath the instrument panel, also on the right hand side.

It’s conventional to fit the engine controls on the left side, since most people are right handed and would prefer to have the control column in their right hand. It’s possible that’s how the Gnôme installation worked on the Scout, since the cockpit is so tiny that it was probably easier to reach across with your left hand to reach the controls!

But the throttle lever operated a Bowden wire, and it didn’t seem to be compatible with the bloc-tube (carburettor) for the le Rhône engine which is a reasonably stiff sliding motion. All the other le Rhône installations we’ve seen use standard parts made by Tampier, including the levers and mixture valve as well as the bloc-tube, and we’ve decided to go with these in order to make things as simple as possible when it comes to flying it. It also means putting them on the left side, since they can’t easily be handed, and this will be in line with all the other installations, making it easier to transition from one type to another.

The controls are operated by pushrod, rather than cable, and we need to make sure there’s a sensible run for them, clear of feet and so on.

Initial throttle linkage showing the levers low down in the cockpit , the mixture valve mounted on the rear engine mount, and the bellcrank just above it.

Initial throttle linkage showing the levers low down in the cockpit , the mixture valve mounted on the rear engine mount, and the bellcrank just above it.

The first lash-up looked like this, with the mixture valve mounted on the rear engine mount on the left side, where it would be accessible from the inspection panel. The inlet would run just outside the line of the fuselage frame (but inside the side shield), and the outlet would run straight through to the bloc-tube inlet. One downside was that the pushrod would be contacted by the pilot’s left foot.

The throttle lever bellcrank is mounted just above it. This photo shows the pushrod runs, which looked to be reasonably clear of the pilot’s feet. There was one major flaw in this arrangement, however; the throttle was operating the wrong way round!

This wasn’t a major problem, however, as we found it wouldn’t be too much of a problem to raise the bellcrank up to the top of the opening in the engine mount and move the pivot inboard. This kept the pushrod well above the toes of the pilot and was a pretty simple and solid mount.

But we weren’t happy about the mixture valve, and on a trip to the Shuttleworth Collection it was apparent that their Sopwith Camel had the mixture valve mounted aft of the levers, which would mean that there were no pushrods in the way of the pilot’s feet.

New location for the mixture valve

New location for the mixture valve

And we’ve come up with this location, which has the benefit of being reasonably easy to mount and a sensible run for the pushrod. There’s a strainer in the top, and this location makes it reasonably accessible from the cockpit too. The bits are on order, and we’ll be looking to get it installed – along with the oil pipework – in the first couple of weeks of 2015…

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