The Merlin started out with a single-stage, single-speed supercharger. In1935 Rolls Royce took out a license on the Farman 2-speed drive. This enabled the supercharger to run at low speed, taking very little engine power to run, as well as still maximizing air supply at altitude.

Sir Stanley Hooker (a mathematician by profession) developed the supercharger even more by examining the supercharger from first principles, as well as improving the inlet air characteristics. This change was fitted to the Merlin XX.

For the high altitude bombers the engine was still not producing the required power and it was Sir Stanley Hooker who suggested putting another supercharger in series as a better alternative to switching to a turbocharger. As a result the supercharger from the Vulture was merged into the engine from the Merlin 46 onwards.    

The next group of pictures shows the donor supercharger before it was cannibalized for parts for the Merlin that was to go on show. Also shown is the state of the original one which was cleaned by the previous group that started the restoration.

The rear of the supercharger

We took these pictures so that when we had cleaned the part and painted it we would know exactly where the component went and what pipes went to it. (You can never take enough pictures, as someone once told me)

The top of the supercharger 

The right side of the supercharger

The left side of the supercharger

Tom painting the carburettor

The supercharger awaiting assembly after painting

Paul assembling the supercharger

Scott and Aaron attaching the supercharger to the engine

 Tom and Aaron attaching the carburettor to the supercharger

The supercharger mock up

This is  the supercharger, carburettor and the cooler on the engine upstairs. We called it the mock-up as we had to remove the supercharger to get the engine through the gap in the railings to take the engine downstairs to get it ready to go on show