Merlin 61 Engine Details Revealed

London (Special cable to Aviation) — Details just revealed by the British Ministry of Aircraft Production show that the new Rolls-Royce Merlin 61 engine gives the new Spitfire which it powers considerably increased performance with little additional weight and a minimum of design changes in the airframe.

One of the outstanding features is the 2-stage supercharger which is, in effect, two superchargers in series. The two supercharger rotors are located on a common shaft, driven by the standard Rolls-Royce 2-speed rotor gearing. Fuel mixture is drawn from the carburetor and compressed by the first stage supercharger, then delivered to the second stage and finally to the induction manifold, the charge being delivered at 6-lb atmospheric pressure at 40,000 ft.

The supercharger system is fitted with a box structure, liquid-cooled intercooler located in the induction system, the fuel charge being passed through the matrix of the intercooler and its temperature reduced to normal. A separate water jacket, located between the first and second supercharge stages, also helps reduce the temperature of the fuel charge. Intercooler and jacket are independent of the engine coolant system, the intercooler being mounted under the wing in a duct which also houses one main engine radiator.

While the power of the new engine is not given, it is understood to show a sizable increase over the Merlin 20, which develops 1,260 hp at 12,250 ft.

A twelve-cylinder Vee engine, the new 61 weighs 1,640 lb, has a bore of 5.4", stroke of 6", and displacement of 1,647 cu in.

Its installation in the new Spitfire makes the plane slightly longer than previous models. There is a slightly different shape of wing and a four-bladed, full feathering propeller is employed. However, the new Spitfire greatly resembles predecessor models in appearance, except for dual radiators — made necessary by the supercharging system — fitted one under each wing.

Armament consists of two cannon and four machine guns.

This news clip was first printed in the "Aviation News" column of the January, 1943, issue of Aviation magazine, vol 42, no 1, p 278.

Note: The Spitfire Mark referred to above is probably the Mk VII.
Performance of the Merlin 61 is listed as 1565 hp at 3000 rpm at 12,250 ft; 1390 hp at 3000 rpm at 23,500 ft. —JLM