Side Valve Engines

The Crusader

Louis' thoughts turned to aero engines. In the autumn of 1912, he designed a V8 engine which could deliver 120h.p. at 2,500 r.p.m. It was called the Crusader and was widely announced in the British aviation press, in March 1913. This was welcomed by the British aircraft manufacturers as no really suitable British engines were available at the time. 

From 'The Engineer', 11th April, 1913.
An English-Built Aviation Engine

Many of our readers are acquainted with the wonderful work which has been done lately by what we may call tiny engines in driving motor cars at enormous speeds. Among these may be mentioned the performance of the Sunbeam car, which won the Grand Prix Race on the Continent last year with an engine which had four cylinders of only 80 mm. bore by 150 mm. stroke. The successful results obtained with this engine on a car have led the Sunbeam Company to embody the main features in an 8-cylinder "V" type aviation engine, which we illustrate below.

This "V" form of construction leads to very great saving in weight, the crankshaft and crankcase being reduced in length, while the crank webs are also reduced and the valve gear is simplified, so that this particular engine, which gives 150 brake horsepower at 2,500 revolutions per minute, only weighs, with its carburettor, 425lb., or less than 3 lb. per horsepower.

This alone is not however, sufficient to make it a suitable aviation engine, as the weight to be taken into consideration is that of the complete motor with fuel, etc. for a trip of a reasonable number of hours' duration, and it is here even more particularly that the Sunbeam engine proves its claim to rank as a very fine aviation engine. The consumption as taken under normal flying conditions works out to only 0.49 pints of petrol per brake horsepower per hour, so that fuel economy has received an equal amount of attention with efficiency and saving of weight.

As will be seen, each pair of cylinders lies in the same plane, so that only two cams are required for four valves of each pair of cylinders, while both connecting rods drive the same crank pin. The cylinders have copper water jackets to save weight, and the big bell-mouth to allow the long stroke connecting rods to clear, is an interesting feature of the design, which otherwise differs very little from ordinary motor car practice, though the water cooling of the valve pockets should be noticed.

The camshaft is cut out of the solid with all its cams, and its big diameter bearings and is another instance of the way in which every ounce of superfluous metal is dispensed with. The revolution speed of 2,500 per minute is of course, too high for the best propeller efficiency, and this is reduced by half by a 2 to 1 gear embodied in the crank case. Altogether this little engine, as we must call it, is a remarkable piece of work, and we should like to congratulate the designer, Mr. L. Coatalen. on the success which be has already attained.


The Crusader's first flying test should have taken place on 6th August 1913, after one of the engines was fitted to a Radley-England Waterplane. It never actually managed to take-off, because of problems with the design of its two hulls. After this tragedy, the Sunbeam Motor Car Company decided to purchase an aircraft to test the new engine. It was a French Farman biplane, and Sunbeam decided to hire a full-time test pilot for the project. This was John Alcock who later became well known for his famous non-stop Atlantic flight with Arthur Brown. The test flights began in the middle of October 1913, and took place at Brooklands. There were initial teething troubles, but these were soon overcome, and in December the aircraft began a long period of intensive flight tests which ranged over most of southern England, and continued until the outbreak of War in 1914. 

The War Office became interested in the engine and one was purchased by the Royal Aircraft Factory. It was delivered to Farnborough for extensive bench testing and delivered a maximum of 135h.p. There were one or two problems to be sorted out, but if they could be resolved the engine looked as though it would be suitable for military use. Some Crusaders were also fitted to power-boats that were built by Brookes, for the Smith's Financial Group. 

In March a Crusader was exhibited at the Aero Show in Olympia. The bore had been increased from 80mm to 90mm and the engine could now deliver 2,000r.p.m. The engine had two side valves per cylinder, was water-cooled, weighed 480lb dry, had two Claudel-Hobson carburettors, and two Bosch magnetos. At the show, Avro ordered one of the engines for the 510 seaplane, which was to be entered in the Circuit of Britain Race. The race was cancelled due to the outbreak of War and Crusaders were in demand for a very different sort of use.

The first military aircraft fitted with the engine was a Royal Aircraft Factory RE.5 biplane, in July 1914. The engine was soon fitted to many other aircraft:

Aircraft Fitted with Crusaders

Aircraft Make and Type

Number of Engines Ordered

Maurice Farman 2 seater biplane 1
Royal Aircraft Factory RE.5 biplane 1
Avro 510 seaplane 6
Sopwith 806 Gunbus 36
Short 827 seaplane 107
Handley Page Type O biplane 2
Blackburn GP seaplane 2
Sopwith biplane bomber 2
Avro 519 bomber 2
Avro 527 reconnaissance biplane 1
Curtiss H-4 biplane 1
Curtis R-2 biplane 14
Coastal non-rigid airship 50
Sikorsky I1'ya Mouromet biplane 30

The 110h.p. Sunbeam

This was the early version of the Crusader, before the bore was increased to 90mm. It was always considered to be a separate engine by Sunbeam, and a number were sold as such.

Aircraft Fitted with the engine

Aircraft Make and Type

Number of Engines Ordered

Radley-England Waterplane No.2 1
Maurice Farman 2 seater biplane 1
Sopwith 806 Gunbus biplane 18
Short 827 seaplane 6

The engine was also fitted to the Sunbeam 24h.p. hill climb car of 1913. Two engines were supplied for use in the Tollier powerboat of 1913, and another was used in the Brookes powerboat of 1914.

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