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Aviation History
1925
1925 - 0119.PDF
FEBRUARY 26, 1925 to the cylinder capacity owing to difficulties experienced in balancing when the bore was more than 90 mm. Carburation was a source of trouble, and sometimes it had been necessary to fit a carburettor to each cylinder. Owing to the com- paratively large dimensions of the cylinders it was not particularly suitable for running at high speeds, but the fitting of a supercharger should enable a reasonably well- balanced engine to be produced giving about 38-40 h.p. at a speed of under 3,000 r.p.m. The type was easy to air cool, and should also have a fairly good power/weight ratio. The lecturer referred to an "xperimental 180° flat four with the cylinders in two blocks of two at 180° which had been built in France. If it was admitted that there was a limit to the capacity of the flat twin it seemed obvious that the flat four could be designed up to double the capacity. The three-cylinder radia! type was criticised by the lecturer on account of its large frontal area, and also because of a greater weight resulting from difficulties in the construction of the big-end bearing. A neat induction system was difficult to arrange, and the central top cylinder was in the way from the pilot's point of view. The balance was superior to that of the. flat twin and the torque-recoil less. The lecturer appeared rather in favour of the five-cylinder radial for larger engines, as the five-cylinder crankcase need be no larger than that required for a three-cylinder radial. Although somewhat expensive, this type was, he thought, very promising. For small engines Col. Fell thought the " swashplate " type of engine, with the cylinders parallel to the driving shaft, could be satisfactorily designed. It should be capable of high speeds, and it should give low head resistance and reliability, and be comparatively cheap and easy to produce. The lecturer thought it curious that the four-cylinder in line type had not come into prominence for light aircraft although it was by far the most extensively used in motor-car practice. He thought it probable that owing to faulty cooling of the rear cylinder it would not be possible to obtain the high duty called for in the air-cooled form of this type of engine, but in the water-cooled form the type had much to recom- mend it. In the air-cooled form the engine must be some- what long to give space between cylinders, and for rigidity it depended entirely on the crankcase. Reference was again made to the small frontal area of the water-cooled four-in-line type, and Col. Fell explained that the engine was intended to be of the inverted type. The water-cooled type had to have the additional weight of water and pipes and radiator, but the weight of these items was largely offset by the increased cylinder and piston weights of the air-cooled. For a light aircraft engine it would be possible to build in the radiators close to the sides of the engine, and so eliminate water piping. In the design shown in the diagram it was intended that the radiators should be formed by two nests of " Brown " tubes, each a block of approximately 3 ins. diameter, and running the whole length of the crankcase on each side of the cylinder liners located at the highest point of the water space. As a luxury rather than an e^ential type the lecturer referred to the straight six and straight eight, and said he had recently had an opportunity of considering a proposal for a 1,500 c.c. eight-cylindcr-in-Iine design to give 70 h.p. con- tinuously at a speed of 5,000 r.p.m. Finally he summed up as suggestions for the most suitable types the following : For single-seaters 180 deg. flat twin air-cooled. For two- seaters five-cylinder radial air-cooled or four-cylinder-in-'ine water-cooled. For luxury or speed machines six or eight- cylinder in-line water-cooled. Installation Col. Fell criticised the installation of some of the engines at Lympne, particularly engine mountings. He thought the engine designer might have rendered considerably more assistance to the machine designer by supplying satisfactory bearers as part of the engine. It 'was sometimes argued aganist this procedure that it hampered machine design, but in practice this difficulty had not become apparent The great advantage was that the engine designer could test his engine in the same way as it would have to run when fitted into the machine. Cowling also might with advantage be designed by the engine designer and supplied as part of the engine, but against this was the difficulty caused by the different body shapes of the various machines. Attention was also called to the importance of adequate fire prevention, of rigid engine controls in place of cable, and of accessibility to the engine and its auxiliaries generally. Conclusion In conclusion Col. Fell said : In the writer's opinion, as is the case with all other air- craft, the successful development of light aircraft for any purpose whatever depends on the engine designer. The competitions so far have indicated that the light aircraft engine builder's problem is a far more serious one than was anticipated. In this lecture the writer has indicated why this is so, and that it is only by the very best work of those most highly skilled in high efficiency internal combustion engine design that an engine sufficiently powerful, and at the same time, durable, can be produced. The light aircraft engine must always be more expensive than any other engine of similar capacity for the simple reason that, in addition to the fact that it will always be called upon to give the maximum duty obtainable from its capacity, as is the case with the racing motor-car engine, it has the further disadvantage of having to be produced at minimum, weight. It will no doubt be stated that the ,maximum possible rating will not be used,, and that reliability shall be accepted in lieu. It has been the writer's experience, however, during the last ten years, if there is anything left in the way of power inside an engine, the aircraft designer will have it out, and he sees no reason why this is less likely to be the case with the light aircraft engine. It is absolutely essential that an aero engine be designed to withstand indefinitely the maximum duty which it is possible to obtain by running full throttle under the best possible settings for carburettor and ignition for maximum power." THE DISCUSSION Colonel Bristow pointed out that it was through no fault of the aircraft people that the capacity limitation was chosen, but that a daily newspaper, the name of which escaped him for the moment, had a competition for motor gliders and wanted the capacity rating. For this year's light 'plane competitions the basis to be used would be one of total loaded weight of the machines. He pointed out what appeared to be an inconsistency in the paper, where the lecturer first stated that capacity rating was definitely undesirable, and then went on to suggest that more power could be got out of an engine for a given capacity by the use of a supercharger. He thought it would be much simpler to get that extra power by a slight increase in the cylinder dimensions, and also a much lighter engine would result. He thought the weight of the super-charged engines on Brooklands track was 11 lbs./h.p. complete with blower. On the subject of motor-car racing engines Col. Bristow pointed out that the plain air-cooled engine was giving 5 h.p. per 100 c.c. capacity on the track as compared with the 4.66 h.p., 100 c.c. mentioned by the lecturer for the supercharged water-cooled racing car engine. He was sorry the lecturer asked for dual ignition, and thought one magneto firing two plugs was sufficient, and this had been lound to give smoother running. He was surprised at the lecturer's statements relative to the respective weights of water-cooled and air-cooled engines, and stated that whereas the lightest type-tested water-cooled engine weighed 2-2 lbs./ h.p. the lightest air-cooled weighed but 1.6 lbs./h.p. Mr. Manning pointed out that the light 'plane engine must be a cheap engine, and that the air-cooled was the cheapest type. The lecturer had stated that it was definitely not possible to fly satisfactorily with motor-cycle engines. He would point out that the Blackburne in the D.H.53 was giving very good service. The lecturer had also said that figures would be given showing that motor-cycle engines were no use. These figures, apparently, had been omitted, as the tables did not refer to motor-cycle engines. YVitn regard to the question of altitude control, he had seen in France on a Claudel carburettor a simple sleeve arrangement which appeared satisfactory. On the subject of water-cooling versus air-cooling he thought the air-cooled undoubtedly scored on the question of weight, as one had to allow about 0-6 lb./h.p. for the water-cooling apparatus. As to the use of super- chargers, the cost was against it. and he thought it better to increase the size of cylinders. The lecturer had objected to the four-cylinder-in-line air-cooled engine. There was in use a French engine of this tvpe which was running very well and was giving no trouble. Concerning the size of the future light 'plane engine. Mr. Manning thought this should develop 50-60 b.h.p. at a speed not exceeding 2,000 r.p.m. He did not quite agree with the lecturer in the need for dual ignition, and thought one magneto sufficient. The question of cost should be kept prominently in mind, and he suggested develop- ing the four-cylinder-in-line and the three-cylinder radial. Mr. Fedden, although he admitted that giving designers an entirely free hand was a very attractive proposition, thought that, in view of the fact that light planes would presumably 119
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