The Air Ministry Laboratory

In the twenties the Air Ministry had a laboratory in premises at the rear of the Royal College of Science in Kensington. I was lent to them for a year or so, in order to get a likely subject for DIC (Diplomate of the Imperial College). This evolved into a study of additives to improve the performance of oils used in petrol engines under conditions of high stress. In fact succeeded in this, though a fact lot of use to me resulted from my labours. Whilst there I got involved in the more routine endeavours some of which are worth relating.

These were the days of the Schneider Trophy races. Seaplanes rather like Spitfires on floats, tore round a triangular course at speeds of nearly 400 mph. attained by squeezing extra power from the engines, This was achieved by various means including doping the fuel, to enable the use of a higher compression ratio, and generally squeezing more of it into the cylinders. The anti-knock properties of Lead Ethide had recently been exploited with mixed success. Although any lead produced makes a good lubricant to the exhaust valve when molten, in big doses it clogs up the inlet valve where temperatures can be below zero. The Americans had recently lost an Airship through this.

We had in The Lab one of the new Ricardo test engines. This was a single cylinder job capable of producing fifty horsepower. The compression ratio could be altered whilst the machine was running under full power by a mighty threaded collar and had-wheel. The valves in the head, (two inlet and three exhaust) were operated by splined rods. It was well supplied with means of metering all necessary fuel flows, power output, temperatures etc. On full power you could change the compression ratio from about three to one to about twelve to one. When racing of course, you are mainly interested in getting the maximum power from an engine. Such niceties as saving fuel take a secondary place.

While I was there somebody got the bright idea that we really ought to find out where all the energy in the fuel finished up. The effect of compression, ratios was well understood but little else at that time. Accordingly we started at the fuel. There were a number of fancy racing fuels used by cars even in those days. but they were not very stable or effective, so we considered for these tests only Alcohol, Benzene, or a light member of the Paraffin family, which was a standard fuel and was mainly Hexanol. Neither of the first two have nearly as much energy as the last. Their virtue is in the cooling of the fuel on evaporation causing a contraction in volume and hence a heavier charge arrives en the cylinders. The petrol we used usually had a total of about 10,000 calories per gramme of fuel as determined on the spot in a calorimeter. Benzene and Alcohol were nearer 7000.

With the petrol as measured, we could weigh the fuel as it entered the Carburettor. With no dope things began to knock at a compression ratio of five to one. More power and more knocking came up to five and a half above this with heavier knocking the power went down.

The test engine had two means of measuring its power output, either as supplied a spring balance friction belt working on a polished pulley, or a calibrated generator. Thus we could at this stage measure the amount of fuel burnt and the power produced. The results were rather interesting with the power produced showing that some 50% was going astray.

The next check was on the amount of energy carried off by the cooling water. The change of temperature and the amount of the flow of water defined this. We then drove the engine at working speed and temperature by means of the installed dynamo/motor. Exhaust gases were collected their temperature taken and the energy bound up in these calculated. Finally there was an enormous amount of energy tied up in unburned fuel, carbon monoxide and a lesser menagerie of carbon and its compounds.

When the project was finally assessed we reckoned we had found all but a few percent. This should have resulted in a major design study on fuel injection and other goodies as indeed it did in Germany but it was not done here until many years later.

I once remember a party of top brass from the Air Ministry was due a marvellous new motor with a valve for introducing a boost of fuel in the middle of the piston. Some six or seven hours before they were due to arrive the piston fell in two pieces. We had some very clever mechanics who turned up a new piston from a block of oak and pinned the valve and it’s seating to the wooden piston. The visitors duly watched the demonstration with great interest, When the motor was taken down later the piece of oak was not even charred.

One thing we missed in the fuel assessment job. It was later found that if things were arranged properly a Spitfire would go three miles per hour faster if the exhaust gasses were all shot out backwards. Still you can’t think of everything.

Eric Vast – July 1998.

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Wilf Gaye Memorial Cup - The clubs annual operating event in the memory of Wilf Gaye M0GYE.
St. Richard's College Buildathon/STEM/ARISS - HERC attends St. Richard's Catholic College for their various events surrounding the Tim Peake ARISS contact.
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Sussex Electronics Radio Fair - SERF Sussex Electronics Radio Fair 2016.
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Experimenters Corner - A selection of Proteus projects by Bob Gornal (G7DME)
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Radio Rallies 2016 - An up to date list of radio rallies scheduled for 2016.
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John Taplin - A bio of the late John Taplin.

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