A Britannia 312 long range aircraft today left Bristol for Singapore, from where, during the next few weeks, it will make an intensive series of weather exploration flights.
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Background: A Britannia 312 long range aircraft today left Bristol for Singapore, from where, during the next few weeks, it will make an intensive series of weather exploration flights.
The aircraft is fitted with Proteus 755 engines incorporating two forms of modification designed to eliminate the engine icing problem encountered in certain monsoon conditions.
Two of the engines are equipped with a device designed by Bristol Aero-Engines Ltd, whereby air tapped from the engine compressor is reintroduced through a number of small nozzles in the engine intake duct. This device has been tested at the Royal Aircraft Establishment, Farnborough, and has given most encouraging results. Its performance in the worst icing conditions that can be found will now be measured.
The entry ducts of the other two engines have an improved heating system, which enables critical parts of the ducts to be heated by gas at a temperature of 280 - 300 degrees C and these engines will be given similar assessment in the worst climatic conditions.
The Britannia will be captained by Mr Walter Gibb, Bristol's Chief Test Pilot, and the trials will be conducted by a team of 40 engineers and technicians.
It should be emphasised that whilst excellent results have been obtained with the ground rigs of these modifications operating under simulated conditions, final conclusions can only be obtained from flight trials in the actual conditions of monsoon weather.
BACKGROUND NOTE ON METEOROLOGICAL CONDITIONS AND PROTEUS MODIFICATIONS
The conditions in which the Proteus powerplants will be tested are found in certain monsoon weather areas and result in a particular form of icing. This is brought about where very high humidity and tropical temperatures combine to result in a high concentration of dry ice mixed with water droplets in the altitude range from approximately 16,000 ft to 20,000 ft at ambient temperatures of 0 C to -8 C.
The modifications which are to be tested are as follows:
In the two outboard powerplants multiple nozzles are fitted to the outer wall of the intake duct and these direct jets of air along the inner surface of the rear wall of the intake in order to accelerate the boundary layer and so prevent ice accumulating on this surface. There are 25 of these air jet nozzles spaced approximately 6 in apart and they are supplied by means of a manifold encircling the intake. The air is fed to the manifold from the cabin air pressure tapping which is taken from the final delivery stage of the engine compressor.
The amount of air tapped from the compressor is approximately 1/2 lb/sec, and when this is in operation it will be appreciated that it causes a slight loss of power and a small increase of specific consumption. Translated into aircraft performance, this would mean a cruising altitude about 1,500 feet lower and a 2% loss of range if the system were in operation all the time. It must, however, be emphasised that the effect on performance persists only as long as the system is operating, and normally only a very small proportion of any flight would be carried out under these conditions. For all practical purposes, therefore, the performance of the aircraft is not affected.
The two inboard engines will have increased heat applied to the walls of the air entry duct which will now be heated by gas at 280 - 300 C instead of the standard 180 C. This hot gas is fed to the rear of the curved wall of the air intake at the bend directing the air into the engine compressor. In addition, the distribution of the hot gas has also been improved.