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Aviation History
1947
1947 - 0022.PDF
18 FLIGHT XV JANUARY 2ND, 1947 Metrovick F.5 Open - Fan Thrust Augmenter *on Standard F.2 Qas Qenerator IN view of the controversy concerning the relative meritsof turbo-jets and airscrew-turbines and the speeds atwhich the one would be more efficient than the other for a particular airframe, additional information on a new and alternative hall-way arrangement, namely, open-fan augmentation, will be of interest. Readers will already be familiar with the Metrovick F.3 which embodies a ducted-fan thrust augmenter. The new Metrovick F.5, with the open-fan type of augmenter, was briefly described and illustrated in Flight of November 21st and 28th. Basically the F.5 comprises a gas-generator unit as used on the standard F.2 series 4A turbo-jet, and a contra-rotating pusher fan unit, 5 feet 6 inches in diameter, driven by a four-stage turbine. The gas genera- tor weighs 1,600 lb and the augmenter 600 lb. The total represents only a 30 per cent increase in weight over the simple jet unit. The augmenter unit is connected with the gas generator GAS FLOW FROM. CAS GENERATOR A section of the open contra-fan augmenter unit The aircraft cowling line isindicated. by hot-gas ducting of 26m diameter, the length being determined by the aircraft installation, although if neces- sary the fan turbine can be mounted directly behind the gas generator, thus eliminating the duct altogether. In the case of the F.5, the augmenter unit is intended to be mounted either at the rear end of the fuselage or behind the trailing edge of a wing. It may be regarded as a contra-rotating, fixed-pitch, multi-blade- airscrew with fourteen blades in the front bank and twelve in the rear one. Additional thrust is supplied from the propelling nozzle behind the turbine. The fans are free-running, their speeds being controlled by the balance between their output and the turbine power input. By comparison with the airscrew-turbine scheme, the open-fan augmenter has the advantage of lightness, sim- plicity and absence ct gearing. Its performance is com- par&Dle over a good range of flight conditions, and at the designed point it equals that of the V.P. airscrew. By comparison with the simple turbo-jet, the open-fan augmented unit gives a much better specific consumption "81 The entry of the contra-fan turbine. There are 14 bladeson the front bank of the fan unit and 12011 the rear. with improved specific weight over a wide range of flight speeds up to 500 m.p.h. The F.5 is approximately 100 lb lighter than the F.3 with ducted fans and gives 100 lb additional thrust. By fitting an adjustable air propelling nozzle the propulsive efficiency of the augmented engine may be maintained at a high level over a greater range of speeds. Auxiliaries are grouped round an external gear box on top of the intake casing and driven by a vertical shaft. An alternative drive may be fitted at the centre line of the intake casing and adjusted in plan view to suit instal- lation requirements. The unit is started by means of a Plessey petrol engine mounted on the auxiliary gear box. The augmenter is designed to give most economical opera- tion at 400 m.p.h. at maximum continuous rating, and augmentation ratios are relative to the performance of the standard F.2 Series 4A turbo-jet. METROVICK F.5 Take off power at 75 m.p.h. sea level fan thrust 2,840 Ib. jet thrust 1,870 Ib. total thrust -4,710 Ib. Climbing at 200 m.p.h., 20,000ft fan thrust 1,8501b. jet thrust 850 Ib. total thrust 2,700 Ib. Specific fuel consumpt. 0.663lb/hr/lb thrust. Continuous cruising at 400 m.p.h., 20,000ft ... fan thrust 1,670 Ib. jec thrust 630 Ib. total thrust 2,300 ib. Specific fuel consumpt. 0.872lb/hr/lb thrust. Fuel consumption at continuous cruising conditions 240 g.p.h. Oil consumption 8 pt/hr. DIMENSIONS Gas generator length 12ft 2.25in. Diameter 37.25in. Augmenter unittangth ... .... ... ... 4ft Sin. Diameter (including fans) 5ft 6in. Diameter blade root fairing ... ... ... ... ..2ft 7.5in. WEIGHTS Gasgenerator 1,600 Ib. Augmencer unit ... ... ... ... ... 6001b. Hot gas duct . r5(b per ft. Rotation (looking forward) Gas generator clockwise. -Front fan Clockwise. Rear fan Anti-clockwise. VIKING CONSTRUCTION THE construction of Vickers-Armstrongs Vikings and theproduction of magnesium-alloy tanks are the subjects of two important series of articles appearing in AircraftProduction. First instalments of both articles are included in the January, 1947, issue.
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