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Aviation History
1944
1944 - 0303.PDF
FEBRTARY IOTH, 1944 FLIGHT CORRESPONDENCE (d) If v is negative (i.e. in the same direction as the aircraft's motion). Efficiency is greater than 100%, however thrust and power are negative (i.e. there is drag). (e) Thrust is proportional to mass of air per second x slip stream speed. Therefore, to increase thrust it is necessary either to increase v and lower the efficiency, or to increase M. Unless it is possible for a jet machine to deal with as much air as an airscrew machine, it will be considerably less efficient at low speeds, and, to get the same take off as an orthodox machine, it will need very much greater power. The chief advantages for a jet machine would appear to be :—- (a) A lighter power unit that is less efficient, giving better performance for short durations (i.e. when fuel load is not important). (b) Efficiency at speeds where an airscrew would be hopelessly inefficient. However, its range would be poor, as at speeds where its efficiency is high, the drag would also be high, and vice versa. J. K. HAVILAND j Aeronautical Crystal-gazing WE should all be grateful to E. H. Miles for his letter suggesting designs for jet-propelled aircraft. He at once enters the privileged company of crystal-gazers in aviation, of 40)om none holds higfier place than the late Will Rogers. ^Will reached his peak in anti-submarine suggestions. He advocated raising the temperature of the sea to boiling point, for, he averred, no submarine could exist submerged in such conditions. Agreeing with his thesis in idea, the question was then asked as to how to raise the temperature. Said honest Will in a hurt voice: "Listen, / give you the Big Ideas—You work out the details." Incidentally, what about a nice black searchlight to blot out the moon ? "FOUGUEUX." Fuel from Decomposed Water IN your issue dated January 27th "Typhoon" discusses the possibilities of broadcast electric power and enquires about other possible sources of power. I have an idea that some time in the future some genius will find a way to speed up the process of electrolytic de-com position of water into its component parts of hydrogen and oxygen at any desired speed. If it were possible now, what a boon it would be to the jet experimenters. I can visualise an aircraft with tanks full of water, one jet of which is de-composed and the resultant jets of hydrogen and oxygen burnt in the inner tubes of a jet engine. A second jet of water, injected into an outer tube surrounding the hot tubes, is instantly converted into steam and the whole mass, burnt gases and steam, ejected through the usual rear orifice. -«Q- A certain amount of the energy would have to be diverted, via a turbine or other means, to drive a dynamo to supply the electricity needed in the de-composing chamber. Such an engine, being independent of the atmosphere, would function at any height, even beyond the atmosphere. When this becomes a practical proposition, there will be no need to buy oil from abroad or to delve for coal at home, as water is about the cheapest and most plentiful material in the world. H. MUNDAY. MERLIN MYSTERY Spitting Back May Cause the " Kick " I WOULD like to point out that a mag. drop cannot possibly cause a kick on the throttle controls unless spitting back in the induction system occurs. The drop in revs is caused by loss of power output due to inefficient combustion, the effect on the boost being insufficient to cause a kick on the controls. "Fitter 11.E" (Flight, December 23rd, 1943). mav be used to large four-engined aircraft in which case spitting back may have occurred unnoticed. A study of the aerodynamic properties of a butterfly throttle ;AS depicted in the diagram shows that spitting back at low \revs when the supercharger offers little opposition to the reversal of the flow tends to kick the throttle butterflies and cockpit levers back to the closed position. The effect is similar to that of the airflow over an aerofoil except that it is considerably reduced by interference from the walls. Perhaps someone will oblige with more details ol this interference. It should be realised that if the boost control closes the butterflies it tends to push the cockpit control forward, and RESULTANT TURNING MOMENT m DIRECTION OF REVERSE FLOW [DUE TO SPITTING J BACK vice versa. Hence suddenly induced high boost pressures will give a kick forward on the cockpit lever. This condition may be obtained by:— (1) Spitting back at high revs, and boost when the super charger damps out the effect on the butterflies, but may not always be sufficient to give a kick forward. (2) Changing the supercharger into high gear. (3) Operation of the boost cut-out valve back to normal. Bringing the boost cut-out valve into operation, and chang ing to low gear causes the lever to kick back. The magnitude of the kick depends on :— (1) The rate of change of pressure in the induction system, and the magnitude of that change. (2) The moment of inertia, and friction of the controls between cockpit and gear box as compared with that of the control between the gear box, and the butterfly. INTERESTED. THE DUCTED RADIATOR Heat Converted to Kinetic Energy IN reply to the query put by a reader about the ducted radiator, the following may be of some use: — Briefly, ducted cooling is a method employed to convert waste heat energy from the engine—heat energy that would otherwise be lost—into useful kinetic energy and so into thrust. The principle can be seen from the diagram. y yzsz. COL_Q_ AIR AIR COMPRESSED AND REDUCED IN SPEED + HEAT -> ENGINE ,-HEAT AIR AT HIGH SPEED ^^^ Expansion of the incoming air occurs after entry to a high pressure (it might be more correct to call it a compression) and a low speed. This air is then heated on passing the engine, which gives the air a high speed. The heat energy thus imparted to the air is recovered as thrust when this high-speed air is discharged to the rear through nozzles or gills. The source of heat is immaterial—it may be the radiatoi, or engine, or even a flame (compare with the jet-propulsion engine). R. SHOHAM. THE WORLD'S BEST AIRCRAFT (Concluded from page 140). published in Flying, presumably in order to save some space. An analysis of the types of engine which power the 22 selected aircraft is of interest—for the engine is essentially the hcaft and the making of any aircraft. The Rolls-Royce Merlin and the Wright Cyclone appear in six types, the Pratt and Whitney Twin Wasp in four types, the Bristol Hercules in two types, and the Allison and the Pratt and Whitney Double Wasp, Wasp and Hornet in one type each. These engines can be fairly said to represent the best in service in the world to-day. Conclusion Such a list is inevitably outdated quickly in the swift march of aeronautical progress. For instance, it is unthinkable that the great name and experience of Hawker will be long absent from the list of the "World's Best," the new Boeing B-29 holds out tremendous promise, the Martin Mars is just coming into service—new transports are impending and a new era is opening with the revelation of jet propulsion. If one could but see to-day a similar list as it might appear two years hence —what advances it would reveal For the Air Age is in the future—not in the past or present.
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