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Aviation History
1961
1961 - 1295.PDF
FLIGHT, 7 September 1961 VTOL PROPULSION.. Tactical Transport Although by no means an ideal solution, a practical step towardsthe large VTOL transport would be an aircraft of the type illustrated. One has jet lift engines; the other has lift fans, with thrust deflectorson the propulsion engines. An arrangement of this type offers little scope for reduction of structure weight, and VTOL capability bringswith it severe range and payload penalties. With such an aircraft it is unlikely to be practical to deflect allthe thrust. For VTOL operation, at 2,000ft at ISA + 20 C, the lift-thrust/weight ratio should be 1.4 to 1.45. Lift-engine Experience Original studies were based on the assumption that lift engineswould run for 3min at full power during each sortie. But the SCI takes 30sec from lift-off to wing-borne flight. Fuel consumption isthus less important than low weight. The ratio of lift-thrust to weight depends on configuration andoperational environment. The size or number of lift engines is decided by matching the take-off rating to the hottest and highestoperational conditions. Lift-engine overhaul life might be about 800hr, equivalent to 16,000 airframe hours. Intensive cycling testswith an RB.108 will give a sound basis for predicting the service life of lift engines. An emergency rating can be offered for use onlyif one engine in a group were to fail. A lift engine must have good starting characteristics, low idlingspeed, fast acceleration and a rapid thrust response to a sudden change in fuel flow. The RB.108 has the rapid thrust response tothrottle movement of about 0.1 sec; this factor is particularly impor- tant if aircraft pitch and roll control is by differential throttling oflift engines as it might be on a VTOL transport. More than 4,500hr of test-bed and flight experience have beengained with the RB.108. Designed in 1954, it gives a thrust of 2,2001b with a 10 per cent bleed, or 2,5001b without bleed. It is now possible to design a much lighter, cheaper and moresimple engine. By using the latest materials and manufacturing techniques, the cost per unit thrust can be reduced to less than halfthat of a propulsion engine of the same thrust. Simplicity is one reason for this. The lift engine has roughly one-quarter as many Tactical freight aircraft with 20 turbofan lift engines of 7,5001b each and two 15,0001b turbojets for propulsion with jet deflection 397 Tactical freight aircraft with 32 turbojet lift engines of 4,7501b each and two Tyne turboprops for propulsion components as a Conway; there are no auxiliary drives and onlyvery simple starting and fuel systems. It takes 22 man-hours to build and strip a lift engine, compared with several hundred forthe Conway. A group of six lift engines with systems is no more complex than a single Conway pod. Lift turbojets of 3,000 to 5,0001b appear the most suitable forsmall military VTOL aircraft. For large freight aircraft turtofans of 8,000 to 12,0001b seem preferable, largely because they produceless noise; but they have a lower thrust-response rate, which affects aircraft control. They also suffer from a relatively high thrustpenalty if they are designed to supply high-pressure control jets. Both turbojet and turbofan lift engines have been built and testedby Rolls-Royce. Composite powerplant Propulsion engine type Pressure ratio By-pass ratio ... Specific weight (engine only) Static thrust/aircraft weight Booster engine Assumed booster specific weight ... Booster thrust/aicraft weight Total installed thrust/weight Structure weight (%) Powerplant weight (%) Fuel(%) Military load (%) Take-off weight ratio to meet mission requirement of 400-600 n.m. at sea-level VTOL Without propulsion- engine deflection By-pass 18 0.95 0.20 0.75 (no deflection loss) Vertical turbojets 0.06 1.20 1.95 17.9 35 28.6 18.5 1.06 With propulsion- engine deflection By-pass 18 0.95 0.20 0.69 (8% deflection loss) Vertical turbojets 0.06 0.51 1.20 IS.I 30.6 28.6 22.7 0.865 STOL All engines with deflection By-pass 18 0.95 0.20 0.46 (8% deflection loss) Turbojets 0.06 0.59 1.05 30.3 25.7 24.3 19.7 1.0 FIRST TRANS-AMERICAN FLIGHT THE golden jubilee year of the first coast-to-coast flight across theAmerican continent—by Calbraith Rodgers in the autumn of 1911 —is to be celebrated by ceremonies at the Smithsonian Institution,Washington DC. >* *--£;"* Piloting a Wright EX-type biplane, named Vin Fiz after a softdrink of the day, Rodgers flew 4,321 miles from Sheepshead Bay, Long Island, to Long Beach, California, in 84 days (September 17-December 10), making 69 landings, some of which were extremely damaging: it is said that he repaired his machine so many timesthat the only original parts to survive were a rudder and one strut. Vin Fiz, recently restored to its original condition, is now one ofthe attractions of the Smithsonian's National Air Museum. He was born at Pittsburgh, Pa, in 1879, a great-grandson ofCommodore Matthew Calbraith Perry, who introduced Western civilization to Japan. At the Wright brothers' flying school nearDayton, Ohio, in 1911, he soloed after 90 minutes of instruction; and two months later, during a nine-day flying meeting held atChicago, he won the award for the most time in the air, flying every day and totalling over 27 hours. In those early days, prizes were offered by newspapers for city-to-city flights. The Hearst newspapers topped them all with a $50,000 prize for the first flight from coast to coast. Rodgers anda number of others entered this competition. He was sponsored by the Armour Company of Chicago, then (as now) meat packers,but also interested at that time in marketing Vin Fiz. Rodgers received $5 for every mile flown with the name of this drink letteredon his machine. Rodgers's Wright biplane had a wing span of 32ft, length of 21ftand weighed 9031b with pilot. It was powered by a Wright four- cylinder water-cooled engine of 35 h.p., driving two pusher pro-pellers and with fuel for three-and-a-half hours. Top speed was 55 m.p.h. F.C.L.
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