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Aviation History
1963
1963 - 0941.PDF
912 PARIS REPORT... blades in phase and bears virtually no stresses. In the wind tunnel one blade was actually disconnected and continued to lead-lag by itself. The big P-310 will have side-by-side intermeshing Derschmidt rotors with connecting shaft and two turbines, either Lycoming T55s or GE T64s, driving both cross-shaft and tractor propellers optimized for high-speed flights. These will be kept in zero pitch in the hover and provide thrust in forward flight. Speeds up to 300kt are said to be predicted. Although the horizontal pylons form a wing, the rotors operate under power at all speeds, and the wing will provide only 10 or 20 per cent of the total lift. The P-310 will carry 18 to 20 soldiers. The complexity of the mechanical system is not viewed adversely, because there is already a good deal of experience with connecting shafts and gearboxes, and there will be much more by the time the aircraft is built. At the moment it is only a project. The Bolkow rigid rotor, a three-blade, 20ft-diameter version of which is now running on a test stand, has entirely plastics blades, the only metal being the balance weights. Rigid rotors, now being flown by several companies in the USA, have become feasible with the much stronger rotor heads and linkages which can now be provided. The rotor has gyroscopic stability and very fast reaction to control inputs, possibly calling for some form of control damping to avoid overstressing. Because of the increased stresses there seems to be a size limitation, presently set at the UH-1, a rigid- rotor version of which Bell have now flown at 150kt; but anything may develop in this exciting field. In about 18 months' time, Bolkow are likely to fly their rigid rotor in the B6105, an experimental four-seater to be powered by two of the new 250 h.p. BMW 6022 turbines, or by equivalent Continental or Boeing turbines. The Wankel engines proposed last year have been abandoned, because development is going very slowly. The rotary-piston Wankel engine is nevertheless very intriguing for small aircraft, because of its great compactness and quietness. Bolkow estimate that two 120 h.p. Wankels driving a single propeller would fit under the cowling at present required for the single 180 h.p. Lycoming O-360 of the 207, as noted earlier. Final rotary-winged innovation at the Show is the Hughes Tool Co hot-cycle research helicopter. A test-rig has proved so successful that a twin-turbine helicopter is now to be built to US military order. Hot cycle apparently involves compressor bleeding with burning inside the rotor blade and tip drive. PROPULSION NEW facts are available on the powerplant of the Concord Mach 2.2 airliner, the 29,3001b-thrust Olympus 593/3. This two-spool turbojet will basically be a modified Bristol Siddeley Olympus Artist's impression of the nozzle for the Olympus 593/3 FLIGHT International, 13 June 1963 22R—a near-relative of which is on the BS stand—with zero-stage and many other alterations, and discharging into a SNECMA exhaust system. BAC install the engines in two underwing boxes, each containing two engines separated by a full-length firewall and fed by a rectangular intake with a variable ramp in the upper surface of the throat, boundary-layer bleed duct (this air cools the nozzle and stabilizes flow in the divergent portion) and an auxiliary intake and quick-acting spill vents below. An accompanying artist's impression shows the basic features cf the SNECMA nozzle. Hardware of this size has to be very care fully designed for minimum weight and maximum thermodynamic efficiency, and SNECMA, in close collaboration with Bristol Siddeley, have had teams working in parallel on different solutions to the severe problems involved. This makes it unwise to assert that the Concord will fly with one particular nozzle, but the artist's impression gives an indication of current thinking. Behind the turbine section an articulated joint and flexible bellows allows engine and exhaust system to expand and contract separately, and the jetpipe and nozzle are cooled by the large flow of boundary-layer air. The primary nozzle incorporates a limited reheat system, reaching about 1,450°K, to augment thrust on certain flight profiles calling for a steeper climb to the point of transonic acceleration. The latter must be carefully controlled to reduce the effects of sonic boom below the flight path, and the optimum altitude is now put at approximately 45,000ft. Noise is also a governing factor determining take-off technique. The auxiliary intakes would be fully open in this condition, as would the auxiliary cooling-air nozzles above and below the nozzle (which can be seen in the drawing, ahead of the reverser outlets). Limited reheat would be used on airfields near residential areas in order to give rapid take-off and climb to a predetermined height. Fuel flow would then be reduced, but r.p.m. and mass flow would be maintained at the maximum level, while the jet velocity would be further reduced by opening the primary nozzle. This nozzle is of convergent form, and its 12 variable petals each have a deep V-gutter admitting boundary-layer air which mixes with the jet to give Greatrex-type silencing. Around the primary nozzle is a divergent secondary nozzle. This is of fixed geometry, and it appears in the illustration as having a square section, although this may not be the form finally adopted. In line with the end of the primary nozzle is arranged a thrust reverser, consisting of a pair of clamshells hinged on each side, a series of upper and lower cascades extended rearwards and two pairs of ejector orifices above and below. Maximum reverse is about 45 per cent of the forward thrust. In cruising flight the reverser installation is fully retracted and is claimed to impose "negligible losses." Although nothing is on view at Paris, it was possible to learn from Avco's Lycoming division details of the fan conversion of the T55 turboshaft engine. This unit, designated PLF1, exists in "A" and "B" versions both differing from the basic T55 in having a single fan stage of very high bypass ratio added at the front and driven by the free output turbine through a central shaft. This fan increases the overall engine pressure ratio and power, in compari son with the basic turboshaft unit. Basis of the PLF1-A is the T55-L-7, already fully developed for the CH-47 Chinook helicopter at 2,650 s.h.p. at a gas-generator speed of 19,280 r.p.m. The fan conversion is rated at 4,6501b thrust, and will weigh 800 to 8501b. The first PLF1-A will run at about the end of 1963. There is also a development turboshaft uait known as the T55 Advanced, with major modifications to increase power and efficiency. Most significant alteration is the incorporation of a redesigned compressor with transonic flow in initial stages, achiev ing a pressure ratio (without added fan) of 10 : 1 at the reduced gas-generator speed of 19,000 r.p.m. The Advanced engine is rated at 3,400 s.h.p. for lOmin, plus 2201b jet thrust, equivalent to 3,488 e.h.p. at a specific fuel consumption of 0.493. The corres ponding PLF1-B fan conversion would be rated at 5,2201b thrust: although only a paper engine, it has already been chosen by SIAT and Weser in Germany for new transport projects described earlier. Among the mass of impressive exhibits by Rolls-Royce is a reheat jetpipe for a Spey turbofan. The complete engine was illustrated ip our May 16 issue, wherein it was noted that in a high-ratio fan engine of this type it is possible to achieve very high augmentation. The Spey afterburner can be controlled to give any desired aug mentation between six and 70 per cent, the full figure representing a thrust of the order of 19,0001b. The unit on display has actually
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