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Aviation History
1960
1960 - 0724.PDF
Two outstanding production engines are the Napier Gazelle (left) and de Havilland Gnome (right). Both are free turbines with rear drive HELICOPTER POWERPLANTS IT is not unfair to assert that during the first 20 years of itsexistence (reckoning from the pioneer VS-300 of 1940) theworld's helicopters have been held in check by their power- plants. Although piston engines have been taken to a high pitchof development, and in certain installations have enabled heli- copter firms to produce outstanding vehicles, it is no exaggerationto say that the introduction of the turbine has brought about a revolution in helicopter performance. At one stroke it has enor-mously increased available power from a given bulk of powerplant, effected a slashing reduction in installed weight, and, while dis-pensing with cooling fans entirely, has removed the problem of engine overheating in adverse conditions at zero forward speed.A significant incidental advantage of the free-turbine engine is that it can drive without using a clutch. Of the piston engines remaining in production the most notableexamples are the British Alvis Leonides 570 h.p. radial and its 14-cylinder counterpart the 795 h.p. Leonides Major; the excel-lent Russian ASh-82 series of from 1,430 to 1,700 h.p. and the American Pratt & Whitney R-2800 of 2,100 h.p. and the 305 h.p.Lycoming VO-540 flat-six. The last stronghold of the helicopter pistol engine is in the smallest sizes, and typical units are theJohnson 35 two-stroke (38 h.p.), three-cylinder ELO (40/50 h.p.), Nelson H-63B (43 h.p.), Porsche 70/2 (62 h.p.), and flat-fourMcCulloch 4318E (72 h.p.). Nevertheless, even in the small-helicopter field the turbine isousting the piston engine, and much may be hoped from the Allison 250 and Boeing 520. As the T63, the former is underintensive development for the American Services, and it is also likely to command a large commercial market. Weighing some951b, it delivers 250 sJi.p. at up to 100° F ambient conditions. Careful design is expected to combine a specific consumption of0.7 at full power with a selling price of the order of $6,000. The new Boeing engine employs a double-sided centrifugal compressorof such advanced design that it can operate at a pressure ratio of 6.5 : 1. Under development for the US Navy as the T60, thehelicopter version is at present giving 400 s-h.p. for a weight of 3251b; the more advanced 520-6 will weigh only 2601b yet willdeliver a minimum military output of 525 s.h.p. with s.f.c. of 0.65. The -6 is expected to be commercially available before 1964. In roughly the same power class is the Canadian Pratt andWhitney PT6B-2, which will weigh 2251b and be rated at 500 s-h.p. with six. of 0.71. Prototypes may be available nextyear at a price of something like $15,000. Turbomeca have delivered over 700 Artouste 2B1 single-shaft, 400 h.p. enginesfor Alouettes and have made a small number of the more efficient 542 h.p. 3B version. About 370 Palouste air compressors havebeen made for Djinns, but no new tip-drive application is in prospect. The most important new Turbomeca engine is thefree-turbine Tormo 3B, three of which are geared to the single rotor in the big Frelon helicopter One of the latest of the com-pany's axial/centrifugal family, the 3B is rated at 812 s.h.p. with Although capable of over 1,000 h.p., the Blackburn Nimbus is limited to 650 s.h.p. in the Westland (Saro) Wasp, in which it is here installed. Its development, to MoA contract, is progressing well s.f.c. of 0.67, and it weighs 5601b fully equipped. ProductionFrelons will have the Turmo 3C, rated at 900 sJbi.p. at up to 100° F. Blackburn's Tunno weighs 2751b and in the Saro P.531 Mk 0is rated at 400 h.p. Blackburn's new engine is the excellent Nimbus, originally known as the A. 129, which is being developedunder contract to the MoA. As the powerplant of the Wasp Mk 1 it is derated to 650 s.h.p. and will maintain this power under anyambient conditions which might be expected. A complete simu- lated type-test to the new schedule has been completed, and whenfully rated the Nimbus will deliver well over 1,000 s.h.p. with s.f.c. below 0.68. Dry weight is 3901b and the selling price isestimated at "£10 per horse power"—a competitive figure. Chief competitor of the Nimbus is the de Havilland Gnome,British version of the General Electric T58. Both the British and American engines have the same 10-stage axial compressorwith four rows of variable stators, and the bare basic power section weighs only about 2501b. Both firms are actively engaged indeveloping this excellent engine towards 2,000 h.p. and de Havil- land have also produced the Coupled Gnome rated at 2,200 h.p.The initial 1,000 h.p. unit for RAF Whirlwinds will enter service with an overhaul life of 400hr, and is priced at something shortof £15,000. One of the best helicopter engines in America is the Lycoming LTC1, now in production as the T53 for a variety ofhelicopters, two of which—the USAF Huskie and Army Iroquois —are being bought in great quantity. This free-turbine unitweighs 4251b and is rated at 700/960 h.p. with si.c. of 0.696. A somewhat larger engine with roughly the same basic layoutis the Napier Gazelle, which is perhaps the most important heli- copter powerplant in Britain. The initial production version hasan inwards-radial intake, weighs about 8301b with full equipment and can run in any attitude. Two Gazelle 101s, each with a2imin rating of 1,650 sJi.p., are installed in the Belvedere; the Wessex Mk 1 has a single Gazelle 161, with a lhr rating of1,465 s.h.p. Both aircraft are next month to undergo tropical trials in Libya, and the Wessex will start Arctic testing in theautumn. The Gazelle has completed a full icing programme in Canada, and was the first British engine to complete these trialsat the first attempt. Napier have now evolved the Gazelle 512, with a high-speed output shaft and a weight of only 6751b. Inmost installations this engine would have an axial intake and it may be fitted with single or quadruple exhaust ducts. The intakeis fined with Napier Spraymat heated panels, and although the accessories are carried around the intake they are driven fromthe front of the compressor shaft through two pairs of bevel gears. To permit higher temperatures, the first- and second-stage turbine blades are respectively of G67 and Nimonic 105, and the 5min and 30min ratings are both 1,640 s.h.p. A rather more powerful free-turbine engine is the LycomingLTC4, which is in production as the T55-L-5 for the US Army's big Boeing-Vertol Chinook. Originally planned to give about1,500 h.p. it now has a military rating of 2,200 h.p. with s.f.c. of 0.595 and has already given over 2,500 h.p. on the bench. Aneven more powerful engine, being developed for the US Navy, is the General Electric T64-GE-2. Like the smaller T58 it hasvery advanced design points, and its pressure ratio of 12.5 :1 brings the s.f.c. down to 0.506 at the maximum rating of 2,650 s.h.p.and to even lower values at partial power. Weight is 8541b and two may be used in the Sikorsky S-64. Napier's Eland single-shaft engine has logged well over l,200hras the powerplant of the prototype Rotodyne and the Eland 229 is at present flying in the hub-driven Westminster. ProductionWestminsters would have the Eland 221, with a 2imin rating of 3,500 h.p. At the time of writing the two most powerful heli-copter powerplants are the Rolls-Royce Tyne for the Westland (Fairey) Rotodyne and the Soviet TB-2BM which powers theMi-6. Both are high-pressure free-turbine engines, and their respective ratings are 5,250 and 4,700 s.h.p. The Russian heli-copter has a straightforward mechanical transmission system to the rotor shaft, but the Rotodyne engine is virtually a completeturboprop together with a hydraulic clutch to an auxiliary rear compressor feeding air to the pressure jets on the rotor.
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