53:
133:
187:
generator core and power turbine revolved in opposite directions, reducing the overall moment of inertia. For the helicopter engine replacement market, this ability allowed previous engines of either direction to be replaced simply. Some turboshaft engines' omni-angle freedom of their installation angle also allowed installation into existing helicopter designs, no matter how the previous engines had been arranged. In time though, the move towards axial LP compressors and so smaller diameter engines encouraged a move to the now-standard layout of one or two engines set side-by-side, horizontally above the cabin.
17:
196:
318:
148:
116:, made a forced landing on the estuary mud. The Proteus gears were redesigned and an emergency fuel shut-off device was fitted to prevent a similar reoccurrence. Writing in 1994, Gunston found it remarkable that protection was not common on free-turbine engines. However, certification regulations allow other methods for preventing excessive overspeed such as disc rubbing and blade interference.
263:
183:
turbine) with the rotor brake, the engine could be started and then, with the gas generator at a speed of 10,500 rpm, the brake released allowing the power turbine to accelerate and bring the rotor to its operating speed from stationary in just 15 seconds and a time from engine start to take-off of only 30 seconds.
249:
For small turboprop engines, the free-turbine design has come to dominate and these designs are also mostly reversed overall, with their air inlet and compressor to the rear, feeding forwards to hot section and power turbine at the front. This places the turbine output close to the propeller gearbox,
206:
Turboprop aircraft are still powered by a range of free- and non-free turbine engines. Larger engines have mostly retained the non-free design, although many are two-shaft designs where the 'power' turbine drives the propeller and the low-pressure compressor while the high-pressure compressor has its
158:
are a major market for turboshaft engines. When turboshaft engines became available in the 1950s, they were rapidly adopted for both new designs and as replacements for piston engines. They offered more power and far better power to weight ratios. Piston helicopters of this period had barely adequate
300:
The advantage of the pusher propfan with a free power turbine is its simplicity. The prop blades are attached directly to the outside of the rotating turbine disc. No gearboxes or drive shafts are required. The short length of the rotating components also reduces vibration. The static structure of
67:
where fuel is mixed with the compressed air and ignited. The combustion gases are expanded through a compressor-driving turbine, and then through a "free" power turbine before being exhausted to the atmosphere. The compressor and its turbine are connected by a common shaft which, together with the
39:
where the power is extracted from the exhaust stream of a gas turbine by an independent turbine, downstream of the gas turbine. The power turbine is not mechanically connected to the turbines that drive the compressors, hence the term "free", referring to the independence of the power output shaft
182:
The free-turbine engine was found to be particularly suitable. It does not need a clutch, as the gas generator may be started while the output shaft remains stationary. For the Wessex, this was used to give a particularly fast take-off from a cold start. By locking the main rotor (and the power
186:
A further advantage of the free turbine design was the ease with which a counter-rotating engine could be designed and manufactured, simply by reversing the power turbine alone. This allowed handed engines to be made in pairs when needed. It also allowed contra-rotating engines, where the gas
92:
to destruction after losing its connection to the propeller load. (In a single-shaft arrangement with a similar gearbox failure the turbine would still have most of its load from the compressor). Such a failure resulted in the 1954 accident of the second prototype
75:
Turboshaft engines are sometimes characterized by the number of spools. This refers to the number of compressor-and-turbine assemblies in the gas generator stage and does not include the free power turbine assembly. As an example, the
43:
The advantage of the free turbine is that the two turbines can operate at different speeds and that these speeds can vary relative to each other. This is particularly advantageous for varying loads, such as turboprop engines.
241:
have free turbines. The TP400 is a three-shaft design, with two compressor turbines and a separate power turbine. Where the turbine is at the rear of the engine, a turboprop engine requires a long drive shaft forwards to the
351:) two-spool gas turbine engine. A commercial derivative has been designed as the TF15 for marine and railroad applications, and a flight-rated version, the PLT27, was also developed but lost a major contract to the
250:
avoiding the need for a long driveshaft. Such engines are often recognisable externally, as they use external 'elbow' exhausts ahead of the main engine. A particularly common example of this is the
293:. Development of these engines stopped abruptly owing to corporate takeovers, rather than technical reasons. Rolls-Royce continued with design studies for such engines into the 1980s, as did
763:
20:
Simplified turboshaft engine, with a rear driveshaft, such as for a helicopter. The compressor spool, turbine and compressor, is in green. The free power turbine is in purple.
124:
Most turboshaft and turboprop engines now use free turbines. This includes those for static power generation, as marine propulsion and particularly for helicopters.
88:
One particular failure scenario, a gearbox failure, showed a free-turbine arrangement to be more at risk than a single-shaft turboprop. It could suffer a turbine
756:
458:
175:
turbine-powered HAR.9. As one of the first anti-submarine helicopters, the HAS.7 had been so weight restricted that it could carry either a search sonar
108:
led to an overspeed and release of the power turbine of Nº3 engine. It cut through the oil tank and started a fire that threatened the integrity of the
692:
672:
484:
749:
219:
503:
151:
Ukrainian MS-14VM helicopter engine, with typical side-mounted exhaust and with the output power shaft from the turbine passing through it
159:
performance; the switch to a turbine engine could both reduce several hundred pounds of engine weight, 600 lb (270 kg) for the
113:
1147:
80:
is a single-spool design that uses a 14-stage axial compressor; the independent power shaft is coaxial with the gas generator shaft.
700:. International Gas Turbine and Aeroengine Congress and Exposition. Cologne, Germany: The American Society of Mechanical Engineers.
1137:
1110:
441:
1142:
680:. International Gas Turbine Conference and Exhibit. Dusseldorf, Germany: The American Society of Mechanical Engineers.
722:
635:
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52:
16:
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199:
884:
168:
1059:
251:
1247:
132:
492:. Gas Turbine Power Conference and Exhibit. Washington, D.C.: The American Society of Mechanical Engineers.
40:(or spool). This is opposed to the power being extracted from the turbine/compressor shaft via a gearbox.
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243:
578:
553:
63:
A free-turbine turboshaft ingests air through an intake. The air passes through a compressor and into a
1090:
861:
606:
285:, rather than the more familiar tractor layout. The first such engine was the very early and promising
1278:
246:. Such long shafts can be a difficult design problem and must carefully control any shaft vibration.
1167:
1085:
945:
290:
286:
105:
56:
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511:
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816:
717:. Reston, Virginia: American Institute of Aeronautics and Astronautics, Inc. pp. 218–222.
532:
359:
215:
712:
301:
the engine over this length is a large diameter tube within the turbine. In most designs, two
1273:
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970:
406:
401:
305:
rings of turbine and propeller are used. Intermeshed contra-rotating turbines can act as the
266:
226:. It first ran in July 1945 and in December 1946 was the first turboprop to pass a 100 hour
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LeMoir, Ken (September 2001). "The
Theseus, our first Gas Turbine engine".
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An attractively simple configuration making use of the free turbine is the
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Textron
Lycoming AGT1500 Engine—Transitioning for Future Applications
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326:
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of 1942 with a ducted fan, followed by the unducted and much lighter
109:
89:
64:
33:
710:
486:
Design and
Development Review of the T64 Turboprop/Turboshaft Engine
68:
combustor, is known as a gas generator, which is modelled using the
1216:
975:
914:
836:
831:
812:
459:"Industry asks US Army, one shaft or two for new helicopter engine"
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826:
352:
345:
274:
714:
The
History of North American Small Gas Turbine Aircraft Engines
202:
with PT-6 engine, showing the exhaust elbows ahead of the engine
1000:
851:
262:
1180:
171:, this converted the inadequate piston-engined HAS.7 to the
167:, and also allow considerably more payload weight. For the
436:(4th ed.). Patrick Stephens Limited. pp. 43–44.
771:
674:
The AVCO-Lycoming TF15: A Regenerative Marine Gas
Turbine
218:
gas turbine and its broad design had been produced by
297:, but they have yet to appear as commercial engines.
309:
for each other, removing the need for static vanes.
482:
233:Some large turboprop engines, such as the original
72:. The (free) power turbine is on a separate shaft.
1148:Engine-indicating and crew-alerting system (EICAS)
210:The first free-turbine gas turbine engine was the
1181:Full Authority Digital Engine/Electronics (FADEC)
573:
571:
569:
254:engine, of which over 50,000 have been produced.
1265:
548:
546:
711:Leyes, Richard A.; Fleming, William A. (1999).
434:The Development of Jet and Turbine Aero Engines
1138:Electronic centralised aircraft monitor (ECAM)
690:
618:
616:
566:
358:Turboshaft engines were used to power several
139:showing the circumferential air intake of the
757:
670:
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1143:Electronic flight instrument system (EFIS)
764:
750:
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419:
143:and the two exhausts (red covers) per side
97:, G-ALRX, which was forced to land in the
316:
261:
194:
146:
131:
51:
15:
483:Ehrich, Frederic F. (March 5–9, 1961).
428:
1266:
600:
745:
508:Britannia Aircraft Preservation Trust
83:
13:
257:
14:
1290:
691:Horan, Richard (June 1–4, 1992).
671:Lauriat, T.B. (June 8–12, 1986).
1011:Thrust specific fuel consumption
652:"Whatever happened to propfans?"
562:. 29 November 1957. p. 838.
704:
684:
664:
644:
533:"Accident description – G-ALRX"
312:
119:
1060:Propeller speed reduction unit
476:
457:Parsons, Dan (18 March 2015).
450:
214:turboprop. This was the first
127:
1:
412:
587:. 26 July 1957. p. 118.
277:engine, with a rear-mounted
7:
971:Engine pressure ratio (EPR)
630:. 1986. pp. 6, 53–54.
380:
244:propeller reduction gearbox
190:
106:propeller reduction gearbox
10:
1295:
1238:Auxiliary power unit (APU)
862:Rotating detonation engine
1225:
1199:
1166:
1123:
1068:
1047:
1038:
938:
870:
800:
786:
377:(United States) service.
362:, most notably using the
179:a torpedo, but not both.
47:
946:Aircraft engine starting
504:"History of Romeo X-Ray"
287:Metropolitan-Vickers F.3
57:Austin 250hp gas turbine
822:Pulse detonation engine
537:Aviation Safety Network
360:gas turbine locomotives
26:free-turbine turboshaft
1016:Thrust to weight ratio
986:Overall pressure ratio
981:Jet engine performance
900:Centrifugal compressor
817:Gluhareff Pressure Jet
330:
270:
203:
152:
144:
60:
21:
1253:Ice protection system
1021:Variable cycle engine
991:Propulsive efficiency
407:Turbo-compound engine
402:Rocket turbine engine
320:
265:
198:
150:
135:
55:
19:
1153:Flight data recorder
910:Constant speed drive
890:Afterburner (reheat)
283:pusher configuration
78:General Electric T64
579:"Aero Engines 1957"
101:. A failure in the
1055:Propeller governor
392:Free-piston engine
331:
271:
204:
173:de Havilland Gnome
169:Westland Whirlwind
153:
145:
61:
37:gas turbine engine
22:
1261:
1260:
1133:Annunciator panel
1119:
1118:
1034:
1033:
925:Propelling nozzle
609:. pp. 18–23.
443:978-1-85260-618-3
342:Honeywell AGT1500
95:Bristol Britannia
84:Risk of overspeed
1286:
1279:Aircraft engines
1248:Hydraulic system
1243:Bleed air system
1233:Air-start system
1096:Counter-rotating
1045:
1044:
1026:Windmill restart
996:Specific impulse
966:Compressor stall
895:Axial compressor
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626:(4th ed.).
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510:. Archived from
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340:is powered by a
338:main battle tank
224:Tockington Manor
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1191:Thrust reversal
1168:Engine controls
1162:
1125:
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1091:Contra-rotating
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1030:
934:
880:Accessory drive
872:
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808:Air turborocket
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709:
705:
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660:. 12 June 2007.
650:
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628:Rolls-Royce plc
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605:. No. 31.
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387:Air turborocket
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303:contra-rotating
260:
258:Pusher propfans
237:and the modern
235:Bristol Proteus
212:Bristol Theseus
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165:Westland Wessex
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103:Bristol Proteus
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161:Napier Gazelle
137:Wessex HAS.31B
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99:Severn Estuary
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930:Turbine blade
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637:0-902121-04-9
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514:on 2015-09-27
513:
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439:
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431:
430:Gunston, Bill
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373:(France) and
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325:turbine in a
324:
321:Changing the
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112:. The pilot,
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81:
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71:
70:Brayton Cycle
66:
58:
54:
45:
41:
38:
35:
31:
28:is a form of
27:
18:
1274:Gas turbines
1212:Flame holder
1186:Thrust lever
1176:Autothrottle
1006:Thrust lapse
961:Bypass ratio
788:Gas turbines
780:gas turbines
728:. Retrieved
713:
706:
693:
686:
673:
666:
655:
646:
623:
603:Sleeve Notes
602:
582:
557:
536:
527:
516:. Retrieved
512:the original
507:
498:
485:
478:
466:. Retrieved
463:FlightGlobal
462:
452:
433:
357:
355:turboshaft.
332:
313:Land and sea
299:
279:unducted fan
272:
269:unducted fan
248:
232:
209:
205:
185:
181:
176:
154:
123:
120:Applications
87:
74:
62:
59:, sectioned.
42:
25:
23:
1126:instruments
1081:Blade pitch
1076:Autofeather
920:Nose bullet
773:Jet engines
307:guide vanes
220:Frank Owner
200:Beech T-34C
156:Helicopters
128:Helicopters
1268:Categories
1069:Principles
1048:Components
1040:Propellers
939:Principles
885:Air intake
873:components
871:Mechanical
847:Turboshaft
518:2015-06-14
413:References
375:Turboliner
371:Turbotrain
344:(formerly
30:turboshaft
1101:Proprotor
951:Bleed air
905:Combustor
842:Turboprop
432:(2006) .
364:Turbomeca
335:M1 Abrams
327:M1 Abrams
228:type test
114:Bill Pegg
110:wing spar
90:overspeed
65:combustor
34:turboprop
1217:Jet fuel
1106:Scimitar
976:Flameout
915:Impeller
837:Turbojet
832:Turbofan
813:Pulsejet
777:aircraft
730:30 March
554:"Wessex"
468:30 March
397:Motorjet
381:See also
349:Lycoming
191:Aircraft
1205:systems
827:Propfan
353:GE T700
346:Textron
323:AGT1500
275:propfan
216:Bristol
163:of the
141:Gazelle
1124:Engine
1001:Thrust
857:Rocket
852:Ramjet
721:
657:Flight
634:
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