Honeywell T55. The Honeywell T55 (formerly Lycoming; company designation LTC-4) is a turboshaft engine used on American helicopters and fixed-wing aircraft (in turboprop form) since the 1950s, and in unlimited hydroplanes since the 1980s. As of 2021, more than 6,000 of these engines have been built. It is produced by Honeywell Aerospace, a division of Honeywell based in Phoenix, Arizona, and was originally designed by the Turbine Engine Division of Lycoming Engines in Stratford, Connecticut, as a scaled-up version of the smaller Lycoming T53. The T55 serves as the engine on several major applications including the CH-47-Chinook, the Bell 309, and the Piper PA-48 Enforcer. The T55 also serves as the core of the Lycoming ALF 502 turbofan. Since the T55 was first developed, progressive increases in airflow, overall pressure ratio, and turbine inlet temperature have more than tripled the power output of the engine.

Variants

Civil and experimental variants
LTC4A-1 Turboprop engine with a power rating of  and dry weight of ; was designated the YT55-L-1 after its 50-hour qualification test was completed in December 1957
LTC4B-1
LTC4B-2 Geared turboshaft engine with an initial power rating of ; completed a 50-hour qualification test demonstrating  in March 1958, and then was designated as the YT55-L-3 with a power rating of 
LTC4B-7 Ungeared version of the LTC4B-2, with an integral oil cooler and tank; demonstrated  in January 1960; the higher power rating resulted from increased turbine inlet temperatures, which came from small modifications learned from YT55-L-1 and YT55-L-3 development experience; completed 50-hour qualification test at  power rating in February 1960, after which it was designated as the YT55-L-5; completed its 150-hour qualification test in September 1960, after which its designation changed from YT55-L-5 to the T55-L-5 production engine
LTC4B-8 Civil designation for the T55-L-7 military engine; dry weight of  also powered the original Bell 214 helicopter as a  engine in 1970
LTC4B-8D  engine powering the Bell 214A helicopter; uprated from the T55-L-7C; 433 engines produced between 1973 and 1977 for this military helicopter
LTC4B-11similar to L-7 with two-stage gas generator turbine
LTC4B-12 Turboprop engine with a power rating of  and a weight of ,  more than the T55-L-11 that it is derived from; brake-specific fuel consumption (BSFC) of 
LTC4C-2 Civil designation for the YT55-L-1A military turboprop engine
LTC4G-3 Turboprop engine with a maximum and normal power rating of ; high-performance version of the T55-L-1
LTC4G-4
LTC4K9-stage compressor
LTC4K-2
LTC4M-1
LTC4R-1 Turboprop engine with a power rating of , weight of , pressure ratio of 8.2:1, and a BSFC of 
PLF1A-2 First experimental high-bypass turbofan engine produced in the United States, initially run in February 1964; two produced; used the engine core of the T55-L-7;  geared fan stage, producing a static thrust of ; predecessor of the ALF 502 and LF 507 production turbofans; bypass ratio of 6:1; weight of  maximum pressure ratio of 1.4:1 (fan) and 9.5:1 (engine), turbine inlet temperature of , maximum rated air flow for the gas generator and fan of , thrust-specific fuel consumption (TSFC) of 
PLF1B-2Turbofan with T55 / LTC4K 9-stage compressor gas generator core
PLF1C-1 Turbofan based on the T55-L-7C turboshaft, producing  of thrust;  length,  fan diameter, 6:1 bypass ratio,  weight, TSFC of 
PLF1C-2 Turbofan based on the T55-L-11 turboshaft, producing  of thrust;  length,  fan diameter, 8.2:1 bypass ratio,  weight, TSFC of 
T5508D Certified September 16, 1975; dry weight ;  engine powering the Bell 214B helicopter, which was produced between 1976 and 1981; 88 engines manufactured for that commercial helicopter; commercial version of the LTC4-8D
AL5512 Certified November 7, 1980; turboshaft engine with a sea-level power rating of  max continuous and  5-minute takeoff; 30-minute power rating of  with one engine inoperative; dry weight ; used on the Boeing Model 234 (civilian version of the Chinook); based on the T55-L-712; produced between 1979 and 1985, with 44 engines manufactured; also used on the Boeing Model 360, a technology demonstrator helicopter, in 1987

Military variants
YT55-L-1 Turboprop engine with a maximum and normal power rating of  and a pressure ratio of 6:1
YT55-L-1A Turboprop version of the YT55-L-3, producing ; length , diameter , dry weight , pressure ratio 6.5:1, air mass flow , BSFC 
YT55-L-3 Turboshaft engine with a maximum and normal power rating of  and a pressure ratio of 6:1; a geared engine that was initially selected to power the Army Chinook helicopter HC-1B (later designated as the CH-47A) in July 1958 by a joint Air Force/Army team
T55-L-5 Turboshaft engine with a maximum and normal power rating of  and a pressure ratio of 6:1; high-speed version of the T55-L-3 allowed for use on the Chinook instead of the geared YT55-L-3 engine due to August 1958 engine contract modification, with the reduction gearing now provided in the helicopter power transmission system instead of the engine;  weight engine; first delivered for the Chinook in August 1960; powered first flight of the Chinook in October 1961; selected for the Curtiss-Wright X-19 tiltrotor aircraft in August 1962; 146 engines manufactured between 1960 and 1963 for the CH-47A
T55-L-7 Turboshaft engine with a power rating of  and a BSFC of ; completed 150-hour qualification test in September 1962 at a  power rating;
T55-L-7B Military and normal power rating of ; used on the CH-47A
T55-L-7C Turboshaft engine with a maximum, military, and normal power rating of ; used on the CH-47B; BSFC of ; passed qualification testing in September 1966
YT55-L-9 Turboprop engine with a power rating of , weight of , pressure ratio of 6.4:1, and a BSFC of ; used on the Rockwell YAT-28E; also powered Piper Enforcer prototype aircraft for flight tests in 1971 and 1983-1984
T55-L-11 Turboshaft engine with a maximum, military, and normal power rating of ; used on the CH-47C; BSFC of ; completed 50-hour preliminary flight rating test (PFRT) in May 1967
T55-L-712  turboshaft engine used on the CH-47D, with production starting in 1978; 849 engines manufactured by 1989
T55-L-714  turboshaft engine used on the MH-47E Chinook SOF
T55-GA-714A  turboshaft engine used on the CH-47F; low-rate initial production started in December 1997
T55-L-714A
5,000 shp (3,729 kW)
T55-GA-714C  turboshaft engine to be tested on an CH-47F testbed aircraft, offering a 25 percent increase in power output and 10 percent reduction in fuel consumption compared to the T55-GA-714A; initial testing of the first engine began in November 2021
T55-L-714C6,000 shp (4,474 kW)
T55-GA-715 A  turboshaft engine upgrade kit proposed in 2008 for a  growth version of the Chinook

HTS7500

Applications
T55/LTC4
 Bell 214
 Bell 309 KingCobra
 Boeing CH-47 Chinook
 Boeing Chinook (UK variants)
 Boeing Model 360
 Boeing RC-135 - One T55 was fitted to the RC-135E variant to drive a generator providing power to the aircraft's phased array radar.
 Boeing Vertol BV-347
 Curtiss-Wright X-19
 North American YAT-28E Trojan
 Piper PA-48 Enforcer
 Sikorsky–Boeing SB-1 Defiant
 Unlimited hydroplanes

HTS7500
 Sikorsky–Boeing SB-1 Defiant X

Specifications (T55-L-714A)

See also

References

Bibliography

External links

 Honeywell T55 page

T55
T55
Mixed-compressor gas turbines
1950s turboshaft engines