General Electric CJ805

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
CJ805
Convair 880 Lisa Marie Graceland Memphis TN 2013-04-01 026.jpg
A CJ805-3A turbojet installed on a Convair 880 airliner
Type Turbojet (CJ805)
Turbofan (CJ805-23)
National origin United States
Manufacturer General Electric Aircraft Engines
Major applications CJ805: Convair 880
CJ805-23: Convair 990
Developed from General Electric J79
Rear view of a CJ805-3 turbojet equipped with a scalloped nozzle hush kit.

The General Electric CJ805 is a jet engine which was developed by GE Aviation in the late 1950s. It was a civilian version of the J79 and differed only in detail.[1] It was developed in two versions. The basic CJ805-3 was a turbojet and powered the Convair 880, while CJ805-23 (military designation TF35), a turbofan derivative, powered the Convair 990 airliners.

Design and development[edit]

Impetus[edit]

Turbojet engines consist of a compressor at the front, a burner area, and then a turbine that powers the compressor. In order to reach practical compression ratios, compressors typically consist of multiple "stages", each further compressing the intake air. In the case of an axial flow design, the stages resemble fan disks or pinwheels, situated behind each other along a common shaft.

One common problem in early jet engine designs was the phenomenon of "surging" or compressor stall. This occurs mostly at low speeds when the airflow through the engine is small, or "off-design", conditions. It may also occur when the airflow is not directly onto the front of the engine. As the air reaches the higher compression stages of the compressor, instabilities can form that, in extreme cases, can damage the engine. One common solution found on early engines was the use of "bleed air", openings near the middle of the compressor stages that feed the air around the high-pressure section and into the burner. These are closed as the engine RPM increases towards operational speeds.

Another solution to this problem is the use of variable stators or inlet vanes. In these designs, the angle of incidence of the stators at the front of the engine can be changed, allowing the degree of compression to be adjusted. At low speeds, the vanes are angled to lower the compression. This has the advantage of being more efficient than a bleed system because the entire compressor is used across the entire power range, but the disadvantage is significant mechanical complexity as each stator blade has to be independently rotated to the desired angles.

Rolls-Royce considered the variable stator idea in the 1940s, but abandoned it.[2] They began development of multi-spool designs, a concept that was also selected by Pratt & Whitney. The variable stator was only selected by GE after a long internal debate on the best way to design an engine that would operate at speeds low enough for easy landings on an aircraft carrier all the way to Mach 2 (2,450 km/h; 1,522 mph). The J79 emerged as a powerful, lightweight design, and GE began considering it as the basis for a high-power engine for commercial use.[3]

CJ805 program[edit]

RB-66A test aircraft powered by two GE CJ805-3 engines, on the ramp at Edwards AFB

In 1952, Chapman Walker's design team at GE built a one-off prototype of a jet engine designed specifically for transatlantic airliners. It used a single-stage fan powered by the same turbine shaft as the main engine compressor, as opposed to the Pratt & Whitney designs that were using a separate power shaft to run the fan. The GE design proved to be difficult to start and operate and was not developed further.[2]

In 1955 Jack Parker took over GE's Aircraft Gas Turbine division. He hired Dixon Speas to begin interviewing executives at airlines to try to get a sense of the future market. Parker asked Speas to interview not the CEO's, but executives that might be the CEO by the time GE was ready to enter the civilian jet engine market. Parker, Speas and Neil Burgess, who ran the J79 program, spent a month meeting with AA, Delta, United, KLM, Swissair and SAS. The meetings demonstrated that those airlines that were flying propeller aircraft across the Atlantic were all looking to replace them with jets.[4]

CJ805-3[edit]

Around the same time, Convair was canvassing US carriers and found demand for a smaller jet aircraft for medium-range domestic routes. They began development of what would become the 880, and approached Burgess to see if GE could develop a version of the J79 for this role. Burgess responded by quickly sketching a version of the J79 with the afterburner removed and replaced by a thrust reverser, giving them an estimated unit price of $125,000 per engine.[2]

The 880's primary sales feature over the competing Douglas DC-8 and Boeing 707 was a higher cruise speed. This demanded more engine power from a lighter design, which naturally led to a design like the J79. To gain experience with the engine in a civil setting, GE equipped a Douglas RB-66 with the new engine and flew simulated civil aviation routes out of Edwards Air Force Base.[5]

As development progressed, the 707 began to enter service, and noise complains became a serious issue. There was already a lawsuit, by residents around Newark airport, concerning the noise from existing propeller-driven aircraft such as the Super Constellation, Stratocruiser and DC-7C.[6] One way to reduce this problem is to mix cold air into the jet exhaust, which was accomplished on early engines with the addition of scalloped nozzles.[a] This solution was also adopted for the CJ805.

CJ805-23[edit]

Cutaway of a CJ805-23, the turbofan version of the engine, with fan at the rear
The turbofan CJ805-23 powered the Convair 990 airliners

Several airlines asked Convair for a larger version of the 880 with potential transatlantic range. Such a design would be larger to hold more seating, as well has having to carry more fuel. To power it, a more powerful engine would be needed. By this time, the Rolls-Royce Conway was entering service, and the Pratt & Whitney JT3D was following close behind. These designs both had twin-spool compressors, as opposed to using variable stators, and the lower speed of the front, low-pressure, spool make it easy to power a fan.[8]

The problems RR and P&W had addressed with the two-spool system had been solved on the J79 with the variable stators, so in relative terms, the single compressor rotational speed was much faster than the low-pressure stage of these other engines. This meant it was not suitable for direct connection to a fan stage. Instead, GE solved this problem with the addition of a completely separate fan system at the rear of the engine, powered by a new turbine stage. The system was essentially a bolt-on extension to the existing design and had almost no effect on the operation of the original engine.[9]

Each turbine blade was an integral part of a blucket, the outboard section of which was a fan rotor blade.[10] Running freely on a stub shaft, a series of buckets, mounted on a disc, made up the aft rotor assembly. The efflux from the turbojet expanded through the (inner) turbine annulus, thus providing power directly to the fan blades located in the outer annulus. A full-length cowl, an annular exhaust system and a bucket thrust-reverser were fitted for the Convair 990.[11]

The unique feature of the -23 was the transonic single stage fan.[12] NACA had done a lot of research on multistage transonic compressors during the 50s. Using this data, GE decided to design and test a high-pressure ratio single stage transonic fan. Much to their amazement the unit more than met the design target, including that of high efficiency. A modified version of this research unit was subsequently incorporated into the CJ805-23 aft fan. With no experience of transonic fan design and little time available, Pratt & Whitney had to resort to using 2 fan stages to produce a similar pressure ratio for their JT-3D turbofan. Although not an overhung design, the -23 transonic fan did not require any inlet guide vanes. There was, however, a series of structural vanes to help support the fan casing.[13]

Production ends[edit]

With additional changes, fuselage stretches, and the addition of anti-shock bodies, the new airliner emerged as the Convair 990. However, by this time the project had suffered several delays, allowing new versions of the DC-8 and 707 to lock up major sales. In the end, Convair sold only 102 880s and 990s in total, losing $600 million on the program.[14]

There was only one other customer for the 805-23. In 1961, Sud Aviation approached GE to pitch them on the idea of adapting the Rolls-Royce Avon powered Caravelle to the 805-23, producing a flying technology showcase for both companies.[15] For this role they introduced a new version with a relatively short fan cowl and thrust reverser, compared to the full-length cowling on the 990.[16] Rolls-Royce quickly built and tested an aft-fan demonstrator Avon to compete with the greater thrust and lower specific fuel consumption of the CJ805-23. In the end, the Caravelle was instead re-engined with the P&W JT8D turbofan.[17]

The CJ805 program was not a commercial success, and GE lost approximately $80 million on the program with only a few hundred engines produced in total.[15] In service, the design proved fragile, but these problems led to the programs ultimate success for the company.[18]

During the time they were talking to airline CEOs, in 1956 the company hired the former head of American Airline's maintenance department, John Montgomery, to run the production lines. Montgomery gathered comments from the industry on the state of the engine market, and found that many were complaining about the unreliability of the large piston engines then being used, notably the Wright R-3350. Wright management refused to put more money into the program to improve the engine, leading to a serious backlash from the customers.[19]

Montgomery hired Walter Van Duyan away from Wright to set up GE's service department, and they provided excellent service in spite of the engine's problems. GE quickly gained a reputation for standing behind their products that endures to this day.[19]

The work on the 805 also had several spin-off products. Among them was another aft-fan design, the General Electric CF700 used in the Dassault Falcon 20 business jet, which was developed from the General Electric J85 in the same way as the J79 was adapted to the 805.[20] Their fan technology was also used in the XV-5 Vertifan.[21]

Variants and applications[edit]

CJ805-3
Convair 880[22]
CJ805-3A
Convair 880-22 : Revised variable inlet guide vane and stator control.[22]
CJ805-3B
Convair 880-22M : Increased thrust.[22]
CJ805-21
[23]
CJ805-23
Flight testing in a Douglas RB-66: Aft-fan variant with a direct drive fan attached to a free-running LP turbine.[22]
CJ805-23A
[22]
CJ805-23B
Convair 990[22]
CJ805-23C
Intended for the proposed Sud Aviation Caravelle 10A. Only a single Sud Aviation Caravelle intended as a prototype for the US market, was equipped with the CJ805.[22]

Specifications (CJ805-3B)[edit]

Data from FAA Type Certificate Data Sheet, E-306

General characteristics

  • Type: Single-spool turbojet
  • Length: 188.9 in (4,798 mm) with thrust reverser/suppressor
  • Diameter: 31.6 in (803 mm)
  • Dry weight: 3,213 lb (1,457 kg) with thrust reverser/suppressor

Components

  • Compressor: 17-stage axial flow
  • Combustors: can-annular
  • Turbine: 2× gas generator power stages
  • Fuel type: Aviation kerosene
  • Oil system: pressure spray/splash

Performance

Specifications (CJ805-23B)[edit]

Data from [1]

General characteristics

  • Type: Aft fan unmixed turbofan
  • Length: 139 in (3,531 mm)
  • Diameter: 53 in (1,346 mm)
  • Dry weight: 3,730 lb (1,692 kg)

Components

  • Compressor: 17-stage axial flow
  • Combustors: can-annular
  • Turbine: 2× gas generator power stages + 1× free running turbine with fan blades on the periphery
  • Fuel type: Aviation kerosene
  • Oil system: pressure spray/splash

Performance

See also[edit]

Related development

Related lists

Notes[edit]

  1. ^ Which has re-appeared in modern form on the Boeing 787.[7]

References[edit]

Citations[edit]

  1. ^ "Aero Engines 1960". Flight International. 18 March 1960. pp. 381–382. 
  2. ^ a b c Garvin 1998, p. 16.
  3. ^ Garvin 1998, p. 12.
  4. ^ Garvin 1998, p. 15.
  5. ^ Garvin 1998, pp. 20-21.
  6. ^ Beranek, Leo (January 2007). "The Noisy Dawn of the Jet Age" (PDF). Sound and Vibration. 
  7. ^ "NASA Helps Create a More Silent Night". NASA. 13 December 2010. 
  8. ^ Garvin 1998, pp. 16-17.
  9. ^ Garvin 1998, pp. 16-18.
  10. ^ "Fig7". Flight International. 30 October 1959. p. 457. 
  11. ^ "Fig8". Flight International. 30 October 1959. p. 457. 
  12. ^ "The Turbofan Emerges: GE's CJ805-23 Aft Fan Engine". Atmospheric Flight in the Twentieth Century. 
  13. ^ "3D sectional view of CJ805-23". Retrieved 2016-02-18. 
  14. ^ Garvin 1998, p. 18.
  15. ^ a b Garvin 1998, pp. 19.
  16. ^ Archer, Robert (8 June 1961). "Caravelle a la General Electric". Flight International. pp. 797–798. 
  17. ^ Rolls-Royce Aero Engines" Bill Guuston, Patrick Stephens Ltd. 1989, ISBN 1-85260-037-3, p.142
  18. ^ Garvin 1998, p. 21.
  19. ^ a b Garvin 1998, p. 22.
  20. ^ Garvin 1998, p. 23.
  21. ^ "The Power to Fly" Brian Rowe, Pen & Sword Aviation 2005, ISBN 1 84415 200 6, p.25
  22. ^ a b c d e f g Bridgman 1955, pp. 62-63.
  23. ^ Bridgman 1955, p. 60.

Bibliography[edit]

  • Bridgman, Leonard (1955). Jane's all the World's Aircraft 1955-56. Jane's all the World's Aircraft Publishing Co. Ltd. 
  • Garvin, Robert (1998). Starting Something Big The Commercial Emergence of GE Aircraft Engines. AIAA. ISBN 1-56347-289-9. 
  • Gunston, Bill (2006). World Encyclopedia of Aero Engines, 5th Edition. Phoenix Mill, Gloucestershire, England, UK: Sutton Publishing Limited. ISBN 0-7509-4479-X. 
  • Neumann, Gerhard (June 1984). Herman the German. William Morrow & Co. p. 269. ISBN 0-688-01682-0. The former enemy alien and Air Corps G.I. whose inventive skills and maverick management techniques made jet engine history 

External links[edit]