General Electric J79

General Electric J79 from the front

General Electric J79 from behind

The J79 -Strahltriebwerk is a turbojet -drive from General Electric . It was developed in the 1950s and used in several combat aircraft. From 1955 to 1982 over 19,000 copies were made by GE and its licensees (including MTU in Germany ); this makes it one of the most successful jet engines. The German-American Gerhard Neumann was in charge of construction .

construction

The J79 is a single shaft engine with a 17-stage axial compressor , a three-stage turbine, a combined tube-ring combustion chamber with ten flame tubes and an afterburner. The compressor has adjustable stator vanes (VSV) and adjustable inlet vanes (VIGV) that prevent pressure loss in the compressor when the engine is started by allowing the airflow to hit the compressor vanes at the correct angle of attack.

history

J79 in an engine cowling for the B-58

The General Electric J79 was developed for the Convair B-58 supersonic bomber . It is the enlarged version of the General Electric J73 and was initially called the J73-GE-X24A. The first flight took place in Schenectady in 1955 on board a North American B-45 . The engine was built into the bomb bay for this purpose. In December 1955 a Douglas F4D was equipped with the prototype engine (Douglas XF4D) and flown. The engine prototype YJ79-GE-3 was then also used in the 17 pre-production YF-104.

Airplanes with J79 engines

Well-known fighters with the J79 are or were the North American A-5 , Convair B-58 , F-4 Phantom II , F-104 Starfighter and the Israeli IAI Kfir . In addition, it was planned in the late 1970s to equip the F-16 with the J79 engine as a cheaper export version, but this did not happen. It stayed with a prototype.

J79 cutaway model. The empty area in the foreground in front of the outlet nozzle is the afterburner

Smoke development

The high level of smoke generated by the engine is characteristic of the J79. The Luftwaffe's F-4 Phantom II in particular could be seen from afar, as they produced an intense plume of smoke. This property is undesirable because it makes it easier to discover the aircraft in aerial combat, so that measures have been taken in more modern engines to reduce or completely prevent the development of smoke. These long plumes of smoke combined with a certain inertia at high altitudes earned the engine the nickname “air defense diesel”.

A relatively small increase in the combustion temperature would make the exhaust plumes almost disappear, but increase the wear and tear on the engine significantly in peacetime. Therefore the temperature was reduced by the engine controller to more moderate ranges. The pilot was able to shut off the smoke formation immediately when the 1st afterburner stage was switched on , but with significantly increased fuel consumption. In the event of a crisis , the controller would have been quickly switched to a higher temperature, thus less smoke and a shorter service life. Similar service life-extending measures were carried out immediately after the reunification with the Klimow RD-33 engines of the MiG-29 of the former NVA . The major overhaul intervals and the overall service life could be extended significantly. This is a common way of reducing costs.

Modification MTU J79-J1K

Section through a J79 engine. (Lettering in English)

The license builds of the J79-GE-11A for the German F-104G have been greatly improved by MTU . The smoke formation has been significantly reduced by modifying the combustion chambers. The "howling" of the J79 engines could be almost completely stopped by redesigning the adjustable afterburner nozzle . The nozzle adjustment, which was susceptible in the original version, has been converted to a new hydraulic system. In this way, the dreaded loss of thrust from an afterburner nozzle remaining in the open position could be completely eliminated. The extreme loss of thrust that occurred after the afterburner failed because the nozzle was still open was in many cases the cause of the crash of the single-jet star fighter: Since the cross-section of the open afterburner nozzle was too large for the air throughput in normal operation, the thrust fell unexpectedly quickly to low values so that a stall occurred that was no longer controllable. Since the internal engine control was also responsible, a lever was provided in the cockpit of the F-104G, which enabled a one-time hydraulic emergency closure of the nozzle. After its activation, the pilot could fly to the next airfield without any problems (but without an afterburner). From this modification onwards, the now J79-J1K engine in the F-104G was a reliable, quick-reacting engine that was valued by pilots.

fuel

The J79 was designed for the NATO standard jet fuels ( kerosene ) in the qualities F-40 and convertible to F-34 and is preset to F-40. If the F-40 fuel could not be provided, the J79-J1K could be converted to the F-34 by an aircraft mechanic by simply adjusting an adjusting screw on the engine controller. The performance was then a little lower.

Derived engine types

General Electric CJ-805-23B on a Convair CV-990

With the CJ805 there is a civil version of the J79, which differs from the military version mainly in the lack of an afterburner and was used in the Convair CV-880 . This was further developed into a turbofan as the CJ805-23 . Instead of an afterburner, it has a single-stage free-wheeling turbine with a fan ( aft fan ). This arrangement is unique in aviation because it consists of an inner, concentric ring of turbine blades in the hot gas flow of the core engine (= driving engine ), framed by a ring of fan blades (= working machine to accelerate the bypass flow ). The unit rotated in a housing that was flanged to the high-pressure turbine housing of the core engine from the rear instead of the thrust tube with afterburner. It was used in the sub-version CJ805-23B on the Convair CV-990 and on a test basis on the Sud Aviation Caravelle in the sub-version CJ805-23C.

The basis for the later General Electric YJ93-GE-3 engine of the North American XB-70 was created from the J79-X275 test engine, essentially by increasing the diameter . This in turn was the basis of the General Electric GE4 of the Boeing 2707 , which was also designed for Mach-3 .

Technical data (J79-GE-17 of the F-4F Phantom II)

• Length 5.301 m
• Diameter 1.0 m
• Weight: 1724 kg
• Compressor: 17-stage axial, with adjustable stator
• Turbine: three-stage axial
• Compression: 13.5: 1
• Thrust: 52.8 kN, 79.6 kN with afterburner
• Air flow: 77 kg / s
• Turbine temperature: 1261 K
• Specific consumption: 200 kg / (h · kN) with afterburner
• Speed: 7685 min ⁻¹

Web links

Commons : General Electric J79  - Album with pictures, videos and audio files

• Subpage for the General Electric J79 on the website of the Gerhard Neumann Museum in Niederalteich, Bavaria
• Colored sectional view of the J79-J1K with explanations
• MacroMedia-FLASH animation of the J79-J1K from the museum in Niederalteich
• F-0644 Convair CJ805 Turbofan Engine Video Progress Report # 7 on YouTube , accessed February 21, 2020 (GE contemporary film about the development of the CJ805).

swell

1. ↑ Patrick Hoveler: Convair B-58 Aviation Classic 6/04
2. ↑ Explanation by an Air Force engine trainer and J1K operations manual
3. ↑ Manual of the J79-J1K