Junkers Jumo 004 Engine

A Junkers Jumo 004 cutaway

The Junkers Jumo 004 was a turbojet engine that was used by Germany during World War II. It was the first turbojet engine ever to see production in aircraft and it was used in several of the late-war German jet designs such as the Messerschmitt Me 262 and Arado Ar 234. The first Junkers Jumo was given the designation 109-004 and it had a total weight of 745 kg. The total length of the Jumo 004 is about 3.8 meters.

Development

Preliminary development work for Jet propulsion was undertaken by Junkers in 1937, with design work for a full scale turbo jet engine beginning in 1939, followed by construction of the Jumo 004 A in early 1940. The first unit was run by December 1940, and several units were ready by the Summer of 1941. Initial flight tests, utilising a Bf 110, were carried out either at the end of 1941 or March 1942, and led to the 004 B, which incorporated several modifications.

The Jumo 004 B was designed at the end of 1941, with the first unit running at the end of 1942. A prototype Me 262 was flown with a pair of 004s in the early summer of 1943.

Description

Type

Eight stage Axial-flow compressor with single stage turbine.

Compressor

Light alloy compressor casing built in two halves and bolted together. Compressor rotor consists of eight light-alloy discs bolted through and located by spigots. A tie-rod passes through the centre of the discs, which increase in diameter from the low pressure to the high pressure end. The outer casing diameter is uniform throughout the length. The blades are dove-tailed into staggered grooves on the periphery of the discs, and are fixed by grub-screws through each root. Stagger of the blades increases and the chord decreases in successive stages through the compressor, and the width of the disc heads becomes correspondingly smaller. All the blades are constructed of light alloy. Between each compressor stage are stator blades fixed to the outer casing, and built up in two half rings. There is a row of entry guide vanes and a row of stator vanes between each compressor stage, making seventeen rows in all. The entry guide vanes and the first row of stator blades are of fairly thick aerofoil section light alloy, the second row being of thinner aerofoil section, and the remainder of cambered sheet steel. The rotor turns on two steel shafts which are attached to the outside faces of the first and last discs. The front compressor bearing is made up of three ball-races, each capable of taking end thrust. The rear bearing consists of a single roller race. Cooling air is bled off between the 4th and 5th compressor stage, and is led into the double skin which surrounds the whole of the combustion chamber assembly. A small amount of air is allowed to pass into the space between the combustion chambers and the inner wall. Most of the air passes down one of the exhaust cone struts to circulate inside the cone, and to pass through small holes to cool the downstream face of the turbine disc. Some of this cooling air also passes into a double skin which extends to within 2 feet of the finale nozzle. After the last rotor stage, air is bled off internally and is taken through tunnels in two of the ribs in the casting to cool the upstream face of the turbine disc. More air is taken through three tunnels in the centre casting into the space between the two plate diaphragms in front of the turbine disc. Most of this air then passes into the hollow turbine nozzle guide vanes, emerging through slits in the trailing edge.

Combustion Chamber

There are six chambers disposed radially around the central casting carrying the rear compressor bearing and the turbine shaft bearing. They are numbered 1 to 6 from the rear, No 1 being horizontal on the left. Sparking plugs for initial combustion are in chambers 1, 3 and 5. Interconnectors are provided between the combustion chambers. A fuel injector in each chamber injects fuel upstream. Swirl vanes are fitted to the forward end of each chamber, with baffles at the rear, the hot gases passing through slot mixers formed in the rear wall. The hot gases then mix with the cold air which by passes the combustion chambers. The chambers are built up from aluminised mild steel sheet, and the combustion chamber housings are free to slide at the forward end to allow for expansion.

Turbine

There are sixty one turbine blades, fixed into the disc by forked blade roots secured in position by rivets. Later, to economise in material and to permit higher operating temperatures to be used, hollow turbine blades were used. The hollow blades are placed on lugs formed in the periphery of the disc, and fixed by a special soldering process, as well as by a 5 mm peg. Cooling air is directed inside the blades, which are manufactured from heat resisting steel containing 30% nickel and 15% chromium.

Tail Pipe

Mounted in the tailpipe is a moveable bullet operated by a servo motor through the throttle lever. A rack-and-pinion device moves it longtitudinally. On the ground the bullet is fully forward under 50% of the max rpm, and fully back (restricted orifice) between 50% and 80% of max rpm. At the beginning of take-off the bullet is near the end of its backward travel, but for flight above 20,000ft and speeds of 400mph, the bullet can be moved even further back to provide maximum thrust. The servo motor control is interlinked with a capsule surrounded by atmospheric pressure, and having ram pressure inside it, so that the position of the bullet is adjusted according to the ram pressure of they forward speed. The rear portion of the tail pipe has a double skin, and air passing over the nacelle is directed into it for cooling purposes.

Lubrication

Oil is carried in an annular nose tank. There are two pressure pumps - one supplying oil to the rpm regulator, oil servo motor and compressor bearing, the other supplying the rear compressor bearing and the two turbine rotor bearings. These bearings are enclosed in an oil tight case. A jet sprays oil into the interior of the splined shaft between the compressor and turbine shaft. Two scavenge pumps remove oil from the rear of the bearing casing and the rear turbine rotor bearing, and return it to the tank. Oil from the front casing drains into the bottom of the auxiliary drive casing, from where it is removed to the tank by a scavenge pump.

Auxiliaries

An auxiliary drive casing is arranged above and driven from the front compressor shaft. The fuel injection pump, rpm governor and thrust regulator pump and bullet servo motor pump are driven from this casing.

Starting System

A Ridel two cylinder two stroke starter engine, providing 10hp at 10,000rpm, is mounted in the air intake, co-axially with the compressor shaft. It can be started electrically from the cockpit, or by hand by means of a cable and pulley. Fuel for the starter motor is contained in a 3 litre tank mounted in the nose, forward of the oil tank. Starter fuel for the turbojet unit is contained in a semi-circular tank mounted mounted forward of the oil tank. Starter fuel was 87 octane petrol with a 5% mix of lubricating oil.

Starting Procedure

After actuating the necessary starting switches, the pilot must depress the required starter handle with right hand for 3-4 seconds, in order to prime the starter motor, before pulling the lever up - if the starter motor fired, the lever was to be held up until 2,000rpm was attained. Beside the lever was a button to be depressed to engage a low reading rev counter. When the revs reached 800rpm, a button on the throttle would be pressed to inject fuel into the main engine until thrust was obtained. with pressure on the throttle button maintained until 2,500rpm had been reached. Throttle to be gradually advanced at 2,000rpm, until pawl dropped into idling gate, permitting release of starting handle.

At this stage the right hand has to release the rev counter button to stwicth on the fuel cock near the throttle lever, which would still be gripped by the left hand, while maintaining pressure on the throttle button. Following activation of the fuel cock, the right hand must return to the rev counter button, remaining there until 3,000rpm had been reached.

Installation

The complete turbo jet unit is fixed at three pick up points, two above the rear compressor bearing, and one above the combustion chamber housing. All pipe lines and electrical connections are brought to a small panel above the compressor casing, in order to simplify installation procedure.

Instruments

The aircraft instrument panel contains an injection pressure gauge, an rpm indicator, an exhaust gas temperature gauge, exhaust pressure gauge and an oil pressure gauge. The RPM indicator has an inner scale reading from 0 to 3,000 used for starting, and an outer scale reading from 2,000 to 14,000 used during flight. The exhaust pressure gauge is connected to both the tail pipe and the compressor intake.

Dimensions and weight

The engine had an overall length, without the moveable bullet, of 3,864.5mm. Maximum diameter – across the intake cowling – was 805.5mm. Weight was 1,585lb.

Performance

Maximum RPM was 8,700. At sea level thrust was 1,605lb at 273 mph, with consumption of 2,920lb/hr, and 1,890lb at560 mph, with consumption of 3,680lb/hr. At 8,200ft thrust was 1,300lb at 273 mph, with consumption of 2,290lb/hr, and 1,600lb at560 mph, with consumption of 2,920lb/hr. At 36,000ft thrust was 572lb at 536 mph, with consumption of 1,080lb/hr, and 715lb at 560 mph, with consumption of 1,275lb/hr.

Fuel

The Jumo 004B used two types of diesel oil. Most installations used J2 oil, which had a specific weight of 0.815kg/ltr to 0.845kg/ltr. The alternative fuel was K1 oil, with a specific weight of 0.81kg/ltr to 0.85kg/ltr.

Variants

Jumo 004 C

Improved Jumo 004 B with auxiliary fuel injection and increased thrust - max at sea level 2,200lbs. Weight of 1,540 lbs + 3%.

Jumo 004 D-4

Development of the Jumo 004 B, with two stage fuel injection and a new regulator to prevent excessively rapid throttle movement. Thrust of 2,200lb permissible at all heights and speeds. The Jumo 004 E was a sub-variant of the D-4 with a shorter tail pipe.

Jumo 012

Projected version of the 004 intended for the Junkers Ju 287 fast bomber, the Jumo 012 had an eleven stage axial compressor and a two stage turbine. Expected thrust was from 6,000lb to 6,400lb, with consumption of 1.2lb per lb thrust per hour. Length was about 17ft, and weight was 4,400lb. No unit or component had been tested by the time of the German collapse. A sub variant with gearing for contra-rotating air-screws was designated Jumo 022.

Bibliography

• Bridgeman, Leonard. Jane's All The World's Aircraft 1945/46 (Reprinted 1998 as Jane's Fighting Aircraft of World War 2). Tiger Books. ISBN 1-85501-996-5
• Brown, Captain Eric Melrose. Wings of the Luftwaffe. Airlife Publishing. 1997. ISBN 1-85310-413-2
• Kay, Antony L. German Aircraft of the Second World War. Putnam. 2002.