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Lavi Part II

The powerplant of the Lavi was the Pratt & Whitney PW1120 turbofan, rated at 6,137 kg dry and 9,337 kg with reheat and was a derivative of the F100 turbofan. The development of the PW1120, according to IDF/AF specifications, started in June 1980. It retained the F100 core module, gearbox, fuel pump, forward ducts, as well as the F100 digital electronic control, with only minor modifications. Unique PW1120 components included a wide chord low pressure (LP) compressor, single-stage uncooled low pressure (LP) turbine, simplified single stream augmentor, and a lightweight convergent/divergent nozzle. Full scale testing was initiated in June 1982, and flight clearance of the PW1120 was tested in August 1984. The PW1120 had 70 per cent similarity with the F100, so the IDF/AF would not need a special facility for spare parts. It would be built under licence by Bet-Shemesh Engines Limited in Israel.

IAI installed one PW1120 in the starboard nacelle of an F-4E-32-MC of the IDF/AF (Number 334/66-0327) to explore the airframe/powerplant combination for an upgrade programme of the F-4E, known as Kurnass 2000 (Heavy Hammer) or Super Phantom and to act as an engine testbed for the Lavi. The powerplant was more powerful, and more fuel efficient than the General Electric J79-GE-17 turbojet normally installed in the F-4E.

The structural changes included modifying the air inlet ducts, new powerplant attachment points, new or modified powerplant baydoors, new airframe mounted gearbox with integrated drive generators and automatic throttle system. It also included a modified bleed managment and air-conditioning ducting system, modified fuel and hydraulic systems, and a powerplant control/airframe interface. It was first flown on 30 July 1986. Two PW1120 powerplants were installed in the same F-4E and it was flown for the first time on 24 April 1987.

This proved very successful, allowing the Kurnass 2000 to exceed Mach 1 without the afterburners, and endowing a combat thrust-to-weight ratio of 1.04 (17 per cent better than the F-4E). This improved sustained turn rate by 15 per cent, climb rate by 36 per cent, medium-level acceleration by 27 per cent and low-level speed with 18 bombs from 1,046 km/h to 1,120 km/h. It was demonstrated at the Paris Air Show in 1987 carrying the show number 229 and civil registration 4X-JPA. However, McDonnell Douglas refused to approve the modification, because it offered a flight performance equal to that of the F/A-18C/D, and endangered any future sales of the F/A-18C/D.

The internal fuel capacity was 3,330 litres (2,722 kg), some 16 per cent less than the F-16, although this was claimed to be offset by the low drag of the Lavi airframe and the low specific fuel consumption (sfc) of the powerplant. Single point high pressure refuelling was adopted for quick turnaround, and provision made for air refuelling with a female type receptable compatible with flying boom-equipped tankers. To aid the flight test programme, the Lavi prototypes were also equipped with bolt-on refuelling probes. The external fuel capacity was 4,164 kg in two 2,548 litre drop tanks on the inboard pair wing stations.

Specification of the Pratt & Whitney PW1120

Performance ratings (ISA, S/L):

  • Static thrust: 6,137 kg.
  • Augmented thrust: 9,337 kg. Mass flow: 80.9
  • kg. Pressure ratio: 26.8.
  • Specific fuel consumption:
  • Static thrust: 22.7 mg/Ns. Augmentd thrust: 52.65 mg/Ns.
  • Dimensions:
  • Length: 4,110 mm. Maximum diameter: 1,021 mm.
  • Weights: Dry weight: 1,292 kg.

The Lavi had an AiResearch enviromental control system for air-conditioning pressurisation, and powerplant bleed air control. A pneudralics bootstrap type hydraulic system with a pressure of 207 bars with Adex pumps was also installed. The electronical system was powered by a Sundstrand 60 kVA integrated drive generator, for single-channel AC power at 400 Hz, with a SAFT main and Marathon standby battery. Sundstrand also provided the actuation system, with geared rotory actuators, for the leading-edge flaps. The Lavi had an AiResearch emergency power unit (EPU) and a Garrett secondary power system.

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The avionics of the Lavi were modular - they could be upgraded by loading new software into the Elbit ACE-4 mission computer. The purpose was that the airframe would not require many modifications during its life. The avionics suite was stated to be almost enterely of Israeli design. The flexibility and the situational awarness were emphasised to reduce the pilot workload at high g and in a dense threat environment. The air data computer was provided by Astronautics. Most of the avionics of the Lavi had already been test flown in a Boeing Model 727 testbed of IAI.

The Cockpit

A wrap around windshield and bubble canopy gave excellent all-round vision. But where a steeply raked seat and sidestick controller similar to the F-16 might have been excepted, IAI selected a conventional upright seat and central control column. The reasoning was as follows. The raked seat raised the pilot's knees, causing a reduction in panel space which could ill be spared while neck and shoulder strains were common in the F-16 when a pilot craned around in his steeply raked seat to search the sky astern while pulling high g. The sidestick controller was faulted on three counts:

1.. It virtually neutralised the starboard console space.
2.. With a force transducer it was difficult for an instructor pilot to know precisely what a pupil was trying to do.
3.. In the event of quite a minor injury to the right arm, the pilot would not be able to recover the Lavi to its base. With a central stick, the Lavi could be flown left-handed with little difficulty.

The cockpit layout was state of the art, with HOTAS (hands-on-throttle and stick), and a Hughes Aircraft wide-angle diffractive optics head-up-display (HUD) surmounting a single El-Op up-front control panel, through which most of the systems were operated. Furthermore, the cockpit had LCD technology powerplant indicators.

Elbit Computers Ltd was selected as prime contractor for the integrated display system, which included the HUD, the three head-down diplays (HDD) (two of them were colour presentations and the third black and white), display computers, and communications controller, which included an Elta ARC-740 fully computerised onboard UHF radio system. Data-sharing between the HDDs would ensure display redundancy. The navigation system included the Tuman TINS 1700 advanced inertial navigation system. Control-column, throttle and display keyboard were all encoded in the display computers, which would themselves had a back-up function to the main aircraft computer, the Elbit ACE-4.

Elbit ACE-4 Mission Computer

The Elbit ACE-4 mission computer was selected for the IAI Lavi. It was compatible with both the MIL-STD-1750A and MIl-STD-1553B standards and could be used for display, digital radar, stores managment and (future) avionics integration. It had a memory of 128 K.

Elta EL/M-2035 Multi-Mode Pulse Doppler Radar

The Elta EL/M-2035 multi-mode pulse-Doppler radar was a development of the Elta EL/M-2021B multi-mode Doppler radar of the IAI Kfir-C2. The radar was very advanced and had a coherent transmitter and a stable multi-channel receiver for reliable look-down performance over a broad band of frequencies and for high resolution mapping. An Elta programmable signal processor, backed by a distributed, embedded computer network, would provide optimum allocation of computing power and great flexibility for growth and the updating of algorithims and systems growth.

The radar could provide speed and position of targets in the air and on the ground, and could provide the pilot with a map of the terrain the Lavi was overflying. It could track several targets at 46 km distance in at least five air-to-air modes (automatic target aquisition, boresight, look down, look up and track while scan (TWS)). The radar had at least two air-to-ground modes (beam-sharpened ground mapping/terrain avoidance and sea search). After the cancellation of the Lavi programme the radar was offered for multi-role fighter retrofits, including the Denel Cheetah E.

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