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F-5 METIS HUD PDU Mounting Cradle

Technical Information

Catalogue No: C0513
Category: Head-Up Display [HUD]
Object Type: Mounting Tray
Object Name: F-5 METIS HUD PDU Mounting Cradle
Part No: 00-098-02
Serial No: 0060
Manufacturer: Unknown
Division: Unknown
Platform(s): F-5
Year of Manufacture: circa 2002
Dimensions:
Width (mm):
300 
Height (mm):
200 
Depth (mm):
360 
Weight (g):
2,350 
Location: Main Object Store
Inscription(s):

Mounting Cradle Assy

Notes:

One of the many derivatives of the F-16C/D Head Up Display design was that for the Republic of Singapore Airforce who procured 36 of the F-5S a single seat reconnaissance version of the F-5S and also 9 of the F-5T which was an upgraded version of the F-5F. The company provided a HUD under a programme called METIS and the PDU differed from the standard unit by having a dual Combiner and an active UFCP. The major elements were common with the RSAF F-16 C/D’s. The first flight was on the 12th September 2002 from Paya Lebar Air Base.
The PDU had a double Combiner but with the upper being about half the lower in length (there is no need for the forward lower section as the image transfers to the upper aft section to enhance the vertical field of view). The UFCP incorporates a multiline display but is otherwise similar to the standard.
The Mounting Tray allows the HUD to be accurately aligned to the aircraft axes a process known as boresighting.

The physical configuration of the HUDWAC was designed to be drop-in compatible with all known versions of the F-5E/F. Other than removal of the Lead Computing Optical Sight (LCOS) no rearrangement of existing systems nor structural modification was necessary; the new HUD mounts onto the same LCOS tray. The HUDWAC was made to be interchangeable between F-5E’s fitted with the APQ-153 radar and AHRS and those fitted with an APQ-159 radar and an INS without any modifications. The HUDWAC monitors the armament panel switch settings and the in-built software determines the required operating mode which overall makes the system easier to use than the original LCOS.

The HUDWAC consists of three line replaceable units; the Pilot’s Display Unit (PDU), an Electronics Unit (EU) and a Weapon Data Input Panel (WDIP).

 

The PDU gives a field of view nearly twice that of the ASG-29 Lead Computing Optical Sight it replaces. The unit hosts a control panel with switches and a keypad through which mission data such as target elevation and barometric pressure can be loaded. A 16mm film camera or a colour video camera can be attached to the aft end of the PDU. In this aircraft the HUD is hard mounted to a pre-aligned mounting frame, rather than an adjustable Mounting Tray i.e. it is already boresighted to the airframe. The drawback to the installation is that the HUD has to be long and narrow which is reflected in the design of the circuit boards within the unit. The High Voltage Power Supply locates on the underside of the PDU and there would be a Gun Camera and an Up-Front Control Panel fitted to customer requirements.

The HUD therefore has to be a long thin design although in these upgrades as many as possible of the F-16 modules were employed.  The alternative involved a reconstruction of the HUD mount to allow a conventional variant of the F-16C/D HUD to be fitted and this was the approach in some of the upgrade projects.

The EU contains 15 circuit cards of which 13 are common to the F-16C/D HUD; the two unique cards are for the interface to the F-5 avionic systems. The system software, also known as the Operational Flight Program (OFP) was written in Jovial J-73 language and the symbology was compliant with the Mil-Std-187 standard.

The F-16C (single seat) and F-16D (two seat) variants entered production in 1984. The first C/D version was the Block 25 with improved cockpit avionics and radar which added all-weather capability with Beyond Visual Range (BVR) AIM-7 and AIM-120 air-air missiles. Blocks 30/32, 40/42 and 50/52 were later C/D versions. The LANTIRN Diffractive optics HUD was designed for the new aircraft but development was delayed by the complexity of the manufacturing problems. As an interim the Company offered a wide angle conventional optic design.

The initial order was placed in 1984 and was valued at nearly $50 million (then about £30 million) to cover both development and production. Over 2300 HUD’s were delivered for the F-16 and the system has been the basis of equipment supplied for other programmes such as for the A-7D/K and F-5 adding another 1500 units to the family. In 1985 the F-16C/D design won the Queen’s Award for Technology Improvements to aircraft Head Up Display systems for the Company.

The HUD Pilot's Display Unit (PDU)

The HUD PDU has both a raster and a cursive capability with the first application of ‘cursive in flyback’ in which the same amount of symbology as in the daytime high brightness mode can be drawn on the CRT using the raster flyback period of the Night mode. A good grey scale was provided for sensor video and the system could operate in 525, 625, or 875-line standards. The system accuracy was enhanced by the ability to apply corrections for the windshield. The F-16 windshield in particular acts as a lens which modifies the focus of the system and this is compensated for in the optical module design but in addition there are linear distortions away from the centre of the field of view caused by the curvature of the one-piece canopy and manufacturing variations. It is possible to provide both a generic and a specific correction for the particular aircraft. The optics provides a 25degree Total Field of View and a 20o by 13.5o Instantaneous Field of View which was the maximum that could be achieved within the limitations of the 6.7-inch exit lens design and the large distance between the pilot and the HUD occasioned by the reclined high ‘G’ seat.  The exit lens is truncated, and the size is limited by the ability of the glass to withstand thermal shock. The field of view is about the maximum that can be achieved with a conventional refractive optics.

The Cathode Ray Tube is circular but with a blank area at the bottom; the beam is deflected into this area so that deflection calibration tests can be carried out without illuminating the phosphor. As usual the delection is magnetic and the focus electro-static. The deflection coils and the matching card are now all constructed by Rank Electronic Tubes and the item is delivered as a Tube Unit Assembly.The venerable P1 phosphor is still used but the first Anode voltage is now a nominal 18kV and the tube operates with a Focus voltage of 2.96kV to 4.76kV.

The Camera was left forward of the Combiner to retain commonality with the LANTIRN design. In a refractive optic design, the outside world and symbology can be captured from aft of the Combiner but with the reflective design this is not possible, and the symbology is added to the outside world view by video mixing after scan conversion in the Electronics Unit.

The Head Up Display castings were all made by Kent Alloys who worked for Medway Investment Castings.

 

The HUD Electronics Unit (EU)

The F-16 C/D Electronics Unit contains twenty circuit boards. The Processor/Symbol Generator uses the MIL-STD 1553B (Standardised Electronic Data Highway) databus architecture, the MIL-STD-1750 (Standardised Computer architecture) processor and the MIL-STD-1589A (Standardised Jovial J73 Computer language) software. This was the first time that all three Standards had been used together and the Company was way ahead of its US rivals in this respect. The foundations for the implementation of these Standards was laid down by FARL from 1978 and led to a highly successful LSI chipset for the 1553 Databus. The HUD EU has comprehensive video mixing and scan conversion and self-contained weapon aiming capability.

 

The Total field of view (TFoV) of a Head Up Display is defined as the “Total angle subtended by the display symbology seen with head movement” and it is largely determined by the size of the exit lens in a conventional refractive optical design.

The Instantaneous Field of View (IFoV) is the “Subtended angle of display seen from one head position using one eye” and the Binocular Instantaneous Field of View is the “Subtended angle of display seen from one head position using both eyes”. Typically a HUD TFoV will be circular and of 25° and may only have an IFoV of 13.5° in elevation and 20° in azimuth. The pilot has two eyes so the actual IFoV is two overlapping circles a bit like a Venn diagram. The exit lens is limited in size by what can be made accurately but also by the environment. The stress of operation over a very wide temperature range (-40°C to +125°C or more in an enclosed cockpit in the desert sun) and extreme temperature shock should the canopy be lost at altitude together with severe vibration especially when the aircraft gun is firing have held this lens to no more than about 6.7inches in diameter.

The vertical field of view can be extended by the addition of a second Combiner Glass forward of the first glass and extending higher up. The optical system then provides an IFoV with a second but smaller double circular field above the first. Now, the image has to transition from the aft glass to the forward glass in a smooth manner and this done by using graded optical coatings which are traditionally a neutral density coating. Thus the coating on the aft glass reduces in reflectance at the top as the forward glass coating increases in reflectance and the transmittance, of course, does the opposite. The whole effect must be achieved without any obvious display artefacts and even more important there must be no false horizon lines created. This last issue is aided by making the top of the Combiner Glass angle down in the forward direction on the sight line from the design eye position. To achieve this gradation of coatings requires a sophisticated deposition technique. The Company used this optical design on the F-5 HUD and increased the vertical FoV by about 3°. Originally the graded coatings were made by Watshams who were experts in coating optical elements.

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