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F-5 HUD Pilot's Display Unit

Technical Information

Catalogue No: C0800
Category: Head-Up Display [HUD]
Object Type: Display Unit
Object Name: F-5 HUD Pilot's Display Unit
Part No: 79-090-03
Serial No: K0656C004
Manufacturer: Unknown
Division: Unknown
Platform(s): F-5
Year of Manufacture: 1984
Dimensions:
Width (mm):
138 
Height (mm):
295 
Depth (mm):
680 
Weight (g):
9,560 
Location: Mezzanine Store
Inscription(s):

Pilots Display Unit
Contract F09603-84-G-1438
Dsgn Act K0656
PN 79-090-03
Mfr K0656
NSN
Ser. No. K0656C004
------------------------------
[Optical Module]
Part No. 2501-00049.
Serial No. F500045
Mfr Code K6111
Mfr Part No. 039909
NSN
Cont No. F09603-84-G-1438/SA15
------------------------------
Optical Module Assy K0656
229-034915
S/N K0656 004
NSN

Notes:

Made up from miscellaneous parts. This unit is typical of designs for the F-5E/F.

Northrop built 792 F-5Es, 140 F-5Fs and 12 RF-5Es. More were built under license overseas: 91 F-5Es and -Fs in Switzerland, 68 by Korean Air in South Korea, and 308 in Taiwan. With this many aircraft there were numerous retrofit programmes and the Company supplied some 177 units for the F-5E/F.

In this aircraft the HUD is hard mounted to a pre-aligned mounting frame, 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.

In 1989, the Indonesian Air Force began to take delivery of its first F-16s, and these were based alongside its F-5s. In March 1995, Belgium's SABCA was awarded a contract to upgrade the Indonesian F-5 fleet so that the planes could act as lead-in fighter trainers for the F-16. The 16 aircraft were fitted with the GEC-Marconi Avionics HUD/WAC and Sky Guardian RWR, new air data computer, stores management system, HOTAS controls, and a MIL-STD-1553B databus.

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 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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