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A-7 Head Up Display

Technical Information

Catalogue No: C1601
Category: Head-Up Display [HUD]
Object Type: Display Unit
Object Name: A-7 Head Up Display
Part No: IP 938/AVQ-7(V)
Serial No: 4652
Manufacturer: Elliott Flight Automation
Division: Airborne Display [ADD]
Platform(s): A-7 Corsair
Year of Manufacture: circa 1970
Dimensions: Width (mm): 192
Height (mm): 297
Depth (mm): 840
Weight (g): 21,100
Location: Rack RAA11 [Main Store]

IP 938/AVQ-7(V)
115V. 3Ø 400~
Ser DGN ??52
Pt. No. 79-0?5-13
Mfr. 27489
Opt. Module
K3111 Assy
Serial No1158
Lens Module
K3111 Assy
[Combiner Assy]


The ILAAS PDU design was repackaged and a new highly innovative optics was added. The same ceramic CRT was used as it had to operate in a high vibration environment with buffeting of high-speed flight but also gunfire since the A-7 gun is only about five feet away from the HUD. The screen was a nominal 2inch diameter and was ground optically flat. The CRT fitted into a mounting ring with shims to maintain focus and alignment and could be replaced in about eight minutes.
The Head-Up Display optics consisted of a seven-part lens system and coated fold-mirror glass worked to tolerances of 0.05 per cent. Anti-reflection coatings were applied throughout. This design had a 5inch exit lens giving a 20deg TFoV and had a two-position Combiner.
The Combiner Glass had coatings that allowed 70% of the outside world to be transmitted to the pilot’s eye and 30% reflection of the display symbology luminance from the exit lens was returned to the pilot. The CRT operated at a maximum of 10,000ft Lamberts and of course this was attenuated by the relay lens system, the fold mirror and Combiner to give about 1260ft Lamberts to the pilot. A nominal 10,000ft Lambert outside world was used (this is equivalent to sunlit white cloud and is still the standard) and this was attenuated by the windshield and the Combiner giving around 6,300 ft Lamberts to the pilot. Equating these two figures the display overall had a Contrast Ratio of 1.2.
The optics incorporated a clever split prism with dichroic coatings to allow the injection of a red Standby Sight from each side which was coupled to small lamps by fibre-optics. (Fig.13.4) The company research laboratory FARL came up with the design for the Standby Sight between 1966 and 1967. This sight was mechanically depressible and was intended to be used as a back-up but in practice the Navy pilots were said to set brightness to a maximum for both the CRT display and for the Standby Sight! For night operation a moveable red Melinex blind could be drawn across to dim the display; incidentally this blind would burn nicely if left across under conditions where direct sunlight would strike it.
The PDU had twin Auto-Brilliance sensors fitted forward of the Combiner Glass. These are more accurately called auto-contrast sensors and controlled the display luminance to maintain a constant Contrast Ratio to the outside world.
The Control Panel by the later standards of sophisticated Up Front Control Panels was very basic with rotary controls for PDU Luminance, Standby Sight Luminance, Mils Depression (with a mechanical read-out window) and to operate the Night Filter. There were switches for Scales Rad or Barometric Altitude, Test and Panel Lights.
The A-7 PDU was fitted with a film recording cameras by Photosonics, fitting round the rim of the optical assembly above the Control Panel control panel.

Ling-Temco-Vought responded to the VA(L) competition which was for a new fighter to replace the US Navy A-4s. In March 1964 the company received a contract for the initial batch of aircraft, designated A-7. In 1965 the aircraft received the popular name Corsair II. It was the first US aircraft to have a modern HUD which displayed information such as dive angle, airspeed, altitude, drift, and aiming reticle. In 1967 it was announced from Dallas in Texas U.S.A that Elliott Flight Automation had been awarded a four year contract to supply LTV with Head Up Displays for the A-7. The initial contract was worth £14million for 1,200 displays and was the largest ever awarded to a British firm.

The highly innovative optics was manufactured by Pilkington in North Wales. It had a 5" exit lens giving a 20° TFoV and had a two position combiner. The optics incorporated a clever split prism with dichroic coatings to allow the injection of a red Standby Sight from each side which was coupled to small lamps by fibre-optics. The A-7 Electronics Unit had a flexible symbol repertoire and the more complex symbols necessitated a faster writing rate. A key new requirement was the specification for a high level of built-in test. The HUD was part of the sophisticated ILAAS weapon system and this introduced predominantly digital serial data links for the aircraft data.

By 1970 the A-7D and A-7E began to move to squadron service and pilots were reported to say that "they like it better all the time". It was doubling the weapon delivery accuracy. Also in 1970 Elliott Flight Automation was awarded a Double Queen’s Award for both Export of all products and Technology of the Digital Head Up Display. In 1971 Vought Aeronautics Corporation donated a silver cup to be known as the Corsair Trophy in recognition of the Division’s achievements in designing, developing and manufacturing the A-7 Head Up Display. Much later in 1978 the Corsair Building was opened at Rochester again to note this very important programme.

The A-7 HUD was the breakthrough into the US market and was the start of a golden era for HUDs; 2534 to of this design were made and build rates exceeded 30/month at one time.

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