A-4 HUD PDU Alignment Master Reference

Technical Information

Catalogue No: C1424
Category: Head-Up Display [HUD]
Object Type: Test Equipment
Object Name: A-4 HUD PDU Alignment Master Reference
Part No: 229 D 2396
Serial No: None
Manufacturer: Marconi-Elliott Avionics
Division: Airborne Display [ADD]
Platform(s): A-4 Skyhawk 
Year of Manufacture: Unknown
Width (mm):
Height (mm):
Depth (mm):
Weight (g):
Location: Archive Object Store

Part No. 229 2396


This is the Master Alignment Reference used in the alignment of the A-4 HUD's PDU.

The Reference holds a mirror which is aligned to the mounting surfaces of the jig. The Master Reference is set into a PDU Alignment Jig and a Theodolite is used to transfer the PDU boresight angle to one or more collimators on the jig. The PDU is then placed in the Alignment Jig and the reference angle from the collimator is checked against the centre of the field of view of the PDU which is defined by a special symbology set derived from a Test Set.

This process ensures that the PDU is accurately aligned on the aircraft to the aircraft boresight. The Master Reference is marked ‘546’ which was the project number for the supply of the HUD systems for the Israeli Air Force.

The Master Reference has a wooden carrying case the dimensions of which are: 200 x 150 x 170mm.

The success of the A-7 Corsair HUD was followed by a system for the H, M and N variants of the McDonnell Douglas A-4 SkyHawk. About 465 systems were delivered, from about 1970 to 1978 to the U.S and elsewhere. The system was distributed into the Pilot’s Display Unit (PDU), Video Signals Unit (VSU), High Voltage Power Supply (HVPSU) and the Electronics Unit (EU). It was recognised that all of the information used in the weapon aiming calculations was already being supplied to the HUD to draw the symbology format for the attack phase. A modified interface design, faster logic and expanded store in the waveform generator gave a very effective and self-contained, greatly improved, gun, bomb and missile sight and aiming system which could be installed in many different existing aircraft. Most importantly: because the unit had its own highly capable A to D interface, it could use the existing sensors, gyros, etc. in any aircraft without requiring major internal systems modifications in the aircraft.

As only one display and one weapon aiming format were required simultaneously the HUD Processor speed was found to be adequate for both tasks. An Air to Air gun aiming and a CCIP bombing mode were provided initially.

The HUD Weapon Aiming Computer HUDWAC allowed a precise calculation of Lead Angle. The wider dynamic range of the HUD also permits closer matching of the pilot and airframe kinematics for target acquisition and tracking. This was a big advantage over even the most sophisticated Gyro Gunsight. It was now possible to give displays with better visualisation to the pilot with bullet line or tracer line and these ‘line cues’ increased the probability of a snapshoot against crossing targets over the ‘point’ cue fixed reticle. The HUD system for the US Marine Corps’ A-4M Skyhawk attack jet was the first product of this new concept a HUD weapon aiming computer or HUDWAC which proved to be a world first for the Company. In later designs the Program Store was increased to 4096 words and the Data Store to 128 words the weapon aiming capability was significantly increased. Such enhanced systems were flown on the Mirage Milan, the YF-16 and the YF-17. This system finally reached an 8k instruction PROM store.

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