Alignment of components is critical throughout the defence industry to ensure both durability and safety of military equipment

Fighter Aircraft Alignment - Harmonisation

The problem - The effectiveness of the navigational system of fighter aircraft depends on the accurate alignment of all systems to the aircraft's longitudinal fuselage datum (LFD). This is termed harmonisation and is normally maintained using the Taylor Hobson Micro Alignment Telescope. Checks need to be made after a front windscreen change or removal of the nose cone, or following any disturbance to the pilots display unit, platform navigational system or radar mainframe.

The Solution - To allow ground crew to check the harmonisation, telescopes and collimators (to provide a line of sight) are mounted in a sighting frame and alignment checking jig. This job is made much easier with the use of CCTV or CCD systems to replace the 'human eye' or provide digital output. During aircraft construction, the gun pod mounting points are accurately aligned to the longitudinal fuselage datum (LFD) and this then provides the datum. An alignment jig incorporating a telescope is bolted to the gun pods and an aircraft sighting board incorporating collimators is attached to the front of the aircraft. The inclination of the checking jig and aircraft roll is checked using a clinometer.

The first stage of the harmonisation sequence is to align the Longitudinal Fuselage Datum jig (LFD) with the Aircraft Target Board (ATB), to provide an accurate datum. Once this is achieved, the target board is then used to align the Internal Navigational Unit (NU) and Pilots Display Unit (PDU).

Aligning Aircraft Target Board (ATB): Micro Alignment Telescopes (focused to infinity) are mounted in the Longitudinal Fuselage Datum sighting frame and sighted onto a collimator mounted in the corresponding bracket of the Aircraft Target Board. The frame assembly is then adjusted in elevation and azimuth until the telescopes crosslines are centred to the collimator graticules. Any movement after this setting is monitored and error corrected.

Checking Alignment of Internal Navigational Unit (INU): A telescope is located in the INU sighting jig and aligned to the corresponding collimator on the ATB. Any necessary re-alignment as required is corrected by re-shimming. Similar procedures are also adopted to align the PDU and FLIR.

Harmonisation of smaller systems such as handheld anti-tank weapons have a similar problem of parallelism setting. Here the sighting aid, tracer rifle and missile itself must all be parallel to each other and can be set using autocollimation.

Contact us today!