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Energy Management Analog Computer (EMAC)

Technical Information

Catalogue No: C0318
Category: Flight Control
Object Type: Signal/Data Processor
Object Name: Energy Management Analog Computer (EMAC)
Part No: 59-002-01
Serial No: 0005
Manufacturer: Elliott Bros (London) Ltd
Division: Military Aircraft Controls [MACD]
Platform(s): C-5A/B Galaxy
Year of Manufacture: circa 1965
Dimensions: Width (mm): 295
Height (mm): 230
Depth (mm): 280
Weight (g): 9,240
Location: Rack RAA01 [Main Store]

[only visible with outer case removed]
Designation: 4L 97502-101 Serial No. 0005
Part No. 59-002-01
Spec EC 41172 Design Code K0656
Stock No.
Computer, Analog, Energy Management
Contract AF33(657)-15053 Mfr Code K0656


The Elliotts EMAC energy management computer for the Lockheed C-5A entered production in 1967. It was designed to provide continuous information for the optimum usage of available fuel and the realisation of range/endurance potential. The unit is missing its outer covers revealing its solid-state electronic modules and the electromechanical nature of the many user controls.

The Lockheed C-5 Galaxy is a large military transport aircraft built by Lockheed. It provides the United States Air Force (USAF) with a heavy intercontinental-range strategic airlift capability. The C-5 Galaxy has been operated by USAF since 1969.

The C-5A and C-5B were fitted with an Energy Management Analog Computer (EMAC).

Three sources of energy are available to generate aerodynamic forces and thus manoeuvre the airplane: kinetic, which increases with increasing airspeed; potential, which is proportional to altitude; and chemical, which is from the fuel in the airplane's tanks.

The airplane is continuously expending energy in flight because of drag. During manoeuvring, the three types of energy can be traded, or exchanged, usually at the cost of additional drag. This process of consciously manipulating the energy state of the airplane is referred to as energy management.

The objective of manoeuvring the airplane is to manage energy so that the three types of energy stay between limits.

The pilot does not directly control the energy but controls the direction and magnitude of the forces acting on the airplane. These forces result in accelerations applied to the airplane. The result of these accelerations is a change in the orientation of the airplane and a change in the direction, magnitude, or both, of the flight path vector. Ultimately, velocity and altitude define the energy state.

This process of controlling forces to change accelerations and produce a new energy state takes time especially in an aircraft as large as the C-5 so a computerised system was devised to take control and optimise the control. Graham Holloway (Elliotts 1961 [Apprentice Technician] –  ?1978 [Project Leader])recalls that this used a technique known as “IMPACT”, integrated modular pulse analogue computing technique, basically the controlled chopping of reference waveforms (sine, cos ramp and triangular) to perform multiplication, division and trig functions. FARL did some work on systems for torpedoes, and the C5 Galaxy crosswind steering system with MACD.

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