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Energy Management Analog Computer (EMAC)

Technical Information

Catalogue No: C0128
Category: Flight Control
Object Type: Control/Data Entry
Object Name: Energy Management Analog Computer (EMAC)
Part No: 59-002-01
Serial No: 0001
Manufacturer: Elliott Bros (London) Ltd
Division: Military Aircraft Controls [MACD]
Platform(s): C-5A/B Galaxy
Year of Manufacture: circa 1967
Dimensions: Width (mm): 292
Height (mm): 228
Depth (mm): 293
Weight (g): 9,480
Location: Rack RAA01 [Main Store]

Designation 4L 97502-101
Serial No. 0001
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. This unit is also marked Contract AF33(657)-15053.
This unit was acquired from the original Elliott Collection as Cat. No.2043

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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