Reflections of an Aerospace Engineer

Introduction to Aircraft Performance and Mission Analysis Part 4 – Energy Maneuverability by John Golan

© John Golan 2015

Material derived from openly published sources No technical data subject to the EAR or ITAR

Energy Maneuverability Theory • In the latter 1960s a new approach to analyzing fighter capability arose: Energy-Maneuverability (E-M) Theory – Prior generations of combat aircraft were developed around a few discrete performance criteria  Maximum Speed  Maximum Altitude

– E-M Theory was developed in 1965 by Major John Boyd (USAF) and Thomas P. Christie, a mathematician and computer scientist employed by the Air Force

• E-M Theory evaluated performance on the availability of excess energy (specific excess power) rather than on the basis of a single, discrete performance criteria – E-M Diagrams plot iso-contours of specific excess power across a range of speed and altitude or speed and turn rate conditions – Approach allows aircraft to be compared across a performance envelope, rather than around single, discrete performance criteria

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Energy-Maneuverability Diagrams • E-M Diagrams describe both the limits of an airplane’s envelope, and the energy state of the airplane throughout that envelope – Sometimes referred to as a “doghouse plot”

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Energy-Maneuverability Diagrams: An Example • E-M Diagrams for opposing aircraft are often overlayed for comparison • Each Diagram will specify the applicable aircraft armament and fuel state, as well as altitude

Source: Roskam, Airplane Design: Part VII, p. 157 4

Combat Aircraft: Other Contributing Elements • There are a number of factors – beyond performance – which can play a role in success or failure – Control Authority  MiG-15 / F-86 match-up in Korean War  Control surface sizing – F-16, F-22  Fly-by-wire controls and relaxed static stability

– Weapons Systems  All-aspect AAMs and the 1983 Falklands War  Combination of high off-boresight missiles and helmet-mounted sights

– Sensors  First-to-see, first-to-shoot  Introduction of AWACS

• The pilot remains the decisive factor

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E-M Still Relevant – Even in BVR Missile Age • Majority of air-to-air kills still occur within visual range – 1986 USAF study found only four BVR kills in preceding decades  Study encompassed all known U.S. and foreign air-to-air kills  4 kills from beyond visual range out of 407 successful missile kills  Vast majority of BVR missiles were fired within visual range

– In 1991 Gulf War 58% of all kills were made within visual range  Only 16 out of 38 allied kills made from beyond visual range

– 73% of U.S. air-to-air kills in the post-Gulf War era have been made within visual range  Only 3 out 11 air-to-air kills were made from beyond visual range

• Even in BVR engagements an energy advantage is essential to maximizing the kill-to-loss ratio

Typical BVR maneuvering engagement

– BVR combat “characterized by very careful power management” Source: Herbst, “Dynamics of Air Combat”, p. 596

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