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Appendix 7:
US engine designations
Each US engine manufacturer has its own entirely individual
designation system. Department of Defense
designations for jet engines are governed by a common
scheme, though the Navy still uses a strictly numerical
sequence of Mk (Mark) numbers for its solid rocket
motors. The following is the DoD scheme for jet and
turbine engines:
Status prefix
J
X
Y
Engine category
F
J
LR
RJ
SR
T
TF
Special test
Experimental
Prototype
Turbofan (current)
Turbojet
Liquid rocket
Ramjet
Solid rocket
Turboprop/turboshaft
Turbofan (formerly)
Manufacturer code
A
Allison, now Rolls-Royce
AJ
Aerojet-General
GA
Garrett, now Honeywell
GE
General Electric
L
Textron Lycoming, Stratford, now
Honeywell
LD
Textron Lycoming, Williamsport
MA
Marquardt
NA
Rocketdyne (North American)
P
Pratt & Whitney (formerly)
PW
Pratt & Whitney (current)
RR
Rolls-Royce
T
Teledyne CAE
TC
Morton Thiokol
WR
Williams Research
Designations are completed by a suffix model number. In
1945 these began at 1 for AF numbers, using odd numbers
only, and at 2 for the Navy, using even numbers. Thus the
prototype C-130 had YT56-A-1 turboprops, while the
first F-8 Crusader had a J57-P-12 turbojet. Today AF
numbers start at 100 or 200 and Navy numbers at 400.
Thus the F-15C has F100-PW-220 turbofans.
Piston engines are designated by a letter giving the
geometrical configuration of the cylinders, followed by a
number giving the cubic capacity (displacement, or swept
volume) in cubic inches rounded off to the nearest
multiple of 5. Prefix letters can then be added (if necessary
in multiple) giving further information. Suffix letters
(previously numbers) indicate successive models of the
same basic design.
Status prefix
X
Y
Prefix letter
A
G
H
I
T
V
Experimental
Prototype
Aerobatic
Geared
Helicopter
Direct fuel injection
Turbosupercharged
Vertical mounting
Configuration letter
L
Inline (upright or inverted)
O
Horizontally opposed
R
Radial
RC
Rotating combustion (Wankel type)
V
Vee
Thus Textron Lycoming’s TIGO-541-E is the fifth model
in a family of opposed engines of 541.5 cu in capacity (in
a new series distinguished by the number 541 from the
original series rounded off to 540) with turbocharger,
direct injection and geared drive.
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