PMA-201, is
currently conducting an Electric Fuzing Dud Investigation
Systems Engineering Analysis of the F/A-18 Fighter
Aircraft. To support that effort, the Naval Air Warfare Center
Aircraft Division (NAWCAD) Air Vehicle/Stores
Compatibility Division (Air 4.11.2) was tasked by PMA-201
to develop a quick install, deployable Electric Fuzing
Instrumentation System (EFUZIS) to collect electrical fuzing
data during practice bombing missions. The system consists
of a commercial off-the-shelf (COTS) digital recorder and
specially designed signal conditioner that will record
real-time non-telemetered electric fuzing data during bomb
drops. The purpose of the testing was to qualify the
instrumentation system for use on testing and training
squadron F/A-18C/D aircraft. Ground testing was done over
a period of four days and consisted of 73 ground drops
utilizing Mk-82 bomb bodies in the parent rack and canted
vertical ejection rack (CVER) configurations. Electric fuzing
data was collected during these drops and analyzed to
ensure that proper signal timing, amplitude, polarity, and
duration were being recorded. The results of the ground
tests showed that the EFUZIS performed as designed. Flight
testing followed to test the effects of the flight environment
on the recorder system. Flight testing consisted of a single
flight during which two Mk-82 bombs were released using
the CVER configuration. In addition, dynamic test
maneuvers were performed to evaluate the effects of load
factors on the EFUZIS. Flight test results showed that the
instrumentation system recorded all the required parameters
and that the recorder was able to withstand the flight
environment. Overall, the EFUZIS demonstrated excellent
potential for gathering electrical fuzing data as proven by the
extensive ground and flight testing performed by the test
team.
T
ABLE OF
C
ONTENTS
1.

I
NTRODUCTION
2.

T
EST
A
IRCRAFT AND EQUIPMENT
3.

B
ENCH
T
ESTS
4.

G
ROUND
T
ESTS
5.

F
LIGHT TESTS
6.

C
ONCLUSIONS
7.

R
EFERENCES
Figure 1 - F/A-18A Test Aircraft
(Test Configuration Not Shown)
1. I
NTRODUCTION
The U.S. Navys weapon system integration team for
the F/A-18A fighter/attack aircraft was tasked to
evaluate the feasibility of installing a digital recorder in
the aircrafts weapon pylon to record electric fuzing
signals during electronically fuzed weapon releases.
Ground testing had been conducted previously on the
F/A-18A with analog recording systems, but such
systems were not viable for obtaining data during flight.
The compact digital recording system could be placed in
the pylon for extended periods of time and record
valuable data during actual weapon releases. To
conduct a flight test, it first had to be proven by bench
and ground testing that the recorder functioned without
effecting normal armament system operation. Electronic
modifications were designed into the recorder firmware for this application that allowed it to be easily integrated
with the F-18 electric fuzing system. With the bench and
ground tests showing that the recorder functioned as
designed, testing continued to demonstrate operation in
flight under bomb release conditions. The qualification effort
is discussed from an overall perspective, as well as details of
the bench, ground, and flight tests.
2. T
EST
A
IRCRAFT AND
E
QUIPMENT
F/A-18A Aircraft
The F/A-18A Hornet is a single seat, dual-engine,
supersonic fighter/attack aircraft built by McDonnell Aircraft
Corporation (now Boeing). Distinguishing aircraft features
include a variable camber mid-fuselage wing with fuselage
mounted leading edge extensions and twin vertical
stabilizers which are angled 20 degrees outboard and located
well forward of the slab-type horizontal stabilators. The
aircraft is configured with nine external weapon stations, five
of which are capable of carrying and releasing air-to-ground
ordnance, and utilizes an integrated Stores Management Set
(SMS) computer with a MIL-STD-1553 data bus for
armament system control. The test aircraft was equipped
with a modified SUU-63 pylon in which the electric fuzing
instrumentation system was installed. The system was
placed in the AMAC compartment of the pylon. No pylon
modifications were required for the installation. Cables were
designed and built for this application and were installed
into the pylon to interface the recorder with the electric
fuzing system of the aircraft. In addition, a jumper cable was
installed in the fuselage to connect the AWW-4 electric
fuzing power supply to the Walleye video lines at the
armament computer to carry the power supply voltage down
to the recorder in the pylon. The video lines were
disconnected from the armament computer to prevent
voltage feedback into the computer. The test aircraft is
shown in Figures 1 and 2.
Figure 2. SUU-63 Pylon with Recorder and Signal
Conditioner Installed in AMAC Compartment
F/A-18 Electric Fuzing System
Electrical fuzing is provided for JSOW, JDAM, Laser
Guided Munitions and General Purpose Bombs with
electrical fuzes installed. The armament computer
provides the control for the Fuze Function Control Set
(FFCS), AN/AWW-4. Electrical Fuzing operation is
provided by the mission computer system control,
armament computer control, FFCS, and weapon
interface. The mission computer (MC) system provides
the program select function for the Stores Management
System (SMS). When electrical fuzing is selected as part
of the program, the MC system provides this data to the
armament computer to control the FFCS. The armament
computer controls the discrete signals to the FFCS for
the electrical fuze options. The MC system sends the
armament computer the selected program. When
electrical fuzing is selected as part of the program, the
armament computer sends the discrete signals to the
FFCS. Depending on bomb type, fuze type and delivery
attitude, the low voltage select and negative polarity
select will be enabled as a part of the selected program.
Pickle relay enable is provided when Air-to-Ground
ready exists. A-t-G ready exists when the priority station
is selected, program complete exists and the MASTER
switch on the master arm control panel assembly is set
to ARM. Weapon release is enabled when the weapon
release mode command from the MC system exists and
the A-t-G weapon release switch on the aircraft
controller grip assembly is pressed. AWW-4 On Enable
provides 28vdc to the Power On Relay during BIT and
when electrical fuzing is part of the selected program.
The FFCS enables ±195 or ±300vdc to the weapons that
require electrical fuzing.
FMU-139 Electronic Fuze
The FMU-139 Series consists of FMU-139/B,
FMU-139A/B, FMU-139B/B, FMU-139(D-2)/B, and
FMU-139(D-2)A/B; hereafter commonly referred to as
the FMU-139 series fuze (Note: All FMU-139/B fuzes are
being removed from service). The fuzes are Joint-Service
(Navy/Air Force) fuzes with multiple settings, which
must be preset during weapon assembly and can be
delivered in either high-drag (retarded) or low-drag
(unretarded) mode. The major physical differences from
other Navy electrical fuzes are: (1) the gag rod and
arming wire housing are located in the center of the
faceplate, and (2) the fuze is secured in the tail fuze well
of the bomb by a separate closure ring, which is
screwed into the fuze well. The faceplate contains a
low-drag arm time rotary switch, a high-drag arm/delay
rotary switch and a 2.0 second/instantaneous interlock
button. The FMU-139 series incorporates three arming
times (2.6, 5.5, and 10.0 seconds) and has three
functioning delays available (10, 25, 60 milliseconds and
instantaneous). The arming times are in-flight selectable and the functioning delay (high-drag arm/delay switch) must
be set during weapon assembly. The FMU-139 arming wire
housing, which protrudes from the center of the fuze
faceplate, contains the gag rod and gag rod sleeve. This
arming-wire housing, together with the gag rods
red-and-black striped sleeve, which will extend from the
housing to indicate an armed/unsafe condition, is roughly
equivalent in function to the pop-out indicator of other
electrical fuzes. Once the sleeve is extended and the
red-and-black striping is visible, the fuze gag rod/sleeve
cannot be reset (pushed back) to render the fuze safe. The
gag rod and gag rod sleeves are secured in the arming-wire
housing by a safing pin. On the FMU-139A/B, the gag rod is
shorter than on the FMU-139/B and the arming wire is
pushed into a slot, rather than threaded as for the
FMU-139/B.
Mk-122 Safety Switch
The Mk-122 arming safety switch (Figure 3) connects the
fuze control circuits in the aircraft to the electric fuze circuits
in the bomb. This switch provides an open circuit and a
radiation hazard shield to prevent electromagnetic radiation
from entering the fuze circuits. While the weapon is loaded,
the coaxial cable of the switch is plugged into the receptacle
of the aircrafts electrical arming unit. When the bomb is
suspended from the bomb rack, the lanyard is attached to a
fixture on the rack or pylon. Upon bomb release, the lanyard
pulls the lanyard pin and closes the fuze circuit. The lanyard
is long enough so the weapon separates from the bomb rack
suspension hooks before the lanyard pin is pulled from the
switch. This is a safety feature that ensures the fuze does
not receive a charging voltage in the event of a weapon
release failure. The coaxial cable is longer than the lanyard,
which permits su