A Century of Ramjet Propulsion Technology Evolution - Faculty of ...

42 FRY
Fig. 12 U.S. BOMARC operational missile (1950–1972).
Fig. 13 U.S. Talos/Vandal operational missile (1950–today).
for recovery and reuse and was later adapted as a ground-launched
supersonic target for the U.S. Army.
The Talos supersonic interceptor missile (Fig. 13) evolved from
the Bumblebee program under the direction of the JHU/APL initiated
at the end of WWII. The Talos engine used a single, oncenterline
ramjet engine with a double-cone configuration mixed
compression inlet that fed to an air-cooled can combustor, which
burned JP-5 fuel. Boosted to supersonic ramjet-takeover conditions
by a separate solid propellant rocket, this ramjet-powered
missile further accelerated and then cruised out supersonically to
the aircraft-intercept point at high altitude. Its main limitations were
in terminal intercept phase due to guidance inaccuracies and the axisymmetric
inlet would unstart at high angles of attack followed by
loss of control. The Talos was first fired in 1951 and introduced
into the U.S. fleet in 1955. After the cancellation of the BQM-90
program in 1973, the U.S. Navy had to look for other target missiles
to simulate attacking antiship missiles. In 1975, it was decided to
convert some obsolete RIM-8 Talos missiles to MQM-8G Vandal
targets as a short-term solution to simulate the terminal phase of a
missile attack. Some 2400 Talos units were built, with the U.S. Navy
presently using a Talos variant (Vandal) as a low-altitude supersonic
target. This is the second and final operational ramjet-powered system
fielded by the United States to date and the only ramjet-powered
system in limited flight service today.
Refined versions of the Leduc-010, whose first flight was in 1949,
followed over the years using air-turboramjet cycles to provide static
thrust, with the most striking demonstration of ramjet supersonic
flight speeds being achieved in the Griffon II from 1957 to 1961,
which reached climb speeds of Mach 2.19 and Mach 2.1 at 50,000 ft
(15.3 km) in 1959. Work on ramjets for aircraft applications generally
stopped in the 1960s when the turbojet design was perfected
and was shown to have lower fuel consumption than ramjets. Following
the initial desires to employ ramjet technology in aircraft,
subsequent development focused on advancing missile technology
In 1955 the U.S. imitiated one of the first SFIRRs ever developed,
ram air rocket engine, RARE. It employed a conical nose inlet
and rocket-ramjet flowpath; the ramjet combustor used the chamber
that housed the booster grain, but had a separate upstream chamber
through which the air and solid fuel mixed and ignited. This dual
in-line combustion chamber approach was used to solve potential
boost-to-sustain transition problems. Magnesium and boron-loaded
fuels were examined. Three flight tests of the RARE vehicle were
successfully conducted at Mach 2.3 between 1959–1960.
In the 1955–1965 time frame, France developed, flight tested, and
made operational three LFRJ missiles: the VEGA, the SE-4400, and
the target vehicle, CT-41.
The U.S. Typhon development began in 1957. The engine employed
an LFRJ design that used a Talos tandem solid propellant
booster. The Typhon missile was much smaller than its Talos predecessor,
yet still capable of flying almost twice the range. In addition
to the reduced sustainer weight (1800 vs 3360 lbm for the Talos) the
conical-inlet can combustor ramjet propulsion was more efficient
and its subsystems and structure were more compact. It was successfully
flight tested nine times from 1961 to 1963. Unfortunately,
the Typhon was not introduced into the fleet because it outperformed
the capabilities of the radar, guidance, control, and battle space coverage
of the time. Despite its success, the program was canceled in
1965. However, the lessons learned and technology developed were
to become the cornerstones of the Aegis weapon system 10 years
later.
The U.S. Creative Research on Weapons (CROW) was developed
with the goal of demonstrating SFIRR feasibility for delivering an
air-launched payload to a desired location. 22 The axisymmetric IRR
configuration used an SFRJ sustainer and an integral booster package
contained within the ramjet combustor. The design employed
ejectables including a bulkhead between the sustainer and booster
grains and a rocket nozzle plug centerbody, which were expelled
by ram air at transition. Six flight tests were successfully conducted
demonstrating operational potential. The CROW concept, although
briefly considered for use as an air-to-air missile and a high-speed
target, never became operational.
The Bloodhound (Fig. 14) and the later Sea Dart (Fig. 15) were
developed and used by the Royal Navy and employed in the role of
long-range air defense. The Bloodhound is most easily recognized
by its profusion of control surfaces and stabilizers; it has one fin
on each of four boosters, two pivoting mainplanes, and two fixed
horizontal stabilizers mounted in line with the wings. Two solid
propellant boosters and an LFRJ sustainer propel the missile. The
Bloodhound maneuvers with its mainplanes employing a twist-andsteer
technique. Initially operational in 1964, almost 800 missiles
were produced until 1991, when it was removed from service.
Ramjet Development: 1960–1980
A major milestone of this 20-year period was the conception and
demonstration of IRR technology for missile applications. Table 3
summarizes ramjet evolution in the era from 1960 to 1980 and provides
originating country, engine/vehicle names, development dates,
performance, physical characteristics, and state of development. The