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

52 FRY
U.S. tests of the Russian proof-test engine were planned, but never
conducted for facility/model safety reasons. NASA engineers analyzed
the final 1998 flight-test results. Although reasonable agreement
was noted between ground- and flight-test data, 32 reportedly
some uncertainty existed whether in-flight supersonic combustion
conditions were achieved. Although these flight tests did not fully
accomplish their original goals, they were a good first step, which
helped build confidence that more ambitious flight tests could be
accomplished, and just as important, they provided the first comparison
between ground test and flight of dual-mode scramjet combustor
data. Although still available, it is unlikely that further flight
tests will be conducted with Kholod because more capable second
generation hypersonic flying laboratories have become available.
The Japanese National Aerospace Laboratory–KPL commenced
design, fabrication, and testing of a side-wall compression-type
scramjet engine in 1991 through 1994. 69 The flowpath design was
based on the results of their research activities on the scramjet engine
systems and components since the 1980s and had the objective
of investigating component design and overall performance. A first
generation hydrogen-fueled engine model E-1 was tested from 1994
to 1999 at Mach 4–6 conditions. The majority of testing was conducted
on heat-sink hardware, with limited water-cooled and liquid
hydrogen-cooled testing. Two new facilities were built to support
these activities; a freejet-type hypersonic propulsion wind tunnel
(RJTF1) and a free-piston high-enthalpy shock tunnel (HIEST2)
from 1994 to 1999.
Design improvements were made, and a second generation E-2
engine was fabricated with testing beginning in early 2000 and continuing
today. Design changes focused primarily on the attainment
of positive net thrust and improvement in combustion performance
at Mach 8 conditions. The majority of the testing was conducted on
water-cooled hardware, with limited liquid hydrogen-cooled and
heat-sink testing. The first successful firing tests at Mach 12 conditions
were conducted in 2002–2003. A plan to conduct scramjet
flight testing is now underway to confirm engine performance under
real flight conditions. A future milestone is to design, fabricate, and
test the combined cycle engine based on the scramjet test results.
French scramjet development activities reemerged in the late
1980s with PREPHA, a jointly funded government–industry–
university program, and subsequently reinitiated in 1992. PREPHA
was aimed at developing a knowledge base on hydrogen-fueled dualmode
ramjet technology for SSTO applications. 70 Generic waverider
configurations were examined, which ultimately resulted in
the design and test of CHAMIOS, a large-scale scramjet engine
design that was ground tested at Mach 6.5. The hardware had a
77 in. 2 (8 × 10 in.) entrance area and incorporated wall measurements
and optical access. 71 Testing began in 1994 and continued
through 1999, with further testing planned under other programs.
Despite the potential of combined cycles for fully reusable space
launchers, the PREPHA program ended in 1999. Follow-on developments
were initiated to preserve the intellectual and material investment
in the form of the WWR (1993–2003), JAPHAR (1997–2002)
and Promethee (1999–2002) programs. 72
Fig. 34 Russian Kholod first generation HFL (1991–1998).
Fig. 35 Russian GELA/Raduga operational flight test vehicle (1995–
today).
The Russian Space Agency initiated comprehensive hypersonic
research and development in the ORYOL (or OREL) program
in 1993 to develop combined propulsion systems for advanced
reusable space transportation, and includes SSTO and TSTO vehicle
designs. 73 This program sought to focus over 40 years of
experience in Russian research and development in supersonic
combustion. Activities are continuing with the development of
the Igla (shown subsequently) second generation hypersonic flying
laboratory (HFL).
GELA or Raduga (Fig. 35) was conceived as a Russian prototype
for a new generation of hypersonic cruise missiles. The GELA
testbed represents a second-phase effort on development work conducted
by Russia between 1980 and 1985 (Ref. 74). The first phase
dealt with Mach 3 ramjet propulsion systems developed from 1973
to 1978, and ultimately used on the SS-N-22 and SA-6. A third phase
of development seeks to build and test a Mach 6 missile, with a final
phase seeking to achieve speeds up to Mach 8. The GELA missile
was flight tested in 1994 from a Tu-22M (specially modified TU-95
Bear) bomber at supersonic speed and boosted by a liquid propellant
rocket motor and reportedly reached Mach 4.5. This vehicle is
designed to conduct hypersonic scramjet research at speeds up to
Mach 6.3 and 295,000 ft. It has been successfully launched upwards
of 500 times. The configuration shown in Fig. 35 is an expendable
vehicle.
The U.S. Air Force has supported hypersonic engine technology
activities since 1995 through the HyTech program. The fundamental
objectives were to enable sustained hypersonic flight for missile
or aircraft applications and to develop and demonstrate Mach 4–8
hydrocarbon-fueled, actively cooled scramjet engine technology
through component direct-connect and freejet testing. The Hypersonic
Technology Development HyTech/HySET program evaluated
concepts proposed by four engine contractors. Each contractor developed
hydrocarbon-fueled scramjet concepts and databases, of
which two contractors were selected for the component demonstration
in the first phase of the program. The Pratt and Whitney concept
was selected to continue into the second phase under the HySET contract.
This predominantly two-dimensional design heavily leveraged