At the more arcane end of military-power plant research, ramjet propulsion remains under active consideration, although deployment time-scales remain considerable.
In Russia two long-term Mikoyan research programmes into high mach-number combat aircraft have been cancelled. In the US programmes are continuing, albeit with funding on a tight rein.
The USAF is continuing work with NASA on the High Mach Turbine Engine (HiMaTE), a combined-cycle air turbo ramjet (ATR) for M0-5 aircraft, and on hydrogen-fuelled supersonic combustion ramjets (scramjets) for M8-12 vehicles.
It is also seeking approval for a scaled-down hypersonic-technology (HyTECH) research programme focusing on hydrocarbon-fuelled supersonic-combustion ramjets (scramjets) for Mach 4-8 missiles.
This is an effort to continue US hypersonic research following cancellation of the X-30 National AeroSpace Plane (NASP) and follows the Air Force's decision not to fund the NASA/USAF HySTP scramjet flight-demonstration programme. Instead of the five-year, $400 million, HySTP programme, NASA and the USAF plan to pursue separate hypersonic-research programmes.
The $20 million-a-year HyTECH research programme is scheduled to get under way in June. Obviously disappointed at the Air Force's decision not to fund the HySTP demonstration, NASA will continue hypersonic research in an effort to leverage the $2 billion already spent on NASP technology development.
NASA's $20 million-a-year hypersonic-research programme will focus on higher-Mach-number, hydrogen-fuelled scramjets and will centre on the completion of tests of the Rocketdyne subscale parametric engine (SXPE) and Pratt & Whitney concept demonstrator engine (CDE) built for the NASP programme. The SXPE and CDE are scale models of the X-30 scramjet.
About 70% of NASA's continued effort will be devoted to aeropropulsion. NASA plans a M6.5 flight experiment with Russia's CIAM engine-design institute in November 1996. This involves flying a Russian-designed scramjet on a modified SA-5 surface-to-air missile and will be a repeat of flights conducted in 1990 and 1991. This time, the results will be correlated with tests of the scramjet in U S and Russian wind tunnels.
Work will also continue on small-scale production of slush hydrogen, the chosen fuel for the X-30. Slush hydrogen (a mix of frozen and liquid hydrogen) is 16% more dense than liquid hydrogen and has 18% more heat capacity for active cooling of the engine and airframe. NASA calculated that using 50%-solid slush hydrogen would have reduced the weight of the X-30 by 30%.
Pilot production of slush hydrogen was one of the highlights of the NASP programme. Both freeze/thaw and continuous slush production were demonstrated and NASA successfully transfered slush hydrogen between tanks, recondensed excess gaseous hydrogen, and actively cooled tank walls by spraying liquid hydrogen.
The USAF's January decision not to fund its share of the HySTP programme ended the NASP saga. In 1992, it was estimated it would cost $15 billion and take eight to ten years to build and fly the M25, single-stage-to-orbit, X-30. Instead, a six-year, $2 billion, hypersonic flight experiments (HyFLITE) programme was proposed to resolve technical uncertainties. When it became clear the money for HyFLITE would not be available, the five-year, $400 million, hypersonic test programme (HySTP) was formulated to establish the performance of a scramjet at M15.
Budget cuts have also hit international efforts to develop hypersonic technology. Germany is in the final year of a DM400 million hypersonic research programme, and had hoped to ground-test a ramjet engine before the end of 1995. Budget cuts have pushed tests into a proposed Phase 2 programme, which the German Government has stated must be an international collaborative effort.
With funding, the ground-test engine could run at M6.8 in 1996. German industry is proposing to build a flight-test engine which could be flown as a "passenger" on a modified Russian Raduga D2 drone in the year 2000. The proposed programme calls for flight-tests of the unmodified drone in 1996 to establish baseline performance.
France ground-tested a scramjet model at Aerospatiale in late 1994/early 1995 and plans to resume tests at the end 1995 with a new fuel-injector design. For these tests the engine will be hydrogen-cooled for the first time.
Japan tested a sub-scale scramjet in 1994 at a test site capable of 60s runs at M4-8. In addition, a 25%-scale model of Japan's ATREX air-turbo-ramjet expander-cycle engine was tested at M0-6 over 30 runs in 1990-92. The ATREX features an air-intake pre-cooler and combustion chamber heat exchanger.
Russia is working on scramjet engines under the Russian Space Agency's Oryol advanced reusable space-transportation-system study programme. The CIAM engine-design institute is working on air-breathing propulsion options for horizontal take-off and landing designs being studied by aero-hydrodynamics-research institute TSAGI.
Source: Flight International