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Appendix 6 – Scramjet Engine Demonstration (SED-WR)

ACKNOWLEDGEMENT

Some of the information for this section was provided courtesy of the HyTech program office in the Propulsion Directorate of the Air Force Research Laboratory. The information contained in this document has been cleared for public release.

BACKGROUND

As a result of Department of Defense interest in the potential of hypersonic propulsion to enable new capabilities for weapons, aircraft and space access, the US Air Force has supported a continuing investment in hypersonic propulsion technology. Most recently that activity has been accomplished under the Hypersonic Technology (HyTech) Program within the Air Force Research Laboratory Propulsion Directorate. This program, started in 1995, has been directed at development of endothermically fueled (hydrocarbon) Mach 8 scramjet technology, including fuels, materials, structures, and subsystems. In 1998, DARPA began the Affordable Rapid Response Missile Demonstrator (ARRMD) program. One of the two competitors for that program was a team composed of Boeing and Pratt & Whitney. That team proposed to use a scramjet propulsion system derived from the hydrocarbon engine research that Pratt & Whitney was conducting for the Air Force under the HyTech program. Although the ARRMD program was cancelled in 2000, the research on the propulsion system continued under the Air Force HyTech program.

HYTECH

The technical challenges for the HyTech program are illustrated in Figure SED-1. The expected issues of flowpath performance and operability are noted along with the key contributing factors such as inlet mass capture, isolator pressure ratio, isolator stability, piloting, flameholding, injection, mixing, and nozzle losses. However due to the nature of the structural cooling and fuel management concept some imposing additional challenges are present such as the performance and durability of the heat exchangers, fuel preheat, system thermal management, and the closed loop control of the cooling/fueling system. Significant work has been done to address the flowpath performance, operability and fuel control challenges through the HyTech program’s Performance Test Engine (PTE) and Ground Demonstration Engine (GDE-1), Ref. SED-1. For example, component performance has been demonstrated for two inlet configurations and combustor performance has been demonstrated in direct-connect tests from Mach 4 to 8. The endothermic fuel properties have been demonstrated without coking. An integrated heavyweight copper engine has been used to demonstrate performance and operability. Component structural durability has been established for both the uncooled C/SiC leading edges and the fuel cooled structures. The flight weight engine performance and durability have been demonstrated, while the flight-weight fuel control system will be demonstrated during testing of the second build of the Ground Demonstration Engine (GDE-2) in 2004. Some of these activities are illustrated in Figure SED-2. Important recent HyTech program activities include the successful completion of the GDE-1 test program with engine performance meeting or exceeding expectations based on the previous Performance Test Engine (PTE) results. Moreover, the fuel cooled structure remained in excellent condition after 60 test cycles. This testing was the first demonstration of a flight weight, hydrocarbon-fueled, cooled scramjet engine.

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SED

In 2002, planning for the National Aerospace Initiative sought to identify candidate flight demonstration vehicles for a range of hypersonic technologies. The two demonstration vehicles from the ARRMD effort surfaced as natural candidates. DARPA and the Navy had already begun an effort to collaborate on the development of the ARRMD-derived concept for a hydrocarbon Dual Combustion Ramjet demonstrator under the HyFly program. The Air Force decided to pursue a demonstration vehicle based on the Boeing / Pratt & Whitney concept that utilized a hydrocarbon scramjet. Thus in January 2004, the Air Force awarded a contract to Boeing and Pratt & Whitney to develop and flight test a hydrocarbon fueled scramjet propulsion system. The program has since been designated the Scramjet Engine Demonstrator - WaveRider (SED-WR).

GOALS

The goal of the SED-WR program is to demonstrate in flight, the HyTech scramjet engine using endothermic hydrocarbon fuel, and associated waverider airframe technologies.

OBJECTIVES

The objectives of the SED program are: – demonstrate acceleration from Mach 4.5 to Mach 6-7+ – demonstrate transition from dual mode to scramjet operation – demonstrate operation for minutes

VEHICLE CONCEPT/CONFIGURATION

The starting point for the vehicle configuration development in this program is the concept originated by Boeing and Pratt & Whitney during the ARRMD program. Thus, although the program was only started recently, the configuration is somewhat mature. The SED demonstration vehicle is illustrated in Figure SED-3. The forebody of the test vehicle was designed using waverider principles to enhance the aerodynamic performance. The airframe structure is designed to utilize cast structures – a legacy of the ARRMD low-cost missile objectives, and a low cost thermal protection system (ablator – Ref. SED-2) for the acreage. Movable fins are provided for active control of the test vehicle during free flight. A solid rocket motor from the Army Tactical Missile System (ATACMS) will be used to boost the test vehicle to the velocity required for scramjet operation. The booster has fixed fins for stability augmentation during boost. (Ref. SED-3). The scramjet uses endothermic hydrocarbon fuel and a 2-D dual mode flowpath configuration derived from the HyTech engine, Figure SED-4. The flowpath is a single module with a fixed geometry inlet. The flowpath structure is actively cooled using the hydrocarbon fuel, which is then injected into the combustor and burned. The propulsion system is intended to be a separate unit that can be installed into the airframe.

CONCEPT OF OPERATIONS - FLIGHT TESTING APPROACH

A typical SED flight test would include the following events. A B-52 will carry the integrated vehicle stack to nominally 30-40 kft and Mach 0.8-0.9 (Ref. SED-3). The stack will be released and the solid rocket motor

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will boost the test article to the scramjet takeover conditions of about Mach 4.5. The test vehicle will then separate from the booster, climb and accelerate to between Mach 6-7. The vehicle will then cruise for several minutes. The propulsion would then be terminated and the vehicle would complete a controlled gliding descent to impact.

TECHNICAL CHALLENGES

Besides the technical challenges for the HyTech program discussed above, the SED will also have system-level technical challenges such as the booster separation, aero control capture at the end of the boost, aerodynamic stability and control, coupled aero/propulsion control and airbreather takeover at the end of the boost.

TECHNOLOGY DEMONSTRATIONS

The principal demonstration for this program is the performance, operability and controllability of the HyTech scramjet propulsion system and the waverider aerodynamics.

DEVELOPMENT SCHEDULE AND MILESTONES

The SED program schedule is currently in its first phase, which should result in a test vehicle preliminary design review before the end of 2004. The program expects to fly between five and 10 vehicles starting some time after 2008, completing activities in 2009. The overall hydrogen scramjet engine development roadmap is illustrated in Figure SED-5.

PARTICIPANTS

At this time, the principal participants in the SED-WR program include the Air Force Research Laboratory, Boeing for the waverider airframe, Pratt & Whitney for the scramjet engine module, GASL and NASA Langley for testing support, and the Air Force Flight Test Center for flight test planning and coordination.

REFERENCES

SED-1. Boudreau, A., “STATUS OF THE U.S. Air Force HYTECH PROGRAM,” AIAA 2003-6947, 12th AIAA International Space Planes and Hypersonic Systems and Technologies 15-19 December 2003, Norfolk, VA. SED-2. Aviation Week & Space Technology, “WaveRider Program To Demonstrate Scramjet Propulsion System in Flight,” 01/19/2004, page 405. SED-3. Aviation Week & Space Technology, “Researchers Plan Civil and Military Scramjet Flight Tests,” 06/02/2003, page 22.

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CombustorIsolator)(Inlet Isolator)(Inlet

Air Flow

Nozzle

Accel MassCapture

CruisePerformance

PressureRatio

Fuel Injectionand Mixing

Piloting andFlameholding

Regeneratively-CooledStructures and ThermalManagement

TECHNICALCALLENGES

Fuel

Starting

Total Pressure Losses

Frozen FlowLosses

DivergenceLosses

VehicleIntegrationPerformance and Operation

Over the Flight and ManeuverEnvelope

Passively-CooledStructures

Exhaust

Air Induction

Structures &Materials

Endothermic

Figure SED-1. Technical challenges for the HyTech program.

Forebody

Inlet Ramp

Cowl Lip

Sidewall

Forebody

Inlet RampInlet Ramp

Cowl LipCowl Lip

SidewallSidewall

Inlet Starting and PerformanceDemonstrated Over Mach 4 to 8 Range

Combustor Operability and PerformanceDemonstrated Over Mach 4 to Mach 8 Range

Freejet Test of Integrated Heavyweight Engine Demonstrated Performance & Operability

6”X30” & Full 75” Sidewall Fuel-Cooled Heat Exchanger Demonstrated

Structural Durability

Figure SED-2. Risk reduction efforts for the HyTech program.

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Figure SED-3. SED vehicle concept.

• Testing initiated Sep 02, completed Jun 03, 60 tests• Mach 4.5: Performance comparable to heavyweight PTE tests• Mach 6.5: Performance exceeded heavyweight PTE tests• Engine fuel cooled structure in excellent condition

Figure SED-4. HyTech scramjet propulsion concept.

PTE

GDE-1 (Jun 03)

SED (FY08)

CCE

Robust Scramjet

In-house Science and Technology

GDE-2 (Dec 04)

In-house research provides a solid foundation for scramjet

engine development

PTE

GDE-1 (Jun 03)

SED (FY08)

CCE

Robust Scramjet

In-house Science and Technology

GDE-2 (Dec 04)

In-house research provides a solid foundation for scramjet

engine development

Figure SED-5. Hydrocarbon scramjet engine development roadmap.

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