consumption per range(kg/km).The two peaks represent the acceleration phases,with the first in dry mode and the second with full afterburner ignition.The two long-time relatively flat,slightly decreasing sections are the cruise phases,with the first in subsonic dry mode and the second in Mach 4.5 RAM-cruise.On a first look it seems surprising that the RAM-cruise efficiency is better than those of the turbofans in subsonic flight.Although sfc is about more than 2 times above for RAM and L/D is approximately 40%lower at M=4.5,the velocity over ground is 5.4 times higher than at M=0.8.These numbers easily explain the lower cruise consumption of LAPCAT-M4 in supersonic cruise.Simulations show that if a direct acceleration to Mach 4.5 already over the European continent would be acceptable,the HSCT could reach its final destination of Sydney. sfr kg/km] 300 250 200 150 100 50 0- 0 5000 10000 15000 20000 25000 flight time[s】 Figure 5:LAPCAT-M4 fuel consumption per range as a function of flight time m. Hypersonic Cruise Airplane at Mach 8 C.HyperSoar Concept Historically,the proposals on hypersonic cruise airplanes seem to be much rarer than those on supersonic airliners.This is obviously due to the fact that in hypersonics the thermal environment is considerably more demanding.The very high heat flux at sufficient dynamic pressure for the airbreathing engines almost excludes any sustained hypersonic flight. An innovative concept dubbed HyperSoar has been proposed by Lawrence Livermore National Laboratory in the US.The vehicle concept found a large public interest when it was illustrated on the title of Aviation Week&Space Technology magazine in 1998 [5].Designed as a global reach military strike airplane with a flight Mach number of 10,HyperSoar has a unique feature of skipping on the upper atmosphere (see Figure 6).After accelerating with Rocket Based Combined Cycle(RBCC)engines,the vehicle would temporarily shut down its propulsion system and begin a periodic hypersonic cruise trajectory.While the configuration is outside the dense layers of the atmosphere the propulsion system and leading edges could cool down.When it falls back the Scramjet of the RBCC is reignited for a short period to accelerate again for another ballistic arc. In the course of continued research in the US,the notional design of the HyperSoar 1998 vehicle was improved using "Osculating Cone waverider"design.Figure 7 shows the layout of this improved shape.The inlet airflow requirements of the propulsion are more adequately addressed and the aft-body shape and flight control layout are more realistic in this design.DLR-SART has recalculated the HyperSoar 2000 configuration.The recalculation intended to develop the tools for a similar but larger LAPCAT-M8 hypersonic airliner.Independent mass assessment of the HyperSoar 2000 configuration with the DLR mass analysis tool stsm based on similar dimensions and loads delivers an empty weight of 94500 kg(+80%compared to data provided in [5D).With a similar amount of propellant(146200 kg+10000 kg reserves)and a new take-off mass(256200 kg)an intercontinental range with a payload of about 10000 kg does not seem to be completely out of reach on the first look. 6 American Institute of Aeronautics and Astronautics Paper 2006-7984
American Institute of Aeronautics and Astronautics Paper 2006-7984 6 consumption per range (kg/km). The two peaks represent the acceleration phases, with the first in dry mode and the second with full afterburner ignition. The two long-time relatively flat, slightly decreasing sections are the cruise phases, with the first in subsonic dry mode and the second in Mach 4.5 RAM-cruise. On a first look it seems surprising that the RAM-cruise efficiency is better than those of the turbofans in subsonic flight. Although sfc is about more than 2 times above for RAM and L/D is approximately 40 % lower at M=4.5, the velocity over ground is 5.4 times higher than at M= 0.8. These numbers easily explain the lower cruise consumption of LAPCAT-M4 in supersonic cruise. Simulations show that if a direct acceleration to Mach 4.5 already over the European continent would be acceptable, the HSCT could reach its final destination of Sydney. sfr [ kg/km ] 0 50 100 150 200 250 300 0 5000 10000 15000 20000 25000 flight time [ s ] Figure 5: LAPCAT-M4 fuel consumption per range as a function of flight time III. Hypersonic Cruise Airplane at Mach 8 C. HyperSoar Concept Historically, the proposals on hypersonic cruise airplanes seem to be much rarer than those on supersonic airliners. This is obviously due to the fact that in hypersonics the thermal environment is considerably more demanding. The very high heat flux at sufficient dynamic pressure for the airbreathing engines almost excludes any sustained hypersonic flight. An innovative concept dubbed HyperSoar has been proposed by Lawrence Livermore National Laboratory in the US. The vehicle concept found a large public interest when it was illustrated on the title of Aviation Week & Space Technology magazine in 1998 [5]. Designed as a global reach military strike airplane with a flight Mach number of 10, HyperSoar has a unique feature of skipping on the upper atmosphere (see Figure 6). After accelerating with Rocket Based Combined Cycle (RBCC) engines, the vehicle would temporarily shut down its propulsion system and begin a periodic hypersonic cruise trajectory. While the configuration is outside the dense layers of the atmosphere the propulsion system and leading edges could cool down. When it falls back the Scramjet of the RBCC is reignited for a short period to accelerate again for another ballistic arc. In the course of continued research in the US, the notional design of the HyperSoar 1998 vehicle was improved using "Osculating Cone waverider" design. Figure 7 shows the layout of this improved shape. The inlet airflow requirements of the propulsion are more adequately addressed and the aft-body shape and flight control layout are more realistic in this design. DLR-SART has recalculated the HyperSoar 2000 configuration. The recalculation intended to develop the tools for a similar but larger LAPCAT-M8 hypersonic airliner. Independent mass assessment of the HyperSoar 2000 configuration with the DLR mass analysis tool stsm based on similar dimensions and loads delivers an empty weight of 94500 kg (+ 80% compared to data provided in [5]). With a similar amount of propellant (146200 kg + 10000 kg reserves) and a new take-off mass (256200 kg) an intercontinental range with a payload of about 10000 kg does not seem to be completely out of reach on the first look
Sustaining propulsion burns Mesosphere Stratosphere Ozone layer Jet aircraftN Mt.Everest Troposphere Range (scale is compressed) Figure 6:Principle idea of the HyperSoar trajectory Figure 7:Artists impression of the HyperSoar 2000 configuration However,this preliminary evaluation should be regarded with a high degree of skepticism.Almost no data can be found on the propulsion system performance characteristics of HyperSoar.The concept developer at LLNL Preston Carter,published a paper on periodic hypersonic cruise [6].This study used an ejector RAMJET/- SCRAMJET rocket engine.Therefore,it seems quite reasonable that a similar RBCC is the basic propulsion system of HyperSoar.The specific impulse model as presented in [6]seems to be very simplified,at least on the ejector rocket side.Very limited historical data of experiments or flight tests on air-augmented rockets have been published. Although the SART assumptions for the recalculation in [2]are less euphoric,the performance data still represent ideal values because actual intake,combustion chamber,and nozzle characteristics were not taken into account D.LAPCAT-M8 The new generic hypersonic cruise airplane for LAPCAT has been initially based on the HyperSoar 2000 shape despite some concerns on its flyability.However,for defining the size and the propulsion system thrust requirements this approach is still acceptable.LAPCAT-M8 is considerably enlarged compared to HyperSoar to accommodate the passengers and the cabin and to meet the ambitious LAPCAT range requirement.Since the beginning of the study the hypersonic-M8 configuration had to be redefined already two times. The TRL of RBCC propulsion is low and a high degree of uncertainty exists on its actually achievable performance in ejector-rocket and SCRAM-mode.Therefore,an iterative approach in defining the thrust requirements and subsequent calculation of the mission performance has been chosen.As the LAPCAT study is in focus of far-term propulsion concepts [1],usually optimistic engine performance assumptions are drawn.This approach is maintained not only in case of missing validation by an actual flight test but also if the efficiency could not yet be demonstrated in a ground experiment.This important difference should be kept in mind if obtained data are compared with the other two transportation options of the chapters II and IV which are based on propulsion systems with much more advanced TRL All variants described here are based on LH2 propellant and on LOX as the oxidizer in rocket mode.Hydro- carbon propellants had also been regarded at an early phase but fuel consumption was found tremendously high due to the poor specific impulse in ejector-rocket operation mode.Therefore,all hydrocarbons were dropped quite early in the study as a feasible propellant for LAPCAT-M8 [2].The following paragraphs give a brief overview on the evolution process In the first iteration cycle with the configuration status of June 2005 (see Figure 8)the lifting body's projected area had been increased to 3000 m2(+150 compared to HyperSoar 2000)to keep the wing loading within an acceptable range.The span grew to 34.2 m,while the total length reached 106.1 m (+74 %when compared to HyperSoar 2000 [7]. The preliminary RBCC performance assumptions of the generic LAPCAT hypersonic cruise airliner were more conservative than those of HyperSoar [7].However,engine Isp was used according to ideal RAM and SCRAM performance not taking into account any actual intake and nozzle geometry.Thrust of the propulsion system was selected as required for simulation of a sustainable trajectory.This very optimistic approach was justified at this design stage because the major intention had been in finding the reference operation conditions of the propulsion system. American Institute of Aeronautics and Astronautics Paper 2006-7984
American Institute of Aeronautics and Astronautics Paper 2006-7984 7 Figure 6: Principle idea of the HyperSoar trajectory Figure 7: Artists impression of the HyperSoar 2000 configuration However, this preliminary evaluation should be regarded with a high degree of skepticism. Almost no data can be found on the propulsion system performance characteristics of HyperSoar. The concept developer at LLNL, Preston Carter, published a paper on periodic hypersonic cruise [6]. This study used an ejector RAMJET/- SCRAMJET rocket engine. Therefore, it seems quite reasonable that a similar RBCC is the basic propulsion system of HyperSoar. The specific impulse model as presented in [6] seems to be very simplified, at least on the ejector rocket side. Very limited historical data of experiments or flight tests on air-augmented rockets have been published. Although the SART assumptions for the recalculation in [2] are less euphoric, the performance data still represent ideal values because actual intake, combustion chamber, and nozzle characteristics were not taken into account. D. LAPCAT-M8 The new generic hypersonic cruise airplane for LAPCAT has been initially based on the HyperSoar 2000 shape despite some concerns on its flyability. However, for defining the size and the propulsion system thrust requirements this approach is still acceptable. LAPCAT-M8 is considerably enlarged compared to HyperSoar to accommodate the passengers and the cabin and to meet the ambitious LAPCAT range requirement. Since the beginning of the study the hypersonic -M8 configuration had to be redefined already two times. The TRL of RBCC propulsion is low and a high degree of uncertainty exists on its actually achievable performance in ejector-rocket and SCRAM-mode. Therefore, an iterative approach in defining the thrust requirements and subsequent calculation of the mission performance has been chosen. As the LAPCAT study is in focus of far-term propulsion concepts [1], usually optimistic engine performance assumptions are drawn. This approach is maintained not only in case of missing validation by an actual flight test but also if the efficiency could not yet be demonstrated in a ground experiment. This important difference should be kept in mind if obtained data are compared with the other two transportation options of the chapters II and IV which are based on propulsion systems with much more advanced TRL. All variants described here are based on LH2 propellant and on LOX as the oxidizer in rocket mode. Hydrocarbon propellants had also been regarded at an early phase but fuel consumption was found tremendously high due to the poor specific impulse in ejector-rocket operation mode. Therefore, all hydrocarbons were dropped quite early in the study as a feasible propellant for LAPCAT-M8 [2]. The following paragraphs give a brief overview on the evolution process. In the first iteration cycle with the configuration status of June 2005 (see Figure 8) the lifting body's projected area had been increased to 3000 m2 (+ 150 % compared to HyperSoar 2000) to keep the wing loading within an acceptable range. The span grew to 34.2 m, while the total length reached 106.1 m (+ 74 %) when compared to HyperSoar 2000 [7]. The preliminary RBCC performance assumptions of the generic LAPCAT hypersonic cruise airliner were more conservative than those of HyperSoar [7]. However, engine Isp was used according to ideal RAM and SCRAM performance not taking into account any actual intake and nozzle geometry. Thrust of the propulsion system was selected as required for simulation of a sustainable trajectory. This very optimistic approach was justified at this design stage because the major intention had been in finding the reference operation conditions of the propulsion system