Uninhabited Air Vehicles Enabling Science for Military Systems (2000) / Chapter Skim
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5 Propulsion Technologies
5 Propulsion Technologies
Pages 59-70
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From page 59... ...
This chapter discusses UAV concepts that require new propulsion technology. Some classes of UAV require new engine technology, new designs, or even new fundamental research and propulsion concepts.
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From page 60... ...
The gas turbine engine is vastly superior to alternative engines in all propulsion metncs. This high level of performance reflects the intrinsic meets of the concept and the $50 billion to $100 billion invested in gas turbine research and development over the past 50 years.
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From page 61... ...
. In contrast, a solar-powered vehicle has zero fuel weight and, thus, very high energy density but low power density (the solar cells and power storage system are heavy)
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From page 62... ...
The additional compression requirement significantly increases the weight of high-altitude propulsion systems. Because the compression process increases the temperature as well as the air pressure, the required pressure ratios result in temperatures that are too high for current technology.
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From page 63... ...
Figure 5-3 illustrates how the amount of power required varies as a function of vehicle size for a class of conventional airplane configurations. In the figure, the flight power curve refers to the power (thrust times flight velocity)
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From page 64... ...
The current DARPA MAV program is investigating four propulsion options: batteries, microdiesels, fuel cells, and micro gas turbines. The last three are projected to have about the same fuel consumption per unit power, but the micro gas turbine is considerably smaller and lighter.
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From page 65... ...
Source: Massachusetts Institute of Technology, Lincoln Laboratory. Significant cost reduction over the lowest cost with current technology will require advances in fluid mechanics, heat transfer, and materials technologies that emphasize cost instead of performance, which is traditionally emphasized.
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From page 66... ...
Currently, most military engines are designed for specific applications; thus development costs for each new aircraft are substantial. One radical approach to reducing these costs would be to develop a miniature, high-performance, lowcost engine that could be grouped to provide greater thrust.
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From page 67... ...
, which are contemplated for UCAVs. Propulsion for High-Speed, Highly-Maneuverable UAVs Current engine designs accommodate steady inertial loads compatible with human life (nominally up to 9g's)
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From page 68... ...
1 1 4 Up |1.2 _ - 1 2 3 4 5 5.5 1 1 1 1 1 1 1 1 8 7 6 5 4 3 2 1 9 Down Up —6 - 5 _ 4 - 3 _ 2 ~1~ - 2 _ 3 _~5 - 7 —8 _ 9 10 Up ~1~ — Down Fore _ 2 _ 3 _ 4 - 5 —6 7 8 _ 9 10 Down / Fore 10 FIGURE 5-5 Typical engine specifications for externally applied forces on takeoff, landing, and maneuvers.
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From page 69... ...
The research topics are summarized in Table 5-2. TABLE 5-2 UAV Propulsion Technologies Type of UAV HALE HSM Very Low-Cost General Topics High-altitude propulsion VTOL propulsion Modeling Cost reduction Specific Topics Low Reynolds number turbomachinery Low Reynolds number heat rejection Turbomachinery tip-clearance tolerance Leakage desensitization Thrust vectoring Magnetic bearings E E I I I I E E I I I I E I Air bearings Solid lubricated bearings Low-cost accessories Low-cost vapor and liquid cooling schemes Affordable high-temperature materials I I I Cooling for small engines I E I I I I = important E = enabling
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From page 70... ...
The following general research topics should be included: · high-altitude propulsion technologies, which may include gas turbines, internal combustion engines, solar-powered motors, or fuel cells · propulsion systems for small, highly maneuverable vehicles, including vertical takeoff and landing (VTOL) capabilities computational modeling capability to reduce the need for engine testing during development · cost-reducing technologies that, for example, reduce parts count and complexity .
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