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Improving the Efficiency of Engines for Large Nonfighter Aircraft
SUMMARY 1 TECHNOLOGY OPTIONS FOR IMPROVEDAIR VEHICLE FUEL EFFICIENCYAIR FORCE SCIENTIFIC ADVISORY BOARDCHAIR: ANN KARAGOZIANMAY 2006
This study identifies potential near-, mid-, and far-term methods for improving air vehicle fuel efficiency in the Air Force. The study also determines relevant benefits of recent government propulsion efficiency programs and technologies (current and future) that could impact fuel efficiency.
Between 2005 and 2025, the percentage of crude oil imported to the United States is estimated to grow from 63 to 70 percent of the total crude oil consumed. Within DoD, the Air Force is the largest consumer of fuel, with 58 percent, or 3.2 billion gallons, used in 2003. Of this, 81 percent was used for fueling aircraft. The largest percentage (54.2) of aircraft fuel is used by tankers and transport planes (FY98-FY04).
In the study, the cost of fuel is estimated by including the actual cost (Defense Energy Support Center (DESC) price to the Air Force) as well as the cost to transport the fuel via tanker. The cost to transport the fuel can be significantly higher than the actual fuel cost. Therefore it is necessary to account for this “fully burdened” cost of aviation fuel when comparing benefits of alternative solutions.
Fuel efficiency can be increased by making adjustments in three areas: aerodynamics (to increase lift to drag ratio), engine fuel consumption (to decrease thrust-specific fuel consumption (TSFC)), and weight (to reduce operational empty weight). It is estimated that large transport aircraft could realize as much as a 12 percent savings in fuel if there is a 10 percent increase in lift to drag ratio, a 13 percent savings for a 10 percent decrease in TSFC, and a 6 percent savings for a 10 percent decrease in operating empty weight (OEW). This information was calculated for an aircraft at Mach 0.8 at an altitude of 36,000 ft.
Over the past 50 years or so, the TSFC of engines has tended to decrease over time, starting with turbojet engines in the 1950s and ending with second-generation, high-bypass turbofans in the early 2000s. The potential for further gains in TSFC is projected to decrease in the next 15 years. However, tankers and transport aircraft tend to have a higher lift to drag ratio and lower TSFC than fighter aircraft, making them better candidates for TSFC improvement.
Current Air Force turbine engine development programs (IHPTET and VAATE) plan to improve engine performance over the next 10 years. These programs generally emphasize goals for military performance, not mobility. NASA aeronautics development programs are focusing on emissions, noise reduction, and engine control as well as ultraefficient engine technology (UEET). UEET has achieved a