National Aeronautics and Space Administration

Glenn Research Center

Dennis Huff

The Space Academy was given the opportunity to learn more about the aeronautic side of NASA at a lecture given by Dennis Huff during the morning of Monday, August 1st. Dennis Huff currently serves as the Deputy Chief of the Aeropropulsion Division at Glenn, and his talk was titled, “Future Challenges in Aeropropulsion.” Mr. Huff explained that aeronautics is traditionally broken into four major categories of flight at NASA, which are subsonic, supersonic, hypersonic, and rotorcraft. Mr. Huff went on to explain each category in detail, but he noted that from these categories it is subsonic flight that has traditionally been the primary research area at NASA, and thus it would be the main focus of his talk.

Mr. Huff started his presentation by discussing the design considerations of aircraft, which include features such as reliability, cost, maintainability, payload size, comfort, and cruise speed. Although Mr. Huff pointed out that safety is undoubtedly the single most important design consideration for aircraft, he explained that the focus of NASA revolves around reducing noise, minimizing emissions, and maximizing fuel economy. Displayed in the presentation were charts that illustrated the goals of NASA in these three areas for the next three generations subsonic aircraft.

The lecture included a review of how turbofan engines operate. He presented a schematic outlining how the inlet flow is split between the core and the bypass duct. He then explained the purpose of various components in the core and the significance of the bypass ratio. Mr. Huff then moved on to explaining the different possibilities for future aircraft designs. With so many competing possibilities it is still uncertain the path aviation will take. Subsonic flight could pursue podded engines above the wing, embedded engines, ultra-high bypass engines, open rotor engines, or some combination of the above.

Many other companies and research groups have proposed aircraft designs to NASA, and the trends that appear include lower cruise speeds, higher altitudes, higher bypass ratios, and higher aspect ratios for wings. To bridge the gap between current aircraft and the next generation Mr. Huff presented a graph of propulsion efficiency. The chart not only demonstrated the progression of aircraft over the years, but also how much more they must improve before any theoretical limits are reached. Additionally, Mr. Huff overviewed both the tradeoff inherit between performance and emissions and some examples of fundamental technologies that must be pursued in order to improve subsonic aircraft. To finish off the subsonic potion of the presentation, Mr. Huff explained current alternative fuels research, which includes investigation into bio-fuels and different jet fuel blends.

Supersonic aircraft were analyzed next, and Mr. Huff began this section by pointing out that commercial supersonic aircraft have not existed since the late 1970s when the Concorde was retired. The biggest issue with supersonic aircraft is the sonic boom must be reduced for over land flight. Mr. Huff displayed a chart of national goals for supersonic aircraft that was similar to the national goals chart for subsonic aircraft. Supersonic aircraft will have to start small and work their way up if they are going to have any sort of commercial success in the near future. The presentation transitioned quickly into hypersonic aircraft, which have the potential to give air-breathing jets access to space. Mr. Huff talked about scramjets and wind tunnel testing, as well as the importance of carefully documenting research when faced with cancelled funding. Finally, Mr. Huff touched on rotorcrafts, which are suited best for point-to-point, or building-to-building, small-scale flights. He showed different designs of how aircraft can lift off like a helicopter then rotate the propellers to fly like a plane. He explained how counter-rotating blades provide stability, and pointed out that the principle challenge in rotorcraft design in meeting the required variability in rotor speed.

Before ending the presentation, He concluded that there are countless challenges to be tacked in aeronautics research that will require the development of many new technologies. Mr. Huff was optimistic that NASA will help to change the face of subsonic aviation, reintroduce commercial supersonic flight, and improve access to space.