 The ability to take off in a short distance, and land in a short distance, or vertically, is something aeronautical engineers have strived towards since World War II. Early attempts at this include the autogyro, the helicopter, the vertiget, and other research aircraft. Today we have machines like the V-22 Osprey, a tilt rotor aircraft, the quiet short-haul research aircraft, or QSRA, and the rotor system research aircraft, or RSRA, which are in flight testing programs at other NASA centers in the United States. There is one aircraft currently being used that is a true Stoval-type aircraft. It is the British-made Harrier Jumpjet. This plane is manufactured in the United States by McDonnell Douglas, under license as the AV-8A and AV-8B. Here at Lewis Research Center we are currently testing scale models of advanced supersonic Stoval concepts, hot gas ingestion, and controls and propulsion system technology. Lewis's main role then is to develop advanced propulsion concepts for air-breathing aircraft. Stoval is an air-breathing aircraft. We develop the engines, we develop the propulsion components that are required to power these type of aircraft. There are five types of propulsion concepts for Stoval-type aircraft. Vector thrust, ejector augmenter, remote augmented lift system, lift plus lift cruise, and the tandem fan configuration. The one that we see the most of in the news today is the Harrier, and that's the vector thrust type of configuration. It uses an engine that has four variable nozzles on it that can be aimed either in the vertical direction or horizontally for forward flight. Each of these systems have specific advantages and disadvantages, but one of the main problems is one of technology. There are several really key concepts that propulsion technologies that have to be developed. One of the more obvious ones is that in order to make these airplanes flyable you have to get lightweight propulsion systems. NASA and the Department of Defense have a major activity going on to develop lightweight high thrust weight basic engine concepts. That applies to all advanced fighters. In the case of Stoval and there are some other special issues, one is the lift concepts themselves. The ejector system, the raw system, lift engines, those all have to be, the technologies associated with those concepts have to be developed. Specifically here at Lewis we're investigating the ejector concept as part of our current program. Then additional items on the list, a lot of these concepts have complex internal ducting that occurs inside the aircraft, fan air collection systems, valves and so on. These things have to be developed to make them compact, lightweight, efficient yet at the same time not have large pressure losses. At the 9 by 15 foot low speed wind tunnel at Lewis we are looking at some of the problem areas, hot gas ingestion avoidance and ground flow field effects on Stoval aircraft. Another technical problem that we're looking at is the hot gas ingestion problem. This is where, well many of these concepts have hot gas which is produced forward on the aircraft usually by burning fuel in the vertical lift system. This hot gas goes down, hits the ground, is reflected back up and ingested by the inlet systems on the aircraft and turbine engines do not like hot gas. They lose their power or something else happens and it's a major problem. There are other problems that are associated with Stoval aircraft and in conjunction with NASA Langley Research Center and NASA Ames Research Center, the NASA Lewis Research Center is continuing in its quest to produce a viable, lightweight, reliable propulsion system. These aircraft have to operate efficiently in supersonic speeds as well as at very low speeds with very high air flows and as a result there's a problem of getting inlets that have high performance both at supersonic conditions and also at essentially static conditions while in hover, possibly at high angles of attack which result in flow problems for the inlet system. Nozzle systems are a key problem here from the standpoint that they tend to be in today's aircraft very heavy if we put the kind of requirements that a Stoval has. So a major program has to be evolved to develop advanced nozzle concepts. And last but not least is a key problem for the pilot and that is the pilot has to be able to control his beast while he's doing his mission. And the Harrier is a difficult aircraft to fly and one of the areas that we in conjunction with Ames, we have a joint program with Ames specifically in this area to address how do we get the right pilot interfaces there to fly the airplane in a manner which makes it easy for him to fly. We could build a Stoval airplane today. The problem is that it would be too heavy and not particularly practical for what it can do for a mission. And the main thing that we're trying to develop now is a supersonic capability, an aircraft with adequate range and reasonable payload. And that's the main thrust of the advanced technology. We know that Stoval works. It's a question of getting an aircraft which meets the requirements that the services want.