Musk is clearly out of his competence when he claims that supersonic electric airplanes are viable, even with the progress in battery technology to be expected in the next few decades. Going supersonic means crossing a drag peak, but beyond that the maximum possible lift to drag ratio is well below that at subsonic speed and decreases again with increasing Mach number. The best lift to drag ratio is achieved in subsonic flight. A Pitot tube on the vertical tail measures a pressure of 2.96x104 N/m2. ![]() If you only want to go fast, the current limit with electrical propulsion and already rather generous assumptions is somewhere around Mach 2.įlying higher does not reduce the thrust requirement since the same lift has to be generated. transonic: adjective being or relating to speeds near that of sound in air or about 741 miles (1185 kilometers) per hour at sea level and especially to speeds slightly below the speed of sound at which the speed of airflow varies from subsonic to supersonic at different points along the surface of a body in motion relative to the surrounding air. A high-speed subsonic Boeing 707 airliner is flying at a pressure altitude of 12 km. However, the energy requirements for doing so will require an energy density of the batteries which is several magnitudes above what is currently possible. Supersonic speed helps to fly high - while subsonic designs run into the coffin corner, supersonic flight helps to maintain high dynamic pressure even at altitude. We had this discussion before, and indeed solar-electric propulsion helped to reach record altitudes: The AeroVironment Helios set a record at 29,524 m which will be hard to break. The composition of the atmosphere does not change too much with altitude, so it is the low atmospheric density which limits maximum altitude. That electric propulsion needs no oxygen is of little help for flying high. I mean somehow there must be limits, otherwise we could just fly higher and higher and fly with 0 thrust and still maintain mach 2 (not talking about space flight here)? These provide reasonable bases for inputs to models. ![]() Would that mean the power or thrust requirement to maintain mach 2 would only be 3.4%? Or is induced drag becoming significant at that point? Or maybe it would even stall at mach 2 if flying 40km high? Emission inventories have been developed for the current subsonic and projected supersonic and subsonic aircraft fleets. Meaning the resistance at 40km would only be 3.4% compared to 18.3km. While technology will definitely advance, it is still not prescriptible to cruise at the most critical part of the transonic regime where the drag divergence is maximum. ![]() Air density at 18.3km is 0.115 kg / m^3, at 30km it's 0.018 kg / m^3 and at 40km it is 0.0039 kg / m^3. thereby obtaining a Mach 0.95 subsonic cruise during the first lower altitude cruise-climb. Instead of mach 2 cruising at 18300 meters, assume it would climb to 30km, or even 40km. Question: is there some kind of limit for altitude and TAS? I mean suppose the Concorde would be retrofitted with batteries and electric fans. His logic seems to be: electric (fan?) propulsion doesn't need oxygen -> can go higher -> less friction -> need less power and thrust to maintain airspeed compared to traditional jet Assuming we have sufficiently energy-dense batteries, where would the limits be in terms of speed and altitude. With this, the waves merge together to form into shock wave which then travels at the speed of sound at Mach 1 which is equivalent to 1,235 km/hour or (767 miles per hour).So I was thinking about Elon Musk's supersonic electric jet idea. It is usually rated at 20 C (68 F), and is about 343 metres per second (1235 km/h 1125 ft/s 767 mph). These sound waves then pass at the speed of sound and when the object rises, the waves are compressed together as they can't pass out from each other's path fast. Sonic speed is the speed of sound in dry air. When an aircraft travels in the air, it creates sound waves both at the front and the rear of the plane. For the lowest subsonic conditions, compressibility can be ignored. When a supersonic aircraft is flying at a low altitude, the sonic boom caused by it may lead to slight tremors similar to earthquakes shaking buildings and shattering glasses. Subsonic conditions occur for Mach numbers less than one, M 1. ![]() The sonic boom causes a large amount of sound energy and sounds like an explosion to the human ear. Sometimes the sonic boom created by supersonic aircraft is so loud that it may cause damage to some structures. Sonic boom phenomenon occurs when an aircraft breaks the sound barrier and travels faster than the speed of sound.
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