However, tests of wind-tunnel models in the DVL high-speed wind tunnel revealed that the Lippisch P.13a design showed exceptional stability into the Mach 2.6 range, even though it never left the drawing board
Dr. Alexander Lippisch created the Lippisch P.13a for Nazi Germany in late 1944 as an experimental delta-wing interceptor with ramjet propulsion. The aircraft was never developed beyond the design phase, although tests on wind tunnel models at the DVL high-speed wind tunnel revealed that the design possessed exceptional stability up to Mach 2.6.
According to aviation expert Nikolas Pullen on Quora, the Lippisch P.13a is possibly one of the weirdest aircraft ever created for a few reasons:
1. Examine its shape. It resembles a menacing alien fish monster you could see in a B-grade sci-fi horror movie from the 1980s.
2. The actual design:
The pilot sits on a ramjet that runs on coal dust that is kept in the middle basket. At speeds of less than 320 km/h, this ramjet would only begin to produce enough thrust to support flight; for higher speeds, the aircraft needed to be towed or use rocket-assisted takeoff pods.
3. Did I mention that coal powers it? Not jet fuel, gasoline, or even synthetic oil (which is made from coal), just straight-up ground-up coal.
By the end of 1944, conventional fuels were incredibly scarce, therefore Lippisch suggested using coal to power the P.13a. Initially, it was suggested to attach a wire-mesh coal basket behind the nose air intake, protrude it into the airflow, and light it with a gas burner. Modifications were made to the ramjet and coal basket after wind tunnel testing in order to enable more effective combustion.
Photo by FlightSim.com