The Lippisch P 13 was an experimental ramjet-powered delta wing interceptor aircraft designed in late 1944 by Dr. Alexander Lippisch for Nazi Germany. The aircraft never made it past the drawing board, with testing of wind tunnel models showing the design had extraordinary stability into the Mach 2.6 range. As conventional fuel was in short supply at the end of the war, the ramjet was to be powered by powdered coal.
As explained by Dan Sharp in his book Secret Projects of the Luftwaffe Volume 1 Jet Fighters 1939-1945, work on the P 13 began in May 1944 and while it utilised the ramjet technology of the P 12 (which had been designed to carry weaponry) its role harked back to the ‘arrows of death’ conceived back in September 1943 – it was a rammer.
It also differed from the P 12, in layout. Where the P 12’s pilot sat low down in the fuselage, with the air ducts feeding the ramjet wrapped around his narrow cockpit, the P 13’s ramjet intake was completely unobstructed — with air entering the intake almost immediately entering the large combustion chamber. This was made possible by shifting the cockpit upwards to create a large combined fin/cockpit sitting on top of the combustion chamber.
Another difference was fuel — the P 12 carried tanks of liquid fuel for its ramjet but the P 13 would be fitted with a wire mesh grate containing a quantity of slow-burning coal or other solid fuel. Under interrogation by US Army officers in July 1945, Lippisch explained his decision to switch fuels: “He felt that at high velocities, solid fuels were more desirable than liquid fuels, the reason being that the solid fuel did not flow out into the velocity stream and, therefore, its burning took place at a predetermined place.
“For a solid fuel to be acceptable it must have good ‘gas producing qualities’, such as has bituminous coal. The most intense heating among the solid fuels was provided by German normal pine wood ‘cooked’ in oil or paraffin in pieces 1 x 1 x 1cm.”
Neither of Lippisch’s 1976 books makes any mention of how the P 13 was to be used on active operations. When the British asked him whether the P 13 had been designed as a rammer, it was stated that: “The possibilities of using the P 13 as a ramming aircraft had been considered but Dr Lippisch did not think that athodyd propulsion was very suitable for this purpose owing to the risk of pieces of the rammed aircraft entering the intake. This would be avoided with a rocket-propelled rammer.”
However, the Luftwaffe’s undated P 13 Baubeschreibung or construction description of 1944, probably produced in October or early November, states: “The aircraft presented here is a jet with the task of fighter. The propulsion is by a Lorin engine, not using liquid fuel (gasoline, gas oil, J2 etc.) but with solid fuels (coal). Studies have been carried out on two forms — bulky pieces in a real grate or secondly with pressed coal in plates and hollow cylindrical shapes. Either can be used.
`The engine used allows, for the time being, no self-launch. The launch itself must be carried out with (powder) rockets, a Madelung catapult or similar. Due to tactical considerations, among other things, the speed difference of fighters and bombers, attack from behind is preferable, though thought was given to the installation of brakes (brake parachute, retractable screens similar to dive brakes etc.), and although ample room for weaponry is present, the task of ram fighter has been taken into account — so that the ramming attack will not lead to the loss of the aircraft, thanks to its shape and static structure.”
The small rammer aircraft would be easily transported: “When the outer wings are folded, transport of the entire aircraft on a small open car is possible on the Deutsche Reichsbahn.”
The fuselage section of the description gives the length of the aircraft as 6m, saying: “The wing attachment fittings (outer wing to wing centre section) are formed so that the outer wings can be folded upwards. This is necessary for two reasons. The `up’ position allows access to the engine through the wing centre section, and secondly for loading and offloading onto vehicles during transport.”
In other words, folding up the wings would allow ground crew to simply reach in and remove the exhausted coal grate before sliding a new one in – completing the type’s refuelling in a matter of minutes.
The P 13 would cut through Allied aircraft using existing technology: “The edge cap is constructed as a deflector to avoid rudder damage if possible during ramming. The entire wing leading edge is reinforced with a knife (similar to the Kutonase).”
The Kutonase was originally developed to cut the steel cables anchoring barrage balloons. It was a hard steel blade that was fitted right the way along the leading edge of an aircraft’s wing beneath an aerodynamic fairing of thin flexible metal. This concealed the Kutonase and made the wing fitted with it appear normal.
The fin was “designed just like the wing and built along similar lines” – presumably meaning that it too housed an aircraft-slicing Kutonase along its length. It was 2.28m high, with this measurement being determined by the need to provide the pilot with good visibility, and was attached to the wing by four fittings, two of them on rockers to allow for expansion of the wing’s surface due to intense heating by the ramjet.
The point of connection between the centre section of the aircraft and the outer wings served “as a cooling passage” and when the inner side changed in length due to heating, this was offset by a rocker.
The cockpit itself was “equipped with front and rear walls and is planned to be extremely spacious” and the glazing was designed to be simple to manufacture and distortion-free. The seat and joystick were to be “mounted on the detachable cabin floor” for “production reasons” and the portion of the fin to the front of the cabin was designed to be easily removable for ease of access to the equipment housed beneath it.
Landing the P 13 would have been tricky given the nose up attitude required. To this end, “a design was chosen where a blade flips open that is rotatable around its front end”. This blade-skid with multiple torsion springs was only attached to the fuselage at one end, the other was intended to contact the ground and allow the aircraft to settle using the springs to cushion the impact.
It was the end of the war that prevented further development of the P 13 (later referred to as the P 13a by Lippisch and replaced by a new design featuring a circular rotating coal grate design, the P 13b) beyond the unpowered DM-1 test glider. After the war, Lippisch, working with American aircraft designer Convair, developed and tested the XF-92 based on his designs, leading to the eventual adoption of the F-102 Delta Dagger and its successor, the F-106 Delta Dart.
Secret Projects of the Luftwaffe Volume 1 Jet Fighters 1939-1945 is published by Mortons Books and is available to order here. Save 10% on all books with exclusive promotional code ‘AVGEEK10’!
Photo credit: U.S. Air Force
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