DeltaDart

The P 13’s construction started in May 1944, and although it used the P 12’s ramjet technology (which had been intended to carry weapons), its function was similar to that of the “arrows of death” that had been conceived in September 1943—it was a rammer.

Dr. Alexander Lippisch created the experimental Lippisch P 13 ramjet-powered delta wing interceptor plane for Nazi Germany in late 1944. The aircraft was never developed past the design stage despite wind tunnel tests demonstrating the design’s exceptional stability up to Mach 2.6 speed. At the end of the war, conventional fuel was in insufficient supply, thus powdered coal was to be used to power the ramjet.

Work on the P 13 began in May 1944 and, although it used 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, as Dan Sharp explains in his book Secret Projects of the Luftwaffe Volume 1 Jet Fighters 1939-1945.

Its design also differs from the P 12’s. The P 13’s ramjet intake was fully unobstructed, with air entering the intake nearly immediately entering the massive combustion chamber, in contrast to the P 12 where the pilot sat low in the fuselage with the air ducts feeding the ramjet coiled around his narrow cockpit. The cockpit was moved upward to create a sizable combined fin/cockpit sitting on top of the combustion chamber, which allowed for this.

The P 12 had tanks filled with liquid fuel for its ramjet, whereas the P 13 would have a wire mesh grate holding a substantial amount of slow-burning coal or other solid fuel. In July 1945, while being questioned by US Army officers, Lippisch gave the following justification for 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 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.”

How the P 13 was supposed to be used during active operations is not mentioned in either of Lippisch’s 1976 publications. When the British questioned him about whether the P 13 had been intended to be a rammer, he responded: “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 a 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 between fighters and bombers, attack from behind is preferable, though the 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.”

Transporting the little rammer plane would be simple: “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 center 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 center section, and secondly for loading and offloading onto vehicles during transport.”

In other words, by folding up the wings, the ground crew may quickly refuel the aircraft by reaching in, removing the exhausted coal grate, and then sliding a new one in.

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. A thin, flexible aerodynamic covering protected a hard steel blade that was installed all the way down an aircraft wing’s leading edge. This kept the Kutonase hidden and gave the wing that had it look normal.

It is assumed that the fin also contained an aircraft-slicing Kutonase along its length since it was designed exactly like the wing and built along similar lines. It had four fittings, two of which were on rockers to allow for wing surface expansion brought on by the ramjet’s intense heating, and was 2.28 meters high, the height of which was dictated by the necessity to give the pilot a good view.

When the inner side changed in length owing to heating, this was offset by a rocker at the point of connection between the center part of the aircraft and the outer wings.

The glazing was made to be easy to produce and distortion-free, and the cockpit itself was equipped with front and rear walls and is planned to be extremely spacious. For production reasons, the seat and joystick were to be mounted on the detachable cabin floor, and the front half of the fin was meant to be easily detachable to provide access to the equipment housed beneath it.

Given the need for a nose-up attitude, landing the P 13 would have been challenging. In order to achieve this, a design where a blade flips open that is rotatable around its front end was chosen. Only one end of the blade skid, which had several torsion springs, was linked to the fuselage; the other end was meant to make contact with the ground, allowing the aircraft to settle while the springs absorbed the impact.

The P 13 (later referred to by Lippisch as the P 13a and replaced by a new design using a circular rotating coal grate design, the P 13b) was only capable of producing the unpowered DM-1 test glider before the war came to an end. Following the war, Lippisch created and tested the XF-92 based on his concepts in collaboration with American aircraft designer Convair, which eventually led to the adoption of the F-102 Delta Dagger and its replacement, 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.

Photo by U.S. Air Force