Lippisch P.11
In October 1941 it was evident that the rocket engines planned for the Me 163 B would take months or even years to be available.
By the beginning of the month, the excellent aerodynamic features of the Me 163 A had allowed it to reach 1,000 km/h (0.84 Mach) and Alexander Lippisch started to consider the possibilities of the new Junkers T1 turbojets that had been successfully tested some days after the record was achieved.
They were too long for a Komet airframe. They should be installed in a bigger airplane, a heavy fighter of six tons, equivalent to the Me 262 that, with the Me 163 aerodynamics, would have better ceiling, climb rate and max speed.
On 28 November 1941 it was presented to the OKL, as Lippisch P.09, a single seat heavy fighter armed with four 20 mm guns. Too advanced for its time, when the Me 163 had not yet engaged in combat, it was decided to favour the manufacturing of the Me 262.
Lipisch decided to modify the basic design as schnellbomber, by installing a second crew member, widening the wingspan 1.4 m and reducing the sweep 3-degrees. The fuselage contained two fuel tanks and a bomb bay underneath them with capacity for an SC 1000 L2.
The new project, known as Lippisch P.11-92 13/09/42, was presented to the OKL as the answer to the specification published by the RLM’s Technical Department on October 20, 1942. It required a bomber with 1,000 kg payload, 700 km/h max speed and 1,046 km penetration depth.
It did not turn out well. Designers had not considered that the acceleration generated by the turbojet was much too lower than the rockets on which the original project was based. It was estimated that a tailless bomber, heavy loaded, would have had difficulties to make the rotation during the take-off, due to the short distance between the elevators and the centre of gravity, even supported by the RATO auxiliary rockets. The P.11-92 was cancelled in November 1942.
On 2nd December, the design team of the Abteilung L (Lippisch) tried again with an improved design (P.11-105) that replaced the radio operator by new electronic equipment for fighters. The cockpit was installed in the nose to reduce the drag produced by the old canopy and the climb rate and ceiling were improved, increasing the wing surface. To solve the problem of the take-off, it was installed a retractable tailplane formed by two trapezoidal surfaces of 3 sq. m each.
The P.11-105 could dive bomb using a Revi C16 reflector gunsight or at high altitude in a flight levelled with the Lofte 7 bombsight. The idea of the retractable tailplane was not liked by OKL who, considering the aircraft unstable, cancelled the project at the beginning of 1943. Instead, production of Me 410 B-1 was initiated.
Abteilung L was dissolved within the Messerchmitt in April and the Lippisch design team moved to Vienna to form the Aeronautical Research Institute
Luftfahrtforschungsanstalt Wien. The works on the P.11 continued there, introducing for the first time the `jet-exhaust deflection flaps´ effect, aerodynamic surfaces located behind the engines that, changing the angle of incidence by hydraulic actuators, helped to maintain the tail low during take-off.