Heinkel Lerche/Wespe

[Basil]

In December 1944, Dr.-Ing. Gerhard Schulze and Dipl.-Ing. Kurt Reiniger fron Heinkel-Wiener Neustädter Flugzeugwerke, designed two tilsitter fighters with annular wing called Heinkel He 355A Lerche and Heinkel He 355 B Wespe.

Justo, there were no "Heinkel-Wiener Neustädter Flugzeugwerke". A Heinkel facility was located at Schwechat, some 30 kilometers east of Vienna, and the Wiener Neustädter Flugzeugwerke were 40 km south of Vienna and part of the Messerschmitt AG.

 

[Justo Miranda]

In January 1944 Daimler Benz built a twenty-four cylinders engine with 3,800 hp, called DB 613, formed by two DB 603 G engines coupled together to drive a single-shaft power with contra-rotating airscrews. But the set weighed two tons and was not useful to propel a VTOL aircraft.



In the last days of the World War Two, high power and reasonable weight was just a dream, piston engines weighed too much and jet engines had very little thrust.

Lacking engines with sufficient power, Heinkel’s designers attempted to increase the efficiency by using ducted propellers, based on those of the Italian experimental aircraft Caproni Stipa, and annular wings based on the aerodynamic theories of Dipl.-Ing. Helmut Graf von Zborowski.

Inside an annular wing the tapered duct compressed the propeller’s airflow applying Benoulli’s principle. As the air forced into Venturi duct it accelerates.

Annular wings with ducted propellers were advantageous in augmenting engine thrust and in providing additional lifting area in forward flight. This means that a larger propeller with a greater pitch not require more engine power.

By incorporating adjustable control surfaces and varying the cross-section, the duct increases thrust efficiency by up 90 per cent in comparison to a similar-sized propeller in free-air.

It must be made rigid enough not to distort under flight, combat and landing loads.

A VTOL fighter needed that engine power to be delivered with rapid response even at the highest power levels.

The thrust needed to get off the ground had to exceed aircraft weight, but it was necessary for the power plant to provide additional thrust for maneuvering vertically.

A typical value for total thrust needed for vertical acceleration and maneuvering in the other axes would be about 1.7 times the aircraft maximum weight, on the contrary the thrust required in cruising flight would be only a fifth of aircraft weight.

In December 1944, Dr.-Ing. Gerhard Schulze and Dipl.-Ing. Kurt Reiniger fron Heinkel-Wiener Neustädter Flugzeugwerke, designed two tilsitter fighters with annular wing called Heinkel He 355A Lerche and Heinkel He 355 B Wespe.

In February 1945, the VTOL project Lerche was proposed to the RLM in three different versions: Leuchter Jäger Lerche I (24.2.45), Schlachtflugzeug Lerche II (25.2.45) and Schwerer Jäger Lerche III (24.2.45).

Lerche I was a light fighter that weighed half as much as a Focke-Wulf Ta 152 C-3, it was powered by one Daimler-Benz DB 603 E and a six-blades ducted propeller with automatic-pitch control. This powerful engine generated a great deal of torque, to compensate this effect deflector vanes were mounted in the duct airstream.

Transition from over to forward flight was initiated by tilting the nose forward and gathering horizontal speed until wing lift took over.

There was a change in trim as the aircraft was rotated but control could be exercised by moving the vanes.

A sophisticated surface-cooling system developed for the high performance interceptor Heinkel project P. 1076, was integrated in the annular wing. The section between the spars housed the condensation tanks, the heat exchangers and the electric-driven pumps.

To avoid turbulence in the air stream produced by a protruding cockpit hood, it was necessary to design a fuselage of circular section based on that of the P. 1077 Julia project, with the pilot lying in prone position.

The automatic landing system was designed by Dipl.-Ing. Walter Hohbach.

In flight the three landing gear wheels were covered to save drag.

Heinkel He 355A (Entwurf A-B) Lerche I technical data

Ring wing diameter: 3.8 m, overall length: 7.75 m, rotor diameter: 3.3 m, wing area: 27 sq. m, surface area: 64.6 sq. m, wing chord: 2.79 m, estimated max weight: 2,500 kg, power plant: one DB 603E, twelve cylinder, inverted-Vee, liquid cooled engine with two-stage TKL 15 turbo-supercharger, rated at 1,810 hp in cruising flight and 2,250 hp at take-off with MW 50 booster, armament: two Mk 108/30 cannons mounted on each side of the fuselage with 3.5 degrees slope, electronics: EZ 42 gyroscopic gunsight, FuG 16 ZY R/T, FuG 25a IFF, FuG 125a radio-beacon, FuG radio-altimeter and Patin PKS auto-pilot.

Dear Justo, great thanks for sharing! Please more on the Lerche / Wespe.

On the bench

Structural question: how do you keep those two propellers in correct alignment with such long load-paths … going from engine mounts all the way out to wing-tips … er … ring-tips … and back inboard to the second propeller?
How close can you mount two propellers - rotating on separate shafts - before they clash?

It all depends on the structural rigidity of the engine mounts, but that information cannot be found in Heinkel's original drawings.

 

[Justo Miranda]

In December 1944, Dr.-Ing. Gerhard Schulze and Dipl.-Ing. Kurt Reiniger fron Heinkel-Wiener Neustädter Flugzeugwerke, designed two tilsitter fighters with annular wing called Heinkel He 355A Lerche and Heinkel He 355 B Wespe.

Justo, there were no "Heinkel-Wiener Neustädter Flugzeugwerke". A Heinkel facility was located at Schwechat, some 30 kilometers east of Vienna, and the Wiener Neustädter Flugzeugwerke were 40 km south of Vienna and part of the Messerschmitt AG.

OK

 

[Justo Miranda]

Lerche II

 

[Justo Miranda]

The Lerche II was a ground attack aircraft powered by two Daimler-Benz DB 605 DC piston engines, each rated at 2,000 hp. with MW 50 booster and 96-octane C3 fuel.

Both engines were mounted nose-to-nose so propellers would rotate in opposite directions without using heavy and complex reduction gears.

Heinkel He 355A (Entwurf C) Lerche II technical data

Ring wing diameter: 4.5 m, overall length: 10 m, rotor diameter: 4 m, wing area: 12 sq. m, surface area: 102.8 sq. m, wing chord: 4 m, estimated max weight: 5,600 kg, power plant: two DB 605 DC, twelve cylinder, inverted-Vee, liquid cooled engines, each rated at 2,000 hp, armament: two Mk 108/30 cannons mounted on each side of the fuselage with 3.5 degrees slope, electronics: EZ 42 gyroscopic gunsight, FuG 16 ZY R/T, FuG 25a IFF, FuG 125a radio-beacon, FuG radio-altimeter and Patin PKS auto-pilot.

 

[martinbayer]

Are there any actual mass, aerodynamics, and powerplant based performance and handling engineering based estimates available, or is this all just end of war desperate handwaving? A somewhat inquisitive German aerospace engineer would be interested in any fact based replies...

 

[Justo Miranda]

Lerche III

On October 25, 1944, the OKL ordered the conversion of the fastest available airplanes -Me 262, Ar 234 and Do 335 - into emergency night fighters, following the Sofortprogramm directive. The modification consisted of installing a Neptun radar and a second crew member to operate it. The Me 262 B-1a/U1 and the Ar 234 B-2N, that were thus transformed, could enter service with some success in 1945. However, the air drag generated by the big Hirschgeweih antennae, installed in the nose, and the removal of one of the fuel tanks, to make room for the radar operator, penalised the maximum speed and endurance and partially overrode the advantage of the initial design.

The Sofortprogramm did not solve the problem.

On January 27, 1945, the OKL published the Vorrückenprogramm for high performance night fighters, equipped with the new radar Telefunken FuG 222 Pauke S with parabolic antenna of 30 cm of diameter. It was installed INTERNALLY, within an aerodynamic container of di-electric material placed in the nose of the airplane. In this model, the scope was replaced by a Revi device equipped with a red filter that did not affect the night vision of the pilot.

By the end of 1944 the Heinkel engineers designed an advanced system of automatic triggering weapons combining the fire control radar FuG 222 Pauke S with the gyroscopic gunsight Askania EZ 42 Adler. The 1078 project was created to prove that the system could be integrated in day time fighters, providing them with additional capacity to act as night fighter or moskitojäger controlled by the ground command by means of the FuG 25a and FuG 125a devices installed onboard.

Heinkel proposed the Lerche III, a two seat bad-weather variant equipped with one FuG 222 radar that had a 30-cm diameter parabolic mirror and the radio altimeter Siemens FuG 101a, with two inverted ‘T’ antennae under the left wing . It also had one IFF discriminator GEMA FuG 25a Erstling with 300 mm rod antenna under the fuselage, shared with the command-relay FuG 139 Barbarossa, one radio goniometer Telefunken Peil G6 Ludwig and one R/T device Lorenz FuG 24 SE with whip antenna.

Lerche III was proposed in both heavy fighter and night fighter configurations, with pilot and radar operator, and two DB 603 N nose-to-nose engines.


Heinkel He 355A (Entwurf D) Lerche III technical data

Ring wing diameter: 4.7 m, overall length: 11.1 m, rotor diameter: 4.3 m, wing area: 24.7 sq. m, surface area: 126 sq. m, wing chord: 4.07 m, estimated max weight: 7,400 kg, power plant: two DB 603 N, twelve cylinder, inverted-Vee, liquid cooled engines, with two-stage TKL 15 turbo-supercharger, each rated at 1,810 hp in cruising flight and 2,250 hp at take-off with MW 50 booster, armament: two Mk 108/30 cannons mounted under the cockpit.

 

[Justo Miranda]

A demonstration of the first jet powered Heinkel He 178 before RLM officials on November 1, 1939 did not produce apparent enthusiasm but had an enormous impact on the aircraft industry. The Germans planned the development of the new technology in four phases, with increasing thrust, between 1,000 and 4,000 kp. The plan was to develop the first turboprops when reaching Phase II (1,300 to 1,700 kp) in 1941, but the Hungarian engineer György Jendrassik got ahead in 1939 patenting the first CS-1 turboprop.

In Germany, Heinrich Focke decided that the turboprop could be used to drive a helicopter rotor by means of an extension shaft. He was defining the working principle of what today we call a turboshaft, a form of gas turbine that is optimized to produce shaft power rather than jet thrust.

The intention of Focke was to build a fast helicopter Schnell-Flugzeug using a ducted fan rotor installed, within a circular wing ringflügel, thus removing most of the drag generated by the conventional rotors.

In the original design patented in 1939, Focke used two huge propellers, with 6 m of diameter, spinning in opposite directions to avoid the torque effect. For more speed, the bifurcated jet exhaust pipe ended in two afterburning combustion chambers. At the ground, the disc would be raised by about 18 degrees while the rotors would be level with the ground.

The VTOL design was named Rochen (Sea Ray) in 1944 but the enormous workload of building 13,300 Focke-Wulf Fw 190 fighters during the war prevented the development of the project. In 1955 a 1/10 scale wind tunnel model was built in Bremen and subjected to aerodynamic testing, but the project was cancelled in 1957.

In May 1944 Daimler Benz received an order from RLM to concentrate on the development of a turboprop version of the Heinkel 109-011 turbojet, dubbed He/DB 109-021, with a third turbine stage, 2,400 hp of shaft power, 585 kp of residual jet thrust and 1,266 kg overall weight. It was selected by Heinkel to power a tail sitter fighter project called Wespe, with Zborowski annular wing and estimated lift-off weight of 6,000 kg.

The turboprop operated one variable pitch, six-bladed propeller, with 1,800 rpm constant speed, through reduction gearing.

Torque could be offset by three deflector vanes mounted every 120 degrees of arc in the duct airstream.

The He/DB 109-021could not be throttled back, 10,500 rpm had to be kept high enough to prevent the compressor from stalling.

The engines of this type allowed to regulate the fuel flow with adjustments in the airscrew pitch, which, together with its low specific fuel consumption of 0.45 kg/eshp/hr made them very suitable to propel long-range airplanes. Turboprops were lighter and more powerful than the conventional piston engines and could work with heavy kerosene.

Compared with pure jet fighters, the PTL airplanes were superior in take-off, climb, acceleration and endurance, but the power of the turboprops rapidly declined with height and were not adequate to propel high-altitude interceptors.

In general, the jet versions were 107 per cent faster and 87 per cent lighter, with the service ceiling 130 per cent higher and a 34 per cent longer range compared with the turboprops versions.

Heinkel He 355B (Entwurf E) Wespe technical data

Wing span: 5 m, ring ext. diameter: 3.14 m, ring int. diameter: 3.00 m, overall length: 7.59 m, rotor diameter: 2.85 m, wing area: 11.3 sq. m, surface area: 54.5 sq. m, estimated max weight: 3,700 kg, power plant: one Heinkel/Daimler-Benz Sk.021.50-6008 turbo-prop developing 2,400 hp shaft power plus 585 kg jet thrust, armament: two Mk 108/30 cannons mounted on each side of the fuselage with 3.5 degrees slope, electronics: EZ 42 gyroscopic gunsight, FuG 16 ZY R/T, FuG 25a IFF, FuG 125a radio-beacon, FuG radio-altimeter and Patin PKS auto-pilot.