Bachem Ba 349B-1 Natter
Dr. Erich Bachem's Ba 349 Natter (Viper) was the world's first, manned, vertical-take-off interceptor. The aircraft was an imaginative solution to a desperate problem but World War II ended before the weapon saw combat. Werner von Braun first proposed the concept in 1939 but the Reichluftfahrtministerium (German Air Ministry or RLM) rejected it as "unnecessary and unworkable." Bachem, an engineer with the Fieseler works, thought the idea had merit. He tried but failed to generate interest in several different proposals for a rocket interceptor.
During spring 1944, the Allied bombing offensive began taking a serious toll on the German war machine. None of the conventional methods employed by the Luftwaffe to intercept the bombers seemed to work so the service began to explore unconventional means. The RLM Technical Office issued requirements for an inexpensive fighter made of non-essential materials that could defend important targets. Messerschmitt, Junkers, Heinkel, and Erich Bachem submitted proposals but RLM officials remained unenthusiastic about Bachem's design. They chose a more conventional offering from Heinkel but Bachem refused to give up. He sought the support of Reichsführer Heinrich Himmler, head of the SS (Nazi Party security forces). Himmler liked Bachem's proposal and signed an order to build 150 Natters using SS funds. It was now possible that the SS might develop an aircraft beyond the RLM's control so they placed their own order for 50 Natters and announced the official designation, Bachem Ba 349.
Bachem's design was simple and easy to build. Semi-skilled labour could construct one in about 1000 man-hours. The wings were plain rectangular wooden slabs without ailerons, flaps, or other control devices. The cruciform tail consisted of four fins and control surfaces. Deflecting these surfaces in various combinations controlled pitch, yaw, and roll, once the Ba 349 had reached sufficient speed to generate adequate airflow. Guide vanes connected to the four control surfaces augmented aerodynamic control. Bachem positioned each vane within the exhaust plume of the main engine, a Walter 109-509A rocket motor. This is the same basic engine used in the Messerschmitt Me 163 Komet. Two liquid fuels combined inside the motor to generate thrust. When T-Stoff (a highly caustic solution of hydrogen peroxide and a stabilizing chemical) mixed with C-Stoff (a hydrazine hydrate/methanol/water mixture), combustion was spontaneous so extreme care was required to handle both chemicals. The Walter motor generated about 1,700 kg (3,740 lb) of thrust but a loaded Ba 349A weighed more than 1,818 kg (4,000 lb) so lift-off required more power.
Bachem got the extra thrust from four Schmidding 109-533 solid-fuel rocket motors that he bolted to the aft fuselage, two per side. Each motor produced 500 kg (1,100 lb) of thrust. At lift-off, all five motors ignited, generating about 3,700 kg (8,140 lb) of thrust. The resulting 1.6 to 1 thrust-to-weight ratio produced acceptable climb performance.
Natter operations were relatively simple and the following account describes a hypothetical mission. A 24 m (79 ft) tower guided the rocket plane during lift-off. The wingtips and lower fin fit inside guide rails to stabilize the aircraft until it cleared the tower. The flight controls remained locked in neutral position until the solid boosters burned out about 10 seconds into the flight. At burnout, explosive bolts blasted away the solids, the flight controls unlocked, and the Natter's 3-axis Patin autopilot began receiving steering commands from the ground via radio. The aeroplane continued climbing but the pilot could intercede at any time and take full control. Bachem calculated maximum climb rate at 11,563 m (37,400 ft) meters per minute but flight tests did not confirm this figure.
American daylight bomber formations often approached a target at an altitude
of 6,250 m (20,000 ft) to 9,375 m (30,000 ft). After the Natter had climbed
even with the formation, the pilot took control, steering his Natter in
close. At a range of about 1.6-3.2 kilometers (1-2 miles) from the formation,
the Natter pilot jettisoned the nose cone and shotgun style, salvoed all
24 Henschel Hs 217 Föhn unguided rockets.