Lotfernrohr 7

The Carl Zeiss Lotfernrohr 7, or Lotfe 7, was the primary late-war bombsight used in most Luftwaffe level bombers. It started replacing the simpler Lotfernrohr 3 and BZG 2 in 1942, eventually replacing them completely. It was an advanced mechanical system similar to the US's Norden bombsight, but much simpler to operate and maintain. There is historical evidence that suggests the basic concept was based on materials provided to the Luftwaffe by Herman W. Lang, a member of the Duquesne Spy Ring who worked in the Norden factory.

The Norden consisted of two primary parts, the bombsight itself and a large stabilization platform that it was attached to. Both were quite complex and had to be separately maintained to keep them operational. In comparison the Lotfe 7 was dramatically simpler, consisting of a single metal box containing the vast majority of the mechanism, with a tube extending out the bottom with a mirror that reflected the image of the target into a small telescope in the box. The mechanisms within combined the functions of the Norden's stabilizer and the bombsight, moving the mirror to stabilize the image as well as track the target as the aircraft moved. The controls were likewise much simpler than the Norden, consisting primarily of three large knurled knobs to adjust aim, which could be differentiated by feel due to the differences in their mounting to the box.

Operation was fairly similar to the Norden. The bombardier would first locate the target in the bombsight and continue to adjust the dials until it remained motionless in the eyepiece. This allowed the bombsight to calculate the wind speed from the cancelled out drift rate, which in turn allowed to make an accurate calculation of groundspeed. Unlike the Norden, the Lofte 7 could view targets directly in front of the aircraft, so the bombardier could use the real target for adjustments, rather than having to "tune" the instruments on a test target located closer to the aircraft. The bombsight could be used against targets between 90 degrees to 40 degrees in front of the aircraft, and up to 20 degrees on either side. On final approach the autopilot was engaged, while the bombsight adjusted the flight path in response to last-minute changes by the bombardier. Bomb release was normally automatic in order to reduce timing errors.

The Lotfe 7 was normally installed near the nose of the aircraft with the mirror tube projecting through the fuselage to the outside of the aircraft. In most installations, like those in the Junkers Ju 88 or Heinkel He 111, the tube ended in a fairing under the fuselage with a flat window in front. In other cases, like the Arado Ar 234 or the prototype bomber conversions of the Messerschmitt Me 262, the tube was open to the air, mounted so the mirror window was almost flush with the fuselage line. In the case of the single-seat Ar 234 the bombsight was difficult to access, so for operation the autopilot was engaged first, allowing the pilot to remove the control yolk and access the bombsight.

After the war about a thousand unused Lotfe 7's were found in the Zeiss factories and shipped to the USSR. There was an attempt to use them in the B-25 Mitchell to replace the much more complex Norden, but the Lotfe 7 interacted badly with the Si-1 autopilot and the problems were never fixed.

Versions

:Lotfe 7 - Junkers Ju 88:Lotfe 7A- Heinkel He 111H-5:Lotfe 7B- unknown:Lotfe 7C - Arado Ar 234, Ju 88:Lotfe 7D - Ju 88 Ar2 34, Focke-Wulf Fw 200:Lotfe 7H - Ju 88, Fw 200 Messerschmitt Me 262A-2a/U2:Lotfe 7K - Ar 234, Me 262A-2a/U2:Lotfe 7K-2 - Me 262A-2a/U2

References

* [http://www.cockpitinstrumente.de/instrumente/katalog/revi/Lotfernrohr%207C.htm Lotfernrohr Lotfe 7D Bombenvisier] (in German)
* [http://www.luftarchiv.de/bordgerate/optisch.htm Optical targeting devices] (in German)
* [http://lend-lease.airforce.ru/english/articles/ratkin/index.htm B-25]