Lotfernrohr 7
Encyclopedia
The Carl Zeiss Lotfernrohr 7, or Lotfe 7, was the primary bombsight
used in most Luftwaffe
level bombers, similar to the United States' Norden bombsight
, but much simpler to operate and maintain. Several models were produced and eventually completely replaced the simpler Lotfernrohr 3 and BZG 2 bombsights. The Lotfe 7C, appearing in January 1941, was the first one to have gyroscopic stabilization.
, Herman W. Lang, who had been employed by the Carl L. Norden Corporation, (manufacturers of the Norden bombsight) was able to provide vital details of the new bombsight to the Germans. During a visit to Germany in 1938, Lang reconstructed plans from memory.
The Norden consisted of two primary parts, the optical system, and a large stabilization platform. Both were 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 (Rohr) 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 optics, moving the mirror to stabilize the image as well as tracking the target. The controls were likewise much simpler than the Nordens', consisting primarily of three large knurled knobs to adjust aim.
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 Lotfe 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 90°
to 40° in front of the aircraft, and up to 20° 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 the autopilot was engaged first, allowing the pilot to remove the control yoke 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.
Bombsight
A bombsight is a device used by bomber aircraft to accurately drop bombs. In order to do this, the bombsight has to estimate the path the bomb will take after release from the aircraft. The two primary forces during its fall are gravity and air drag, which makes the path of the bomb through the air...
used in most Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
level bombers, similar to the United States' Norden bombsight
Norden bombsight
The Norden bombsight was a tachometric bombsight used by the United States Army Air Forces and the United States Navy during World War II, and the United States Air Force in the Korean and the Vietnam Wars to aid the crew of bomber aircraft in dropping bombs accurately...
, but much simpler to operate and maintain. Several models were produced and eventually completely replaced the simpler Lotfernrohr 3 and BZG 2 bombsights. The Lotfe 7C, appearing in January 1941, was the first one to have gyroscopic stabilization.
Design
A member of the German Duquesne Spy RingDuquesne Spy Ring
The Duquesne Spy Ring is the largest espionage case in United States history that ended in convictions. A total of thirty-three members of a German espionage network headed by Frederick "Fritz" Joubert Duquesne were convicted after a lengthy espionage investigation by the Federal Bureau of...
, Herman W. Lang, who had been employed by the Carl L. Norden Corporation, (manufacturers of the Norden bombsight) was able to provide vital details of the new bombsight to the Germans. During a visit to Germany in 1938, Lang reconstructed plans from memory.
The Norden consisted of two primary parts, the optical system, and a large stabilization platform. Both were 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 (Rohr) 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 optics, moving the mirror to stabilize the image as well as tracking the target. The controls were likewise much simpler than the Nordens', consisting primarily of three large knurled knobs to adjust aim.
Operation
Operation was fairly similar to the Norden. The bombardierBombardier (air force)
A bombardier , in the United States Army Air Forces and United States Air Force, or a bomb aimer, in the Royal Air Force and other Commonwealth air forces, was the crewman of a bomber responsible for assisting the navigator in guiding the plane to a bombing target and releasing the aircraft's bomb...
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 Lotfe 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 90°
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
to 40° in front of the aircraft, and up to 20° on either side. On final approach, the autopilot
Autopilot
An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. An autopilot can refer specifically to aircraft, self-steering gear for boats, or auto guidance of space craft and missiles...
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
Junkers Ju 88
The Junkers Ju 88 was a World War II German Luftwaffe twin-engine, multi-role aircraft. Designed by Hugo Junkers' company through the services of two American aviation engineers in the mid-1930s, it suffered from a number of technical problems during the later stages of its development and early...
or Heinkel He 111
Heinkel He 111
The Heinkel He 111 was a German aircraft designed by Siegfried and Walter Günter in the early 1930s in violation of the Treaty of Versailles. Often described as a "Wolf in sheep's clothing", it masqueraded as a transport aircraft, but its purpose was to provide the Luftwaffe with a fast medium...
, the tube ended in a fairing under the fuselage with a flat window in front. In other cases, like the Arado Ar 234
Arado Ar 234
The Arado Ar 234 was the world's first operational jet-powered bomber, built by the German Arado company in the closing stages of World War II. Produced in very limited numbers, it was used almost entirely in the reconnaissance role, but in its few uses as a bomber it proved to be nearly impossible...
or the prototype bomber conversions of the Messerschmitt Me 262
Messerschmitt Me 262
The Messerschmitt Me 262 Schwalbe was the world's first operational jet-powered fighter aircraft. Design work started before World War II began, but engine problems prevented the aircraft from attaining operational status with the Luftwaffe until mid-1944...
, 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 the autopilot was engaged first, allowing the pilot to remove the control yoke 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
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
. There was an attempt to use them in the B-25 Mitchell
B-25 Mitchell
The North American B-25 Mitchell was an American twin-engined medium bomber manufactured by North American Aviation. It was used by many Allied air forces, in every theater of World War II, as well as many other air forces after the war ended, and saw service across four decades.The B-25 was named...
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 88Junkers Ju 88The Junkers Ju 88 was a World War II German Luftwaffe twin-engine, multi-role aircraft. Designed by Hugo Junkers' company through the services of two American aviation engineers in the mid-1930s, it suffered from a number of technical problems during the later stages of its development and early...
- Lotfe 7A- Heinkel He 111Heinkel He 111The Heinkel He 111 was a German aircraft designed by Siegfried and Walter Günter in the early 1930s in violation of the Treaty of Versailles. Often described as a "Wolf in sheep's clothing", it masqueraded as a transport aircraft, but its purpose was to provide the Luftwaffe with a fast medium...
H-5 - Lotfe 7B- unknown
- Lotfe 7C - Arado Ar 234Arado Ar 234The Arado Ar 234 was the world's first operational jet-powered bomber, built by the German Arado company in the closing stages of World War II. Produced in very limited numbers, it was used almost entirely in the reconnaissance role, but in its few uses as a bomber it proved to be nearly impossible...
, Ju 88 - Lotfe 7D - Ju 88 Ar 234, Focke-Wulf Fw 200Focke-Wulf Fw 200The Focke-Wulf Fw 200 Condor, also known as Kurier to the Allies was a German all-metal four-engine monoplane originally developed by Focke-Wulf as a long-range airliner...
- Lotfe 7H - Ju 88, Fw 200 Messerschmitt Me 262Messerschmitt Me 262The Messerschmitt Me 262 Schwalbe was the world's first operational jet-powered fighter aircraft. Design work started before World War II began, but engine problems prevented the aircraft from attaining operational status with the Luftwaffe until mid-1944...
A-2a/U2 - Lotfe 7K - Ar 234, Me 262A-2a/U2
- Lotfe 7K-2 - Me 262A-2a/U2
Specifications for Lotfernrohr 7C
- Height: 662 mm (26.1 in)
- Width: 350 mm (13.8 in)
- Depth of Lotfernrohr: 390 mm (15.4 in)
- Weight, complete: 28 kg (61.7 lb)
- Power requirement: 90 W without heating, 190 W with heating (under +5° Celsius)
- Magnification: 1.4x
- Field of View: 35°, equivalent to 630 m (2,066.9 ft) at a range of 1000 m (3,280.8 ft)
- Range of movement for the sight tube: +80° to -20°
Limits of operation
- Altitude above target: 100–850 m (328.1–2,788.7 ft) altitude non-synchronized; 850–10000 m (2,788.7–32,808.4 ft) altitude synchronized
- True Air Speed: 150–600 km/h (93.2–372.8 mph)