I've always been interested in the gun system on the B-29. I understand that they were all remotely controlled from a central aiming station, or stations. Does anyone have any good sources of information on just how they worked, how the aiming systems were interfaced, and how effective they were, compared to say B-17 or B-24 manual systems. Or for that matter, how the remote turrets were controlled on those planes. I've done some searching, but what I've come across hasn't been very satisfactory.
Thanks.
The B-29 central station fire control system had five sighting stations: nose, upper, left blister, right blister, and tail. There were also five turrets: upper forward, lower forward, upper rear, lower rear, and tail. Each station could control one or more turrets in a priority system. A sighting station had primary control of a turret when the gunner at that station could obtain control of the turret at any time. A station had secondary control of a turret if the gunner could obtain control only if the primary control of the turret was released.
The nose station had primary control of both forward turrets. A control box had IN/OUT switches for these turrets to release control of one or both. This station had no secondary control of any turret.
The upper station had primary control of the upper rear turret, and secondary control of the upper forward turret. The blister stations shared primary control of the rear lower turret, depending on a LEFT / RIGHT switch in reach of both men. They had secondary control of the lower forward and tail turret. This could get complicated. One man could fire the lower forward turret in secondary control while his partner on the other side fired the lower rear and tail turret in mixed primary and secondary control. There were even switches for the blister gunners to select machine guns only, or guns and cannon when firing the tail turret.
The tail station had primary control of the tail turret and no secondary control of any turret.
Each sighting station had a reflector sight which displayed a reticle focused at apparent infinity. Before combat, the gunner would set the wingspan of the expected attacker on a dial. When the enemy appeared, the gunner put a central "pipper" (dot) on the center of the target and tracked it smoothly. At the same time he adjusted a range wheel to expand or contract a circle of dots around the pipper so they matched the wingspan. This was similar to the operation of a lead computing sight on a fighter, but the B-29 sights did no computing. They just transmitted sighting data to the computers, which were below the floor in the rear compartment (except the nose computer which was near the navigator).
Computer inputs and outputs were electrical, but internally the calculations were performed mechanically. The factors taken into account included lead due to target motion, drop due to gravity, and windage. That last correction depends on airspeed, altitude, and air temperature, so there was a panel for the navigator to set the values. And because the sights were remote from the turrets, a parallax correction was required. This is much like harmonizing a fighter's wing guns. They have to be angled in slightly to converge on the line of sight at the desired range. On the B-29 this correction had to be computed in real time due to the large distance from sight to turret and the different directions from which attackers could approach.
Amplidyne generators stepped up the computer outputs to power the two 0.5 hp drive motors in each turret. Each turret had provision for mounting a GSAP (gun sight aiming point) camera. An "overrun" control maintained camera operation up to 3 seconds after firing ceased in order to record the results of the burst.
Reference:
T.O. No. 11-70A-1, "The Central Station Fire Control System," 5 December 1944.