B-17 FLYING FORTRESS PILOT DIRECTOR INDICATOR (PDI)

One of the most hazardous and nerve-wracking times for all bomber crews was the bomb run up to the target.

Until then, the pilot may well have been throwing the aircraft around the sky, dodging anti aircraft fire and enemy fighters, as he desperately tried to fly the bomber along a series of waypoints.

The last of these waypoints was called the IP, which was usually located near the target with a highly visible landmark so that the B-17’s navigator could get a good fix on their position.

Once they reached the IP however, the aircraft had to be flown straight and level whilst maintaining a set speed and altitude - all preset by the bombardier in the nose of the aircraft. 

At this point, the pilot engaged the B-17’s C1 autopilot and told the bombardier he was now controlling the aircraft.

Having dialled in the plane’s altitude and speed into the bombsight before placing the Norden's cross hairs on the target, the bombardier would then get the direction and wind strength over the target and program that into the bombsight along with bomb type they were carrying.

The bombsight would calculate the path that the bombs would fall to the target based on all this information; correct the plane’s speed, altitude, and heading through the autopilot to keep these factors properly set, and when the proper release point was reached, would automatically drop the bombs on the target.

The course changes inputted to the aircraft’s C-1 autopilot from the Norden bombsight, were then relayed to the Pilot Director Indicator (PDI) mounted on the pilot's main flying panel.

Manufactured by the Roller Smith Company, the PDI had four graduation marks to the right and the left of a centre zero.

The pointer would fluctuate left or right in response to the signals received from the automatic pilot’s directional stabiliser. Movement of the aircraft in the desired direction would return the pointer to the zero position.

In the early days of bombing, the pilot would manually correct the bomb run course by manoeuvring the aircraft to bring the PDI's pointer back to zero as directed by the bombardier but with the later refinement of the Norden bombsight's computer and its integration with the aircraft's autopilot, course changes were done without any pilot involvement.

It's not difficult to imagine the pilot's growing anxiety as he sat, totally powerless with flack and enemy fighters screaming across the sky around him, waiting for the bombardier to announce 'bombs gone' and give him back control of the aircraft.

Most bomber formations had a designated lead bombardier and a couple deputy leads. The deputy leads would take over if for some reason the lead bomber or bombardier incapacitated over the target. 

During the early part of the air war, every bomber had a fully trained and qualified bombardier on board so any plane could take over lead if required. This was essential as the USAAF were suffering massive bomber losses in the early air battles of the war.

Toward the end of the war however, when the German Luftwaffe’s fighters had been all but destroyed, the bombardier was often replaced with a 'toggler'. 

Where the bombardier was a commissioned officer, the togglers were enlisted men. When a toggler was on the aircraft, it did not carry a Norden Bombsight and he would simply toggle the bomb load when he saw the lead plane drop theirs.  

When not on the bomb run, the bombardier or toggler, would man the nose guns, which usually comprised a handheld .30 caliber or .50 calibre machine gun on a fixed mount through the plexiglas nose cone. 

The Pilot Director Indicator (PDI) was installed in most USAAF heavy bombers such as the B-24 Liberator, B-29 Super-fortress and medium bombers like the B-25 Mitchell and B-26 Marauder, as well as the USN’s PBY Catalina and PB4Y Privateer.  

This model PDI is in excellent condition for a B-17 flight instrument over 75 years old. The face dial glass is unmarked as too the PDI’s rear casing and would make a fantastic pilot gift or a one-of-a-kind gift for that special aviation enthusiast in your life. 

This B-17 Flying Fortress Instrument comes complete with detailed Scale Model, Mango Wood Stand & Plaque plus Printed Fact Sheet featuring photo of instrument in aircraft cockpit.

***PLEASE NOTE - ONLY 1 AVAILABLE***

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