# Gyro Gunsights



## Zipper730 (Dec 31, 2019)

I remember for the YFM-1, there was a type of thermionic fire control system that (if I recall correctly) was gyroscopically controlled. I'm curious if anybody has even a basic idea how the system worked and if the configuration necessarily required two members to operate it?

I'm also curious how quickly it could have been modified or replaced with a gyro-sight that was effectively suitable for one-man use?



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## 2banaviator (Jan 2, 2020)

Zipper730 said:


> I remember for the YFM-1, there was a type of thermionic fire control system that (if I recall correctly) was gyroscopically controlled. I'm curious if anybody has even a basic idea how the system worked and if the configuration necessarily required two members to operate it?
> 
> I'm also curious how quickly it could have been modified or replaced with a gyro-sight that was effectively suitable for one-man use?
> 
> ...



I'm assuming that you picked some of this up from the YFM1 Wikipedia entry, herewith: 
_"The crew of five included the pilot and gunners; a copilot/navigator who doubled as a fire-control officer, using a Sperry Instruments "Thermionic" fire control system (originally developed for anti-aircraft cannon) combined with a gyro-stabilised and an optical sight to aim the weapons;[2] and a radio operator/gunner armed with a pair of machine guns stationed at mid-fuselage waist blisters for defense against attack from the rear". _ 
As with other Sperry gyroscopic gunsights, the gyro likely stabilized an illuminated reticle projected on an angled glass lens in the aimer's line of sight to the target. I doubt that more than one person was required to operate it.

I checked my original YFM1-A Flight Handbook dated Dec 1940, and the only references to the guns are on this page. It make a brief remark regarding the location of the fire control 'box' in paragraph J, below, and that it seems only to have controlled the forward-facing cannons. Note that a primary function of the gunners (one seated on each wing in front of each rear-facing engine) was to load the cannons. As an interceptor with forward-firing cannons of limited traverse, it seems odd not to simply give full control to the fuselage-seated gun director. Not an efficient use of personnel IMO. 

The YFM1 had so many other problems in trying to meet its original design objectives that aiming the guns were probably the least of its issues. Which is why they only ever made 13 of them.

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## Zipper730 (Jan 2, 2020)

2banaviator said:


> I'm assuming that you picked some of this up from the YFM1 Wikipedia entry, herewith:
> _"The crew of five included the pilot and gunners; a copilot/navigator who doubled as a fire-control officer, using a Sperry Instruments "Thermionic" fire control system (originally developed for anti-aircraft cannon) combined with a gyro-stabilised and an optical sight to aim the weapons;[2] and a radio operator/gunner armed with a pair of machine guns stationed at mid-fuselage waist blisters for defense against attack from the rear". _
> As with other Sperry gyroscopic gunsights, the gyro likely stabilized an illuminated reticle projected on an angled glass lens in the aimer's line of sight to the target. I doubt that more than one person was required to operate it.
> 
> I checked my original YFM1-A Flight Handbook dated Dec 1940, and the only references to the guns are on this page. It make a brief remark regarding the location of the fire control 'box' in paragraph J, below, and that it seems only to have controlled the forward-facing cannons. Note that a primary function of the gunners (one seated on each wing in front of each rear-facing engine) was to load the cannons. As an interceptor with forward-firing cannons of limited traverse, it seems odd not to simply give full control to the fuselage-seated gun director.


I'm curious why they had two guys operating a system that needed only one. That said, I'm not sure if the gyro system was a 3-axis gimbal or something more primitive. A three-axis gimbal will work fine for this purpose, but if it's an erected gyro, you could tumble the system during aggressive maneuvers.

The YFM-1 wasn't designed to do them, but a properly designed fighter should be able to do this -- frankly, the YFM-1's biggest problems

Single point of failure: The auxiliary power unit
Lack of speed
Lack of agility


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