Are the "sweet spots" on the wing-guns fixed or adjustable?

[VBF-13]

Sorry but I cant find a source on that anywhere. I was told on the Hellcat it was fixed at 300 yards. I just always assumed that meant at the factory, but I never see it referenced in any of the factory specifications. Thanks.

 

[FLYBOYJ]

Old thread...

http://www.ww2aircraft.net/forum/weapons-systems-tech/bore-sighting-processes-13404.html

 

[VBF-13]

Thank you! No further questions.

 

[renrich]

The guns in the wings of Hellcats and Corsairs could be adjusted but the Navy found that whether adjusted for point convergence or for a pattern, the guns moved around so much in their mounts they were getting a pattern. They were adjusted often on the carrier and usually for a point convergence which produced a pattern.

 

[davebender]

Were the guns moving inside the wings or were the wings flexing? Or perhaps both?

 

[renrich]

I believe from what I have read, (two sources) they were moving inside the wings.

 

[tyrodtom]

Wings flex under flight manuvers, the guns would have to have some give in their mounts, both to isolate the aircraft structure from vibration when the gun fires, and to isolate the gun from structure flex.

 

[VBF-13]

Also I believe they didn't have to fire all six guns at once although each pair was synchronized to fire in tandem so as to distribute the stress equally between the wings. Any truth to that?

 

[drgondog]

I would imagine 5 and 6 G carrier landings would be a contiuous problem. As to not firing all six guns at once I have not seen any selector switch on the F6F that would permit 'choice'.

As to building in flex to absorb the recoil or reduce effects of aeroelasticity, that would be dubious design. In those days, as now, you bolt the suckers to the airframe and provide a stiff loadpath. If the airframe bends, the point of impact will change from boresighting but you don't want the point of impact to change for any other reason.

I also suspect Navall ops aboard a carrier did not provide for live firing to perform QA on the optical boresight process.

 

[Shortround6]

at some point some guns got spring or hydraulic buffers in the gun mounts. The guns could move fore and aft a bit as they fired and like any such system a bit of side play. The area of the wing where the mounts go should be a rigid as possible with any "flex" being in the mount or recoil buffer in the gun. A much easier design problem, a much easier quality control and build situation. Any variation in wing structure (rib thickness or even rivet location/tightness) will affect the "flex" of the wing and unless the "Flex" is the same from shot to shot the accuracy goes to pot. Much easier to change out a mount that isn't "flexing" right than a section of wing.

 

[renrich]

The F4U had gun switches for each gun which allowed the pilot to select how many guns would fire. I have read that some pilots turned off two guns so as to have more firing time when the four guns ran out of ammo. I believe that before Midway, the new F4F4s aboard the Carriers had their guns regulated aboard ship. I think there is a photo of that in "First Team."