LW defensive armament, MG 15... why?

[JAG88]

The MG 17 appeared shortly after the MG 15 and, unless something escapes me, being belt fed it would have been a much better proposition for a defensive gun on a flexible mount, and without too much work it could have been twined as the MG 81 eventually was so... why didnt they do it?

What am I missing?

 

[The Basket]

Hindsight.
The standard rifle of the German army was still a bolt action rifle in 1939 so a MG 15 would have been a phased plasma rifle by comparison.
The He 51 only had 2 machine guns and the early 109s were not much better so a single MG 15 would have been spot on by 1930s standard.

 

[Shortround6]

The MG 17 appeared shortly after the MG 15 and, unless something escapes me, being belt fed it would have been a much better proposition for a defensive gun on a flexible mount, and without too much work it could have been twined as the MG 81 eventually was so... why didnt they do it?

What am I missing?

you are missing mechanics.

It was a lot easier to make a flexible machine gun using some sort of magazine than using a belt unless it was a short belt in a box attached to the gun and moving with it, and then what is the point?

Getting belts to curve and bend without jamming as the gun was pointed left and right and up and down took a lot more doing and getting the guns to pull the weight of the belt from some locations (height or distance) without slowing the gun (or stopping it) took a bit more work.
It was done, eventually, by just about everybody but it took a few years.

for instance

This early installation had brackets/trays for a box of belted ammo for each gun. Once the ammo in the box was gone the gunner had to remove the ammo box from the bracket/tray, put a new one in, open the top cover of the gun, insert beginning of belt and close top cover and pull charging handle.
Later versions or versions on other aircraft had belts fed from below the mount and the gunner had much less fiddling to do.

edit,
I would also note that belt fed machine guns had been used in WW I in flexible mounts and had been found wanting.

Of course the flapping canvas belts had something to do with it, not to mention wet canvas froze and stopped the gun.

 

[The Basket]

The Me 110 and Ju 87 rear gunner space was limited so a compact gun is the ticket. In my view a rear gunner is mainly there to act as a deterrent to stop a fighter climbing up the exhaust ports so against a determined fighter with 20mm cannon then a belt fed or box fed 7.92mm machine gunnner in a Ju 87 is seriously wishing they joined the Navy.

 

[JAG88]

Thx to all, sounds reasonable.