On Topic. I thought the mounted gun was for a local defence for the gun ie ground attack to your potition and very low flying AC where the Bofors would be completley useless.

I doubt that very much. The Bofors was actually pretty good at short range, and in any case it would have been far better to put the MG on a separate mounting so it could be rapidly swung around by hand rather than cranking away at the handles on the Bofors mounting.

Tony Williams: Military gun and ammunition website and discussion forum

Large slow speed marine engines used cross and loop scavenging with only liner ports and no valves for decades despite being super charged.

The two go together – if you have supercharging plus direct injection with a two-stroke (petrol or diesel) then you don’t need valves. The supercharger blasts fresh air through the cylinder the moment the piston drops low enough to expose the inlet and exhaust ports, then fuel is injected into the pressurised air as soon as the ports have closed.

Until recently, this only worked with very low-speed diesels (like marine engines) because of the technology required to time and deliver the fuel. This has now been cracked at car-engine speeds so it will be interesting to see if anyone takes it up.

Tony Williams: Military gun and ammunition website and discussion forum

Not really relevant but it’s quite possible to make a two stroke with no valves as such. Many British motorcycles (and the majority of modern 2-stroke model aircraft engines) had engines where the induction and exhaust were controlled simply by the piston uncovering holes in the cylinder wall.

The BSA Bantam springs to mind, a single cylinder engine with 3 moving parts.

Correct, but that’s only suitable for low-performance engines. 2-stroke racing engines have valves.

Tony Williams: Military gun and ammunition website and discussion forum

…as for sleeve valves, typical british over engineering, just cos it can be done doesn’t mean it should be!!!

When you consider that sleeve valves were competitive with poppet valves, despite having enjoyed only a tiny fraction of the development time, and that many of the late-war big engine projects would have used them, it is clear that they had more potential.

If it hadn’t been for the invention of the jet engine, sleeve valves would probably have become standard for aircraft engines in the postwar era.

Tony Williams: Military gun and ammunition website and discussion forum

What type of ammunition will it get? The fancy Rheinmetall fragmenting sabot rounds (which seem to me great for A2A but not so good for strafing)?

Not sabot rounds, no – they are not compatible with use in a fighter plane, because the plastic sabots tended to get sucked into the engine where they melt and coat the turbine blades and are the very devil to clean off…

There are three types of HE round (with electronic delayed-action nose fuzes), five types of AP and SAP, and a Raufoss Multipurpose. I’m not sure if a FAP is available yet, but Diehl has already qualified the similar PELE type – both have no chemical content but fragment after penetration, sending a shower of high-velocity fragments through the target.

Tony Williams: Military gun and ammunition website and discussion forum

The difference is about 22 kg with or without munition. Not that much at all.

One round of the 27x145B Mauser ammo weighs 516g. So 22kg would only get you 43 rounds of ammo. Since the magazine capacity is for 150 rounds, that will weigh 77 kg. The gun only weighs 100 kg.

None of which explains why a 100 kg lead weight (or 177 kg) would not have done the ballasting job.

Tony Williams: Military gun and ammunition website and discussion forum

That is good news!

But I’ve always been dubious about the “weight is so critical that you have to use a real gun” argument. After all, the gun comes with ammo, and there’s one heck of a weight difference between a full magazine and an empty one. If all they wanted was ballast, a simple lead weight in the gun bay would have done the job.

I think that the main reason was that the RAF was contractually committed to buying the first 55 guns anyway, and some far-sighted chap thought of a good excuse to fit them to the plane, just in case they might come in useful later – in which case, he deserves a medal.

Tony Williams: Military gun and ammunition website and discussion forum

They don’t carry guns though, which IMO is still a disadvantage in a close-support plane when you might need to engage an enemy too close to your own side to use bombs or unguided rockets. The laser-guided 2.75″ rockets might compensate for that to some extent – if the Harriers get them.

The AV-8B has the 25mm GAU-12/U, the Su-25 the 30mm GSh-30, and of course there’s the A-10…

The F-35 will come with a gun either installed or in a conformal pod according to model – the 25mm GAU-22/A

Tony Williams: Military gun and ammunition website and discussion forum