Author Topic: Hispano MkI and MkII (Read 821 times)

zorstorer · « **on:** November 11, 2005, 09:14:48 PM »

Maybe Tony can help out with this. Is there any real difference between the hispano Mk I and the Mk II? Other than moving to being belt fed rather than a drum.

Pongo · « **Reply #1 on:** November 11, 2005, 10:03:58 PM »

In his book Tony says that a Mk 2 is a Mk one done to british standards with minor improvements.

zorstorer · « **Reply #2 on:** November 12, 2005, 03:01:27 AM »

Ahhh so the Mk I was still built to the french engine mounted standard? And the Mk II was the first hispano built to english specs?

Angus · « **Reply #3 on:** November 12, 2005, 08:38:11 AM »

Wasn't there some improvement like reliability, velocity and ROF?
Or maybe I am mixing it up with later models?

zorstorer · « **Reply #4 on:** November 12, 2005, 11:50:31 AM »

I have no idea Angus

I looked through Tony's site but only saw info about the round and not the gun. Just wondering because the scenario is today and they changed our Spitfire in mid stream

Tony Williams · « **Reply #5 on:** November 12, 2005, 02:31:35 PM »

The Hisso Mk 1 was indeed built to French standards (all that metric stuff - we need Imperial!). There were also a number of detailed improvements made, but some of these were also applied retrospectively to the Mk 1 guns so it's difficult to draw a clear distinction; the ultimate production Mk 11 ended up as a sort of hybrid between the two. The Mk II was made in far greater numbers, and was the standard RAF 20mm cannon throughout the war, the lighter, shorter and faster-firing Mk V only making an appearance late in the war, primarily in the Hawker Tempest.

Tony Williams: Military gun and ammunition website and discussion forum

zorstorer · « **Reply #6 on:** November 12, 2005, 04:29:20 PM »

Thanks much Tony

So the ROF and that stayed the same for the MkI and MkII and only changed for the MkV?

Tony Williams · « **Reply #7 on:** November 13, 2005, 12:16:33 AM »

Yes - the French Hispanos fired at 700 rpm but this was found to cause case 'crush-up' problems so the British slowed it down to 600 rpm. The Mk V was boosted to 750 rpm.

Molins built a version capable of 1,000 rpm but it required various new parts, non-interchangeable with existing guns, which would have disrupted production, so it was not accepted.

As a matter of interest I heard recently from someone whose father was responsible for maintenance of Hispanos in a unit during WW2. They had a competition to see who could get the RoF as high as possible by careful work including polishing various parts etc, and he won - with his gun clocked at 1,000 rpm. But not very practical for mass production.

The 'hottest Hispano' award goes to the USN, with the Mk 12 of the 1950s (as used in the F8U Crusader). This was not only chambered for a new and more powerful cartridge but cranked up to around 1,000 rpm. It was rather inaccurate and unreliable, though.

Tony Williams: Military gun and ammunition website and discussion forum

Debonair · « **Reply #8 on:** November 13, 2005, 01:09:59 AM »

I'm sure I am not the only one wondering what happened between Mk.II & Mk.V.
I assume Hizooka Mk.III & Mk.IV werent very good

Tony Williams · « **Reply #9 on:** November 13, 2005, 10:06:16 AM »

The Hispano Mk III was a proposal from the Army Design Department (who had just produced the Sten SMG) to produce a sort of 'big Sten' - a cheap and nasty version of the Hisso. The Air Staff were not impressed and the proposal died.

The Hisso Mk IV was a short-barrelled version of the Mk II intended for use in bomber turrets. A few were made and worked fine but it didn't go into production, due to the lack of a decision to produce 20mm turrets in time.

TW

Pongo · « **Reply #10 on:** November 13, 2005, 10:33:32 AM »

Dont you say in one of your books that the Hispano was over engineered though Tony? Like made to last way longer then the predictable service life of any plane made in the war? I thought you theorized somewhere that a lighter built faster firing Hispano would have been a good idea. Is that what the army was proposing?

Debonair · « **Reply #11 on:** November 13, 2005, 01:47:46 PM »

Thanks TW, you always come through with the goods

Tony Williams · « **Reply #12 on:** November 15, 2005, 02:57:28 AM »

Quote

Originally posted by Pongo
Dont you say in one of your books that the Hispano was over engineered though Tony? Like made to last way longer then the predictable service life of any plane made in the war? I thought you theorized somewhere that a lighter built faster firing Hispano would have been a good idea. Is that what the army was proposing?

I don't have any details on the Mk III (AFAIK it was a paper proposal only). I don't know that it would have been any lighter or faster-firing - just cheaper!

Tony Williams: Military gun and ammunition website and discussion forum

Kurfürst · « **Reply #13 on:** November 15, 2005, 08:13:53 AM »

Tony, do you have any figures when and how the Hispano's orginal reliability problems were fixed? I am seeing some problems with all aircraft that mounted it, though this may have to do with incorrectly designed aircraft mounts. Spitfire, Typhoon, Tempest, Meteor all reported some jamming problem with the Hisso, the Meteor being the worst case.

I also wonder about the lifespan of the barrel, firing so powerful rounds, it must have been shorter than other 20mm cannon, unless something cool was used, chromium barrels liners etc.

Tony Williams · « **Reply #14 on:** November 15, 2005, 02:24:03 PM »

The original reliability problems for the Hispano came from several sources, and concerned both the gun and (more crucially) the mounting.

The gun initially suffered from misfires due to the firing pin hitting the primer with insufficient force. This was partly because the case tended to 'crush up' a bit from the force of the blow from the breechblock. This was solved by shortening the firing chamber by 2mm (the US was advised to do this but instead only shortened theirs by 1mm, which may help to account for the continual reliability problems of the US-built Hispano).

When the belt feed was fitted, it was driven by the recoil of the gun (which moved back about an inch at each shot). It was important that the recoil length was sufficient to operate the action, but that the blow wasn't too hard when it hit the buffer. This proved difficult to achieve with the original recoil springs so a new arrangement was made whereby a two-stage spring was fitted, giving small initial resistance then firming up at the end. That solved that problem.

One good thing did come from the US work - the Edgewater front mounting without which the Mk V had problems working at all.

The mounting really was crucial for the Hispano, because it wasn't really a 'complete gun'. As the whole gun recoiled, it had to be firmly braced against something rigid. In its original application for engine mounting this wasn't a problem - the engine was plenty rigid enough. Fuselage mounting was generally OK as well (and in the case of the P-38, an external cradle to hold the gun was used). But fitting into flexible wings was a different matter altogether and remained a source of considerable development problems, with the installation having to be 'fine tuned' for each aircraft. In the first application in the Spitfire, the situation was made even worse by turning the gun on its side in order to bury the magazine within the wing. The Hisso really didn't like that!

I wasn't aware of any specific problems with the Meteor installation.

Longevity of the Hisso parts was more than enough. It was originally designed for a 10,000 round life, but it was discovered that very few lasted longer than 1,000 rounds before being lost in accidents or combat. So some parts were cheapened, but the barrel remained one of the longest-lived items.

With all the improvements made the reliability of the Hisso was acceptable at one jam every 1,500 rounds. This was still about three times worse than the .50 M2.

Tony Williams: Military gun and ammunition website and discussion forum