Spitfire Mk.IB

[Pips]

The first attempt to fit cannon's into the Spitfire in June 1940 (19 Squadron) ended in failure, due to the constant jamming. The problem was due to the Hispano 20mm having to lie on their side to fit into the thin wings of the Spitfire.

Anyone know why a trial wasn't conducted with Hurricane's concurrently? The thick wings of the Hurricane were perfectly suited.

[phylo_roadking]

Pips - it was! There were IIRC two built, and one flew operationally during the BoB. Compared to the Spifire it was rated a success.

[Pips]

Any further details phylo? eg plane codes. squadron etc.

[phylo_roadking]

I'll have a look back through Bishop's BoB:Day By Day, that's where I most recently saw it.

EDIT: having to go through it page by page, Bishop's indexing isn't great But in the meantime...

Heavy cannon had been originally been evaluated beginning in 1939 on a Mark I that had been modified to carry twin Oerlikon 20 millimeter cannon, one under each wing. The aircraft had metal wings, as wooden wings had been judged unable to stand the recoil of large cannon. Apparently this aircraft did some fighting in the Battle of Britain and scored a kill on a Do-17.
However, the Oerlikon cannon was too heavy, required greased cartridges, and wasn't designed for carriage by a fighter anyway, and the Hispano cannon was a better solution. The four-cannon fit was evaluated on a Hurricane Mark I in 1940, but the machine was regarded as underpowered, and the four-cannon configuration had to wait for the Mark II with its Merlin XX engine

http://www.faqs.org/docs/air/avhurr.html

From Wiki

In addition, early trial installations in the Hawker Hurricane and Supermarine Spitfire had shown a tendency for the gun to jam during combat maneuvers, leading to some official doubt as to the suitability of cannons as the sole main armament. This led, briefly, to the Air Ministry specifying 12-gun machine gun armament for its future fighters

[phylo_roadking]

Here we are...

http://www.k5083.mistral.co.uk/PROJECTS.HTM

Two Cannon Hurricane
Originated as trial installation of two Oerlikon 20mm guns under the wings for Service trials in 1939. Fought in the Battle Of Britain with 151 Sq., 1940.

L1750 trials aircraft during 1940.

And here's the Bishop reference...

Page 174...

As Fink's bombers wheled away from ther target to racr for the protection of the clouds, they were set upon by fighters from 111 and 151 squadrons. Flight Lieutenant Roddick Smith of No. 151 Squadron was flying the only Hurricane in the RAF that currently had cannon: "I ordered the attack, telling my pilots to dive through the enemy formation and on into the clouds, as I assumed the rear formation were Messerschmitt 110s and three quarters of my pilots were new. I opened
fire at about 300 yards with my cannon, firing into the general mass as the enemy were in exceptionally close formation. One immediately burst into flames and another started smoking when my windscreen front panel was completely shattered by enemy fire, and I broke away downwards and returned to North Weald."

Bishop references the quote to a footnote on page 189 of Francis Mason's Battle Over Britain, 1990.

[Pips]

Thanks for that info phylo, just what I was after.

So it would appear that the Hurricane was fitted with the oversized, overweight Oerlikon instead of the slimmer and lighter Hispano. Ok, as a trial it had to be done, and the results were found to be unsatisfactory (given the engine performance of the time). However, why wasn't a Hurricane also trialled with the Hispano?

Weight wouldn't have been the issue, as two Hispano and associated ammo was lighter than eight Brownings and ammo. Also the wing of the Hurricane was stronger than that of the tested Spitfire - where flex had been highlighted as an issue.
From: http://www.the-battle-of-britain.co.uk/ ... ricane.htm

The wings were fabric covered over a framework of light metal ribs. . In 1938 a completely new stressed-skin outer wing was designed. It was introduced on the production Hurricanes in 1939. The new outer wings are built up on two main spars of extruded s-section booms with double webs at the inboard end which are reduced to T-sections with single webs towards the tip. A diagonal bracing system in the gun bay was found to be convenient. The diagonals are now made of T-section extrusions with plate webs. Immediately outboard of the gun bay the wing is of the fully-stressed-skin type and has two light auxiliary spars as well as the two main spars. The whole wing is covered with a stressed skin of light alloy, 20gauge thick on the top surface and 22 gauge on the bottom.
The new pair of wings is about 70 lb. lighter than the fabric-covered wings and has much greater stiffness although the section and plan forms remain unchanged. In this latest form, with metal wing, ejector exhausts and Rotol constant-speed airscrew the Hurricane I has a top speed of 335 m.p.h. at 17,500 ft.

Another point on the Hurricane's wing structure was that it was thick enough to allow the Hispano to be fitted upright as it was designed, as opposed to the Spitfire's thin wing which required the cannon to be layed on the side - and contributed to the jamming.

Perhaps some perservence with the Hurricane might have resulted in the RAF having a cannon armed fighter available in (albeit) small numbers during the BoB.

[phylo_roadking]

So it would appear that the Hurricane was fitted with the oversized, overweight Oerlikon instead of the slimmer and lighter Hispano. Ok, as a trial it had to be done, and the results were found to be unsatisfactory (given the engine performance of the time). However, why wasn't a Hurricane also trialled with the Hispano?

Pips, look back at some of the other stuff I posted up -

Heavy cannon had been originally been evaluated beginning in 1939 on a Mark I that had been modified to carry twin Oerlikon 20 millimeter cannon, one under each wing. The aircraft had metal wings, as wooden wings had been judged unable to stand the recoil of large cannon. Apparently this aircraft did some fighting in the Battle of Britain and scored a kill on a Do-17.
However, the Oerlikon cannon was too heavy, required greased cartridges, and wasn't designed for carriage by a fighter anyway, and the Hispano cannon was a better solution. The four-cannon fit was evaluated on a Hurricane Mark I in 1940, but the machine was regarded as underpowered, and the four-cannon configuration had to wait for the Mark II with its Merlin XX engine

Weight wouldn't have been the issue

It wasn't The issue was that the original HS404 Hispano was designed as a "motor cannon" - for engine inline fitment - and when the licensed-copy "Hispano MkI" was fitted in both the Spitfire and Hurricane wings....the majority of jams were due to them being beltfed; it looks like the belts flew around a bit in the hoppers under combat conditions and didn't feed straight. The fist attempt at a cure was moving to a drum-feed - which was partially successful - then the weapon was redesigned as the MKII by Martin-Baker with a revised beltfeed which cured the majority of problems.

In the meantime, because it looked like a lost cause, in late 1940 the Air Ministry specified twelve MGs for future fighter designs, leading to the twelve-gun Hurricane option.

Where the thinner wing of the Spitfire DID still affect the Spitfire was that in European conditions, it led to the outside pair of guns in FOUR-cannon Spitfires jamming because of "freezing" - both literally icing-up and cold air thickening the lubricant in the gun mechanism. Therefore for a lot of its European history we see Spitfires in various marks with a mixed TWO-cannon/MG installation.

[Pips]

Shame they didn't trial a Hurricane with just two Hispano instead of the four, as they did with the Spitfire. Whilst jamming may still have been a problem (although not to the extent of the Spitfire), at least the Hurricane would not have suffered a performance hit. And who knows, the RAF just may have received cannon armed Hurricanes in (albiet) small numbers whilst the BoB was still on.

At least one pilot thought the cannon armed Hurricane's were worth persisting with.

"F/L R.L.'Dick' Smith joined No 151 Squadron on the 10th of June 1940 as "B" Flight commander. His flying ability was rated "Exceptional". Realising he had no combat experience where as the men under his command did from their time in France, he put in as many hours as he could practising dog-fighting with them prior to his first sortie. He flew 133 sorties during the Battle of Britain. Some of these sortie's were at the controls of a two cannon armed Hurricane (L1750) or a four cannoned Hurricane (V7350) which until then were idle as no one wanted to fly them. The cannon slowed the Hurricane down and also made it less agile. On top of that it was said that the cannons lacked reliability. He flew them on 110 operational sorties from North Weald. On the 13th of August 1940 he scored his first confirmed victory, a Do 17. He ended the Battle with this one kill, three probables, and two damaged and no recognition for having proved the cannon armed Hurricane's to be effective."

[phylo_roadking]

Pips -

at least the Hurricane would not have suffered a performance hit.

Some of these sortie's were at the controls of a two cannon armed Hurricane (L1750) or a four cannoned Hurricane (V7350) which until then were idle as no one wanted to fly them. The cannon slowed the Hurricane down and also made it less agile.

I'm not sure it would be safe to plaud the benefits of a two-Hispano armed Hurricane until we would know something about WHY it was felt that the four-cannon installation both slowed it AND made it less agile. Weight MAY of course been the major issue - did four cannons and ammo really weigh less than the later twelve Brownings and ammo? - but there may have been far more aerodynamic factors involved, such as the location of the weight, stress factors, etc..

[gbav8r]

I found this discussion as I was looking for some other info on the Spitfire, but I may have the answer for you. My late Grandfather who was an engineer in London during the war (kept back rather than sent to the front because of his skills) tells the story that one day he was seconded by the RAF. They needed to know whether the Spitfire airframe could take the stress of the recoil of the cannon. He had to do this in a matter of days without the aid of a Spitfire, since they were in short supply. Basically with a cannon, a test bed, Spitfire blue prints and a slide rule he figured it out and gave the green light from a stress view point.

[phylo_roadking]

Thanks for the above; now that this thread has come back to the top of the pile, It's jogged my memory about something I'd read since, in Jonathan Glancey's "Spitfire:A Biography" in relation to this...

I'm not sure it would be safe to plaud the benefits of a two-Hispano armed Hurricane until we would know something about WHY it was felt that the four-cannon installation both slowed it AND made it less agile. Weight MAY of course been the major issue - did four cannons and ammo really weigh less than the later twelve Brownings and ammo? - but there may have been far more aerodynamic factors involved, such as the location of the weight, stress factors, etc..

...and this -

The four-cannon fit was evaluated on a Hurricane Mark I in 1940, but the machine was regarded as underpowered, and the four-cannon configuration had to wait for the Mark II with its Merlin XX engine

There WAS one factor I'd forgotten - recoil! Glancey notes that the 8xMG Hurricane was "steadier" a weapons platform than the 8xMG Spitfire, as the Spitfire suffered more from the effects of recoil; if the MkXX Merlin in the MkII Hurricane with its power upped to 1,280 bhp and top speed to 340 mph helped the MkII Hurricane to cope with the extra recoil of four cannons and allow it to come into service with the four cannon armament as regular fitment - and the 8xMG armament's recoil created problems for the Spitfire MkI - what additional problems must the extra recoil from four cannon have caused for the manners/handling of the test-fitted MkIB???