F8F guns

[comiso90]

Why did the Navy all of a sudden switch to 20mm on the Bearcat and some Corsairs?

"For extra firepower" is not a good enough answer...

Most of the adversaries either plane was likely to encounter in the Pacific would be shredded just fine by .50's. Except for some flying boats, there were no large bombers to be concerned with.

Changing to 20mm that late in the game is almost like admitting they were wrong for the previous 4 years.

I'm not saying that it was a bad decision but it is a significant change... what was the though process?

.

[HoHun]

Hi Comiso,

>Why did the Navy all of a sudden switch to 20mm on the Bearcat and some Corsairs?

Two possibilities ... poor reliability of the 12.7 mm machine guns in prolonged bursts (something the US Navy had been complaining about at the Joint Fighter Conference), and - at least for the F8F - the intention to achieve the desired firepower at a reduced weight.

Here is a weight and firepower comparison for a 4 x Hispano II battery (with 145 rounds per gun, like in the Sea Fury) and a 6 x 12.7 mm M2 battery (with 400 rounds per gun, as in the F6F):

4x Hispano II - 145 rpg - 343 kg - 249% firepower - firepower per weight: 318%
6x ,50 Browning M2 - 400 rpg - 438 kg - 100% firepower - firepower per weight: 100%

You'll notice a substantial weight saving along with a massive increase in firepower.

(The total energy of the 2400 rounds of 12.7 mm ammunition is 51.1 MJ, the total energy of the 580 rounds of 20 mm ammunition is 61.6 MJ, so the ammunition supply actually increases in destructive potential with the 20 mm cannon.)

Acutally, if you were simply trying to preserve the firepower while aiming for the lightest possible weight, this would be a good option:

2x Hispano II - 250 rpg - 223 kg - 125% firepower - firepower per weight: 246%

This is a 215 kg weight saving at a 25% firepower increase.

Regards,

Henning (HoHun)

[KrazyKraut]

As far as the Corsair is concerned I always thought it was due to the increasing use as an attacker aircraft.

[comiso90]

Hola HoHun,

The weight issue does make sense.. the Bearcat was a streamlined little beast.

I didn't realize 12.7 had poor reliability.

I'd rather see the pilots trained NOT to indulge in prolonged bursts

.

.

[drgondog]

Originally Posted by comiso90

Hola HoHun,

The weight issue does make sense.. the Bearcat was a streamlined little beast.

I didn't realize 12.7 had poor reliability.

I'd rather see the pilots trained NOT to indulge in prolonged bursts

.

.

The Brownings didn't have poor reliability per se. Having said that the 50's required burst management to prevent burning out the barrels.

The feed system on the P-51B Did have poor reliability, particularly in manuever with high G's.

I haven't seen the statistics lately, but IIRC but the 20mm cannon used by both the USN and USAAF experienced more stoppages and also firing pin strike failures than the Browning 50's and the issues continued into the Korean War.

The Brits solved the Hispano Suiza 20mm Mk2 and above variants by shortening the chamber slightly but the US did not follow suit. The Corsair, the P-51A, the Lightning and P-61 all experienced issues with this weapon.

In Korea the Mk3 was introduced, then the Colt Mk12.. after that the Vulcan dominated production US fighters.

Net - the 20mm is a better choice than the .50 for aircraft combat, given the solution of the reliability issues. The US should have just used the German designs and paid them a suspended royalty.

[kool kitty89]

The P-51A (and the A-36) didn't have 20mm cannon. THe P-51A had the same armament as the P-51B/C.

The Mustang I (NA-83) had 4x .30's and 2x .50's in the wings, and 2x .50's in the lower fusalage.
The Mustang IA (NA-91) was armmed with 4x 20mm cannon, and NA-91's recevied by the USAAF (P-51's and F-6A's) retained the 4x 20 mm's.
North American P-51/F-6A Mustang

In Korea the Mk3 was introduced, then the Colt Mk12.. after that the Vulcan dominated production US fighters.

Don't forget about the M39


[quote]The US should have just used the German designs and paid them a suspended royalty.[/qiote]

The Japanese showed that the .50 Browning could be developed into a good 20mm cannon in the Ho-5. (though due to the use of weaker alloys on high stress components, production models had reduced muzzel from 830 m/s down to ~720 m/s)
Also, seeing as the US mounted the majority of their armaments in unsynchronized positions, a development of the Oerlikin FFL may have been a good choyce. (again shown by the Japanese)


Some good info and discussions on Tony Williams' site:
BOOKS BY ANTHONY G WILLIAMS
IDEAL WW2 FIGHTER ARMAMENT
ANOTHER MISSED OPPORTUNITY: THE OERLIKON FFL CANNON
Modifications and Attempts at Standardization (of the US 20mm)
CANNON OR MACHINE GUN

[kool kitty89]

Also, I believe the F8F didn't get 20mm's until after the war. (the F8F-1B model)
The majority produced were armmed with 4x .50 M3's (high rate of fire).


Grumman F8F Bearcat

When production ended in May 1949, Grumman had built 1,266 Bearcats: 765 of the F8F-1; 100 of the F8F-1B, which differed by having the four standard machine guns replaced by 20 mm cannon; 36 of the F8F-1N variant equipped as night-fighters; 293 of the FBF-2 with redesigned engine cowling, taller fin and rudder, plus some changes in detail design, and adoption of the 20 mm cannon as standard armament; 12 of the night-fighter F8F-2N; and 60 photo-reconnaissance F8F-2P aircraft, this last version carrying only two 20 mm cannon. In late post-war service, some aircraft were modified to serve in a drone control capacity under the designations F8F-1D or F8F-2D.

[comiso90]

Originally Posted by kool kitty89

Also, I believe the F8F didn't get 20mm's until after the war. (the F8F-1B model)
The majority produced were armmed with 4x .50 M3's (high rate of fire).


Grumman F8F Bearcat

I didnt know that.

50 cals were good enough for the F-86.

[drgondog]

Originally Posted by comiso90

I didnt know that.

50 cals were good enough for the F-86.

In my opinion MiGs got away because the the 86 didn't have weapons that detonated fuel above 35000 feet. Every 86 ace i talked wished they had 20mm at high altitude.

[Broncazonk]

The Hispano-Suiza HS 404 autocannon was licensed for use by the United States as the M1. Both the Army Air Corps and Navy planned on switching to the 20mm as soon as sufficient production was ready.

In 1941, a massive cannon / ammunition production program was created. Unfortunately, the cannons proved to be extremely unreliable. By late 1942, the USAAC had 40 million rounds of ammunition stored, but the cannons were unsuitable.

In April 1942, a copy of the British Mk II (2nd generation HS 404) was sent to the U.S. for comparison. The British version, using a slightly shorter chamber (and much looser tolerances) did not have the same problems as the M1.

The U.S. declined to shorten the chamber of the M1, and loosen the tolerances. Nevertheless, they made other modifications to create the M2. The M2 was less reliable than the M1.

The Navy had been trying to go all-cannon throughout the war, but for obvious reasons, the conversion never occurred.

As late as December 1944, the Army's Chief of Ordnance was still attempting to modify the M2 to allow it to enter service. (All they had to do was loosen the machining tolerances...)

The M3 came out on the F8F but reliability problems continued.

After World War II, the USAF adopted a low machining tolerance version of the M3 cannon as the M24!!

Bronc

[drgondog]

[QUOTE=kool kitty89;383463]The P-51A (and the A-36) didn't have 20mm cannon. THe P-51A had the same armament as the P-51B/C.

The Mustang I (NA-83) had 4x .30's and 2x .50's in the wings, and 2x .50's in the lower fusalage.
The Mustang IA (NA-91) was armmed with 4x 20mm cannon, and NA-91's recevied by the USAAF (P-51's and F-6A's) retained the 4x 20 mm's.
North American P-51/F-6A Mustang




Don't forget about the M39

The US should have just used the German designs and paid them a suspended royalty.[/qiote]

The Japanese showed that the .50 Browning could be developed into a good 20mm cannon in the Ho-5. (though due to the use of weaker alloys on high stress components, production models had reduced muzzel from 830 m/s down to ~720 m/s)
Also, seeing as the US mounted the majority of their armaments in unsynchronized positions, a development of the Oerlikin FFL may have been a good choyce. (again shown by the Japanese)


Some good info and discussions on Tony Williams' site:
BOOKS BY ANTHONY G WILLIAMS
IDEAL WW2 FIGHTER ARMAMENT
ANOTHER MISSED OPPORTUNITY: THE OERLIKON FFL CANNON
Modifications and Attempts at Standardization (of the US 20mm)
CANNON OR MACHINE GUN

According to Gruenhagen and the NAA drawings for Xp51 through P-51M, the P-51A had 4 20mm Hispano suiza with 125 round each

[comiso90]

Originally Posted by drgondog

In my opinion MiGs got away because the the 86 didn't have weapons that detonated fuel above 35000 feet. Every 86 ace i talked wished they had 20mm at high altitude.

incendiary rounds didn't ignite tanks above 35??

[kool kitty89]

North American P-51A Mustang

These aircraft had the same external stores capability as the A-36A Invader, but had no dive brakes and no fuselage guns, the armament being limited to four 0.50-inch machine guns mounted in the wings. The inboard pair had 350 rpg and the outboard pair had 280 rpg. An underwing load consisted of two 250 lb, 325, or 500-pound bombs.

And from: http://aerofiles.com/_noram.html

P-51A


P-51 (NA-91)

[evangilder]

Bill Gunston, in "Aircraft of WWII" wrote:

So successful were the US Army trials that 150 were ordered as the P-51 Apache (later the British name was adopted), with four M-2 cannon. The basic aircraft resembled the RAF Mk IA with four Hispano cannon.

[drgondog]

Originally Posted by evangilder

Bill Gunston, in "Aircraft of WWII" wrote:

Thanks - I was just looking at the 20mm installations on the p-51A bill of materials and they weren't referenced as Browning 50 's. Mustang about Edgar Schmeud and Gruenhagen's book also talk about the Hispano 20mm.

The A-36 was a mod of the P-51A airframe and imbedded the two 50's in the fuse and scrapped the 20mm