Luftwaffe Cannons and Machineguns topic.

[CharlesBronson]

You also referred to "the shorter stroke in the bolt's travel" which would olnly be possible with a shorter cartridge: the bolt stroke length is directly linked to the overall cartridge length.

Yes, now I see that having the same cartrigde overall lenght the gun need to have the same bolts stroke lenght in order to feed it. Quite logic. Several sources claim a bigger rate of fire in the 20mm variant however.

[Erich]

CB again the under weapons pod was short lived. Granted it had much firepower , maybe too much similar to the He 219 a reason the crews had half of the cannons removed. the same applies for the Bf 110G-4 it was already overladen with radar/radio equipment and the four cannons were enough to take down any Allied bomber. In the photo you can imagine the loss of total air speed in trying to overtake an RAF heavy

E

[CharlesBronson]

Jawol, I would be suprized if that Messers can reach the 500 km/h.


MG 151 Family part 3, MG 151/20 Elecktrish.

The differences with the normal MG-151/20 was purely internal. The spring loaded firing pin was replaced with a fixed needle wich was energizated by the 24v aicraft electric circuit. The sincronization device consisten in a electromechanical gear, the use of electricar primer wich was detonated by a spark, mean that a more instantaneous ignition was provided. That allowed the MG 151/20E to shoot through a high rpm 3 thick blade propellers like the BMW 801 engine and still had a rate over the 600 rpm. The production of the Mg-151/20E were delivered almost entirely to the Fw-190 and the Ta-152H variants, some other aircraft in use were the Do-335 ( 2 above the engine), Me-209 stüfe II (wingroots) and the Me-309 (wingroots and above engine)

The 4 guns in a FW-190A-6.


Experimentally the fitting of an MG 151 pod under the fuselage to fire through the prop was tested. This apparently worked very well, providing a valuable improvement in firepower without the performance and handling penalties of the underwing pods. However, the belly gun had to be synchronised, which meant it had to use the electric-primed gun, whereas the engine gun used percussion priming. The risk of mixing up the ammo was considered too great, so the idea was dropped

MG 151/20E below Bf-109G-4.

[Denniss]

BTW the image of a Bf 109 G-4 with underwing gun pod is not af a G-4/R6 but of a G4 with Rüstsatz 6.
R6 (Rüststand 6) would denote an all-weather capable fighter which had some special navigation and radio equipment.

[CharlesBronson]

Hmmmm...sure about that ?

[Denniss]

Adding a Rüstsatz never changed an aircraft designation, the /Rx designation always refers to Rüststand.
For the 109G, R1 was a fighter-bomber (probably with two drop tanks under the wing and a bomb on the centerline wing rack or at least with underwing bomb rack for smaller bombs of the 50kg type), R2 to R5 were different recon variants.
Then we have the /U designation for Umbausatz or Umrüstsatz, U1 is a special prop, U2 is GM-1 injection, U3 should be either MW-50 or another recon variant (it is said that MW-50 was used in the G-6 by using /U2 variants with a modified tank), U4 is the MK 108 engine cannon

[genkideskan]

Well the synchronisation was the reason to develope the MG 151. Its not possible to synchronise an FF properly. Aircraft used MG 151 used mostly electrical primed ammo. The primer wasnt ignite by spark but by an thin wire that becomes red hot and ignite a primer pellet. The syncronised guns used a special tested round. These rounds where marked "gest". These means "gesteuert" and indicates ammo that was reliable enouth to fire through the prop. The outer guns used normal ammo but electrical ignited, too.

[CharlesBronson]

Adding a Rüstsatz never changed an aircraft designation, the /Rx designation always refers to Rüststand.
For the 109G, R1 was a fighter-bomber (probably with two drop tanks under the wing and a bomb on the centerline wing rack or at least with underwing bomb rack for smaller bombs of the 50kg type), R2 to R5 were different recon variants.

Whatever, I always saw the R6 designation refered to the underwing Mausers.

Well the synchronisation was the reason to develope the MG 151. Its not possible to synchronise an FF properly. Aircraft used MG 151 used mostly electrical primed ammo. The primer wasnt ignite by spark but by an thin wire that becomes red hot and ignite a primer pellet. The syncronised guns used a special tested round. These rounds where marked "gest". These means "gesteuert" and indicates ammo that was reliable enouth to fire through the prop. The outer guns used normal ammo but electrical ignited, too.

Too many variables in the ammo, I guess thats why the allied used few sinchro weapons.

[Tony Williams]

Originally Posted by genkideskan

Well the synchronisation was the reason to develope the MG 151. ... Aircraft used MG 151 used mostly electrical primed ammo.

Not really. Only the Fw 190 family used electrically-synchronised MG 151 in service, I believe. The first installation was as an engine gun in the Bf 109, and that used percussion priming.

[Tony Williams]

Originally Posted by CharlesBronson

Too many variables in the ammo, I guess thats why the allied used few sinchro weapons.

The principal reason was that the Allies started the war relying on machine guns (the USAAF continued to do so, for the most part), and had to mount several of them to get sufficient destructive effect. They couldn't all fit around the engine, so it made sense to standardise the installations and put them all in the wings. Also, the Browning fired much more slowly when synchronised. Finally, the Hispano could not be synchronised at all.

[genkideskan]

I always wonder about the use of 7,7 cal. and .50 use - there is no place for explosive. May be its enouth to bring down early bombers HE 111 and Do's.
I wouldt like to know how many bursts a Hurricane or Spitfirw wouldt need to bring down a B-17 with the 8 x .303 guns.
There is a need for Germany to use canons in 20mm or in 1943 30mm and larger. It was nessessary to bring as much as possible explosive into the target.
So the 30mm becomes standard and a lot of MG 151 becomes free for other tasks, f.e. as AA guns. Late war development brings the MG 213 in 20mm. These gun used an extended case and was designed for the Mine X projectiles
and a rate of fire beyond 1200 rd./m. Than the 20mm was dropped and the 30mm version shouldt become the german main gun.
Annother feature of the MG 151 was the low recoil -always a problem in aviation. The use of an electrical priming system make it possible to realise an ignition exactly 8mm befor the forward move of the barrel and bolt was finished. So the gun fires when most of the moveable parts of the gun are still in move forward. That swallows a lot of recoil.
BTW I was told that a Spitfire burst of all 8 guns produced an recoil that costs you about 40 miles of speed. Any idea ?

[Tony Williams]

Originally Posted by genkideskan

BTW I was told that a Spitfire burst of all 8 guns produced an recoil that costs you about 40 miles of speed. Any idea ?

Absolutely not. This is what I put in Flying Guns – World War 2: Development of Aircraft Guns, Ammunition and Installations 1933-45:

"This might be an appropriate moment to dispel one of the favoured myths of big-gun aircraft; that the recoil had a drastic effect on their speed. To take the example of the USAAF's B-25 fitted with a 75 mm M4 gun; the aircraft weighed around 12,000 kg and attacked at perhaps 400 km/h, the gun fired a 6.8 kg projectile at around 2,200 km/h. A simple rule of thumb is to multiply the weight by the speed to achieve a rough "momentum index" (it is actually a bit more complicated than this, as the expanding propellant gasses contribute to the recoil). It will be apparent that the aircraft has at least 200 times the momentum of the projectile, and a single shot will therefore not greatly slow it. In fact, at the end of an attack run in which several shots were fired, the plane would typically be slowed by 10-15 mph. The effect on fighter speed of long bursts of heavy gunfire (especially from automatic cannon) could be noticeable, particularly in a turning battle when the aircraft might be manoeuvring at the extremes of the flight envelope, close to stalling."

[CharlesBronson]

The principal reason was that the Allies started the war relying on machine guns (the USAAF continued to do so, for the most part), and had to mount several of them to get sufficient destructive effect. They couldn't all fit around the engine, so it made sense to standardise the installations and put them all in the wings. Also, the Browning fired much more slowly when synchronised. Finally, the Hispano could not be synchronised at all.

Incidentally the Bell P-39 and the early P-40 have sincro MGs but according t the pilot it jammed a lot more than desirable. I was aware of the simple recoil weapons like the Oelikon were not suited for shot trough the propellors, ididt know about the Hispano.

Do you have any figure of RPM for the Browning sincro M2 mounting ?



15x96mm Ammunition for the MG-151/15.

Panzergranatpatrone, L-spur.




Armor piercing steel shot, with tracer, projectile weight 72 grams initial speed 850 m/s. The tracer elemente endure at list 1100 meters.

Penetration table for Pzg.Ptr. L-spur. 25 mm at 100 meters and 13 mm at 600 meters, both in vertical (90º) plate and direct mode..




Brandsprenggranatpatrone



Incendiary-explosive. 57,5 grams bullet, muzzle velocity 960 m/s, pretty fast one.


Brandsprenggranate L-spur Mit Zerl.



Same as above but with an tracer and self destruction element in the bullet base. Green

Hartkern-Panzergranate ohne-zerl.




This is a pretty unusual variant. It consist in a miniaturized hard core Panzergranate 40 as used in the Panzers. Bullet weight 53,5 grams, it had an 9,5mm diameter tugsten-carbide core with a aluminium-magnesium envelope. It was propelled by 24,5 grams of gunpodwer an it can reach 1000 m/s. Due his cost a relative rarity it was to combat tanks only, no for air-to-air use. Probably it went to the Hs-129B-1 attack craft, and for some experimental 15 mm antitank rifles.



Penetration table of the Hartkern 15 mm bullet, 48mmm at 100 meters in a 160 kg/square mm steel ( wich is equivalent to a SAE 4340 alloy), excellent figure...

[Tony Williams]

Originally Posted by CharlesBronson

Incidentally the Bell P-39 and the early P-40 have sincro MGs but according t the pilot it jammed a lot more than desirable. I was aware of the simple recoil weapons like the Oelikon were not suited for shot trough the propellors, ididt know about the Hispano.

To be effectively synchronised, a gun required a short "lock time"; the delay between the gun receiving the message to fire and the cartridge actually firing. This had to be as short as possible, in order to provide the precision needed to avoid hitting the propeller.
A lot of MGs and cannon (the Hispano included) fired from an open bolt; the starting position for the gun was with the chamber empty and the bolt held back. When the gun received the message to fire, the bolt was released, began to move forwards, picked up a cartridge, loaded it into the chamber, locked up the action and, only then, fired. This took far too long. There were a few open-bolt guns which retained a separate control of the firing pin (the MG 17 was one) which did enable them to be synchronised.

Do you have any figure of RPM for the Browning sincro M2 mounting ?

The Browning fired from a closed bolt (except for the British .303 version) but still lost a lot of performance in the big .50 calibre, possibly because the firing pin assembly was heavy and took some time to move forward to fire the cartridge. I have seen figures of 400-450 rpm in its synchronised form.

[CharlesBronson]

Thanks, I really preciated your input Tony.