Tony Williams said:
To sum up, it seems to me that you have become very fixed on your theory that gun recoil was a major limitation on aircraft armament, but I have seen no evidence to support this. On the other hand, it is clear that armament weight (especially out in the wings) was a major concern because of its effect on performance and handling, and this caused all air forces to restrict the number and size of guns.
I may be fixed to the idea, but only because I believe it is not covered enough and because I think in ww2 there was little if even any covering of the problem, altough it undoubtly existed.
Actually, the Yak-9T unsurprisingly suffered from heavy recoil issues:
"Yak-9T - Yak-9 armed with a 37 mm Nudelman-Suranov NS-37 cannon with 30 rounds of ammunition instead of the 20 mm ShVAK cannon, cockpit moved 0.4 m (1 ft 3 in) back to compensate for the heavier nose. Initially poor quality control lead to multiple oil and coolant leaks from
cannon recoil.
Recoil and limited supply of ammunition required accurate aiming and
2-3 round bursts. Yak-9T was widely used
against enemy shipping on the Black Sea
and against tanks, but also successful against aircraft with a single cannon hit usually sufficient to tear apart the target." The designation alone implys a specialized tank hunter variant:
Yak 9 Tyazhelowooruzheny" (Heavily Armed), the design bureau was asked for a -
tank destroyer -altough it now is generally assumed to be a fighter plane because of the use in this role by VVS-Garde units. (It actually served in the tunk hunter role as well). Even with this in mind, nobody claims the Yak-9T to be good in the dogfighting role, it´s one and only reputation is incredible devastating firepower.
According to the Hurricane, Yakolev wrote (translated):
"...the GKO accepted the Hurricane, but the armement was considered to weak by Suprun and others, so subsequent changes in weapon layout to two Shvak and two 12.7mm guns became necessary. Later Hurricane with four high velocity 20mm guns suffered from heavier weight and lower firing accuracy and thus were deligated to the ground attack role or refitted with 4 12.7mm guns". (Yakolev, zehl dschisin, p.402)
Note that "lower firing accuracy" may be caused due to heavier recoil as plausible explenation.
According to the P-39 in VVS use, Yakolev wrote (translated):
"The airplane Airacobra was well known to us since the land lease treaties. Initially it made problems because of the weak tailplane, a number of planes were lost without enemy actions due to this weakness. Eventually we removed parts of the armour and sometimes even the 37mm gun in order to improve the dogfighting abilities and the
stability of the gunplatform. With more experience, pilots soon learned to use the advantages of this big gun against german bombers, so most Airacobras retained the centreline gun in the end, despite it´s negative aspects" (ebd.p.418 )
This leads us to a certain point: Altough you made clear that other reasons may cause the lower armement, You did not disproved my theory. It is interesting to note that certain recoil-weight relations were never exceeded for fighter A/C and some ratio´s are too close to be explained as random events:
(Yak-3 and La7bis for example but also Bf109G10/G6 and Fw190A8, Ki-84Ib and A6m5b, Spitfire Vc and Typhoon, P47D and P51D)
And there were enough examples to put more firepower on planes, however, none of them reached combat status. Best example for this is the tiny He-162A1 with originally two 30mm MK 108 mounted in the lower fuselage (better than mid wing), but the recoil exceeded 0.1 (actually 0.123 plus gaz effects), hence test pilots were concerned about the comparably large recoil issues for the pretended fighter role. Subsequent changes (He-162A2) to a twin 20mm armement eased the problem, the later A-3 variant again with 30mm had substantial structural reinforcements and a heavier weight to match 0.100 (plus gaz effects). All random?
Question still remains wther or not the recoil of a six mid wing mounted 20mm high velocity guns would detrementally affect the stability of the fighter gunplatform rating. I do believe it does, You disagree.
the brutto recoil is around 152 Kp per one single shot. Depends on the geometry of the placement of the gun. assume the gun is placed in the middle of the wing, ~4.5 ft. away from the centreline and ~1 ft. below the central, longitudinal energy axe of the plane. Any recoil impulse generated there will cause some rapidly or slowly applied force (depending on gunmount) to the airframe, which may slew the plane out of course by a tiny fraction. (Note that fractions are important here) Rof for one gun is as low as 600 rpm, but maybe as high as 1000 rpm for a tweaked gun. This implys there will be never absolute, contemporary balance in firing. (this is also true because of different barrelwears=slightly different mv, different gunstate, different ammo type mixings and so on) A single, uncoupled shot will aplly 152Kp to the right wing 4.5ft. from the energy axe, if the right gun is fired. For the energy axe, this results to a course difference of 1.8712 deg (assuming some stabilizing factors by speed [~300 mp/h] and air density [500 hectopascal or~18000ft alt]) or in other words, a 20ft. wide, circular target originally aimed at 306 ft. distance will be thrown completely out of aim due to the recoil of a single shot fired from a mid wing mounted Hispano 20mm MK II in our example. That´s pretty much recoil for fighter purposes, if You ask me. Now, we know that firing 6 guns simultaneously will positively affect the gunstability but only to some degree (debatable), there is no question that eight 0.50cal do perform much better in this respect than would do six 20mm.
By the way, thanks for the cartridge infos!
best regards,