gun synchronization to fire through propeller arc

[Harri Pihl]

Finnish experience on wing vs fuelage guns appear to be rather contradictory. One of the first Fokker D.21s (FR-76) was ordered with 20mm Oerlikon canons mounted on gondolas below the wing. The installation was unsuccesfull, pilots reported poor accuracy, apparently the wooden wing was too flexible. However, later Fokkers with P&W Wasp Junior had only the wing guns (4x 7,7mm Browning).

The Myrsky had four fuselage guns (LKk 42 12,7mm) and the Pyörremyrsky as well as VL Humu had only the fuselage guns (all these featured wooden wing...). Also many war time pilots avdocated for fuselage guns; Juutilainen as example thought that inertia caused by wing guns is a bad thing.

One of the most succesful wartime weapon upgrades in Finland was wing gun related; the wing guns of the Brewster (Colt MG53) were replaced with the LKk 42. The LKk 42 had about twice higher rate of fire than the Colt and in the wing the LKk 42 could exploit this advantage fully because no synchronization was needed so the end result was about 50% higher firepower than before the upgrade.

Anyway, I agree pretty much with Graham; wing gun installations, even relatively weak, proved to be succesfull so apparently other factors are more important than location of the guns in the plane.

[Bruce Dennis]

Hello Graham et al,
I think the engineering questions and the historical data should be separated: I suggest that the only reason guns were ever put in wings in the first place was because the front of the plane was taken up with the engine and prop. As soon as jet propulsion was reliable enough, single-engined fighters appeared with the guns back in front of the pilot. There was no longer any need to put them in the wings, but designers would have done so if there had been an advantage to exploit.

Having said that, I don’t want you to think that I am blind to the reasons for guns to be wing mounted. That was a simple place to put them, the armourers wouldn’t be tripping over the erks servicing the engine, and in all probability, it was cheaper. Aerodynamically, if the wing concept had a thick enough cross section, there was no penalty to pay in that respect either. One point I had forgotten until this interesting thread came along was that with wing-mounted guns it was generally possible to store the ammunition perpendicular to the CG. While this didn’t alter the fact that several hundred pounds of ammunition might be outboard (in the wings), it was better than having it in the nose.

Bruce

[kennethklee]

Originally Posted by Bruce Dennis

The Fokker Eindekker, if I recall correctly, was experimentally fitted in 1916 with four guns firing through the propeller with an interrupter gear. The advantages didn’t justify the extra weight. Although I can’t access it at the moment, I recall an account of a similar installation on a Morane mono-plane.

Originally Posted by Bruce Dennis

Having said that, I don’t want you to think that I am blind to the reasons for guns to be wing mounted. That was a simple place to put them, the armourers wouldn’t be tripping over the erks servicing the engine, and in all probability, it was cheaper. Aerodynamically, if the wing concept had a thick enough cross section, there was no penalty to pay in that respect either. One point I had forgotten until this interesting thread came along was that with wing-mounted guns it was generally possible to store the ammunition perpendicular to the CG. While this didn’t alter the fact that several hundred pounds of ammunition might be outboard (in the wings), it was better than having it in the nose.

Bruce-

Thanks for your interesting comments on the gun synch topic. I was intrigued to read that the Fokker Eindecker was experimentally fitted with four machine guns. Just some innocent comments from curiosity: If it could fly with four machine guns, why did the Eindecker not operationally carry two machine guns instead of one? In the WWI-era fighter aircraft, the increase from one machine gun to two was considered major progress; it was one of the primary reasons for the temporary ascendency of the Albatros fighter over its one-gunned opposition. Also, my impression of the Eindecker was that it was a bit underpowered and I can imagine the Eindecker would be straining to carry four machine guns.

Your point that fuselage guns placed several hundred pounds of weight in the nose is also intriguing. I must admit I hadn't considered this aspect of engine cowling-mounted guns. In a informal and fast visual survey, I noticed that many fighters with fuselage-mounted armament have the breeches of their cowling guns (and presumably the ammunition supply) located either just atop the front part of the wing and landing gear struts or behind them. These include the Bf 109, Fw 190A/D series, Ta 152, A6M-series (Reisen, "Zero"), Ki-61 (Hien, "Tony"), Ki-84 (Hayate, "Frank"), IL-2, La-7, and Yak-3. Would this location still "count" as making the aircraft nose-heavy? I'm not trying to nitpick for nitpick's sake, but just trying to understand better the mechanical aspects of cowling-located armament and its effect on flying characteristics.

Thanks to all who responded to this thread; the responses were all interesting and I learned much from them.

Kenneth

[kurlannaiskos]

the Ilyushin Il-2 Shturmovik is a ground-attack aircraft ,not a fighter.
I think you have mixed up two different aircraft here.
in the case of the Il-2 the
twin 12.7 mm UBT and twin 23 mm VYa all were in the wings and had long rectangular ammunition loading hatches outboard of the guns/cannons.
and with all that armor (6 mm to 13 mm) up front to protect the engine,oil,radiator and pilot there was no room for guns or ammunition.

[kennethklee]

Originally Posted by kurlannaiskos

the Ilyushin Il-2 Shturmovik is a ground-attack aircraft ,not a fighter.
I think you have mixed up two different aircraft here.
in the case of the Il-2 the
twin 12.7 mm UBT and twin 23 mm VYa all were in the wings and had long rectangular ammunition loading hatches outboard of the guns/cannons.
and with all that armor (6 mm to 13 mm) up front to protect the engine,oil,radiator and pilot there was no room for guns or ammunition.

Thanks, until now I did not realize the IL-2's machine guns were carried in the wings. Since I was a teenager, for some reason, I had thought the machine guns were cowling mounted and thought I had read it somewhere. Sorry for propagating this error. BTW, the IL-2's two forward-firing machine guns were 7.62mm, not 12.7mm. I had just read last night that even its successor, the IL-10, had 7.62mm, not 12.7mm, machine guns firing forward. Here's a reference from the Century of Flight website:

http://www.century-of-flight.net/Avi...Shturmovik.htm

I have found that its WWII aircraft references generally seem to be accurate and consistent with the aircraft books I have read. It also confirms that all of the IL-2's forward-firing armament are in the wings and none in the fuselage--again, my error for suggesting so before, especially because I had read this reference previously and missed the gun configuration.

However, I knew/know the IL-2 was a ground attack aircraft, I had mentioned it with the fighters only because I had thought its guns were cowling-mounted and therefore subject to the same synchronization as the cowling-gunned fighters and therefore relevant to this topic.

Kenneth

[martin66]

hello

I remember an article in aviation magazine when Adolf Galland said in an interview he prefered the Bf -109 over the Fw-190 because the guns of the Messerschmitt was less prone to jamming in high g. factor maneuvres.

I think the cause is the wing guns of the FW-190 were more far of the centre of gravity of the plane and they had problems with the feeding of ammo in high g conditions than the nose guns of the Bf-109.

Martin

[kurlannaiskos]

well, how could I have gotten that wrong?
oh , I know-I usually concentrate on the cannon armament.
(my favorite is the NS-37)

however that website also still uses old and inaccurate designations like Yak-1M , Il-2M and Il-2M3.
these are not the correct Soviet designations , but a largely typographical error in those cases.

[kennethklee]

Originally Posted by martin66

hello

I remember an article in aviation magazine when Adolf Galland said in an interview he prefered the Bf -109 over the Fw-190 because the guns of the Messerschmitt was less prone to jamming in high g. factor maneuvres.

I think the cause is the wing guns of the FW-190 were more far of the centre of gravity of the plane and they had problems with the feeding of ammo in high g conditions than the nose guns of the Bf-109.

Martin

Originally Posted by kurlannaiskos

well, how could I have gotten that wrong?
oh , I know-I usually concentrate on the cannon armament.
(my favorite is the NS-37)

however that website also still uses old and inaccurate designations like Yak-1M , Il-2M and Il-2M3.
these are not the correct Soviet designations , but a largely typographical error in those cases.

Martin--good point, I had forgotten that outboard guns are more prone to jamming. I can't recall the source, but I also recall reading commentary from an American pilot stating this (IIRC, he was comparing the wing armament of the P-51 Mustang to the centerline guns of the P-38 Lightning).

kurlannaiskos--I had forgotten about the 37mm guns carried by the later models of the IL-2, quite formidable. I find interesting that as the IL-2 progressed and eventually evolved into the IL-10, the two 7.62mm machine guns remained steady and were not upgraded to 12.7mm or even 20 mm cannon. I suppose the machine guns were not regarded as primary armament and were used primarily for their tracer ammunition? Do you know the IL-2 with the 37mm cannon performed compared with the 23mm-gunned versions? The installation of the IL-2 37mm cannon certainly appears more graceful than the underwing 37mm cannon of the Ju 87G-1. Your note also reminds me that I am not very familiar with the formal designation nomenclature of WWII Russian warplanes.

Thanks again,
Kenneth

[kurlannaiskos]

I did look into it a bit further and the machine guns were apparently for aiming purposes only.
...as you say the tracer rounds.
(I can't imagine the 7.62 would be effective on anything but infantrymen)

the 37 mm cannons were more effective against German Armor ,but the pilots found the effect on the aircraft to be sluggish handling and more effort to pull up after making an attack run.
there was also a problem with asymmetrical recoil causing the pilot more difficulty in aiming.

[Kutscha]

Originally Posted by kurlannaiskos

I did look into it a bit further and the machine guns were apparently for aiming purposes only.
...as you say the tracer rounds.

The Hurricane with the 40mm cannons used their .303s for aiming.