Why so few planes that fired thorugh the propeller hub?

[tomo pauk]

In the discussion between whether "centre fire (hub)" was better than "wing platform" configuration, I have read in several books and mags, that most German Ace pilots believed that the "wing platform" configurations were more effective for the following reasons:

1). There was more "lead" thrown at the target with a wing platform arrangement.
2). It was more difficult to bring the weapons to bare with the hub arrangement, especially in dog fight situations.

Another thing not mentioned in the discussions so far, is that a relative number of Hurricanes and Spitfires did have 2 40mm wing-mounted cannons in addition to 6 machine guns on the Hurricane and the 4 machine guns on the Spitfires.

Also, I'll get the quote if necessary, many German pilots complained that if they fired too long the 30mm cannon would cause them to lose airspeed. RAF pilots had a similar experience if they fired the 40mm cannons too long.

I've got the info I just need to get it scanned in.

I look forward to the scanned stuff. In the meantime:
-most of the German aces racked up kills with 'central battery'
-2 x 40 mm was never installed in/on a Spitfire (bar for trials?), the Hurri with 2 x 40 mm was the tank buster, with 2 x .303 installed, too

 

[Jabberwocky]

4 x 20 mm was used on the Spitfire, but only in limited use.

Mk Vc's with the SAAF used the configuration in the MTO and some Mk VIIIs with the RAAF used it in the PTO.

The major problem wasn't the weight, or the slightly adverse effect on roll response, but the fact that the second 20 mm was much more prone to jamming, due to issues with gun heating related to the ducting. The Hispano was tempremental if not treated properly.

When the wing was redone for the Mk 21, the ducting was redesigned and the problem solved, so 4 x 20 mm was adopted as standard. They also went with the Hispano Mk V, which had a better (and smaller) feed design, that also reduced jamming. Around 50% of all Hispano Mk II jams in 1944-1945 were traced to feed problems, at least with the 2 TAF.

 

[Rufus123]

In the discussion between whether "centre fire (hub)" was better than "wing platform" configuration, I have read in several books and mags, that most German Ace pilots believed that the "wing platform" configurations were more effective for the following reasons:

1). There was more "lead" thrown at the target with a wing platform arrangement.
2). It was more difficult to bring the weapons to bare with the hub arrangement, especially in dog fight situations.

Another thing not mentioned in the discussions so far, is that a relative number of Hurricanes and Spitfires did have 2 40mm wing-mounted cannons in addition to 6 machine guns on the Hurricane and the 4 machine guns on the Spitfires.

Also, I'll get the quote if necessary, many German pilots complained that if they fired too long the 30mm cannon would cause them to lose airspeed. RAF pilots had a similar experience if they fired the 40mm cannons too long.

I've got the info I just need to get it scanned in.

I thought the Germans really liked center line weapons if they will work on the plane. I wonder how three 20mm (one in the hub and 2 in the wings) would compare with 4 20mm in the wings against fighters. Run in parallel the center gun fills the void in the center. Go with a 30 in the hub for bombers.

 

[Rufus123]

If they had put a single 20mm in each wing of the 109 along with the hub gun as well as the pair of 13mm in the cowl sounds like a strong combination.

 

[silence]

I thought the Germans really liked center line weapons if they will work on the plane. I wonder how three 20mm (one in the hub and 2 in the wings) would compare with 4 20mm in the wings against fighters. Run in parallel the center gun fills the void in the center. Go with a 30 in the hub for bombers.

That's your FW 190 D-13 setup (D-12 had a 30mm in the hub). The Ta-152H was the same as the D-12. The Ta-152C had 20mm in each wing root, 2x20mm on the cowl, and a 30mm through the hub.

Personally, I love this setup.

 

[silence]

If they had put a single 20mm in each wing of the 109 along with the hub gun as well as the pair of 13mm in the cowl sounds like a strong combination.

That was the projected K-14, although the wing armament could also be 30mm.

Here's a some nice pictures of a 109 model customized as a K-14:

http://109lair.hobbyvista.com/models/bn1/bn1_k14/bn1_k14.htm

(love the four-blade propeller!)

 

[modelwiz]

How much it was based on the Hispano is subject to question. Some Russian accounts say the V-2 predecessor (the BD-2)was being worked on in 1933-34 which is before the Russians really got going on building the Hispano. The cylinder heads are totally different, 4 valves instead of 2, dohc instead of sohc, intakes inside the V , the engine uses a longer stroke.

A version of the BD-2 was developed for aircraft use and test flown in 1936.

As far as I have found out, he V-2/VD-2 was a direct descendant of the AM-38 diesel aero engine, itself derived from the AM-35. An aero diesel V12 seems quite the advanced concept to go for in 1933-34, what with aluminium tech barely started in the USSR and all. The AM-35/38 seems to have been quite different from the 12Y in many ways. No doubt the Russians learnt a whole lot from HS (and everybody else) but their engineering seems to have been first rate (their production methods may have been a different story). The V-2 is a sturdy and fairly efficient design, even if the fuel injection is rather simple. The same goes for the aero engines. And there is no way they could have adapted the design for a gun mounting through the prop hub. I am not aware of what other engine they used to do that with.

I am in the process of finishing a functional 3D model of the V-2 and have been toying with making an AM-38 (and -42!) but then the V-2 itself has had 80 years worth of descendants-the V-92 that powers the T-90 tank develops TWICE the power of the original for the same displacement and nearly the same envelope. And I want to produce models of several of them. I already have too many projects!!

It is nearly impossible to separate an engineering achievement from the political scene that gave it rise, but I do try. I am very happy to read fairly learned discussions like the ones in this forum. I do need to research the 12Y further.

 

[tomo pauk]

As far as I have found out, he V-2/VD-2 was a direct descendant of the AM-38 diesel aero engine, itself derived from the AM-35. An aero diesel V12 seems quite the advanced concept to go for in 1933-34, what with aluminium tech barely started in the USSR and all. The AM-35/38 seems to have been quite different from the 12Y in many ways. No doubt the Russians learnt a whole lot from HS (and everybody else) but their engineering seems to have been first rate (their production methods may have been a different story). The V-2 is a sturdy and fairly efficient design, even if the fuel injection is rather simple. The same goes for the aero engines. And there is no way they could have adapted the design for a gun mounting through the prop hub. I am not aware of what other engine they used to do that with.

Could you please elaborate about the V2 being a direct descendant from the AM-38? AM-38 being diesel aero engine?

 

[Shortround6]

Early (late 20s early 30s) Soviet engine development is a mess.
The V-2 diesel dates to the early 30s and it's first use was in the BT-8M tank?

However a comparison of the bore and stroke shows it to be bigger than the Hispano engines and smaller than the AM series of engines. Building a diesel by boring (or using larger cylinder liners) and stroking an light weight aircraft engine seems dubious. Using thicker cylinder walls and a shorter stroke than the AM series of engines seems more likely but the branch of point would have been the M-34 engine and not the later ones.
The V-2 was in production and being fitted to tanks in 1939 (?)/1940.

 

[fliger747]

Distribution and type of armament varied in favor depending on the marksmanship and experience of the pilot. Not that their opinion was usually asked. The P-38 and F7F Bearcat had unusually powerful concentration of firepower on or near the CL. Better marksman and fliers appreciated a concentration of firepower. Wing guns were generally harmonized for a convergence at a certain distance, say 400 yards. A close grouping of the rounds would favor a pilot able to achieve a short accurate burst. More of a shotgun effect was more likely to obtain some hits for others. Against a lightly built aircraft, this might be enough. A tougher aircraft needing a more concentrated effect.

 

[Milosh]

I think an edit is required.

The P-38 and F7F Bearcat

 

[modelwiz]

Could you please elaborate about the V2 being a direct descendant from the AM-38? AM-38 being diesel aero engine?

AFAIK the AM-34 (M-34), which was developed in the early 30's, had a distinctly different layout not used in any contemporary engine-everything was shaft driven through bevel gears (it must have been torture to build a prototype!). Not a belt or chain anywhere. And it was a V-12 aero diesel. The AM-35 and AM-38 were further developments. All had superchargers. The VD-2, that was mounted in the BT-7 and BT-8 tanks in about 1937-38 was a reduced size imitation of the AM-38 with no parts really in common but even the bore and stroke had the same proportions. I should have stated that the V-2 design was a direct descendant of that of the AM-38. The V-2, which was used in the T-34, KV and even IS tanks of WWII was a further refinement of the VD-2. And it has been redeveloped, produced in mass quantities and installed in most tanks and many armoured vehicles and even tractors ever since WWII. It is a remarkably sound design. And creating a functional 3D model of it has been a tour de force of engineering study for me. I am not aware of any other significant aero diesel engine than the AM's in the 30's and 40's. The AM-38 and later AM-42 powered the Illyushin Il-2 ground attack aircraft. For more info you could google двигатель М-34 and tanslate the results - wikipedia in Russian has an excellent article on it in АМ-34 — Википедия

 

[tomo pauk]

AFAIK the AM-34 (M-34), which was developed in the early 30's, had a distinctly different layout not used in any contemporary engine-everything was shaft driven through bevel gears (it must have been torture to build a prototype!). Not a belt or chain anywhere. And it was a V-12 aero diesel.

The M-34 was not aero diesel, it used gasoline - just like most of other aero engines in service in the 1930s. Belts and chains were rarely used on aero engines of the time.
M-34 was a descendant of the M-17 engine, that can trace it's lineage to the unsupercharged BMW VI engine, that was a V12 version of engine that 1st run back in ww1. All of whom used gasoline.
Version of the M-17 was also used to power tanks.

The AM-35 and AM-38 were further developments. All had superchargers.

Of course all of them had superchargers.
The supercharged versions of the M-34 were also produced, can be denoted by suffix 'N'.

The VD-2, that was mounted in the BT-7 and BT-8 tanks in about 1937-38 was a reduced size imitation of the AM-38 with no parts really in common but even the bore and stroke had the same proportions. I should have stated that the V-2 design was a direct descendant of that of the AM-38. The V-2, which was used in the T-34, KV and even IS tanks of WWII was a further refinement of the VD-2. And it has been redeveloped, produced in mass quantities and installed in most tanks and many armoured vehicles and even tractors ever since WWII. It is a remarkably sound design. And creating a functional 3D model of it has been a tour de force of engineering study for me. I am not aware of any other significant aero diesel engine than the AM's in the 30's and 40's. The AM-38 and later AM-42 powered the Illyushin Il-2 ground attack aircraft. For more info you could google двигатель М-34 and tanslate the results - wikipedia in Russian has an excellent article on it in АМ-34 — Википедия

I'm having a hard time understanding how the VD-2 engine of 1937-38 was any kind of imitation of AM-38 engine of 1941. Both bore and stroke of V-2 and Mikulin's engines were different.
As above - there were no AM aero diesels around, for example the M-40 diesel was designed by Charomskiy. AM-42 powered no Il-2, apart perhaps prototype/test beds. Version of the M-34 for tanks was called GAM-34VT.
Don't think that anyone here is questioning the validity of V2 engine.
BTW - care to elaborate a bit on VD-2 engine? Googling about it returns nothing.

 

[wuzak]

There are zero belts or chains in a Merlin, Griffon, V-1710 or DB 601/3/5 either.

They all used some sort of gear drive for cam shafts, supercharger drive, oil pumps and other accessories.

 

[GrauGeist]

M-34 was a descendant of the M-17 engine, that can trace it's lineage to the unsupercharged BMW VI engine, that was a V12 version of engine that 1st run back in ww1. All of whom used gasoline.

Tomo, going by memory, I thought the AM-34 was born from a Fiat design and shared nothing in common with the M-17 except both being roughly the same size?

 

[Reluctant Poster]

Tomo, going by memory, I thought the AM-34 was born from a Fiat design and shared nothing in common with the M-17 except both being roughly the same size?

The analysis of the V2 by the British School of Tank Technology (May 1944) points out the similarities to the M34 and even includes a photo, although it does point out that there maybe internal differences. It further notes that the M34 was thought to have been originally designed by Fiat.

 

[tomo pauk]

Tomo, going by memory, I thought the AM-34 was born from a Fiat design and shared nothing in common with the M-17 except both being roughly the same size?

It shared plenty with M-17 - bore, stroke, and, unlike Fiat V12s, articulated connecting rods. Contrary to the M-17, it was an en-bloc engine, with DOHC valvetrain featuring 4 valves per cylinder (indeed, like Fiat's V12s). Why would the Italians design a big engine to the ideological enemy in early 1930s, while not making one for themselves is a mystery to me.

The analysis of the V2 by the British School of Tank Technology (May 1944) points out the similarities to the M34 and even includes a photo, although it does point out that there maybe internal differences. It further notes that the M34 was thought to have been originally designed by Fiat.

The V2 might as well be a derivative of M-34 engine - it shared features found on the later, including DOHC, 4 valves per cylinder, articulated connecting rods.
FWIW, no Soviet source states the M-34 as foreign-designed engine.

 

[Reluctant Poster]

It shared plenty with M-17 - bore, stroke, and, unlike Fiat V12s, articulated connecting rods. Contrary to the M-17, it was an en-bloc engine, with DOHC valvetrain featuring 4 valves per cylinder (indeed, like Fiat's V12s). Why would the Italians design a big engine to the ideological enemy in early 1930s, while not making one for themselves is a mystery to me.



The V2 might as well be a derivative of M-34 engine - it shared features found on the later, including DOHC, 4 valves per cylinder, articulated connecting rods.
FWIW, no Soviet source states the M-34 as foreign-designed engine

Agreed. The Fiat connection seems to have been western speculation. Gunston claimed the M34 was a monoblock M17, but others are not so sure. If it was true that would mean the V2 was originally a BMW design, which is what the Germans claimed.

 

[tomo pauk]

Agreed. The Fiat connection seems to have been western speculation. Gunston claimed the M34 was a monoblock M17, but others are not so sure. If it was true that would mean the V2 was originally a BMW design, which is what the Germans claimed.

While BMW genes can be traced from BMW VI -> M-17 -> M-34 -> V2, I'm not sure why would we accept that V2 was originally a BMW design. The 1st monobloc BMW V12 engine was the 117 of 1934 (36L, fork-and-blade rods) - the M-34 pre-dates it.

 

[GrauGeist]

It shared plenty with M-17 - bore, stroke, and, unlike Fiat V12s, articulated connecting rods. Contrary to the M-17, it was an en-bloc engine, with DOHC valvetrain featuring 4 valves per cylinder (indeed, like Fiat's V12s). Why would the Italians design a big engine to the ideological enemy in early 1930s, while not making one for themselves is a mystery to me.

The Germans were selling technology to the Soviets even by the late 30's, so an Italian designed engine made available to the Soviets comes at no surprise.

In regards to the M-17's similarities to the M-34: many engines in the aviation industry had parallels.
The V-1710 was a 60° V with four valves per cylinder driven by an overhead cam, just like the Merlin. They both had a 6" (152mm) stroke and a nearly identical bore: 5.4" (137mm) for the Merlin and 5.5" (140mm) for the Allison.
That however doesn't mean they shared any lineage as they were both developed independantly.

Also, from a visual standpoint, the M-17 doesn't bear much of a resemblance to the M-34.
However, the M-34 looks a great deal like Fiat's engines from the same time period, such as the AS.3 or the larger A.25 for example.