WI RR Merlin or Allison had motor-canons?

[riggerrob]

Motor-canons were invented by Hispano-Suiza during WW1. The V-8 engine had a .303 Lewis machine gun laying between its cylinder banks and firing throughout by the propeller speed reduction unit.
HS engines were so popular they were license-built in the UK Woolsley), USA Wright Hisso) etc. during WW1.
By 1938, the HS 12Y engine was the best available 1,000 hp engine. Large numbers were built for the French Air Force and licensed to other countries, most notable by Klimov in the USSR. Most HS 12Y engine’s were built with HS 404, 20 mm motor cannons. See Justo Miranda’s new book “Enemy at the Gates, Panic Fighters” or the “Panic Fighter 1938” thread on www.alternatehistory.com.
WI Rolls Royce built a V-12 engine with a 20 mm motor-cannon?
WI Allison offered an optional 20 mm motor-cannon on their V-1710 engine?

 

[Peg Leg Pom]

The Luftwaffe would suffer heavier casualties in the Battles of France and Britain, and the lightly built Italian fighters would suffer badly in North Africa.

 

[tomo pauk]

Motor-canons were invented by Hispano-Suiza during WW1. The V-8 engine had a .303 Lewis machine gun laying between its cylinder banks and firing throughout by the propeller speed reduction unit.
HS engines were so popular they were license-built in the UK Woolsley), USA Wright Hisso) etc. during WW1.
By 1938, the HS 12Y engine was the best available 1,000 hp engine. Large numbers were built for the French Air Force and licensed to other countries, most notable by Klimov in the USSR. Most HS 12Y engine’s were built with HS 404, 20 mm motor cannons. See Justo Miranda’s new book “Enemy at the Gates, Panic Fighters” or the “Panic Fighter 1938” thread on www.alternatehistory.com.
WI Rolls Royce built a V-12 engine with a 20 mm motor-cannon?
WI Allison offered an optional 20 mm motor-cannon on their V-1710 engine?

By 1938, the best engine in service was Merlin II. It offered 1030 HP at 16250 ft, on 87 oct fuel. A HS 12Y engine that made 1000 HP did that on ~10000 ft and required 100 oct fuel. Most of actual engines installed on MS-406 fighters were capable for 860 HP at ~10000 ft (yes, the person who made entry about specifications for the MS 406 entry in Wikipedia messed up kW and HP). Soviets made the M-100 as licence of HS21Y, then M-103, and then M-105 (30-50% heavier than M-100) that finally gave more than 1000 HP at 13000 ft.
French were trying with supercharger made by engineers Szydlowsky & Planiol, that much improved altitude power and cut the difference by half vs. DB 601A and, later, vs. Merlin II/III. Unfortunately, the new versions (-45 and -49) were installed in small quantities on service aircraft, if ever the -49, and both DB and RR upped the bar. There was a reason why HS moved on the 12Z before occupation.

With that said - having a Merlin with prop cannon feature enables the Hawker and Supermarine to make a fighter that has a cannon in a trouble-free installation from the get go, and later to have a 3-cannon Hurricane and Spitfire. Should make a life of LW crewmen worse than it was the case.
V-1710 with prop cannon renders uneccessary the P-39 hoopla, so it can be a simple A/C. OTOH, V-1710 needed far more a better S/C than it needed the prop cannon.

 

[USS_Ward]

Nose guns do tend be more accurate too...

 

[sonofpegasus]

As a matter on interest what is the biggest calibre cannon that could be mounted in the v of a Merlin. Also how much of a redesign would the Merlin require to fit a motor cannon in the V.

 

[ennobee]

In the overall scheme of things, I don't believe a Merlin engine with built-in autocannon would change much. It might give the early Spitfires and Hurricanes a bit of an extra punch, but it will not give the UK enough planes and pilots to significantly change the Battle of France, nor prevent the bombings of London in the Battle of Britain. The only long-term effect I could think off would be that now Napier would build an autocannon into their new Sarbre engine, slowing it's deployment even more. Still, if we extend the lifespan of the Hawker Hurricane by one year, it will not be because the last generation of autocannon-Hurricanes is so fantastic but because the first generation of autocannon-Typhoons has even more teething problems slowing down it's deployment.

The autocannon-Allison engine, if it were available by 1938, however would -like @tomo pauk already mentioned- butterfly away the Bell P-39 and possibly Bell as a major aircraft as well. It may also give the Curtiss P-40 the extra punch it needed against the Japanese. It would however not change the main cause of Japan's air superiority, namely that it caught the US and UK unaware and with outdated training and dogfighting doctrines.

Also, it would not change the US Navy's preference for air-cooled radial engines.

 

[marathag]

Allison

Wanting a Cannon between the Vee means redoing the intake system and gear reduction housing.

Doable, and best when the early Merlin was using the ramp heads and decided to switch to the simpler flat head design

 

[tomo pauk]

In the overall scheme of things, I don't believe a Merlin engine with built-in autocannon would change much. It might give the early Spitfires and Hurricanes a bit of an extra punch, but it will not give the UK enough planes and pilots to significantly change the Battle of France, nor prevent the bombings of London in the Battle of Britain. The only long-term effect I could think off would be that now Napier would build an autocannon into their new Sarbre engine, slowing it's deployment even more. Still, if we extend the lifespan of the Hawker Hurricane by one year, it will not be because the last generation of autocannon-Hurricanes is so fantastic but because the first generation of autocannon-Typhoons has even more teething problems slowing down it's deployment.

Having a provision for cannon can make a difference if engine power is down to 700-1100 HP. With +-2000 HP (as Sabre/Vulture/Centaurus were designed), that need is moot - we can have 4 cannons in the wing ans still be blazing fast & climb well.
We can think of many, many scenarios (techincally- or strategically-minded, or both) where RAF does either a bit better or a lot better in 1940 even if the engines stay as they were historically.

Also, it would not change the US Navy's preference for air-cooled radial engines.

Certaily not. That preference was pretty much hard-baked there

 

[riggerrob]

Yesterday I got a close look at both Allison and Merlin engines at the museum in Langeley, B.C.
Both Allison and Merlin fhad superchargers mounted at the rear of nds of their crankshafts and intake manifolds ran forward, low between the V cylinder banks. Central intake manifolds hogged the best position to mount a cannon. They filled their “Vs” with intake manifolds and spark-plug wires.
The lowest you could mount a cannon would be level with valve covers (ala.cowl-mounted MGs on P-40 Warhawk).

OTOH WW1 vintage Hispano-Suiza engine’s had carburetors mounted high, level with intake valves. This left the deepest part of the”V” free to mount a Lewis gun.
Later Hispano-Souza engines also mounted super chargers at the rear end of the crankshaft, but had bifruncated intake manifold sThe 1938-vintage Hispano-Suiza 12Y took a different approach by routing intake manifolds outboard, again leaving the deepest part of the “V” free for installing a cannon.

 

[Cryhavoc101]

There are several issues with doing the Merlin Motor canon thing

Firstly Supercharger is in the way - and these got bigger!

Secondly both the Spitfire and Hurricane had a fuel tank or tanks between the Engine and Cockpit

Thirdly the motor cannon either fires through the Prop using interrupter gearing or the prop is raised by a gearing so that the weapon can fire through the hub as shown below (the 'Vees' of the cylinders have been removed from this HS 12Y Engine).

Note the ickle supercharger - awwwww bless

You can can see then how much of an impact to the engine design having a motor cannon inflicts

In my opinion too much in the way of compromise and it limits growth etc

Where the rear of the weapon and magazine is - this is where the Super charger and then Fuel tank/tanks fit on both the Spitfire and Hurricane (this is a PR Spit so no guns but it does show the position of the Fuel tanks etc)

Basically I think RR had enough on its plate getting over the Ramp Head debacle to also ask them to also include a Motor Cannon.

Shoe horning the HS404 into the wing was by far the lesser of 2 evils - I note that BF109 initially resorted to gondolas in order to carry 20mm cannon.

 

[tomo pauk]

There are several issues with doing the Merlin Motor canon thing

Firstly Supercharger is in the way - and these got bigger!

Secondly both the Spitfire and Hurricane had a fuel tank or tanks between the Engine and Cockpit

Thirdly the motor cannon either fires through the Prop using interrupter gearing or the prop is raised by a gearing so that the weapon can fire through the hub as shown below (the 'Vees' of the cylinders have been removed from this HS 12Y Engine).

Motor cannon = a cannon that fires through the prop shaft. Cowl-mounted (like at La-5) and wing-root-mounted cannons/guns (like at Fw 190) are not motor cannons.
With a V12 engine designed to have a motor cannon, and an airforce requiring such a wepon, aircraft designer will fit fuel tanks elsewhere - in the wings and/or under/aft the pilot.
'Vees' is what defined V12 engines, and were present on the HS 12X, Y, or Z engines by default.

Basically I think RR had enough on its plate getting over the Ramp Head debacle to also ask them to also include a Motor Cannon.

Agreed.

Shoe horning the HS404 into the wing was by far the lesser of 2 evils - I note that BF109 initially resorted to gondolas in order to carry 20mm cannon.

Granted, two cannons in the wing are not just easier to fit on Spitfire, but also bring more firepower than a single cannon, even if it is on centreline.
Bf 109 initially carried cannons within the wings, in series on 109E3/E4/E7, retrofit on 109E1, and experimentlly on 109D. The gondolas were mid-war add-on, and not always carried.

 

[Peg Leg Pom]

There are several issues with doing the Merlin Motor canon thing

Firstly Supercharger is in the way - and these got bigger!

Secondly both the Spitfire and Hurricane had a fuel tank or tanks between the Engine and Cockpit

Thirdly the motor cannon either fires through the Prop using interrupter gearing or the prop is raised by a gearing so that the weapon can fire through the hub as shown below (the 'Vees' of the cylinders have been removed from this HS 12Y Engine).

Note the ickle supercharger - awwwww bless

You can can see then how much of an impact to the engine design having a motor cannon inflicts

In my opinion too much in the way of compromise and it limits growth etc

Where the rear of the weapon and magazine is - this is where the Super charger and then Fuel tank/tanks fit on both the Spitfire and Hurricane (this is a PR Spit so no guns but it does show the position of the Fuel tanks etc)

Basically I think RR had enough on its plate getting over the Ramp Head debacle to also ask them to also include a Motor Cannon.

Shoe horning the HS404 into the wing was by far the lesser of 2 evils - I note that BF109 initially resorted to gondolas in order to carry 20mm cannon.

This is all true but not really relevant as if it was intended for the Merlin to have a Motor Cannon then it would have been designed from the start with that aim in mind, as would the aircraft intended to use the Merlin.

 

[Cryhavoc101]

This is all true but not really relevant as if it was intended for the Merlin to have a Motor Cannon then it would have been designed from the start with that aim in mind, as would the aircraft intended to use the Merlin.

Yes but in order to do so it would have imposed compromise into the design - not worth it IMO

 

[marathag]

You can can see then how much of an impact to the engine design having a motor cannon inflicts

In my opinion too much in the way of compromise and it limits growth etc

Where the rear of the weapon and magazine is - this is where the Super charger and then Fuel tank/tanks fit on both the Spitfire and Hurricane (this is a PR Spit so no guns but it does show the position of the Fuel tanks etc)

Basically I think RR had enough on its plate getting over the Ramp Head debacle to also ask them to also include a Motor Cannon.

so yeah, intercooler is in the way, and the fuel tank.
CG was close to the CoG, to limit trim changes as fuel is burned.

US usually wanted the oil tank in this location, less a problem than fuel

Now Supermarine could do what they did later

and put tanks in the leading edge, and relocate the intercooler

 

[tomo pauk]

so yeah, intercooler is in the way, and the fuel tank.
CG was close to the CoG, to limit trim changes as fuel is burned.

That is a cutaway of the Merlin 61, outfitted with a 2-stage supercharger (note two impellers) and intercooler. The Merlins used on most of pre-1943 aircraft were outfitted with 1-stage superchagers, without intercooler (like something like this: link)
Granted, the cannon will most likely need to go away once a 2-stage S/C is thinkered with.

US usually wanted the oil tank in this location, less a problem than fuel
Now Supermarine could do what they did later
and put tanks in the leading edge, and relocate the intercooler

On P-40 (no letter), P-40B and P-40C, the oil tank was located behind the pilot (link). Once the armament was relocated in wings with P-40D, the oil tank was relocated on a place previously occupied by HMG ammo boxes.
As for Spitfire - it was a big aircraft when compared with vast majority of other European fighters, with a lot of space suitable for fuel tanks, like under and behind the pilot, and indeed in the wings.

 

[marathag]

On P-40 (no letter), P-40B and P-40C, the oil tank was located behind the pilot (link). Once the armament was relocated in wings with P-40D, the oil tank was relocated on a place previously occupied by HMG ammo boxes.

Interesting

On the P-36. Looks like there were more changes behind the firewall than I had assumed earlier

 

[Cryhavoc101]

so yeah, intercooler is in the way, and the fuel tank.
CG was close to the CoG, to limit trim changes as fuel is burned.

US usually wanted the oil tank in this location, less a problem than fuel

Now Supermarine could do what they did later

and put tanks in the leading edge, and relocate the intercooler

That leading edge tank was in addition to the 2 fuselage tanks not instead of and they appear to be a lot smaller than the 48 and 37 gal tanks behind the engine

Be interesting to see what their capacity was though?

 

[Rickshaw]

Something that appears to be missed when comparing the Merlin to the German engines. The German engines were inverted V, whereas the Merlin was an upright V. This left a lot more room for a motor cannon on the German engines than the British one. There were less mechanical gadgets in the way. When coupled with a gearbox which raises the thrust line even higher, there was even fewer problems.

Now, how about giving the Merlin a gearbox to raise it's thrust line? It would make for a deeper fuselage, having a motor cannon above the engine. It would it's installation easier and its ammunition storage easier IMO. It would not get in the way of the supercharger behind the engine and it could have ammunition stowed on either side.

However, IMO there is actually no advantage to the motor cannon, apart from increased accurarcy. Wing mounted cannons are equally free of the engine and allow a larger spread of fire. This in turn results in a greater chance of hitting the target being fired on. It allows the fuselage to mount larger fuel tanks and superchargers. None of these things should be sneezed and handwaved away.

 

[riggerrob]

Justo Miranda suggests that HS 404 cannon was designed light because they expected it to be stiffened by the crankcase. When Britain tried wing-mounted 20mm cannons, they took a while to de-bug feed problems.
Spitfires needed repeated wing reinforcements to accommodate heavier guns and faster air speeds.
WI Supermarine installed extra fuel tanks in wing root, behind wheels?

 

[Rickshaw]

Justo Miranda suggests that HS 404 cannon was designed light because they expected it to be stiffened by the crankcase. When Britain tried wing-mounted 20mm cannons, they took a while to de-bug feed problems.
Spitfires needed repeated wing reinforcements to accommodate heavier guns and faster air speeds.
WI Supermarine installed extra fuel tanks in wing root, behind wheels?

Basically there isn't room. The wing is thin there and it is bent upwards for the most part into a gullwing to meet the fuselage at that point. Yes, the wing needed stiffening but so would any wing which was designed originally in 1932.