Merlin Motor Cannon, was it possible?

[fastmongrel]

Was there any reason why Rolls Royce couldnt have built a version of the Merlin that could be fitted with a cannon firing through the prop shaft. Hispano V12Y engines could be fitted with motor cannons as could the Rusain built versions of it, the Hispano is roughly similar in layout to a Merlin. When this idea first came to me I dismissed it only inverted V12s could carry a motor cannon I thought but then a thread on this forum made me go and do a bit of research into Russain fighters and I realised that wasnt true.

I quite like the idea of a Hurricane carrying a 20mm Hispano moteur-canon, without the large fuel tank the Spitfire carried in front of the pilot I wonder if there would have been room.

 

[tail end charlie]

My dear chap, simply out of the question, I mean Airfix would have to make new moulds.

I dont know but I think to do it you would have to start with it in the design, I think RR had enough on their plate as it was.

 

[Kurfürst]

Was there any reason why Rolls Royce couldnt have built a version of the Merlin that could be fitted with a cannon firing through the prop shaft.

Yup - the supercharger was mounted in the back of the engine block, and I believe it was in the way.

The Germans got around this by mounting the supercharger on the side, though possibly this was easier to do if the engine was inverted.

I am not sure how it was done on the Hispano-Suiza engines (French fighters and Russian Yakovles using derivates of the same engine).

 

[Colin1]

Was there any reason why Rolls Royce couldnt have built a version of the Merlin that could be fitted with a cannon firing through the prop shaft. Hispano 12Y engines could be fitted with motor cannons as could the Russian built versions of it, the Hispano is roughly similar in layout to a Merlin. When this idea first came to me I dismissed it only inverted V12s could carry a motor cannon I thought but then a thread on this forum made me go and do a bit of research into Russian fighters and I realised that wasn't true.

...without the large fuel tank the Spitfire carried in front of the pilot I wonder if there would have been room.

They certainly never tried
closest they got to firing through the hub was firing through the disc with either the 12.7mm or the 25.4mm and there were reservations on the latter.

hmmm, you want to take the large fuel tank out of an already short-legged fighter and put a motor-cannon in...

 

[fastmongrel]

They certainly never tried
closest they got to firing through the hub was firing through the disc with either the 12.7mm or the 25.4mm and there were reservations on the latter.

hmmm, you want to take the large fuel tank out of an already short-legged fighter and put a motor-cannon in...

I always thought the Hurricane only had a small gravity tank in front of the instrument panel and that its main fuel tanks were in the wing roots thats why I thought maybe the Hurricane would have had a bit more room for the extras than the Spitfire. Oh well obviously got that wrong

 

[Colin1]

I always thought the Hurricane only had a small gravity tank in front of the instrument panel and that its main fuel tanks were in the wing roots thats why I thought maybe the Hurricane would have had a bit more room for the extras than the Spitfire. Oh well obviously got that wrong

I may well have misinterpreted your earlier post
I thought you were talking about 'the Hurricane and the Spitfire', not 'the Hurricane unlike the Spitfire'.
As I recall, the Hurricane's fuselage fuel tank wrt the thrust line would have interfered with the motor cannon installation, along with possibly the hydraulic header tank so the fuel tank's inevitable omission would have affected the already modest range of the Hurricane too.

As mentioned in the thread, the biggest non-starter would be the location of the supercharger installation.

 

[Civettone]

The main fuel tanks of the Hurricane were in the wing roots! There was an armoured reserve tank in front of the cockpit.

Yup - the supercharger was mounted in the back of the engine block, and I believe it was in the way.

The Germans got around this by mounting the supercharger on the side, though possibly this was easier to do if the engine was inverted.

I am not sure how it was done on the Hispano-Suiza engines (French fighters and Russian Yakovles using derivates of the same engine).

Kurfürst, on a side note, did the installation of the larger supercharger of the 605AS give some problems in terms of space?
And is this also why they had problems coming up with two-stage superchargers?

Kris

 

[Kurfürst]

Hi Civettone,

I am not sure what kind of space issues you are interested in, but yes, the large AS/D type superchargers did require to enlarge the cowling. On the 109K prototype these were symmetrical, but if you look at drawing of a G-/AS, G-10 or K-4, you can see that the port cowling bulge is larger.
As for the two-stage supercharger, according to a document the 605L 2-stage s/c would fit into the existing AS/D cowling.

A bit offtopic, so lets leave the rest for the engine threads...

As for not coming up with one earlier, I believe the reason was rather found in the relatiely large displacement and compression ratios of German aero engines - they had much less need for powerful supercharging leading to the introduction of 2-stage s/cs to achieve similiar high altitude performance with the engines, compared to Merlins/Allisons. Simply one needs a lot more supercharging with 27 liter engine than with a ca 35 liter one to get the same performance, larger displacement engines can do that with smaller boost pressures. 2-stage supercharging, from what I have learned in this forum, has advantages in effiency at higher boost levels.

 

[NZTyphoon]

In the initial design stage for the Merlin there was some thought of developing the engine as an inverted Vee but Rolls-Royce and the Air Ministry chose the more traditional layout, which Rolls-Royce had used throughout most of its aero-engine designs.Although the supercharger was mounted at the back of the engine this wasn't the problem; the Hispano-Suiza 12Y had a rear mounted supercharger but it had a hollow drive shaft for the supercharger rotor, and the reduction gear at the front was also specifically designed to allow a motor cannon (Docavia 4 Le Dewoitine D. 520 page. 245.). The reason Hispano-Suiza designed its engines to mount motor cannon was because during WW I they had developed a geared version of the V-8 '8' series, the 8Cb which allowed a 37 mm cannon to be fitted to the [url=http://www.theaerodrome.com/aircraft/france/spad_xii.php] SPAD S. XII. As a result most inter-war Hispano aero engines were designed to use motor cannon.

 

[Civettone]

thx Kurfürst


Kris

 

[Colin1]

The main fuel tanks of the Hurricane were in the wing roots!

Gee thanks
and the exclam too, just in case anyone thought you were kidding. I think most of us know where the Hurricane kept the greater part of its fuel, what's obviously not apparent here is that the loss of roughly 30% of its fuel capacity to accommodate the unlikely prospect of a bigger gun would (hopefully) have been deemed unacceptable.

 

[spicmart]

Sorry, I know it's none of my business, but why was Kurfürst banned?

 

[fastmongrel]

Unfortunately even though Kurfurst had lots of excellent information which he put over very well he just couldnt stop his personal views coming through particulary when he felt he was losing an argument. He got warned many many times and I think his latest transgressions on the Bomber Command thread was the straw that broke the camels back. By his standards some of what he wrote wasnt bad but I think it was the general tone and my personal feeling that he was going down a very rocky road that simply wasnt going to end well that led to his ban.

If a mod gives you a warning and you dont back down you get what you deserve, we might not like them sometimes but they stop the place descending into anarchy.

 

[Civettone]

He has been banned before; I hope this time it will also not be permament ...

I'm against banning people ...

Kris

 

[Shortround6]

Was there any reason why Rolls Royce couldnt have built a version of the Merlin that could be fitted with a cannon firing through the prop shaft. Hispano V12Y engines could be fitted with motor cannons as could the Rusain built versions of it, the Hispano is roughly similar in layout to a Merlin. When this idea first came to me I dismissed it only inverted V12s could carry a motor cannon I thought but then a thread on this forum made me go and do a bit of research into Russain fighters and I realised that wasnt true.

There is also the question of where the intake manifolds are. The Hispano and Russian versions had both the intake and exhaust manifolds on the outside of the "V" leaving the inside totally free. The Hispano was also a rather large engine displacement wise (36 liters) for it's power and didn't need (or couldn't use) quite the supercharger installation that the Merlin could. The supercharger was offset somewhat low on the engine increasing the overall hight a bit but once again leaving the "V" clear.
The front gear case also has to be designed with the gun in mind with the prop shaft axis displace a great enough distance for the gun to clear the crankcase. I have read that some of the German engines came in two models. A fighter version and a bomber version with different distances between the propshaft and the crankshaft.
It pretty much means an engine has to be designed from the beginning to take a gun. Redesigning rear supercharger mounts and supercharger drives, rerouting ducts from supercharger to rear of inlet manifolds around the gun, designing new intake manifolds that will ensure proper distribution of the fuel/air mixture and clear the gun barrel and designing a new front gear case ( and in some cases a new crankcase to fit the gear case) may mean it was more trouble than it was worth to modify an existing engine to take a gun in the "V" firing through the hub.