RAF after BoB: mid-term strategy, tactics technology?

[Juha]

Indeed, my bad

Still, Hitler ordered a redeployment of some of his armed forces from SU to Italy.

In the end only LAH went to Northern Italy and after leaving its tanks to the other 2 SSPzGrDivs of the Corps (it picked up new ones on the way to Italy), 2nd and 3rd SSPzGrDivs had to be diverted to Mius River where Soviet forces were close to achieving a breakthrough and in fact suffered there heavier losses than during the Oper. Zitadel (the German offensive at Kursk).

Juha

 

[OldSkeptic]

In 1940/41 Commonwealth forces had engaged Germany in Norway, Belgium and France. Withdrawn its expeditionary forces intact (if ill equipped) from the continent (together with a substantial French force). Engaged the Italian forces with a supply line that extended around the Cape, taken Ethiopia, Eritrea, Somaliland, Iraq, Syria and Lebanon whilst defending Britain against a seaborne invasion threat and an actual air assault as well as showing its determination to prosecute the war by the sad destruction of the French fleet and diverting forces to defend Greece and the Far East to the extent of sending an armoured division to Egypt whilst the invasion threat was at its highest. All against the background of a continuous naval battle from the Channel to the Indian Ocean and sending war resources to Russia in 1941. Not to mention starting a priority air assault against Germany.

The detail had to meet the exigencies of the moment and hindsight shows us where the execution was flawed but the strategy was clear. To risk defeat at home in order to clear the enemy from Africa and remove Italy from the war whilst acting to engage the USA and USSR in the war to allow a return to a continental assault on Germany from the west in concert with the night bombing campaign over Germany. A year later this is what happened.

A lot of that was post war rationalisation. At the time they were totally confused as to what they were doing or wanted (at one point they nearly went to war with the USSR...). Plus they had aspirations far beyond their capabilities.

Greece was the classic. Even the Greeks didn't really want the British in, because (correctly) they argued that if they did then the Germans could come in and they were handling the Italians quite well by themselves. Which the Germans did and very quickly cleared them out. At that time the British Army was in no shape to take on the Germans (or the Japanese).

Instead of focus and winning one thing at a time and rebuilding and retraining their army until they could take on the Germans on something like an equal basis, they threw away large numbers of irreplacable troops in largely pointless exercises. Even by '42 Britain was hitting manpower limits.

To claim afterwards that it was some sort of a win because Germany redirected a couple of divisions towards them, while they themselves lost far more, is a bit of stretch. At that time the British themselves certainly didn't think so, questions in Parliament, no confidence votes and all that and Churchill and Allan Brooke were in despair.

 

[tomo pauk]

Sorry for a late reply

...
Supermarines stopped working on the 324/327 in 1938, having never received an order to proceed. So that wasn't an issue.

Okay, thanks.

It is telling that the Air Ministry chose the "interim" Mk V over the more advanced Mk III. The Mk III was refined aerodynamically and would have (probably) been a match for the Fw 190A and Bf 109F.

Not going with the Mk. III seem like a bad idea indeed.

A Hercules version, like the Griffon version, would have required significant strengthening of the fuselage. That adds weight. As does the need, identified earlier, to install counterweights in the tail to correct the CoG.

The Spitfire XIIs were conversions of the Spit V at 1st - seems like not much strengthening was not needed after all? The weight of the Hercules Spitfire should be somewhere in between the Spit Vb and XII, ie. at about 7000 lbs.

The Centaurus was somewhat closer in size (frontal area) to the Vulture and Sabre than the Hercules was to the Merlin.

Wikipedia gives 55 in dia for both Centaurus and Hercules, and, indeed, the R-2600 - wonder whether there are factory specs anywhere to get the real measures?

Let's look at the prop diameters again.
Mk V and Mk IX had prop diameter of 10'9".
Mk XII and MK XIV had a prop diameter of 10'5". The difference to the Merlin types is due to the lower thrust line.
The Hercules is ~10" taller than the Griffon. So we can expect a reduction of thrust centreline of ~5". That would mean a prop of ~9'7". That is a reduction of area of 21% over the V/IX and 15% over the XII/XIV.
The shorter engine may give some extra clearance, so if we assume a diameter of 10' that is still a loss of 13% and 8% respectively.

Thanks again. We can recall that Germans installed, on a captured Spit V, the DB-605A with a 3m (9.84 ft) prop, on a distinctively lower thrust line than what would be for Hercules. The Italian V-12 fighters also received a low-thrust DB engine coupled with 3m prop, the combination worked fine. The Soviets managed to convert both Lagg-3 and Yak-3 to radial powerplants.
Vs. the Merlin 45 and it's 3-bladed prop, the 4-bladed prop should cater a good deal for the lost prop area.

As regards to adding blades, the XIV got 5 blades in 1943. A 5 blade prop didn't exist in 1941 - it would have to be built.
Also, due to the smaller diameter the XIV spun its prop faster. The Hercules VI would need new reduction gearing to do that.
Also, ~1/5-1/4 of the prop will be blocked by the engine behind. The frontal area of the Bristol being roughly twice that of the Griffon.

I'm not trying to have a 5-bladed prop in 1942
The 'blocked' part of the airframe seem not to hamper very much the radial-engined fighters.

 

[tomo pauk]

This seems like another one of those ideas/projects that requires working on a version of plane that will NOT be very good in service for 1 to 2 years so you can be ready with a tooled up production line when the version of the engine you really want to use shows up.
It also requires a fair amount of jiggery-pokery to get it to work.

The Spitfire V was a most numerous Spitfire mark from mid/late 1941 to start of 1944 - not what we want to have against a 400 mph opposition? The British can access the NACA data by early 1942, and introduce improved radial engine installation in early 1943, that should give some extra performance.

AS for availability of Hercules engines, details seem to be a bit sketchy but it took until Dec of 1941 to get the first 200 Short Stirlings.
The first Wellington Prototype with Hercules engines flew May 19th 1939 but the first production version didn't fly until the Jan of 1941 with the Hercules XI engine.

Thanks.

It is not question of unbolting the Merlin and it's radiators and bolting on a Hercules "power egg" and bashing some sheet metal to fill the gaps. The Hercules has a higher carburetor than the Sakae and some other radial engines. It often used a remote drive to the accessories. Good for servicing the accessorizes, not so good for a short engine installation. The exhaust system is going to offer a lot less exhaust thrust than the Merlin. The cowl is not exactly low drag.

The lower, but wider intake on the Hercules might solve the issue, at least a good deal of it. Preferably also a longer one, like at P-40s and Allison Mustangs. The unrestricted, external intake is an advantage vs. BMW's internal intake.
If we add exhaust thrust HP equivalent to the Merlin 45's power (+10% at 15000 ft, with usual, non-individual exhausts), it's total of 1430 HP at 15500 ft. The lousy exhaust system of the Hercules will still give some extra power there, +5%? Makes 1620 HP total.
The BMW-801C has individual exhausts, for 12% extra power*? 1360 HP + 163 HP = 1523 HP at 15100 ft. Yet, the Fw-190A-1/A-2 can beat 400 mph mark even on 'Kampfleistung', ie. with 1292 + 155 = 1447 HP at 14435 ft (no ram), despite the less-than-ideal internal intakes. Maybe Bill/drgondog might help us with these power vs. speed vs. drag questions.
Maybe installing a fully-covered undercarriage might've really helped, regardless the engine on the Spitfire? Ditto for individual exhausts, and longer ramming intake?

Everything can be 'fixed' with enough time and effort but the longer it takes the less need for it.
The Early Hercules doesn't offer anything the Melrin doesn't at the time and even a Hercules VI giving 1545hp at 15,500ft (Lumsden) is fighting higher weight and much higher drag than the Merlin.

Interestingly enough, Lumsden gives for the Herc IX: 1590 HP at 13500 ft on 87 oct, and 1510 HP at 11250 ft on 100 oct fuel? Typo somewhere?
Even with lower power listed, in 1941 there is more power under 17-18000 ft from the Herc IX than from any Merlin available, including the Mk. XX - the over-boosting of those was allowed from early 1942 on.

*at least when going by the chart for the DB-601A, where 12% extra power via the exhaust thrust is available at 4500 m; for individual exhausts

 

[wuzak]

The Spitfire XIIs were conversions of the Spit V at 1st - seems like not much strengthening was not needed after all? The weight of the Hercules Spitfire should be somewhere in between the Spit Vb and XII, ie. at about 7000 lbs.

The XIIs needed stronger longeropns in the fuslage to take the engine loads.

Wikipedia gives 55 in dia for both Centaurus and Hercules, and, indeed, the R-2600 - wonder whether there are factory specs anywhere to get the real measures?

RRHT may be able to help with the Bristols.

What I was saying is that the Sabre was 46" high x 40"wide and the Vulture something similar. So the size and shape of these are closser to the round engines than the Merlin or Griffon (which were tall and narrow).

Sorry for a late reply



Okay, thanks.



Not going with the Mk. III seem like a bad idea indeed.



The Spitfire XIIs were conversions of the Spit V at 1st - seems like not much strengthening was not needed after all? The weight of the Hercules Spitfire should be somewhere in between the Spit Vb and XII, ie. at about 7000 lbs.



Wikipedia gives 55 in dia for both Centaurus and Hercules, and, indeed, the R-2600 - wonder whether there are factory specs anywhere to get the real measures?



Thanks again. We can recall that Germans installed, on a captured Spit V, the DB-605A with a 3m (9.84 ft) prop, on a distinctively lower thrust line than what would be for Hercules. The Italian V-12 fighters also received a low-thrust DB engine coupled with 3m prop, the combination worked fine.

The DB engines are similar in shape (although upside down) to the Merlin. The frontal area is little changed.

The Soviets managed to convert both Lagg-3 and Yak-3 to radial powerplants.

In those cases the power gain was more substantial than we are suggesting for the Merlin -> Hercules.

Vs. the Merlin 45 and it's 3-bladed prop, the 4-bladed prop should cater a good deal for the lost prop area.
I'm not trying to have a 5-bladed prop in 1942

More blades may also cause instability. It happened with the IX, requiring more rudder area, and the P-51B.

The 'blocked' part of the airframe seem not to hamper very much the radial-engined fighters.

Usually because they swung a bigger prop.

The Fw 190 had a 3.3m (10'11.75") diameter prop.

 

[Aozora]

Interestingly enough, Lumsden gives for the Herc IX: 1590 HP at 13500 ft on 87 oct, and 1510 HP at 11250 ft on 100 oct fuel? Typo somewhere?
Even with lower power listed, in 1941 there is more power under 17-18000 ft from the Herc IX than from any Merlin available, including the Mk. XX - the over-boosting of those was allowed from early 1942 on.

*at least when going by the chart for the DB-601A, where 12% extra power via the exhaust thrust is available at 4500 m; for individual exhausts

Weight of Hercules XI (dry) = 1,870 lbs for 1,460 hp max; Hercules VI XVI = 1,930 lbs for 1,675 hp

Weight of Merlin XX = 1,450 lbs for 1,480 hp max; Merlin 66 = 1,650 lbs for 1,750 hp @ +18 lbs boost or 2,000hp @ +25 lbs boost using 100/150 grade fuel

Question: what was the fuel consumption of the Hercules vs the Merlin?

While it might be interesting to compare a radial engined Spitfire with the Fw 190, the Fw 190 was designed from the outset to be powered by a radial engine, with all that entailed in regards to weight distribution, fuselage design, how the control surfaces were jigged, etc. To expect a similar performance from an airframe that was designed for a lighter, far more streamlined engine, without a major redesign? Highly unlikely. To redesign the Spitfire to cater for the Hercules would have been a major exercise, plus there would be major disruption of the production lines at, arguably, one of the most important times of the war

Why would anyone bother redesigning the Spitfire to use the Hercules when there were already perfectly good Merlins available, in quantity, with the more powerful Griffon engines pending?

Interesting article on Sleeve-Valve engines vs Poppet valve: http://www.enginehistory.org/members/articles/Sleeve.pdf

 

[stona]

Not going with the Mk. III seem like a bad idea indeed.

It was a matter of expediency. From StH.

'It was obvious from trial reports that the converted Spitfire Mk 1 with the modified engine was an unqualified success and the Air Ministry wanted to have a production machine in service in large numbers as quickly as possible. Supermarine could not produce the projected Mk III Spitfire in the time specified by the Air Ministry and a compromise had to be reached. It was decided that the Merlin 45 would be married to a strengthened Mk I airframe, a larger radiator installed and the resulting Spitfire be called the F Mk V. The contract for 1,500 Mk III Spitfires was cancelled and the serials allocated to the new Mk V."

My italics.

If only the RLM could have made decisions like that

Cheers

Steve

 

[Juha]

Yes
the stop-gap solutions were the rule in Spit development, all the main production machines were stop-gaps (Mks V, IX and XIV) During a war it is better to choose good-enough that can be delivered soon enough than to wait the optimal solution and took heavy losses while waiting its perfection. Of those versions designed to give a significant boost of performance only Mk VIII was produced in significant numbers (was that 1,600+) but still significantly less than its stop-gap half-sister Mk IX (was that appr. 6,500)

 

[stona]

Yes
the stop-gap solutions were the rule in Spit development, all the main production machines were stop-gaps (Mks V, IX and XIV) During a war it is better to choose good-enough that can be delivered soon enough than to wait the optimal solution and took heavy losses while waiting its perfection. Of those versions designed to give a significant boost of performance only Mk VIII was produced in significant numbers (was that 1,600+) but still significantly less than its stop-gap half-sister Mk IX (was that appr. 6,500)

It was the result of a superb airframe. As Rolls Royce developed better engines it was an obvious expedient to bolt them on to airframes already in production and requiring minimal (if any) alterations. The Spitfire and Bf 109 stand head and shoulders above the rest in this particular respect.

The Fw 190 D was also a stop gap that proved its worth in the limited time it had before the end of the war. It even underwent its own development whilst waiting for the Ta 152 to arrive.

Cheers

Steve

 

[tomo pauk]

Weight of Hercules XI (dry) = 1,870 lbs for 1,460 hp max; Hercules VI XVI = 1,930 lbs for 1,675 hp

Weight of Merlin XX = 1,450 lbs for 1,480 hp max; Merlin 66 = 1,650 lbs for 1,750 hp @ +18 lbs boost or 2,000hp @ +25 lbs boost using 100/150 grade fuel

Both timeline and weights for the Merlins are off.
In 1941 Merlin XX was making, in all-out level flight, some 1400 HP on rated boost (+12 lbs/sq in) at 8000 ft. 1st notes of +14 psi of allowed boost were issued in late Nov 1942. The Merlin 66 was introduced in (mid?) 1943, the 150 grade fuel was introduced during the Spring of 1944.

For the single stage Merlin, we need to add some 300+ lbs for cooling system, so it's now within 100 lbs of difference vs. Hercules XI. Two stage Merlin needs 500+ lbs of cooling inter-cooling (in P-51B it was 663 lbs, but the radiators were bigger there?) - that makes 2150-2200 lbs, together with engine itself. Two stage Merlin will also increase aircraft's drag, due to the need to stick out another radiator in the slipstream.

Question: what was the fuel consumption of the Hercules vs the Merlin?

I'd also appreciate the data.

While it might be interesting to compare a radial engined Spitfire with the Fw 190, the Fw 190 was designed from the outset to be powered by a radial engine, with all that entailed in regards to weight distribution, fuselage design, how the control surfaces were jigged, etc. To expect a similar performance from an airframe that was designed for a lighter, far more streamlined engine, without a major redesign? Highly unlikely.

For 1942 (Herc VI vs. available BMW 801s in respective airframes) I expect at least better climb rate, due to a far better power to weight ratio. A major redesign was not required for the La-5, nor for the Ki-100, both worked fine.

To redesign the Spitfire to cater for the Hercules would have been a major exercise, plus there would be major disruption of the production lines at, arguably, one of the most important times of the war

Disagreed about the need for a 'major exercise'. No major disruption of the production lines, either - it would require a minor modification of one of production lines. Once Germans turn East, there is much less pressure on British.
If someone is bothered about the production lines after the BoB, maybe it would be handy to phase out the Hurricane from production. 'Production' of pilots was a much more important thing anyway.

Why would anyone bother redesigning the Spitfire to use the Hercules when there were already perfectly good Merlins available, in quantity, with the more powerful Griffon engines pending?

How ever the Merlins were good, the Spitfire did not received the Merlin XX (bar the token numbers for the Spit IIC), but the second best, Merlin 45, that was also later in production than the Mk. XX. The two stage Merlin was considered for the Spitfire only once LW extracted a major toll on the Spit V.
The Griffon might be pending, but it was not available for 1941-42 time frame.

Interesting article on Sleeve-Valve engines vs Poppet valve: http://www.enginehistory.org/members/articles/Sleeve.pdf

Thanks.

 

[wuzak]

Both timeline and weights for the Merlins are off.
In 1941 Merlin XX was making, in all-out level flight, some 1400 HP on rated boost (+12 lbs/sq in) at 8000 ft. 1st notes of +14 psi of allowed boost were issued in late Nov 1942. The Merlin 66 was introduced in (mid?) 1943, the 150 grade fuel was introduced during the Spring of 1944.

All true.

The Merlin 61 Mk IX was introduced in July 1942.

I doubt a Hercules-Spitfire would perform as well as the IX, certainly not at higher altitudes. And probably wouldn't be available any sooner.

For the single stage Merlin, we need to add some 300+ lbs for cooling system, so it's now within 100 lbs of difference vs. Hercules XI. Two stage Merlin needs 500+ lbs of cooling inter-cooling (in P-51B it was 663 lbs, but the radiators were bigger there?) - that makes 2150-2200 lbs, together with engine itself. Two stage Merlin will also increase aircraft's drag, due to the need to stick out another radiator in the slipstream.

The two stage Merlin will still have less drag than the typical Hercules installation of the time.

The Hercules XI is also a lower altitude engine than the two stage Merlin.

For 1942 (Herc VI vs. available BMW 801s in respective airframes) I expect at least better climb rate, due to a far better power to weight ratio. A major redesign was not required for the La-5, nor for the Ki-100, both worked fine.

I would suggest an improvement in climb rate could be achieved by fitting the Merlin XX. And it would require a lot less work to do. You could dump the Hurricane, or convert them to the Hercules (which would suit their soon to be role of ground pounding better).

The Ki-100 gained about the same hp over the Ki-61 as the Hercules would over the Merlin 45. It also lost a little bit of weight. Performance was about the same.

The La-5's power gain was about twice that of the Hercules over Merlin. Probably greater than that over the altitude range. The in-line used in the LaGG-3 wasn't that brilliant. The weight gain was ~900lb.

A Hercules-Spitfire would work. The question is whether it would be worth the effort.

Disagreed about the need for a 'major exercise'. No major disruption of the production lines, either - it would require a minor modification of one of production lines. Once Germans turn East, there is much less pressure on British.
If someone is bothered about the production lines after the BoB, maybe it would be handy to phase out the Hurricane from production. 'Production' of pilots was a much more important thing anyway.

The problem was that there was the development of the VII and VIII, which needed modifications to production lines, production of the IX, which needed fewer changes, development of the Griffon Spitfire and general performance improvements to the V. Something has to be sacrificed to perform the modifications for the Hercules-Spitfire.

How ever the Merlins were good, the Spitfire did not received the Merlin XX (bar the token numbers for the Spit IIC), but the second best, Merlin 45, that was also later in production than the Mk. XX. The two stage Merlin was considered for the Spitfire only once LW extracted a major toll on the Spit V.

The two stage Merlin was being tested in the Spitfire III before it became clear that the IX was necessary.

 

[wuzak]

fuel cons | gipsy major | ib | 1946 | 1809 | Flight Archive

This gives the consumption of the (post war) Hercules 630 as:
0.8/0.86 pt/bhp/hr at maximum power, 1,795hp @ 7,250ft.
0.68/0.73 pt/bhp/hr at maximum cruise power, 1,550hp @ 4,750ft.

The Merlin 620 (also post war) is given as
0.669 pt/bhp/hr at maximum power, 1,795hp @ 4,500ft.
0.517 pt/hp/hr at max continuous, 1,175hp @ 10,250ft.

miles | bell aircraft | 1946 | 2181 | Flight Archive provides the corrections for the Merlin's figures.

It also gives values for maximum weak mixture cruise for the Hercules, which is:
0.465pt/hp/hr, 1,330hp @ 9,250ft.

Thanks to former member J.A.W.

 

[Aozora]

For the single stage Merlin, we need to add some 300+ lbs for cooling system, so it's now within 100 lbs of difference vs. Hercules XI.

You are ignoring the weight distribution;all of the extra weight - and drag - of the Hercules would be well forward of the Spitfire's cg, with no cooling system to help counter-balance it. The only way that such a weight transfer could be compensated for would be to use heavy ballasting, meaning extra weight. Chances are the tail surface would need to be redesigned because of the Hercules' different thrust line

Two stage Merlin needs 500+ lbs of cooling inter-cooling (in P-51B it was 663 lbs, but the radiators were bigger there?) - that makes 2150-2200 lbs, together with engine itself. Two stage Merlin will also increase aircraft's drag, due to the need to stick out another radiator in the slipstream.

Can't quite work out the maths here - the cooling system of the two-stage Merlin did not weigh an extra an extra 2,150 - 2,200lbs over the weight of the engine. The extra drag of the new radiator installation, which did, at least, contribute some thrust because of the Meredith effect (albeit not as efficiently as the P-51's installation), would have been nothing like the extra drag developed by the Hercules engine installation, as it was manufactured in 1941. The exhaust-collector system alone added to the drag and contributed none of the jet-thrust of the two-stage Merlin's exhausts.

For 1942 (Herc VI vs. available BMW 801s in respective airframes) I expect at least better climb rate, due to a far better power to weight ratio.

Not with the extra weight and drag of the Hercules.

A major redesign was not required for the La-5, nor for the Ki-100, both worked fine.

I disagree that a major redesign wasn't needed for both the LaGG 3 to La-5 and Ki-61 to Ki-100: the LaGG's wooden airframe was more easily adapted to such a redesign, while the Ki-100 benefited from Japanese studies of the Fw 190. Both engine installations were far more efficient than anything the British had in 1941. It would have taken a major effort to redesign both the Spitfire airframe and the Hercules installation (including a complete rethink by Bristol on how to design exhaust systems) before the combination would have been worthwhile to be used in frontline operational service. It goes back to the question, why do it at all when installing the Merlin 60 series would have been so much easier?

Disagreed about the need for a 'major exercise'. No major disruption of the production lines, either - it would require a minor modification of one of production lines. Once Germans turn East, there is much less pressure on British.

In 1941 the British would have had no idea that the bulk of the Luftwaffe would be stuck on the Eastern front for over two years - it would have been foolish in the extreme not to have planned for the possibility that the Germans would be able to start a new "Battle of Britain" in 1942. The Spitfire III was dropped in favour of the "interim" Spitfire V to avoid too much disruption to the assembly lines. Why would a redesign to accommodate the Hercules be a more acceptable alternative?

How ever the Merlins were good, the Spitfire did not received the Merlin XX (bar the token numbers for the Spit IIC), but the second best, Merlin 45, that was also later in production than the Mk. XX. The two stage Merlin was considered for the Spitfire only once LW extracted a major toll on the Spit V.

There would be absolutely no guarantee that the Hercules would have been any better than the Merlin 45; chances are it would have been a retrograde step.

The two stage Merlin was considered for the Spitfire only once LW extracted a major toll on the Spit V.
Thanks.

Wrong - the two-stage Merlin installation was underway well before the Fw 190 appeared, such that the first Spitfire/Merlin 60 combination (N3297 - the ex-Spitfire III) was flown on 27 September 1941, just a week after the Fw 190 made its debut.

 

[wuzak]

Can't quite work out the maths here - the cooling system of the two-stage Merlin did not weigh an extra an extra 2,150 - 2,200lbs over the weight of the engine.

He is saying that 2,150-2,200lb is the installed weight of a 2 stage Merlin including coolant and intercooler radiators.

 

[wuzak]

I would guess that the Hercules would require a larger oil cooler. It would also require a larger fuel tanks and oil tank to have the same endurance - even if the engine has better specific fuel consumption, it is making more power and therefore using more fuel.

As Aozora says, having the heavier radial up front will require ballasting in the tail. The Hercules is similar in weight to the Griffon 65, so would probably have similar ballasting requirements. Griffon Spits were quite a deal heavier than Merlin 45 Spits.

 

[KiwiBiggles]

I'm not sure the Hercules would require ballasting beyond what is required by the removal of the cooling system. The firewall in a Spitfire is pretty much at the CoG, and although the Hercules is heavier than the Merlin, it is also shorter (1350 mm vs 1753 mm) and so the total moment about the CoG would be very similar.

 

[wuzak]

I'm not sure the Hercules would require ballasting beyond what is required by the removal of the cooling system. The firewall in a Spitfire is pretty much at the CoG, and although the Hercules is heavier than the Merlin, it is also shorter (1350 mm vs 1753 mm) and so the total moment about the CoG would be very similar.

And can the Hercules be pushed up against the bulkhead?

The bulkhead is behind the leading edge of the wing.

 

[wuzak]

Also, most of the Hercules' weight is at the front. The Merlin's weight is more evenly distributed along its length. That is, the CoG of the Hercules may still be as far forward as the Merlin's.

 

[Aozora]

He is saying that 2,150-2,200lb is the installed weight of a 2 stage Merlin including coolant and intercooler radiators.

Yep, I see that now.

I'm not sure the Hercules would require ballasting beyond what is required by the removal of the cooling system. The firewall in a Spitfire is pretty much at the CoG, and although the Hercules is heavier than the Merlin, it is also shorter (1350 mm vs 1753 mm) and so the total moment about the CoG would be very similar.

Fair enough, there would not be a great deal of problem with the ballast - assuming that the Hercules could be fitted anywhere near the firewall!

What is being discussed is a heavy, draggy installation stuck in front of an aircraft that was designed around the Merlin. To make the Hercules/Spitfire combination work, without compromising the Spitfire's performance too much, would require some careful work on a new engine cowling design (hopefully ditching the collector ring in favour of a well designed free-flow exhaust system), plus careful fairing of the Spitfire's forward fuselage. All of this would have to cater for the cooling requirements of the Herc, which would probably mean that a cooling fan a-la the BMW 801 would be very useful. Goodness only knows how many manhours at the drawing board would have been needed to produce a decent Hercfire, considering that in 1941 the British hadn't yet cottoned on to designing a radial engined installation as good as that in the Fw 190.

I'll rephrase the question I've already asked tomo - why on earth would Vickers-Supermarine bother with the complication involved in executing such a conversion, when they had already passed over the Spitfire III in favour of the V and, by mid-1941, were working on a two-stage Merlin installation, which offered a quantum leap in performance over any forseeable Spitfire/Hercules redesign, for far less trouble (noting that the conversion was based on the passed over Spitfire III)?

 

[Edgar Brooks]

The Spitfire fuselage is 36" wide; the Hercules is 55" diameter, so it won't fit. If you butcher the airframe, to get it in, and keep the same thrust-line, the top of the engine would be so high, the pilot couldn't see over it, or use a gunsight. Lower the thrust-line, so he can see, and you can't have a propeller bigger than 8' diameter.
The Spitfire III was cancelled because the Merlin XX was needed for the four-cannon ground-attack Hurricane, which was needed to replace the obsolescent Whirlwind; the Spitfire III also needed a completely new set of cowlings (like the Hurricane II it was 4" longer,) while the Merlin 45, with only minor adjustments to the carburettor intake, could fit into the same space as the Merlin II/III.
The broader-chord rudder was first fitted to the XII, not the IX, but extended onto other Marks later.