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Indeed, my bad
Still, Hitler ordered a redeployment of some of his armed forces from SU to Italy.
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 Withdrawn its expeditionary forces intact (if ill equipped) from the continent (together with a substantial French force).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.
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Supermarines stopped working on the 324/327 in 1938, having never received an order to proceed. So that wasn't an issue.
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.
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 Centaurus was somewhat closer in size (frontal area) to the Vulture and Sabre than the Hercules was to the Merlin.
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.
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.
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
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?
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 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.
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.
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
Not going with the Mk. III seem like a bad idea indeed.
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)
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
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.
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.
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.
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.
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.
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.
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.
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 considered for the Spitfire only once LW extracted a major toll on the Spit V.
Thanks.
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.
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.
He is saying that 2,150-2,200lb is the installed weight of a 2 stage Merlin including coolant and intercooler radiators.
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.