Radial engines more favored in Germany, 1935-45?

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Cylinder count, and the difference of radial vs inline, is greatly modified by the displacement of each cylinder.

Smaller displacement engines are at a disadvantage to larger ones in most ways, except for drag.

RAF missed out by not ordering larger displacement radials and inlines both
 
bf109xxl said:
At the State tests, no changes in production according to Maslov and Kotelnikov (more reliable data from a later version of his book in Russian).
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Can that book be bought at the usual on-line stores?
 
tomo pauk said:
Can that book be bought at the usual on-line stores?
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I have no idea. I purchased the paper version about 10 years ago. You can download an illegal scan. The author (Vladimir Kotelnikov), to my great regret, has already died.
 
marathag said:
RAF missed out by not ordering larger displacement radials and inlines both
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Order from who????

It takes 3-5 years to design, develop and put an engine into production. It turned out that that the more sophisticated (read trick or tricky) an engine was the more trouble they had with them. This went for the US, Germany and the Soviets so it just wasn't the British. However a number of designers may have over estimated their abilities and underestimated the problems.

A-S was non-started for the British in Radials.
Alvis tried but trying to flog British built G-R engines (which weren't very good to begin with) would have been a dead end. Perhaps a temporary expedient 1938-41 but no growth potential.
Leaves Bristol and the Sleeve valves. Fedden was working on the Centaurus in 1938-40 but had to side-line it while they sorted out the problems with the Hercules and the 1938-41 Hercules was NOT the answer to a single engine fighter. It took quite a while for the Sleeve valve engines to handle more than moderate amounts of boost so they needed large amounts of displacement.

For inlines you had RR and Napier, period, end of story.
A number of prototype aircraft were dropped due the unavailability of Vulture and Sabre engines. ordering engines that aren't working correctly gets you nothing.
Griffon was sidelined for a while due to the BoB.

Air Ministry was also trying to be too clever. While small twins can often be quite good large twins have problems. Large twins have problems flying with one engine out.
This is somewhat relative. What matters is the power to weight of the plane while flying on one engine. You either have a negative climb rate, or just barely stay in air but had trouble turning/maneuvering or you have enough surplus power to actually fly at low but reasonable speed and can fly at reasonable altitudes and not just clear wave tops at moderate temperatures. Many light twins don't work with one engines, Whitley's, Manchester's, Warwicks didn't work with one engine out.

A lot of fun is poked at the He 177, at least they tried to keep the 2nd prop turning at reduced power if part of the powerplant failed. Staying in the air on 3/4 power. The actual engine installation meant they were much more likely to have engine problems but the Idea was there. The Big British twins didn't even have that.

The British did order Griffons and Sabres and Centaurus engines as they became available, sometimes before they became available (reliable).
 
Shortround6 said:
A-S was non-started for the British in Radials.
Alvis tried but trying to flog British built G-R engines (which weren't very good to begin with) would have been a dead end. Perhaps a temporary expedient 1938-41 but no growth potential.
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Either of these companies should've tried to find a way to make Wright or P&W radials instead of what they were up to by mid-1930s.
 
tomo pauk said:
Either of these companies should've tried to find a way to make Wright or P&W radials instead of what they were up to by mid-1930s.
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Alvis tried to sneak into the market by getting the licenses for several G-R engines. I don't know what they paid for them. I don't know what P&W and Wright were asking for Licenses.
G-R was offering a range of engines. At least a 9, the small 14, the big 14 and an 18 (?), There may have been a 7 cylinder as well (?), all using the similar size cylinders (the 18s used 180mm stroke) except for the small 14 and the 9.
This might have looked very attractive during the build up of British defense spending. Except that the Air Ministry did not bite.

Alvis is supposed to have built a small factory and been already to start production. I can't remember if it was 15 engines a week or 15,000 hp worth of engines per week or some other number, It seemed to sound impressive but at 60 or fewer engines a month it really wasn't. It might not have intended to work 3 shifts either so who knows?
The 1938 Jane's lists two 18s (different supercharger gear ratios), two big (38.67 L) 14s (different supercharger gears) the small 14 (G-RM) and the small 9 (11.78 L.)
Other sources say either none or only one of the big engines were ever built in Britain. The small 9 did become the Leonides after WW II and was produced in decent numbers after the war.
It was under test/development before the war. Used the same bore size as the 14M engine but 4mm less stroke.

A-S tried to go with the "dog" engines and aside from their 'flash in the pan' with the two speed supercharger had tried to hang on to the 1920s technology/designs for too long.
Besides, somebody had to make Cheetah engines for trainers


I do wonder about the actual factories, like could they actually make the US engines. The US engines tended to bounce back and forth a bit between cast and forged heads but at certain times they were using cast heads when the British companies were using forged heads for about the same power levels because the British industry could not supply cast heads in the needed quality. Sometimes forgings and castings were supplied by outside contractors and then machined in house.
Alvis did do a lot of subcontracting and repair work and added a number of buildings to the "works" during the war years.

very little British factory space or machinery sat idle for very long during the war years.
 
Want an unpopular take?
Original Ramp Head Merlin was pure trash, whole line should have been dropped for the Griffin, right then in 1936, than upscaling the Kestrel to make the Merlin II in time for 1939

In 1937, the R-2800 first ran, with production types in 1940, so '36 to '39 should be enough

That gets a big V-12 in service for the War. No need to rush for the Vulture or Exe, all that development goes to the Griffon, or to a 2900 class V-12, call that the Griffon Major if that's desired. or a 1800 cubic inch Griffon Junior to take the place of the OTL wartime Merlin

Bristol makes a poppet four valve, two row powerplant from the 1519 cubic inch Mercury to a 2360 cubic inch 14 cylinder and an 3039 cubic inch 18 cylinder, to take the place of the sleeve valved Hercules and Centaurus before WWII starts.

The Aquilia/Taurus line is dropped completely, just too small.

The development effort wasted there is instead made more towards a larger displacement sleeve valve radial to scratch that more sophisticated/tricky itch, while the poppet valve units are in service.

And this is just fixing RR and Bristol
 

Perhaps a result of the amount of elbow-grease needed to make a worthy engine was increasing rapidly in the inter-war years. Humans are notoriously bad at eyeballing exponential phenomena. Same for airframes, FWIW.


Had Fedden not been bitten by the sleeve valve bug Hercules could have been ready a couple of years earlier, Centaurus might have been available mid-war-ish, and they could have spent more of their brainpower on SC development. Oh well..

The British did order Griffons and Sabres and Centaurus engines as they became available, sometimes before they became available (reliable).
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In retrospect, Britain could have won with just the Merlin in the 1000+hp category. Later in the war when higher performance engines and planes were starting to be deployed in numbers, the LW was largely a spent force anyways. (Of course, at the time, it would rightly have been seen as a horribly risky industrial policy to put all eggs in one basket, as well as ill advised to give RR a monopoly position in aero engines.)
 
marathag said:
Want an unpopular take?
Original Ramp Head Merlin was pure trash, whole line should have been dropped for the Griffin, right then in 1936, than upscaling the Kestrel to make the Merlin II in time for 1939
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The heads were trash but was the whole engine?
The Ramp heads showed up on the Merlin B, the first two prototypes did not have them, we are also using the retrospectoscope as we KNOW what worked and what didn't

Next question is what Griffon? The "original" 6 X 6.6 (2239cu in) Engine, Buzzard was about 1140lbs and was good for 2300rpm. Ran in 70-77 octane.
We have the R race engines and then we have the Buzzard I, never flown and dropped in 1933 I don't have the weight. The R in one version, went about 1640lbs.
The Griffon II went about 1790lbs and was good for 2750rpm.

Now in 1933-36 nobody knew how soon or even if 100 octane fuel would get there. They knew it existed, they knew it was possible and in 1935 they knew it cost about 10 times per gallon what 80 or 87 octane fuel cost. Maybe they could get the price down but until the price came down a LOT it was not a commercial fuel. They had 87 octane (and not every country used quite the same 87 octane).
going from 885-955lb Kestrels to 1600-1800lb Griffon X (experimental) is a stretch.

The whole idea of the Vulture was to get a 2592 cu in engine that would run on 87 octane fuel and give close to 2000hp, They were hoping for 3000rpm but we all know the problems with connecting rods. There were reasons that a lot of these designers were resorting to "tricks". They could not see a how to get the desired power out of the existing fuel without going to high rpm.
Merlin vs the Griffon X offered several small advantages in theory. Smaller cylinders cooled a bit better, even liquid cooled ones. Smaller cylinders had better volumetric efficiency. Smaller cylinders offered higher rpm (lower piston speed).

Now we can look at the competition, the HS 12Y (2197 cu in) the DB 600 (2070 cu in) and the Jumo 211 (2134 cu in) to see how they handled things.
They kept the engines light, like somewhere between 1050lbs to 1370lbs (?) which puts the Merlin near the top. A Griffon X doesn't fit many of the existing designs. It is also going to be rather more costly, like around 20% just based on weight.
2900 cu in V-12 gets counter productive. Really big cylinders run into physical problems. The Soviet AM-35 engine was 2847 cu in. It also weighed 1830lbs. It ran at 2050rpm.
could you make a 1900 cu in engine that ran at 3000rpm to get the same power? It would be smaller, now we can argue about weight.
The Soviet AM-35 was about as large as you could make a cylinder without resorting to triple ignition. The flame only can burn so fast and even with two flame fronts you have limited amount of time for flame paths to cross the piston and get done as the piston gets to about 20% of stroke. If the fuel is still burning below that point you wind up wasting a lot of power (poor fuel economy)

Now in the early and mid 30s you also have not the best propellers in the world ( especially for the British) and trying to put high powered engines in small planes using small propellers was problem, nobody had 4 blade propellers that weren't two 2 bladed wooden propellers stuck together. One reason (but not the only one) that the Corsair used the bent wing. Needing a 13 ft 4 in propeller to handle 2000hp was a problem for a fighter.
Big bombers had more room for big props
marathag said:
Bristol makes a poppet four valve, two row powerplant from the 1519 cubic inch Mercury to a 2360 cubic inch 14 cylinder and an 3039 cubic inch 18 cylinder, to take the place of the sleeve valved Hercules and Centaurus before WWII starts.
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And here we have another company (or the same company) believing their own advertising or not doing enough testing of the competition and sticking with a solution that worked in the 1920s but was not needed in the mid 1930s.

Fedden spent a lot of time overcoming a lot of the problems that the IC engine had in WW I and the early 20s. But once he found solutions he stuck with them and did not look at what other people were doing. In the early 20s valves failed (broke) and warped and burned. Valve springs broke, frequently. We can also note that intake tracts/manifolds were generally pretty crappy, anybody who doubts this one can look at the Fairey engines
two small valves (for each function) offered not only better breathing but the smaller valves were lighter and put less load on the valve system, like the springs. They offered better heat transfer to the valve seats and ran cooler, less burning and warping. Now in the late 20s with sodium cooled valves and better valve springs there were some significant changes in valve and valve spring life. Fedden had jumped to the sleeve valve ship as way to solve some of these poppet valve problems and chase some of the theoretical advantages and he just stuck with 4 valve heads as that required the least amount of R&D to the existing engines while he chased the unicorn of the Sleeve valve. Yes Bristol adopted sodium cooled valves and got better springs for the valves but so did everybody else.
By the way, the G-N 14K was 2360 cu in 14 cylinder radial using the same exact bore and stroke that the Hercules used. A lot these engines were adaptations of each other.

Two big valves in a hemi head offered pretty good breathing. Maybe not as good as 4 small valves but now we are starting to get into port size and shape in the late 30s. Also as boost goes up valve curtain area may become less important?
the Mercury and derivative engines used 146 X 165 cylinders. The R-2800 used 146 X 152.
Less piston speed for equal rpm or more rpm for a given piston speed. But that may be another post.
 
Shortround6 said:
well, they got to 1500-1700hp for a lot of the planes pretty quickly but that required the 100/130 fuel.
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Indeed. Merlin became a war winner via a number of lucky improvements, few of which could have been foreseen back when the Merlin first entered service. Like I mentioned, easy to see in retrospect, but would have been completely reckless to focus solely on the Merlin at the time.
 
Well, RR had several other projects in hand. Like the Vulture, which had the advantage that it used some of the tooling from the Kestrel/Peregrine. Maybe the parts were not interchangeable like K/P piston being used in a Vulture but since they were the same diameter perhaps some the jigs/fixtures could be used or even the same forgings?

And there is the question of timing. From Wiki so......................
'In 1937 the idea was raised of attempting a new world landplane speed record with a modified Spitfire."
"Rolls-Royce began work on a sprint version of the Spitfire's Merlin engine, to run on a special fuel mix."
"On 11 November 1937 an appropriately modified Messerschmitt Bf 109 V13, D-IPKY, flown by Herman Wurster, raised the world speed record to 379 mph (610 km/h). It was still believed that a modified Spitfire, with a Merlin delivering a forecast 2,000 horsepower (1,500 kW), stood a good chance of doing better than this, so the Air Ministry decided to go ahead and issued a contract."
"Rolls-Royce abandoned the glycol coolant of the production Merlin and adopted a more efficient pressurised water system."
"By May 1938 the sprint version of the Merlin II, running on a special racing fuel of leaded petrol with benzol and methanol added, was achieving 2,100 hp (1,565 kW) on the test bench, for short periods."

Now somewhere around this time they had run the sprint version of the engine at either 1600 or 1800hp (?) for 10 hours without failure. There was still a question of getting better than 87 octane fuel but RR was relatively assured that the basic engine could stand up to much more than 1030hp without much or any modification.

Doesn't mean they could cancel the Vulture at the time or even throw out the Griffon which was sort on on hold. It did take the pressure off somewhat. It also means there was NOT an "aha" moment when they dumped 100 octane into the tank and wound the boost up to 12lbs and yell at each other "we are saved, we are saved".
Things were not quite as cut as dried as we may think they are. The Griffon rotated the opposite way from the Merlin and they broke the first two crankshafts in a few hours each before somebody noticed that the Griffon crank used the same spiral (crankpins followed the same pattern) as the Merlin. They made a 3rd crankshaft and mirror imaged the crankshaft pin layout, installed in the block and ran it for several hundred hours.
Vibration patterns were not as well understood and harder to measure than they are now.
This work with the Speed Spitfire engine was about 5-6 years after the start of the Merlin project and 3-4 years before the Merlin was giving 1500hp or above in service use.
Main difference on the single stage Merlins between 15lbs of boost and 18lbs was a stronger supercharger drive shaft. There were a lot (several hundred?) minor changes but bottom end would stand up to higher power settings with very little trouble.

But like aircraft, a good engine company wanted to be working/starting on the next project when the currant one is going into service and not waiting a few years before getting to work again.

Perhaps if RR and the Air Ministry did not have knowledge of the Merlin's potential capability they might have kept the Vulture more active in 1940/41.
With the Vulture's crankshaft/rods being the problem and the cuts in power needed to ensure reliability the gap between the Merlin and the Vulture got a lot closer.
With the Merlin they could work on making more power, not keeping the engine alive. With the Vulture they were working on keeping the engine alive, not improving the supercharger/performance.
 
More displacement gets you more power with existing compression ratios, without having to spin extreme rpms

smaller bore size limits the width of the valves that can decrease engine efficiency and thus horsepower. Piston speed is one of the main limits on overall top RPM.
Oversquare engines tend to be more reliable

Soviet had to deal with 95 octane for the AM-35, and follow on engines had continually lowered C/R to account for that, even though L-L fuel would have alleviated that, had they known that would be possibility. They planned for worse case.

But UK didn't need a crystal ball to see 100 octane for 1940, with plans for changing C/Rs to match for what fuel would be around


The Soviets did OK with big displacement 2500 rpm V-12, still got to 2000HP

So yes, RR works the R into a production ready Griffon, beefing up weight to increase reliability before 1939

Have an aircraft that doesn't need the full 2000hp, and the weight? Baby Griffon, either scaled down V-12, or fewer cylinders as a V-8 or V-10

V-8 Griffon would be great for Tanks.
All that good parts commonality between models.
 
marathag said:
But UK didn't need a crystal ball to see 100 octane for 1940, with plans for changing C/Rs to match for what fuel would be around
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By 1939 (and spring of 1939 at that) they could see 100 octane was coming, they were placing orders for it. The question was the deliver schedule. How many tons in which months.
marathag said:
The Soviets did OK with big displacement 2500 rpm V-12, still got to 2000HP
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Didn't get to 2000hp until 1944, in actual service, not trials. Weight had gone to 2150-2200lbs
Comparing to Soviet engines gets tricky as the Soviets would run the engines harder than the British/Americans would and accept shorter engine life to get the increased performance.
After a 3 gap in production for the AM-42 they resumed production in 1951 with version that gave a 400hr service life. Something that Merlins were doing in 1945.
marathag said:
Baby Griffon, either scaled down V-12, or fewer cylinders as a V-8 or V-10
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Scaling up or down is helpful but it can also result in new vibration problems. Airplanes are not cars or trucks. Airplanes and their engines don't have extra mass to help dampen vibrations. V-10s were not popular with engine designers (especially in pre computer days) because of difficulties with firing order and vibration. You can make V-8s smooth, you just have to use a different angle between the banks which cancels some of the benefits.
marathag said:
V-8 Griffon would be great for Tanks.
All that good parts commonality between models.
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The British really, really, really screwed up tank engine production in WW II. I mean REALLY.
They had a pretty good candidate staring them right smack in the face. What they didn't have was production capacity.
The Kestrel would have powered any, repeat ANY, British tank up until the Centurion. What they didn't have was a factory to make it or get RR blessing.
So the British wound up with the Bedford twin-six in the Churchill, The Meadows flat 12 in the Covenanter and the Leland V-12 (Liberty) all being made in 3 different factories, all making 340-410hp and all not able to do the job. Except for the Bedford, barely.
Solved by the Meteor, sort of, which was actually too much engine for the job and had to be geared to down to keep from breaking running gear and crewmen in the Cromwells.
Might have been OK in the Comet tank but that used the geared down final drives.

The Kestrel was the same size as the early Tiger and Panther engines and only 10% smaller than the later production German engines.
By 1938 you could get an supercharged Kestrel to give 560hp at 2350rpm at sea level, that was throttle back to suit fixed pitch props. Wide open it would give 635hp at 2900rpm so there was certainly "room" to detune the thing for tank use (lower compression to suit lower grade gas, longer engine life).

The Meteor came into being as the result of a "Staff" requirement where they "estimated" they wanted 20hp per ton for new/future tanks. or a 600hp engine for a 30 tank.
No test data from trials or experiments needed. That was the requirement, deal with it.
Nothing wrong with the Meteor itself. It just wasn't needed until 1945. And it kept (indirectly through that staff requirement) a perfectly good engine from being used for several years because the Kestrel/Peregrine would only give in the high teens per ton at the 27-30 ton weights.
A Kestrel/Peregrine could have given just about 500hp at the same levels as the Meteor gave 635hp.
 
Shortround6 said:
The Kestrel was the same size as the early Tiger and Panther engines and only 10% smaller than the later production German engines.
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Maybach were very High Speed, 3000rpm units that needed more gears to be useful from its 1410 cubic inches. Soviet V-2 were detuned enough(1800-2000rpm) that wasn't a problem, and extra displacement gave plenty of torque from its undersquare 2368 cubic inches, 1591 ft-lbs to the Maybach was 1365ft-lbs

Meteor was in the middle, 1649 cubic inches, 2400rpm and 1450 ft-lbs

The Kestrel would have been lower power to these at 1296 cubic inches, more in the class of the Ford GAA, but would been better than the other underpowered engines the UK used in Tanks
 
Kestrel/Peregrine was not ideal but it was available in 1939.
It was much more powerful than the alternatives.

The British didn't need a 1450ftlb torque engine to power their tanks. At least not until you get past the Comet.
The Comet was under 80% if the weight of a Panther. It doesn't need the number of gears that the Panther needed even if it has a bit less torque.

The Bedford twin six only got 960ft lbs from 800-1600rpm. (1100ft bs at 1200rpm?)

And the Suspension/track system was speed limiter there, You could install more power in it but to what purpose?
Drop the V-12 in and use smaller carbs or govern the engine down.
 
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