People tried with X, H and W layouts, some worked better than the others, even if the layout was the same. So how should the least troublesome, not too heavy or bulky, and very powerful 24 cyl engine looked like? We need it for the 1st version(s) to be in service when ww2 erupts, ie. in September of 1939.
A 'proper' way to have a 24 cylinder liquid-cooled aero engine for the ww2?
- Thread starter tomo pauk
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I think RR could have made the Vulture work if it wasnt for all that other "Merlin" nonsense and that silly carry on called a "war". Maybe not in time for the outbreak of the war but certainly in time to see off the Fw190 threat more reliably than the Sabre.
swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
My first thought would be that one would want to limit the engine to banks of six cylinders, so this means only the X (and and possibly hex), double-V (like the Allison V-3420), and H layouts are likely (the W layout would have 3 banks of 8). Of the three, my preference would be an X-configuration, as it would have only one crankshaft, which eliminates all the issues with phasing plus, since the crankshaft is the heaviest moving component in any engine, probably saves some weight.
My tendency, if I wanted to get an engine into production soonest, would also be to eschew sleeve valves, especially for a company that's not done it before.
My tendency, if I wanted to get an engine into production soonest, would also be to eschew sleeve valves, especially for a company that's not done it before.
cherry blossom
Senior Airman
- 504
- Apr 23, 2007
One way that worked if you had time and materials was Dobrynin VD-4K - Wikipedia
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
How about Packard's X-2775?
oldmachinepress.com
Packard X-2775 24-Cylinder Aircraft Engine
The Packard X-2775 (1A-2775) X-24 was a light, compact, and powerful aircraft engine. Trouble with the Kirkham-Williams and Williams Mercury Racers prevented the engine from proving itself.
oldmachinepress.com
Admiral Beez
Captain
No other 24 cylinder liquid cooled aero engine has flown as fast in as many aircraft as the Napier-Sabre. Address quality control and production shortcomings whilst tweaking the engineering and you're all set.
Forget the Sabre, have Napier make Griffons freeing up RR so they can make Merlin XX's then 60 series so we have Spitfire MkIII's and XII's late 1940, MkVIII's in '41 and MkXIV's in '42. If you really want Typhoon's and Tempests fit them with multi speed multi stage Griffon's.
Admiral Beez
Captain
Sounds like you've arrived in the wrong thread. We're discussing the best possible 24 cylinder engine, not if the resources to make it are better invested elsewhere.
don4331
Senior Airman
You're really asking the wrong question. If you're asking what is the best layout for 1,500hp on 1/Sept/'39, the answer is 14 cylinder radial - It will give you 1,500 hp on 87 octane fuel reliably when war erupts. It will have room to improve 1,900 hp with 100/130 fuel and improvements to supercharging (mechanical and/or turbine) and inter-cooling.
But what goes around comes around, and the question rears its head again late war - what is the best layout for 3,000 hp on 17/Aug/'45. 18 cylinder radials/V-12s are really pushed to make that power. Is the best solution for 3k hp, a double 11 cylinder radial - Wright R-4090; quad 7 cylinder radial - P&W R-4360 or some liquid cooled engine with 24 cylinders - Napier Sabre/RR Eagle, Double V - DB610/Allison V-3420 or Hex Jumo 222.
Wright only made 3 - R-4090s. (OK, they were having issues with the R-3350 at time, and need to focus). And its not a very streamlined engine (58" diameter)
P&W R-4360 was made in qty (almost 20k) but only couple hundred by end of war. I'm not sure you could start in '35 and have a running engine in '39 (P&W R-2800s were busting cranks left, right and center during that period, 4 row radial has even more complex crank) and at 3,700lbs probably too heavy. But can you start with a quad version of the Twin Wasp Junior for 1,500hp in '39 and improve/enlarge it to quad Twin Wasp for 3k hp (on ~2,500 lbs) without completely retooling the factory? (Interesting R-4360 with only 7 cylinders in larger than the 11 cylinder R-4090 at 61" diameter, Twin Wasp is over a foot smaller in diameter).
The hex 24 has all the connecting rod bearing issues of the X engine with 2 more slaves per rod. You also have to deal with primary and secondary vibrations of 6 - 4 cylinder engines which a hex more/less is. Junkers couldn't get them past the prototype stage even by end of war and built fewer than 300. We don't have until '50 when Dobrynin got a couple dozen running.
Vulture is done in more by 100 octane fuel than by the Merlin. In '35, RR is working on engines in 4 classes: Kestrel XXX - 750hp (engine is changed so much it is renamed Peregrine), Merlin - 1,000hp, update R (will be name Griffon) - 1,250hp and Vulture of 1,500hp. With an expectation that the fully developed version with make about 20% more on 87 octane fuel (900, 1,200, 1,500 & 1,800hp respectively). The nail in the coffin from 100 octane fuel - it allows 60%+ increase in power. RR can't figure out a way around the French multi speed patent, so until France falls, you are stuck with single speed engines.
So, the Peregrine needs to be redesigned for 1,200hp, the Merlin for 1,600, the Griffon for 2,000 and the Vulture for 2,400. And there is a war on so pick 2 - RAF needs Merlin for its front line fighter, FAA has funded the Griffon, Avro says they can redesign their bomber around 4 Merlins and it will be better able to take war to Germany.
However, if we never start the Vulture but rather commence with a double V Kestrel, we are sacrificing 2/3 of mid-war Merlin production. Vulture heads and cylinder blocks have same bore spacing as Merlin (even though the Vulture has same bore and stroke of Kestrel), so the manufacturing floor equipment could be converted to making Merlins with relative ease. Also, depending on supercharger setup of the double V Kestrel - i.e. if you keep individual superchargers ala DB605 superchargers on DB610, you don't have the tooling for the 1st stage for 60 series Merlin. Only just over 500 produced, not exactly a roaring success.
Even with those caveats and the weight advantages noted by
swampyankee
, I can't put my money on the "X-24". I know the solution for the connection rods is built up crank, but that gets horribly complex (maintaining tolerances). And the engine needs balance "pucks" like a radial as the rotating mass doesn't follow a circular path (its a funky ellipse) so, its still going to be hard on bearing.DB601/605/603 all had issues with oil foaming. When oil foamed, bearing failed with disastrous consequences. When you are running a double V, the failure of one V, doesn't immediately fail the outer - which has severe consequences - Ronson: lights every time. Messerschmidt and Daimler-Benz fought over what caused the issue (oil tank or oil pump design), in the end, Messerschmidt installed oil/air separators and resolved their issues. I am not aware that Heinkel ever did (Not enough planes made it back to properly diagnose the issue and resolve it?)
Allison V-3420, lost critical head way when V-1720 was prioritized, and then more when engineers fought to make a single supercharger and experimental turbo-supercharger work. Someone in management needed to step in and have them get the engine working with individual superchargers/production turbos. Then work on the single supercharger/fancy turbo.
Germany and USA made very limited numbers (~2,500 & 150 respectively) so not very successful compared to 70k V-1720 and 60k DB601/605s.
I'm not aware of any "flat H" engines with poppet valves in the power range we are talking. I suspect that having poppet valves with their associated springs and cams made the engine too wide for the air frame guys. I've seen the drawings for the Merlin "vertical H" engine, and it is seriously tall.
Which leaves us with the sleeve valve engines for H engines - and sleeve valves were definitely the "fad" in '35 and pretty good solution if you are stuck with 87 octane. You can't replace a 2,000 hp Napier Sabre (87 octane rating) with a hypothetical 1,250hp RR Griffon in '39 (the engine that is being completely redesigned to be a 2k hp engine on 100 octane, while Napier is forecasting well over 2,400hp for Sabre on same fuel). OK, Napier could have used a little assistance from the gov't to pass on how Bristol resolved the sleeve valve issue. (As gov't is paying for the engines, assigning the patent for center-less grinding and bringing in efficiency experts from automotive e.g. Ford would have solved most of Napiers issues). >5k Sabres isn't the 100k for Merlin, Cyclones or Wasps, but given the limited number of planes using (chicken/egg thing?), still more than all the other combined during war.
Based on historical - flat H sleeve valve.
I still think a double Peregrine has merit as you could start double Kestrel in '35 and get 5 years experience in before you are at war with your 1,750hp double Peregrine. Makes for a very different looking Typhoon...
If there was a better 24 cylinder engine it would have been made, from where I sit engines like the sabre didn't do anything other than waste resources, maybe that's why 12 cylinder engines won out?.
Admiral Beez
Captain
If that's your view, that the entire premise of the question is unfounded, why are you here?
- Thread starter
- #12
??
I'm asking a specific question, namely about a surefire way to have a working 24 cyl aero engine in service in September 1939. Thread is not about a general engine development in the 'major' countries, ie. not about Merlins, DB 605s or V-1710s.
But anyway:
Kestrel was making 754 HP. Peregrine did 885, and about a 1000 on 100 oct fuel.
DB made the oil deaerators. MTT and Heinkel were airframe companies (Heinkel later did the jet engines).
Okay.
How bad would've been the Sabre with popet valves?
wuzak
Captain
The Lycoming XH-2470 was a poppet valve H-24 of roughly the power required. ~2,300hp rating as used in the Vultee XP-54.
But it was not available in the time frame.
It was developed when Lycoming worked out that the opposed 12 cylinder O-1230 was not going to be powerful enough to meet requirements. So they doubled it up to make the XH-2470.
There were some issues with the design - it was a development of the Army's "hyper cylinder", which meant it had 2 valves per cylinder and was constructed with separate cylinders. It was also unreliable.
And, like many other companies, they were developing myriad variations before sorting the core engine. 2 speed reduction gearing, contra props, integration with turbochargers, etc.
wuzak
Captain
You would be speaking of the R-2600. Which is a big and heavy engine for its power.
The fact that, as you pointed out, it only ever made it to 1,900hp with development suggests that its potential was limited. Hence the R-3350.
wuzak
Captain
Oops double post
wuzak
Captain
How about Packard's X-2775?
Packard X-2775 24-Cylinder Aircraft Engine
The Packard X-2775 (1A-2775) X-24 was a light, compact, and powerful aircraft engine. Trouble with the Kirkham-Williams and Williams Mercury Racers prevented the engine from proving itself.
Perhaps too much of an older generation design. Very lightweight for its size, may limit development.
wuzak
Captain
The Hex 24, as you call it, has a slight problem with the firing order.
Most 4 stroke radials have an odd number of cylinders. On one crankshaft rotation the odd number cylinder fire in sequence, on the next rotation the even numbered cylinders fire. That way the power strokes are evenly distributed - every second cylinder fires in order.
For the Jumo 222 the firing order was uneven. If the cylinders were numbered 1 to 6 around, 1 and 2 fire in sequence, then 5 and 6 in sequence and then 3 and 4 in sequence. So the firing spacing is 60 - 180 - 60 - 180 - 60 -180.
Not sure what you mean there. On 100 octane fuel the Merlin of '40 was making ~1,300 - 1,400hp, the Vulture ~1,800hp - 2,000hp.
The problems with the reliability of the Vulture meant that it had to be run at lower power in order to survive longer, which brought its power levels back closer to that of the Merlin.
The Merlin X was displayed at the Paris Air show in 1938. Complete with 2 speed supercharger using the Farman design. So they paid royalties for at least 2 years?
(These royalties may be why the V-1650-3 went to a Wright design supercharger drive, though they continued to make single stage, 2 speed engines for the British with the Farman design.)
The Vulture also had the 2 speed supercharger.
The Peregrine was dropped because the power it could deliver was not enough. Why design an aircraft around a 1,200hp engine when you could use a 1,600hp engine of only slightly larger size?
The Merlin didn't get to 1,600hp until 1943?
The single stage Griffon was capable of about 1,800hp, but the 2 stage engines were capable of 2,000hp in 1943.
The Vulture had been tested on the bench at 2,500hp in 1941, just before its cancellation.
wuzak
Captain
Of the 24 cylinder layouts I think the X-24 is the most compact, particularly with evenly spaced banks.
The W-24, such as the V-3420 is OK for height, but very wide.
The V-3420 has ~6" less height compared to the Vulture, but ~24" more width.
wuzak
Captain
The Vulture has a similar bore spacing to the Merlin, but not the same.
Bore spacings are:
Vulture – 6.1in
Merlin – 6.075in
Kestrel/Peregrine – 5.625in
Griffon – 6.9in
- Thread starter
- #20
There was no such nonsense before 1939, at least not from the British perspective.
RR can ditch the Exe and make a liquid-cooled engine instead of it. Say, a 40 liter H layout engine that uses Kestrel/Peregrine bore and some internals to speed up the development.
