WW2 Without the Merlin: Options for the British

[wuzak]

as was the 2,600bph type approved RM-17

Just to be technical, the RM.17SM was rated at 2200hp MS and 2100hp FS - can't recall the altitudes.

The RM.17SM was also flight cleared for 2380hp @ 3300rpm, +30psi boost.

The other fact was that the 130's (RM-16s) used in the Hornet were 2,000bhp ... at 20lb boost on 100 grade fuel was also amazing

I believe that the 130 series were RM.14SM rated.

But you are correct - an engine originally designe for ~1000hp to be stretched to over 2000hp is impressive.

 

[Shortround6]

You are pretty much right. The Merlin was R-R's 6th or 7th V-12 aircraft engine (depends if you count the Buzzard and "R" together or separate). For there to be no Merlin R-R has to go out of business.
Then you have to assume that the air ministry decides they don't want a V-12 built by another company. And assume that the R-R people who worked on the previous engines don't find jobs with the other British engine companies.
Fairey wanted to become and engine maker. The Air Ministry already had Armstrong, Bristol, Napier, and R-R so they 'discouraged" him. If R-R had gone bankrupt would the Air Ministry just accept 3 suppliers or would they encourage Fairey to take up the slack?
R-R pretty much had the British V-12 market sewn up. The other companies, while competing with R-R did so not by building competing V-12s but by building alternative engines. If there are no R-R V-12s then do one of more of the existing companies build a V-12 rather than some of the engines they did build?

AS for the Merlin topping out at 1300hp without Hooker?
The engine for the Speed Spitfire was running at over 1800hp on the test stands before Hooker went to work for R-R. Most of the 2000hp Merlins had about zero effect on the war.

The two things that allowed the Merlin to go from 1000hp to 2000hp were the better superchargers and the better fuel. without the better fuel the supercharges could only do so much and in fact, without the better fuel there is little point in designing the two stage superchargers.
It is kind of a chicken and egg thing.

 

[OldSkeptic]

Even with poorer fuel (ie 87 octane) the advantages of increasing the full throttle height with 2 stages would have been worth it, but the boost and hence the power levels would have been lower. Instead of the (approx) 1,700/1,500bhp for the max 1st and 2nd FTHs (most Merlins 60 with 18lb boost) might have been around 1,300 levels with water, 1,150 levels without it.

The estimate of 1,300bhp (and I should have stated that this was the 2nd stage FTH, you would have had more for the lower FTH of course and at 18lb boost) is inferred by comparing pre and post Hooker supercharger Merlins at the same boost. His work added about 150bph at 12lb boost. The gap would have gotten a bit bigger with higher boost levels, because of the better efficiency levels (as you work the supercharger more) and the FTH would have been a bit lower.

Maybe 1,400bhp, as I said an estimate.

Efficiency counts, you compare the 100 series to the 60 series (on a like by like basis), even on the same boost and supercharger size FTH was raised by 1,000ft, just due to the better efficiency.

And Wuzak you are perfectly correct it was the RM-14SM. But they tested the RM-17SM at 2,632 bhp, 3,150 rpm, 36lb boost and water injection.

All of them are amazing numbers of course.

But of course RR's genius was to make an engine capable of those mechanical and thermal loads. All the superchargers in the universe would have been useless if the engine couldn't take that power and be reliable.

North American found that out when testing (post war I think) a very late model 2 stage Allison (forgotten the model number) which had terrible misfiring issues, finally traced to the inlet manifold (unchanged since the first one) being unable to handle the airflows at such pressures and volumes. So there was a lot of work by a lot of people in many different areas getting everything right.

 

[wuzak]

And Wuzak you are perfectly correct it was the RM-14SM. But they tested the RM-17SM at 2,632 bhp, 3,150 rpm, 36lb boost and water injection.

And special fuel.

But of course RR's genius was to make an engine capable of those mechanical and thermal loads. All the superchargers in the universe would have been useless if the engine couldn't take that power and be reliable.

RR did a lot of testing and strengthening to make it capable of such power.

Another amazing thing, to me, is that lat war Merlins coudl cruise at power levels which were 5 minute ratings in the BoB.

 

[OldSkeptic]

No the 2,600bhp test was on 150 octane, RDE/F/290 (115/150 grade), water injection of course.

Sorry forgot to add the source. The Merlin 100 Series, RR Heritage trust.

 

[tomo pauk]

Good options for the FAA with Merlin absent, anyone?

 

[parsifal]

well the ultimate prop engine for the FAA was the Centaurus, which was ready by 1942 and offered a LOT of power

 

[Shortround6]

Even with poorer fuel (ie 87 octane) the advantages of increasing the full throttle height with 2 stages would have been worth it, but the boost and hence the power levels would have been lower. Instead of the (approx) 1,700/1,500bhp for the max 1st and 2nd FTHs (most Merlins 60 with 18lb boost) might have been around 1,300 levels with water, 1,150 levels without it.

The fuel limits the amount pressure inside the cylinders. with 87 octane the engine was limited to 1030hp at 16250ft plus the power to turn the engine over (friction and pumps) plus the power to run the supercharger. Adding a second stage increases the power to run the supercharger at higher altitudes. The higher the compression of the air, even if limited to 6lbs in the intake manifold heats the intake charge more (6lbs boost[42in] requires the air to be compressed about 2.5 times at 16,000ft. at 23,000ft the air needs to be compressed about 3.5 times) and intercoolers do NOT remove all of the heat. the power to run the second stage has to be subtracted plus the lower density of the intake charge has to be figured in.
That gives you the "power" of the engine. Now add the weight and bulk of the two stage system and the actual improvement in performance of a fighter is not that great.

 

[Aozora]

I have read somewhere that it took about 200 hp to drive the F.S stage on the Merlin 60/70 series - can anyone confirm this?

 

[Shortround6]

It depends on the gear ratio.

For the Merlin XX in high (F.S.) it took 219hp at 15,000ft to get 48.24in pressure. 225hp at 20,000ft 48.24in, 202hp at 25,000ft for 42.12in and 167hp at 30,000ft for 34.30in. for the single stage.

Power required changes with the square of the speed of the impeller. changing from the 6.39 low gear to the 8.03 high gear on some of the two stage engines requires about 57% more power. Changing impeller size without changing gear ratio changes power requirement.

200hp certainly doesn't seem out of line depending on gear ratio ane model of engine ( The first stage on the P&W R-2800s could take close to 350hp to drive in high gear or caused a 350hp power loss.

 

[swampyankee]

One of the advantages of turbo-chargers is that there is no mechanical connection to the engine, which should, hypothetically, result in greater net output at a given level of boost. While there was an increased pumping loss due to the back pressure resulting from the presence of exhaust turbines, this would probably result in less power loss than the mechanical supercharger.

 

[tomo pauk]

well the ultimate prop engine for the FAA was the Centaurus, which was ready by 1942 and offered a LOT of power

Centaurus was indeed a powerful machine, though we need something to propel the fighters (mostly) in the rough 1st half of the ww2. The Peregrine, even if it is updated, would be hard pressed to serve in a 2-seat fighter, so it's either Hercules (from mid 1940?), or updated Buzzard (late 1930's)?

 

[Glider]

I am sure something could have been designed around the Hercules.

 

[parsifal]

I am sure something could have been designed around the Hercules.

I mentioned this before, but the F5/34 was designed as a long ranged single seat fighter with just 840hp, and a max speed of 316mph. Its almost unfathomable that the RN did not ressurrect this design in 1937 when it finally got control of its own procurement again.

The F5/34 with a Hercules powerplant would have been a formidable carrier fighter. Whilst the hercules was being brought up to speed, it would have been possible to substitute the twin wasp using imported engines until domestic product was developed.

As I said, it defies logic that this pathway was not followed. The RN convinced itself that it needed a multi role fighter recon which was the basis of the Fulmar. I would defend the Fulmar anytime against its detractors, but 1st line material it was not. A Hercules/twin wasp powered f5/34 would have been as good or better than a Zero if it had been developed.

 

[fastmongrel]

I still think an Alvis Pelides (modified Gnome Rhone 14K) could have been a decent alternative for the Merlin for 1940 and it would have been a good fit for a Glster F5/34. If boot can be applied to Bristol backside pre war then maybe the Hercules could be the Merlin alternative from 1940 but I dont think its going to be any earlier thats why I think the Alvis engine can help hold the fort till the Hercules is ready with a decent supercharger.

 

[Shortround6]

I still think an Alvis Pelides (modified Gnome Rhone 14K) could have been a decent alternative for the Merlin for 1940 and it would have been a good fit for a Glster F5/34. If boot can be applied to Bristol backside pre war then maybe the Hercules could be the Merlin alternative from 1940 but I dont think its going to be any earlier thats why I think the Alvis engine can help hold the fort till the Hercules is ready with a decent supercharger.

Alvis Pelides is NOT a substitute for the Merlin. It is may be a substitute for the Armstrong-Siddeley Tiger but that is about it. It needs a total redesign to become a decent engine by 1941-42 standards keeping ONLY the bore/stroke and 14cylinder layout, EVERYTHING else needs to be changed.

AS for 1940? the engine was rated at 1050hp/ 2150 rpm/37.0in for take off and 1050hp at 2150rpm at 5000ft on 87 octane. It would have offered under 850hp at 15,000ft. 100 octane would have very little effect on power, with no center bearing on the crank it is going to suffer from crankshaft flex if you try boosting the pressure. The same problem that the Tiger suffered from. With the Bristol Mercury already offering 840hp at 14,000ft at 400lbs less weight I don't know why ANY fighter designer would pick the Pelides. The Pelides had passed a 50hr Civil test but only 15 were made and none may have flown.
The Tiger had passed tests and was used in a several aircraft but had a lot of trouble with it's crankshaft. Perhaps the "boot" should have been applied to Sir Siddeley to put a center bearing in the engine and give Britain the rough equivalent of the R-1830.

 

[fastmongrel]

I wasn't proposing an imperial GR14K as a replacement for the Merlin in 41 that should be a Hercules with a decent supercharger but an engine is needed for 39 and 40 and I think the GR14K could do the job sufficently to hold the line. The best figure i can find for the GR14K weighed 1,190 pounds and put out 1,065 hp at 8,530 feet on French 87 octane. The best pre war Mercury I can find is the Mercury XV weighing 966 pounds and putting out 825 at 14,500 on British 100 octane. Neither engine is a true Merlin replacement but needs must and without something the RAF is stuffed.

 

[Aozora]

I wasn't proposing an imperial GR14K as a replacement for the Merlin in 41 that should be a Hercules with a decent supercharger but an engine is needed for 39 and 40 and I think the GR14K could do the job sufficently to hold the line. The best figure i can find for the GR14K weighed 1,190 pounds and put out 1,065 hp at 8,530 feet on French 87 octane. The best pre war Mercury I can find is the Mercury XV weighing 966 pounds and putting out 825 at 14,500 on British 100 octane. Neither engine is a true Merlin replacement but needs must and without something the RAF is stuffed.

Just found a Flight article from 1937 describing British aero engines British Aero Engines December 2 1937 Flight Archive
including a rundown of vital statistics: Specifications Flight Archive

and another 1937 article on the Alvis radial engines 1937 | 0981 | Flight Archive I didn't know they were also working on an 18 cylinder radial, the Alcides.

Adapting the GR14K to use 100 octane would have potentially yeilded more power; one question is how efficient was the supercharger compared with that of the Hercules? There were two versions with low and medium rated superchargers.

 

[Shortround6]

The GR14K can't do the job and any attempt to use it means the RAF is stuffed anyway. The Gnome-Rhone company themselves were developing the "N" series engine from 1935 onward and were flying the First "R" series engines in 1940.
The Alvis engine was sort of a "imperial" mish-mash of the K and N. The N used beefed up crankshaft, crankcase and more fins on the cylinder heads.

Sources are rather contradictory on the K and N engines but weights generally run between 1200-1500lbs. Engine life at the higher powers is suspect. Please remember that best the Russians got out of this line (the M-88 series) was 1100hp for take-off and perhaps 1000hp at 6000meters using 95 octane fuel and a weight of 1500lbs. Compared to earlier versions the M-88 the 88B had increased ribbing (finning?) on the cylinder barrels and heads, strengthened connecting rods and pistons, modified drives to the units (accessories?) a carburetor with economizer and oil injectors on the crankshaft (?). Of course ALL M-88s used a two speed supercharger drive instead of the single speed used on the parent engines. It took until Nov 1939 for an earlier, lower powered version to pass it's 100 hour test but problems dogged the M-88 (about 100 engines had to be removed from aircraft after flight testing at the aircraft factories) and it's production was suspended in and then resumed in late 1940. Designer Tumanskiy was removed from his post and replaced by E.V. Urmin.
British quality may well have been better but the basic design seems to have had some fundamental flaws that would take a lot of modification to change. The "K" may have been a decent engine in 1931 when it was introduced (not design started) at 626hp but trying to push the design to 1000hp may have been asking too much.

The Mercury could pull 840hp at 14,000ft using 87 octane gas from 1935 on (VIII). With 100 octane it couldn't do any better at altitude but picked up power at lower altitudes.

 

[Shortround6]

Adapting the GR14K to use 100 octane would have potentially yeilded more power; one question is how efficient was the supercharger compared with that of the Hercules? There were two versions with low and medium rated superchargers.

The G-R series had the flaw of no center bearing on the crankshaft between the two cylinder rows. Increasing the force acting on the pistons (higher boost and cylinder pressures) is going to result in more crankshaft flex and failed crankshafts or failed bearings or both. The structure of the engine is limit on power with this engine. Please note that the G-R "R" series engine being flown in 1940 DID USE and center bearing but it needed a new crankshaft and crankcase and picked up several hundred pounds in weight.