Author Topic: RR Merlin vs the DB series (Read 9460 times)

Angus · « **Reply #30 on:** November 15, 2002, 07:55:13 PM »

Niklas
I bow for thee!
I must say, that:
Your information database,just as your enthusiasm in putting in data,is a great contribution to the AH community. As to myself, it is a most pleasing opportunity to be able to shoot out a thesis,based on brief assumptions, (well, not always), and through the AH community getting very professional answers or at least backed-up opinions.
I have to study your post better, and may be able to add some to it, or at least figure out a teasing new post from the material

(unfortunately a bit busy at the moment)
Anyway, untill later..........and I hope we have some new stuff adding to this thread.

HoHun · « **Reply #31 on:** November 15, 2002, 08:00:16 PM »

Hi Niklas,

>P.S Did you ever heard that they change the valve opening times in the Formula 1 cars, and recently also in the BMW 7 series?

Here's a photograph of a Ferrari opposed 6-cylinder engine with variable inlet timing. I took the photograph at a recent visit to Maranello.

In front of the Official Ferrari Giftshop, I met a physicist who was designing automotive crankshafts, and it turned out he was a history freak as well, so soon we were chatting about WW2 aero engines :-) He really knew his stuff! I guess I should have asked for his email to get him onto this forum, but I was so amazed to meet someone with that level of expertise and enthusiasm regarding my favourite topic that I lacked the necessary presence of mind :-/

He wasn't particularly impressed about the above Ferrari engine, by the way, since apparently variable inlet timing was very much a standard technique when they experimented with it.

Regards,

Henning (HoHun)

gripen · « **Reply #32 on:** November 16, 2002, 01:33:29 AM »

Niklas,
The competion between the Merlin and the DB 601/605 happened mostly in the supercharger arena, with the given MAP the DBs did allways better simply because they were larger (27l vs 33 or 36l).

During BoB (1940) there was not much difference between them, the DB 601A did about as well as Merlin III while the Merlin XX had a slight edge over the DB. The Merlin 45 gave a little advantage to the Merlin at spring 1941 (improved supercharger and two speed Merlins got same iprovements simultaneously). I don't see hydraulic coupling as a big advantage over fixed gear, in practice the "power hole" (or what ever) is barely noticeable in the real world data; climb and speed values do not change that much. The hydraulic coupling wastes allways some power, the pilot just can't feel it like he/she feels the gear change. Also the Merlin could use interconnected propeller and throttle levers so there was not much difference in the engine handling in the combat.

At autumn 1941 the DB 601E reached service and did about as well or bit better than Merlins at high altitude. The DB 605A came at autumn 1942 and had advantage over single stage Merlins at high altitude (again because it's a larger engine). But the single stage Merlins got higher ratings same time and had a advantage at low altitude (16lbs boost and later 18lbs). It should be noted that the DB601E was pretty much a major redesign of the DB 601A and technically closer to DB 605 (supercharger system was totally redesigned, double pump system for hydraulic coupling).

At spring 1942 the Merlin 61 reached service and had a clear advantage at high altitude, more than 200hp at 10km and also the Merlin 66 did better than DB 605A at high altitude (say more than 100hp), at low altitude it was better until DB got the MW50 (but that time, 1944, Merlin got the basta).

The DB 605AS did about as well as the Merlin 66 at high altitude, say around 1000hp at 10km. But as noted earlier, it came quite late. And the DB 605D was not available before autumn 1944 and it did about as well as the 605AS at high altitude. Again the DB605D was a major redesign of the DB 605A.

The DB 605L was a promissing engine and it did about as well as best high altitude Merlin developements. The major problem in the German WWII aviation industry was that they did not get advanced engines and airframes to the mass production. The DB 605 specially lacked an advanced airframe to combine with.

In the fuel and oil consupmtion the DBs had an advantage over the Merlin but again I don't see it as very signifiqant; the Mustang could reach berlin but the Bf 109 did have problems to reach London (well, it could but not much more). The Merlin was installed to the several advanced and mass produced airframes like the Mustang and Mosquito while the DB 605s were mostly installed to the prewar airframes like the Bf 109 and Bf 110. IMHO the Bf 109 was not a bad airfame, actually underestimated nowadays, but it could not combine required performance, armament and range like for example the Mustang did.

gripen

Angus · « **Reply #33 on:** November 16, 2002, 04:04:23 AM »

A little question, or two:
With the Merlin having so much less volume, - like approx 2/3 of a DB, and (Didn't I read that somewhere?) lower pressure, how was it able to deliver about the same power? Certainly not because of the injection, - but just by using more fuel?
Also, boost comes into this. How much would one be able to boost a DB compared to a RR Merlin.
Then, I cannot but consider a little "what if" What if a DB had to run on a humble carburettor, or if a Merlin was blessed with an advanced german injection system???
hmmm.

gripen · « **Reply #34 on:** November 16, 2002, 06:52:25 AM »

Angus,
The Merlin did well mostly because higher boost. This was caused by somewhat better fuels, lower compression ratio (which allowed high boost), mixture cooling by fuel itself (which did not happen in the direct fuel injection engines) and intercooler (two stage Merlins). Also strong construction helped a lot; the Merlin passed test for 2640hp at 3000rpm and +36lbs boost with water injection. Of course a bit higher rpm (smaller engine) helped a bit. Anyway, as noted earlier RR could put their advanced engines to the large scale production fast, but the competion (namely DB and Allison) had problems to put their advanced engines to production.

Seems that people tend to overestimate advantages of the direct fuel injectition. While it gives very exact fuel metering it does not give mixture cooling advantage which carburator and single point injection systems give (later Merlins had Bendix injection carburators or single point injection systems by SU, Hobson or RR).

gripen

niklas · « **Reply #35 on:** November 16, 2002, 10:45:00 AM »

Gripen, according to my source the critical altitude of a 66 was in only 16k.
The V-1650-7 was surprisingly a bit better with 18.5k

Staga, thx for the link, i didn´t know that they used it after the war in so many cars (i didn´t wanted to say that they developed it first btw.). Most cars seem to be sports cars (?).
F1 cars of course use a completly different system, based on hydraulic control of the valvles exclusivly without a shaft, but the idea to control valve times like many other ideas go indeed back into the 20ies or 30ie of the last century.

niklas

Staga · « **Reply #36 on:** November 16, 2002, 11:58:05 AM »

-Same goes with disk brakes; they were invented in the beginning of the last century but were "forgotten" 'till the ww2 when they were used in the airplanes and after that in '50s car manufacturers begun to use them again.
-Superchargers were also from WW1, iirc Daimler-Benz was one of the firsts developing them. Supercharger was mounted under ordinary engine and was having a chain-drive wrom the propellors shaft.
-Anti-lock brakes; again developed for airplanes first.

btw I believe that F-1 cars are having electric or electro-pneumatic valves, my guess is hydraulics would be little too slow to operate when engines has +17000rpm on tachometer

gripen · « **Reply #37 on:** November 16, 2002, 04:14:08 PM »

Niklas,
Yes, the Merlin 66 did 1580hp at 16k without RAM. With RAM it did roughly 1000hp at 10km which is pretty much same as the DB 605AS did with RAM. The V-1650-7 had FS gear ratio 7,35:1 while the 66 had 7,06:1 (sources: "The Merlin in perspective" by Alec Harvey-Bailey and SIHL).

gripen

niklas · « **Reply #38 on:** November 16, 2002, 04:37:39 PM »

Sorry i disagree. In case you refer to the RAM power chart that includes the 66-68 and the 1650-7 - this chart seems to be based on the 18.5K critical altitude (1650-7, 68), because 4k altitude due to Ram would be a bit high. Or the best case, when RAM changes completly into pressure what wasn´t the case.

If you draw the line down form 16k instead of 20k you ´ll end in 33k or 10km very close to 800PS (even a bit lower) what was very comparable to the 790PS of the 605A in 10km.

niklas

gripen · « **Reply #39 on:** November 16, 2002, 05:14:11 PM »

Niklas,
Well, feel free to disagree but check for example this , 18k at climb and 22k at max level speed (actually FS height for +18 lbs was a bit higher because it still did +18,5 lbs at 22k).

gripen

funkedup · « **Reply #40 on:** November 17, 2002, 12:08:46 AM »

Quote

Originally posted by Staga

btw I believe that F-1 cars are having electric or electro-pneumatic valves, my guess is hydraulics would be little too slow to operate when engines has +17000rpm on tachometer

F1 cars use cams to open the valves and nitrogen to close the valves. But there are mechanisms which alter the cam profiles and camshaft phase, which are hydraulically actuated. Hydraulic power is also used for the steering, differential, and shifter on F1 cars.

Honda was the first company to use the hydraulic variable valve timing system on road cars. They had developed the system first in motorcyle and F1 racing, then on road bikes, before using it in autos.

gripen · « **Reply #41 on:** November 17, 2002, 02:44:09 AM »

Niklas,
I also checked some Bf 109G data (with DB 605A) and with RAM it's FTH was about 6200m at max speed (2800rpm and 1,42ata) at climb it's FTH appears to be about same as stated in the DB 605A manual ie about 5700m. So at max speed the Merlin 66 did 1580hp at 6700m with RAM while the DB 605A did 1355hp at 6200m with RAM.

At climb speed (358km/h true) the Merlin 66 did 1580hp at 5400m with RAM while the DB 605A did (climb speed about 400km/h true) 1355hp at 5700m.

Also we can see from the test data, the Merlin could maintain +6 lbs (MAP required for about 1000hp) up to about 32k even at climb speed.

So conclusion is that the Merlin 66 could do roughly 1000hp at 10000m with RAM while the DB 605A did roughly 800hp at 10000m with RAM. The DB 605AS did about 1000hp at 10000m with RAM so it was about equal with the Merlin 66. As for comparison the Merlin 70 could do roughly 1000hp up to 10900m even at climb speed. Late Merlin developements could do even better.

gripen

Angus · « **Reply #42 on:** November 17, 2002, 04:18:21 AM »

So there you go.
Merlin eats the DB
Thanks Gripen

gripen · « **Reply #43 on:** November 17, 2002, 04:47:44 AM »

Well, the DB 603L and DB 605L certainly had potential to compete with the best Merlins and Griffons. But these DBs came too late and did not reach mass production and there were no mass produced advanced airframes for them.

IMHO Junkers did better than DB, the Jumo 213A reached at least more than limited production and service and the Jumo 213E did saw some service too. And there were at least some advanced airframes for them but not really mass produced (Fw 190D, Ta 152H, Ju 188 etc.).

gripen

HoHun · « **Reply #44 on:** November 17, 2002, 05:15:39 AM »

Hi Angus,

>So there you go. Merlin eats the DB

Nice summary :-)

The truth is: With the advent of the two-stage supercharger, the Merlin held the high-altitude advantage (ignoring GM-1 for the moment).

The operational value of this advantage is another question. The Merlin 61 was deliberately designed for a very high full throttle height, so the RAF must have been convinced that it was important.

What the Merlin 61 did not do, however, was to make the Spitfire competetive with the Fw 190A at low to medium altitudes where the Focke-Wulf was strong. The Merlin 61 improved the Spitfire above 20000 ft mainly, and superiority over the Focke-Wulf was only achieved above 25000 ft. (Compared to the Messerschmitts, the Spitfire IX was better than the Me 109F-4 above 20000 ft and better than the Me 109G-2 above 25000 ft).

This seems to collide with two popular myths ;-)

1) With the Spitfire IX, the Spitfire series matched the performance of the Focke-Wulf. (Actually, while it was superior at high altitude, the Spitfire IX didn't much to close the gap at low and medium altitude.)

2) The Messerschmitt was designed for high altitude combat. (Actually, it was a mainstream fighter. It was the Spitfire IX that was designed for high altitude combat.)

How were the fighters used operationally? Well, the Spitfire IX undoubtly flew high-altitude fighter sweeps at its optimum altitude over France. The Luftwaffe fighters were employed against the British bombers who probably flew a bit lower than the Spitfires ...

Another interesting question regarding high altitude is raised by the history of the P-51. The P-51B at first was equipped with a V-1650-3 which gave a similar performance profile as that of the Spitfire IX with Merlin 61 engine - it was the best at very high altitude. For some reason, Mustang production soon switched over to the V-1650-7 with a reduced full throttle height for the high gear, reducing high-altitude performance for a bit more performance at medium level.

I've never found a good explanation for this change, but I've been told that some pilots didn't like this change as it reduced the performance at their typical operational altitude. However, I'd speculate that such an important change was not done without a great amount of operational research justifying it, but I've never even found something like that mentioned anywhere.

At least, it seems to show that best high-altitude performance is not always results in the best overall fighter, and that the optimum is dictated by the current operational requirements.

So I'd be a bit more careful with summaries ;-)

Regards,

Henning (HoHun)