RR Merlin vs the DB series

[Angus]

By starting this thread, I am basically looking for information so I can compare those two wondeful pieces of machinery. However, the best way to gather information in this place is to throw a flamer. Hmm...maybe the thread topic should have been something like "RR MERLIN BEATS DB!!!"....but...I'll skip that.
But yet, which engine was the better one? Weight to power?  Durability? Maintenance? Ability to be tuned to further power output? Wear and tear?
For what it's worth, I'd put my money on the Merlin. Now, as far as I remember, the Merlin weighted less pr.hp, needed a smaller coolant surface, and would have a longer lifetime. I am not sure about maintenance, fuel consumption etc, but anyway, this is all about info, so please shoot:D

[VOR]

Then again, history is written by the victor......

[HoHun]

Hi Angus,

>But yet, which engine was the better one?

I'd say they were perfectly matched :-)

The Rolls-Royce Merlin generally yielded a higher specific power output than the Daimler-Benz, but the DB series engines generated equivalent total power despite employing inferior alloys and lower grade fuel (not by choice, but by necessity). The key to that was greater displacement and the use of a sophisticated fuel injection system which the Merlin didn't have.

Early in the war, the DB series engines held an advantage in high-altitude power due to the variable-speed supercharger. When the two-stage supercharger was introduced, the high-altitude advantage went to the Merlin-engined fighters. On the other hand, in specialized aircraft GM-1 injection restored the Daimler-Benz superiority at extreme altitudes.

While the Merlin was capable of running at higher revolutions than the Daimler Benz, MW50 injection gave the DB engines as much or even more power. Engine life probably was greater with the Merlin engines, but the DB engines were reliable throughout their design life, even if it was shorter.

The Merlin had a small frontal area due to the supercharger being aft of the engine and not on the side as with the Daimler-Benz, which was especially pronounced when the latter was fitted with large high-altitude superchargers. On the other hand, the inverted layout of the DB engine allowed a better view over the nose, and the lateral supercharger placement allowed fitting of a ballistically favourable engine cannon.

There are probably quite a few more pros and contras for each of the two engine series, but in the end, it came down to the performance of the aircraft fitted with these engines - which was very close for most of the war, including the last few months when the DB engines reached their peak (while Merlin development continued for a while after the war.)

Actually, the comparison probably could be extended beyond the Merlin and the DB605 to the Griffon and the DB603, and yield similar results.

When the British analyzed German piston engine technology after WW2, they were impressed by some of the detail solutions, but generally found they couldn't learn much from it since both sides had achieved similar results using different methods - an obvious case of parallel evolution.

(However, they might have been more interested in the details, redundant to British technologies or not, if it hadn't been for the jet engine which obviously was destined to replace the piston engine in the near future :-)

One important technology which the Germans didn't develop and the Merlin didn't employ was the turbo supercharger. The Merlin had satisfactory high-altitude performance even on its engine-driven supercharger (plus residual exhaust thrust), and Germans were facing shortage of high-quality alloys as well as shortage of engineering man power because most of the experts with the know-how to design turbo supercharger were working on jet turbines instead.

Regards,

Henning (HoHun)

[funkedup]

If you want to compare the Merlin to a DB engine, the best choice would be the DB601 and DB605.

If you are interested in the DB 603 you should compare it to the Gryffon.

Generally, the two-stage Merlins were better than the later 605's.  But Single stage Merlins weren't at a big advantage over the 601's and earlier 605's.  The DB's had fuel injection from the start, while Merlins didn't get fuel injection until the 60 series.  DB's were also designed to have a cannon firing through the prop spinner, a definite packaging advantage.  I don't have any information on cooling requirements.

It would be interesting to look at the following for several versions of each engine:

Max HP
Max HP/weight
Max HP/displacement
gal/hp-hr
Highest critical altitude and power at that altitude.

Those will pretty much tell you who was the boss.

[VOR]

On the other hand, in specialized aircraft GM-1 injection restored the Daimler-Benz superiority at extreme altitudes

I understand this little bit, but could one of you please explain to me what exactly "water injection" was/ is? I know this is a little off- topic with the thread, but I have read about it to a small degree in the few reference books I have and am very curious how injecting water into an engine could boost it's performance


Thanks!

[J_A_B]

The DC 600 series would hav ebeen a great engine if they weren't upside-down  


J_A_B

[funkedup]

Originally posted by VOR
I understand this little bit, but could one of you please explain to me what exactly "water injection" was/ is? I know this is a little off- topic with the thread, but I have read about it to a small degree in the few reference books I have and am very curious how injecting water into an engine could boost it's performance


Thanks!

Water injection allows higher supercharger boost (or compression ratio) without damage or wear on the engine.  Basically it cools down the fuel/air charge and prevents detonation.  Methanol was added to prevent the water from freezing at high altitudes.  Systems of this sort are variously known as "water injection", "ADI", "methanol-water injection", "MW 50" and probably some other names.  All are referring to the same technology.

GM-1 was something completely different.  It was an injection system that used nitrous oxide.  This was used to give the engine more power at high altitude.

[VOR]

Thanks Funked, that's been a mystery to me for a while

[Angus]

The Germans tried to run captured and restored Spitfires on DB engines, but had troubles with overheating due to the Spitfires lack of radiator surface (probably) Makes me wonder how their total frontal area including radiators compares.
As it goes for boost and robustness, 60 years old Merlins being squeezed up to a whooping 3000 HP are still running in P51's at the Reno air races.
The late DB's would wear out quite quickly, but it is most likely a result of alloy shortage rather than design.

[whgates3]

Originally posted by Angus

...The late DB's would wear out quite quickly, but it is most likely a result of alloy shortage rather than design.

would this make the DBs relativly more vulnerable in combat?
which engine was easier to knock out in air-to-air combat?

[Staga]

http://w1.1861.telia.com/~u186104874/db605.htm

btw those "60 years old Merlins" are usually using strenghtened post-war engines / cylinder blocks which were made to be used in commercial planes after the WWII.

[GScholz]

The German jets were copied by the russians, and powered the Yak-15, Yak-17 and Mig-9 fighters. After the war German aircraft production was devestated, and early post-wwii the germans were forbidden to produce aircraft engines (among other things). This led to the Allied nations getting a significant lead in engine development. To give an example of the rediculous restictions forced upon a post-war german industry, they wern't even allowed to participate in auto-sports like Formula One until the '60's (or late '50's, I'm not sure), but when they did they swept the (former) allied nations away. Winning nearly every race with DB and BMW engines.

[niklas]

hmm let´s see:

DB605:
- inverted engine, allowing better view, and (more important) better aerodynamics with low mounted wings
- central propeller shift, going right through the COG, allowing for very aerodynamic nose shape, while RR engines had the shaft quite high, reducing nose shape aerodynamic quality and producing pitch down moments (but allows mounting a larger propeller or shorten the gear)
- no "power hole" due to gear shift of the supercharger. Continous power in all altitudes.
- optional 2nd gear (GM-1)
- better fuel consumption due to higher compression, lower RPM, and direct fuel injection.

I really can´t see advantages of the Merlin. It was already said that RR engines didn´t suffer from shortcomings ofalloys, this was the major point. Nevertheless the 605DC engine could run with 1800PS on B4 fuel (87 oct.).
But RR engines were of course very reliable. Lerche said in his book: The Rolls Royce engine run like you expect it from a Rolls Royce.

About racing engines: Before the war the 209 was powered by a DB601 engines. They just changed the compression and gear ratio, everything else remained the same. It run with 2770PS.

niklas

[HoHun]

Hi Oedipus,

>For instance VW still made the pre-war Beetle in post war Germany to help get the economy rolling,

In WW2, Volkswagen had turned out military vehicles based on the Beetle technology, but the Beetle itself didn't really enter mass production until after WW2. The Beetle was a technologically advanced high-quality car that competed successfully against later designs all over the globe for decades to come. The cars that got the German economy rolling were much more modest than the Beetle - and they were build by companies with names you might recognize. The Heinkel "Kabinenroller", the Messerschmitt "KR175" and "KR200", the BMW "Isetta" - they all were swept away when the economy got going and the Germans could afford expensive high-quality cars - which at that time simply meant the Beetle.

http://www.pcsystems.com/messerschmitt/mess.html

http://vintagecars.about.com/library/weekly/aa121497.htm

>Same with the German jet engines. If they had indeed been superior they would have been copied.

You don't see many jet engines today that still have radial turbines, unless you're into RC models. Radial turbines were the Allied way of building jets. Today, jet engines universally have axial flow turbines, and that's just how the German jet engines were built.

In 1945, even the Germans would not have copied the Jumo 004. The experience they had gained with the Jumo enabled them to build much better engines - and so all over the world, German engineers were working on new jet engines after 1945. The Soviet Union was lacking the basic technology as well as the German top experts, and so they copied the old WW2 jet engines (and improved them, demonstrating their untapped development potential) to get the best understanding of the new technology that was possible in the short time.

Regards,

Henning (HoHun)

[GScholz]

Originally posted by Oedipus
GScholz those Russian planes had poor performance at best with those copied German jet engines. It wasn't until the Mig-15 with it's RD-45 engine (which was a copy of the Rolls Royce Nene. A WWII engine from early-mid 1944)  that a real threat was posed to Western air forces.

 Oed

The RR Nene wasn't available for production until 1946, when the US bought a license for it and used it in the Phanter. The Soviets got it in '47 I believe. So if you mean that the development of the Nene started in '43-'44, I believe you. The development of the Jumo and BMW jets started in the late '30's.