Author Topic: RR Merlin vs the DB series (Read 9459 times)

gripen · « **Reply #15 on:** November 13, 2002, 04:30:42 PM »

IMHO the DB 605 and the DB 603 were good designs and mostly par with the competion. The problem was that neither them did not really get advanced and mass produced airframes to combine with.

gripen

M.C.202 · « **Reply #16 on:** November 14, 2002, 12:22:16 AM »

Quote:
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.
End quote.

The reason the main allied jet engines were "radial" was that it gave the best life span for thrust, and were easer to build given the state of the art of the time.
The axial flow type was known, hell Lockheed had started prototype development of an axial flow engine with a built on afterburner in 1940-41 to go into Kelly Johnsons' FIRST jet design. The one the government told them to stop work on, and then made them sell the engine design to a non airframe company. They did not want wasted time on "Buck Rogers" programs:rolleyes:

If I had to build a jet engine I would fly with using 1940-45 theory and production tools, the GE J-33 series made from 3,750lbs thrust (J33) up to 5,500 lbs (J33-A-35) thrust with good life spans.

GScholz · « **Reply #17 on:** November 14, 2002, 03:17:50 AM »

The simple fact of the matter is that the Jerrys got a jet-fighter operational in good numbers (considering their supply problems) that was a serious threat to the allies. The Brits got their jet operational too late to have an impact (proven by the fact that the 262 and the Comet never faced eachother in combat), and the Yanks never got a jet operational at all during WWII.

GScholz · « **Reply #18 on:** November 14, 2002, 03:24:29 AM »

Another point: A wealthy American, whos name I no longer recall, owned a 262 in the 50's, and he was BANNED from using it in a jet air-race. The US A/C manufacturers was afraid that this aging German warbird would out fly its modern US competition. Hmmmmmm

HoHun · « **Reply #19 on:** November 14, 2002, 03:47:37 AM »

Hi MC202,

>The reason the main allied jet engines were "radial" was that it gave the best life span for thrust, and were easer to build given the state of the art of the time.

Actually, Whittle invented the jet engine as a radial turbine in an evolutionary process coming from conventional superchargers. Von Ohain skipped the evolutionary process and invented his jet engine as an axial flow turbine right away, but built the first technology demonstrator as radial turbine as well for ease of production.

The jet engine comparison is a quite complex topic as well, and Gersdorff et al. give some good information. However, I'd think we'd need a new thread for that :-)

Regards,

Henning (HoHun)

Angus · « **Reply #20 on:** November 14, 2002, 04:25:17 AM »

Oopsie, we're all into jet engines now!
Well, the German way of making it was more modern, but a tad too much ahead of its time. The brits made a more sensible choice for the time, building engines that ran reasonably well, and are even still powering old birds TODAY.
Oh, and they sound so cool:)
But back to the old DB and RR. It has been pointed out that the DB has quite some things in its favour, - as a design, - it may be excused a bit for alloy shortage and lack of proper fuel. Makes one wonder WHAT IF, etc.
Oh, and as expected, Niklas pops up with his affection for german machinery, or as he puts it:
"I really can´t see advantages of the Merlin".
But the Merlin had advanages in Real Life! It was lighter, and had a smaller frontal surface for the equal or better amount of power.
That looks like an advantage to me.
However the DB had a better power output pro octane and as pointed out by Niklas, an upside-down engine gave an opening for a more aerodynamic nose.
Does a more aerodynamic nose definately make up for a shorter propeller? And do not forget that the surface was larger both because of the coolant surface and the position of the Turbine.
Hmm, don't know, - look like a pretty even pair to me.
Oh, btw, - here's a nice Merlin thread:
http://www.wwiitechpubs.com/hangar/ac-uk/ac-uk-eng-rolls-royce-merlin/ac-uk-eng-rolls-royce-merlin-br.html

niklas · « **Reply #21 on:** November 14, 2002, 11:00:32 AM »

"Does a more aerodynamic nose definately make up for a shorter
propeller?"
Yes

"And do not forget that the surface was larger both because of the coolant surface and the position of the Turbine. "

The compressor was no problem, with the enlargement due to the Mg131 the fuselage had to be widen anyway.

"It was lighter..." (the merlin)
Here you are completly wrong. Don´t forget that DB and all other engine manufacors had to deliver engine sets, not engine alone. So if you compare weights you need to compare the dry weights, which are as follow:
The merlin6x had a dry weight of 1645lb, 745kg.
The 605A had a dry weight of 1585lb, 720kg.
The DB605 was lighter.

" ...and had a smaller frontal surface"
Here u are wrong again, especially if u compare the space necessary for the installation in a aircraft with low mounted wings. Just compare the attachement. Though the G-6 is already shown with the bulges the frontal area was lower. The merlin was quite "high", just compare the height of a mustang too.

You can also see very well the steep fuselage gradient right below the propeller shaft of the spit compared to the smoth "dart" nose of the 109.

I´d really like to see on which data your opinion is based. Please show me

Thank you
niklas

F4UDOA · « **Reply #22 on:** November 14, 2002, 12:08:32 PM »

Gsholz,

You statement about the Yanks never having a Jet by the end of the war is a little off.

The P-59 was flying in 1944 and the P-80 was in production by wars.

Few airplanes in the history of aeronautics have been as successful as the Lockheed Shooting Star. It was the first operational jet fighter in the United States when it went into service in 1945. It emerged as victor in the world's first all-jet combat, and it won the distinction of remaining in production for a full 15 years after the experimental model was first flown.
The airplane had its origin in June 1943, when Lockheed was requested to design a fighter around the De Havilland turbojet engine developed in England in response to Germany's twin-engine jet fighter, the Messerschmitt Me 262. The XP-80 was designed and built in the amazing period of only 143 days--37 days less than the original schedule. It was flown for the first time on January 8, 1944, and its performance was considered sensational.
The Army Air Force planned to build the Shooting Star in large numbers. However, only two of the machines arrived in Italy before the end of the war in Europe, and these were never used in operations. Despite the cessation of hostilities, production was continued on a reduced scale.

FYI,

At this years air race at Reno there was a Jet class. Mig 15/17 and some L-39 Albatross. The fastest Jet lap speed was slower than the Props IE P-51's and Sea Fury's.

Fishu · « **Reply #23 on:** November 14, 2002, 12:54:57 PM »

Quote

Originally posted by Oedipus
If the DB had been the better engine then boat and aircraft racers would have been using them the for the past 45 years or so and not the Merlin.

Maybe it's just easier to obtain parts for engines of the winning side

Besides I really doubt the most used parts in the engine are half century old :>

gripen · « **Reply #24 on:** November 14, 2002, 04:29:33 PM »

Niklas,
There is not much sense to compare weights of the Merlin 6X and DB605A or should we compare outputs at 10000m? Generally single stage Merlins were lighter than single stage DB605s but single stage DBs did a bit better at high altitude than single stage Merlins. It should be also noted that the high altitude DB605AS did not reach production before spring 1944 while the two stage Merlins had been around about two years by that time. Two stage DBs failed to reach more than experimental service during war. RR was able to develop engines to service stage faster than DB.

gripen

Angus · « **Reply #25 on:** November 15, 2002, 09:01:33 AM »

DB 605 has from my sources the same weight as the absolute heaviest Merlins 60 series), almost to the pound. Merlins: 744-746 kg's, DB 605 730-745 KG. Dryweight of course. However that is a Two stage Merlin! At altitude it was quite superior to the DB 605 for whole two years, from spring 1942 to spring 1944.
To compare something with the same alt performance would be nearer to the Merlin 46/47 weight 628 kg's, and that is still a high level engine.
Now going back to DB 601 which was also a competitor of the Merlin, the DB 601 yealding 1175 hp weights 600 kgs while a Merlin 45 weights 628, Merlin is heavier here, but also peaks at 1515 hp! I am aware that the DB 601 was squeezed up to 1400 hp or more, but sadly have no data on how it affected the weight.
The thing about the frontal area I had from HoHun in this thread, but I'll measure your picture anyway.
What also just crossed my eye is how much bigger volume the DB engines have, DB 605 has practically the same volume as a Griffon so maybe that would be a better comparison

oh, BTW, Niklas: Do you have a similar picture of a Mustang? Wonder what the overall nose area of a Mustang was, that's all.
Well, again the Mustang being faster than any 109 with the same engine size, I guess the wing-design+ prop length more than made up the drag of a bad nose, hehe.

niklas · « **Reply #26 on:** November 15, 2002, 03:41:02 PM »

Hi Agnus

With your last sentence you instinctivly came to an import conclusion.

But first some technical data.
The dry weights of the 605 were:
605A 720kg
605AS 730kg
605D 740kg

The single stage merlins were no high level engines. You were wrong about the power output too.
The only single stage merlin with 1515hp in 11k was the 55A.
The 45 peaked out at 1470hp in only 9250ft
The 45M at 1585hp in only 2750ft
The 46/47 at 1415hp in 14000ft

The DB601 was available in at least 3 major variants. The most powerful was the 601E which was 30kg heavier than a 45 and could do 1320PS in 15700ft. So over 16k feet both engines put out approximatly the same.

Comparing power one must always be careful because RR engines list always highest power in critical altitude. Power at sealevel was always a bit lower.

Only the 61 was really better at high altitudes. The 65 was in 20 and 30k approximatly as good as the DB605A. The 68 again had 2k higher critical altitude, giving the advantage a bit back. Maybe it should be better compared to the early 605D which was available also in 42, at this point without the larger supercharger.

DB engines did not have 2-stage supercharger, except for the very late 605L which was mounted on 2 109 at the very end. But they did not have a single stage either. It was a multi-stage if you want, the supercharger speed was continously adjusted over 2km. This avoided the power hole.

If you reduce the question down to a power comparison, neglecting material, fuel, design, installation and other things, RR engines will lead, especially in a power/volume comparison, even if you bring them down to same RPM.
But it is really also a question of material and design. Turbo-Diesel car engines have usually a lower life expectance, because they use same power as normal engines on smaller components.
More power is wasted when the installation forces you to have more drag or weight. A merlin was build with the design philosophy of WW1 engines at the end. Don´t forget that the first spits and hurricanes didn´t even have constant speed propeller ( the first prop speed gear was used only for takeoff anyway), so a high shaft for a large propellor was necessary. Unfortunatly this cost some power due to the inferior installation.
A power to weight comparison becomes even more difficult. How much energy had to be taken away from the engine by the coolant? This would give you a hint for the necessary cooler area/weight. How heavy was the necessary propeller to drive it? Compare the fuel consumption, this means necessary weight of the fuel (lower on DB), the necessary oil (lower on DB).
So at the end it becomes really more and more a question of the whole aircraft design, what you instinctivly did in your comment.

If you compare power/volume and altitude performance the RR will lead in most cases, but the DB could get close by compensating for the inferior power due to more modern layout.

And when you include also engine managment systems, oh my... . On the other hand, the spit14 copied the german single lever system, so at this point the advantage was neutralized.

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? Imagaine, the 601N could do the same, using a hydraulic-mechanical system. So this idea is actually very old, and now they celebrate it as a high-tech idea

(ok, they can adust parameters much better today of course)

Staga · « **Reply #27 on:** November 15, 2002, 04:36:50 PM »

Quote

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? Imagaine, the 601N could do the same, using a hydraulic-mechanical system. So this idea is actually very old, and now they celebrate it as a high-tech idea (ok, they can adust parameters much better today of course)

O.K, you got me awake. Where can I found more info about this?

niklas · « **Reply #28 on:** November 15, 2002, 06:33:36 PM »

ups , i made a mistake. It wasnt the 601N but the 603N. Big sorry. 601N was too present in my memory

To understand the reason to change valve opening times you need some background information.

The advantage of direct fuel injection was not mainly a better combustion due to the injection. The main reason was that you could let the inlet valve open way earlier withour risking a "backfire" (?) to the carburator, which would have had desastrous effects.
Usual engines with carburators had 20-30° angles where the outlet and inlet valve where open simultanously.
With direct fuel injection much longer time periods where possible, what increased the cleaning of the cylinder of exhaust gases a lot - so the new combustion process took place with much more clean fresh air, this way you got more power.

Now that works fine at low level with angles of equal opening up to 120° or so, BUT at high altitudes a negative effect took place: Because the chain supercharger-inlet-outlet-atmosphere was open during this period, and atmospheric pressure drops with altitude, it could happen that your cylinder wasn´t filled anymore with supercharger pressure at high altitude. So valve opening times were a compromise in direct fuel injected engines, or let´s say, direct fuel injection couldn´t be used to the maximum.

For that reason they developed an adustable system for the valve opening times (the absolut times were of course the same).

I only have this drawing in pretty bad quality, but it shows the basic concept quite well.

niklas

Staga · « **Reply #29 on:** November 15, 2002, 07:17:55 PM »

Looks like a Vanos-system used in BMW's. IIRC Alfa-Romeos did use similar system already over 10 years ago where oil-pressure was changing timing of the camshaft.

http://autozine.kyul.net/technical_school/engine/vvt_3.htm