DB 603 vs Ju 213

[silence]

I understand that Kurt Tank favored the 603 over the 213, being of the opinion that it was a better high-altitude engine. Why is this? What made it better for high-altitude use? Also, is there any special reason why they had their supercharger intakes on opposite sides, and could they have been reversed easily?

 

[tomo pauk]

I'm not sure that Dr. Tank was favoring the DB on the grounds that it was a better high altitude machine, but at the grounds that 603 was available about one year earlier.
The supercharger intake position was a non-issue, the airframe producer can easily produce the part(s) needed for the cowling of any of those two.
As for what one was better - prior 1944 there is no match, since only the 603A is available. Once the 213A is available, it's higher RPM can counter the greater displacement of the 603, so the output was roughly equal above 6 km.

 

[spicmart]

The exhaust tubes of the Jumo 213E were to produce more thrust than those of the DB 603L, which had 74 kW more power than the Jumo,
so much that the 213 E was considered to have superior propulsion performance to the 603 L.

 

[tomo pauk]

Care to elaborate the part about the Jumo 213E producing more thrust than 603L?

 

[rinkol]

Tank's thinking may have been motivated by several factors:

- 4 valves per cylinder (1 more than Jumo 213)
- variable speed supercharger drive (though later versions of the 213 benefited from a three speed supercharger drive)
- presumed early availability of DB 603 versions having improved high altitude performance (DB603E and G)

In practice, the early DB603s had unacceptable reliability for single engined aircraft and the high altitude versions only became available at the end of the war or not at all. It may be that, of the versions having two stage superchargers, the Jumo 213E was available earlier than the DB 603L, though neither was available much before the end of the war.

 

[tomo pauk]

The inital batch of the 213As were having issues on their own. By Dieter Hartmann about why the the early tests (Oct. 1944) of the Fw-190D-9 fell short vs. estimates/guarantees (here):

Those first production engines produced 60-100PS less than the book values used for performance calculations.

(another reason being the differences between mock-up(s) and real airplanes)

We can note that really early 213As were produced almost a year before those tests (those went to the Ju-88/188), yet even with a year of the lead-in they were not making the advertised power.

Rinkol:

In practice, the early DB603s had unacceptable reliability for single engined aircraft

Any good data about that (when the problem was encountered/remedied, etc.)? Maybe from an easily obtainable reliable source?

 

[spicmart]

Care to elaborate the part about the Jumo 213E producing more thrust than 603L?

I don't quite understand. My source mentioned just that. And I am an absolute layman to answer those details.
But I'd like to know how this exhaust thrust is measured.

 

[rinkol]

There is the circumstantial evidence: up to late in the war, the DB 603 was only used in twin engined aircraft (Do 217, He 219 and Me 410) despite promising performance figures obtained with some of the FW 190C prototypes.

Suzuki (Romance of Engines) mentions problems with the distortion of the cylinder liners.

Griehl's book (Do 217-317-417) makes numerous mentions of problems with the Do 217 engine installations and the effects of DB 603 engine shortages on production of this aircraft.

(pg 92) "The 100 hour engine endurance trials began at Rechelin on 21 December 1942, the pistons burning through after 91 hours. Testing of the newly installed DB 603A-2 inline engine was carried out beteen 28 April and 8 May 1943, but the program was beset by continual breakdowns and many defects and was abondoned."

pg 96 "As early as 2 June 1942 - at least from the viewpoint of Generalingenieur Eisenlohr - the DB 603 was at a stage of development which was far removed from any possible introduction into service. Defects in the transmission, oil circulation system and supercharger coupling all combined to frustrate the smooth performance that had been expected."

Pg 97

" ... it was realized finally [June 29, 1943] that the DB 603's unreliability and its unfitness for series production had thown the entire program into disarray. Only a modest requirement for equipping the HE 219 was assured of going ahead, albeit with many misgivings."

"For a few weeks in August 1943, it seemed as though all Do 217 variants which had been planned to have DB 603 engines would have to be abandoned"

pg. 97.

"In September [1943] fresh reports had been submitted to the Luftwaffe leadership detailing the mass of defects in the DB 603. One such report, for example, originating in July stated that all 14 Do 217Ns of II/NJG 3 had been grounded with severe engine troubles." By October, the situation had deteriorated further ... " Apparently, the situation had reached the point where some aircraft were refitted with BMW 801s.

(pg. 212) "... in this period [Summer 1943], 107 sub-standard DB 603 engines alone were produced in June. In addition, a further 43 engines did not have crankshafts and were also useless."

It is also mentioned that plans to install DB 603s in five Ju 88s were abandoned.

There is also a reference in Irving's book on Milch to him making a negative comment about DB that probably refered to the DB 603 .

On the other hand, the DB 603 did not seem particularly troublesome in tests carried out by the allies on captured aircraft, at least judging rom Eric Brown's account of the Do 217 testing described in his book "Wings of the Luftwaffe". It may be that the main problems were eventually solved later in the war.

 

[davebender]

RLM eliminated funding for the DB603 engine program during 1937. Some funding was grudgingly restored after the 1940 Mercedes-Benz T80 publicity stunt. The T80 was powered by the the third DB603 engine prototype (modified of course).

RLM couldn't kill the DB603 program completely because influential aircraft designers such as Dr. Tank wanted it. So they did what every bureaucracy does under these circumstances. RLM put a series of administrative obstacles in the way which prevented the engine from being fully developed and produced in large numbers.

Jumo 211 and Jumo 213 had the opposite situation. Almost unlimited support from 1937 onward. However it took Junkers longer then expected to achieve performance similiar to the DB603.

 

[Tante Ju]

The Jumo 213A and DB 603A were practically identical engines in output, including high altitude output. They weighted pretty much the same, though visually the Jumo engine does seem to be a bit larger.

 

[tomo pauk]

Rinkol, thank very much for the typing effort, appreciate it You do make a strong case re. unreliability of the 603 in 1943.

I don't quite understand. My source mentioned just that. And I am an absolute layman to answer those details.
But I'd like to know how this exhaust thrust is measured.

I'm not an expert, too. IIRC the exhaust thrust depends upon the weight of exhaust gases (more HP = bigger weight) and the gases' exit speed (should be about the same, for same altitude speed; design of the exhausts might intervene here). I'm obviously looking to be educated here

 

[rinkol]

The German development programs were certainly beset by political infighting and many questionable decisions were made by senior officials.

On the other hand, it is not unusual for industrial organizations to find ways of blaming governement and other external factors for their own shortcomings. DB certainly must have made optimistic promises - among other things, the He 219 was originally designed around the DB 603G, an engine that was never really available. It also appears that they overextended themselves - there was a nearly unbelievable proliferation of engine development projects. While many of these were based to some extent on existing designs, the dispersion of resources would have militated against the overall prospects for the timely completion of projects.

Junkers was not without their own problems. The cylinder dimensions of the Jumo 222 were changed three times with the last versions of the engine reverting to the original cylinder size. I think I've seen the expression "developed to death" in connection with this engine.

 

[Shortround6]

The "1940 Mercedes-Benz T80 publicity stunt" never happened. It was canceled so it is a little hard to see how it influenced things.

Land speed record engines ( or water speed or even air speed) have darn little to do with service engines and anybody with any brains in anybodies air ministry knew it.

The British got the old Napier Lion (designed in 1918) up to 1350hp for racing use by 1930/31 (or a bit more?). They never used a service engine at more than 600hp.

Rolls Royce got their "R" racing engine (same bore and stroke as the Griffon) up to over 2500hp in 1931.

Getting that power from gasoline instead of racing fuel and with service level reliability and durability took a few more years.

Ground tests of the Merlin for the "Speed Spitfire" not only touched over 2100hp they held 1600hp for over 10 hours but it took another 5-6 years for a service Merlin to approved for over 2000hp.

DB's own 601 racing engines used in the He 100 and Me 209 also show the same disconnect. Being pushed to over 2000 hp (or well over?) in 1939.
3000hp in a record car might mean 1500hp (or less) from a serviceable aircraft engine.

 

[Shortround6]

I'm obviously looking to be educated here

Wish I could help but most of what I know (or think I know) comes from a Rolls-Royce Heritage book. A couple of NACA reports and some very scattered references/remarks. For example when Allisons were approved for WEP ratings the exhaust stacks had to sawed off as shortening them opened up the area to suit the higher exhaust flow. While the original size gave the best exhaust thrust at the original exhaust gas flow, the increased flow of the WEP airflow was restricted too much causing high back pressure and loss of crankshaft HP.
Getting the exhaust thrust to give optimum power was quite a trick as the exhaust thrust varies with the weight of the "charge" (air+gasoline+any additives like MW50) and the gas exit speed as you stated. The charge weight varies with altitude slightly until critical altitude is reached, since even the temperature of the ambient air affects the charge weight. Above the critical altitude the charge weight drops as the the supercharger can no longer supply the volume (weight) of air as it did below the critical height. Exhaust speed is not only dependent on volume and exit size (assuming like exhaust passages) but the ambient air pressure. At around 20,000ft the air, having about 1/2 the air pressure of sea level, offers much less resistance to the exhaust so that the exit velocity can be several hundred ft/sec higher.

Turning this variable exhaust thrust into exhaust power is even more difficult since the power is related to the speed. The faster you go the more power you get from the same thrust ( at least for most normal aircraft. Planes that exceed 1200-1400FPS may well show decreased power?)

Even if you really, really know what you are doing you can only set up the exhaust stacks to be optimum for ONE flight condition. That is ONE throttle setting (boost level) at ONE altitude (both intake air pressure/temperature and exhaust back pressure) at ONE speed.

I have no idea how wide a range of conditions you can get a useful benefit from if you try for a "general use" opening vs one that is too specialized or even if there is a "general use" opening. I would be wary of statements that say engine "A" had better thrust than engine "B" without some idea of what altitudes/throttle (boost) settings and speeds were being compared. It may be true or it may be that one engine was optimized for a different condition than was being tested.

 

[rinkol]

I would think that, all things being equal, any differences in the exhaust thrust would result from differences in the velocity of the ejected exhaust gas. This is going to depend on the diameter and shaping of the exhaust stacks. Reducing their diameter might increase the exhaust velocity, but also increase the back pressure and thereby reduce the engine mechanical power. Consequently, there has to be some effort made to optimize the overall engine effectiveness. This is very speculative, but possibly the use of a single exhaust valve in a cylinder by the Jumo 213 might have altered the tradeoffs here.

 

[davebender]

More RLM meddling. If it were up to Junkers the Jumo 222A engine and Ju-288 bomber would have entered mass production during 1942.

 

[Shortround6]

A boon to the allies.

The Jumo 222 never worked properly in any of it's various incarnations.

And which Ju-288? the 581 sq ft wing version, the 635 sq ft wing version, the 645 sq ft wing (or is it 696sq ft?) version?

Which defensive armament set up and what bomb load? both in a constant state of flux.

Estimated performance or actual tested performance?

And of course the Germans would have no trouble "what so ever" with the remote controlled guns and sighting periscopes ( which never really worked for anybody that tried them).

 

[Siegfried]

I understand that Kurt Tank favored the 603 over the 213, being of the opinion that it was a better high-altitude engine. Why is this? What made it better for high-altitude use? Also, is there any special reason why they had their supercharger intakes on opposite sides, and could they have been reversed easily?

The Jumo 213 used a compression ratio of about 6.5:1 whereas the DB603 used a compression ratio of 7.5:1 and likely 8.5:1 for C3 optimised versions. The 603 also had more swept volume.

Thus the Jumo 213 would need to use considably higher pressure ratios to achieve the same power as the 603.

Hence the single stage supercharger on the 603 would have more reserve for altitude compensation.

Both engines moved towards two stage supercharges both with and without inter cooling.

The Db603 seems to have been ready nearly 1 year before the Jumo 213.

It seems to me that with the benefit of hindsight that the huge effort put into the DB604 could have been redirected to the DB603 and even 605 since the X24 DB604, despite its good test results was cancelled in favour of the Jumo 222. One would then at least expect the DB603 to level peg with the DB605 but with about 30 % more power well ahead of the Jumo 213 in timeline and also altitude performance.

Something like a Fw 190D13 or even Me 309 could have been in production around mid 43 in time to meet the P-51B onslaught starting December 43 with an engine offering better altitude performance than the BMW801 and about 15-20mph drag reduction. With potentially 2250hp on tap in early 44 some 444 mph should have resulted. A rather fast Ju 88S bomber or Ju 88G night fighter would have resulted.

 

[GregP]

Exhaust thrust is not an issue at low power or cruise power. The only time exhaust thrust is important is at rated power or WEP, when all the power and speed you can get is what is needed.

Exhaust thrust depends on several factors including exhaust mass and volume. Another one is the shape of the exhaust manifold / pipe / pipes. If the area starts at the exhaust exit and decreases gradually to the end of the pipe, the exhaust increases in velocity, much as air does through the front half of a venture tube. It is usually called an "ejector" exhaust. That ALSO increases back pressure. SOME back pressure is needed for highly-tuned engines and exhaust systems. If the pipe starts at the exhaust exit and then slightly increases in area, then the exhaust velocity is reduced a bit and thrust is not likely a factor. If the area stays the same all the way down the pipe, then the exhaust velocity depends entirely on the exhaust mass and speed coming from the exhaust valve. The Mistubishi Zero had exhaust ejectors and they helped top speed by some 10 – 15 mph at full throttle and at critical height. Probably didn't help much at takeoff or lower throttle settings.

I am not an expert on German engines, but the performance at altitude also depends on the supercharger gear ratio, impeller diameter, number of impeller blades, impeller design, smoothness of the stator intake and exit from the supercharger, and the shape and efficiency of the intercooler if so equipped. It is difficult to believe all these factors were identical for two engines developed by different companies, but not impossible. Probably one or the other had advantages, even if slight at particular heights. At max height, they could well be almost equal, so the nod SHOULD go to the one that is more reliable, with the better time between overhauls, and/or ease of maintenance service … in no particular order.

The Jumo 213 was perceived as a "bomber engine" by Kurt Tank and he told as much to the fighter pilots, but it gave yeoman service in the Fw 190D-9. It was a better engine than either the designer OR the pilots expected.

 

[Tante Ju]

This may be interesting.

b = DB 603A
c = Jumo 213A

The DB engine is better at mid altitudes but the Jumo is just as good at high altitudes. Of course the DB 603 had a lot of room for development (as shown by the ultimate DB 603N).