On big radials

[tomo pauk]

The major big radial from Germany was the renown BMW 801. The 801A was introduced on Do 217 bomber, quickly followed by the sibling 801C on the Fw-190 (A-0 to A-2). The initial troubles with the 801C almost doomed the Fw 190 program, but the major efforts to increase the reliability of the engine and installation eventually saved the day. The 801A was erstwhile rated for lower power, the Do 217 have no major issues with it's BMW.

A rather compact engine for the displacement was cowled tightly, necessitating the cooling fan to fight the high temperatures involved.

 

[tomo pauk]

Power chart table for the BMW 801A, as used in 1941 on the Do 217. Note the discrepancy for the manifold pressure for take off power in them:

 

[tomo pauk]

The power vs. altitude table, along with exhaust thrust (in kg), specific consumption of fuel and consumption of oil. For different level speeds, presumably in case the usage of ram effect is not restricted by intake layout.

The 'fighter's engine' family started with BMW 801C, in combat use from second half of 1941. The powerful, tightly cowled engine, with an excellent layout of exhaust stacks pushed the compact and streamlined Fw 190 at and above 650 km/h.A true example of 'smallest airframe for biggest engine' philosophy.
We can note that BMW 801C was rated for 2700 rpm for use in Fw-190A-1/A-2, even when compressor is in high gear, but the question of 'when' remains. See the table for the A-1/A-2 here. The 'Drehzahl uber 5km' column states so.
Also please note on that table that fuel specified is C3 ('Kraftstoff C3'), so now we can bury another myth: that greater compression ratio was needed for higher oct fuel to be used on the BMW 801. Of course, the Merlin and plenty of other engines worked fine with lower compression ratios, that always mean more boost can be used before onset of detonation.
For the 801C operating on 2700 rpm please also look here (stated in the attached pdf), too.

 

[tomo pauk]

To use this double post

Sometimes the maximum power for the BMW 801C is listed at 1560 PS, sometimes as 1600 PS. The 1st value is for take off power (= at sea level), the 2nd value is available at 0,90 km. Both values are true after the power for the cooling fan is deduced.
The engine limitations and consumption on the Fw 190A-1 (still a 2550 limit for the high gear):

Power vs. altitude graph for the BMW 801C, Kampfleistung for different level speeds, at the bottom are exhaust thrush values in kg:

 

[GregP]

Nice info Tomo. Thank you for sharing these data.

 

[tomo pauk]

Once this is about done (and there is quite a work to do here, even just scrape the surface), I'll try to do the thread about the V-1710.

 

[tomo pauk]

Production of the BMW 801 engines, from the US bombing study:

Some internal stuff. The layout of oil cooler and it's cooling air. Also, adjustable cowling ring, of the type that was used, if I'm not mistaking it badly, on 'bomber's' engines only.

More about the internals:

Luftbleche: baffles that direct the coling air
Ansaugkanal: air duct for the carb
Luft fur Zylinderkuhlung: air that cools the

 

[tomo pauk]

The next major iteration from the C version was the 801D. One of the changes was the upping of the compressor gearing ratio, that, increased rated height of the engine. The increase of compression ratio was also undertaken, and the maximum boost was also increased, from 1,32 to 1,42 ata. All of this meant the greater power at all altitudes, in case all goes well.
At 1st, it did not. The engine was quickly down-rated, both in permissible RPM and manifold pressure. The table covering this was posted in the forum many times, here it goes one more time:

Meaning - from April 1942, the values in the brackets represent the allowed maximums. B - 1st (low) gear; H - 2nd (high) gear.

The compression ratio was changed through use of convex pistons, instead of flat pistons used on the 801A and 801C:

The 801D issues were cured through changes and improvements: different type of spark plugs (manufactured by Bosch), chrome-plated valves, nitrated supercharger blades, strengthened starter shafts, fixed spark plugs sockets. Fully rated engines were capable for this level of power, exhaust thrust (in kg) and specific consumption, from October 1942:

 

[GregP]

I'd be pleased to help out in the V-1710 thread. Love that engine and only wish the US Government had specified a 2-stage engine to start with. As it is, they got exactly what they ordered, with the high altitude boost being a turbocharger, ot turbo-supercharger as they were known back then.

 

[tomo pauk]

The US Government have had nothing to do with supercharger set-up on a particular engine. Rather, it was what US Army wanted, specified, and sometimes financially supported.
The US Navy, for example, financially supported the Pratt Whitney when they pursued the 2-stage supercharger for their R-1830 at 1st, and later for the R-2800.

Back on topic - the power chart for the BMW 801D, also showing the exhaust thrust vs. altitude, from the translated manual for the Fw-190A-8. Thin lines are for values with ram, for a particular power setting. Keen eye will notice that non-ram lines show greater power than what is shown on the table from the post #28 - the difference is what the cooling fan will consume. That also points to why some publications state the power of the BMW 801D as 1800 PS (even HP).

 

[tomo pauk]

The Allied analysis of the BMW 801 were published in wartime publications, specialized for aviation. People can go to the searchable Flight archive, while the American analysis can be read here.

The specific item found on aircraft with BMW 801 was the 'Kommandogeraet'. The unified control of powerplant parameters (RPM, throttle, manifold pressure, fuel mixture, prop pitch), main benefit of that being the ease of pilot's workload. More on that: NACA report.

As it can be seen on the graph posted above, the difference in engines's rated altitude with and without ram is pretty low - 600m. For comparison, the Bf-109 of same era was managing around twice as much. Better use of ram effect mans the plane will fly in a less dense air, hence lower drag -> more speed (for same HP used). Also the greater distance is covered for same fuel burn. At higher altitudes also the exhaust thrust is greater, for same manifold pressure and RPM -> again, more speed. Works also for rate of climb.
The culprit was quickly found - the internal air intakes, too much 'squashed', and the use of turbulent air probably didn't helped either. The external intakes were tested in some Fw190s, the aircraft rated altitude ( equaling engine's rated altitude with ram) was around 6500-7000 m, vs. 6300 m for the Fw-190s with internal intakes (all for high speed, pdf). The speed gain was 10-15 km/h above ~6800 m.
The shortcoming of external intakes was that they add quite a bit of drag, as if they are added as afterthought (maybe it was so?), result being the speed loss of 5 km/h at low altitudes and 10 km/h at medium altitudes (all for the Fw 190A-6).
A bit cleaner and lightened version of the Fw-190A-3 (reduced protection, only 2 cannons), the A-3/U-7, outfitted with external air intakes, almost managed 700 km/h above 7000m (test).
Be is as it is, the external intakes were rarely seen on the aircraft with BMW 801 aboard. There was a number of the Fw 190Fs with those, since it was easier to install air filters than on the internal air intakes.

Internal intakes:

External intakes:

 

[tomo pauk]

The tests that included the short external intakes (vs. regular long ones) were also conducted. A speed gain of some 10 km/h was recorded vs. long external intakes, but sometimes the performance fell down, the culprit judged to be either the influx of the air from oil cooler, or the flow separation at the scoop. report
The report where the speed is compared with aircraft having internal and external intakes. Up to 50 km/h (!) difference at 10 km of altitude.

Once the BMW 801D was sorted out to produce the expected power, the next effort was to take advantage of the C3 fuel and increase the boost under the rated altitudes. Similar thing as the well known efforts for the Merlin III, for example, that went from +6,25 lbs boost to up to +12 lbs boost, 87 vs. 100 oct fuel.
The 1st tests report I was able to find is the one with Fw 190A-4, W.Nr. 783, dated April 9th 1943. The boost limiter stop was unscrewed, so maximal boost pressure the supercharger could provide can be admitted to the cylinders. Without ram (on a test stand) the maximum manifold pressure was 1,54 ata, and in a flying aircraft (= with maximum ram) 1,7 ata was achieved at sea level; speed gain of 50 km/h at sea level was recorded. The engine power gain was judged to be 450-500 PS on 1,7 ata (= seal level, on max speed possible). The test was limited to 1st supercharger gear.
link

The further tests were conducted with the Fw 190A-5, the limits being 1,58 ata in 1st gear and 1,65 ata in second gear. The engine power was, without ram, ~1950 PS at sea level and ~1660 PS at 4,7 km, according to the climb chart at the test. test report

 

[tomo pauk]

Another way to increase the boost and power of the BMW 801D was the injection of the fuel in the supercharger's inlet elbow. The changes recommended for the engine were small (in order to avoid any problems), eg. modification of the exhaust system, and new oil cooler's armor bearer. Boost allowed was 1,65 ata, only for 1st supercharger gear. The benefit vs. the 'normal' over-boost was the lower temperature of cylinders, the shortcoming was much increased consumption vs. the later. It of course adds another system to manufacture, install and maintain. test report
Speed gain was between 30-45 km/h at sea level vs. 'normal' Notleistung.

Another way of increase of engine power was the use of water-methanol injection. According to this article, the results were not satisfying (Schlechte Ergebnisse mit MW 50). The article can be translated. Max. manifold pressure, according to the article, was 1,5 ata at SL, and speed gain at 100 m was mere 16 km/h, vs. 25-40 km/h when other methods of over-boosting were used.

The article also mentions the 'case' of the twinned ( 2-in-one) exhaust stacks, from cylinders no 9 and 10 - apparently, it cost the engine 80 PS, causing the engine go to rough running, also causing the spark plugs and injection nozzles malfunction. The problem was identified early in 1942, but was never cured with BMW 801D?? Focke Wulf was stated as having problems with installation of single exhaust stacks.
Goes without saying that I'd like to learn about this more.

 

[Denniss]

The merged exhausts may have cause some backpressure issues, AFAIR they were to be separated in the 801E/F.
Absolutely no idea why this wasn't cured within weeks if this caused a significant performance loss and maintenance costs.

 

[tomo pauk]

Maybe the issue (malfunctions power loss due to those exhausts) was exaggerated?
It would be cool if we'd have facsimiles of the original reports about that.

 

[tomo pauk]

The 1st documented installation use of C3 injection that I'm aware of seem to be in August 1943. The Fw-190 manuals describing the state of August 1943 ("stand August 1943") that were issued in November and December 1943 ('Heft 6' and 'Heft 7' of the manual; "Ausgabe November 1943" for the 'Heft 6'). Roughly: a number of Jabo aircraft are outfitted with C3 injection system, purpose of it being to increase, for a short time, the 'Emergency power' under 1000 m. See part 7 of the manual:

The excerpts from the 'Heft 7', saying roughly:
-installation of the additional C3 fuel injection is undertaken for certain aircraft, by the Nr. 104 technical advice/order
-the installation is allowed only for fully rated engines, to be used in emergency under 1 km of altitude, in order to increase the 'Emergency power', only during the flight, max use 10 to 15 minutes (taking care to the oil temperature)
-next goes the description of how the system works
-the throttle will be fully opened under 1000m, so, instead of 1,42 ata, the manifold pressure of up to 1,65 ata can be attained
-extra injector is employed, since the regular injection system cannot provide the necessary amount of fuel needed

The schematics of the system - the injector (item 3) will deliver the extra fuel into the supercharger inlet (item 8 )

 

[tomo pauk]

Even before the BMW 801D was completely debugged, the work on the improved 801E started. The goal was 2000 PS (take off). The supercharger's impeller received the 'Vorsatzlaufer', ie. the additional set of blades right before the 'main' impeller. How those additional blades looked like can be seen here, though that is for the Jumo 213. The impeller was also further refined, per v. Gersdorff at al.
The reinforcements were incorporated in pistons, cylinder heads (being cast), reduction gear, while the oil system received the de-aerator centrifuge. Also the gearing for the 1st supercharger gear was increased. The result was the increase of 'normal' greatest boost at 1.62 ata, vs. 1.42 ata in the fully rated BMW 801D, on about the same altitude. The bench tests gave 2000 PS for take off, and 1710 PS at 5650 m. The time for the Notleistung was also increased from 3 (for 801D) to 5 minutes, and the engine was tested on the bench for up to 2300 PS. My guess is that those values are without the power needed for the cooling fan.
All the required changes were eventually the undoing for the BMW 801E. Basically, nothing from the 801D, the engine in volume production, could not be used on the 801E. Only about bout 80 were produced.

The allied post-war table, taken from the AEHS, lumps the 801E, F and S together:

The BMW 801S was based on the 801D, while incorporating some changes from the 801E: supercharger system, cylinder heads, increased 1st speed S/C gear ratio. The power achieved was on par with the 801E, but the engine was also running pretty much too late to matter - service use from late 1944 on. Increase of the boost up to 1.82 ata was to give 2200 PS for take off, again that would be without the power needed by the fan. A thread about the 801S: here.

An offspring from the 801E was to be the 801F. Changes involved were: strengthening of the crankshaft, counterbalances with dampers for the crankshaft, bigger valves, different valve timing, bigger fuel injection pump, refined outer air intake starting from wing root, further increase of S/C gear ratios, improved internal and external aerodynamics of the 801TF power egg. The take off power was to be 2400 PS, the 'Kampflesitung' 2200 PS at sea level. During the bench testing 2600 PS was achieved, but the whole program was too late to matter.

Sometimes there is an argument whether the 801F ever saw service use, I always claiming it did not. For honesty sake, there are some documents around that state the Fw-190A-9 was outfitted with it. Mostly, the engine is noted in the same time being the 801F and 801TS - the 'TS' being the power egg package of the 801S.

added: the web page talking about the BMW engines, among other. In Russian, but most of the stuff can be translated: link

 

[tomo pauk]

The BMW 801 was one of rare German engines to see service as a turbo-charged powerplant. The hollow-blade turbine was employed, that enabling efficient cooling of the blades with the air admitted inside the blades. That further meant the turbo-charger can be installed rather close to the engine, resulting in a compact installation, that was able to be retro-fitted in existing airframes. The turboed BMW 801J was based on the BMW 801D, and some 310 such powerplants were produced, used is service aboard the Ju-388. Th engine cowling was a bit enlarged vs. the non-turbo engines, diameter measuring now 1410 mm.
The turbine max RPM was 22000, the max tip speed was 376 m/s. The air compressed by the turbo was cooled by 4 intercooler radiators, down to 95-100°C when exiting the radiators. Engine-stage compressor gear change was still allowed for the 801J (contrary to the US practice, thus enabling a considerable gain in power at high altitudes.
The take of power was 1810 PS, max power at altitude 1485 PS at 11500 m (37730 ft!). My understanding is that those powers are without the power needed to turn the cooling fan, but still quite a power at such a high altitude. Max RPM was supposed to be 2650 RPM.
All data above is from V. Gersdorff et al.

The Allied post-war data:

The article in German (can be translated); the engines are currently in the USA: link.

The power graph, for 'Steig und Kampfleistung' power setting. Please note that power is listed as 'gross' power, ie. sum of the power on the prop shaft and the power consumed by the cooling fan. Also please note the 'kink' at 8.5-9 km, when the engine-stage compressor gear was shifted in 2nd speed, with appreciable rise in power.

 

[tomo pauk]

To wrap up the BMW 801, at least for the time being. Contrary to the eperiments with MW 50, that gave no more power than other two means of overbosting the engine, the trials with GM-1 were considered successful. The GM-1 system was to be use above 8 km of altitude. The tank for the needed mixture was located, in the Fw 190As, behind the pilot, where the later versions usually carried extra fuel.
The terminology: depending on how the power eggs were complete, they were designated like, say, MA, or TJ for example. The 'M' stands for 'Motoranlage' - the engine with cowling and all the extras needed for it to work. The 'T' stands for 'Triebwerkanlage', basically whatever the Motoranlage had, plus the engine bearer and exhausts.
The second letter in the designation does not necessary mean that basic, naked engine of same designation is the ingredient of the power egg.

 

[Balljoint]

MW 50 uses the heat of vaporization to cool the mixture. While it provides a bit denser mixture the primary improvement is to suppress detonation. If it didn't provide an improvement this would suggest the engine wasn't seeing unstable fuel combustion.

GM-1 is laughing gas, i.e. nitrous oxide that contributes more oxygen to the fuel mixture. Sort of chemical supercharging. The results make sense.