Interesting, I was not aware of all of that. At least in the case of the Daimler Benz motors few are still airworthy because of the use of electron, an aluminum/magnesium alloy that is very light and strong was so widely used for their large castings. Having a large magnesium component they degrade badly with time and exposure to moisture. Same thing happened to their Gran Prix cars of the same period. I have always been intrigued by the supercharger drive on them though I must confess I have done little to research it. I have been told it was hydraulic and seems like it would have been a good alternative to the complex and heavy 2 speed system on the Merlin. Hydraulic could have given infinitely variable speed capability in a simple system. If the 40's had not proven to be the end of high power inline piston aviation engine development it may have had a future. I guess I should read more about those motors. They were large displacement wise but had lower RPM limits and quite a bit less power than similar motors from the West. I have always wondered what limiting factors caused that.
Yes Brian, the supercharger drive was hydraulic indeed on the DB engine, and infinitely variable. And if my memory, etc...the engine also has the peculiarity of having a slightly different compression ratio on the left and right cylinder banks. I shall dig into my library and see what I have, will report, but probaly not immediately... Rgds
I can understand that: I was born two miles from the border with Germany, in a part of land that was annexed (not occupied, but annexed) to Germany from 1871 to 1918, then again from 1940 to 1944 (and liberated by a US regiment mainly staffed by texans...). I have a german family name, and was bilingual at birth; but since working and living mainly in Paris, I am slowly forgetting it, so I still understand German well, but speaking gets more difficult. But culturally, I am rather close... Rgds
Sorry man, what exactly has been 'disproved'? We know higher RPM's is 'good', and my understanding at least is one big limitation to high RPM's are poppet valves & their springs. As Nero noted, why F1 engines went pneumatic. Cheers, Ian
Poppet valves and pushrods. The demise of both have been predicted over and over since the 20's and they are both still here on high output efficient engines making great HP/LB figures. F1 engines occupy a tiny corner of the graph and the needs of those motors have nearly no application in anything else. Their cost and lifespan limits them to their current role. And besides they still successfully use one of the 2 designs (poppet valves) mentioned so even in their very limited niche they support my point. In any event, those motors only exist because of the current rule structure. If propulsion of an F1 car was open to any technology it would long ago have veered in another direction.
Gotcha. Thanks. (Although I'd rather have OHC than pushrods any day!) OK, understood. For sure doing it pneumatically is really kind of a PITA, but at least there's not the valve bounce we grew up with. What direction might that be? I'm probably way off here, but I really kinda like the 'rotary distribution' system Nero mentioned above. Almost analogous to a two stroke, and we know those things can rev! Cheers, Ian
Having known a few Unlimited Racing Boat mechanics I recall that they liked the Merlins because at higher rpm they didn't experience valve float and the breathing was much better than the Allison. And then there was Blumer's description of the big fight he was in and forgot that his P-38's engines were in war emergency for about 15-20 minutes and held together. His crew chief was unhappy when he pulled into the hardstand and saw the damage to Larry's airplane and run out engines.
Much as I appreciate the complement, not sure I can dream up the technology in the next few minutes that untold number of very bright engineers could have in the last 50 or so years were they left up to their imaginations. I suspect it would use an expanding gas as an energy source like now but I also suspect most of the parts would be going round and round rather than up and down.
I don't know Allisons very well but I find your comments funny. With the time I have had examining Merlins I have always been impressed with the very Victorian understanding they had of breathing and combustion chamber design. Applying modern understanding to both in the design of all new heads would result in far more power than the basic structure could handle. The breathing capability of the motor pretty much required a supercharger, altitude air density problems or not. Something had to shove a charge in there, suction alone would not have done it. The same could be said for many piston engines of the period but some of the design really crippled it. The few PW round motor heads I have seen reflected a far better understanding. The Pent Roof combustion chamber design from Britain in the 60's and still used today, if applied to the Merlin would have been a very different story. Then we would have to work on the manifolding.
Expanding gas definitely works very well for our purposes. I guess Mazda tried the round & round thing. Not bad, but didn't really work out. Up & down seems to work pretty well with expanding gases. Cheers, Ian
Rotary only failed due to emission regs. Made a boat load of power in a small package and RPM was limited only by how fast you can get fuel to burn. Couldn't make them run clean enough though.
Totally agree on the small package & lack of RPM limit. Didn't know they were 'dirty' though. (Thanks for that) Surely there has to be a solution to that issue these days? Stick a modern cat on the things? Cheers, Ian
Its a 2 stroke. Lots of things can be done and lots were done but a 2 stroke will never emit babies breath. Finally they threw in the towel. I am not married to the idea of a Wankle, it is just one of many possibilities for a round and round kind of motor. I still blame them for causing race cars to have mufflers.
Brian, Been to my library; in the Hershel Smith book "A history of aircraft piston engine" (mine has been used so often that all pages have come unglued...) there is a short description page 85: "The DB601 introduced two major steps over the DB600: Injection and the infinity variable speed fluid-clutch supercharger, in which the fluid coupling was so connected to the outside atmosphere as to slip more when the ambient atmospheric pressure was high. This very clever device constituted an automatic altitude compensator, making the blower run faster as altitude got higher" There is a slightly more thorough description with a cut-away drawing in Bill Gunston's "The development of piston aero engines" pages 78 and 79. And finally, it was the larger (44 litre capacity) DB603 that had different compression ratios on both cylinder banks, 7,5 /1 on the left; 7,3 on the right. Rgds
His words, Taz. He and his squadron made a long shallow descent from 22,000 to the fight at near ground level. He said that he noticed that his power was still at war emergency during the fight. So it was probably more like 5 minutes or so. When he noticed that his fuel was low , he ordered his guys to break it off and go home. On the way home , they shot up a German convoy and and a train.
So it worked more like a turbocharger then in a sense. Turbochargers spin faster and partially make up for air density all by themselves due to a decrease in drag from that density. Not enough to fully compensate but it helps. The waste gate settings or controls take care of the rest. I bet knowing how DB looks at things they detected a bank to bank difference in charge quantities due to manifolding or something and varied compression ratio accordingly. On their V8 auto engines the left bank and the right bank cams are timed differently because as the chain wears it will retard the cams by different amounts and the net lifetime cam timing stays more consistent to each other that way. Almost certainly inconsequential in both cases but the Germans routinely ignore important issues to focus on minutiae. They would have been better served figuring out why the Allies were getting the same power out of 27 liters as they were out of 44 or how to keep the Tigers from sinking in the spring mud while the T34's drove circles around them. Not unlike in 1953 or so when DB thought they had invented desmodromic valves. While applying for a patent they discovered your countrymen had invented it more than 30 years prior and they had been racing against desmo motors and had no idea. Higher compression than a Merlin BTW.
Two Cougars looking pretty IMHO at the Pima Air and Space Museum this past Wednesday across the street from Davis-Monthan AFB on our way to Sebring. Image Unavailable, Please Login
Two usually accepted explanations to that, Brian. -Their engine designs were on the whole good, even excellent, but they were more conservative in their exploitation. - The Germans were very hampered by their isolation for procurement of quality oil, and therefore production of high octane petrol. They knew that they would not be able to produce a steady flow of high octane petrol, so they had to accept that as for standard petrol they would always have to use lower octane that the Allies, therefore they more or less compensated this drawback by larger engine capacities. Rgds
The summary from the articles I have found: The family of Daimler-Benz V12 aero-engines, which were in-line inverted V12, began in 1934 with the DB600, which was fed by carburetors, and supercharged by a mechanical single-speed supercharger. The 600 was not produced in large numbers, as it evolved very soon into the DB601, which is a 600 fitted with direct injection and a supercharger which is hydraulically driven, with a continuously variable speed adjusted to altitude. 19322 DB601 engines were built. The quest for more power led directly from the 601 to the 605 engine: the 605 is a direct development of the 601, in so far as it is a slightly enlarged 601, from a 33,9 litres capacity to 35,7 litres; the cylinders have been rebored, but the 605 external dimensions are identical to those of the 601. It is more powerful and able to rev slightly faster. 42400 DB 605 were built. A different engine, but of really larger capacity, was evolved, apparently without the agreement of the ReichsLuftfahrtMinisterium at first, the DB 603, which has a capacity of 44 litres. 8758 DB 603 were built, in 36 different versions. The DB600, 601 and 605 were mainly fighter aircraft engines, and identified as such in the industrial production scheme of the Air Ministry. The 603, as said, was an initiative by the engineers of D.B and as such was not officially sanctioned by the procurement committee of the Luftwaffe, but ended being considered mainly as a heavy fighter and bomber engine. Daimler-Benz A.G (Aktien Gesellschaft, company with shares) was created in 1926, by merging Daimler-Motoren-Gesellschaft on one hand, and Benz and Company on the other. Production of aircraft aero engine began almost immediately, in 1927 with the type F2, which was already a V12. The studies for an update or replacement of the F2 began in 1932 and led to the conception of the DB600A, production of which began in 1937. The 600 was an inverted, in-line V12 of 33,9-litre capacity, which has four valve per cylinder (Junkers Jumo family had three: two inlet, one exhaust) but a single overhead camshaft. It gave 1050 hp at 2400 rev per minute; with a single-speed mechanical supercharger, it was able to maintain that power until a 4.000 metre (about 13.000 feet) altitude. It burned 87-octane gasoline (“B4” gasoline, in Lutwaffe table of reference for gasolines) in a pressure carburetor, which was situated between the supercharger outlet and the inlet valves. There was a “booster” for the admission pressure, that was time-limited by a clock to one minute, which allowed for an “emergency” admission pressure of 110%. A Junker 90 with four DB600A established an altitude record of 7242 metres, with a 10-tonnes load on June 8th, 1938. Some of the prototypes for the new fighter, the Bf109, were also fitted with a DB600A. Daimler-Benz decided very soon after production of the first 600 engines (total production reached only 2281 engines), to follow the example of Junkers, which has adopted direct injection of the mixture, invented by Bosch for Diesel engines; that gave the DB601, which was more powerful and also more reliable than the 600. But its main novation was the supercharger; instead of the mechanical drive common at the time, which used toothed gears, and usually had only a single speed which had to be selected and engaged by the pilot, the supercharger on the DB601 engine used a hydraulic drive, or fluid coupling, which was barometrically controlled by the outside air pressure, through a manometer; the speed ratios at which the supercharger was revolving were varying continuously, automatically compensating the lowering of air density with higher altitude; the main attraction of this very clever device was that it sustained a continuous power output for the engine, and did not waste engine power when not at rated altitude like a standard mechanical supercharger. The 601 engine evolved mainly by tweaking the drive of the compressor to better compensate the variation of altitudes, and also by switching from “B4” gasoline to the higher-octane “C3”, which was a 100-octane. The DB601E and its developments F and G then adopted pressurized cooling, which allowed high maximum revolution periods. The german oil industry was working in a context of sources and lines of replenishment always under threat, and this isolation did not allow it to develop high-octane petrols as easily as the Allies did. Daimler-Benz compensated this drawback mainly by increasing capacity and engine revolutions, and the German industry itself developed a serie of additional power supplements, from Nitrous Oxide for instance, such as the MW50, GM1, etc…which unfortunately necessitated additional tanks, so increased the weights. On the subject of capacity, Daimler-Benz decided to boldly enlarge the 601 by 33%, this apparently without having the program duly sanctioned by the technical staff of the Luftwaffe at first, which gave the DB603 with larger bore and stroke, different engine block; but it was not a success as fighter engines go, because it was considered too heavy for these, and was used mainly as a bomber engine. The DB605, on the other hand, was a better tweak: it was a 601 very slightly enlarged by re-boring the cylinders from 150 to 154mm, to 35,7 litre capacity, but with modified heads, valves and pistons; it was able to rev 200/400 rpm faster (early DB601 revved at 2400, later at 2600) and gave a noticeable increase in power, due also to altered valve timing that increased the inlet period, and gave greater volumetric efficiency. Otherwise, dimensionally its outside measurements were the same as those of the 601, but it was heavier, 756 kilograms dry weight versus 700. The first variant of this engine, the DB 605A, was able of 1475 hp at 2800 rpm with an admission pressure of 1,42 ATA using “B4” petrol, but was hampered by a default in the spark delivery of the Bosch DW 250ET7 spark plugs and some piston problems; so the first engines produced were detuned to only 1,3 ATA, giving only 1300 hp at 0 m. Problems were solved and full power restored with adoption of Bosch DW 250ET7/1, then DW 250ET7/1A spark plugs. But another major design difference was the switch from ball bearings to plain bearing that, combined with increasingly poor grades of lubricants, led to very serious problems in service, including the infamous engine fires that were baffling the pilots of the first Messerschmitt 109Gs; see Heinz Knoke book “Die grosse Jagd” (1953) (“I flew for the Führer’, in English) for instance. Short technical description: All three engines of this serie are using the classic german architecture of “inverted V-12”, with four valve per cylinder, but only one overhead camshaft; the “tail” of the exhaust valve is hollow for sodium-cooling. Lubrification is by dry-sump. The engine block is cast in a single piece of silumin-gamma alloy; the sleeves, of hardened steel, are screwed directly into the engine block. The engine crankshaft is forged in steel, in one single piece, with counterweights for balancing. It revolves on seven steel-reinforced bronze bearings. For the DB 601, bore is 150 mm (5.91 inch) stroke is 160mm (6.30 inch); exact displacement is 33,93 litre (= 2,070.54 cu.inch) For the DB 605, bore is increased slightly to 154 mm, stroke stays at 160, displacement is 35,7 litre (= 2,176.00 cu.inch) There are four valve per cylinder, but a single overhead camshaft. Exhaust valves are sodium cooled. Pistons are made of aluminium alloy and are using floating rings. Compression ratio is 6.9 /1 for the 601 engine; The 605 engine, like the bigger 603, has a different compression ratio for each cylinder bank: 7.5/7.3:1 with 87-octane fuel; and 8.5/8.3:1 with 100-octane fuel Injection is provided by one high-pressure pump per cylinder, so twelve pumps in total, fitted between the cylinder banks and fed by a Graitzin transfer pump; injection pressure is 90 bars. Ignition is provided via two Bosch magnetos to two spark plugs per cylinder. The engine lubrication is dry-sump, with one pressure and two scavenge pumps. The propeller reduction is very compact with only three toothed pinions, of which two are imbricated, this to allow a streamlined cowling; the center wheel is hollow in its center to allow the passing of a weapon tube, if a weapon is fitted between the cylinder banks. The reduction gear is 0,594/1 on the DB605 engine.
Thanks. Actually the injection system they used is something I have some familiarity with. It was based on diesel direct cylinder injection from Bosch which at the time they were the leaders in and most of the high speed diesel engines world wide used either their systems or their patents. Interesting, I didn't know their avgas was so bad. Explains a lot. Also explains some pictures I saw years ago of Gallands personal 109. There were markings on it calling for very high octane fuel, even by our standards. Don't remember the number but it was high. It was pointed out in the picture. I guess the General had the juice to get a special airplane to give him an edge. Since that picture I assumed their fuel was at least as good as ours, at least that which was made available for front line fighters. When that lightning war thing didn't work out as planned it really put the pin in the party hog for Germany.
The Germans did not have access to high-quality crude oil, and the necessity of securing their oil procurement, and their lines of replenishment was paramount for the Germans during the whole war. It was one of the main drivers behind their decision to invade Romania, this to secure the Ploesti oilfields and refineries. And this was well understood by the Allies, so much that the USAAF accepted very high losses in its endeavor to destroy Ploesti. It is also one of the main drivers behind the spring and summer 1942 german offensive which was turned towards the Caucasus: to secure the oilfields of Baku and Azerbaïdjan. It also explain why the pioneers of synthetic gasoline, Fisher and Tropff, were Germans Rgds
Just the opposite from WW-I, when the Germans were experimenting with and operationally deploying over-compressed engines from Mercedes, BMW, Siemens, and Maybach with high octane fuel mixtures and dual zone throttles. Meanwhile, the allies had determined they would get by with low octane fuel supplied in bulk by the US, so used relatively low compression engines. Oil was still a big problem for Germany in WW-1, especially castor oil for rotary engines. They ran out in 1917 and the blockade by the Royal Navy dictated using a compromise synthetic of mineral and fish oils. Times change.
