Monday, July 30, 2012

Leaning Towards France: A Technical Appendix

Last time, I buried a snide criticism of the Fascist-fighting work of the design bureau of Lavochkin and Gorbunov in a footnote. That's a bad place for it, and an argument that can be taken too far.

The mood?


That's the boot of the Red Army of Workers and Peasants in the face of race science and national socialism forever.

That's a good thing with a terrible human cost, not all of it forced on Soviet Russia by the Fascists. In order to defeat Nazi Germany, the peoples of the Soviet Union paid a toll in blood for the follies of their own government as well. So did the men and women of the Red Army, and so did the pilots of the Red Air Force.

As anyone caught in the machinery of a human institution (which is pretty much all of us, I think) can tell you, it's easy to become a victim of a terrible self-reinforcing cycle of failure, with policy makers just looking at you and shrugging their shoulders to say, "Yes, it's terrible, and I feel for you, but whatcha gonna do?" The Royal Flying Corps ran into that in 1917, when its training cycle was delivering undertrained pilots to the front and matching them up with dangerous planes that killed them before they gained the experience needed to be good air fighters, much less instructors who could train the next generation of pilots. It's a bad, broken process that flows from bad human resources management far more than from mistakes of technological policy. But, well, it's the latter that we talk about here, so there you go: The Lavochkin-Gordunov LaGG-1, -3, LaG-5, La-5, La-7, and La-9.

Technically, the Red Air Force did not have an easy time of World War II. Its material was derivative: the standard V-12 liquid-cooled inline engine, the Klimov M-105, was probably (Wikipedia says "undoubtedly," so I assume that there's a doubt here) a development of the Hispano-Suiza 12Y, first run in 1932, while its standard 14 cylinder air-cooled radial was the Shvetsov ASh-82, similarly a development of the Wright Cyclone R-1820, an engine that entered service in 1931.  The LaGG series was built of plywood in order to conserve light metals, and the engines were adjusted to burn 95 octane fuel. This was still a higher-rated fuel than the German standard, but forced lower compression ratios than the 100+octane used by the RAF for most of the war.

This, in itself, is a pretty key point. Andrew Nahum pointed out that the apparent Russian conservatism with engine designs in comparison to British practice flows from the Aeronautical Research Committee's pinpointing of compression rating limits as the Achilles' heel of interceptor development in the 1930s.* David Ricardo's insistence on technologies, such as sleeve valves, higher engine speeds, and smaller cylinders, that could bypass the predetonation limit imposed by existing gasoline stocks led directly to the exotic new engines of World War II. Bristol's new line of sleeve valve radials was a direct attack on the most challenging and promising of the new technologies. The ....innovative Sabre engine had sleeve valves, and small cylinders, and high piston speeds. Even Rolls-Royce's tentative moves away from the 5.4" bore of the Merlin and back towards the 5" cylinder of the Kestrel, in the Peregrine and Vulture can be explained in this light.

As we know, the RAF actually fought the war with 100 octane or higher rated fuels. Its future thus lay with the Griffon, rather than with the innovative but hard-to-build sleeve valve designs. Whether the Armstrong Siddeley Tiger could have kept up with Merlin development, we will never know. So when we see the increasingly exotic list of new, high-powered British aeroengines of the war and postwar era (1, 2, 3, 4, 5, 6), we need to keep the question of octane rating in mind. The new engines were largely funded as a result of concern that these highly-refined fuels would not be available, and the very high power ratings wrung from these engines (well, more the Merlin, but the 'exotic' engines, too) has a great deal to do with the high compression ratios available from these new fuels.

Of somewhat more concern was the material of manufacture. Plywood is not a bad material of which to make a military aircraft. I will grant that the "strategic" aircraft of the early war (Albemarle, Miles M. 20,  Caudron C. 714) have a bad reputation for excessive airframe weight, and the less said of the Heinkel He. 162, the better. (Talk about technological utopianism.) but no air force general in his right mind would turn down a de Havilland Mosquito, much less a Hornet!

Well, okay, actually they would. The problem that the Air Ministry so carefully explained to their supposed "ring" of favoured designers way back in 1925 had nothing to do with the strength or weigh of plywood, but the fact that it got wet, and rotted. That, eventually, they bought the Mosquito has a great deal to do with the kind of plywood de Havilland used, and with a great deal of incremental development  in incorporating the new material science of plastics into their structures. The Russians were actually at the forefront of progress in plywood development in the interwar years, the "Baltic" method for making plywood driving out the "American" method throughout the world, not that you're going to hear that in your average history of technology.**

So the Russians had the method, and they had lots of forest. Unfortunately, it wasn't always the best wood, just the most available. The LaGG designed used solid birch formers with plywood covers, and the wood work does not seem to have been of the best, per the somewhat sneering comments of the Finno-Swedish-British evaluator-writer-translators. (Not, as I incorrectly said last time, German.)

So, as I have earlier noted, the LaGG-1 was a bit of a disappointment. Per Wikipedia:





Notice the wing loading of 35 lb/sq feet, calculated from the cited loaded weight, probably not a good idea for a wood-built aeroplane that could easily end up carrying a substantial load of water. It is only lower than the 37.75 lb/sq feet of the loaded Hawker Tempest at significantly higher power loading (.17 hp/lb versus .21 for the Tempest). I would guess that the Tempest also enjoyed more effective controls and better wheel brakes. Certainly Dowty*** (or Dunlop, if it turns out to have been George Dowty's great rivals who supplied the brakes) did not get its reputation by accident.

So the design group tried again. Here's Wikipedia on the LaGG-3:


Data from Jane’s Fighting Aircraft of World War II[10]

Weight down, power up, speed ...down? Is this the point, sufficiently well-buried deep in the posting, where I admit that I made a snide little boo-boo in pointing to the Vmax series and letting conclusions be drawn? I think that the comparison between the LaGG-3, with its presumably "official" numbers, and the ones published in the international press for the LaGG-5 are telling, but the reason that Vmax reverts to its upward climb in the La-5 probably has a great deal to do with the replacement of the M-105 with the more powerful ASh-82 radial in what looks like it might be a FW190 inspired "slim" installation, giving these numbers:


That's a pretty impressive plane. Notice the power loading! It's also probably a bit of a cheat, in that the FW190 solved the problem of fitting a big radial into a small circumference by introducing a big mother of a cooling fan. That's as true of the Sea Fury and the P-47 as it is of any other later war radial, of course. I'm just saying that it's something to take into account when calculating "true" power loading. It was also the general late war practice was to use an over-sized oil cooler as a "stealth" radiator by adding oil pumps in the crankcase that sprayed cooling fins on the under side of the pistons. I've seen a butter-won't-melt-in-his-mouth sermon from a Rolls-Royce engineer (Derby of course, would never do something so dishonest) that estimated the "lost" power off the official rating from this practice as 28hp from the 1100hp Daimler-Benz DB601A, or 2.5%.**** I also notice that Wikipedia only supports the remarkably high figure of 1800hp from 1800 cubic inches of displacement in the (presumably) postwar turbocharged FNU version. One could also pick up on German criticisms of the complexity of the La-5's engine controls in comparison with the FW190's remarkable "master control unit." The Germans were, of course, spoiled by the FW190, but there was a reason they were spoiled. The Kommandoger├Ąt was a timely, necessary, and creditable bit of technological progress, even if BMW and Focke-Wulf did manage to miss yet another opportunity to coin the word "computer" before John von Neumann got to take the credit.*****

So the long and the short of it is that I shouldn't run around accusing Lavochkin et al of killing Russian pilots with their incompetence. On the contrary, they were doing the best they could with what they'd been given. What I am calling out is the notion that production numbers beat design imperative. No fighter plane design, until we get to the unguessed future state of the perfect fighter (hint: it will not look like this) is a success. They're all, in some critical sense, failures. That's why we keep building new designs. We're failing forward. If we settle for the design we've got, we need to understand whose (technological/industrial) strategy we're settling for. The one that tries to use lots of failures to make up for the failing.

Which, I admit, is how we're going to fight in the 31st century. 

 




*Nahum, Andrew. “Two-Stroke or Turbine: The Aviation Research Committee and British Aero Engine Development in World War II.” Tech. Cult. 38 (April, 1997): 336-48.


**[Hey, look! It's a text dump from the semi-abandoned monograph again]: Plywood is the earliest example of a composite material, consisting of tin shavings of wood glued to each other by various glues. This preindustrial product was brought into the engineering age in the first decade of the 20th century with the introduction of factory level production in Germany and above all the territories of the then-Russian Empire. Laminates of birch and alder were glued with dissolved mixtures of the traditional organic glues (blood, albimin, and casein) in hot steam presses to produce water resistant pieces of up to 8ft width for construction, furniture, and boatmaking implications. Over the next few years these plants displaced traditional American-style factories that had introduced industrial-scale plywood manufacture, and various improvements can be noted, particularly automatically-controlled saws that could produce very thin laminates. Chemical engineering also came to the assistance of manufacturers with plastic resins of more reliable behaviour than organic glues, although they often admitted of difficulty due to their inferior temperature responses. By the early interwar years an “aeronautical” grade three-ply panel only 1/25 of an inch thick was available, although the Aviation Ministry would not approve its commercial use in the U.K. The plywood in the Mosquito used a urea-formaldehyde resin binder, although casein was still used to glue separate pieces together due to its wide range of temperature tolerances. SourcesT. M. C. Wegener, “European Progress in Hot-Press Bonding of Plywood in the Last Ten Years,” Trans. ASME 60 (1938): 69–76, and discussion by Robert L. Davison and Emanuel G. Wolf, Ibid, 615–16; S. Livington Smitth, “A Survey of Plastics from the Viewpoint of the Mechannical Engieer.” Proc. Inst. of Mech. Eng.152 (1945): 37-8; A similar use of plastic resin laminates can be found in airscrews.


***Now a wholly-owned subsidiary of Smiths Group. Apparently, Mr. Smiths owns almost all the old technology niche firms I talk about on this blog. If it were Mr. Johnson, I'd be really worried.


****Frank Nixon, “Aircraft Engine Oil Cooling,” Jour. Roy. Aero. Soc. (1946): 123–198.

*****Are you still reading? Thank you: because this is an awesome link, and I've somehow buried it, and my declaration of John von Neumann as honourary Patent Troll of the Week, way down here.

5 comments:

  1. A couple more nitpicks:

    1. I think the low German octane thing is a myth based on confusing lean & rich ratings: see the bottom of this page http://www.madabout-kitcars.com/kitcar/kb.php?aid=124. Don't know if this also applies to the Soviets.

    2. The P-47, along with all other US radial engine planes, didn't have a cooling fan (except for the experimental J model).

    But very interesting posts. Keep it up! (Are you ever going to get back to the missing French fighters of 1940?)

    ReplyDelete
  2. Note on 2: that's why they don't have the fat prop spinners everyone else used.

    ReplyDelete
  3. D'Oh on the P-47. I'm always getting stuff about that plane wrong.

    On octane ratings, the Germans really were at a disadvantage, which is an interesting strategic point. The Allies produced 100 octane (and higher ratings) through mixing, but the base was catalytic reformed gas. Early gasolines, with a typical 60--65 octanes, are simple refined fractions. In the late 20s, "cracking" was introduced, a high temperature process that produced more gasoline from the crude feedstock, and also raised octane ratings to the mid-80s.

    There's an ongoing argument (or was, until all the engineers died of old age) about whether it was Standard New Jersey or the French Houdry firm that invented catalytic reforming in the mid-30s, but it produced a 94 octane that could be doctored up to 100 or higher at the expense of reducing yield. So that's why the Germans didn't go for it: they didn't have the crude supplies to be throwing away (relatively good) gasoline.

    In a massive historical irony, Houdry was one of the first customers for the Brown-Boveri gas turbines that were the first commercially offered "jet engines," which, of course, it made sense for the Germans to push, on account of jet engines using a much-less refined fuel stock.

    Anyway, "100 octane" is a pretty unhelpful label, because predetonation works differently in lean (enough air to oxidise all the gas, ie more air than gas) and rich (enough gas to reduce all the air) mixtures. High octane rating lean mixtures are good for fuel economy, but rich mixtures have excess gas to cool the cylinders, and thus are good for power. So some of the nominal 100 octane of 1940 is 100/130, where the 130 is (I think) the rich mixture rating, and then you get 115/125, and ultimately 130/150.

    The question, then, is what you do with it. The normal use of superchargers is to get the weight of charge at higher altitudes up to the weight of charge at sea level. In 1940, that meant that high octane fuels only made a tactical difference above the supercharger's critical height, making them almost irrelevant on the Eastern Front. However, there's no reason (apart from losing high altitude performance) not to set your supercharger to boost pressure at sea level, normally to improve takeoff performance so that you can lift more stuff. The Germans (and everyone else) eventually used methanol/water and NO injection for that, but high octane fuels help, too.

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