Tuesday, June 11, 2013

Postblogging 1939, May: A Technical Appendix


The past is a foreign place. They do things differently there.
Armstrong Siddeley Tiger VI
Then we come to the shock of the new

Bristol Taurus
And the tragedy of roads not taken.

Rolls Royce Kestrel

Which requires some clarification:

Image credits go mostly to Wikipedia (yes, I donated this month), but that was such an awful lot of scraping that I grabbed the Westland Whirlwind from www.aviationtrivia.info

So with credits out of the way, I want to talk about some of the technical stuff that I intended to footnote in my last post before I hit "publish" too soon. And, yes, I do know that there's an update capability. It's just that that post was getting too long. I may do June--August semi-monthly.

We have heard by now of three mostly lost and forgotten aircraft: the Boeing 314 Yankee Clipper, the Short S-26 "G-boat," the mysterious Whirlwind that the French press are allowed to talk about, and which Flight feels permitted to discuss in this context. (Contrast the Short Stirling, which is described in a spring number of the American Aero Digest, but which is ignored in Flight.)

We have also heard about the Hawker Hurricane, which isn't mysterious at all: a classic example of Kingston-upon-Thames' philosophy of incremental development, the Hurricane pushes the structural techniques developed on the Fury to their highest pitch of development, adopts the monoplane/retractile undercarriage formula, and achieves world-beating performance as of the June 1936 production order. In a fit of animal spirits, the first squadron to receive the Hurricane organises a stunt in which one flies from Edinburgh to London at an average speed of 408 mph. (I link to a March story in the Argus of Melbourne that claims that a "500mph flight" in a Spitfire is being planned, because it's colourful.)

What is mysterious, or should be mysterious, or, actually, shouldn't be mysterious at all, is that if you are reading about the Hurricane in the technical media in the spring of 1939, it is a 335mph fighter. If you read about it in the fall of 1939, it is a 316mph fighter. (I hoped to link to Wikipedia for this, but the performance box there lists the Hurricane IIC flying with a Merlin XX at 340mph at 21,000 feet, but there's so much automotive engineering under the bridge here that I can only hope to begin to unpack it.)

The downward revision reflects the fact, pretty clearly laid bare by the AAEE reports, that no Hurricane with full service equipment ever hit 335mph in a useful way. That's not to say that they didn't fly that fast, because the usual method for assessing aircraft top speeds in the peaceful spring of 1939 was to dive the thing at the ground until it was low enough for observers to triangulate usefully, than fly at level speed and open throttles for as long as seems advisable before the engine melts. You can get a pretty good top speed that way. Also an excess of dead high speed flight pilots, because if you think the Hurricane revision is big, consider the Whirlwind's reduction from a supposed 420mph to 365mph. That's a lot of test pilots crashing into the ground. Fortunately, they were probably all bipolar II, and, after a while, your patience tends to ebb away. . . .

Anyway, the Air Ministry released downward revisions for the performance of most combat aircraft at some point in the spring or fall (you'd think that I would have the date this at my fingertips, what with the ongoing postblogging and all, but I don't), and there was a kerfuffle in the letters pages of Flight about the Air Ministry losing the war or something.

The Hurricane is a good example of what ought to be a better known phenomena: synchronic aircraft performance statistics are hard to produce, and people get them wrong. The Hurricane was never a 335mph fighter until the Hurricane II got itself a Merlin XX engine running a constant speed propellor. This is not a big deal: but was the Yankee Clipper really a 6400hp, 84,000lb auw 'plane when it took off on the first commercial trans-Atlantic flight in May of 1939? Not to tip my hand or anything, but the idea that the Wright Double Cyclone R-2600-3 engine is achieving 1.16lb/hp when the Rechlin data gives the Hercules X of circa summer 1940 a 1.21 pretty much decouples the level of state military spending from outcomes. Apparently, you can pretty much choose not to fund your air force, and the plants are going to produce competitive aeroengines regardless. What is even odder is that the Wright Cyclone GR1820 GW 2A in the Rechlin sample shows 1.408lb/hp.* Things come into  a little clearer focus when one notes that early Double Cyclones are rated at 1500hp, giving a somewhat less impressive 1.23lb/hp. The rest of the mystery is clarified by the discovery that the Double Cyclone was huge:

Bore: 61⁄8 in (155.6 mm)
Stroke: 65⁄16 in (160.2 mm)
Displacement: 2,603.9 in3 (42.7 L)
Length: 62.06 in (1,576 mm)
Diameter: 55 in (1,397 mm)
Dry weight: 2,045 lb (930 kg)
Compare this to another 14 cylinder radial of virtually identical displacement, the BMW801, of Focke-Wulf 190 fame:

Bore: 156 mm (6.15 in)
Stroke: 156 mm (6.15 in)
Displacement: 41.8 litres (2,560 in³)
Length: 2,006 mm (79 in)
Diameter: 1,290 mm (51 in)
Dry weight: 1,012 kg (2,226 lb)

And, of course, the Hercules:

Type: 14-cylinder, two-row, supercharged, air-cooled radial engine
Bore: 5.75 in (146 mm)
Stroke: 6.5 in (165 mm)
Displacement: 2,360 in³ (38.7 L)
Length: 53.15 in (1,350 mm)
Diameter: 55 in (1,397 mm)
Dry weight: 1,929 lb (875 kg)

Note that Wikipedia may be using data based on different criteria here. I have a description of the 801A before me that gives its length at 58", making it shorter as well as slimmer than the Double Cyclone, and another for the Hercules giving it an overall diameter of 52".** 

It should not be surprising that an engine that debuts in service in 1939 is less advanced than one that debutes in 1941, and the Double Cyclone's job, after all, is to get a very big plane into the air and cruising at a moderate speed. Its drag, which will be a function of its frontal area and thus its diameter, is much less important at low speeds than at high.  That being said, I do not think that American aviation in general was well-served by the large-diameter engines produced by the Wright and Pratt & Whitney shops. On the other hand again, they won the war. It's not what you have, but what you do with them --and what your postwar labour force learns by working through their limits!

Now, the meat of this post is that we have a  key conjuncture in the spring/summer of 1939: we are at the end of a huge, peacetime, debt-financed investment in the highest of high military technology, aviation. In a perfect world, Hitler would back down at the brink and the war of nerves would continue for a few years before subsiding. We would have a better dataset for economic historians to play with, some idea of how open economies can exit this kind of fiscal stimulus-driven expansion, and, in this historical counterfactual, no Holocaust.

But that's not the history that we have. The history we have terminates this run-up in the first week of September, 1939, and from there leads ineluctably to the most horrible single policy failure of the Twentieth Century, the French Republic's defeat in the spring of 1940. Leaving that aside, we learn from the data that we have. 

From what we have, we have tantalising fragments. As spring enters summer, news is reaching us of the "Rolls Royce Kestrel XXX," the first aeroengine designed, or, rather, redesigned, to operate over atmospheric air pressure (+9lbs boost) from the ground up; the Taurus, the last word in radial engine compactness, and of the disorderly retreat from service of an older, but not obviously obsolete engine, the Armstrong-Siddeley Tiger. This is all the more surprising given that just a year-and-a-half-ago, the Tiger VIII was being trumpeted as the first service aeroengine with a two-speed supercharger. 

The failure of the Kestrel/Peregrine and Taurus is probably not that surprising, given the war. Britain entered the world war balanced between pressure for smaller engines that would give less predetonation, and larger engines coupled with all of the exotic avgas formulations and TEL that could be crammed into a charge. War tipped the balance in favour of the latter, and the Griffon and Centaurus won out over the Peregrine and Taurus. Neither were the champions of the two engines very obviously aeroplanes worth keeping. The Whirlwind was a technological tour de force, one fundamentally unnecessary design novelty after another; the Bristol Beaufort was designed for reconnaissance and coastal defence, built to fight another Jutland. No Jutland, no Beaufort, although it survived in Australian production, albeit with another engine, on the basis of industrial inertia, and the formula was revisited with a true brute, the Bristol Brigand

What is more interesting is to see the thinking behind them. The Taurus carries compactness as far as it goes. Dr. Hadfield, commenting on Roy Fedden's talk on sleeve valves, stresses that when Fedden announced his intention to go down that road in 1926, he laid out a roadmap of metallurgical progress that required British steel manufacturers to radically improve every aspect of the material being provided to Bristol save for modulus of rigidity --probably the only one that they couldn't improve. Hadfield's February, 1939 comment is, understandably, a bit of a pat on his own back, but as the Rechlin study underlines, all of the British and French manufacturers (and, implicitly, the Germans) have been pushing metallurgical science to its limits over the last five years. 

The Kestrel, on the other hand, explores the limits of dynamics --big math, as it were. The problem of pushing more air through an engine is a problem of mechanics. The aerodynamic components have to be refined, but so do the moving bits that drive them. In his 1943 historical survey of the development of superchargers, R. P. Gordon Jones focusses a great deal on clutching arrangements, which is to say, the devices that engage and disengage supercharge impellers.*** Below is an exploded diagramme of a  Napier Sabre, as of this first week of June, 1939, under feverish development in a North London workshop. I don't expect the reader to be able to pick out the clutches amidst all of the gears and rods and such in this mechanical monstrosity, just to get a sense of the kind of machine that we're talking about. Mad crazy complicated ones. The Peregrine doesn't get this wrong, although it has gas leakage problems that cannot have weighed in its favour when production decisions were made. It gets it, more-or-less right. Now you know what Derby has been up to the last few years.

Finally, there is the Armstrong Siddeley Tiger. It is old, to be sure. The Wikipedia article is succinct and doesn't specify just how old, and it would be hard to fix a date, anyway, given that it was a development of the Jaguar, but the Tiger IV it was selected for the A.W. 19 offered to G.9/31 that first flew in February of 1934, and short of (gasp) looking it up, I will let that serve as an indication of the age of the engine. It's not just archaic looking compared with the Taurus, mainly due to the poppet valves and the telling choice of a wooden hub spinner, it is old.

But why is it old? Or, to put it another way, why has Armstrong Siddeley abandoned the engine? The traditional answer is the gossipy one. Harald Penrose, for one, says that A.S. was under the technical direction of an asshole, John Lord. However, dysfunctional as the firm was, it had certainly not abandoned development. On the contrary, it seems to have gone a little crazy. The Armstrong Siddeley Deerhound, like the Whirlwind, was far too many innovations and oddities rolled into one experimental design. (Not that Derby was immune to this, 1, 2, 3, 4.)

If I step back from drawing larger conclusions, "too much money rots the brains" will do quite sufficiently as an explanation for the Deerhound, Exe, Vulture, Crecy and their ilk. There is a gap here, though, that could quite credibly be filled with a modern redesign of the Tiger. The full story of that decision will probably only be told when someone has done a proper corporate history of Armstrong Siddeley, but I suspect, given A.S.'s "precocious" turboprops (1, 2), that the outline of the story will look like this: A.S. was exiting a dying industry ahead of the turbojets and turboprops that would soon start appearing. Development money on developmental engines, in contrast, paid off immediately. Show the Air Ministry something kooky, and you have to bring your own wheelbarrow to cart away the banknotes!

Okay, that's a little facetious. I am not going to pull a grand historical thesis out of these details, many of which I have retailed before. All that I really want to make clear is that the Air Ministry's defence spending binge in the spring of 1939 was giving manufacturers a considerable cushion with which to take great developmental risks. We underestimate the actual technological progress made during the peace years in favour of the war years because, for the most part, they have not delivered impressive figures of merit yet. But most of the actual developmental work has, in fact, been done. The failures emphasised here underline why "private enterprise" is not going to take up the slack for a small national security apparatus. (Hence my deconstruction of the Double Cyclone.)

What remains is to talk about spinoff effects. One way to do that is to wave at the Sabre and say, "Oh, hey, complicated! You know what else is complicated? Computers! Could it be more than just coincidence? Look for my upcoming show on Blaze!"

Another way is to drill down and look for more subtle signs, down in the grass. The biggest of these subtle signs, in my opinion, is the Baby Boom, which will be the focus (through the lens of technology and economics) of my next postblogging effort.

*Once again, P. K√∂tschke, "A German View on Allied Engines: an Enemy Report on Five English, Three French and Two American Types Captured," Aircraft Engineering, September 1941; originally published as C. E. Michaelis, "Die Flugmotoren des fiendliche Auslandes," Luftwissen 7, 5 (1941), 149[ff]. 

**"The BMW801A," Flight, 13 August 1942, 162ff. Not that you can open an aviation periodical from the summer of 1942 and not find an article on the 801; "Hercules Progress," Flight, 11 November 1943, 528ff. The Hercules, as a sleeve valve engine, will be slimmer than poppet valve types such as the BMW and Wright, regardless of other engineering features.

***R. P. Gordon Jones, "Development of the Aircraft Supercharger," Flight, 23 November 1943, 342ff.


  1. The thrust produced by the exceptionally loud two-stroke exhaust was estimated as being equivalent to a 30% increase in power at the propeller on top of the rated output of the engine

    Sorry? Pardon? I can't hear a word...

  2. Too bad for a later generation of hearing loss workers' compensation claim adjusters that the day of the direct-drive airscrew was done, or a Crecy-powered Lancaster would have given them all of East Anglia as clients.

    I'll give Derby this, though. They came up with an engine design that made the Sabre and Deerhound look sane.

  3. And also this: "A 100 litre 5,000hp version of the Exe/Pennine, known as the Exe 100, was to have become the Rolls-Royce Snowdon." Must have been something in the water....

  4. The guy who did the Edinburgh-London 400mph flight, by the way, was nicknamed "Downwind" for the rest of his life.

  5. It's a much more impressive record than if his nickname turned out to be "Wrong Way."

    By the way, I'm patting myself on the back for ending a post on overreach by private technology contractors in service of the security state with the discovery of the Rolls Royce Snowden....

  6. I'm not quite sure why A-S managed to get the Deerhound/Boarhound funded; certainly the AM Director of Engine Development didn't have a particularly high opinion of the company (though the specific comments I'm thinking of were made in 1941 or 1942).

    From what I can tell, development work on the Deerhound started sometime in the mid-1930s; The A-S board rejected collaboration with Whittle in the late 30s, but hired Heppner to look at gas turbine designs in the early 1940s(?). So I think the lack of piston development predates the move to gas turbines.

    1. Okay, sure. But, and here imagine that I'm addressing the rest of my audience and not Jakob, who knows far more about this than I do---

      Griffith floated the idea of the axial compressor-turbine running a prop in a 1926 paper, the problem, as always with early turbines was getting more power than was put in, since every increase in compression needed another axial stage to bleed off mechanical power.

      Whittle's centrifugal design didn't impress many people (until the MiG-15) because it substituted radius for length. Centrifugal engines had simpler engineering, but get fatter as they get more powerful.

      So much for the tedious argument from the mid-30s about whether a turbojet/prop engine was possible, and, if it were possible, whether it ought to be an axial (the consensus choice) or centrifugal. With the Deerhound, we're in a weird situation where A-S is setting out on a well-known and to this point rather sterile path of improving the radial piston-engine concept, which also tends to get fatter as it gets more powerful. (Unless it gets longer and more technically complicated.)

      The issue here is controlling air flow around and in the engine: through it to run whirling blades, around it to cool it; into the air intake in the first place. A.S., it seems to me as it might have been thinking in the mid-30s, had an enviable expertise with air-flow control. Why not, I wildly speculate, move on in an evolutionary direction from a pioneering multi-row radial (the Deerhound) into an axial turbine?

      The speculation requires a prehistory of turbine development at A.S., that is, an interest in axials that predates Heppner's hiring and might even have informed the decision not to work with Whittle.

      Basically, in interpreting A.S.'s actions, we have two alternatives. One is bad management. The other is a corporate trend that is obscured by a focus on personalities. From the belly of the beast, both seem plausible to me.

      Conversely, Griffith's big