mdiehl wrote:Yep, that's about how it seems to me. Of course there's a certain irony in the phrase "license built" after Dec 1941. Hamilton: "Hey Sumitomo, now that we're at war with each other your license is void." Sumitomo: "OK. Just hand deliver that note to our office in Tokyo and we will comply with our legal obligations."
Well, my business ran short so I'm back early. Just in time, I see, too.
[indent]"While the cat's away the mice will play."
[/indent]You shouldn't go off half-cocked with this "license" stuff. It wasn't anywhere near as bad as it looks on the surface. I researched this last night and I'll more or less paraphrase what I have before me for the gist of it.
The technology Japan was licensed dated back to 1920's for all intents and purposes, and by 1930 Hamilton Standard, working off these ideas, introduced the world's initial workable controllable-pitch propeller. To achieve maximum takeoff power, the pilot shifted a lever in the cockpit, oil pressure from the engine actuated a piston attached to the propeller which twisted the blades to low pitch. The propeller revolved rapidly, taking small bites of air and maximizing thrust. When the aircraft reached cruising altitude the pilot would reposition the lever which changed the blades into high pitch via centrifugal force on two counterweights attached to the hub and blades. About a year down the road HS (collaborating with the Woodward Governor Company) added the constant speed governor to the propeller. This device was known as the "automatic gear shift of the air" and enabled the pilot to choose and maintain an optimum propeller speed during flight no matter the conditions.
I've found a couple of sites (reliable of nature as far as I'm concerned) which peg this second technology as the one Japan got its paws on--it was widely available and used throughout the international commercial aviation industry soon after release. What isn't known is the material on construction Japan used (early-, mid- and late-war) for construction of the propeller. (I assume it was a metal alloy.) What Japan did
not get their paws on was the "hydromatic" technology which Hamilton Standard came up with later in the decade.
Technologically marvelous as variable-pitch/constant-speed propellers were in their day advancement in aeronautical design quickly demanded more sophisticated propeller solutions: larger and better powerplants required larger and better-constructed propellers with more finely-tunable pitch characteristics. The faster a plane flew the more strident its demand became for these pitch variations, more maneuverability called for these changes in pitch to be affected at faster and faster intervals in order to maintain constant rpm. Controllable propellers up to that point used internal hydraulic pressure acting on a piston to move blades toward low pitch. Counterweights, mentioned previously, were attached to the root of the blades to provide the force to change blades to high pitch. Actuating forces, however, did not keep pace with the increased size of propeller blades that were designed for larger aircraft and more powerful engines. The introduction of multiengined aircraft to improve flight safety didn’t fully meet this objective, for if an engine failed, its propeller would continue rotating, creating excessive drag and vibration, so that the operative engines didn’t necessarily guarantee a safe landing--the vibration was so severe in some cases the engine separated from the aircraft. Braking the propeller on an inoperative engine--with the blade angle set to the maximum allowable high pitch--became a standard emergency procedure to minimize vibration. But the blade angle this pitch setting still produced high drag, decreasing performance. The propeller brake shoes also needed to be isolated from engine and propeller hub oil to maintain dry surfaces to act immediately to stop the prop, otherwise, the brake drum could overheat and burn out the lining.
Enter the Hydromatic propeller, designed with a larger piston that could be actuated bi-directionally through hydraulics. This piston sat in a dome in front of the propeller and with a longer cam the excursion of the pitch-change cam slot was increased to permit a much wider range of pitch variability as well as allowance for higher slope cam slots which gave a faster rate of pitch change. A flat portion on the cam slot combined with independent oil supply provided a feathering feature, enabling an engine to stopped by turning its propeller blades parallel to the line of flight, thus eliminating a "windmill" effect and subsequent drag and vibration. Bottomline: safer engine shutdown inflight with better control afterward and this is the propeller technology the Allies possessed over and above what was found on "Zeroes." And it was found on a lot of different aircraft. In terms of fighters the 4-blade configurations were used with the Mustang and Thunderbolt, 3-bladed props on the British Wildcat (F4F-4B), Corsair and Hellcat. The Avenger also was fitted out as well most of the level bombers and transports.
Re the Aleutian ("Koga's") A6M2: I still can't find a copy of the report of official test results, only "reports" of The Report, but it would appear that after initial repairs "the boys" fueled Koga's "Zero" with 100 octane and just went for it. Now I can understand how this mistake would have been made--they probably just assumed Japan used the same juice, when in fact no such animal existed within the Imperial Regime.
So right away whatever the test results turned out to be the parameters became corrupted, besides which the tests revealed above all the else the A6M2's relative weaknesses and outright failings, less in the way of aerodynamic innovation--it actually only helped to dispell the "Zero" myth, as it were. (We keep hearing that the Americans stole the design ideas in order to incorporate these in our own aircraft. Nothing could be further from the truth. American and Japanese aeronautical design philosophies did not run together. The Japanese sought to trade compromises in strength and safety and armament in exchange for greater speed and range with the little engines they had to work with, basically. The American design approach thought of safety and durability as qualities equally important to performance and hitting power. Frankly speaking, Japanese airplane design ideas were looked on rather askance by the other side, and were eventually demonstrated in combat to be unsatisfactory aerodynamic compromises all around.)
Ironically, I haven't run down a propeller fix for the P-39 though I wouldn't be at all surprised if it used an American Standard (constant-speed) as well, same as the "Zero." Except in that plane's case it's doubtful a cheaper alloy might have been resorted to, while with the "Zero" that might well have been the case. In
Eagles of Mitsubishi Jiro Horikoshi, who headed the project, said this was one of the reasons the original "Zero" frame was so fragile (forced to use an unproven alloy) and in fact on a couple of test flights the prototypical frames simply went
Pop!, in a dive one time as I recall.
No matter what prop was spun onto the P-39 its handling characteristics would have been, of course, unique to it, while the "Zero's" would have been the same within its own flight context. A propeller tends to behave differently on each plane it's fitted to and as the demands of a given flight are placed on it. Think of a prop as a sort of wing that converts its lift into thrust with the propeller's rotation and the angle at which the blades strike the air, control the aircraft's speed during flight, while the engine's speed remains constant even when the aircraft's speed and altitude vary as well as velocity of the air flowing through and across the propeller's blade. The environment in which a propeller operates can be severe--lots of stuff hits it constantly besides air, like sand, stones, hail, salt water, lightening and the odd bird, with outside air temperatures ranging from considerably below zero to going on 160+ F. A prop has to be able to take the stresses put on it--its blades bend, flex and vibrate all over the place and these tremendous steady and dynamic loads and stresses are transmitted directly to the engine and airframe. Tons of pull develops on blades from centrifugal forces with the thrust of its spinning action generating other significant force; blade speeds reach up toward that of sound and any change in the aircraft's speed will alter the angle of air flow across those blades which will in turn cause imbalance and magnification of these dynamic forces. So structurally speaking the blades must up to snuff, thick and strong and resilient to cope with these stresses and loads. But they also have to be thin enough to achieve the best efficiency in terms of thrust while light enough to minimize the propeller's weight (and I suppose especially so with the "Zero" because that plane's engine wasn't so beefy, its airframe not so rugged) and so the propeller must be
carefully integrated with that engine/airframe structural combination so that these ever-changing aerodynamic loads and mechanics are transmitted with the least amount of dynamic issues.
What I'm trying to get at is I'm not exactly sure what "problems" the "Zero" had at various altitudes but at least one pilot's account says the performance dropped quite a bit due to the inferior propeller designs installed--and he wasn't happy about it! Assuming the P-39 used the same propeller design then I do not deny the possibility that this plane, too, might have run into its own dynamic issues with regard to that propeller--though we know from pilots who flew the Aircobra that it behaved more or less in a "high-performance" kind of way all the way up to 15,000 feet. Above that altitude I don't really know, but
whatever propeller issues the P-39 might have experienced at altitudes greater than 15K these would have tended to be
unique to that plane's engine/airframe structural combination as this reacted to the various propeller dynamics in play and are in no way
necessarily the same to what has been reported with respect to the "Zero."
All of which assumes the same props were employed, and we don't even know that for sure.
. Sorry TJ
