tlb wrote:Relax wrote:TLB: IF I could give you a major THUMBS UP
on your previous post on page 1 I would. Instead I give this post as kudos instead.
Thank you, that is very kind. Let me take some time to apologize for the last argument that I had with you, because we were talking at cross purposes and I am embarrassed that I did not recognize that was the case and express myself more clearly. As you probably remember, it was about the problem with the p-38 fighting at high altitude during winter over Germany. The troubles stemmed from the Allison engines needing turbochargers, because they lacked the superb supercharger used by the Merlin and Packard engines. In the extreme cold the turbo set-up had mechanical difficulties, which were not present in the much warmer air war in the Pacific. You took me as saying that the Allison lacked a supercharger (it did have a single stage one) and I kept brushing you off, because it was inadequate to get to the heights where the Army specified a turbocharger needed to be added (which was my point of interest). The problem as I should have stated it before,was not that it lacked a supercharger; but that it lacked a multi-stage supercharger that could have boosted it to the same heights as the Merlin.
1) Your memory about said argument is much better than mine.
2) Turbo powered superchargers by efficiency standards are superior to mechanical superchargers for efficiency at all altitudes by a couple percent and MUCH superior at high altitudes by even more. Why all civilian aircraft used them. Now at some point the extra weight becomes an issue depending on range of course... SNIP my rambling: Here is a much MUCH better link...
http://enginehistory.org/Piston/InterWa ... Cdev.shtml End result is that below 20,000ft little to differentiate between mechanical and turbo supercharging, but above this in terms of power, turbos increase in superiority with increasing altitude. Several NACA reports if you wish to look them up on theory and practice comparisons in the 20's and 30's between mutlitple types of supercharging. With the larger civilian airliner fleet in the 30's USA engine manufacturers were already using them everywhere with different shades of success.
2a) The USN who demanded simplicity and kaboshed all turbos especially since a lot of turbos failed early on sending shrapnel flying in all directions. USN went with 2 stage 2 speed superchargers for instance. It would be interesting to see a write up on the Brit side of development, but in all my years I have never seen one... the RR just magically appears with its 2 stage 2 speed supercharger sometime in 1942 on the Spit IX. Best I have ever read is that development of 2 stage 2 speed did not start until 1941... Maybe this was part of the Tizzard diplomatic ensemble that went to USA and the USA sent back old WWI destroyers and 2 stage 2 speed supercharger which had already been developed for the F4F Wildcat in the late 1930's? and was in service in 1940? Got me. Something that is lost to history?
3) If you go to say,
http://www.wwiiaircraftperformance.org and compare power curves you will note that the mechanically driven aircraft "best speed" charts look like jigsaw puzzles, but the turbocharged 2nd stage aircraft have a ~fairly constant curve.
4) P51 designers never even contemplated using a turbo as they had the engine mount adaptable for both the Allison and the Merlin from the beginning and their first customer natively were producing the Merlin.
5) Why the P47 was superior at high altitude over any Mechanically driven engine type before or after the war when comparing prop planes. One can say it was WAAAYYY over built with dual stainless steel main wing beams, and many other stainless steel parts making it WAAY too heavy but if you just look at its engine + supercharging setup...
6) P38 got its turbos fixed, but by then it couldn't actually USE said HP as its MASSIVE design flaw of the center cockpit created massive gargantuan compressibility problems. It was so bad that if any more HP, superior propellers/spinners were added it would literally fly into its coffin corner at a mere M0.6~450mph or so and why it was never upgraded and sent to other roles. It could not dive at basic fighter speeds of the time without turning into a lawn dart due to shockwaves formed by center cockpit interfering with its twin fuselages... this is a massive problem without any way to fix. In 1940, P38 was good(top speed only, horrible maneuverability), but by end 1943 it was junk even for pure energy fighting.
7) If you do go down the rabbit hole of looking at the old test documents be keenly aware of dates of introduction, fuel used, aircraft load condition, aircraft flying condition as all tests are NOT equal. An example would be that UK testing and USAAF testing were not equal as the philosophy of the testing was different and both are valid. A good way to put this is that Boscombe down testing in the UK was interested in MAXIMUM's while USAAF at Dayton Wright Patterson was more interested in averages and minimum's and German numbers vary by translation and the major problem they had an enormous number of variants which compounds the translation problem as they had both fighter and bomber threats to deal with. Just as an example, UK testing for instance would usually test with half fuel weight, gun ports tapped closed, no aerial radio antenna, engine radiator ports closed to get a maximum speed etc and then the fanboys of said aircraft publish this number as if it is equal. USAAF testing generally had a standard aircraft off the production line with EVERYTHING in it, full fuel, radio antenna, radiator open, etc.
8) If you REALLY want to go down the weedy path of old engines and supercharging issues an excellent youtube channel is Greg's Airplanes and Automobile's where he goes into a little bit of math and quite a bit of history of different aircraft types. 95% of what he says is correct which by internet standards is high praise indeed.
Cheers!
