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| | From:  -TinCan (Original Message) | Sent: 10/10/2007 12:04 PM |
Of all the weapons of war ever developed has there ever been one that came so far in such a short amount of time as the airplane? Think about it for a moment. How many thousands of years have men hacked at each other with swords? They get a little break when they figure out how to get a little range on their enemies with the bow and arrow. Next, that range is increased with the invention of gunpowder and cannon but this all takes hundreds of years to come about. Then, all of a sudden, in 1903 we get the Wright Flyer, forty one years later we have the ME-262, and it just keeps getting bigger and better. (I'm not counting ballons here for you that will point out they were around before the WF) |
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No TinCan you are very clear. My point is any old aircraft could be introduced, one at a time, and its features be publicised as an advance. So much was regarded as acceptable. EG with your first passenger aircraft, flight crew and cabin staff outnumbered passengers. But firearms had to be cheap from day 1. My best example will be Brigadier-General Ridley (?Ripley) binning the Spencer Carbine (8 shot repeater, Blackslee quick loader) and retaining the Enfield Rifle-Musket Now by your standards of measurement, it would appear magazine breech loaders appeared 10 years after they actually did. (You remember the tale? Lincoln personally tried the Spencer out and insisted on its general issue, which never happened) Tell you the truth I am being very pedantic. It's just I feel everytime something new came out with air craft it was the latest thing. But firearms went from muzzle loading smooth bore to magazine fed breech loading rifled in 50 years. But not for general issue. Peter |
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| | | From: Bob39 | Sent: 10/16/2007 10:30 AM |
FM, # 33: BTW Bob Your Power recovery turbine; is that the same as a Turbocharger? I'd have thought that by using exhaust gas as a drive for compressing blades it would be much simpler than a supercharger No. Superchargers and turbochargers vary only in the source of the power used to compress more air into the cylinders. They increase the compression ratio of the air going into the cylinders, so that piston engines can maintain sea level air density, to a much higher altitude, than they could without supercharging. A PRT does not compress the air going into the cylinders. They already had superchargers doing that. The PRT simply makes use of the exhaust heat to drive a turbine that is attached to the aft end of the engine crankshaft. It is a method of turning heat energy into kinetic energy. Similar to the principle of using the hot exhaust gases that come out of the burner cans in jet engines, to drive the turbine blades in the aft end of the jet engine, which in turn drives the compressor blades in the front of the jet engine. Gas turbo chargers (using the exhaust heat to drive the compressing turbine) are used on light planes in civil aviation today. But, they only raise the compression ratio of the air going into the cylinders. They do not drive a turbine attached to the aft end of the crankshaft, as was the case in the DC-7 and other planes that had variations of the engines you mentioned. |
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| | | From: Bob39 | Sent: 10/16/2007 10:51 AM |
FM, # 33: You seem to have a prejudice against them. ????????? I cannot imagine why/what of anything I have said, that would lead you to think that.......  Superchargers were very necessary, to get the large planes and fighters to the higher altitudes that gave them advantages they needed, to win the air war. The big advantage of the B-29s, was that the Japanese fighter planes could not fly high enough to shoot them down. That was because of the superchargers on the B-29 engines. Superchargers also made airliners more efficient and profitable, than non-supercharged types. I have only pointed out that the biggest and most powerful piston engines of all times, proved unprofitable to the airlines, and forced them to phase those planes out of service, much earlier than would have otherwise been the case, because the maintenance costs were so high, especially on the engines that had the PRTs. Airlines pay heavy costs when their planes have to make unscheduled landings, because of engine failures. The engines on the DC-7 failed at a much higher rate than they did on the DC-6. The DC-6 R-2800 engines also had superchargers, but they were much less prone to swallow valves, than were the 3350s. The PRTs were prone to failure too, so that greatly increased the operating costs of the planes that had that feature. |
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| | | From: Bob39 | Sent: 10/16/2007 11:06 AM |
BTW FM, Tanks much for posting those excellent pics in # 28 & # 32. I am adding them to my extensive collection. |
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"You seem to have a prejudice against them. ????????? I cannot imagine why/what of anything I have said, that would lead you to think that....... " No Bob, I wasn't meaning you individually I was meaning you Yanks collectively. You had an engine which was designed for supercharging (the Allison,) you remove the superchargers, but still fit the engine, and have 4 underperforming aircraft. |
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PRT Is that a kind of afterburn then? Peter |
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| | | From: Bob39 | Sent: 10/17/2007 1:42 PM |
FM, # 40: You had an engine which was designed for supercharging (the Allison,) you remove the superchargers, but still fit the engine, and have 4 underperforming aircraft. That gets into a long and very complicated story, about the development of the various versions of that engine (Allison V-1710), which started out with 1000 HP, and ended up with 2900 HP. Unfortunately, politics from the Allison people and bureaucratic red tape from the Army itself, was a significant factor in the slowing of supercharger technology advancement, on our side of the Atlantic. The best solution to the high-altitude air battles over Europe was the Merlin engine for the P-51, because it had a two-stage supercharger with additional features that dealt with problems of detonation and power loss, like its "pressure-altitude governed two-speed gearbox and the intercooling system." However, that Merlin engine design was greatly enhanced by new design mods and innovations, created by our American engineers at Packard, which manufactured it under license from you Brits. One thing our Packard engineers did to that engine was to produce it with a tighter uniform standard for all parts, with more demanding tolerances, that could be produced only with our mass production techniques. You Brits were still fitting your versions of the Merlin via individual craftsmen. But, in the Pacific the battles were at the lower altitudes, where the Allison engine proved to be a real winner, especially in the P-38. It was super strong and very resistant to damage from Japanese machine gun bullets. Engine reliability was crucial and that was improved greatly by not having superchargers on those engines. So, in my mind, it made good sense to not supercharge that engine for the Pacific War Theater. They were able to produce more than adequate power, for flight levels below 15,000 ft. (the P-51 was a lot faster than the spitfire, in that regime, with the Allison engine). |
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Very interesting. I know the Soviets liked the Airacobra and Kingcobra for their low level performance. To digress, it shows the Soviets' paranoia. They had a better gun than either Hispano 20mm or the 37mm Oldsmobile cannon, the 23mm and Nudelmann 37mm. The 23mm is used to this day, and has a far higher MV than the 20mm. But they wouldn't fit them in the Bells. Your 37mm was a copy of a French WW1 AA job. Japanese MGs were horribly underpowered, and a Jap quartermaster's life was a unhappy one, having to supply 7.7, 6.5, rimmed and rimless, because of their slavish copying habits (Italian kit). They did actually progress to a bomber killing 105mm gun, in the twin engine gecko. Packard Merlins, I've heard exactly the reverse, their quality was inferior to British made ones. I myself have never heard of any complaints of quality of the Merlin. As far as I'm aware they were only fitted to P51s and we did not operate nearly as many as you did. I think the Griffon Spitfirs were on their way by then. 2900 Allison. Into what were they fitted? I still have a mental love affair with the Airacuda. Cheers Peter |
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| | | From: Bob39 | Sent: 10/18/2007 1:18 PM |
FM, # 43: 2900 Allison. Into what were they fitted? That was the V-1710-127 version. It was supposed to be able to generate 2,900 hp at low altitudes and and still put out 1,550 hp at 29,000 feet, without being supercharged. It actually static tested at 2,800 hp. The plan was to install it in an experimental aircraft, designated the XP-63H. But, the war ended too soon, so that one never flew. They gained the additional power by attaching an exhaust turbine to the crankshaft, which was called a "turbo compound" unit. I am not certain, but I think this is the first instance of a PRT on a piston engine. At least, I haven't been able to find any earlier ones to date. The advantage of a PRT is that it utilizes wasted heat from the exhaust and converts it into additional kinetic energy, without taking away from the power that the engine generates by itself. That is different that a supercharger, which uses part of the generated HP of the engine to compress the air going into the cylinders, so that sea level pressure is available to the engine, at much higher altitudes than would be the case without supercharging. The disadvantage of PRTs is that they proved to be a very high maintenance item. So much so, that the airlines that used them, soon found they couldn't make any money flying planes so equipped, because of the high maintenance costs on the engines. Not to mention the additional costs incurred when an engine failure forced an unscheduled landing. |
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Bob, is this correct? In a car we have superchargers which are belt or gear driven and therefore sap a bit of the power. A turbo is a freewheeling fan which at certain revs produced by exhaust speed stuffs enough fuel to accelerate further. Cheaper but you have the dreaded turbo lag. And in cars you have to idle them before switching the ignition off. say 30 secs. Daughter was asking me and if I don't produce the right answer..... BTW what do you do for a living, or did you do which makes you so clued up? Peter |
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| | | From: Bob39 | Sent: 10/19/2007 9:45 PM |
FM, # 45: BTW what do you do for a living, or did you do which makes you so clued up? |
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| | | From: Bob39 | Sent: 10/19/2007 11:22 PM |
FM, # 45: In a car we have superchargers which are belt or gear driven and therefore sap a bit of the power. A turbo is a freewheeling fan which at certain revs produced by exhaust speed stuffs enough fuel to accelerate further. Cheaper but you have the dreaded turbo lag. And in cars you have to idle them before switching the ignition off. say 30 secs. Actually, they are not free-wheeling, at least not the ones of today's technology. Their speed and output pressure is controlled via a wastegate, that "dumps" some of the excess exhaust gas before it is channeled to the turbine side of the turbocharger. That wastegate is controlled/modulated by an electronic "boost controller." That is necessary because without such a control, the turbo charger could easily overboost the engine (force too much atmosphere pressure into the manifold and cylinders, which would exceed the mechanical and thermal limits of the design of a specific engine, blowing it all to hell...........). To control the turbo lag that you mention, anti-surge dump valves, which are also electronically controlled, vent off the excess pressure that can build up between the turbo compressor and the air inlet, when the engine throttle is suddenly closed. Since the closed throttle takes away the capacity to accommodate that very high pressure air, it would probably cause damage to the induction system. Without the relief of the dump valves, there would also be back flow compression to the turbo compressor, and that would cause all kinds of problems, one being the sudden slowing down and then necessary re-acceleration of the turbine, which is counterproductive. The ideal goal is to keep the turbine spinning within a fairly consistent high speed RPM envelope, and regulate the inlet air pressure, according to the need and demands of the engine itself, as signaled by the position of the throttle plate. While turbo compressors are more efficient than mechanical superchargers (they use a smaller percentage the engine's horsepower to drive themselves), they do cause back pressure in the exhaust system and that does force the engine to work somewhat harder, to drive that turbo compressor. The reason hotrodders of old wanted extremely noisy machines to drive around in, was because muffling the exhaust sounds had the effect of creating exhaust back pressure, and that forced the engine to use some percentage of its power just to get rid of the exhaust, which in turn reduced the amount of available horsepower to the wheels, when the hotrodder wanted to win a drag race............... Turbochargers do cause increased fuel and air flow into the cylinders, but the higher compression ratios also increase the efficiency of fuel burning itself. That is one reason why today's vehicles are able to get more than twice the miles per gallon/pound of weight than those of 50 years ago. My first car, a 1951 Plymouth, only developed about 90 horsepower and got about 12 miles per gallon. Today, I get better mileage than that with my SUV, which has more than double the horsepower and considerably more weight. My Honda Accord has at least that much horsepower and I get about 30 MPG with it. My turbo charged Ford Diesel truck gets about 15 MPG and it weighs 80% more than my SUV. |
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Bob. very good. I've piloted a chipmunk and a DH Dove. Under close supervison. In level flight. nearest thing to me is riding a British bike. Fuel consumptions, yes. 1976 Ford 1.3 escort, 28 mpg 1.6 Cortina, 25 mpg 1988 2.8 Granada (Taurus to you) 27 mpg. 2002 Citroen 2 L HDI diesel. 53 mpg (open road use). I think downside is maintenance is a garage job at garage rates. I would buy a second hand car for $100, replace spark plugs, distributor cap, condenser, coil, breakers, hoses, belts in an afternoon, and know that car was reliable for a year save for running gear breakdown. Many cars now you can't get at the spark plugs even Cheers Peter |
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