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General control line discussion => Open Forum => Topic started by: Steve Helmick on February 11, 2013, 02:48:13 PM
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I was having breakfast out with Gary Letsinger, NW Skyraider, NW native and retired Boeing aero engineer. Around here, it is well known that when Gary speaks about aerodynamics and all things stunt, you pay attention...including Paul, Howard, and even Daniel. We were discussing propellers and how important they were to making a stunter fly well...or not. Gary said that after the war, somebody tested a P-39 with the prop off a P-51, and it was transformed and easily bested the performance of the P-51! The P-51, when tested with the P-39 prop, was a total dud. You'd think they would have known enough to do some prop testing, even then.
Oh, Gary is a fan of APC props. D>K Steve
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No offense, but - this sounds like a bunch of bull. The P-39 had a 1200 hp engine and 3 blade propeller. I doubt it could even spin the P-51 four blade propeller. The P-51 had a 1500 hp engine and if equipped with a P-39 prop would probably spin it to beyond redline engine rpm. I happen to have some original Hamilton Standard propeller design book and charts, and, there's no doubt in mind mind that they knew very well what they were doing.
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I read a book written by a P-47 pilot who was an ace in WWII. I recall him telling that a Spitfire would out climb a P-47 until they got a new prop which resulted in P-47s out climbing Spitfires.
I am a big advocate of propeller testing on stunt airplanes. I have been surprised several times.
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I did a quick search: The P-39 had a 10'5" Curtis Electric 3 blade prop on a 1200 hp engine. The P-51 had a 11'2'' Hamilton Standard 4 blade prop on 1500 hp engine.
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I would assume that both were Allison powered, wouldn't you? Which P-51's had Allisons, beyond the A model? I would not swear to it, but I don't think the Merlin hit until the D model. Could be wrong, but the point was that with them both being Allison powered, the prop made a world of difference. H^^ Steve
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The British modified the first Mustangs with the Merlin engine, converting P-51A models I believe, and the P-51B razor back was the first production P-51 with the Merlin. I believe it's widely know that the Allison powered A model was faster than the Merlin powered D model at sea level, but it was at altitude that made the Merlin powered versions shine and fulfill it's intended mission of long range bomber escort. I do, however, prefer the look of the A model Apache, the original name for the airplane. The British,who were the original customer for the airplane, put the name Mustang on it. I think the name Invader was also considered, but rejected because of a conflict with another airplane.
That's all I can remember at 2AM after a 9 hours on the road!
Dan McEntee
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Qoute from Wikipedia on P-51 history:
The addition of the Rolls-Royce Merlin to the P-51B/C model transformed the Mustang's performance at altitudes above 15,000 ft, giving it a performance that matched or bettered the majority of the Luftwaffe's fighters at altitude.
The definitive version, the P-51D, was powered by the Packard V-1650-7, a license-built U.S. version of the Rolls-Royce Merlin 60 series two-stage two-speed supercharged engine.
By the way, the experimental version of the P-51 used a three blade prop on the Alison, and the fastest P-39's used in unlimited racing (2000 HP+) still had 3 blade props.
Propellers are very important in stunt as in all aircraft performance, but the best stunt prop is not about the highest RPM's, most horsepower, or the highest speed at all. Unfortunately the real "optimum" prop for your latest stunt ship, whatever you fly, almost certainly isn't a standard one you can buy at the hobby shop :o
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The "never officially named Apache" had an Alison 1325 horsepower engine and was designed and flown in combat as a dive bomber. The A-36 was called Apache by North American's sales department as a marketing tool. This is from the January 2013 issue of Aviation History. The Collings Foundation had one restored by American Aero Services, of New Smyrna Beach, FL. It won Grand Champion at Oshkosh.
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Regarding the name for the P-51: Reference is made to the book - North American Aircraft 1934-1998, Volume 1, by Norm Avery, published by Jonathan Thompson, 1998. This book gives a detailed account of the design and production of every North American aircraft. The following is a very brief summary from the book.
In February, 1940, the "British Purchasing Commission" approached North American to produce P-40s for the RAF. Instead of tooling up to produce the P-40's, North American decided to design a new airplane that led to Britain ordering 300 examples of the aircraft designted NA-83, Mustang Ia. The first aircraft delivered in Britain in October, 1941, were called Mustang Is. Meanwhile, two XP-51s were built for the US Army, one being delivered to Wright Field in August, 1941. From the book, "Not having been designed for the Air Corps, the P-51, initially named Apache for American service, was not considered very important at the time and this was a serious concern in Britain." In July, 1941, the Army ordered 150 NA-91 as P-51 Apaches intended for the RAF under Lend-Lease. That production ran out in late 1942 and the British had not placed any more orders and the Army had no budget at that time for additional fighters. There were funds for attack aircraft and decisions were made by April 1942 to order 500 NA 97s as A-36 Invaders. "This name, like Apache, was dropped soon afterword in favor of Mustang for all models."
And the rest of the story with the transition to the Merlin engine is now history and legend.
Keith
I did not mean to hijack this thread on propeller testing with this discussion on the names for the P-51. The subject came up here and I felt that some comments from a definitive source were appropriate. -- KT