From: jfb@ihlpl.att.com (Joseph F Baugher)
Newsgroups: sci.military
Subject: Re: In-flight refueling in WWII
Summary: Experimental Mustangs
Keywords: refueling, flight, WWII
Date: 29 Sep 92 12:59:57 GMT
Organization: AT&T Bell Laboratories -  Naperville, Illinois


From Joseph F Baugher <jfb@ihlpl.att.com>

In article <Buq5EH.JyB@lawday.DaytonOH.NCR.COM>, ntaib@silver.ucs.indiana.edu (Iskandar Taib) writes:
> 
> By the way, does anyone have a listing of all the various experimental 
> Mustangs from the same era (late war, early postwar). I've heard of 
> a 51J and a 51K for instance..

Experimental Mustangs?  I can think of only three, the XP-51F, G and J 
Mustangs, all designed to meet a 1943 AAF requirement for an extremely 
light, high performance fighter designed to British load factors.  The 
British Air Commission was also interested in the project, and they 
requested two of these fighters for evaluation.  

Five XP-51Fs were ordered by the USAAF in June of 1943.  Serials were 
43-42222/43336.  The engine originally specified for these aircraft 
was the Packard Merlin V-1650-3, but the 1695 hp V-1650-7 was 
substituted for it during construction.  An extensive redesign of the 
basic airframe of the P-51D was undertaken with the main goal being 
the saving of weight through the simplification of the structure, the 
deletion of some equipment, and the use of new materials such as 
plastics.  A new, low-drag wing was fitted, which eliminated the 
familiar broken leading-edge of all the earlier versions of the 
Mustang.  The elimination of the broken leading edge was made possible 
by the use of a simpler undercarriage with smaller wheels.  In order 
to eliminate even more drag, the bubble canopy was made longer and the 
radiator fairing was modified.  The oil cooler was replaced by a heat 
exchanger.  The propeller blade was three-bladed rather than 
four-bladed as it was on the P-51D.  The armament was reduced to four 
0.50-cal machine guns in the wings.  

The first XP-51F flew on February 14, 1944.  The weight reduction 
program resulted in the savings of nearly a ton of weight as compared 
to the P-51D.  Weights were 5635 lbs empty and 7610 lbs normal loaded, 
as compared with 7125 lbs empty and 10,100 lbs normal loaded for the 
standard P-51D.  A speed of 466 mph at 29,100 feet was attained.  An 
altitude of 19,500 feet could be attained in 4.9 minutes.  Service 
ceiling was 42,500 feet.  Maximum range was 2100 miles.  Weights were 
5635 lbs empty and 7610 lbs normal loaded.  The third XP-51F was 
shipped to the United Kingdom on June 30, 1944, where it was given the 
RAF serial number FR 409.  

The XP-51G was produced by fitting the last two XP-51F airframes 
(serial numbers 43-43335 and 43-43336) with the 1910 hp Rolls-Royce 
Merlin 145M obtained from the UK under Reverse Lend-Lease.  The 
propeller had five blades.  The armament was the same as that of the 
P-51D, namely six 0.50-cal machine guns in the wings.  The aircraft 
was otherwise quite similar to the XP-51F.  The first XP-51G flew on 
August 9, 1944, and the second XP-51G was shipped off to the United 
Kingdom in January of 1945 for evaluation by the RAF.  A speed of 472 
mph at 20,750 feet could be attained.  An altitude of 20,000 feet 
could be reached in 3.4 minutes.  Maximum range was 1865 miles.  
Weights were 5750 lbs empty and 7265 lbs normal loaded.  

The XP-51J was yet another high-speed version.  It was powered by an 
Allison V-1710-119 engine rated at 1500 hp for takeoff and 1720 hp 
with water injection at 20,700 feet.  The carburetor intake was 
incorporated into the ventral radiator, giving an extremely 
aerodynamically-clean nose configuration with no scoop below the 
propeller hub.  Two of these XP-51Js were ordered.  Serials were 
44-76027/76028.  The first flight of the XP-51J was on April 23, 1945, 
but the Allison engine was insufficiently developed to permit 
full-power operation, and the plane was loaned to Allison for use in 
engine development work.  The second XP-51J was not actually flown, 
but was used by Allison for spare parts to keep the first one flying.  
A maximum speed of 491 mph was anticipated at 27,400 feet, but was 
never achieved under tests.  The end of the war brought further 
development of the XP-51J to an end.  

The P-51K was not experimental.  It was basically the same as the
P-51D but with an Aeroproducts propeller in place of the Hamilton-
Standard unit.  Most of these were built in North American's Dallas
plant.  It had no rocket stubs under the wings, and the performance
of the P-51K was slightly inferior to that of the D.

The work on the XP-51F and G experimental lightweight Mustangs was to 
bear fruit in the last Mustang variant to see service, the P-51H.  The 
P-51H was powered by a Packard Merlin V-1560-9 engine delivering a war 
emergency power of 2218 hp at 10,200 feet with water injection.  The 
P-51H was similar in appearance to the XP-51F apart from having a 
shorter bubble canopy, a four-bladed propeller, a dorsal extension to 
the fin-and-rudder assembly, and an increase in overall length.  It 
had the same shallower carburetor air intake and modified cowling with 
integral engine mounting as did the XP-51F.  It had the new low-drag 
wing with the elimination of the broken leading engine.  It could 
carry either four or six 0.50-cal machine guns in the wings.  

The P-51H was quite a hot ship.  It could attain a maximum speed of 
444 mph at 5000 feet, 463 mph at 15,000 feet, and 487 mph at 25,000 
feet.  It was perhaps the fastest production piston-engined fighter of 
any of the combatants to see operational service during World War 2.  
It could reach 5000 feet in 1.5 minutes and 15,000 feet in 5 minutes.  
Range was as high as 1500 miles with a pair of underwing drop tanks.  
Weights were 6585 lbs empty, 9500 lbs normal loaded.  

The P-51H was too late to see service in the war against Germany.  It 
was in the process of re-equipping a number of fighter groups in the 
Pacific at the time of the final push against Japan, but I don't think 
that the P-51H actually saw any combat.  

The P-51L was to have been similar to the P-51H but with a more 
powerful V-1650-11 engine.  The end of the war with Japan resulted in 
the cancellation of this project without a single example ever being 
built.  

The P-51M was to have been the Dallas-built version of the P-51H but 
with a Packard Merlin V-1650-9A engine.  One example was actually 
flown, (Ser No 45-11743), but the end of the war with Japan resulted 
in the cancellation of an order of 1628 P-51Ms.  

Sources: 

  Famous Fighters of the Second World War, William Green, Doubleday, 
  1967.  

  War Planes of the Second World War, William Green, Doubleday, 1964.  

  Fighting Mustang: The Chronicle of the P-51, William N. Hess, 
  Doubleday, 1970 

Joe Baugher       AT&T Bell Laboratories    2000 North Naperville Road 
		  Naperville, Illinois 60566-7033.   (708) 713-4548