Subject: Number Sixty-Seven in the Series--McDonnell XP-67 Bat

From: [email-masked]
Date: 12 May 93 16:25:11 GMT

>From [email-masked]

The McDonnell Aircraft Corporation of St Louis, Missouri was 
incorporated on July 6, 1939.  McDonnell was certainly not a company 
to start small--as its first military project, the company immediately 
began a design study for a long range fighter.  A rather ambitious 
first project for such a new aircraft corporation! 

In June of 1940, the new McDonnell company submitted an unsolicited 
proposal to the USAAC for an unconventional fighter powered by either 
an Allison V-3420-B2 or a Pratt & Whitney H-3130 engine equipped with 
a two-stage supercharger.  The engine was to be buried in the fuselage 
aft of the pilot.  The engine was to drive a pair of pusher propellers 
situated aft of the wings by means of a complicated system of 
extension shafts and gear drives.  Although the USAAC rejected the 
proposal because of excessive weight and complexity, the Army was 
sufficiently impressed that it bought the engineering information from 
McDonnell on June 6, 1940 and encouraged the new company to keep 
trying.  

The next McDonnell proposal to the Army came later that same month.  
This time the company issued a proposal for a twin-engined, two-seat 
heavy fighter powered by a pair of Continental I-1430 twelve-cylinder 
inverted-Vee liquid-cooled engines.  Initially, the USAAC expressed no 
interest, but during subsequent discussions with McDonnell some 
revisions were made and on May 5, 1941 a formal proposal was submitted 
to the Army.  The project was given the company designation of Model 
S-23-A and called for a single-seat long-range fighter with a 
pressurized cabin.  An unusually heavy armament of six 0.50-inch 
machine guns and four 20-mm cannon was proposed.  McDonnell's design 
team attempted to maintain true aerofoil sections throughout the 
entire airframe, the center fuselage and the rear portions of the 
engine nacelles merging smoothly together.  This gave the aircraft a 
unique bat-like appearance.  The forward member of the tricycle 
undercarriage retracted into the fuselage, whereas the mainwheels 
retracted into the engine nacelles.  Guaranteed maximum speed was a 
rather optimistic 472 mph at 25,000 feet, and gross weight was 
estimated to be 18,600 pounds.  

This time the Army was definitely interested, and on August 2, 1941 
the USAAF issued an authority for purchase of two prototypes.  The 
contract was formally approved on October 29, 1941.  The designation 
XP-67 was assigned, and the serial numbers of the two prototypes were 
42-11677 and 42-11678.  

By the time that detailed design of the XP-67 got underway, the 
armament was changed to six 37-mm cannon with 45rpg in the inboard 
wing sections.  The pair of Continental XI-1430-1 engines were fitted 
with General Electric D-1 turbosuperchargers and drove four-blade 
propellers.  A unique idea was to use the engine exhaust to augment 
the thrust.  The increased armament and other changes caused the 
estimated gross weight to rise to 20,000 pounds.  

With the exception of armament, cabin pressurization equipment, and 
the oxygen system, the first XP-67 (42-11677) was ready by December 1, 
1943.  The aircraft had conventional ailerons rather than the planned 
drooping ailerons.  By this time, the engines were XI-1430-17/19s, 
with D-23 turbosuperchargers.  The Continental engines were rated at 
1350 hp for takeoff and 1600 hp at 25,000 feet.  

The initial flight tests of the XP-67 were delayed by fires in BOTH 
engines that broke out during a high-speed taxiing run at Lambert 
Field in St Louis on December 8, 1943.  After being repaired, the 
XP-67 was trucked to Scott Field in Illinois.  The first flight of the 
XP-67 took place there on January 6, 1944 with test pilot E.  E.  
Elliott at the controls.  However, this flight had to be abruptly 
terminated after only six minutes owing to engine problems.  

The XP-67 was grounded while modifications were made to the engine 
compartments.  A stainless-steel bulkhead was installed to seal off 
the turbosupercharger compartment from the rest of the engine, 
improvements were made to the cooling air circulatory system, and the 
aft ends of the engine cowlings were shortened.  With these 
modifications, two test flights were completed successfully.  However, 
on the fourth flight (on February 1, 1944), the Continental engines 
were deliberately overspeeded and the bearings burned out, forcing yet 
another emergency landing.  

This mishap had damaged the Continental engines beyond repair, and 
since replacements were not immediately available, the XP-67 was 
returned to McDonnell in St Louis for modifications.  Wind tunnel 
testing had suggested that the tailplane should be raised one foot in 
order to improve longitudinal stability, and this was done while the 
aircraft was awaiting replacement engines.  

Test flying resumed on March 23, 1944, and five more successful 
flights were made during the month of May by USAAF test pilots.  
During this time, some problems were encountered with engine 
roughness, with improper aileron balance, and with unsatisfactory main 
undercarriage door closure.  However, the USAAF pilots reported that 
the cockpit layout was adequate and that ground handling was 
satisfactory.  Handling in the air was considered as being 
satisfactory and the roll rate was deemed to be good at high speed.  
The fighter was stable longitudinally, but it was neutrally stable 
laterally and tended to "Dutch roll".  

However the performance of the XP-67 fell quite short of that which 
was promised.  The takeoff run was excessively long, the initial climb 
rate was poor, and the acceleration was slow.  The aircraft was clearly 
underpowered with its troublesome Continental engines, which failed to 
develop their design rating of 1350 hp, barely reaching 1060 hp.  

Test flights continued throughout the summer of 1944.  A dorsal fin 
and an additional two degrees of dihedral were added to the tailplane 
to improve lateral stablity.  The XP-67 was scheduled to begin 
official performance tests in September, but before they could get 
underway a fire broke out in the right engine nacelle while test pilot 
E. E. Elliott was taking the XP-67 for a test flight.  Elliott 
safely landed the aircraft, but the wind blew the flames over the 
fuselage and caused major damage to the structure.  

The XP-67 was deemed to have been damaged beyond economical repair.  
This accident, plus the seemingly endless series of problems caused by 
the temperamental Continental engines, caused the USAAF to recommend 
that work on the XP-67 project be halted.  On September 13, both 
McDonnell and the USAAF agreed that the project should be terminated.  
The contract was formally cancelled six weeks later.  

The second prototype (42-11678) was cancelled before it could be 
completed.  This prototype was to have been powered by I-1430 
liquid-cooled engines with war emergency power ratings increased to 
2100 hp.  Contrarotating propellers were to be fitted in place of the 
handed propellers of the first prototype.  There was even some talk of 
fitting a mixed powerplant arrangement to later production P-67s, with 
either a Packard V-1650 or an Allison V-1710 engine with two-stage 
supercharger in front of each engine nacelle and an I-20 turbojet in 
the rear of each nacelle.  However, nothing ever came of these plans, 
since the USAAF requirement for long-range escort fighters was more 
than adequately satisfied by the North American P-51H Mustang, the 
Republic P-47N Thunderbolt, and later by the North American P-82 Twin 
Mustang.  

The maximum speed attained by the XP-67 during tests was 405 mph at 
15,000 feet and 357 mph at 10,000 feet.  Initial climb rate was 2600 
feet per minute, and service ceiling was 37,400 feet.  Maximum range 
was 2385 miles.  Weights were 17,745 pounds empty, 23,114 pounds 
loaded, 15,400 pounds maximum.  Dimensions were wingspan 55 feet 0 
inches, length 44 feet 9 1/4 inches, height 15 feet 9 inches, and wing 
area 415 square feet.  The planned armament of six 37-mm cannon was 
never actually fitted.  

Sources: 

  McDonnell Douglas Aircraft Since 1920: Volume II, Rene J.  Francillon, 
  Naval Institute Press, 1990.  

  The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.  

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

Joe Baugher		AT&T Bell Laboratories   	
2000 North Naperville Road      Naperville, Illinois 60566-7033