XP-67 Bat
Encyclopedia
The McDonnell XP-67 "Bat" or "Moonbat" was a prototype for a twin-engine, long range, single-seat interceptor aircraft
Interceptor aircraft
An interceptor aircraft is a type of fighter aircraft designed specifically to prevent missions of enemy aircraft, particularly bombers and reconnaissance aircraft. Interceptors generally rely on high speed and powerful armament in order to complete their mission as quickly as possible and set up...

 for the United States Army Air Forces
United States Army Air Forces
The United States Army Air Forces was the military aviation arm of the United States of America during and immediately after World War II, and the direct predecessor of the United States Air Force....

. Although the design was conceptually advanced, it was beset by numerous problems and never approached its anticipated level of performance. The project was cancelled after the sole completed prototype was destroyed by an engine fire.

Origins

In 1940, the U.S. Army Air Corps issued Request for Proposal R-40C, requesting designs for a high-speed, long-range, high-altitude interceptor intended to destroy enemy bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...

s. The specifications were very bold, encouraging manufacturers to produce radical aircraft that would outperform any existing fighter in the world at the time. Upstart aerospace
Aerospace
Aerospace comprises the atmosphere of Earth and surrounding space. Typically the term is used to refer to the industry that researches, designs, manufactures, operates, and maintains vehicles moving through air and space...

 parts manufacturer McDonnell Aircraft
McDonnell Aircraft
The McDonnell Aircraft Corporation was an American aerospace manufacturer based in St. Louis, Missouri. The company was founded on July 16, 1939 by James Smith McDonnell, and was best known for its military fighters, including the F-4 Phantom II, and manned spacecraft including the Mercury capsule...

, eager to begin manufacturing its own aircraft, responded to the proposal with drawings and specifications of the proposed Model I, which would be powered by an unusual geared drivetrain with a single Allison V-3420
Allison V-3420
|-See also:-References:* Bridgman, L, Jane's fighting aircraft of World War II. Crescent. ISBN 978-0-517-67964-7-External links:...

 engine buried in the fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...

 powering twin wing-mounted pusher
Pusher configuration
In a craft with a pusher configuration the propeller are mounted behind their respective engine. According to Bill Gunston, a "pusher propeller" is one mounted behind engine so that drive shaft is in compression...

 propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...

s in the wings. However, 22 other manufacturers also issued proposals to meet the Army’s request; the McDonnell proposal had relatively unimpressive anticipated performance, and its odd drivetrain was unproven. The Model I fell in 21st place when the 23 proposals were examined and scored. (The top proposals would become the similarly ill-fated XP-54, XP-55
XP-55 Ascender
|-See also:-References:NotesBibliography* Balzer, Gerald H. American Secret Pusher Fighters of World War II: XP-54, XP-55, and XP-56. North Branch, Minnesota: Specialty Press, 2008. ISBN 1-58007-125-2....

, and XP-56
XP-56 Black Bullet
|-See also:-References:NotesBibliography* Allen, R.S. The Northrop Story. New York: Orion, 1990. ISBN 0-517-56677-4.* Andersen, Fred. Northrop - An Aeronautical History: a Commemorative Book Edition of Airplane Designs and Concepts. Century City, California: Northrop Corporation, 1976. Library of...

.)
Despite the apparent setback, Air Corps leaders were impressed by the nascent company’s efforts, and granted McDonnell a $3,000 contract to re-engineer the airplane.

Final design

McDonnell engineers returned on 30 June 1941 with the Model II, which was also rejected, so it was reworked into the Model IIa, which emerged on 24 April 1942. The new design was powered by a more traditional layout, a pair of engines in wing-mounted nacelles with 4-bladed propellers in a tractor configuration
Tractor configuration
thumb|right|[[Evektor-Aerotechnik|Aerotechnik EV97A Eurostar]], a tractor configuration aircraft, being pulled into position by its pilot for refuelling....

. However, the design was still quite ambitious; the design team tried to maintain a true airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....

 section through the center fuselage, merge the rear portions of the engine nacelles with the wing, and radically fillet all edges of the fuselage and nacelles into the wings in an effort to reduce drag. The design used laminar airfoil sections throughout. McDonnell designers promised that the design would deliver a top speed of 472 mph (760 km/h) with a gross weight of 18,600 lb (8,440 kg), although the anticipated gross weight was soon increased to a somewhat more realistic 20,000 lb (9,070 kg).

On 30 September 1941, the USAAC granted McDonnell a $1,508,596 contract, plus an $86,315 fee, for two prototypes, a wind tunnel
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...

 model, and associated engineering data, The Model IIa was designated as the XP-67. The production aircraft was intended to have a pressurized cockpit
Cabin pressurization
Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...

, a novel innovation at the time. A number of armament configurations were considered including six .50 in
.50 BMG
The .50 Browning Machine Gun or 12.7×99mm NATO is a cartridge developed for the Browning .50 caliber machine gun in the late 1910s. Entering service officially in 1921, the round is based on a greatly scaled-up .30-06 cartridge...

 (12.7 mm) machine gun
Machine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....

s, four 20 mm (.79 in) cannon, and even a 75 mm (2.95 in) cannon before the configuration of six 37 mm (1.46 in) M4 cannon
M4 cannon
The 37 mm Automatic Gun, M4, known as the T9 during development, was a 37 mm autocannon designed by John Browning and used in the Bell P-39 Airacobra and P-63 Kingcobra fighters, as well as experimentally on other designs. It provided interceptors with a weapon that could shoot down any...

 was chosen. Power would be provided by two Continental XIV-1430-1 inverted V-12 engines, fitted with turbosuperchargers, and the engine exhaust gasses would augment thrust.

Aerodynamic test program

The XP-67’s radical design would require extensive wind tunnel testing to fine-tune its numerous advanced aspects. An extensive aerodynamic test program was begun by three different entities: McDonnell, NACA
NACA
- Organizations :* National Advisory Committee for Aeronautics, the forerunner of the U.S. federal agency NASA* National Association for Campus Activities, an organization for programmers of university and college activities...

 and the University of Detroit. The design demanded skin that was perfectly smooth and precisely shaped to maintain its laminar-flow characteristics, mandating the development of new construction techniques, as the company had never produced an entire aircraft before. Wind tunnel testing uncovered problems with engine cooling airflow through the engine nacelles, problems that would ultimately never be fully resolved. Difficulties were also encountered in obtaining engines, as wartime production demands hampered Continental’s efforts to deliver running examples of the experimental XIV-1430 engines to competing aircraft test programs. The project was also delayed by intense competition for testing time at the NACA
NACA
- Organizations :* National Advisory Committee for Aeronautics, the forerunner of the U.S. federal agency NASA* National Association for Campus Activities, an organization for programmers of university and college activities...

 wind tunnel facility in Langley, Virginia
Langley, Virginia
Langley is an unincorporated community in the census-designated place of McLean in Fairfax County, Virginia, United States.The community was essentially absorbed into McLean many years ago, although there is still a Langley High School...

.

Flight test program

The first XP-67, 42-11677, was ready for ground trials on 1 December 1943, although it was not yet ready for flight. The aircraft was fitted with XIV-1430-17/19 engines and General Electric D-23 turbo-superchargers. No pressurization equipment or armament would ever be installed in the prototype. On 8 December, the aircraft was damaged by fires in both engine nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...

s, caused by a malfunction of the exhaust manifold slip rings. By 6 January 1944, the damage was repaired and the XP-67 made its first flight. The flight, however, ended after six minutes due to difficulties with the experimental engines. After a number of modifications were made to the engine installations, two test flights were carried out. On the fourth flight, the engine bearings burned out when the engines were unintentionally overspeeded.
By this time, it was becoming obvious that the XP-67 was hampered by a serious lack of power. The engines were only delivering 1,060 hp (790 kW), well short of their promised 1,350 hp (1,007 kW) rating. Company founder Jim McDonnell
James Smith McDonnell
James Smith "Mac" McDonnell was an American aviation pioneer and founder of McDonnell Aircraft Corporation, later McDonnell Douglas.-Early life:...

, frustrated by ongoing engine procurement delays and the XI-1430's subpar output, began to campaign for funding to re-engine the prototype with a pair of Allison
Allison Engine Company
The Allison Engine Company was a U.S. aircraft engine manufacturer. In 1929, shortly after the death of James Allison, the company was purchased by the Fisher brothers. Fisher sold the company to General Motors, who owned it for most of its history...

 or Rolls Royce
Rolls-Royce Limited
Rolls-Royce Limited was a renowned British car and, from 1914 on, aero-engine manufacturing company founded by Charles Stewart Rolls and Henry Royce on 15 March 1906 as the result of a partnership formed in 1904....

 piston engines augmented by auxiliary Westinghouse turbojets in the aft nacelles. Although McDonnell promised a very impressive 500 mph (805 km/h) top speed with the new powerplants, the Army rejected the proposal, demanding more testing of the existing design. As a result of wind tunnel tests, the tailplanes were raised 12 in (31 cm) while the XP-67 waited for replacement engines.

Operational history

On 23 March 1944, flight trials restarted. Army pilots finally got to fly the aircraft on 11 May 1944, and judged the cockpit layout fair and ground handling satisfactory, but deemed the aircraft underpowered due to its poor initial rate of climb, slow acceleration, and long takeoff roll, particularly when operating with only one engine. Other flight characteristics were generally good during gentle maneuvers; stick forces were light, roll rate was adequate, and control was effective at all speeds with good longitudinal stability. However, a tendency to dutch roll
Dutch roll
Dutch roll is a type of aircraft motion, consisting of an out-of-phase combination of "tail-wagging" and rocking from side to side. This yaw-roll coupling is one of the basic flight dynamic modes...

was prevalent. The prototype also displayed several disturbing behaviors as its stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...

 speed was approached. It began to buffet well above the actual stall speed, it felt tail-heavy in fast turns, and its nose would tuck upwards during the stall. The problems were serious enough that test pilots declined to test the XP-67’s spin
Spin (flight)
In aviation, a spin is an aggravated stall resulting in autorotation about the spin axis wherein the aircraft follows a corkscrew downward path. Spins can be entered intentionally or unintentionally, from any flight attitude and from practically any airspeed—all that is required is sufficient yaw...

 characteristics, fearing that a spin might be unrecoverable. This irregular and unstable stall behavior has been attributed to advanced aerodynamic principles that were not fully counteracted until the advent of electronic
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 stability controls years later. Although the final flight test report was generally positive, the aircraft’s maneuverability was deemed inferior to existing types such as the North American P-51 Mustang.

Upon return to the factory, the cooling ducts were reworked. Several problems were cured during the ensuing test flights, but the engines continued to be plagued by chronic overheating and deficient power output. The XP-67 only reached a confirmed top speed of 405 mph (652 km/h), which was far short of its promised top speed of 472 mph (760 km/h), and was unremarkable compared to other fighters in service at the time.

Project cancelation

On 6 September 1944, the starboard engine of the XP-67 caught fire during a test flight, and test pilot E.E. Elliot executed an emergency landing at Lambert Field
Lambert-St. Louis International Airport
Lambert-St. Louis International Airport is a Class B international airport serving Greater St. Louis. It is located approximately northwest of downtown St. Louis in unincorporated St. Louis County between Berkeley and Bridgeton. It is the largest and busiest airport in the state with 250 daily...

 in St. Louis, Missouri
St. Louis, Missouri
St. Louis is an independent city on the eastern border of Missouri, United States. With a population of 319,294, it was the 58th-largest U.S. city at the 2010 U.S. Census. The Greater St...

. He attempted to park the craft pointing into the wind to blow the flames away from the airframe, but the starboard main landing gear
Landing Gear
Landing Gear is Devin the Dude's fifth studio album. It was released on October 7, 2008. It was his first studio album since signing with the label Razor & Tie. It features a high-profile guest appearance from Snoop Dogg. As of October 30, 2008, the album has sold 18,906 copies.-Track...

 brake
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....

s failed, pivoting the XP-67 so the flames blew directly towards the aft fuselage. Elliot escaped safely, but the blaze gutted the fuselage, engine, nacelle and starboard wing; the aircraft was a total loss.

The destruction of the lone flying prototype dealt a serious blow to the entire program because the second prototype was only 15% complete at the time. Army leaders decided to re-evaluate the XP-67, ultimately deciding on 13 September that it offered no significant advantages over existing fighters already in service. The project was canceled, the remains of the first prototype were scrapped, and work was halted on the second prototype.The ultimate fate of the incomplete second prototype is not revealed in the consulted reference sources.

Specifications (XP-67)

See also

External links

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