The 1930s were an interesting time for military aircraft, with the breakneck pace of technological development pushing the envelope farther with every year. Nations around the world were experimenting with all sorts of unconventional designs, some of which were far more successful than others.
On November 27th, 1939, the United States Army Air Force issued Circular Proposal R-40C. R-40C was for a new fighter that would be superior to all existing types, while having a low cost and easy maintenance. Specifically mentioned was the willingness to see unconventional configurations. More than 50 designs were submitted, though only a handful made it to the end. The winners of the competition all had created advanced, and highly unorthodox, pusher fighters.
The 'pusher' configuration for combat aircraft had been around since 1915, and offered several advantages over what is now seen as the conventional 'tractor' configuration, the most notable being improved visibility for the pilot and the ability to cluster weapons in the nose. Even so, this wasn't really explored in the United States until the 1930s with Bell aviation leading the way with aircraft like the deeply flawed Bell Aircuda, and other projects like their Model 16 and the XP-59 (no relation to the jet, and one of the winners of the contest, though no prototype was ever made).
The three companies that built prototypes were Northrop with the XP-56, Curtiss with the XP-55, and Vultee with their XP-54. Preliminary contracts were issued on June 22nd, 1940, and all called for single-seat aircraft, powered by the mighty liquid-cooled Pratt & Whitney X-1800-A3G, which would produce 2,200 horsepower from its 24 cylinders. But the engine's potential was never realized, as it was canceled in October 1940, forcing the use of other powerplants for the new fighters.
The first prototype on the ground
Like all of the aircraft that were spawned from the program, the XP-54 possessed several groundbreaking features for its time, though many of them were less than useful. It was the largest of the aircraft that came from the program, in dimensions and weight. Part of this was the result of significant changes in the role of the aircraft, resulting in massive feature creep that doomed the aircraft. As such, the first part of the design section will be about the planned XP-54, and the second will be about what it became.
A three-quarters view of the first prototype
The main fuselage was bullet-shaped, and was built of a welded magnesium alloy, which made it very light. It's twin tails were on booms that extended from the back of the gull wings. Like the rest of the program's aircraft, the XP-54 was fitted with tricycle-style landing gear. The nosewheel retracted into the cockpit, while the main wheels retracted into the booms. One result of this was that the cockpit was so high off the ground that the pilot used an elevating seat to get into the aircraft. The control cables were routed around the opening and the pilot's control wheel was mounted on an inverted U-column. Intended for low to medium altitude combat, the cockpit was unpressurized.
The elevating seat allowed a very clean cockpit canopy, which provided the pilot excellent visibility, and in the event of an emergency, the pilot and his seat would be dropped out the bottom of the plane on a swinging arm to catapult him out of the path of the propeller behind him. This makes the XP-54 the first American aircraft with a sort of ejection seat. Unfortunately, there don't seem to be any photographs showing the entire mechanism.
The day the post went live I found this photo of the pilot seat with a man in it.
At this stage, the only known plan for armament was a cluster of six .50 caliber M2 Browning machine guns mounted in the nose.
The first prototype in the sky
Air for the engine was provided by an innovative system in the leading edge of the wings. The NACA Ducted Wing directed air over the oil and coolant radiators for the engine, the intercoolers, and finally into the engine itself via ducts in the trailing edge of the wing. The landing flaps were also designed to regulate the airflow, which allowed the entire cooling system to be contained inside the wings.
All told, the XP-54 would have weighed 11,500 pounds maximum, could climb to 20,000 feet in six minutes, and have a speed of 510 miles an hour at that altitude.
The cockpit of the XP-54 was now pressurized, and it and the engine were more heavily armored. At higher altitudes, a turbosupercharger needed to be added to provide adequate performance.
What is probably the first prototype undergoing maintenance. Several features of interest can be seen, such as the unpainted metal around the exhausts, the guns in the nose, and part of the pilot's chair and elevating apparatus.
The armament was also changed to two 37mm T-13/T-14 cannons with 60 rounds per gun and two Browning M2 .50 caliber machine guns with 500 rounds per gun, all of which were still mounted in the nose. One problem with mixed batteries like this is that the trajectories of the different weapons are very different, making the already complex task of air-to-air gunnery even more difficult. Vultee's solution was a system that would elevate the nose section with the machine guns by as much as three degrees, and depress it by six degrees while the cannons remain fixed. An entire gunsight apparatus to use this system was installed, but in practice this would probably be less than usable.
A Lycoming XH-2470
Power was still going to be provided by the X-1800 until that program was killed in October 1940. So the Lycoming XH-2470-1 was chosen instead. This engine provided as much as 2,300 horsepower to the 12' 2'' four bladed Hamilton Standard propeller. The XP-54 was one of only two aircraft to be designed for the engine (the other was the Navy's Curtiss XF14C), and its use was fraught with problems. A turbosupercharger was added behind the cockpit to improve performance, which first burned the paint from the cowling, resulting in the cowling being replaced with an unpainted panel (which can be seen in the photographs of the first prototype on the ground), then the turbosupercharger suffered damaged impellers and was sent to be repaired by Lycoming. But the price of repairs was more than the AAF was willing to pay, which spelled the end of the first prototype.
Another view of the first prototype on the ground, giving a good view of the sheer size of the XP-54, as well as the Lycoming XH-2470
The second prototype (S/N 42-108994, painted as S/N 41-1211) was fitted with an experimental General Electric XCM Turbosupercharger for at least three flights before eventually being replaced with an entirely new unit after both the engine and the turbosupercharger were damaged by some sort of incompatibility. Another problem with the XH-2470-1 was that the engine oil would foam at high RPMs or above 20,000 feet.
This inadequate level of performance, when combined with the final weight of the XP-54, which had skyrocketed to more than 19,337 pounds fully loaded, gave the aircraft an actual top speed of only 381 MPH. Below the intended 403 MPH at 28,500', and far below the originally planned 510 MPH. Though the XP-54's performance in other aspects was apparently not bad though.
The R-40C program was only the second fighter design attempted by Vultee, the first produced the uninspiring P-66/ Model 48 Vanguard which saw most of its service in China. Despite this poor start to fighter design, Vultee's proposal was judged to be the best of the entrants, and a contract for wind tunnel models and technical data was issued on June 22nd, 1940. The first prototype was ordered on January 8th 1941, with the serial number 41-1210. The promised delivery date was in July 1942.
On March 17th, 1942 a second prototype was ordered. This is where the situation has become confused over the last several decades, as the actual serial number for the second prototype was 42-108994. Not 41-1211. This is the serial number of a BT-13A trainer, and would be exceedingly strange for an aircraft ordered more than a year after the first. In all probability this is the result of a simple error in painting, and by the time of the second flight the issue had been resolved.
But the major changes in role and the required design changes that were required took years to resolve. July 1942 was long gone when the first XP-54 (S/N 41-1210) took to the air on January 15th, 1943 from Muroc Field in California (now Edwards AFB). This flight lasted 31 minutes with test pilot Frank Davis in the pilot's seat. During this flight, the aircraft worked fine except for the Curtiss propeller. Later flights were made with a Hamilton-Standard propeller. Come the 11th of March, 1943, it was clear that the XP-54 had fallen far short of its planned performance. The engine also needed to be changed because traces of metal were found in the engine oil.
Front quarter view of one of the prototypes
86 more flights were made until October 28th when the XP-54 was flown to Wright Field for further testing. Once again the Lycoming failed, and damage to the turbosupercharger grounded the plane. The AAF was unwilling to pay Lycoming for repairs, and the first XP-54 was static tested until it was destroyed at Wright Field. All told, the first prototype managed 63.2 hours of flight time over 86 flights.
In late 1943, the Navy pulled out of the Lycoming XH-2470 program, leaving the XP-54's engine in dire straits. Another experimental engine from Wright, the R-2160 Tornado, was investigated. The R-2160 was an oddity of an engine, being a liquid cooled radial engine, that had 42 cylinders and produced 2,350 horsepower. This possibility was designated the XP-68, and would have a set of counter-rotating propellers, but it was abandoned when the R-2160 was killed. The XP-68 was cancelled officially on November 22nd, 1941.
The Allison V-3420 engine, powerplant of several other experimental aircraft (including the XB-19A which has been covered before), was seen as a possibility. Installing a jet engine was also considered, but by then the XP-54 was on its way out. These modifications would be complex, time consuming, and expensive.
The second prototype first flew on May 24th, 1944 for 20 minutes from Downey to Ontario, California. It was delayed by the need to install the General Electric XCM turbosupercharger, but by then other programs had overtaken the XP-54. Over nine more test flights, the last was on April 2nd 1945, the combination of XCM and Lycoming wasn't workable. Another engine was fitted, but the second and last XP-54 never flew again. It was scrapped except for the nose, which was sent to Elgin Air Force Base for testing of the gun elevation system.
Neither XP-54 fired its guns in the air. The XP-54 was the last solo Vultee project for the AAF. In June 1943 Vultee Aircraft Inc. merged with Consolidated Aircraft to form the Consolidated Vultee Aircraft Corporation, later abbreviated to Convair.
About the nickname of the XP-54:
There are two theories about the origins of the name 'Swoose Goose'. The first theory is that it's because of how it looked like a goose when in flight, and 'Swoose' is a misspelling of the word 'Swiss'. The other is that it was based on a deeply bewildering song which is linked at end of this post.
A three-view drawing of the XP-54
About the nickname of the XP-54:
There are two theories about the origins of the name 'Swoose Goose'. The first theory is that it's because of how it looked like a goose when in flight, and 'Swoose' is a misspelling of the word 'Swiss'. The other is that it was based on a deeply bewildering song which is linked at end of this post.
Specifications:
Lycoming XH-2470-1
2300 hp @ 25,000'
Dimensions:
Wingspan: 53' 10''
Length: 54' 9''
Height: 14' 6''
Wing Area: 455.5 ft^2
Weight:
Empty: 15,262 lb
Gross: 18,233 lb
Maximum: 19,335 lb
223-395 gallons of fuel
Performance:
Top Speed: 381 mph @ 28,500
At Sea Level: 290 mph
Cruising Speed: 328 mph
Landing Speed: 110 mph
Service Ceiling: 37,000 Feet
Rate of Climb: 26,000'/17 minutes
Normal Range: 500 Miles
Maximum Range: 850 Miles
What is Left?
The National Air and Space Museum has a single XH-2470-7 engine known to be in storage, which was never installed in an aircraft. It is configured with two speed gear reduction, and for counter-rotating propellers. Allegedly, another XH-2470-1 from a XP-54 is also in storage, though it hasn't been seen.
The XH-2470-7 engine at the National Air and Space Museum
Notes:
Most radial engines are air-cooled, which is what made the R-2160 so strange. It was designed to have a very small diameter, allowing aircraft to be made more slender. Though the required cooling system outside the engine to radiate the heat could very well reverse all the aerodynamic gains from the more slender design.
Sources:
Wagner, Ray. American Combat Aircraft
https://web.archive.org/web/20121017112426/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2269
http://www.joebaugher.com/usaf_fighters/p68.html
The song, Alexander is a Swoose: https://www.youtube.com/watch?v=r8gVgOV-G6Y
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