Curtiss XP-55 Ascender – The Flawed Fighter

The Curtiss XP-55 Ascender was an experimental aircraft devised by Curtiss-Wright following a US Army appeal for groundbreaking fighter planes in November 1939.

It was scrapped in 1944 and jokingly named ‘Ascender’ by a Curtiss technician at the same time as production and development ground to a halt. It was a nickname that ironically characterized the deadly fault largely responsible for its abandonment.

Contents

Background

In November 1939, the US Army issued a document called the Circular Proposal R-40C, which called on engineers from around the country, using the latest technology, to come up with advanced experimental fighter concepts.

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Full scale wind tunnel testing was conducted.
The early mockups went through full-scale wind tunnel testing.

They wanted a warplane that could fly quicker, climb higher, and maneuver better than all others. As well as being inexpensive and easy to maintain, the designs were also required to push the boundaries of existing aeronautical knowledge.

Nearly 50 companies rose to the challenge, with only a handful being seriously considered. A twin-boom pusher called the XP-54 was created by Vultee, and Northrop offered up their radical prototype, the XP-56 Black Bullet.

Curtiss-Wright would impress adjudicators with their own entry, the CW-24, which possessed some notably unorthodox features.

The engine was important to performance. Lots of testing was done.
XP-55 engine run up testing.

It was the first time that a completely retractable tricycle landing gear array was to be fitted on a Curtiss-Wright airplane. Engineers were also keen to test out the laminar flow-wing, which would reduce drag. 

Furthermore, the XP-55 was to be installed with the X-1800-A3G (H-2600) liquid-cooled engine being developed by Pratt & Whitney, who promised the state-of-the-art propulsion system would be available by 1942. With such a powerful new component, the team predicted the XP-55 would be flying at a top speed of 507 miles per hour.

Pratt & Whitney’s engine, however, would never see the light of day after suffering serious mechanical failures. It would force the XP-55 team to resort to the more conventional Allison V-1710 engine, which sacrificed speed for reliability.

The XP-55 powerplant
The Pratt & Whitney X-1800 used in the XP-55. Photo credit – Kimble D. McCutcheon CC BY-SA 1.0

Development

In June 1940 Curtiss-Wright was offered a contract by the US Army, and from November they undertook wind-tunnel tests on a 1/4 sized model, evaluating 2 different types of sweptback wings.

Designated ‘P-55,’ the project aimed to compare the efficacy of a conventional sweptback wing with their own experimental creation. Intensive wind-tunnel tests lasted until January 1941 when a further study on the laminar flow-wing was requested by officials, who saw potential in the unusual innovation.

There were, however, some who remained skeptical. To prove the doubters wrong, Curtiss-Wright, spending their own money, constructed a manned flying test bed called the Model 24-B, which flew 169 flights in total at Muroc Dry Lake in California from November 1941 to May 1942, and was propelled by a 275 hp Menasco C68-5 engine.

The XP-55 ready for testing.
The XP-55 rolling out of the hangar for testing.

Although the basic concept of the XP-55 was proven, concerns were raised because of its dangerous level of directional instability. Engineers addressed the problem by increasing the area of the wingtip fins and moving them four feet further out on the wings.

The wingtips were also extended and accompanied by the addition of vertical fins placed on the top and bottom of the engine cowling.

Overall the project was considered a success, being transferred after May 1942 to Langley Field in Virginia for additional analysis. The US Army was encouraged by the data, and in June 1942 funding was approved for the assembly of 3 prototypes under the moniker of ‘XP-55’.

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Design

The XP-55 was 9 meters in length, 3.5 meters tall, and had an empty weight of 2882 kilograms.

The XP-55 Cockppit
The XP-55’s cockpit was cramped and visibility was not good.

It was launched through the air by an Allison V-1710 engine which was unusually located on the extreme rear, differing from the more conventional placement mounted at the front, meaning the pilot had excellent visibility.

It gave the XP-55 a maximum speed of 390 miles per hour, a cruising speed of 296 miles per hour, and enabled it to soar up to 34,900 feet. It took 7.1 minutes for it to reach an altitude of 20,000 feet, with its maximum range 1440 miles and its normal range 635 miles.

The main wing had a wingspan of 40 feet and 7 inches, a length of 29 feet and 7 inches, and a wing area of 235 square feet. The wings were swept in contrast to traditional straight wing configurations, and it was equipped with two forward canard wings.

The XP-55 had an unusual undercarriage design.
The XP-55 did not use a traditional tail dragger undercarriage design.

Because the engine was situated further back, it created space in the nose of the aircraft for 4 0.5 millimeter Colt-Browning M2 machine guns, each with an ammo capacity of 200 rounds that could provide heavy concentrated fire on targets.

As well as the retractable tricycle landing gear assembly, the plane possessed a revolutionary ejection system in which the propellor was discharged before the pilot activated his escape. It was one of the last models to incorporate an old-fashioned propeller, which was soon to be replaced by jet technology. 

Testing

By July 1943 the first iteration of the XP-55 had been fabricated at the Curtiss factory in St. Louis, Missouri, with flight tests organized soon afterwards. Test pilot J. Harvey Gray commanded it for its maiden voyage on July 10th at Scott Field near the Curtiss-Wright plant at St. Louis.

The first thing that engineers noticed was its takeoff run was extremely long. By increasing the area of the nose elevator and connecting the aileron up-trim with the flaps, the aircraft was able to operate the aileron when the flaps were lowered, which solved the issue.

The XP-55 did not use the taildragger configuration.
The XP-55 underwent a lot of ground testing before taking to the air.

Apart from this, the first few months of the program saw the XP-55 perform well, but its progress was stunted by a setback that occurred in November of that year, when an engine failure mid-flight made the plane pitch forward in an outside loop, causing it to perilously drop straight down from the sky.

After plummeting 16,000 feet in an inverted position, pilot Harvey Gray safely employed his ejection seat before his craft erupted into a smoking heap on impact.

To avoid another similar incident, design revisions were sketched out to be incorporated into the third prototype, for it was already too late to add them to the already-built second. During the wait for the latest edition, the second prototype was flown in January 1944, but with limitations on in flight maneuvering.

The third model, which was also subject to weapons testing, was analyzed in April, the results seemingly suggesting that the miscalculations responsible for the previous year’s mishap had been fixed.

The XP-55 in flight
The XP-55’s top speed was impressive for the early 40s.

Confident in the reliability of their latest make, the second XP-55 prototype was fitted with the same corrective components.

The overhauled third XP-55 made its first flight in April 1944. The engineering team had improved it by increasing the canard wing elevator surface, the vertical stabilizer, the limits of nose elevator travel, and by installing four-foot wing tip extensions, yet stability problems persisted.

By increasing the elevator limits the pilot could sharply raise the elevator angle to such a degree that it made the elevator fail.

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Even after repairs and satisfactory results from tests, pilots were still uneasy to fly the XP-55. They disliked the fact that there was no warning signal to indicate when a stall was going to happen, and that a disproportionate amount of altitude was required for it to return to level flight after stalling.

The remaning XP-55
The remaining XP-55 now lives at the Air Zoo Museum. Photo credit – Aaron Headly CC by SA 2.0.

As a result, an artificial stall warning device was put in place on both remaining models.

With new stall control introduced, the second XP-55 was assessed between September and October 1944. Although it satisfactorily performed during climbing and level flight routines, it was still littered with inconsistencies.

At low speeds and during the landing procedure, for instance, pilots developed the habit of over-controlling the elevators because they could not intuitively feel the aircraft well.

Moreover, the stall detection system was inconsistent, the engines had a cooling issue, and it was still losing a lot of altitudes when it was struck by a stall.

In addition, the XP-55 was simply not as good as other existing aircraft, which were far superior because of their jet-powered capabilities. After a disappointing assessment, production and development were terminated in 1944.

The YP-59. The first American Jet aircraft.
The YP-59A was the first U.S. jet aircraft and flew in 1942.

Crash

The crash of the third XP-55 at the Wright Field airshow in May 1945 confirmed the wisdom of the decision to cancel the program the previous year.

The event was a War Loan rally attended by around 100,000 people who were to see some of the earliest public displays of many legendary aircraft such as the C-46 Commando, the B-29 Superfortress and the Douglas XB-19, with demonstrations given by renowned war aces Richard ‘Dick’ Bong and Dominic ‘Don’ Gentile.

The man operating the XP-55 that day was Captain William C. Glasgow, a decorated war hero who had escaped a Nazi jail cell to be awarded the Distinguished Flying Cross, Silver Star, Purple Heart, and Air Medal.

As Glasgow was attempting a slow roll, the plane started wobbling and Glasgow lost control. His plane then careened low to the ground, destroying 150 feet of the fence before erupting into an inferno.

The first prototype crashed in 1943.
The first prototype also crashed during a test flight in November 1943.

Just before it smashed into a ditch and ended the life of William Glasgow, the XP-55 grazed a passing car, splashing it with gasoline that ignited, killing local resident William Roehm and his friend Kathleen Eyre as well as critically injuring Rohem’s wife Susan and their 2 children.     

In the end, the XP-55’s slow speed and outdated propeller design in combination with its lethal tendency to stall were the principal reasons it was discontinued.

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The only surviving XP-55 was flown to Warner Robins Field in May 1945 before being transported to the National Air Museum at the Smithsonian Institute in Washington. After being restored in 2001 at the Kalamazoo Aviation History Museum, it was put on display in the main campus area, where it still resides today.

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Specifications

  • Crew: One (pilot)
  • Length: 29 ft 7 in (9.02 m)
  • Wingspan: 40 ft 7 in (12.37 m)
  • Height: 10 ft 0 in (3.05 m)
  • Empty weight: 6,354 lb (2,882 kg)
  • Max takeoff weight: 7,930 lb (3,597 kg)
  • Powerplant: 1 × Allison V-1710-95 liquid-cooled V12 engine, 1,275 hp (951 kW)
  • Maximum speed: 390 mph (630 km/h, 340 kn) at 19,300 feet (5,900 m)
  • Range: 635 mi (1,022 km, 552 nmi)
  • Service ceiling: 34,600 ft (10,500 m)
  • Guns: 4 × 0.50 in (12.7 mm) machine guns in the nose