Subject: Number Fifty-Five in the Series--Curtiss XP-55 Ascender

From: [email-masked]
Date: 4 Mar 93 17:20:13 GMT

>From [email-masked]

The Curtiss XP-55 Ascender was another response to Circular Proposal 
R-40C, which was issued on November 27, 1939.  It called for a fighter 
that would be much more effective than any extant--with a top speed, 
rate of climb, maneuverability, armament, and pilot visibility, all of 
which would be far superior to those of any existing fighter.  In 
addition, the fighter was required to have a low initial cost and had 
to be easy and inexpensive to maintain.  The Army specifically 
mentioned in R-40C that they would consider aircraft with 
unconventional configurations.  

No less than 50 responses came in.  Many of them were quickly ruled 
out, but by the end of 1940, four designs were considered sufficiently 
worthy of further study.  These were designs submitted by Bell, by 
Curtiss, by Northrop, and by Vultee.  

The Curtiss entry, designated CW-24 by the company, was perhaps the 
most unconventional of the four finalists.  It was to be one of the 
last projects supervised by Donovan Berlin before he left the Curtiss 
company to go over to Fisher to work on the P-75.  The CW-24 was a 
swept-wing pusher aircraft with canard (tail-first) elevators.  The 
low-mounted sweptback wings were equipped with ailerons and flaps on 
the trailing edge as well as directional fins and rudders mounted near 
the wing tips both above and below the airfoil.  The elevators were 
located near the front of the nose in a horizontal surface.  A 
completely-retractable tricycle undercarriage was to be used, the 
first time such an undercarriage was to be employed in a Curtiss 
fighter.  Curtiss proposed to use the new and untried Pratt & Whitney 
X-1800-A3G (H-2600) liquid-cooled engine, mounted behind the pilot's 
cockpit and driving a pusher propeller.  Project maximum speed was no 
less than 507 mph! 

On June 22, 1940, the Curtiss-Wright company received an Army contract 
for preliminary engineering data and a powered wind tunnel model.  The 
designation P-55 was reserved for the project.  

Since the USAAC was not completely satisfied with the results of the 
wind tunnel tests, Curtiss-Wright took it upon itself to build a 
flying full-scale model.  Designated CW-24B by the company, the flying 
testbed was powered by a 275 hp Menasco C68-5 engine.  It had a 
fabric-covered, welded steel tube fuselage and a wooden wing.  The 
undercarriage was fixed.  

After completion, the CW-24B was shipped out to the Army flight test 
center at Muroc Dry Lake (later Edwards AFB) in California.  It made 
its first flight there on December 2, 1941.  Although the maximum 
speed was only 180 mph because of the low engine power, the CW-24B 
proved out the basic feasibility of the concept.  However, early 
flights indicated that there was a certain amount of directional 
instability.  The original auxiliary wingtip fins were increased in 
area and moved four feet farther outboard on the wings, which enhanced 
the directional stability.  The wingtips were made longer, and further 
improvements were obtained by adding vertical fins to both the top and 
the bottom of the engine cowling.  169 flights with the CW-24B were 
made at Muroc between December 1941 and May 1942.  After that, the 
airplane (having been assigned the USAAC serial number 42-39347) was 
transferred to Langley Field, Virginia, for further testing by NACA.  

During the flight testing of the CW-24B, work on the CW-24 fighter 
project continued.  On July 10, 1942, a USAAF contract was issued for 
three prototypes under the designation XP-55.  Serial numbers were 
42-78845/78847.  Since the Pratt & Whitney X-1800 engine was 
experiencing serious program delays (it eventually was cancelled 
outright before attaining production status) Curtiss decided to switch 
to the Allison V-1710 (F16) liquid-cooled inline engine for the sake 
of reliability and availability.  Armament was to be two 20-mm cannon 
and two 0.50-inch machine guns.  During the mockup phase, it was 
decided to switch to the 1275 hp Allison V-1710-95 engine, and the 
20-mm cannon were replaced by 0.50-inch machine guns.  

The first XP-55 (42-78845) was completed on July 13, 1943.  It had 
essentially the same aerodynamic configuration as did the final 
CW-24B.  It made its first test flight on July 19, 1943 from the 
Army's Scott Field near the Curtiss-Wright St Louis plant.  The pilot 
was J. Harvey Gray, Curtiss's test pilot.  Initial flight testing 
revealed that the takeoff run was excessively long.  In order to solve 
this problem, the nose elevator was increased in area and the aileron 
up trim was interconnected with the flaps so that it operated when the 
flaps were lowered.  

On November 15, 1943, test pilot Harvey Gray was flying the first 
XP-55 through a series of stall tests when the aircraft suddenly 
flipped over on its back and fell into an uncontrolled, inverted 
descent.  Recovery proved impossible, and the plane fell out of 
control for 16,000 feet before Gray was able to parachute to safety.  
The aircraft was destroyed in the ensuing crash.  

At the time of the crash, the second XP-55 (42-78846) was too far 
advanced in construction for its configuration to be conveniently 
modified to incorporate any changes resulting from an analysis of the 
cause of the loss.  The second XP-55 was essentially similar to the 
first one, apart from a slightly larger nose elevator, a modified 
elevator tab system, and a change from balance tabs to spring tabs on 
the ailerons.  It flew for the first time on January 9, 1944, but all 
flight tests were restricted so that the stall zone was carefully 
avoided until the third XP-55 had been satisfactorily tested.  

The third XP-55 (42-78847) flew for the first time on April 25, 1944.  
It was fitted with the designed complement of four machine guns.  It 
incorporated some of the ideas learned from the investigation into the 
cause of the loss of the first XP-55.  It was found that stall 
characteristics could be improved by adding four-foot wingtip 
extensions of greater area and by increasing the limits of nose 
elevator travel.  However, the first flight revealed that the 
increased elevator limits resulted in the pilot being able to hold 
such a high elevator angle during takeoff that the elevator could 
actually stall.  After modifications, stall tests were performed 
satisfactorily, although the complete lack of any warning prior to the 
stall and the excessive loss of altitude necessary to return to level 
flight after the stall were undesirable characteristics.  

An artificial stall warning device was introduced to try and correct 
some of these problems, and between September 16 and October 2, 1944, 
the second XP-55 (42-78846), which had been modified to the same 
standards as that of the third aircraft, underwent official USAAF 
trials.  The trials indicated that the XP-55 had satisfactory handling 
characteristics during level and climbing flight, but at low speeds 
and during landings there was a tendency on the part of the pilot to 
overcontrol on the elevators because of a lack of any useful "feel".  
Stall warning was still insufficient, and stall recovery still 
involved an excessive loss of altitude.  Engine cooling was also a 
problem.  

The performance of the XP-55 was not very impressive and was in fact 
inferior to that of the more conventional fighters already in service.  
In addition, by 1944, jet-powered fighter aircraft were clearly the 
wave of the future.  Consequently, no production was undertaken, and 
further development was abandoned.  

The name *Ascender* had originated as a joke on the part of a Curtiss 
engineer.  The name stuck, and eventually became official.  

One XP-55 survives today.  Its fuselage is on display at the Paul 
Garber facility in Suitland, Maryland.  Perhaps it will someday be 
restored to better condition.  I don't know its serial number.  

Specs of the XP-55: 

One 1275 hp Allison V-1710-95 (F23R) twelve-cylinder liquid-cooled Vee 
engine.  Four 0.50-inch Colt-Browning M2 machine guns with 200 rpg.  
Maximum speed 390 mph at 19,300 feet, 377.5 mph at 16,900 feet.  
Normal range was 635 miles at 296 mph.  Maximum range was 1440 miles.  
An altitude of 20,000 feet could be attained in 7.1 minutes.  Service 
ceiling was 34,600 feet.  Weights were 6354 pounds empty, 7330 pounds 
normal loaded, and 7939 pounds maximum.  Dimensions were wingspan 44 
feet 0 1/2 inches, length 29 feet 7 inches, height 10 feet 0 3/4 
inches, wing area 235 square feet.  

Sources: 

  American Combat Planes (3rd Edition), Ray Wagner, Doubleday, 1982.  

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

  War Planes of the Second World War, Fighters, Volume Four, William 
  Green, 1964.  

  Curtiss Aircraft, 1907-1947, Peter M. Bowers, Naval Institute Press, 
  1979.  

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