Engineering Division TP-1/XCO-5; The US Army’s Final Fighter

July 3, 2024

I’ve written in the past about the US Navy’s Naval Aircraft Factory, which was created in 1917 to help design and build aircraft suitable for maritime use. Indeed, I’ve already covered one of their most famous and enduring creations, the NAF N3N.

The reason for the NAF being built was because the United States Army Air Service at the time was generating the largest contracts for aircraft development and building, which naturally caught the attention and efforts of the aviation companies. This is turn left the US Navy’s far more modest requirements tending to be overlooked or completely ignored, hence the need for their own design and building capability – at least until the end of First World War when suddenly the private corporations decided they did want to build the Navy’s planes after all!

With the rapidly expanding aviation companies – names that would go on to be giants such as Boeing and Curtiss – competing to build the Army’s aircraft for them, you would think that this service would be content to allow private ventures to do the work.

But you’d be wrong.

The US Army Corps of Engineers has a long and proud tradition of innovation and so at around the same time that the Navy were setting up their aircraft factory the US Army created the Engineering Division of the Aviation section. This was to investigate foreign aircraft designs that the US was then using and see about improving them, especially with American components. And in those early years they also had a crack at designing their own aircraft, leading to today’s topic.

The Engineering Division TP-1 and XCO-5.

The original idea was to build for the US Army Air Service a new high performance two-seat fighter with better armament than the ones then in service. The single TP-1 built, which first flew in 1923, was a biplane design but with the usual feature of having the upper wing being of smaller span and chord than the lower wing, a reversal of usual practice.

Armament was also comparatively heavy, with the TP-1 being fitted with twin machine guns forward firing for the pilot, a pair of Lewis gun pintle mounted on the back seat and operated by the observer, and a single Lewis fired through a hatch in the bottom of the aircraft.

The design was powered by a Liberty 12 engine which produced 423hp; a very specific number but that’s what all the sources seem to state.

Unfortunately, the powerful engine and somewhat unconventional design meant little in terms of the aircraft’s performance. Handling was apparently not very good and with a top speed of 129mph (207km/h) the TP-1 was thought to be too slow to be useful and ideas of production abandoned. With mounting political pressure from lobbying by the aviation companies to protect their business, it was to be the final fighter designed and built by the US Army itself.

But it wasn’t going to be wasted and the aircraft was fitted with an experimental turbocharger, with which it set several payload-to-height records in 1924.

However, the records of the second prototype were to exceed those of the first. Changed while in production to be an experimental high-altitude research aircraft, the XCO-5 was fitted with substantially enlarged wings to provide the necessary lift for high altitude operations and a supercharged engine.

This was reported as being capable of producing the same amount of horsepower at 32,000 feet (9,754m) as at sea level, but those early experimental engines proved unreliable in this regard.

On 29 January 1926 Lieutenant John Macready took off in the new aircraft looking to seize back the absolute height record for a single-crewed aircraft that he had originally taken in 1921 but lost two years later. The flight started well enough, with the high-lift wings lifting the XCO-5 into the air in a mere fifty feet (15.24m).

Unfortunately, at 25,000 feet the supercharger’s pressure began to drop, and Macready found the aircraft losing power as it continued to climb. Despite his best efforts he “only” managed a top altitude during the flight of 38,704 feet (11,797 meters). This was 269 meters (883 feet) lower than the existing world record, so Macready didn’t reclaim his crown, but he did establish a new United States national altitude record.

I mean, this in a biplane with the pilot having to wear what was practically a prototype space suit made a leather, fur and bottled oxygen, so I feel credit for the bravery of these early pioneers really does need more recognition.

On inspection the supercharger was found to have developed a crack which caused the pressure problem, and once repaired the XCO-5 was all set for more record-breaking attempts.

In 1928 Captain Albert Stevens, commander of the Aerial Photography Unit at Wright Field approached his friend, the daring test pilot and explorer Captain Bill Streett, to ask him to help Stevens prove a theory of his. Stevens thought that he could more accurately determine the altitude an aircraft had reached by taking pictures from it of set points on the ground. The idea was that this might prove more accurate than the then-used barometric pressure sensors, the reliability of which were subject to a fair bit of argument.

On the 10 October 1928 the two took off in the XCO-5 to test the idea. Obviously operating at such high altitudes in a largely open aircraft required special consideration, and along with specially insulted flight suits and full-face masks for breathing oxygen, Stevens had his specially built and electrically warmed camera, as well as electrically heated gloves so his hands didn’t freeze while taken the photographs.

Capts. Stevens (on left) and Streett with their camera and barographs

In addition Streett, anticipating some of the problems that they might face, drilled small holes in his googles so that if they froze up he should still be able to see something, which as the lowest temperature they recorded on the flight was -60C (-76 F) was pretty chilly.

As Streett later put it:

“Cold up there? You don’t know what 76 below zero feels like until you’ve been there.”

As it turned out, despite all their precautions, it almost wasn’t enough.

Streett took the XCO-5 up to as high as it would literally get, which took an hour and forty minutes, and then held it there while Stevens took the shots he needed. But when Streett tried to cut the engine…nothing happened.

The controls had frozen, effectively trapping the two men in the Stratosphere.

Streett tried to dive the XCO-5 down, but knew the fragile aircraft wasn’t built for that sort of maneuver and if he pushed it, he would tear the wings off. And as soon as he took the pressure off, the XCO-5 did what it was designed to do and bobbed back up to the maximum altitude its big wings could sustain.

Streett and Stevens now had to wait it out and hope that their oxygen didn’t run out before the engine’s petrol did.

Fortunately for the intrepid pair, the engines supply ran out after about twenty minutes and the XCO-5 gradually drifted down to earth. Streett admitted that he didn’t have a clue where they were by this point, and as his googles were frozen solid his only view was limited to the holes he had cut in them. Streett was able to put the XCO-5 down in a field, despite the aircraft having no engine and at these low altitudes, in the words of Captain Stevens, “…handling like a barn door”; a feat of airmanship that was widely recognized as exceptional.

Not finished there, Streett went out, scrounged up some fuel and, finding the throttle controls had unfrozen, the two men flew back to base near Dayton, Ohio.

Steven’s photographic calculation showed that the XCO-5 had reached an altitude of 39,250 feet (11,963 meters) while the US Bureau of Standards calculated from the barographic instruments carried on the flight that they had ceilinged at 39,606 feet (12,072 meters). These figures were only marginally below the absolute height record of the time for a single person aircraft, a pretty remarkable feat.

Unfortunately, though this was undoubtedly the true altitude record for a two-manned aircraft at the time, it remained unofficial because the rules required the aircraft to return directly to its launch airfield to prevent tampering with monitoring equipment.

But though not officially recognized, it remains a remarkable flight, both for the two crewmen, who went on to other achievements, and the XCO-5 which was soon to be replaced by more advanced aircraft which benefitted from the experience the aircraft had given in cutting edge flight research.


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