Aerospace technology advanced very quickly in the years between the First and Second World Wars. Over roughly twenty years, the state of the art evolved from fabric-covered and wire-braced open-cockpit biplanes, to sleek, metal-skinned monoplanes with retractable landing gear and enclosed cockpits. Generations of aircraft passed quickly, and many airframes were obsolete after only a few years in service.
The American-designed Curtiss P-1, which entered service in 1924, shows an early stage in that evolution. Its construction and overall layout, with the cockpit set far back behind an inline engine and fuel tank, followed the German Fokker D VII, which had arguably been the best fighter of the late war. After the war, many D VIIs had been seized by the Allies and studied.
The Curtiss P-1 was a simple machine by later standards—you can see its few indicators, controls, and its very rudimentary gunsight in this cockpit panorama from the Naval Aviation Museum. (This is the nearly identical naval F6C-1).
On the other hand, certain aspects of the P-1 reflect emerging post-war advances. Its water cooled inline engine, the 443 hp (330 kW) Curtiss D-12, was substantially more powerful than the last generation of First World War inline engines such as the Hispano-Suiza 8 or the BMW IIIa, which were around 200-230hp (~150-170kw). The D-12 was also the first aircraft engine to incorporate a cast aluminum engine block, giving it a very high power-to-weight ratio.
This powerful engine made the P-1 very fast for its time. The D-12 had powered the first aircraft past 200mph, and pushed the P-1’s racing precursor, the R-6 to average speeds above 200mph. The P-1’s various derivatives won many air races and set a number of speed records.
This P-1's sleek Art Deco lines reflect its racing heritage. Like a number of WW1-era fighters, the P-1 was equipped with two machine guns in front of the cockpit. Unlike its precursors, its guns were hidden under a streamlined fairing. Likewise, most of the inline-powered fighters of late WW1 (D VII, SPAD series, S.E.5) had a snub-nosed look because the radiators were located in front of the engine. The P-1 placed the radiator in a streamlined fairing under the fuselage, an arrangement that later became standard.
The Base of the Tree
The P-1's airframe proved extraordinarily adaptable. The family of aircraft that developed from it is sometimes referred to as the “Curtiss Hawks”. You can imagine the P-1 at the base of a branching tree. Of course, all aircraft are part of an evolution from one thing to the next, but the same fundamental design is visible throughout the Hawk line. I can’t think of another airframe that has gone through so many variations.
In army service it underwent a series of incremental improvements, ultimately leading to the P-6E, delivered between 1932 and 1934, which featured a more streamlined front section, a three-bladed propeller, wheel spats, and a next-generation V-1570C engine rated at 700hp.
In 1925, the P-1 entered US navy service as the F6C. The F6C-2 and 3 models were modified with arrestor hooks and strengthened landing gear for use on early US aircraft carriers. These were the last aircraft with inline engines used on American carriers. Beginning with the F6C-4, the airframe was fitted with an increasingly powerful series of Pratt and Whitney radial engines. Air-cooled radials were mechanically simpler and easier to maintain at sea.
With the adoption of the radial engine in navy service, the plane began to change very noticeably. By 1932, the navy radial-powered Hawk line was developed into the F11C Goshawk, which featured aerodynamic landing gear spats and a cowling around the radial engine. This evolved into the BF2C-1, a carrier-born fighter-bomber, first delivered in 1934, which looks a bit like a pregnant guppy due to a bulge houseing hand-cranked retractable landing gear.
Another branch of the Hawk tree emerged when the design sprouted a second seat and a larger wing to become the Falcon series.. First introduced in 1925, the falcons were used by the army as trainers and attack planes, typically with a gunner in a second seat behind the pilot. They were also used as radial-powered observation planes and dive bombers by the navy. The ultimate version was the radial-engined F8C Helldiver dive bomber variant, which was probably the Hawk branch furthest from P-1 root. These were the planes that attacked King-Kong at the top of the Empire State Building in the 1933 film.
An article written in 1934 counted "some thirty-five more or less distinct hawk types..." The Hawk airframe was fitted with skis to operate off snowy fields, and floats to operate as a seaplane . It was used to pioneer aircraft carrier operations, as well as naval dive bombing. Various versions of the two-seat Falcon variant were used as mail carriers, with the front seat space used for storage. The hawk airframe was modified several times for racing, by both the American army and navy, sometimes pretty radically. Hawks were fitted with a staggering variety of experimental engines, superchargers, cooling systems, and cowlings. They were exported around the world, from Cuba to Turkey, often in unique variants.
Despite their wide adoption, the Curtiss Hawks rarely saw conflict. The notable exception was their Chinese service. Already close to obsolete when the first Hawk IIs were purchased by the Chinese government in 1933, they were badly outclassed by newer Japanese aircraft in the Sino-Japanese War that began in 1937.
At the beginning of the 20th century, the American military was small compared to the European powers. By its end, it had grown into the most disproportionately powerful military that has probably ever existed, at least in terms of wealth, resources, and technological sophistication. Within the field of aviation, the interwar period is especially interesting. During the First World War, the United States relied on France and Britain—mostly France—for its military aircraft. By the Second World War, practically every major allied power had adopted American aircraft to some extent, or would come to rely on them during the war.
The P-1 was an important step in the development of the American military aircraft industry. It also represents a period when the tactical possibilities for using aircraft were rapidly changing, leading to many new ideas, and more than a few dead ends. The United States, with its enormous wealth and industrial capacity, played an ever greater role in this process of military experimentation.
The P-1 entered service in 1924, a year after its prototype, the PW-8, had flown. A decade later, though still in service, the airframe was close to obsolete. This was the rapid evolution of a technology in its infancy. Compare this to the current trillion-dollar F-35 program, whose prototype flew in the year 2000 and is only now, eighteen years later, finishing its testing phase. The F-35 platform is expected to serve for another fifty years as its designers incrementally upgrade and replace its enormous network of complex systems.
This model prints in a number of pieces that require gluing and assembly. Fine structures like struts are printed flat against the bed so that they come out within scale. In its current state, it should build up into something that looks convincingly like a Curtiss P-1A at 1/72 scale. If you have a .2 nozzle or an SLA printer, this should work nicely at 1/144.
Bi-plane models are hard to build because of the alignment between the upper and lower wings and the thin struts between them. This model comes with a set of jigs that let you position the upper wing and glue the struts relatively easily. Although FDM-printed PLA isn't as nice to work with as injection-moulded styrene, the material is cheap so making customized jigs and guides is an option.
To make this thing, you'll need, at minimum, some CA glue. A bit of 200 grit sandpaper and some small files would also be a good idea.
These steps are illustrated in the images above:
1) Glue the engine halves together. Glue on the engine cap and the horizontal stabilizer.
2) Place the lower wing in the "Wing Guide" jig and glue the fuselage onto it.
- At this point, you'll probably want to finish this section, the upper wing, and the other various pieces to the level that you want.
3) Slide the side supports onto the jig. Glue the main wing struts to the indentations in the lower wings. These should lean outwards so that their tops touch the corner of the side supports as illustrated. Make sure that the struts are facing the right way.
4) Put the top wing into place in the side supports. Now glue the top of the main struts to the upper wing. Try not use too much glue or you might glue the struts to the side supports. If you do, just separate them with an X-Acto knife and start over.
- Glue the fuselage struts first to the small indentations in the fuselage, then to the upper wing. This can be a bit tricky, but you'll get the hang of it. Makeup tweezers are helpful for this sort of thing. Wait until the glue is set before removing the side supports. The wing structure is surprisingly sturdy once it's all glued together.
5) Bend the gear struts to loosen the hinges. Glue the gear struts into the recess at the base of the fuselage. Glue the gear cross into the two holes in the gear struts. Bend each side of the gear struts so that they touch the tips of the gear cross and glue them down.
- Glue the vertical stabilizer in place.
6) Paint the wheels. They are in two parts so that you can paint the tires and hubs separately.
- Glue the propeller blades into the propeller hub.
- Glue on the wheels, rudder, and propeller.
- Separate the two halves of the exhaust piece, paint them, and glue them into the sockets on either size of fuselage.
- Fold the tail skid in half and glue it into the slot in the fuselage near the tail. You might want to trim this a bit with an X-Acto blade to get it to a convincing shape.
7) There are two more pieces—I've called this file "aileron rod" because these pieces probably actuate the ailerons. These print in one piece that is cut in the centre. They sit vertical to the earth and tilted forward from the bottom wing to the lower side of the aileron.