Curtiss H-4 'Small America'

The Curtiss H-4 ‘Small America’ was the production version of the earlier H-1 America, and was produced for the British RNAS after the outbreak of the First World War. It proved to be somewhat disappointing in service, but inspired a series of experiments that resulted in the Felixstowe F.1, which combined the wings of the H-4 with a new hull to produce a more successful aircraft.

The Curtiss H-1 America was a twin engined biplane flying boat that was developed before the First World War for an attempt to fly across the Atlantic. In April 1914 John Porte, a former officer in the Royal Navy, joined Curtiss’s team, and would have been the pilot for the trans-Atlantic flight. However this was cancelled after the outbreak of the First World War, and Porte returned to Britain and rejoined the Navy. 

In September 1914 Porte was given command of RNAS Felixstowe, and he used his influence to convince the Admiralty to purchase Curtiss flying boats. By March 1914 both of the H-1s and four H-4s were at Felixstowe, and the H-4 had been ordered in fairly large numbers.

The RNAS’s H-4s came in three batches. First was a batch of four from Curtiss (1236 to 1239). Eight aircraft were ordered from Airco in Britain (1228-1235) and the largest batch, of fifty, from Curtiss (3545-3594). All four of the first batch of Curtiss aircraft were in service by 12 March 1915. The first Airco aircraft were delivered in 1915, but the final aircraft wasn’t recorded until 15 January 1917. The first of the large Curtiss batch arrived in July 1915 and the last in August 1917. Most of these aircraft had the original Curtiss engines replaced by 100hp or 125hp Anzani radial engines.

The second Curtiss batch were slightly modified. Their tail was 2ft longer and the fore-and-aft angle was reduced from 10 degrees to 7 degrees, which reduced the angle of incidence of the wings, meaning that it needed to each a higher speed to take off.

The H-4 had the same unequal span biplane wings as the H-1. It was powered by two 90hp Curtiss OX  engines, as it didn’t need to carry the very heavy fuel load that had forced Curtiss to briefly add a third engine to the H-1. It kept the simple enclosed cockpit canopy of the H-1.  The hull had a shallow V-form, with large sponsons carried on either side of the forward fuselage to improve buoyancy.

In service the H-4 was found to have a weak hull and under-powered engines. The hull of the H-1 had been designed to operate from sheltered waters, not on the rough North Sea. In addition they often needed to be towed back to base after suffering various problems on their patrols.

Porte and his team carried out a large series of experiments with various shapes of hull. Eventually this led to the creation of the Felixstowe F.1, which combined the Curtiss wings with a new hull, and greatly improved the aircraft’s performance during take-off and landings. The F.1 became the basis of a series of production models, starting with the Felixstowe F.2.

A number of H-4s were built by the Aircraft Manufacturing Co (better known as Airco, an early employer of Geoffrey de Havilland. Some of these aircraft were built with experimental hulls produced by S.E. Saunders. No.1230 had an experimental Saunders hull with a rounded under surface for the tail, which proved to be less effective than the original flat Curtiss design. No.1231 had a slightly different experimental hull. The Saunders hulls (1230-1232) were covered with Consuta, a copper-sewn plywood developed by Saunders. This made the hulls 300lb lighter than the standard H.4, but also weakened them and No.1230 was recorded as having a short life.
 
Porte used several H-4s for his experiments.

H-4 No.3579, which was delivered to Felixstowe on 30 July 1916 kept the original shallow bottom to the hull, but was given modified side fins (sponsons). It didn’t survive for long, and was deleted from charge on 14 November 1916. 

H-4 No.3569 saw a key development. It was the first of Porte’s experimental aircraft to have a steep V-bottomed hull. This was achieving by raising the tip of the nose from its original low position until it was almost level with the base of the lower wing, and lifting the sponsons. However the surface between the keel and the tips of the sponsons lost their concave curve. 3569 was originally completed without a step in the hull, as the step was considered to be a weak point in the hull. However without a step the aircraft couldn’t take off. A single step was added 5ft behind the centre of gravity, and in this configuration it was able to take off, although only at a lighter weight than the H-4. However the new hull gave the aircraft much better landing qualities, proving that the steep ‘V’ bottom was the way to go, eliminating shock in a normal landing and reducing it greatly in low speed landings. The step was later moved forward, making it even easier for the aircraft to take off. No.3569 survived until 25 April 1917 when it was deleted.

Not all of the experiments were directly related to the problems with the hull. Aircraft No.3546 became known as The Incidence Boat. It entered service in the summer of 1915, when it was powered by two 110hp Clerget rotary engines. There was later replaced by 100hp Gnome Monosoupape rotary engines, then by two Anzani engines. At some point it was given a modified fuselage. The enclosed cockpit was removed and a bulbous nose was added, with two portholes in the front. The purpose of these portholes is unclear.

On 29 September 1916 one H-4 was used in an attempt to scout the German High Seas Fleet in the Schillings Roads, in preparation for a torpedo attack. The plan was for the H-4 to rendezvous with a destroyer from the Harwich Force near the German coast, land and refuel, then carry on to its target. The first part of the mission was a success, with the flying boat finding the destroyer, but after that everything went wrong. The weather was no longer suitable for the reconnaissance, so the H-4 was ordered to land, refuel, then return home. However the sea was too rough and the flying boat collided with the destroyer, badly damaging its wing. The crew (which included the famous author Erskine Childers) was rescued, and an attempt was made to tow the H-4 home, but it sank just as the coast came into sight. The advent of successful sea plane carriers saw this sort of long range flying boat mission replaced by shorter ranged missions supported by the carriers.

The H-4 was also used at the Killingholme Seaplane School.

H-1 Stats but H-4 should be very similar
Engine: Two Curtiss OX engines (as built)
Power: 90hp each
Crew: 3
Span: 74ft (upper), 46ft (lower)
Length: 37ft 6in
Height: 16ft
Empty weight: 3,000lb
Gross weight: 5,000lb
Maximum take-off weight:
Max speed: 65mph
Climb Rate:
Service ceiling:
Range: 1,100 miles

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How to cite this article: Rickard, J (5 January 2021), Curtiss H-4 ‘Small America’, http://www.historyofwar.org/articles/weapons_curtiss_H4_small_america.html

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