The production of the model machine only served to show us some of the problems which must be overcome before we could secure a standard design that could go into quantity production. Experimental work on the De Haviland continued during December, 1917, and January and February, 1918. The struggle, for it was a struggle, to secure harmony between this English design and the American equipment which it must contain ended triumphantly on the 8th day of April, 1918, when the machine known as No. 31 was completely finished and established as the model for the future De Havilands. The characteristics of the standard American De Haviland-4 were as follows:
- Endurance at 6,500 feet full throttle, 2 hours 13 minutes.
- Endurance at 6,500 feet half throttle, 3 hours 3 minutes.
- Ceiling, 19,500 feet.
- Climb to 10,000 feet (loaded) 14 minutes.
- Speed at ground level, 124.7 miles per hour.
- Speed at 6,500 feet, 120 miles per hour.
- Speed at 10,000 feet, 117 miles per hour.
- Speed at 15,000 feet, 113 miles per hour.
- Weight, bare plane, 2,391 pounds.
- Weight, loaded, 3,582 pounds.
Endurance here means the length of time the fuel supply will last. The ceiling is the maximum altitude at which the plane can be maneuvered in actual service. Ground level means only far enough above the ground to be clear of obstructions.
The first De Havilands arriving in France were immediately put together, such remediable imperfections as existed were corrected then and there, and the machines were flown to the training fields. The changing and increasing demands of the service indicated the advisability of certain changes of design. The foreign manufacturers had brought out a covering for the gasoline tanks, making them nearly leak-proof, even when perforated by a bullet. In the first De Havilands the location of the principal gas tanks between the pilot and the observer was not the best arrangement in that the men were too far apart from each other so that, if the machine went down, the pilot would be crushed by the gas tank. Also the radius of action was not considered to be great enough, even though the later machines of this type carried 88 gallons of gasoline.
As a result the American aircraft designers brought out an improved De Haviland known as the 9-A. This carried a Liberty-12 engine; and the main differences between it and the De Haviland-4 were new locations for pilot and tanks, their positions being changed about, increased gasoline capacity, and increased wing surface. The machine was a cleaner, more finished design, showed slightly more speed, and had a greater radius of action than the De Haviland-4 which it was planned to succeed. We ordered 4,000 of these new machines from the Curtiss Co., but the armistice cut short this production.
The difficulties in the way of producing new service planes on a great scale without previous experience in such construction is clearly shown in the attempts we made to duplicate other successful foreign planes. On September 12, 1917, we received from the aviation experts abroad a sample of the French Spad. We had previously been advised to go into a heavy production of this model and had made arrangements for the Curtiss Co. at Buffalo to undertake the work. This development was well under way when in December a cablegram was received from Gen. Pershing advising us to leave the production of all single-place fighters to Europe. As a result we canceled the Spad order, and after that we attempted to build no single-place pursuit planes.
THE LEPERE CORPS OBSERVATION PLANE.
THE LEPERE (CAMOUFLAGED). THE ENGINE IS A LIBERTY 12-CYLINDER, 400-HORSEPOWER.