ChapterGram: September 2013
EAA Chapter 478's Replica 1911 Curtiss A-1 Triad
By Thomas A. Weiss, EAA 205604
This article discusses EAA Chapter 478's construction of a replica 1911 Curtiss A-1 Triad. The aircraft was built as accurately as possible to represent the construction methods and materials used by the Curtiss Aeroplane Company in 1911. This replica is not intended to fly; it's displayed in the Patuxent River Test and Evaluation Museum located next to the Naval Air Station in Maryland.
More than a decade ago, EAA Chapter 478 was asked to build a nonflying replica of the 1911 Curtiss A-1 Triad to coincide with the 100th anniversary of naval aviation. The A-1 was delivered to the Navy on July 2, 1911, the first Navy-procured aircraft. The aircraft design was typical of Curtiss aircraft of the period, consisting of a biplane main wing, horizontal tail with elevators, single rudder, and nose-mounted movable "bow header" canard. A monofloat was incorporated in place of landing wheels. Curtiss added retractable wheels that he called "beaching gear" to allow the aircraft to be rolled up on the beach when not in operation, but the gear had to be raised to minimize the drag when operating on the water.
The A-1 was a two-seat aircraft with dual controls to allow training of Navy pilots. The engine was a liquid-cooled 75-hp V-8, designed and built by Curtiss and installed in a pusher configuration with a nearly 8-foot-diameter propeller.
Construction of the A-1 replica was undertaken by a group of chapter member volunteers. Individual members built specific components in their workshops with larger processes, such as fabric covering of the flight surfaces and modular assembly of the aircraft components, involving small teams. Coordination of the project changed hands a couple of times over the 10-year build period with the author being the last coordinator. A few critical decisions were made at the beginning of the project.
- The A-1 would be built as accurately as possible with currently available materials using a set of drawings procured from the San Diego Air & Space Museum (produced in 1961 for a flying A-1 replica to celebrate naval aviation's 50th anniversary).
- The A-1 would be for display only, thus allowing the latitude to use construction methods and materials similar to those used by Curtiss in 1911, which would not meet modern FAA safety standards.
- Material substitutions could be made to keep the costs reasonable while retaining the look of the original design. For example, non-aviation grades of wood and hardware were used for significant cost savings.
The original 1911 A-1 aircraft had conventional flight control surfaces, utilizing a rudder for yaw control, an aft-mounted horizontal tail with elevators, a forward-mounted bow header for pitch control, and ailerons mounted between the wings for roll control. Pilot-actuated controls for the aircraft, however, were very different from those of today.
The pilot's control yoke consisted of a wheel attached to a column. Fore and aft motion of the column moved the elevator and bowheader surfaces for pitch control, but the wheel controlled the rudder instead of the ailerons as in conventional aircraft, thus providing yaw control. The single control wheel could be moved left or right of the column centerline to position it in front of the left or right seat occupant.
Aileron movement for roll was controlled by a shoulder yoke assembly that consisted of a U-shaped seat back that cradled the pilot's shoulders, shifting laterally when the pilot leaned left or right. Several people surmise this was natural to Curtiss because of his experience racing motorcycles, where turns were initiated by leaning left or right. There were shoulder yokes for each seat (side-by-side seating), and they were connected to each other; so when the aircraft commander leaned left or right, the passenger had to move with him so as not to hinder control of the aircraft.
In addition to these controls, the engine throttle was actuated by a foot pedal with one for each occupant. The A-1 constructed for the Patuxent River Test and Evaluation Museum replicated the same control systems Curtiss provided in the original A-1 delivered to the Navy in July 1911.
The flying surface structures are all wood milled to match the drawing dimensions. The aircraft has a total of ten wing panels (five per wing). The center panels of each wing are identical, and the eight outboard wing panels are also identical but are smaller than the center panels. All wing panels were constructed on a fixture to ensure the correct camber of the single-surface airfoil. Wooden structural joints were all reinforced with brass sheeting, attached to the wood with brass-plated nails to prevent corrosion. All flying surfaces were covered with materials donated by the Poly-Fiber Inc. and tinted to mimic the look of the original linen covering, which is no longer available.
Wing panel wood structure
The four booms that hold the tail section are made from bamboo, identical to the original A-1. Bamboo provides a light structure that is strong for the weight. When the bamboo cracked, the common practice was to wrap the cracked section with rope and varnish the rope to make it very stiff and strong. This was also done on the replica A-1 as a demonstration of the repair technique of the period.
The retractable beaching gear is a somewhat complicated assembly that allows the gear to be lowered and retracted from either seat by mounting the cable-actuated extension/retraction handle between the seats. The gear design allows it to free-fall to the extended position where it locks. It is retracted by pulling up on the gear handle and is held in that position by the retraction cables. Details of the actuation system have been lost; this system was fabricated based on historical pictures and what made sense to ensure operation by one person.
Finding an engine was one of the most difficult challenges of the replica A-1 building project. Several members investigated building an engine mock-up from wood, but available details for the Curtiss model O engine were insufficient to permit construction. Fortunately, an engine appearing very similar to the model O - a 1916 OXX - was found at the National Naval Aviation Museum in Pensacola, Florida, and the museum loaned it to the Patuxent River Museum for installation in the A-1 replica.
This engine was previously exhibited to show a portion of its internal parts, having some of its structure cut away to reveal inner workings. An original propeller very similar to what would have been used on the aircraft was also included in the loan agreement.
The 1961 drawings called for AN standard hardware, which included nuts, bolts, washers, and all flying wires, cable fittings, and turnbuckles to ensure predictable strength characteristics for a flight-worthy replica. The specification for AN hardware was developed in the 1920s, and shortly after that the hardware began to be produced.
However, after conducting some research and talking to historians at the Glenn Curtiss Museum in Hammondsport, New York, the collective group decided that hex-head nuts and bolts were probably not readily available in 1911, but coarse-thread square-head nuts and bolts were.
Therefore, all nuts and bolts in the replica are square-headed and painted black to represent a best guess of what was used in the 1911 original. When square-head hardware could not be provided, the hardware was fabricated to a square-head configuration. Likewise, all machine and wood screws have slotted heads, since the now common Phillips-head screw was not developed until the 1940s.
A major decision was made to replicate the hardware used in the original 1911 aircraft for tensioning the bracing and control cables, even though the 1961 drawings called for aircraft-grade AN turnbuckles. An early version of the now standard turnbuckle design was developed by Curtiss in 1912. The original 1911 aircraft, however, used motorcycle spoke assemblies for tensioning.
A bracket was made to hold the single-threaded hollow nipple into which the threaded end of the spoke was inserted and the other end of the spoke was bent into a half-loop that hooked into the cable termination. Again, Curtiss's experience building and racing motorcycles dictated this evolutionary adaptation to aircraft. The A-1 has approximately 150 bracing and control cables, each requiring tensioning.
Although several details about the A-1 have been lost over the past century, this replica will help preserve what is known and allow future generations visiting the Patuxent River Test and Evaluation Museum to see many of the circa-1911 aircraft design features and construction practices.
The aircraft is now completed and on display in the museum in a manner simulating flight operations (retracted beaching gear). The aircraft will be hung from the museum ceiling in the future.
Curtiss A-1 on display in Patuxent River Naval Aviation Test and Evaluation Museum
Chapter 478 Curtiss A-1 Primary Build Team
The author would like to recognize the past and present members of EAA Chapter 478 for their efforts in the research, fabrication, and assembly of the A-1 Triad. Costs for all materials were paid for by donations of individual members or out of the chapter treasury. Several companies donated materials to the project including Poly-Fiber Inc. and Bike Doctor.