EAA Chapter 478

of Southern Maryland

The Curtis A-1 Triad -- Construction of a Non-flying Replica

This replica was built as accurately as possible to represent the construction methods and materials used by the Curtiss Aeroplane Company in 1911. It was not intended to fly. It is displayed in the Naval Air Museum located next to the Naval Air Station at Patuxent River, Maryland.

 

The Lexington Park Chapter of the Experimental Aircraft Association (EAA) was asked to build a non-flying 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, and nose-mounted movable “bowheader” canard. A mono‑float 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 operations, but the gear had to be raised to minimize the drag when operating on the water. The A-1 was a 2‑seat aircraft with dual controls to allow training of Navy pilots. The engine was a liquid cooled 75-horsepower V-8, designed and built by Curtiss and installed in a pusher configuration with a nearly 8 foot diameter propeller.

 

The construction of the replica A-1 was undertaken by a group of volunteers who are members of the EAA Chapter #478 in Lexington Park Maryland. 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.


(1) 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 the 50th anniversary of Naval Aviation).

 

(2) 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.


(3) 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 substituted for significant savings.


The San Diego Air & Space Museum drawings were produced for the purpose of producing a flyable and reasonably safe aircraft that would meet 1961 aircraft safety standards. All steel components were specified as 4130 steel alloy, all fastener hardware was specified by an Army-Navy (AN) standard designation that is still in place today. All bolts, nuts, washers, and all flying wires, cable fittings, and turnbuckles were replaced with hardware similar to that was available in 1911. Several changes were also made in 1961 to improve aircraft performance and safety, included increasing the size of the wing tip floats from 6 to 8 inches in diameter and changing the nose fitting on the mono-float to a stronger design. As a safety consideration, conventional flight and engine controls replaced the original designs.

 

The original 1911 A-1 aircraft had conventional flight control surfaces, utilizing a rudder for yaw control, an aft mounted horizontal tail with elevators and a forward mounted bowheader (canard) for pitch control, and ailerons mounted between the wings for roll control. Pilot-actuated controls for the aircraft, however, were very different from 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 torso (rib cage), 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 to not hinder control 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 that was milled to match the drawing dimensions. The aircraft has a total of 10 wing panels, 5 per wing. The center panels of each wing are identical and the 8 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 reinforce with brass sheeting, being attached to the wood with brass-plated nails to prevent corrosion. All flying surfaces were covered with vinyl cloth, as used on modern light aircraft, but tinted to mimic the look of the original linen covering, which is no longer available.

 

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.


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.

 

Finding an engine was one of the most difficult challenges of the replica A-1 building project. Several members investigated building an engine mockup 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” was found at the National Naval Aviation Museum in Pensacola, Florida. The National Naval Aviation Museum loaned a 1916 “OXX” engine to 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 model “O”propeller was also included in the loan agreement.


The 1961 drawings used for the building of the replica called for AN standard hardware, which included nuts, bolts, washers, and all flying wires, cable fittings, and turnbuckles to assure predictable strength characteristics for a flight-worthy replica. The specification for AN hardware was developed in the 1920’s, 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 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 1940’s.

A major decision was made during the construction phase 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 that used a central barrel with left- and right-hand female threads in opposite ends to join the aircraft structure anchor point (a threaded termination) to the cable end termination (also threaded). The barrel was simply rotated to shorten or lengthen the length of the cable. 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 bent into a half-loop that hooked into the cable termination. Again, Curtiss’s experience with motorcycle manufacture and racing dictated this evolutionary adaptation to aircraft. The A-1 has approximately 150 bracing and control cables, each requiring tensioning. The development of the standard aviation turnbuckle greatly simplified cable installation and rigging in later aircraft designs.

 

Although several details about the A-1 have been lost in the 100 years since it joined the Navy, this replica will help to preserve what is known and allow future generations visiting the Patuxent River Test and Evaluation Museum to see many of the aircraft design features and construction practices used in 1911.

The aircraft is now completed and on display in the Patuxent River Test and Evaluation Museum. The aircraft is displayed in a manner simulating flight operations meaning that the beaching gear is retracted. At a later date, the aircraft will be hung from the ceiling of the museum. Below are some pictures from of the completed aircraft.

 

Acknowledgments. Thomas Weiss, Author would like to recognize the past and present members of the Experimental Aircraft Association (EAA) Chapter #478 for their efforts in the research, fabrication and assembly of the A-1 Triad. The cost for all materials were paid for by either donations of individual members or out of the EAA Chapter #478 Treasury. Several Companies donated materials to the project including Poly Fibre Inc and Bike Doctor.

 

 

 

 

 

 

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