Changes made to EAA’s Waco YKS-7 (NC17716)

EAA’s Waco YKS-7 is an authentic aircraft, not a replica. Its paint scheme and overall appearance today are remarkably faithful to what they were when it was built in 1937. However, the plane has experienced many changes over the years. A knowledgeable observer will notice several differences between the airplane as it flies today and how it looked when it left the Waco factory. While some replica aircraft are built with the sole purpose of display and with great care to match original specifications, NC17716 has been a working aircraft for more than sixty-five years. In that time, many changes have been made to enhance its utility and increase its safety.

A major change was the installation of a more powerful Jacobs engine and a constant speed propeller. The original engine installed on NC17716 was a Jacobs L-4 engine, rated at 225 hp., with a Hartzell wood propeller. An accident early in the airplane’s history damaged the propeller and it was replaced with a metal propeller. More recently a larger Jacobs engine was installed, along with a Hamilton-Standard constant-speed propeller. This combination greatly improved the airplane’s performance, especially in terms of lifting heavy loads out of short-fields. The constant-speed propeller allows the full engine power to be used both at low airspeeds, as in takeoffs, and also at cruise.

Over NC17716’s sixty plus years, improved technology has allowed many safety improvements to be incorporated in the airplane without compromising its authentic passenger experience. In November of 1997, the EAA Museum Committee approved NC17716 for active flying status at Pioneer Airport. During the winter of 1998 the aircraft was completely inspected and evaluated by the EAA Aircraft Maintenance staff.

One major improvement by the EAA Aircraft Maintenance staff was installation of Cleveland hydraulic disc brakes to replace the original mechanical brakes. The original brakes were actuated with a single “Johnson bar” lever. This slowed the airplane, but provided no assistance in controlling its direction. The new brakes are individually activated through controls on the pilot’s rudder pedals. This allows the brakes to be used as a backup to the steering provided by the rudder and tailwheel.

Years of rough field landings had taken their toll on the original tailwheel and it was replaced with a sturdier Scott tailwheel. A mechanism was added to allow the new tailwheel to be steered with the rudder pedals or allow it to caster freely. The steerable tailwheel feature adds safety for takeoff and landing rolls, while allowing it to caster freely permits sharper ground turns.

A few changes in NC17716 involve compromises of authenticity for the sake of safety. An anti-collision strobe is installed on the top and bottom of the fuselage and a VHF communications radio is installed in the instrument panel. These changes help allow a 1937 aircraft to operate safely in 21^st century airspace.

After a successful flying season at Pioneer Airport in 1998, further restoration work was undertaken. Both lower and upper wings were rebuilt and the empennage was also restored. This work was competed in April of 2000 and the plane returned to daily passenger service at Pioneer Airport.

The EAA Aircraft Maintenance staff has made great efforts to retain authenticity where possible, even in areas not visible on the aircraft. An example of this is the recent repair of the airplane’s wing tanks. Early in 2001, leaks were found in each fuel tank. A decision was made to build new tanks using the old tanks as a guide. The original tanks were made of aluminum with multiple internal baffles. All of the aluminum rivets in the tanks were welded in place to prevent leaks. The original aluminum sheets on the exterior of the tanks had hydroformed ridges to add stiffness and resist distortion caused by the welding process. The special tooling used in 1937 to make the original tanks was unavailable, so new tooling was designed and built. Special roller tools were built to replicate the original stiffening ridges. All of the rivets in the tanks were heliarc welded to match the original construction technique. After the glistening new tanks were installed in the upper wings, the fabric covering concealed them from view.