Curtiss-Wright X-100

The Curtiss-Wright X-100 was, by intent, a short-lived research program used to demonstrate the radial lift concept being developed for the Curtiss-Wright M-200 aircraft, which eventually became the X-19. As such, the X-100 had only two purposes. One was to test the radial lift force concept and the gimbaled nacelles needed for a tilt prop configuration. The other was to test the glass fiber propellers needed to enable the use of radial lift. The X-100 was successful in that it verified the characteristics of the props, and produced data on noise, vibration, downwash, ground effect, stability, and control, and the piloting techniques needed to hover and transition a tilt prop VTOL.

The airframe itself was simple and straightforward. It was all aluminum construction except for the aft half of the fuselage starting just aft of the cockpit, which was fabric covered. Design and fabrication was completed in just over a year, using what is now called concurrent design and construction. Basically, this means the design, fabrication, testing, and documentation of components occurred in a continuous and ongoing process. The design process started in February 1958. The first prop assembly was fabricated soon after and tested in NASA's 12m x 24m wind tunnel starting in October 1958.

It was run through the expected power operating range and at shaft angles from 0 to 90 degrees. These tests demonstrated that thrust in hover would be 10 percent below prediction (which was later confirmed in flight test), but there was enough excess thrust that the 10 percent loss was acceptable. Preliminary wind tunnel tests using models were performed at the Massachusetts Institute of Technology, then a powered model was run in the wind tunnel to determine stability and control characteristics. Tests using the actual aircraft eventually were run in NASA's 12m x 24m wind tunnel. Reasonable correlation was achieved between wind tunnel tests and flight tests.

Roll out of the completed X-100 occurred on December 22, 1958, at Curtiss-Wright's Caldwell, NJ, facility, and the first engine run was performed on January 14, 1959. The first hover was made in a tether rig on April 20, 1959, to verify control power and feel. The first free hover test was performed on September 12, 1959, but extra weight was added to prevent the X-100 from getting out of ground effect. After three days of testing, hover flights of up to 20 minutes duration were made. The outflow velocities of air along the ground at various distances from the hovering X-100 proved to be similar to those of a helicopter of similar weight. The basic test program was completed on July 21, 1960. Test pilots from NASA visited Curtiss-Wright and flew the X-100 on August 12 and 13. This concluded test operations for the X-100 at the Caldwell, NJ, facility.

With Curtiss-Wright satisfied that they had proven the radial lift concept, they turned the X-100 over to NASA. It was shipped to the Langley Research Center in October of 1960. However, it was not really used to test flight characteristics, but to study the effects of downwash on several types of ground surfaces, such as snow, grass, pavement, and packed dirt. NASA also studied problems associated with visibility in snow during hover and slow forward transition. This role, too, was finished by October 1961.

Following the completion of tests at Langley, the X-100 was donated to the Smithsonian Institution. During its short career, the X-100 completed a total of 14 hours flying time and 220 hours of ground engine run time. It successfully proved the radial force concept, the feasibility of tilting nacelles, and low noise levels. It successfully showed the value of using a demonstrator aircraft to highlight technical concerns quickly and to reduce risks for higher cost development programs.