Every research aircraft poses a question. Sometimes the answer is "forget it."
- By The Editors
- Air & Space magazine, August 2011
We asked aerospace researchers, authors, and historians to name the "worst X-planes, with ‘worst’ to be interpreted any way you like: Useless? Dangerous? Ill-conceived? Downright silly?" Our responders are: •Richard P. Hallion, former Air Force historian and author of numerous books and articles on military and research aviation; •Raymond L. Puffer, recently retired from a 33-year career with the Air Force history program, nearly half spent at the Air Force Flight Test Center History Office at Edwards Air Force Base; •Curtis Peebles, author of several books about X-planes and a historian at the History Office of NASA’s Dryden Flight Research Center; •J. Campbell Martin, also at Dryden, who initiates symposia, lectures, and publications about X-planes; •Jay Miller, aviation journalist and the author of dozens of books, including The X-Planes: X-1 to X-45.
1. Douglas X-3
Designed to achieve Mach 2 cruise speeds, the X-3 Stiletto looked fast even when parked on the Edwards ramp. It had the most refined airframe of any X-plane of the nifty fifties. What it didn’t have were the right engines. At best, it could exceed Mach 1 in a dive. The X-3’s elongated fuselage and stubby, razor blade wings made the airplane susceptible to inertial coupling, in which a rolling maneuver causes uncommanded pitching and yawing. Joe Walker, a research pilot with the National Advisory Committee for Aeronautics, experienced the phenomenon when flying the X-3; the forces came perilously close to overstressing the aircraft’s structure. Ironically, the data produced on inertial coupling was the X-3’s most valuable contribution. Had the intended engines been available, the aircraft would have performed better, but likely people would have been killed.
An elegant design with the potential for Mach 2-plus flight, it was penalized when the engines intended for it—Westinghouse J46s—grew so big they could not fit within it. Instead, lower-rated J34s were used, dooming the aircraft to transonic performance.
—Richard P. Hallion
2. Republic XF-84H
The Worst X-Plane to Be Around was a turboprop-powered experimental version of the swept-wing F-84. Early jet engines were extremely slow to spool up, which made carrier landings, with the need to go to full power at touchdown, even more hazardous. As a result, the Navy became interested in the use of turboprop engines, which would alleviate the slow-ness. Even at idle throttle, the XF-84H’s three-blade prop rotated so fast that the tips were supersonic, which generated severe noise and vibration. This (1) caused the ground crew to experience crippling nausea, and (2) earned the aircraft the nickname Thunderscreech (see "ZWRRWWWBRZZ!," June/July 2003).
The XF-84H made history—on the ground—by gaining the reputation among crew chiefs as Aviation’s Most Acoustically Abusive Vehicle. Over the years, the stories have been embellished: According to one, it was loud enough to turn the Rogers lakebed into tapioca pudding (false). XF-84H serial number 17059 spent years mounted on a pole outside the Meadows Field airport terminal at Bakersfield, California, where an electric motor turned the propeller ever so slowly. A life-size Santa was placed in the cockpit to greet seasonal holiday travelers. The airplane is now on more dignified indoor display in the National Museum of the U. S. Air Force at Wright-Patterson Air Force Base near Dayton, Ohio.
—J. Campbell Martin
3. Boeing X-20
The Worst Lost Opportunity, the Dyna-Soar was a manned, winged spacecraft, the culmination of the rocketplane projects from the X-1 through the X-15. It would have been launched into orbit on a Titan III, then would have reentered the atmosphere and landed like an airplane. The delta-wing airframe, with fins at the wingtips, was built of high-temperature metals rather than employing an ablative heat shield like that on the Mercury capsules. Plagued by a cutesy nickname, the X-20 vacillated between being an experimental vehicle and an operational space reconnaissance and bombardment system. Secretary of Defense Robert McNamara cancelled it in December 1963.
4. Schweizer X-26A
The Airplane That Least Deserves an "X" Designation, hands-down. The X-26A is a very-well-behaved, off-the-shelf production sailplane. Yes, the Navy Test Pilot School had a couple of beautiful examples, and X-26s are extraordinarily useful for demonstrating what rudder pedals do in aircraft made before the development of fly-by-wire technology. But everywhere else, the model is known as a Schweizer 2-32. They are workhorses, used to give paying customers sightseeing rides. Oh, and they have been soloed by 14-year-olds building time toward their 16th birthday, when they can take the private pilot check ride that the Federal Aviation Administration requires for their licenses. Not exactly what comes to mind when someone says "experimental aircraft."
—J. Campbell Martin