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Monday, December 9, 2013

You Know It Don’t Come Easy


Technological advancement, particularly in aeronautics, is not easy.  This fall, as we remembered the passing of President Kennedy, his speech proposing the landing of Americans on the moon was played often.  "We choose to go to the moon in this decade and to do these other things not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills,…”

This fall also marks the 60th anniversary of the introduction of the F-100 Super Sabre into the United States Air Force. Like the Boeing 787 Dreamliner, the F-100 pushed the boundaries of conventional technology.  The F-100 Super Sabre was the first operational aircraft to be designed for and capable of supersonic speed in level flight.  The pioneering technology necessary to accomplish this, from aerodynamics to propulsion, was no less dramatic than that of the Dreamliner.

Unlike the Boeing 787, propulsion requirements for the F-100 to achieve its intended supersonic capability could not be satisfied by current turbojet technology.  Therefore, a new turbojet engine design was needed.  The progeny of that effort was the Pratt and Whitney J-57 (JT-3).  The engine design was so revolutionary that the 1952 Collier Trophy was awarded for the J57.  Fitted with recently developed afterburner technology, the J57 met the expectations for the F-100 design objectives.  That engine proved to be integral to the success of not only the F-100, but other famous aircraft as well.  The legacy of many iconic airplanes like the F-101, F-102, U-2, F-8, B-52, B-57, Boeing 707 and Douglas DC-8 was created in no small part because of the J57.

North American Aviation Chief Test Pilot, George Welch (pictured above), flew the first production F-100A on October 29,1953.  On a second flight that day, USAF test pilot Lt. Col “Pete” Everest Jr. set a world speed record of 755.149 over the Southern California desert near the Salton Sea.  This was the last speed record established at low altitude. Welch had also flown the YF-100A prototype the previous May 25 on its maiden flight that included speeds above Mach 1.0.  Welch was no stranger to either first or supersonic flights.  He piloted the North American Aviation F-86 on its first flight October 1, 1947. Also, although not officially recorded and in a dive, Welch exceeded the Mach 1 in an F-86 just days before Chuck Yeager exceeded the sound barrier in level flight in his “Glamorous Glennis” Bell X-1A.

Welch’s career is less widely known than Yeager’s, but his story is equally interesting.  On the morning of Sunday December 7, 1941, after an all night party, Lt’s George Welch and Kenneth Taylor were intending on going for a swim at their auxiliary base Haleiwa Field about 10 miles from the Wheeler Field at Pearl Harbor when the Japanese attack began.  On their own initiative the pilots drove to the aux field where Welch had called ahead to have two P-40s readied for takeoff.  The two pilots took off without orders and engaged the attackers.  Their actions are highlighted in many war movies about Pearl Harbor, including the 1970 film, Tora Tora Tora.  Welch recorded 4 kills that day and, as well as Taylor, received the Distinguished Flying Cross for his heroism.

Unfortunately, George Welch lost his life October 12, 1954 on a test flight of the F-100.  While performing one of the final evaluations of the Super Sabre’s design, a maximum load high-speed pull up maneuver, the aircraft became uncontrollable and was lost.  The 36-year-old Welch was able to eject, however, the injuries he sustained in the accident were fatal. Stability issues were reported by all of the pilots that had test flown the F-100A.  Most troublesome were poor longitudinal stability in high-speed flight as well as poor low-speed handling characteristics.  The low-speed qualities of the F-100 would prove to be fatal for many pilots who failed to acknowledge it’s unique handling characteristics.  The high-speed instability would be solved, but would require all new high speed jet fighters to respect a phenomenon that cost George Welch his life, inertial roll coupling.

Prior to the F-100, fighter aircraft were neither heavy nor fast enough to experience inertial coupling.  Inertial coupling, simply explained is where the inertia of a longer heavier fuselage overpowers the aerodynamic forces of the wings and tail. It became problematic with the introduction of the supersonic F-100 with its long heavy fuselage versus its relatively narrow wingspan.   The inertial coupling problems were eventually overcome, but not before six fatal crashes and a grounding of the aircraft in October of 1954.  Modifications to the F-100 were made that included increasing the size of the vertical tail, adding a yaw dampener as well as increasing the wingspan. The low speed characteristics of the F-100 remained troublesome for its entire history.


Although the F-100's low speed performance benefitted greatly from the aerodynamically controlled slats introduced on the F 86, they allowed for higher angles of attack that also had distinct disadvantages.  Also, the F-100 had large conventional ailerons that were responsible for the Super Sabre’s legendary adverse yaw.  When the aircraft was turned the aileron on the “up wing” or the outside of the turn would deflect downward into the relative wind.  This aileron’s deflection would create drag and induce a yawing motion away from the turn.  This tendency was greatly exaggerated at low airspeed with high angles of attack.  If the yawing were not corrected with rudder, the plane would eventually roll over in the opposite direction of the turn.  If this happened in the landing pattern or close to the ground both the pane and pilot were often lost.



Also, through the use of the aircraft's automatic slats the F-100 was capable of a very tight turning radius that was useful in air-to-air combat. This ability to achieve high angles of attack also had disadvantages.  The airplane’s unique aerodynamic characteristics caused the airplane to experience large amounts of induced drag from the F-100s wings.  The 45-degree wing sweep also contributed the center of lift to moving forward at high angles of attack and causing a pitch up.  During air combat maneuvers this pitch up would cause the airplane to slow dramatically and lose energy quickly.  The J57 did not have enough thrust to overcome this substantial induced drag. Although the F-100 could turn tighter than its opponent, the energy deficit would leave the pilot vulnerable to a faster enemy plane.  Even more pernicious were the consequences from the enormous induced drag in the landing pattern or maneuvering close to the ground.  The F-100 wing could fly without stalling at a speed low enough to create more drag than the J57 could overcome.  This flight regime is described as the area of reverse command. Pilots refer to it as being “behind the power curve”.  It is the condition of the aircraft filmed doing the infamous “Sabre Dance”.  The engine could not provide enough thrust, even in afterburner, to overcome the induced drag and allow the pilot to “fly” out of his situation.

 

In spite of its initial difficulties, “the Hun” became an essential part of the UASF inventory as a potent tactical air support fighter. The F-100 D and F were fitted with the latest weapon systems for testing as well deployment.  The two-seat F-100F was used for the "Misty" fast FAC (forward air controller) missions.  The "F" was also called upon to introduce the successful “Wild Weasel” concept for destroying surface to air (SAM) batteries in North Viet Nam. F-105 and F-4 aircraft used this successful tactic until radar homing missiles were finally deployed against the SAMs.  The F-100 flew more operational sorties than any other aircraft in Viet Nam. 


 Numerous models of the F-100 Super Sabre were flown by the air forces of Turkey, France, Denmark and Taiwan.  Air National Guard pilots flew the last USAF F-100 operational sortie in November 1979.  During the 25 years the F-100 Super Sabre was in the USAF inventory, all who flew it, including the USAF Thunderbirds, admired as well as respected this remarkable airplane.  I feel very lucky to be in a small group of pilots that have had the priveldge to fly both the Super Sabre and the Dreamliner.



“You’ve got to pay your dues if you want to sing the blues
‘Cause you know it don’t come easy”
                                                            Richard Starkey

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