THE 456th FIGHTER INTERCEPTOR SQUADRON

THE PROTECTORS OF  S. A. C.

 

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Chasing The XB-70 Valkyrie

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by Marrett, George J

 

"HOLD YOUR POSITION !"

Crackled the UHF radio transmission from the Edwards AFB Command Post. "We are changing your mssion: the SB-70 Valkyrie has crashed!" The date was June 8, 1966. I was a test pilot assigned to the fighter section of the Air Force Flight Test Center (AFFTC) at Edwards AFB, California, in the Mojave Desert. On that day, I was acting as an instructor pilot in a Northrop T-38 Talon. Sitting in the front cockpit was my student-- a Strategic Air Command colonel who was getting supersonic flight experience in the T-38 before checking out in the Lockheed SR-71 Blackbird. We had preflighted the aircraft and were preparing to start our engines when we received that chilling call.

It did not surprise me to hear that it was the XB-70 that had crashed. In the year and a half I had been acting as a safety chase pilot (flying in McDonnell F-4 Phantoms and Lockheed F-104 Starfighters, as well as Talons), the XB-70 had had many close calls. While the official USAF name for the XB-70 was "Valkyrie," North American Aviation, its builder, called it "The Great White One." Because of all the aircraft's mechanical problems, we safety chase pilots called it "Cecil, the seasick sea serpent." With its long, thin neck and curved body, it did resemble a sea creature, and it got sick on every test flight that I can recall.

Chase pilots routinely accompanied the XB-70. We would fly a "loose" formation about 100 feet abeam it and look for fuel and oil leaks, trailing smoke, missing side panels and any other unusual conditions, and we'd report them to the XB-70 test pilot. We had to be alert; aircraft problems showed up on every flight--some of them very serious.

"One of these days, Cecil will stub its toe and go down," I had predicted to other pilots. Little did I realize the strange and ironic sequence of events that would make June 8 "the darkest day in Edwards' flight-test history."

After the Command Post reported that the XB-70 had crashed--about 35 miles from the base, just north of Barstow, California--it directed us to take off, orbit the crash site and act as a radio relay. We would relieve a Lockheed T-33 T-Bird that had been giving information at the site, but had run low on fuel. Additionally, a helicopter was scrambled from Edwards to rescue survivors, but would not arrive for another 10 to 15 minutes. Since the Command Post could not maintain line-of-sight radio contact with the helicopter while it was on the ground, our job was to orbit overhead and relay information.

As soon as we were airborne in the T-38, I spotted black smoke from the XB-70 crash site drifting up to around 10,000 feet in the clear blue Mojave sky. As the rescue helicopter approached the crash scene, we relayed a report from the Command Post to the pilots to look for evidence of another downed aircraft, a NASA F-104. Parts of the XB-70 were still burning intensely (a picture that is still fresh in my memory even after 34 years). I knew all the XB-70 pilots and many of the NASA pilots. Death was a frequent visitor to the test community; once again, I feared its presence.

Orbiting over the smoking ruins, I recalled the first time I had seen the XB-70. At the time, in 1964, I was a student at the USAF Test Pilot School. On a visit to the North American Aviation facility at Palmdale, California, I watched as the incredible XB-70 rolled out into the world's aviation spotlight. The long-secret plane had looked like a hooded cobra in the shadows of the huge hangar in which final assembly was completed. The majestic plane, covered with a special, white ablative paint that would resist the searing heat caused by air friction, was designed to ride on its own shock wave. Its needle-like nose was designed to push air to the sides and beneath its triangular wing. Its wingtips could fold down to 65 degrees and provide the same type of lift as the wave created under a high-speed planning boat. Its eight landing gear tires appeared to have been sprayed with aluminum paint that gave the Valkyrie a futuristic look.

The aircraft was gigantic--196 feet long with a 105-foot wingspan and a height of 30 feet. Even the ducts that supplied air for the six General Electric J-93 engines were huge--seven feet high and 80 feet long. The engines were in the 30,000-pound class and designed to gulp air through twin ducts controlled by a very complex and troublesome intake system. At 550,000 pounds, the XB-70 was in a class by itself.

My mind flashed back to the many flights I had made chasing the Valkyrie as it was put through flight-test maneuvers. Because hydraulic, electrical and other mechanical failures occurred on practically every flight, several safety chase aircraft accompanied the XB-70 on takeoff, during the test mission and during landing. The T-38 usually accompanied the XB-70 on takeoff and landing to confirm that the landing gear worked properly. Because of the complexity of the landing-gear retraction and extension system, the takeoff safety chase crew did an "inflight pick-up." The takeoff chase pilot would launch first, climb out over Rogers Dry Lake and pull up into a downwind pattern, heading in a direction opposite that of the XB-70, which awaited the sign to start its takeoff roll. When the XB-70 pilot called out, "Rolling in 30 seconds," the T-38 pilot would time the start of his 180-degree descending turn to be directly abeam the XB-70 as it became airborne. Standard practice called for the XB-70 test pilot to delay gear retraction until the T-38 pilot had moved under him and was in a position to watch the complex gear-retraction motions. Another XB-70 test pilot frequently rode in the rear cockpit of the T-38 and confirmed correct gear retraction.

Flying safety chase, I saw many gear malfunctions. Several times, I saw the four wheels on one gear arranged perpendicular to the ground--an eerie sight. Once, I even saw the entire landing gear rotated 90 degrees away from the fuselage centerline--a condition that, uncorrected, would require the test pilots to eject. We always had a sense of impending doom as we flew near this beautiful Mach 3 bird; disaster could be moments away!

Once, when I was flying in the back seat of a Lockheed F-104D piloted by fellow test pilot Joe Stroface, the XB-70 pilots asked us to fly directly underneath them and check a landing-gear linkage in the wheel well. The F-104's T-tail extended about eight feet above the pilot's head, so clearance for our tail from the underside of the XB-70's lower wing edge was critical. Joe deftly flew the F-104 directly underneath the XB-70--within 12 feet of its belly.

Without my own hands on the flight controls and throttle, I was absolutely terrified that we would collide. Instinctively, I pressed my body as far into the corner of the ejection seat as I could, knowing full well that this strategy could not possibly save me in a collision. At that moment, though, doing something made me feel better.

In the early days of the XB-70 flight-test program, the J-93 engines could not be restarted in flight unless the aircraft was flown to at least 0.8 Mach--an excessive speed for a standard procedure. North American Aviation and GE engineers suspected that an irregular fuel pattern was to blame. The engineers requested that I attempt to fly a T-38 with a North American Aviation photographer in the rear cockpit directly behind the XB-70's engine exhaust nozzles to photograph the fuel pattern. I flew the T-38 so its nose came to within 10 feet of the engine exhaust nozzles-slightly low so the photographer would be able to aim his camera above my flight helmet and at the nozzles. Flight procedures had neither been published nor given to safety chase pilots about any special precautions to be taken when dying very close to the XB-70. We relied on constant verbal communications with the XB-70 test pilots, and we used the flight-control movements we needed to slide into position and stay there. We were considered members of the test-pilot fraternity and were expected to use good judgment. We got the photos.

To complete flight tests at Mach 3, the XB-70 flew a huge circular flight path covering the five western states of California, Nevada, Idaho, Utah and Arizona. Frequently a Convair B-58 Hustler with another XB-70 test pilot at the controls would fly a circle at Mach 2, staying inside the XB-70's path. That practice ensured that another test pilot who had intimate knowledge of the XB-70 would be able to quickly join up and render assistance if it was needed. Also, a Lockheed F-104 could be positioned at Mountain Home AFB, Idaho, or Hill AFB, Utah, ready to join up in formation if the XB-70 needed to land at either base or on one of the dry lakebeds nearby. A massive armada of support aircraft was required for each XB-70 flight--similar to that accompanying a North American X-15 rocket-ship mission.

My most demanding and dangerous experiences with the XB-70 involved flying formation in supersonic flight. North American Aviation management wanted photographs of the XB-70 with its wingtips at their full-down position of 65 degrees. The aircraft took off with the tips level. As the plane accelerated to 500 knots, the tips were lowered to 30 degrees. Above Mach 1.2, the tips could be moved to full-down. Aircraft flying at supersonic speeds create shock waves that can be heard on the ground but not by the pilot; he feels only slight changes in his flight controls and sees a momentary hesitation in his airspeed indicator at around 0.95 Mach; then it jumps to above Mach 1. The North American photo would have to be acquired near the shock wave.

From both a visual and an aerodynamic perspective, the XB-70's shock wave had a great impact on a chase plane flying in formation. Portions of the shock wave were seen as an optical distortion of the XB-70 airframe. In high school physics, students observe an optical distortion by placing a pencil in a glass of water; because of the difference in the index of refraction between air and water, the pencil looks bent, or displaced. A similar effect occurred with the Valkyrie; the plane was not exactly where it appeared to be.

Shock waves came off the XB-70's nose and tail and gradually bent backward at a greater angle as the plane accelerated. It was important for the pilot in the photo chase plane to fly in front of the shock wave created by the XB-70's nose--in undisturbed air. If he got behind the shock wave, his plane-with tip tanks installed in the tandem cockpit version--would not have enough engine power to "punch" back through the wave. Because this shock wave was conical and surrounded the supersonic XB-70, a chase aircraft's pilot flying in it felt its effects on the wing nearest to the XB-70. This disturbance caused his plane's nose to oscillate; the plane would get very "squirrelly." We had to fly many chase flights before we snapped that perfect "supersonic" photo. As we circled over the crash scene in the T-38, we watched the helicopter land and evacuate North American Aviation's chief test pilot, Al White. He had severe back and arm injuries, but was alive. Though he survived, Al never flew the XB-70 again.

The helicopter crew reported one unnamed fatality and we relayed the message to the Edwards Command Post. I later found out that the pilot killed was Maj. Carl C. Cross, a USAF bomber cargo test pilot on his first XB-70 flight as copilot. Carl was a quiet, unassuming type and had recently returned from a tour in Vietnam. Ironically, after a year of dodging ground fire in that war, he died in the skies over the Mojave Desert. His death was a tremendous loss.

Several months before that tragedy, I had flown as Carl's copilot in a Lockheed C-141 Starlifter performing "speedpower" performance tests. He had allowed me to make several touch and-go landings. As a fighter pilot, this was a huge thrill for me--a chance to fly the most modern and advanced USAF military transport. (Follow-on versions of the C-141 are still on active duty in the USAF more than 35 years later.)

Only two XB-70s were ever built. The second--and most advanced--model was the one involved in the accident. Following the crash, the remaining XB-70 was grounded pending the outcome of one of the most extensive investigations ever conducted at the Flight Test Center.

The final accident report stated that GE (as maker of the Valkyrie jet engines) had requested that publicity photographs be taken from a civilian Learjet, showing the Northrop F-5 Freedom Fighter, LTV F-8 Crusader, Northrop T-38 Talon and Lockheed F-104 Starfighter--all equipped with GE engines--flying with the XB-70 in formation.

That's when the XB-70 went down. The F-104, captained by Joe Walker--NASA's chief test pilot at Edwards--flying on the XB-70's right wing, had collided with the larger aircraft. The F-104 disintegrated after ripping off the XB-70's left vertical tail and half of the right one. Without a vertical tail to provide directional stability, the XB-70 fell into an uncontrollable spin. The planes' wreckage plainly showed what caused the accident. Why it happened has never been determined.

When two aircraft fly in wing formation, the airflow between their wings is disrupted. Their wingtip vortices are slightly modified, and this causes each wing to produce a small increase in lift. With two similar aircraft in formation, each pilot "holds a little aileron" into the other air craft. When the two aircraft have very disparate wing sizes and sweep angles, as is the case with the XB-70 and F-104, the smaller plane will be more affected. When you pass a truck in a car at high speed, you are buffeted by the larger vehicle's airflow. To maintain a straight course down the highway, your steering wheel must be turned toward the truck slightly. As you pull in front of the truck, to remain aligned with the road, you must return the steering wheel to its original position. A driver makes these corrections automatically. Pilots don't look at their control sticks any more than drivers look at their steering wheels. Maintaining a safe position requires continuous visual contact with other vehicles and smooth, quick adjustments of the steering wheel or, in the case of an aircraft, the control stick.

Joe Walker had been a NASA test pilot for 21 years and was a very experienced pilot. He had flown every experimental rocket aircraft from the early Bell X-1 to the North American X-15--this at 4,104mph and at a record altitude of 354,200 feet. He had logged thousands of hours in practically every jet aircraft produced in the United States; in fact, he was scheduled to be the next pilot to qualify in the XB-70. Evidently, Joe was distracted for a split second and drifted in too close to the XB-70's right wing; or perhaps, the strong wingtip vortices flowing off the XB-70 overpowered the small F-104. In any case, his aircraft disintegrated and his death was immediate.

The "black cloud" that shadowed Cecil's flights continued to darken the sky above the Mojave Desert. A couple of days after the accident, my friend Joe Basquez, a USAF military helicopter test pilot, was ferrying members of the accident board between the crash site and the Edwards flightline in a Bell UH-1 Huey. After landing on the ramp, he shut down the jet engine and started to walk away. A sudden gust of wind caused a rotor blade to arc down and strike his head; he was evacuated to the naval hospital in San Diego and never flew again.

Flying safety chase for the XB-70 Valkyrie was thrilling-never a dull moment. The challenge was to fly far enough away from it to maintain a safe position yet remain close enough to be of value to the test pilots. We always flew with great caution, never forgetting that we were swimming through a great sea of air with a creature named Cecil whose habits were not known and who could consume us in a flash, as he had my friends on that tragic day above the high Mojave Desert.

by Marrett, George J

George Marrett--"Valkyrie"  George is an associate fellow in the Society of Experimental Test Pilots. In 1964, he graduated from the USAF Test Pilot School, otherwise known as "Chuck Yeager's Charm School." He flight-tested the F-4, F-5, F-104 and F-111A at Edwards AFB, California. After 193 combat missions in Vietnam as a "Sandy" rescue pilot flying the A-1 Skyraider, he became a test pilot for Hughes Aircraft Co. in Culver City, California, where he flight-tested the USN F-14 and F-111B. Currently, he flies his tail wheel equipped, wooden-propeller 1945 Stinson L-5 Sentinel at 0.2 Mach with the Confederate Air Force.

 

 

 

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Last Updated

02/10/2014

 

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