Too Much, Too Soon

  • By General Robert L. Cardenas, U.S. Air Force (Ret.) As told to James P. Busha
  • Air & Space magazine, July 2009
 
The YB-49 demonstrated that putting jet engines on an airframe designed for piston engines made the aircraft faster but not better. The YB-49 demonstrated that putting jet engines on an airframe designed for piston engines made the aircraft faster but not better.

NASM (SI Neg. #93-11863~A)

(Page 3 of 3)

General Boyd sent Major Russ Schleeh out to spot-check some of the flight data that Glenn and I had collected. After Russ made three flights in the Wing, he confirmed our data points and concurred with our thoughts on the YB-49. On a later flight attempt, the nose gear collapsed out on a Muroc lakebed, destroying the last of the test aircraft and almost killing Russ. That ended the program.

Robert Cardenas retired from the U.S. Air Force after 34 years of service.

A police detective lieutenant by day and an aviation writer by night, Jim Busha takes frequent breaks in his 1943 Aeronca L-3.

In 1941, When it appeared that Britain’s battle against Germany might fail, the U.S. Army Air Forces called for a bomber that could fly 10,000 miles with a 10,000-pound payload. Northrop responded with the XB-35 Flying Wing; Consolidated offered the XB-36 Peacemaker.

In 1947, my boss, Colonel Albert “Bullet” Boyd, chief of the Army Air Forces Flight Test Division at Wright Field in Ohio, sent Glenn Edwards, Danny Forbes, and me—“los tres amigos”—to the barren California wasteland known as Muroc Army Air Field, along with civilian flight test engineer Richard Smith. We shared Danny as copilot. We had all the fun of flying, and Dick Smith had all the work of reducing our collected data into readable form.

I was supposed to have flown the propeller-driven version of the Flying Wing, the XB-35. But I had told Colonel Boyd that any engineer who put a propeller on the trailing edge of a wing did not deserve his diploma. The air flowing over the top of the wing has a different temperature, velocity, and dynamic pressure than the air flowing under it, so those little propeller blades had to cut through two different air masses in microseconds, and the difference caused flutter.

The Army Air Forces decided the XB-35 needed jet engines, so Northrop converted two -35s to YB-49 all-jet Flying Wings. No. 42-102367 was instrumented for stability and control; no. 42-102368 was built for performance flight tests. In early 1948, my crew—copilot Danny and flight engineer William Cunningham—flew no. 368 from the Northrop factory in Hawthorne to Muroc to begin performance tests.

Early tests consisted of finding the best speed for takeoff, climb, stall, opening the bomb bay doors, and landing. Each test had its own set of problems—some minor, some that almost killed me. On my first takeoff, the airplane accelerated too rapidly, causing the gear doors to blow off. I could either pull the Flying Wing up at a high angle of attack on takeoff or pull back on the power and wait the 90 seconds for the gear to retract. The problem was that the jet-powered Wing was designed around the propeller-driven XB-35, which operated at slower speeds. Northrop had simply swapped prop engines for jets, and of course the speed of the aircraft increased.

After leveling off, I would be rocked back and forth in my seat in unison with the sloshing of the fuel that was stored behind me in a big rubber bag, with no baffles, buried in the wing. I tried opening the bomb bay doors—they were sucked right off.

Concerned about the upcoming stall tests, I consulted Paul Bikle, chief of the Flight Test Division’s performance engineering branch, who told me I would not get a clean stall with the YB-49—I’d get a wingtip stall. He said that unlike the airflow over a standard wing, air over the Flying Wing would be pushed sideways, or span-wise, and as the flow increased toward the tip, lift at the wingtip would rapidly decrease, causing the wing to pitch up. The split flaps were on the wingtips with the rudders, and he advised me that I might get a full wing stall if I were to trim the entire split flaps either up or down, rather than use the yoke.

Along with getting the Flying Wing to stall, I also got the ride of my life.

I leveled the YB-49 at 20,000 feet, pulled back on the throttles, and waited for it to stop flying. Because most of the shudder you get in a stall comes from the tail, not the wing, I knew I wouldn’t get a big shudder. Sure enough, when the tailless airplane quit flying, instead of the normal shudder just before the nose drops, I experienced a violent pitch forward into a negative-G tumble, which pulled my rear end out of the seat. In a microsecond, I realized that I had no aerodynamic flow over any control surface that would allow me to recover. It was as if you took a nice, crisp, clean dollar bill out and let it go; it would go spinning around its center. The engineers later called it a lateral roll and said I had encountered inertial coupling.

Fortunately, the throttles were mounted up above my head, not down on the console where they normally are. There were two handles, one for the four left engines and one for the four right, just an arm’s length away. I was able to grab the left throttle and apply full power, which caused the aircraft to cartwheel. I was thrown into an inverted spin—one thing I knew how to get out of. I recovered at about 800 feet. After I landed, I wrote a brief report: “This aircraft is never to be intentionally stalled.” Later that night, I went to Pancho’s Happy Bottom Riding Club for a drink.

On June 5, 1948, Glenn Edwards and Danny Forbes were killed at Muroc while flying YB-49 no. 368. It hit the ground upside down, so flat it didn’t have much of a sideways motion. The wing areas outboard of the engines were found 15 miles downstream. Colonel Boyd told me to finish the tests in the other airplane.

In the fall of 1948, I flew no. 367 in a series of stability and control tests. The YB-49 was beautiful—it was just like flying a fighter. But it was not a bomber, and it had many deficiencies: The biggest problem was that it was way ahead of its time, well before the advent of computers. The sensory and response capabilities of a human were too slow to keep up with the Flying Wing’s ever-changing dynamics. I’ve been accused of saying the YB-49 was unstable, but what I actually said was that it was marginally stable about all three axes and could go unstable at aft-center-of-gravity loadings. That’s why I would not sign off on the airplane. The YB-49 would have to wait for technology to catch up.

In November 1948, I briefed Air Force generals about my concerns. In the audience was Jack Northrop. After I spoke, he stood and said, “I have the highest regard for Major Cardenas and his abilities as a test pilot. Obviously I have not been kept informed.” He looked at the people he brought with him. “It looks like Northrop has a lot of work to do,” he said. An engineer in the audience said, “You have an impossible task,” to which Mr. Northrop replied, “General, I’m surprised you have people in your employ who think the impossible really is impossible.” That sort of broke up the hearing.

On February 9, 1949, I was ordered to fly the YB-49 to Andrews Air Force Base, near Washington, D.C., for President Harry Truman’s air power demonstration. We flew nonstop to Andrews in four hours and 20 minutes, setting a transcontinental speed record. President Truman inspected the Flying Wing and even climbed up in the cockpit. While I was showing him the interior, he turned to me and said, “Looks pretty good to me, son. I think I’m going to buy some.” I bit my tongue and just smiled. The president asked the chief of the Air Force, “Why don’t you have this young whippersnapper fly this down Pennsylvania Avenue at treetop level? I want the people to see what I’m going to buy.” I knew my boss was never going to order me to fly a huge experimental aircraft at treetop level over the heart of the nation’s capital.

Well, he did.

As I dodged radio towers, I lost track of Pennsylvania Avenue along the way. I never realized how heavily forested Washington was. All the trees made it very hard to see straight ahead  as I roared low over the city. Toward the end of my flight I thought I was in the clear—until the big white dome of the Capitol filled my canopy. I abruptly pulled up to avoid smashing into it.

General Boyd sent Major Russ Schleeh out to spot-check some of the flight data that Glenn and I had collected. After Russ made three flights in the Wing, he confirmed our data points and concurred with our thoughts on the YB-49. On a later flight attempt, the nose gear collapsed out on a Muroc lakebed, destroying the last of the test aircraft and almost killing Russ. That ended the program.

Robert Cardenas retired from the U.S. Air Force after 34 years of service.

A police detective lieutenant by day and an aviation writer by night, Jim Busha takes frequent breaks in his 1943 Aeronca L-3.


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Comments (3)

Brigadier General Robert is a genuine "WORLD CLASS LEADER" and an inspriratinal example for those of us who aspire to study and understand the integral qualities of leadership
essential to all levels of global society during this 21st
century of unrelenting challenge.

Perhaps, the most appropriate descriptive definition of the quality of leadership which makes General Cardenas unique in a field of many is this, "DOING THE RIGHT THING, AT THE RIGHT TIME, FOR THE RIGHT REASON."

General Cardenas, this salute is for you.

Most respectfully,

Hobert Robbins

USAF Veteran

Posted by Hobert Robbins on January 12,2010 | 05:30 PM

It has always appeared to me that there were two problems with Northrop's flying wing, or any pure flying wing for that matter. These were that it did not have enough sweepback -- for added stability. And the second is that it did not have a centric 'nacelle' big enough to carry all of the payload the wing was capable of lifting. The 'nacelle' would also have had to have some vertical and horizontal lifting surfaces at its rear for added stabilization that would have been required with the 'nacelle'. You could then call this modified flying wing a typical airplane.
Or flatten the 'nacelle' so that it will work like the blended-wing-body (BWB) which does a good job of putting a wing-like body to work to not only carry the payload, but also to do much of the lifting.
The Northrop B-2 bomber seems to have incorporarted both features - larger sweepback and BWB.

Posted by John Tomassoni on June 23,2011 | 05:48 PM

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