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