normal flight. When Col. Cass Hough later reported exceeding Mach 1 in a dive over England, we knew that would have been impossible. The P-38 just could not have withstood that; it had to be an inaccurate airspeed reading because of instrument lag in the rapid change in altitude—speed of sound, of course, being different at different altitudes.
Several pilots were lost in the early days of testing. The aircraft would pitch nose down in an uncontrollable dive from which they could not always recover. It would happen at about Mach .67 to .80, building up rapidly once started. We tried all the usual methods to improve the elevators and made them so powerful that they pulled the tail off; our test pilot Ralph Virden crashed to his death.
Lockheed test pilot Marshall Headle, taking up the first of an initial production model, the YP-38, had proclaimed it the “easiest” plane he ever flew. The counter-rotating propellers produced no torque, or one-sided pull. But other test pilots—including Lockheed’s Milo Burcham and Tony LeVier—encountered the compressibility phenomenon. “A giant … hand … sometimes shook it (the plane) out of the pilot’s control,” was how LeVier described it.
We had to find the solution in the wind tunnel; the aircraft was just too dangerous to fly.
Meeting with a committee at Wright Field in Dayton, I pleaded with NACA to let us put a model in its wind tunnel sothat we could measure what forces were at work because there had been no high-speed tests of fighter or any other aircraft at that time. Our own tunnel could not achieve the required high speeds above 300 mph. NACA officials protested that every time they had approached such speeds in the tunnel, the model had thrashed around so violently they feared it would cause damage to their tunnel, a risk they did not want to take.
With a model of the P-38—one of the United States’ most deadly fighter aircraft of the World War II era—engineers W. A. “Dick” Pulver, Johnson, Hall Hibbard, Joe Johnson, and James Gerschler .
Lieutenant Kelsey went to Gen. H. H. “Hap” Arnold, then head of Army Air Forces, with the problem.
NACA got the message from the General.
“Put that airplane in the tunnel and run this test for Kelly.
Find out what’s wrong with my airplane. To hell with the tunnel. If it blows up, call me,” was the gist of it.
We proved that the problem wasn’t flutter, and we began to make some progress on a scientific approach to handling compressibility.
Although never solving the problem of compressibility, welearned how to avoid it. In the NACA tunnel, we learned about pressure distribution on the wings, how effective was the tail, and what was causing the compressibility effect that pitched the nose down and resulted in such extreme buffeting.
On returning to Burbank, we decided that if we could not solve compressibility, we could discover a way to slow the airplane to a speed where the effect no longer was a factor. The answer was external dive flaps, or brakes. Put in the right place, they would cause the nose to come up out of a dive and stop buffeting. That right place was on the front wing spar. It also changed the pressure distribution on the wing’s lower front so that the diving force was thoroughly counteracted.
It worked so well that if a pilot extended this flap and just let the wheel alone the airplane would pull itself out of a dive.
There were those who didn’t agree that we should go to this expense and effort during a war. The airplane had been in service for some time before we confronted compressibility. Kelsey was one of the doubters.
“Let me fly that one with the compressibility flap on it, Kelly,” he said on a visit to the plant. “I want to see what there is to this thing.”
Kelsey certainly knew the XP-38. Shortly after its first flight he had flown it across country to Mitchell Field, Long Island—with stops at Amarillo and Dayton—at 420 miles an hour in seven
Several pilots were lost in the early days of testing. The aircraft would pitch nose down in an uncontrollable dive from which they could not always recover. It would happen at about Mach .67 to .80, building up rapidly once started. We tried all the usual methods to improve the elevators and made them so powerful that they pulled the tail off; our test pilot Ralph Virden crashed to his death.
Lockheed test pilot Marshall Headle, taking up the first of an initial production model, the YP-38, had proclaimed it the “easiest” plane he ever flew. The counter-rotating propellers produced no torque, or one-sided pull. But other test pilots—including Lockheed’s Milo Burcham and Tony LeVier—encountered the compressibility phenomenon. “A giant … hand … sometimes shook it (the plane) out of the pilot’s control,” was how LeVier described it.
We had to find the solution in the wind tunnel; the aircraft was just too dangerous to fly.
Meeting with a committee at Wright Field in Dayton, I pleaded with NACA to let us put a model in its wind tunnel sothat we could measure what forces were at work because there had been no high-speed tests of fighter or any other aircraft at that time. Our own tunnel could not achieve the required high speeds above 300 mph. NACA officials protested that every time they had approached such speeds in the tunnel, the model had thrashed around so violently they feared it would cause damage to their tunnel, a risk they did not want to take.
With a model of the P-38—one of the United States’ most deadly fighter aircraft of the World War II era—engineers W. A. “Dick” Pulver, Johnson, Hall Hibbard, Joe Johnson, and James Gerschler .
Lieutenant Kelsey went to Gen. H. H. “Hap” Arnold, then head of Army Air Forces, with the problem.
NACA got the message from the General.
“Put that airplane in the tunnel and run this test for Kelly.
Find out what’s wrong with my airplane. To hell with the tunnel. If it blows up, call me,” was the gist of it.
We proved that the problem wasn’t flutter, and we began to make some progress on a scientific approach to handling compressibility.
Although never solving the problem of compressibility, welearned how to avoid it. In the NACA tunnel, we learned about pressure distribution on the wings, how effective was the tail, and what was causing the compressibility effect that pitched the nose down and resulted in such extreme buffeting.
On returning to Burbank, we decided that if we could not solve compressibility, we could discover a way to slow the airplane to a speed where the effect no longer was a factor. The answer was external dive flaps, or brakes. Put in the right place, they would cause the nose to come up out of a dive and stop buffeting. That right place was on the front wing spar. It also changed the pressure distribution on the wing’s lower front so that the diving force was thoroughly counteracted.
It worked so well that if a pilot extended this flap and just let the wheel alone the airplane would pull itself out of a dive.
There were those who didn’t agree that we should go to this expense and effort during a war. The airplane had been in service for some time before we confronted compressibility. Kelsey was one of the doubters.
“Let me fly that one with the compressibility flap on it, Kelly,” he said on a visit to the plant. “I want to see what there is to this thing.”
Kelsey certainly knew the XP-38. Shortly after its first flight he had flown it across country to Mitchell Field, Long Island—with stops at Amarillo and Dayton—at 420 miles an hour in seven
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