THE ORIGINAL LOCKHEED ELECTRA begat a line of characteristically twin-tailed commercial transports. The first of these was the Model 12, followed by the Model 14 and an advanced experimental model—one of a kind—the XC-35, which won for the U.S. Army Air Corps the Collier Trophy for pioneering high-altitude flight. The Model 14 led to Lockheed’s first airplane for World War II.
The Electra became a very successful airplane—with the airlines, military, and private customers.
It was comfortable, carrying five persons on each side of the aisle, and had a roomy cockpit for pilot and copilot. It was the first airplane with an all-metal surface to go into production in the United States. And it was fast—190 miles an hour cruising speed.
The first derivative was a smaller version, Electra Jr., or the Model 12, for customers who didn’t need or couldn’t afford the Model 10’s capacity and performance. It carried only six passengers, was somewhat faster at 206 miles-an-hour cruising speed, and, at $40,000, cost $10,000 less. Introduced in 1934, it set a number of new world speed marks for transports. Production didn’t halt until 1942, and then only because facilities were needed for military projects.
Next came the Model 14 Super Electra—and it was. It had the latest advances in everything to do with aircraft design and manufacture. When it first flew in 1937, it was the fastest, at 237 miles an hour cruising speed, 257 top speed, of any commercial transport in the United States. It beat the DC-3’s flying time from Los Angeles to New York City by four hours.
It used the newest Wright Cyclone engines, the newest and strongest aluminum alloy then available, a new Plexiglass for windows. And it had two totally new innovations: the Lockheed-Fowler flap which significantly increased wing area for takeoff and landing, and to direct airflow, “letterbox slots,” so-called because that’s what they resembled.
The third Electra derivative was developed in secrecy for the U.S. Army Air Corps. The XC-35 was the world’s first successful pressurized substratospheric plane.
Wiley Post’s work in 1935, with his pressure suit and supercharged engine, had proved that man and machine could operate above 30,000 feet.
That next year, the Army Air Corps gave Lockheed a contract to modify an Electra cabin to hold air pressure—a 10-pound-per-square-inch differential between inside and outside. The extra weight required to strengthen the cabin was 1,486 pounds. The XC-35 flew and was delivered to the Air Corps in 1937, and won the Collier Trophy for having made the most valuable contribution to aircraft development during that year.
My own experiences with high-altitude flight began with Wiley Post, but another involvement during Electra flight testing with our chief test pilot, Marshall Headle, led me to direct my attention very early to this field. We needed to demonstrate to the Brazilian government that the airplane it had purchased could climb to an altitude of 23,000 feet. And they wanted proof, not just the word of a flight test engineer or pilot. They required that we fly to that altitude with a sealed barograph, an instrument that automatically records barometric pressure.
At that time, the prevailing opinion was that you should not breathe any more oxygen than necessary at altitude because of the threat of oxygen poisoning. And, of course, all we had to breathe with was a cigarette holder connected to an oxygen line. It took us three flights before we reached the altitude requirement. We’d climb and climb and not make it. Finally we changed airspeeds and some other factors and managed to reach the desired altitude.
But when we landed, I felt so ill that someone had to drive me home. I literally fell onto the bed and practically had to hold on to keep from falling off. I was really, really sick. It was a frightening experience, and sparked my continuing interest in oxygen systems, pressure suits, and pressure cabins from that day to this. I’ve had ample opportunity since, in the light of later developments, to respect those early pioneering tests of Wiley and others.
Some of our other test equipment in those days was as primitive as that cigarette-holder oxygen system. But it worked. To determine the drag of the tail wheel in flight tests on the Model 12A, I rigged a standard fish-market scale to the wheel and strut—just in front. The drag force would register on the scale by causing the arm to move. In this case, it showed that the drag was not important enough that we need make the gear retractable.
The first flight of the Model 14 was one I won’t forget. Marshall Headle was pilot and I was flight engineer, having worked on design of the new wing flaps and a good deal of the rest of the airplane. It was an important flight. No one had been able to put the Fowler flaps on a commercial airplane successfully. They weren’t the usual wing flap that was lowered to act as an air brake. They slid backward out of the wing and added effectively to wing area, allowing a large wing for landing and takeoff control and a small wing for speed in flight.
Lockheed didn’t yet have its own wind tunnel, but I had run a great many tests at California Institute of Technology (Cal Tech) in Pasadena, where Lockheed and six other aeronautical companies would rent tunnel time. I had set the design conditions for installation of the flaps in the airplane and was confident that I knew something about it.
We took off from the old runway behind the factory, and when we got to altitude and started to lower the flaps for the first time to test their operation, there was a “bang.” The flaps went all the way down and we couldn’t raise them. We had lost hydraulic pressure in the system—not a serious defect but critical at the moment. We experimented with different approaches to getting the airplane back on the ground and discovered that the slower we flew the more the flaps came up. Not too healthy a situation for a landing—at least, not with the limited runway length we had.
But I happened to recall, fortunately, that at about a 20 percent flap setting there was a bend in the flap tracks that would stop the flaps. So we went on in for a landing with flaps free; and as we slowed and they came to that 20 percent setting, they held that position and we landed safely. Most of our Lockheed aircraft now have triple or quadruple redundancy in hydraulic as well as other key systems.
At the time of the Model 14 flight test program, I still hadn’t learned my lesson about not taking on more than I was authorized to do. We had a lot of work to complete and I wanted to get on with it. On one Sunday when our chief pilot Headle wasn’t available, I prevailed on another pilot, “Mac” McCloud, to fly the plane while I went along as flight engineer. He was a licensed pilot but hadn’t been checked out in that airplane by a qualified pilot.
I had no license to fly the airplane, but I knew very well how to fly it since I’d been on every flight from the first. I gave him takeoff speeds, direction on handling the flaps, and power settings for the engines. If all had gone well, no one would have known about our unofficial status.
The flight itself went off just fine. I gave directions for landing—hold up the tail, put the nose gear down first, then let the tail settle. The landing also was fine until we got about 800 to 1,000 feet down the runway. The airplane suddenly yawed to the right and ended up going sideways. I looked out my side of the cockpit and there, sticking up through the right wing was the main landing gear strut! Migawd, I thought, here I’ve taken an airplane, checked out a pilot illegally, and wrecked the plane. There goes my job.
But when the inspectors checked they found that, instead of six bolts holding the landing gear, only three had been installed when it was signed off by inspection. McCloud and I were in the clear.
A very, very serious danger in those days was icing, because few airplanes could provide enough heated air for the carburetor to prevent ice formation in it. And with ice in the carburetor, the engines would lose so much power that you were in real trouble even if they didn’t die completely.
For the first time, with the Model 14 we had available a carburetor designed to correct that—the Chandler-Evans non-icing carburetor. We decided to incorporate it in the airplane. Fortunately, we didn’t rely on it solely.
One of the tests that had to be passed before the aircraft could be certificated with this modification by the CAA—now the Federal Aviation Administration—was performance in icing conditions. The local CAA inspector, Lester Holoubek, was aboard to see how the new carburetor operated on one flight out of Mines Field. We had to fly up through about 3,000 feet of heavy undercast and had just broken clear for another 1,000 feet when the left engine gave a few hiccups and quit. It wasn’t long before the right engine slowed and gave every evidence that it would follow suit.
It was a scary situation, especially since we couldn’t see the airport and knew that we had 3,000 feet of icy clouds to drop through on the way down—with the CAA inspector aboard. But we had not relied totally on the new carburetor and had provided for alcohol injection, too. We turned on a small, hand-operated pump and quickly dissolved the ice before we had descended below 1,500 feet. The engines operated again and we were able to maneuver down out of the overcast and land. We found we not only had a problem with the non-icing carburetor but with the CAA inspector, who decided—quite rightly—that if we were going to fly with that carburetor, we had to prove it with a lot more flying in icing conditions.
The problem was compounded when about that time one of Northwest Airlines’s Model 14s, flying between Seattle and Minneapolis-St. Paul in icing conditions, crashed near Bozeman, Mont. The cause of the crash, of course, wasn’t immediately known. I was on the investigating team and joined in inspecting the wreckage.
It was apparent immediately that the two vertical tails were not on the airplane—they were just gone. Absence of the tails, of course, would lead the airplane into a very unstable flight regime and inevitable crash. Heavy snow was on the ground and we accepted the offer of the Bozeman ski club to hunt for the missing tail pieces. I even joined the search on skis one time—profiting by my boyhood experience in the winters of northern Michigan.
When the tail was found and brought to the accident investigation center, the rudder was missing completely. Just the control to the rudder tab was hanging there, with nothing behind the hingeline.
The regulatory agencies immediately imposed requirements for lead balances on both vertical tails above and below the horizontal stabilizer as well as some other specific changes.
But I wondered if we weren’t overlooking something. I had seen the tab control, the ball bearing that is supposed to keep the tab in proper position as the rudder turns left or right. The bearing had been broken and there were no balls in it. The whole center race—the track the ball bearings ride in—was gone. And so was the tab—the movable trailing edge of the tail rudder.
Back at the plant, I convinced Hibbard and others that we should run a tunnel test on a full-scale vertical tail and find out what conditions would cause flutter. We built our own wind tunnel in 1939, the first sophisticated one in private industry. But at that time we were able to use the Guggenheim wind tunnel at Cal Tech under the distinguished Dr. Theodore von Kármán and Dr. Clark B. Millikan. The test section was a cylinder ten feet in diameter, obviously a very difficult space in which to work when changing models, but the tunnel had enough capability to exceed by far the speed at which the Northwest aircraft was cruising when it was lost.
That tail wouldn’t flutter in the wind tunnel no matter what we did. But then we disconnected the tab, simulating the broken bearing, and immediately the rudder blew off the tail assembly. We went ahead with the lead balances decreed by the CAA; but the real cause of the accident in my opinion was that someone, a mechanic on the production line or in the airline’s overhaul shops had not held the bearing properly when he adjusted the tab setting and had cracked the race but not broken it completely. The break occurred later in rough air and caused immediate violent flutter. I had never seen such violent flutter as with the simulated condition in our wind tunnel.
We still had to conduct 50 hours of flying in icing and rough weather to satisfy CAA conditions. And it had to be in the same air corridor where the plane had been lost. So Headle, Holoubek, and I headed for Minnesota. We stayed on the ground when the weather was nice and everyone else was flying, and took off in the worst of it.
We would fly into the roughest air we could find to prove stability of the aircraft, and in the worst icing conditions to prove the new non-icing carburetor. We’d have two to four inches of ice on other parts of the airplane, but the engines kept running. On one of our most exciting flights, we collected so much ice in just four minutes that with both engines on full power our indicated airspeed was just 90 miles an hour. And we landed with full power on.
I was so impressed with the rapidity with which ice can build up and its severe effect on aerodynamics and control that I was prompted to write one of my first technical papers on the subject for the benefit of others. (“Wing Loading, Icing and Associated Aspects of Modern Transport Design,” Journal of the Aeronautical Sciences, December 1940). To this day, the only thing I fear more than ice is hail. A separate icing wind tunnel later was built as another research facility at Lockheed. Pilots who haven’t experienced it do not realize that it takes damned little ice to cause a horrible crash.
Another little detail we had to prove was that the control cables would not go so slack because of the low temperatures that they would allow flutter under certain conditions. To do this we had to measure elevator cable tension, and the only place to reach the cable was by removing the toilet and reaching down through that space to attach a tensiometer. This was Holoubek’s job as inspector. One day while he was checking this instrumentation, we hit a particularly severe bump. I still can see his feet sticking up through the opening as he yelled for help to get out of there.
The Model 14 had so much power with those new Wright-Cyclone engines that this actually produced a problem. With so much of the inboard wing in the propeller slip stream, it was almost impossible with power on in flight to stall the middle of the wing. So the wing, if it stalled, would stall—that is, lose lift—on the outboard end near the aileron, the trailing edge flap used for lateral control. This was not good, especially if one wing tip stalled before the other. It would cause the plane to roll badly.
All sorts of corrections were considered, including change of the wing shape itself, to control local stall characteristics. In the wind tunnel, we put hundreds of tufts of yarn on the wing so that we could watch stall patterns develop in simulated flight. When would air flow separate and under what conditions? It wasn’t the first time we had used yarn to observe air flow, but it certainly was the most complete such test we ever had conducted.
And for the first time we had an AO, automatic observer. A complete set of instruments was connected to the airplane’s systems. One camera would show the time and all flight conditions—airspeed, altitude, rate of roll—28 different recordings. This was synchronized with two other cameras that took pictures of the left and right wings when a stall developed.
That test program probably was the most thorough for specific aircraft performance characteristics undertaken to that time. And then in flight I joined the pilots in making 550 stalls and falling all over the sky in the San Fernando Valley for several months. It was an interesting way to make a living.
But it was not possible then to make these tests in the wind tunnel because we could not simulate the slip-stream effect of the propellers. When the electric motor models were scaled down to fit into the proper-scale engine nacelle they simply could not produce enough power for a realistic test. We had no choice but to fly.
The result of this work was the “letter-box” modification already mentioned. A venturi-like opening at the bottom of the wing narrowed as it carried air through the wing, so that it was released over the top surface at much higher speed than normal at that point on the wing. And it was fresh air, not tired of flowing over half the wing. It was able to do this at angles of attack much more successfully than could any wing section alone. There were at the time other retractable wing slots—notably by De Haviland—but we found the complexity and maintenance problems not tolerable.
What we did was based on the Coanda effect, named for the French engineer who discovered that if he blew air on a curved surface, the flow did not separate from it but tended to remain stable on that surface. The principle is used routinely now in boundary-layer control.
These were good times for me personally. In 1938, I became chief research engineer for Lockheed.
When Lockheed’s engineering department began to expand I recruited some of the students I knew from the University of Michigan. Willis Hawkins was first; I had corrected his papers for Professor Stalker and knew his scholastic ability. Rudy Thoren and John Margwarth followed. Carl Haddon, who had been a year ahead of me in college, joined us.
It was almost like a university club. And then in night classes at Cal Tech I met another group of young engineers. Phil Colman was recruited there. With Irv Culver and E. O. Richter, these were the stalwarts I started with as chief research engineer.
The work on the “Lockheed-Fowler Flap” brought me my first major award as an engineer, the Lawrence Sperry Award for “important improvements of aeronautical design of high speed commercial aircraft”, in 1937.
The two major developments arising out of the Model 14 design, the Lockheed-Fowler flaps and the “letter-box” slots—both of which give the airplane excellent handling characteristics—were to become especially important in light of the unexpected role this airplane was to play in history.