The comfort, we all enjoy now, of a pressurized cabin is a feature of modern aircraft that few people think about or realize how it all came about. Today, however, we will talk about how it happened, who made it happen, and which manufacturer brought this innovation to the flying public.
As early as the 1700’s, scientists were hypothesizing that the air around them was not just empty space, but filled with a fluid-like substance with volume and mass. Two centuries and many scientific advances later, Léon Teisserenc de Bort, a French meteorologist, and aerologist, discovered the existence of two of the atmospheric layers, and named them……we now know those two layers as the stratosphere and the troposphere. So, how did we decide that pressurization could work?
The concept of a pressurized cabin has existed in the aviation imagination as early as the 1910s when early aviators started making improvements to their aircraft designs that would allow them to climb ever higher. Within just two years, between 1910 and 1912, the world altitude record for fixed-wing aircraft spiked from 4,603’ in a Wright biplane to a then-unprecedented 18,405 feet by Roland Garros in a Blériot monoplane.
In 1934, Wiley Post created and demonstrated the first pressurized suit. The full-pressure suit allowed him to fly at altitudes as high as 40,000 feet comfortably. However, forcing pilots and airline passengers to wear bulky suits to travel onboard an airplane was not an alternative, and so the search for an alternative solution to the dangers of thin air continued.
In 1935, the United States Army Air Corps (the predecessor of the US Air Force) contacted Lockheed Aircraft Corporation to request an experimental aircraft capable of extended flights above 25,000’, with a ten-hour flight endurance, for a grand total of $112,197. Two structural engineers at the Air Corps Engineering Division at Wright Field, Major Carl Greene, and John Younger, were the brains responsible for the birth of the pressurized cabin.
To begin their journey to a pressurized cabin, the men and their teams, modified a Lockheed Model 10 Electra, a twin-engine all metal military monoplane which would soon gain fame as Amelia Earhart’s plane flown on her attempted ‘round-the-world expedition in 1937. The Electra was fitted with a circular cross-section fuselage that could withstand up to 10psi of atmospheric pressure, small, thick windows that wouldn’t blow out dealing with high-pressure differentials, and two turbo supercharged Pratt & Whitney XR-1340-43 engines with 550 horsepower each.
The fuselage was separated into two sections; a forward pressurized compartment that could hold two pilots, a flight engineer, and even a couple of passengers, and an aft compartment (not pressurized) that provided additional accommodation at lower altitudes.
The cabin pressurization system created by Major Green and Younger paved the way for the system most airliners still use today. The cabin was pressurized using air rerouted from the engine’s turbo supercharger, which was then pushed through a compressor outlet, controlled manually in-flight by the onboard engineer. All this provided the flight crew and passengers with a cabin altitude of about 12,000 feet, which was outstanding for the time.
After these extensive modifications the Electra was transformed into the XC-35 and after flight-testing at the Lockheed plant in Burbank, CA, the plane was delivered to Wright Field in Ohio to complete its first performance flight.
The Lockheed XC-35 met and exceeded each expectation placed in front of it, earning the Army Air Corps the Collier Trophy. The presentation of this award is an annual aviation event, administered by the US National Aeronautic Association, and awarded to those who have made the greatest achievement in aeronautics, or astronautics, in America. This award takes in to consideration, the improving the performance, efficiency, and safety of air or space vehicles, the value of which has been thoroughly demonstrated by actual use during the preceding year.
With this award and the confidence that goes with it, the Army Air Corps allowed the XC-35 to become the executive transport of Louis Johnson, the assistant secretary of war at the time, and future Secretary of Defense. Nowadays, the Lockheed XC-35 is hidden away in the Smithsonian and the engineering feat this airplane represents has long been forgotten.
Now, let’s talk about the manufacturer, Boeing, that first brought pressurized flight to the flying public.
It was introduced 75 years ago, and only 10 were built. Hollywood movie producer and aviation pioneer Howard Hughes bought one of them. But Boeing’s Stratoliner changed commercial aviation.
For the first time, passengers could “fly above the weather” at high altitudes because of the airplane’s pressurized cabin. The Stratoliner, the world’s first pressurized commercial airplane, was born in the 1930s, during a time of rapid evolution in the science and technology of flight, beginning with dramatic advancements in aircraft structures. Wood and fabric gave way to metal, monoplanes replaced biplanes and, before the decade was out, another great innovation would revolutionize flight—cabin pressurization.
Throughout the 1930s, pressurization experiments were taking place in Europe as well as the United States, where the U.S. Army was testing cabin pressurization with a modified Lockheed Electra designated XC-45. Boeing researchers were also experimenting with the technology and made it workable with the innovation of a cabin pressure regulator.
In 1932, Boeing had introduced the fast, all-metal Model 247, considered the first modern commercial airliner. It was a leap ahead of the competition, but its success was brief, as Douglas Aircraft quickly developed a challenger with the DC-2 and followed with the legendary DC-3. Faced with being shut out of the commercial airplane market, Boeing had to design the next leap in air travel.
Fortunately, Boeing had already developed the Model 299, a giant four-engine bomber that would become the B-17 Flying Fortress. The successful design of the B-17 became the basis for a new commercial airplane that would be that great leap: the Model 307.The new airplane combined the wings and tail surfaces from the B-17 with a cigar-shaped fuselage purposely designed to be a pressure vessel. Not only would its size, four engines, and long range be a market advantage, but the addition of cabin pressurization would allow Boeing to market an airplane that could fly passengers higher than 20,000 feet (6,100 meters)—“above the weather.” To reflect this capability Boeing named the Model 307 the Stratoliner.
Orders for the plane came in from Pan American Airways and TWA. Hughes also ordered a Stratoliner for his attempt at a world speed record. On New Year’s Eve in 1938, the Stratoliner prototype took off from Boeing Field near Seattle on its inaugural flight. Tragically, that prototype and a crew of 10 would later be lost in an airline demonstration flight.
But the Stratoliner’s success was short-lived. With the outbreak of war, Boeing turned to a maximum effort to build bombers and ended production after just 10 airplanes. During the war, Stratoliners were drafted into military service and made thousands of accident-free crossings of the Atlantic serving as VIP transports.
Only two Stratoliners remain: Howard Hughes’ personal Stratoliner is now a houseboat and continues to be a popular attraction in Florida; the last flyable 307, Pan Am’s Clipper Flying Cloud, was fully restored by Boeing and delivered in August 2003 to the National Air and Space Museum, where it is on display at the Stephen F. Udvar-Hazy Center in Chantilly, Va.
Take care, be safe, and enjoy the video below; however, more importantly, please remember that life on planet earth is short and tomorrow my life, and yours, is one day shorter……keep family and friends close.
December 2, 2022