In 1934, with financial support from
Frank Phillips of the
Phillips Petroleum Company, Post began exploring the limits of high-altitude long-distance flight. The
Winnie Mae's cabin could not be pressurized, so he worked with Russell S. Colley of the
B.F. Goodrich Company to develop what became the world's first practical
pressure suit. Three pressure suits were fabricated for Post. Only the final version was successful. The first suit ruptured during a pressure test. The redesigned second suit used the same helmet as the first but when tested was too tight. They were unable to remove it from Post, so they had to cut him out, destroying the suit. The third suit was redesigned from the previous two. The body of the suit had three layers: long underwear, an inner black rubber air pressure bladder, and an outer layer made of rubberized parachute fabric. The outer layer was glued to a frame with arm and leg joints that allowed him to operate the flight controls and to walk to and from the aircraft. Attached to the frame were pigskin gloves, rubber boots, and an aluminum-and-plastic diver's helmet. The helmet had a removable faceplate that could be sealed at a height of , and could accommodate
earphones and a
throat microphone. The helmet was cylinder-shaped with a circular window. In the first flight using the suit on September 5, 1934, Post reached an altitude of above Chicago. Eventually flying as high as , he discovered the
jet stream and made the first major practical advances in pressurized flight. As of 2022, the suit is on display.
Attempted high altitude non-stop transcontinental flights flown by Post on all four of his attempts to make the first high altitude non-stop transcontinental flight from Los Angeles to New York, February–June 1935 Between February 22 and June 15, 1935, Post made four unsuccessful attempts to complete the first high altitude non-stop flight from Los Angeles to New York, all of which failed for various mechanical reasons. The first attempt on February 22 ended 57.5 miles north of Los Angeles at Muroc Field, CA (Now
Edwards AFB). This was followed by attempts on March 15 (Cleveland, Ohio; 2,035 miles), April 14 (Lafayette, Indiana; 1,760 miles), and June 15 (Wichita, KS; 1,188 miles). As the attempts were meant to be the "First Air Mail Stratosphere Flight" over U.S. Air Mail Route #2 (AM-2) from Los Angeles to New York, Post carried a quantity of "cacheted"
covers sponsored by
Transcontinental & Western Air, Inc on all four flights. When he was killed on August 15, 1935, ending the possibility of any more attempts to complete the AM-2 stratosphere flight, the covers were cancelled in Los Angeles on August 20, 1935, and forwarded to their addressees. ==Final flight and death==