Between the first and second world wars, aircraft development was moving apace in Europe. One of the many people pushing aircraft technology was Alexander Lippisch, the designer of the rocket powered Messerschmitt Me 163 Komet.
Lippisch proposed a triangular delta wing would reduce drag and increase lift, while its shape would make it inherently strong. At the end of WW2, Lippisch and a delta-wing glider fell in Allied hands and were transferred to the US.
Consolidated-Vultee, adapted Lippisch’s ideas into the XF-92A which took to the skies in 1948. The aircraft wasn’t the easiest to fly (later pilot by Scott Crossfield remarked “It was a miserable flying beast”). As a consequence the Consolidated civilian pilots expanded the aircraft’s envelope with painful slowness.
After a year the aircraft had only been taken to 0.85 Mach and the frustrated USAF took over flight test. Specifically, they handed it to Chuck Yeager.
Yeager agreed that the aircraft was tricky to fly, but he still pushed the aircraft to Mach 1.05 on his second flight.
More amazing were the landing characteristics. In Consolidated’s hands they had only brought the landing speed “down” to 170mph.
On that second flight Yeager decided he could do better. As he approach the Muroc lakebed he pulled back on the stick.The aircraft slowed so he pulled back further, bringing the nose up and gaining more lift from the wings. To his amazement he kept pulling back on the stick until he was at 45 degrees angle of attack, and landed at a mere 67mph – a full hundred miles an hour slower than Consolidated had achieved in a years development.
A 45 degree angle of attack means the aircraft was moving roughly horizontally through the air while the nose was pointing up by 45 degrees. At that angle he would have had no forward visibility and landed on his peripheral vision alone. Quite apart from the courage it must take to balance several tons of metal and fuel a few feet above the ground at such extremes, its got to take a massive amount of skill and experience to feel when the aircraft was at its limits and know when to stop using angle of attack to keep the aircraft airborne.
Consolidated-Vultee put out a promotional video, complete with a formal voiceover, describing the XF-92A’s benefits.
Those slippery characteristics that allowed Yeager to perform his landing feat were to catch another pilot out. After the aircraft was handed over to NACA, Scott Crossfield took the aircraft out on the Muroc lakebed for a taxi test. He’d been briefed on the aircraft’s tendency to roll a long way, but during the run he let the nose of the aircraft come down. The aircraft was now rolling on all three wheels, wings level, the minimum drag configuration. The aircraft kept rolling. He tried to bring up the power but couldn’t get the nose wheel up (and hence be able to use the drag from the wings for braking). The edge of the lakebed loomed. He had no choice but to use the wheel brakes, even though he knew he was going too fast. In his last few moments on the lake he spotted a country road and steered for it. In a cloud of dust, the aircraft bumped up the road a good hundred yards. When he came to a stop the brakes were gone, completely melted. Inevitably the road became know as the “Crossfield Pike.”
The XF-92A wasn’t loved, but it did prove the viability of delta wings. Today the US uses variations on the delta wing concept in aircraft such as the F-15 and F-22, but it is the Europeans who have gone back to Lippisch’s original idea with the current Dassault Rafale and the Eurofighter Typhoon.
The XF-92A has one last story up its sleeve, but I’m going to keep it there until next week 🙂