Here is a fact that sounds invented: to bail out of the Douglas XB-42 Mixmaster, you first had to blow your own propellers off. The two blades spinning behind the tail would have shredded anyone who jumped, so Douglas wired the tailcone with explosives to fling the props clear before a crew took to their parachutes. That single detail tells you everything about how far this airplane bent the rules.

The idea started as a private venture. Douglas pitched an unsolicited proposal in 1943, promising a small bomber with the range of a B-29 Superfortress but a fraction of the size and cost. The trick was to strip drag out of the airframe entirely. Instead of hanging engines off the wings, Douglas buried a pair of Allison V-1710 liquid-cooled V-12s inside the fuselage, right behind the crew.

Long drive shafts ran aft to a set of contra-rotating propellers mounted at the very tail. Air came in through slots in the wing leading edge, which left the wing and fuselage almost perfectly clean. When the first prototype flew on 6 May 1944, it delivered on the promise: roughly as fast as a de Havilland Mosquito, but with defensive guns and, over short distances, twice the bombload.

Clever, and slightly dangerous

The buried-engine layout solved one problem and created several. That elegant cruciform tail put a ventral fin underneath the fuselage, tipped with a small tailwheel to keep the coaxial props from scraping the runway. Ground clearance was tight enough that taxiing, takeoff, and landing all demanded careful hands.

In the air, the Mixmaster was fast but fidgety. Test flying turned up excessive yaw, propeller vibration, and poor engine cooling — the sort of teething troubles that were probably fixable given time. And then there was the propeller-jettison system, that grim reminder that a pusher layout hides a guillotine at the back of the plane.

None of these were disqualifying on their own. But the calendar was working against Douglas. The war in Europe was ending, the jet engine had arrived, and the Army suddenly had the luxury of time. Rather than nurse a piston oddity toward production, its leaders decided to wait for a new generation of jet bombers.

The record run and the crash

Before the program wound down, the Mixmaster made its mark. In December 1945 the second prototype flew from Long Beach, California, to Washington, D.C., covering roughly 2,300 miles in 5 hours and 17 minutes for a transcontinental speed record of 433.6 mph. For a piston bomber in 1945, that was electric.

That same record-setting airframe was lost days later. On a routine flight it suffered a landing-gear problem, then lost one engine, and finally the other as coolant temperatures climbed. The crew bailed out and survived — but only after triggering the propeller jettison. The classified blow-off system caused its own headache afterward: witnesses on the ground swore they had seen the aircraft explode.

From Mixmaster to Jetmaster

The Mixmaster’s clean, engine-free wing made it an almost perfect canvas for pure jet power, and Douglas had seen that coming. The company converted a second airframe into a turbojet bomber, the XB-43 Jetmaster. Out came the Allison V-12s and drive shafts; in went two General Electric J35 turbojets fed by intakes cut into the fuselage sides.

With no propellers to protect, the entire ventral fin was deleted and the dorsal fin enlarged. The XB-43 flew from Muroc on 17 May 1946, becoming the first American jet bomber to take to the air, and topped out around 515 mph. History, though, had already moved on: the purpose-built North American XB-45 Tornado promised more in every category, and no production order followed. Today both survivors sit at the National Museum of the United States Air Force in Dayton, awaiting restoration.

Sources: Wikipedia (Douglas XB-42 Mixmaster; XB-43 Jetmaster); FLYING Magazine (Jason McDowell); National Museum of the USAF.