I first saw a reference to the B19 in a book I had as a child on air tactics and strategy. Back then I had not feel just how much larger it was than other aircraft of the time like the B17.
The Xb19, like the Xb15 was that army aircorps ongoing effort to address the fact that as a nation surrounded by oceans and potential enemies on other continents, the air corps was going to have the ability to strike over transcontinental ranges. this led to these very large aircraft.
Of course the penultimate of these large was the B36. The b36 was the only one of the Air force’s big bomber to enter production. This was driven by the necessities of the Cold War, the large size of early nuclear weapons and the need to reach the heart of the Soviet Union from air bases in the US when mid air refueling didn’t exist.
The issue with these large aircraft was power plants. The Air Corps, in the 1930’s and 1940’s Pursued a program that worked to improve octane, compression ratios, and power to weight limits for aircraft engines. You can sort of see why when you get a close look at the engines from WW1.
Starting in the late 1920’s the aerospace industry and the air corps started to develop higher performance engines. For a variety of reasons, the US aircraft industry engine advancements were in radial designs rather than liquid cooled engines.
By the late 1930’s with the world heating up and the general feeling that radial engine technology was not keeping up with the liquid cooled engines, the air corps initiated the hyper engine program, which in many ways, while useful, was too little, too late.
Still, by ganging the engines together to get the power needed together some remarkable designs were created.
In the end though, for the big bombers, the radials, by now multibanked and supercharged won the power race. Unlike any liquid cooled engines, it would be the big radials and especially the Pratt and Whitney R-4360 that would power the super bomber and the new breed of commercial aircraft that started the aviation boom right after the war.
While the engine was never mounted in an airframe this monster engine would be the largest piston engine ever designed for and aircraft. But it turned out that it was never needed.
That’s the story of the American big bomber project and the engines to power them. Interesting aircraft that were always out of sync with what was needed.