the WWII guys probably did not either. That was the “barrier”. when they got close to sonic speed (in a dive) the controls went wonky and they had trouble pulling out of the dive.

The x-1 was not very sharp or thin (8% thickness/chord). the rocket engine and heavy contruction (good for 18g positive or negative) gave it the oomph. It had a adjustible stabilizer that kept it controlable. the prototype f86 was flying and they could go supersonic in a dive.

I saw Yeager just a few weeks at at the C. R. Smith Museum in Fort Worth. You know, he just can’t get rid of that smile, and he can’t stop talking about how much fun it is to fly.

Happy anniversary, Chuck Yeager!

But I’m not sure if aircraft during WW II routinely broke the sound barrier. They did indeed often go so fast, in a dive, that they crashed but there were a lot of reasons for that happening. The concept that there was a sound barrier and that they may have been approaching it or crossing it, and thus losing control, breaking up, crashing, etc arose at that time and added mystery and fear to the whole concept of a sound barrier that could not be broken. But most of those cases may have been aircraft going slower than the sound barrier.

Having said that, keep in mind that is all relative. An aircraft can travel at the speed of sound ground speed if it is in a very fast wind, but still be going subsonic in relation to the air around it. By the same token, an aircraft can be going at, cay, 80 percent the speed of sound and the air passing over the controll surfaces, which are curved, is actually moving relative to the aircraft’s surface at faster than the speed of sound. Which, of course, has those sound barrier effects.

Why the qualification “in level flight”?

Did someone else break the sound barrier in *non-level* flight before Yeager?

BTW, the design for the Bell-X-1 was originally devised by the British aircraft company Miles, who actually flew a remote-controlled scale model (there is a film of the model in flight, but I did not find it on the internet). The British minister of aviation ordered the program to be handed over to the Americans. A British flight pineer had died using a different aircraft to try and reach Mach 1, and the minister apparently considered the whole affair too dangerous…

Also, the first aircraft to reach 1000km/h was a prototype of Messerschmitt 163 Komet, but the wings were not swept back far enough to allow it to reach Mach 1. Bell X 1 had no swept wings, but had razor-sharp wing edges on ots straight wings instead (incidentally, that works well at Mach 2, but very draggy at Mach 1).