In all the realms of fiction, there’s a certain something you can be sure to find over and over again…the underground runway.
That is, an aircraft runway built underground inside a cavern or a bunker. (ou know what I’m talking about.
Now, my question is…what would really happen if you tried to fly a jet out of one of a runway like this?
Let’s say the runway-tunnel…is 3,500 feet long, 400’ wide, and 200’ tall. There’s a single enterance/exit at one end of the runway, which is, of course, 414’x200’. (I’m ignoring, if only for the setup, any doors, ventilation systems, or hanger space.) The walls, ceiling, and runway are made of concrete.
Now the aircraft I want to try and launch is a Lockheed SR-71. (Johnny Quest and G.I. Joe never settled for Cessna-172s.) It’s two engines, by my figures, produce 34,000 lbs of thrust, afterburning. The exhaust gas temperature from each engine is something like 2000 degrees fahrenheit. (According to my flight sim, 1,200 degrees on the runway)
Now…what happens to the runway-tunnel if I, parked in my Blackbird near the closed end of the tunnel, go to full throttle?
Noise, I assume, would be tremendous. But what else would happen? Would the engines melt or burn the walls—and does concrete burn? I thought I saw some sizzling on a Wings documentary on experimental jet VTOLs—? Would there be any weird air pressure effects?
And if anything really disastrous would happen—explosive overpressure, walls bursting into flames, etc.—could there be an engineering workaround?