Not Quite A Vapor Cone

For lack of anything better to discuss today (or two brain cells to rub together in order to ignite a creative spark), let’s look at a simple but graphic demonstration of atmospheric condensation in an aircraft wake.

From the April 1, 2007 airshow at Point Magu in Ventura County, here’s an F-22 fighter doing a high speed pass (probably something in excess of 500 mph) about 50 feet off of the deck.

Afterburners lit, he’s really moving. You can see the elevators on the tail just starting to tip up, which will lower the tail and tip up the nose. Then, 0.37 seconds later (the Canon XTi shoots at 2.7 frames per second in burst mode):

The plane is surrounded by fog of its own creation. From the smooth, streamlined airflow in the first picture, the airflow is now totally chaotic with a huge low-pressure area building up behind the plane as the airflow is disrupted. The air was cool and moist (we were only a quarter-mile or so from the beach), the pressure dropped dramatically in a fraction of a second, the air at lower pressure couldn’t contain nearly as much moisture, so the “extra” moisture gets squeezed out into microscopic droplets which we see as fog.

The pilot, on the other hand, is pulling about 9 G’s and transitioning from straight horizontal flight to straight up vertical flight — this is what is know in the vernacular as an “E-Ticket”!

Note that while similar in cause, this is not quite the same as a Mach 1 “vapor cone“. The vapor cone is also caused by a sudden change in air pressure, but the change is caused by the shock wave coming off of the plane (or rocket) as it passes through the sound barrier. Because that shock wave is conical in shape, the vapor cone is as well.

I haven’t seen a vapor cone personally — they don’t go supersonic at air shows very often, and when they do they’re usually at 40,000 feet (or more) and over the desert. But there are some fantastic pictures and video out there.

Maybe someday I’ll see one. In the meantime, you can see the effect shown by this F-22 at an airshow near you. In addition, now that our governmental “leaders” aren’t shutting down the government this year, the service demonstration teams (Navy Blue Angels, Air Force Thunderbirds, Army Golden Knights) are all flying a full airshow circuit this spring, summer, and fall. There are several good websites for keeping track of where airshows in your area are and who’s going to be there — here‘s my favorite.

Don’t forget your sunblock and stay hydrated! Most importantly, when you’re taking your thousands of pictures, remember to occasionally just watch, marvel, and enjoy. And keep an eye out for the sneak pass.