Interesting read: Supercavitation

[Piwoslaw]

Originally Posted by bnmorgan

I've heard it referred to as "aero-spike" although all my research ended up being about a centralized cone linear arranged rocket engine. I was wondering the other day, seeing all the boat tail stuff, if anyone had tried some kind of retractable pre-wake generator, punching a hole for the car to run in. The ones used on hypersonic missiles are generally just a simple flat disc of a calculated size on a pole at a calculated distance ahead of the main body. Calculations based on effective speed and size of the vehicle. Can't punch a hole for the whole thing or you loose aerodynamic effective steering.

This might work at close-to-sonic speeds, but down where we hypermilers drive at, it'll just increase frontal area. This is because the wake behind something is usually cone shaped, so if you hold a plate with an area of 1 sq. foot, then the wake's cross section is going to be smaller the farther behind it you are. So maybe you catch half of that wake, reducing the car's FA by 0.5 sq.ft., but you're still pushing 1sq.ft., so the net is a 0.5sq.ft. increase of FA. I hope I got that right.

I read recently that a ship is testing injecting high-pressure air under its bow to reduce water drag. I think the article said something like 10%-15%?

[Christ]

RE: Ships

The last thing I ever saw about this was

1. Ships using high pressure air under the hull "somewhere" to reduce hydrodynamic drag.

2. Someone figured out that if you quickly release air bubbles under yourself while immersed in water, you'll rise. Oh jeez. Who couldn't have known that?