I fully get the “pushing gas” behind it part. In this case I assume if they ARE pushing gas it is heat from the engine and exhaust. That part I fully understand how it works. What I don’t get is if they are NOT pushing gas and just have a hole then why is the wind resistance drastically less? Assuming the cross sectional area is the same then why would a hollow cylinder give less wind resistance than a round object like a solid bullet.

While I was writing this I happened to remember this weapon.

Ring Airfoil Grenades

https://www.angelfire.com/art/enchanter/RAG.html

These supposedly went farther, straighter and were more lethal. They do not answer the question if the cross sectional area is the same. They say it has less drag because of the hole but, so what, if there’s less cross sectional area then having a hole or not means nothing.

I don’t believe you are correct about this. Gerald Bull, I believe, invented this or at the least had a great deal to do with it. He sold a bunch of artillery to South Africa based on this. Of course the Jews killed him when he started working wit Saddam. I read a book about him,”Bull’s Eye: The Assassination and Life of Supergun Inventor Gerald Bull”.

Base bleed leaks hot exhaust gases from a small reservoir full of some sort of fuel.

https://en.wikipedia.org/wiki/Base_bleed

This motorcycle best as I can tell is just a hole. Now if they are pushing the exhaust through it then I understand completely. It’s called “air augmentation” and is used in some rockets but they say not a word about this.

I just happened to remember that the P-51 mustang had a system where the heat from the radiator added a LOT of power by heating incoming air on a duct and releasing it[Meredith effect]. Quote,”…So this meant that while (compared to a standard radiator) the Mustang radiator had a radiator drag reduction at high level speed of 90%…North American calculated that the Mustang’s radiator was worth 200bhp to it…”

https://www.quora.com/Was-the-P-51s-cooling-system-designed-to-take-advantage-of-the-Meredith-effect-and-produce-jet-thrust-or-was-it-just-by-accident?share=1

Maybe this is it. They are running the engine heat and radiator through the duct. 200bhp for the plane is a whopping big figure. Maybe they are ding the same with the motorcycle.

Might work. Basebleed artillery rounds work on that principle

A idea. If it “is” vortexes, could you not cover the body with a lot of vortex creating rings, think golf ball covered with dimples but vortex rings in place of dimples. Open the front up and channel air around the body and exit in the vortex rings all over the body.

They have something similar for RV’s and trucks, called Airtab Fuel Savers, vortex generators. I read reviews on these and found high positive feedback.

Engineers put no small amount of effort into making NASCAR race cars more aerodynamically “pure,” preventing as much air as possible from getting under the car (air dams) and making the underside as smooth as possible.

I’m sure NASCAR has (or would immediately make) rules against it, but I’ve wondered why no one has tried a “center tunnel” through the car to exhaust radiator cooling air into the vacuum behind the car instead of “dumping” it under the car at the firewall. I’d think that, plus engine exhaust, to fill the partial vacuum there (and eliminate some of the air under the car) would be worth several miles per hour.