Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - "Faster than the wind," impossible they say but the Blackbird settles the debate

bizzybody · 07-31-2021, 03:18 AM

A boat can tack alternating to port and starboard, downwind, with an averaged speed parallel to the wind vector, faster than the wind speed.

Now take two boats scissoring back and forth and connect a rope between them that somehow won't get tangled and always stays taught. Connect a 3rd boat, without a sail, to the midpoint of the rope.

Since both sailboats are exceeding the linear wind speed and they're dragging the 3rd boat with them, the 3rd boat must also exceed the linear wind speed in a straight line.

It's like a 2 dimensional projection of the two boats on a steady tack around and along a cylinder, linked solidly together. The midpoint of the connection is not tacking yet since boat boats are on a wind speed + tack, the connection between them must also exceed the wind speed.

Something else to think on is how fast aircraft and the Cheetah "decelerate" air flowing into their engine intakes and nostrils so they can breathe properly.

"Decelerate" is the wrong word even though it's commonly used to describe what's being done. They're really accelerating the air up to close to the velocity of the aircraft or animal right as it flows into the intakes and nostrils.

When a Cheetah bursts up to 70 MPH the shape of its nose must "grab onto" the air in the immediate area and alter its speed so that as it goes into its nostrils the airspeed relative to the notsrils is perhaps 2 MPH. But relative to the outside environment if there is no wind, what the Cheetah's nose is doing is pushing a bit of air up to ~68 MPH. I wonder if anyone has examined the aerodynamics of the nose as a limiter on the cat's top speed duration? Perhaps it can only keep the high relative speed air moving ahead of its nostrils for a few seconds at a time? Could be that the air pressure overcomes the strength of any muscles involved in adjusting nose shape or the stiffness of nasal tissues. Once the pressure distorts the nose from optimal shape, the pressure wave enters the nostrils and the cat suffers a "compressor stall".

Suddenly having the 60+ MPH relative airspeed moving into its nostrils would be analogous to the intake shockwave on a supersonic aircraft falling too far back into the engine intake. (Minus the engine flameouts, flat spins, and crashing.)

Could a Cheetah maintain top speed for longer with a strong tailwind so its nose doesn't have to push the air in front of it as strongly?

07-31-2021, 03:18 AM	#131 (permalink)
bizzybody EcoModding Lurker Join Date: Apr 2009 Location: Idaho Posts: 12 Thanks: 0 Thanked 1 Time in 1 Post	A boat can tack alternating to port and starboard, downwind, with an averaged speed parallel to the wind vector, faster than the wind speed. Now take two boats scissoring back and forth and connect a rope between them that somehow won't get tangled and always stays taught. Connect a 3rd boat, without a sail, to the midpoint of the rope. Since both sailboats are exceeding the linear wind speed and they're dragging the 3rd boat with them, the 3rd boat must also exceed the linear wind speed in a straight line. It's like a 2 dimensional projection of the two boats on a steady tack around and along a cylinder, linked solidly together. The midpoint of the connection is not tacking yet since boat boats are on a wind speed + tack, the connection between them must also exceed the wind speed. Something else to think on is how fast aircraft and the Cheetah "decelerate" air flowing into their engine intakes and nostrils so they can breathe properly. "Decelerate" is the wrong word even though it's commonly used to describe what's being done. They're really accelerating the air up to close to the velocity of the aircraft or animal right as it flows into the intakes and nostrils. When a Cheetah bursts up to 70 MPH the shape of its nose must "grab onto" the air in the immediate area and alter its speed so that as it goes into its nostrils the airspeed relative to the notsrils is perhaps 2 MPH. But relative to the outside environment if there is no wind, what the Cheetah's nose is doing is pushing a bit of air up to ~68 MPH. I wonder if anyone has examined the aerodynamics of the nose as a limiter on the cat's top speed duration? Perhaps it can only keep the high relative speed air moving ahead of its nostrils for a few seconds at a time? Could be that the air pressure overcomes the strength of any muscles involved in adjusting nose shape or the stiffness of nasal tissues. Once the pressure distorts the nose from optimal shape, the pressure wave enters the nostrils and the cat suffers a "compressor stall". Suddenly having the 60+ MPH relative airspeed moving into its nostrils would be analogous to the intake shockwave on a supersonic aircraft falling too far back into the engine intake. (Minus the engine flameouts, flat spins, and crashing.) Could a Cheetah maintain top speed for longer with a strong tailwind so its nose doesn't have to push the air in front of it as strongly?