Speculative Aerodynamic Model of Thrusters

[MESM]

You are right - Elon might be using actual thrusters that can push and corner a two tonne car but I also think that you are right to guess that that solution might not be road legal.

My bet is still for suction using an air curtain rather than small directed nozzles. In the last month or two I redid the estimates and I got about 400 mph for the speed of the air in the curtain. Pebbles that were thrown up would not break your skin (surprisingly).

(PS I have assumed 10,000 psi because that was a figure that Elon used in an interview. My earlier calculations used 5,000 psi but it turned out that 'ordinary'/typical was not good enough for SpaceX!)

 

[AirKuhl]

Thank you Megan for digging into the science behind a fascinating topic. I just have 2 comments that may be useful.

A rubber car tire on pavement has many forces involved besides friction, thus there is nothing magical about 1 G. Dragsters and F1 cars can break 3-6 G's during acceleration, braking and cornering. Note that early acceleration and late braking are too slow to involve aerodynamics.

You may want to look into the Chaparrral 2J race car from 1970, which used active aerodynamics much like you describe in actual race conditions (quite effectively).

 

[MESM]

@AirKuhl Thanks for that. I am hoping that he will announce the car soon.

 

[Brando]

Jim Hall of Chaparral Cars - American Inventors Interview

Jim Hall an engineer and became one of the leaders in aerodynamics
[vertical forces was his new insight - down forces - in racing of course]
note: timestamps under this video clip.

cares about his reputation - unusual ?

Chaparral Cars - Wikipedia

Jim Hall (racing driver) - Wikipedia

Jim Hall II to demonstrate winning Chaparral 2 at Sebring

 

[Brando]

side note: Drag Race - Thruster only need to operate for about 1 second, maybe 2 seconds to improve 0-60 mph.
Obvious, right?

 

[MESM]

It is better than 1.8 to 60 according to the test driver. In an early model I experimented with Bernoulli for 0 to 30 because in that regime you are friction limited - at (some) higher speed you will be traction limited.

If you still like the pure thrust story then a similar argument could be applied.

But of course Elon might choose to use the thrusters for longer to go faster anyway. Those tanks have phenomenal energy content

(Finally there is a detail about the Bernoulli solution - because the gas flow rates are lower you have time to warm the exhaust gas - and that would affect your timing choices as well.

It sounds as though we will find out soon enough!

 

[MESM]

If you are interested in this stuff there is a really good Sandy Munro interview with NowYouKnow here

.