newbie needs help with math

[hawk_za]

i noticed that the gigantor now have a 3kpa dynamic pressure tolerance can anyone help me to figure out how to convert that to a speed for a rover

 

[Leafbaron]

Dynamic pressure is the kinetic energy per unit volume of a fluid - a liquid or gas - and can be expressed as

p_d = 1/2 ρ v²         (1)

where

p_d = dynamic pressure (Pa)

ρ = density of fluid (kg/m³)

v = velocity (m/s)

Some common densities at atmospheric pressure:

• Water - 0^oC - 1000 kg/m³
• Water - 32^oF - 62.4 lb_m/ft³
• Air - 20^oC - 1.2 kg/m³
• Air - 59^oF - 0.0765 lb_m/ft³

So if you know what you dynamiuc pressure is and the density of the fluid you will be traveling through you can solve for V and get this equation V= √(P_d/.5p) hope this helps!

 

-Leafy

[ment18]

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

Dynamic Pressure (pa) = (1/2)*(air density (kg/m^3))*(speed)^2

3000 = (1/2)(1.225)(x)^2  //sea level on Earth for air density, I think Kerbin is the same.  If otherwise, please say so.

4897.96 = x^2

x = 69.99m/s

This seems highly suspect because I don't think that the solar panels can actually survive going 70 m/s on Kerbins surface.

This the speed that you can go increases as you go higher (because density is partly based on pressure) and on other planets with lower pressures.  If other planets have atmospheres with different compositions, it may change based on different densities as well,

[Sharpy]

3 minutes ago, ment18 said:

This seems highly suspect because I don't think that the solar panels can actually survive going 70 m/s on Kerbins surface.

Shaking of a rover will destroy them pretty fast. I'm not sure about airspeed near the surface, but as I reentered with standard panels open, they would break at some 10km during descent, with speed around 200m/s. They survived the flaming reentry at 30km.

OTOH driving a rover on Eve... aaargh. I don't think they survived more than 6m/s.

 

[Leafbaron]

9 minutes ago, ment18 said:

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

Dynamic Pressure (pa) = (1/2)*(air density (kg/m^3))*(speed)^2

3000 = (1/2)(1.225)(x)^2  //sea level on Earth for air density, I think Kerbin is the same.  If otherwise, please say so.

4897.96 = x^2

x = 69.99m/s

This seems highly suspect because I don't think that the solar panels can actually survive going 70 m/s on Kerbins surface.

This the speed that you can go increases as you go higher (because density is partly based on pressure) and on other planets with lower pressures.  If other planets have atmospheres with different compositions, it may change based on different densities as well,

Can rover tires even go 70 m/s without blowing up, I thought their max speed was 60 m/s

[ment18]

3 minutes ago, Leafbaron said:

Can rover tires even go 70 m/s without blowing up, I thought their max speed was 60 m/s

Well, rocket or jet engines.  Ion rovers are useful for Duna etc.

[Corona688]

1 hour ago, Leafbaron said:

Can rover tires even go 70 m/s without blowing up, I thought their max speed was 60 m/s

This is misleading in some ways, speed is not the only thing that matters.  Stationary weight alone can break a wheel.  So the truth is somewhere inbetween.

Edited September 15, 2016 by Corona688

[hawk_za]

wow okay thanks for all the replies i will munch on these equations and see what tests i can come up with  ps makes sense that solar panes would survive at higher speeds in higher orbits due to the atmosphere density being less.

 

[Vanamonde]

As there is actual math taking place in this thread, Science subforum seems like a better place for it. 

[ment18]

70m/s is actually reasonable.  I was able to get a rocket rover going 80-90 m/s on the runway before they broke.