Re: [Phys-L] Dirigible Flight Question

[Bernard Cleyet <bernardcleyet@redshift.com>]

On 2012, Nov 05, , at 09:49, Paul Nord wrote:

> Since we're still at zero velocity we can ignore the viscous effects of the air for just a moment.



My take after only skimming JD.


Very quickly the R # will be huge.  In that case the drag is very ~ modeled as quadratic and the viscosity is largely irrelevant.


R = speed* characteristic length / kinematic viscosity



Very very ~ the L is 16 m
kv ~ 16 e-6  m^2 / s

so R = speed  *1 e+6

R in the quadratic region already at a few hundred microns /  second,  no?

then drag = v. ~  0.5* (speed^2) (fudge factor***)*(characteristic area)*(the fluid's density)



*** in this case similar to a cylinder   ~  0.9  length/D ~ 20  [drag coefficient]

area 1000 m^2?


of course moving forward instead of down the Cd and area will be much smaller