Re: [PSUBS-MAILIST] fairings drag vrs entrained mass

[EM <emuller@naic.edu>]

I think I've hit on why fairing might be a larger concern for me:.
I'm hoping to build a VERY small ambient machine.. about 800 kg. So
plugging on an extra 100 kg of water (which isn't really very much,
equivalent to a fairing space of about 20 wine casks..) has just boosted
the mass I need to accelerate (and overall momentum!) by more than 10%.

I think that in my case, it's better to streamline the hull (not a
pressure hull in my case. not a 'real' one anyhow), than to patch on big
gobs of sheeting.
I have a rhino-generated 3-d picture somewhere on moki I think..

EM.


On Mon, 28 Nov 2005, Paul Kreemer wrote:

> Yeah, it'd be great to test some models...  Regarding fairings, I haven't
> even checked the Busby book but was watching the Russian Mirs recently on
> video and noticed how streamlined they are.  I agree with EM that having
> flow through the fairing would definitely increase your drag.  But I don't
> see a huge problem with dragging the water around inside the fairing - at
> least within reason.
> 
> And yeah, these speeds are pretty low but from the little math I did you
> could see that streamlining does make a difference.  If you want to hit 4
> kts with something shaped like a pickup truck you need more power than if
> you have a streamlined hull.
> 
> 
> fun stuff!
> 
> On 11/28/05, EM <emuller@naic.edu> wrote:
> >
> > Fairing is something I'm curious about too..
> > It seems to me that fairing defines a comoving volume that you have to
> > cart along, which really WILL affect the acceleration.. unless you allow
> > the water to flow THROUGH the fairing, which will just double your drag
> > (since you now have TWO surfaces exposed to the flow).
> >
> > So you loose a lot with fairing. In one case you carry around a lot of
> > water, and your acceleration dies, in the other you just up your drag
> > (though hopefully the whole point of installing the fairing was to
> > re-divert flow away from lossy turbulent eddies etc.).
> >
> > To be honest, the only use I can imagine for fairing is to re-divert the
> > flow away from potentially turbulent corners, and at the speeds
> > we're talking about.. is that often a big concern?
> >
> > I think somone should make a flow-box.
> >
> >
> > EM.
> >
> >
> >
> 




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