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Date: Sat, 19 Feb 2005 17:18:41 -0500
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From: "Lorn H. Olsen" <lorn@dynacomm.ws>
Subject: RE: Air intake formula 

>> Following is an article that I wrote last year. I have also included 
>> an
>> Excel spreadsheet where you can plug in your own engine size and scoop
>> diameter.  Lorn H. Olsen
>
> Lorn,
> The calculations you presented appear to recommend the inlet to be 
> sized for
> a 1:1 velocity ratio - in other words the velocity in the inlet is 
> equal to
> the free airstream velocity.  I see other recommendations that are for
> velocity ratios between 0.4 and 0.7, producing much of the pressure 
> recovery
> ahead of the inlet.  The advantage of that, as I see it, is that 
> pressure
> recovery ahead of the inlet is quite efficient and requires less 
> recovery
> inside the duct, reducing the required length.  Also, at lower 
> airspeeds the
> inlet is more efficient as there is less chance for flow separation 
> inside
> the duct.  What do you think?
>
> Gary Casey

Gary,

My calculations only have to do with the straight forward mathematics 
used to calculate the diameter of the scoop. I make an assumption that 
there is no air compression and no air friction.

In order to calculate the most optimum size of the scoop when both air 
compression and friction are considered, the equations become much more 
complex. I think, so complex in fact, that wind tunnels should be used. 
I have neither a wind tunnel nor the thermodynamic engineering 
background to do these more advanced studies (calculations).

My spreadsheet does not recommend a specific scoop diameter (velocity 
ratio). The spreadsheet simply shows, based upon the scoop diameter, 
the extra percentage of air that you, the builder, have chosen to 
incorporate into your design.
--
Lorn H. 'Feathers' Olsen, MAA, DynaComm, Corp.
248-345-0500, mailto:lorn@dynacomm.ws
LNC2, O-320-D1F, 1,000 hrs, N31161, Y47, SE Michigan