----- Original Message -----
From: <rogersda@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, March 24, 2003 6:18 PM
Subject: [FlyRotary] Re: Thick or Thin?


> Hi All,
>
>    Would someone please help me better understand the physics involved
with this?
>
>    It appears to me that, especially given the airspeeds we're talking
about, as long as there is significant temperature differential between the
air and the tube/fin at the trailing end of the air path, the radiator is
working.
> Isn't it the case that our biggest concerns with thick cores are (1)
saturation of the airstream, (2) weight per transferred BTU, (3) drag?
>
>    So, for a given transfer rate, one might expect a thick core radiatior
to be heavier than a thin one, but offer less drag.  If the load due to
additional weight is less than the drag of the lighter thin core, aren't we
ahead?
>
> Dale

Your observations are correct Dale, but in reality the weigh factor is
insignificant.  Of course  there is a limiting factor on how far we can go
with thick rads.  At some point there is not enough dynamic pressure to push
enough air through a very thick rad to carry away the required BTUs, even if
the air is heated to the theoretical limit equal to (almost) the coolant
temperature.  An airplane flying at 200 MPH has a lot of dynamic pressure
potential so the limit is relatively high (compared to passenger cars).

It is worth noting that the dynamic pressure at only 120 mph is enough to
support the weight of your body.  120 MPH is the terminal velocity of a sky
diver in free fall.

Tracy Crook