----- Original Message -----
From: "Eric Ruttan" <ericruttan@chartermi.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, December 07, 2003 6:55 PM
Subject: [FlyRotary] Re: K&M and Thick Radiators


> From: "Ed Anderson" <eanderson@carolina.rr.com>
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Sent: Sunday, December 07, 2003 8:36 AM
> Subject: [FlyRotary] Re: K&M and Thick Radiators
>
> > Ok, Paul.  Based on my back of the envelope calculations at a fuel burn
of
> > 8.5 gph with that size radiator, you would need an airspeed of around
142
> > mph to provide adequate air mass flow.  So it should have no problem
> cooling
> > you at your typical cruise airspeed provided your ducting brings in the
> air
> > stream adequately.  So, I would think you need to concentrate on how you
> > would handle the heat rejection defficit between take off and 142 mph.
I
> > have no idea how long it takes your type aircraft to go from application
> of
> > take off power to 142 mph.  That could make a big difference in how much
> of
> > a challenge your high power/low airspeed regime is. Cowl flaps? Spray
> bars?
> >
> > Good luck.
> >
> > Ed Anderson
>
> Ed
> How do the Mass Air requirments change with altitude.  For example, if the
> fuel burn was 8.5gph and altitude was 25K would the mass air requirements
> change do to thiner air?  Would the lower temp make a difference?
>
> Thanks for your help.
>
Two things come to mind, Eric.

    At high altitude the density of the air does lessen and this does lower
the mass flow for the same number of cubic feet of volume flowing through
your radiators. First, you would have to have a turbo to get the 2 rotor to
burn 8.5 gph at 25000 MSL.  An NA would have to turn around 10600 rpm to
ingest enough air to burn 8.5 gph at that altitude.   My calcuations might
be a bit off,  but it looks that if you did manage to burn 8.5 gph at 25000
MSL, you would need to hit over 230 MPH to provide sufficient air mass flow
to cool that 91 HP being produced (assuming two GM evaporator cores).  My
number could be off a bit due to the lower temperatures at altitude.  But,
basically, the lesser air density would pretty drastically reduce your
cooling abilities there.  Lower temps would help off set it to some degree,
but mass flow is what you really have to have.  Even with temps in
the -10-15F range, if the mass flow is insuffuicient, your cooling is going
to be hurting.

Ed  Anderson

The air mass flow at 7500 at