REFLECTOR:Engine ram air

Jim Agnew reflector@tvbf.org
Tue, 28 Oct 2003 18:29:12 -0800 (PST)


Rene, the point is that ram air is slight at best and a
large plenum after the inlet is needed to develop the
increased air pressure.  

I in fact have no scoop at all, I have an oval slot (8 sq.
in.) in the under side of the wing aft of the spar which is
a high pressure area that leads to an air filter (Brackett
4" x 10")into a 5" x 6" x 12" plenum area that feeds via
air duct to the fuel controller.  

My thought was minimum drag, a giant vacuum pump (the
engine) trying to get air and the high pressure air on the
underside of the wing trying to get to the top of the wing.
 In fact in ground effect the pressure is even higher at
takeoff.  

Alan Shaw found that the air flow from the underside of the
wing to the low pressure top side was large when he wing
mounted oil coolers like I have my intake air setup.

Jim

--- Rene Dugas <rdugas@bayou.com> wrote:
> Thanks Jim,
> It seems the point would be that we would need to know
> the velocity of
> the air moving through the 3" opening in the controller. 
> That should be
> calculable based on displacement and RPM's to get a
> volume per second.
> I thought that at cruise one would want some slight
> pressure for ram air
> based on the volume of air being drawn through this
> opening.  To much
> pressure and the air just spills over the lip of the
> scoop and never
> even enters the scoop.  Under non-ram arrangements this
> should be a
> suction but if one can obtain a slight ram pressure at a
> little more
> than would be sucked in at cruise of if desired at 25
> squared then the
> size of the opening could be determined.  I just don't
> know how.  The
> pressure delivered to the scoop would depend on many
> factors but I would
> think the main factor would be speed of the air and the
> extent one can
> slow the high speed air down to get static pressure. 
> This may all be
> wrong or too obvious to comment on but before I sleep at
> night my mind
> wanders.
> Rene'
> 
> PS   I built my scoop separate from the air box so it can
> be removed and
> the filter removed from a 3 " flange mounting for the
> K&N.  The approx.
> 11" x 9" box has a side spring door flap to open in the
> case of scoop
> obstruction allowing heated air from inside the cowl but
> still it would
> be filtered.  No water problems and I do have a 3/16"
> hole in the most
> dependent point of the scoop.
> 
> -----Original Message-----
> From: reflector-admin@tvbf.org
> [mailto:reflector-admin@tvbf.org] On
> Behalf Of Jim Agnew
> Sent: Wednesday, August 20, 2003 6:54 PM
> To: reflector@tvbf.org
> Subject: Re: REFLECTOR:Engine ram air
> 
> The air intake should not be less in square inches than
> the
> area of the fuel controller intake.  If the controller
> intake is 3" then the area is a little more than 7 Sq.
> In..
> 
> Jim
> 
>  
> --- KeithHallsten <KeithHallsten@quiknet.com> wrote:
> > Rene',
> > 
> > I have no particular expertise on this subject to share
> > with you, but this month's Sport Aviation has an
> article
> > on engine cooling that may have some principles you can
> > put to work.
> > 
> > Keith
> >  
> >   ----- Original Message ----- 
> >   From: Rene Dugas 
> >   To: reflector@tvbf.org 
> >   Sent: Wednesday, August 20, 2003 10:18 AM
> >   Subject: REFLECTOR:Engine ram air
> > 
> > 
> >   I've asked this before but did not get an answer.  I
> am
> > no engineer either.  How big should the opening be on a
> > ram air scoop feeding air to the engine on an IO 540 at
> > 2300 rpm's?  I understand it is best to not have the
> > scoop any bigger than necessary because of the overflow
> > forms a slow mushroom of backed up air pushed ahead of
> > the scoop.  Any takers?  Mine is about 2.5 by 2.75"
> > expanding into an airbox with a K& N filter then into
> the
> > 3 inch orifice under the engine.
> > 
> >   Rene'
> > 
> 
> 
> =====
> James F. Agnew
> Jim_Agnew_2@Yahoo.Com
> Tampa, FL
> Velocity 173 Elite Aircraft Completed
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=====
James F. Agnew
Jim_Agnew_2@Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying