REFLECTOR: ram air vs filter

Jack Sheehan jsheehan at ncam-sats.org
Fri Jun 15 10:06:49 CDT 2007 

I have had very good performance with the 
alternate air system from airflow performance 
http://www.airflowperformance.com/. I actually 
use it differently. The photo is looking up at 
the engine the straight tube ( without the filter 
has the butterfly valve controled by a cable. In 
the open position the induction air comes thru 
the air scoop under the belly through scat tube 
making a S bend up to the fuel controller. This 
provides Ram air. If the environment is bad ie 
dust rain sleet etc (ground operations), I close 
the ram air and induction air is thru the K&N filter. The K&N is a RU-2790
There is almost 1 inch difference in manifold 
pressure due to the Ram air. Take off on the 
filtered air or unfiltered(ram ) is essentially 
the same since the effect of ram at slow airspeed 
is very little.. I thought the increased 
temperature of using air from within the engine 
compartment would cause an issue but it has not. 
The idea was to keep the filter protected from 
the elements so it would not clog due to ice dirt etc.
the air scoop I used was one velocity sells it 
was a mold used under the wings of older models.

Jack
N55XL
Race 55

At 10:14 AM 6/15/2007, you wrote:
>Scott,
>
>Yep, my air intake does take a turn over 90 
>degrees and I will have some measure of 
>disturbed flow in there.  It is a compromise 
>design like so much of this is.  I am not sure 
>we need a ram air.  The engine intake will suck 
>air sufficiently, hopefully,  thru that turn­it 
>is shortest distance I can make it with a pretty 
>straight run after that.  We are talking a short 
>distance.  I know airliners are not a good 
>comparison, but I did have these jet experiences 
>that I included (best I recall) as Collier and I 
>discussed the issue.   The B-727 center engine 
>is actually in line with the two pod engines 
>thru a big S duct.  I was unheard of at the 
>time.  Compressor stalls were is big issue on 
>start up or even on the ground when I guy would 
>make a rolling takeoff in a big crosswind the 
>pour the coals to it with inlet air all 
>disturbed.   It took some testing in the early 
>development years but it works.  Douglas, in the 
>DC-10, rejected it in its bigger trijet, while 
>Lockheed in the L-1011 included it.
>
>Of course cylinders sucking air are different 
>than compressor blades which are more flow 
>sensitive.  I opted for what we did.  My 
>thinking for anybody not up to this point could 
>include these points:  I saw Chuck Jensen’s 
>intake.  He uses a portion of what would be 
>cooling air by ducting out of his roof 
>NACA’s.  (And his intake ducting took some big 
>turns too, and didn’t have a lot of ram quality 
>to it per se.)  He never mentioned any oil 
>temp/cooling issues that I recall.  I think a 
>good hunk of that approach would have to include 
>a good cooling plenum.  I never asked him about 
>this, but I am glad myself to have the space 
>free for other stuff in the 
>engine-block-to-firewall real estate.  Lots of stuff has to go there.
>
>Belly intakes maybe like Rene would be the best 
>for ram air advantage.  His has worked 
>too,  based on his 500 hours.  I would worry 
>about sucking in water/slush kicked back from 
>the nose tire.  That was a problem in the later 
>stretched versions of the DC-9.  In fact they 
>put mud flaps on the nose tire.  For us
well we 
>are not all weather operators.  Personally, I 
>would, and I bet most others would delay a 
>takeoff or landing if there was active moderate 
>precip that could otherwise be avoided for lots 
>of reasons other than intake debris.  Just my 2 
>cents.  Oh, and thanks.  I guess it is a K&N filter not K&M.
>
>Terry
>
>
>
>
>----------
>From: reflector-bounces at tvbf.org 
>[mailto:reflector-bounces at tvbf.org] On Behalf Of Scott Derrick
>Sent: Thursday, June 14, 2007 9:34 AM
>To: Velocity Aircraft Owners and Builders list
>Subject: Re: REFLECTOR: ram air vs filter
>
>Terry,
>
>are you blowing air backwards through the 
>K&N?  Does it matter which way the air flows. into the cone or out of the cone?
>
>Scott
>
>
>Terry Miles wrote:
>
>Keith,
>
>Here's what I got...mostly this is a Malcolm Collier/Hangar 18 effort.   He
>did the actual carving, and it was his idea.  I took it from there.   I can
>send more pics if you need them.  It is the carved foam block routine.  Note
>the scoop is away from the underside of the wing, and you can see the outlet
>duct going into what would be the eng compartment.  We will use a short hunk
>of hose to connect.  The wing root section fits the standard size
>rectangular K&M filter and has the suction 2ndary door on a spring for
>filter bypass.
>
>The intake plenum that came with the engine didn't work.  Mine now goes off
>to the right at about 35 degrees (to the left if you talk to Don George!)
>He was good about swapping out the straight on one we had to begin with.
>I've got the Ly 540.  I think there are 3 different induction
>chambers/plenums whatever they are properly called.  They come on and off w/
>a couple of bolts.
>
>Hope this inspires!  Good luck.
>
>Regards,
>Terry
>
>
>-----Original Message-----
>From: 
><mailto:reflector-bounces at tvbf.org>reflector-bounces at tvbf.org 
>[mailto:reflector-bounces at tvbf.org] On
>Behalf Of Keith Hallsten
>Sent: Tuesday, June 12, 2007 9:05 PM
>To: 'Velocity Aircraft Owners and Builders list'
>Subject: Re: REFLECTOR: ram air vs filter
>
>Rene',
>
>This sounds like a pretty practical set-up for induction.  Do you have any
>pictures?  Is the "midline scoop" available, or was that a one-off custom
>part?
>
>I am in the midst of engine installation, and the induction system seems to
>be the part I'm having the most trouble with.  I have made a couple of air
>boxes using the "lost foam" method, but found their design to be
>unsatisfactory.  I'm definitely looking for inspiration on this.
>
>Keith Hallsten
>XLFG, Roseville, CA
>
>
>-----Original Message-----
>From: 
><mailto:reflector-bounces at tvbf.org>reflector-bounces at tvbf.org 
>[mailto:reflector-bounces at tvbf.org] On
>Behalf Of Rene Dugas
>Sent: Tuesday, June 12, 2007 4:22 PM
>To: 'Velocity Aircraft Owners and Builders list'
>Subject: Re: REFLECTOR: ram air vs filter
>
>I use the midline scoop mounted to the lower cowl and the rear of the
>fire wall.  I used a K & N cone shaped filter mounted to a 3 inch
>aluminum flange with an identical flange mounted the opposite direction
>in a fiberglass box.  This is attached to the induction by 3 in. scat
>tubing to allow for vibration.  I mounted a spring operated door in the
>side of the box for emergency air that sucks open if I close the scoop.
>I made the box by forming foam and coating it with glass.  I used
>acetone to dissolve the foam and presto custom air box.  I seem to get 1
>to 2 inches of MP based on side by side flights with others at the
>Velocity Symposium.
>My scoop starts out about 1.75 by 2.25 inches and opens up into
>approximately a one foot square air box with the K & N in it.
>Just FYI.  I can remove the lower cowl and the scoop screws to the box.
>I can remove the two screws in the scoop and remove the filter for
>cleaning.
>Rene'
>
>-----Original Message-----
>From: 
><mailto:reflector-bounces at tvbf.org>reflector-bounces at tvbf.org 
>[mailto:reflector-bounces at tvbf.org] On
>Behalf Of Tom
>Sent: Thursday, June 07, 2007 8:01 PM
>To: <mailto:reflector at tvbf.org>reflector at tvbf.org
>Subject: REFLECTOR: ram air vs filter
>
>My problem was that I went from ram air to what was too small of a
>filter. It was a 3" diameter x 5" long. I clamped it directly to the
>induction air tube. I really need a larger filter with filtration on the
>
>end also (this was closed). Very space limited under there as I share
>the ram air inlet with a 2nd oil cooler mounted on the baffling. (large
>aeroduct hose). I may just go with a screen.
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