REFLECTOR: Fwd: My Velocity setup

Alex Balic alex157 at direcway.com
Fri Dec 3 23:44:29 CST 2004


Doug- you might had at least plan on a ram scoop somewhere- the NACAs just
won't build too much pressure differential to effectively move air through a
radiator- you never know, but I would at least plan on having one.
  -----Original Message-----
  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Douglas Holub
  Sent: Friday, December 03, 2004 1:22 PM
  To: Velocity Aircraft Owners and Builders list
  Subject: Re: REFLECTOR: Fwd: My Velocity setup


  Ronnie,

  Al just convinced me that the propeller isn't sucking much air out of the
cowl. I'll stick a fan on the drive shaft (next year when I get to the
engine installation) and let everybody know how it works. I'm going to
install the DeltaHawk diesel, so I've got one or two radiators, and like
Kurt, I'm hoping I don't need any external bulges from ram scoops. Have you
seen that big, honkin' belly scoop on DeltaHawk's Velocity?

  Doug
    ----- Original Message -----
    From: Ronnie Brown
    To: Velocity Aircraft Owners and Builders list
    Sent: Friday, December 03, 2004 12:21 PM
    Subject: Re: REFLECTOR: Fwd: My Velocity setup


    Hi Doug,

    Not to be a wise A_ _, but there already is a fan there, most of them
are three bladed.

    Kidding aside, there has to be a lot of vacuum at the cowl exit created
by the prop.  I have the top NACA inlets, and my engine runs nice and cool,
even on the ground on hot days.  I didn't have any problems at Oshkosh last
year, although it was not the worst Oshkosh kind of day when I landed and
lots of taxiing to get to "Area 51".  Take off was a non issue as it was low
over cast and nobody was leaving except me and Gilles

    Even on 90 degree days taxiing on medium runways has not been a
problem - no more than 350 degrees CHT.  My cowl is within 1" of the prop
leading edge, a number that Alan Shaw said was optimum for pulling air out
of the engine.  By the way, I have a temperature sensor mounted at the
bottom of my alternator - near the outlet of the cowl.  It hardly ever goes
over 180, I have seen it at 200 after a climb out on a hot day.

    Ronnie

    ----- Original Message -----
      From: Douglas Holub
      To: Velocity Aircraft Owners and Builders list
      Sent: Friday, December 03, 2004 12:19 PM
      Subject: Re: REFLECTOR: Fwd: My Velocity setup


      Would it help to suck air through the NACA ducts if I put a fan on the
prop extender just before it exits the cowl?

      Doug Holub
        ----- Original Message -----
        From: Al Gietzen
        To: 'Velocity Aircraft Owners and Builders list'
        Sent: Friday, December 03, 2004 10:54 AM
        Subject: RE: REFLECTOR: Fwd: My Velocity setup


        My idea behind this is to scavange some of the flow that comes
through the bottom radiator, across the bottom of the pan, and out the
"suction slot".  at about 18" from the center of prop rotation, it should
also add to the suction the prop places on the cowl opennings. Well.. at
least that is my idea, we'll see if it works out. I am hoping that I can get
away without an oil cooler with that setup. No worries though, I have a
backup to put an inline cooler on the #2 NACA scoop if I need it.



        Keep in mind that the reduced pressure (“suction”) generated by the
prop dissipates rapidly (exponentially) as you move away from the prop, so
even a foot is a long way - and at cruise it is almost non-existent; you
have to rely on dynamic pressure and whatever gradients are produced by the
flow.  Remember, the air is standing still, the airplane is moving.  Some
air is getting pushed/pulled downward by the airfoils, some is being pushed
back by the prop, the rest is getting out of the way as best it can.



        Al



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