REFLECTOR: Fwd: My Velocity setup

[Douglas Holub]

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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