REFLECTOR: updraft cooling

[Gary Stull]

I have updraft cooling on my Velo. It has an IO360, even in torrid Florida summers temps never exceed 375. Took some finessing to achieve these numbers. I added deflectors in the armpit scoops to direct the air to the forward cyls. I also opted not to cut down the scoops as per the plans. The are as received and probably increase drag slightly, but I wanted max cooling. In a descent with idle power they do cool rapidly, so I usually keep more power and either plan a shallower descent or deploy the speed brake. 
  ----- Original Message ----- 
  From: Al Gietzen 
  To: 'Velocity Aircraft Owners and Builders list' 
  Sent: Saturday, February 17, 2007 5:52 PM
  Subject: Re: REFLECTOR: updraft cooling


  Subject: REFLECTOR: updraft cooling



  I can understand why Burt Rutan and Nat Puffer are proponents of updraft cooling. From an engineering point of view, it has a lot going for it. You need more cooling when the airplane is climbing. If the cooling intake is below the wing, the pressure is higher during a climb so you automatically get more cooling during a climb. Similarly, it would be nice if cooling was minimized during descent. The pressure is reduced under the wing during descent, and so there is less cooling to the engine. Also, you've got convection working with you instead of against you with an updraft system.

  Doug;



  I'd think that both climbing and descending are high AOA, and would have similar air pressure under the wing; and given the strake configuration, it is not clear that there is increased pressure during climb.  I also think that the main reason for difficulties with the stock armpit scoops and updraft is they are poorly designed scoops.  Need to have ever increasing x-section after the entrance, and possilby placing them a bit further outboard from the strake/fuselage intersection would be helpful. 



  I have an 'armpit' scoop for my radiator which is very effective.



  But the down draft is a lot simpler to implement, and that's probably going to be the deciding factor for me.



  And since it seems to work well, why not?  The amount of natural convection driving force is likely overcome by a few knots of forward speed.

  Al 





  Doug Holub



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