----- Original Message -----
Sent: Wednesday, October 15, 2003 11:04
AM
Subject: [FlyRotary] Re: rooster-tail
drag
What is roster tail drag? how and where does it
get created? Is there anything about that written up on the
net?I'd like to know since I'm in the
process of figuring out where to put my radiators in the Long
EZ.ThanksMarko
Marko, Think of rooster tail drag as drag that's created when air
leaves the cowl at steep angle. The air, instead of turning and moving along
the side of the cowl like you'd think it would, shoots straight out from the
cowl for a small distance [ 6" may seem small but it will create a huge
drag penalty!] Another way to think of it is when your driving and you throw
that apple core out the window, notice how it goes straight out for a little
bit and then the on-coming air slows it down and it 'appears' to go back.. Air
leaving the cowl of your plane will follow basically the same sort of path. So
if we smooth this exit we'll find that we reduce drag. Its one of the reasons
that NACA ducts are soooo popular, they create a very smooth exit [ the
air is coming out parallel to the side of the cowl and then as the duct
narrows it is accelerated and gradually pushed out into the normal airstream.
So simple yet it took years to understand it all.
My 2
cents
Jarrett Johnson
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