REFLECTOR: Performance

Brent Bourgeois bjb3013 at yahoo.com
Thu May 9 22:30:19 CDT 2013


If the exhaust is straight down how can this create drag or slow the plane down? The exhaust gas or plume is not connected to the plane in any way, it is always left behind as soon as it comes out. Laminar flow on the cowl that far back is doubtful. Possibly if the exhaust plume is close enough to the prop it could cause turbulence.
 
Just my observations,
Brent

From: Dave T Nelson <dtnelson at us.ibm.com>
To: reflector at tvbf.org 
Cc: reflector-bounces at tvbf.org 
Sent: Thursday, May 9, 2013 9:03 PM
Subject: Re: REFLECTOR: Performance

For what it's worth, and my memory could be wrong here, I seem to remember either Burt or perhaps Mike Melville saying that the exhaust thrust could contribute perhaps 1-2 knots.... 
  
Dave

Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering


To:  
Subject:  Grover,

I think the thrust you'd get from the exhaust would be minimal.  Think about this - if you had the exhaust pointed back and took the prop off.  Even with the engine at full power it would not likely push the plane on the ground a even a little.  I think it is the disruption of laminar flow around the cowling that is thought to create drag.  Intuitively, if I had a smooth airfoil, but then had a bunch of jets inducing air low normal to its surface, I would think that would be bad for its aerodynamic efficiency.

Also that the exhaust is throwing turbulent flow into the prop is thought to be a problem.  The prop may not be able to perform with the same efficiency it would if a smooth air flow was feeding it.

Geoff

On Thu, May 9, 2013 at 2:43 PM, Grover McNair <grover at mcnairperformance.com> wrote: _______________________________________________To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflectorVisit the gallery!  www.tvbf.org/galleryuser:pw = tvbf:jamaicangooseCheck new archives: www.tvbf.org/pipermailCheck old archives: http://www.tvbf.org/archives/velocity/maillist.html
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