REFLECTOR: Performance

[Dave T Nelson]

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
                                                           
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 Subject: Re: REFLECTOR: Performance                       
                                                           


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:
  I’m not an engineer but I would think the thrust from the exhaust aimed
  to the rear might be part of the benefit. Also when the exhaust exits
  perpendicular to the laminar flow around the fuselage it makes sense that
  it would cause turbulence and drag.


  Grover McNair


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