REFLECTOR: Performance

[Kevin Baker]

I would agree.
This is the type of info I've read about as well on the cozy /long forums with similar results 

Thanks
Kevin Baker

.

On May 10, 2013, at 10:12 AM, David Rene Dugas <renedugas at gmail.com> wrote:

> David,
> I would suggest that #2 is significant because the large plume of hot exhaust is forcing a dramatic change in direction on a large shout of air traveling at 200 mph. This would act like a speed break.   The energy to move this air would be parasitic drag and would be substantial.   I realize there is no mechanical connection but there is a gaseous connection the same as one has with the earth when in flight so very real. I'm not an engineer so I do not has the formulas to calculate it but my 2 cents worth is that that plume and pipes are a big source of drag. Just my maniacal machinations. 😳
> 
> Rene' Dugas
> Sent from an Apple. 
> 
> On May 10, 2013, at 8:06 AM, "David Ullman" <ullman at robustdecisions.com> wrote:
> 
>> IF I added up all the speed increases I could get from the topics discussed
>> here, my plane would be supersonic.  
>> 
>> I too would like to see proof that rear facing exhaust helps.  I have now
>> heard four theories: 1) the exhaust gas acts like a jet, 2) the
>> perpendicular flow adds drag, 3) The exhaust disturbs the boundary layer on
>> the cowl, 4) the exhaust gas disturbs the flow seen by the prop.  
>> 
>> The first one I calculated, and the thrust due to increased velocity of the
>> exhaust gas is minimal.  For #2, the plum has no way to transfer its drag
>> back to the plane.  Picture the plume as a cylinder projecting into the
>> airstream.  It is not connected to the plane in any way to slow it down, so
>> #2 is out.  The boundary layer at the back of the plane is already well
>> chewed, so #3 is not much of a possibility.  I hadn't thought of disturbing
>> the prop flow before.  The wings are already doing a good job of this, could
>> the exhaust add to this disturbance in a significant manner?   I can see
>> where moving the exhaust to the hub area (or outside the prop radius) may
>> have an effect, the first three are just noise.  
>> 
>> David Ullman
>> N444DX
>> President EAA 292
>> 541-760-2338
>> david at davidullman.com
>> 
>> 
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>> Behalf Of reflector-request at tvbf.org
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>> Subject: Reflector Digest, Vol 98, Issue 27
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