REFLECTOR: Performance

Fri May 10 13:12:14 CDT 2013

I think that would be a perfect start.
One small change at a time is the way to go

Thank you Geoff for doing this.
Kevin Baker

.

On May 10, 2013, at 12:31 PM, Geoff Gerhardt <geoff.gerhardt at gmail.com> wrote:

> I could likely do something similar, just put an elbow on my exhaust exit so it points to the rear instead of down as a first pass and see if any improvements in speed are observed.
> 
> Heres what my exhaust currently looks like.
> 
> Geoff
> 
> 
> On Fri, May 10, 2013 at 12:44 PM, Scott Derrick <scott at tnstaafl.net> wrote:
>> I did change from straight down to rearward facing exhaust. I saw a 3-5 knot increase.
>> 
>> I attached before and after images.
>> 
>> 
>> Scott
>> 
>> 
>> 
>> -------- Original Message --------
>> Subject: Re: REFLECTOR: Performance
>> From: Richard J. Gentil <richard at naples-air-center.com>
>> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>> Date: 05/10/2013 09:47 AM
>> 
>>> I would say we need someone (Geoff, Geoff) who only changes the exhaust and nothing else, runs a test and reports back to the Reflector with the findings
>>> 
>>> Richard
>>> 
>>> Sent from my iPhone 5
>>> 
>>> On May 10, 2013, at 11:38 AM, Kevin Baker <flykb at verizon.net> wrote:
>>> 
>>>> 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
>>>>>> 
>>>>>> 
>>>>>> -----Original Message-----
>>>>>> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
>>>>>> Behalf Of reflector-request at tvbf.org
>>>>>> Sent: Thursday, May 09, 2013 7:47 PM
>>>>>> To: reflector at tvbf.org
>>>>>> Subject: Reflector Digest, Vol 98, Issue 27
>>>>>> 
>>>>>> Send Reflector mailing list submissions to
>>>>>>   refle
>>>> 
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>> 
>> -- 
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>> Eleanor Roosevelt
>> 
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