REFLECTOR: Performance

Fri May 10 12:31:39 CDT 2013

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@**tvbf.org<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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