REFLECTOR: Performance

[Scott Derrick]

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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