REFLECTOR: Performance

[John Dibble]

On 5/9/2013 9:22 PM, Scott Derrick wrote:
> Yeah, I always thought the point was the drag from the exhaust plume?

I attended a presentation at OSK a few years back about things you can 
do to increase speed.  One thing was for pointing the exhaust to the 
rear AND sizing the exhaust pipe diameter to the optimum size. Simply 
pointing it to the rear may give varying results depending on the size 
of the exhaust.

John

>
> Just because its a tube of air and not a steel tube doesn't mean the 
> drag of the air flowing by the plane breaking it off or bending it 
> into the slip stream doesn't impart some drag to the plane?
>
> Scott
>
> -------- Original Message --------
> Subject: Re: REFLECTOR: Performance
> From: Kevin Baker <flykb at verizon.net>
> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> Date: 05/09/2013 08:12 PM
>> Any/ or also with the removal of down pointing exhaust drag.
>>
>> Kevin
>>
>> .
>>
>> On May 9, 2013, at 9:03 PM, Dave T Nelson <dtnelson at us.ibm.com 
>> <mailto:dtnelson at us.ibm.com>> wrote:
>>
>>> 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
>>>
>>> *To:*
>>> 	
>>>
>>>     Velocity Aircraft Owners and Builders list <reflector at tvbf.org
>>>     <mailto:reflector at tvbf.org>> 
>>>
>>> *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_ 
>>> <mailto: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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