REFLECTOR: Performance
Scott Derrick
scott at tnstaafl.net
Fri May 10 10:35:33 CDT 2013
Obviously I agree with Rene, if you read my prior post in bringing this
aspect of exhaust plume drag into the conversation.
I would say that this is the largest contributer to any increase in
airspeed if you switch from a downward facing exhaust to a rearward
facing exhaust.
Scott
-------- Original Message --------
Subject: Re: REFLECTOR: Performance
From: David Rene Dugas <renedugas at gmail.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Date: 05/10/2013 09:12 AM
> 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
>>
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>> Today's Topics:
>>
>> 1. Re: Performance (Dave T Nelson)
>> 2. Re: Performance (Kevin Baker)
>> 3. Re: Performance (Scott Derrick)
>> 4. Re: Performance (Rene Dugas)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Thu, 9 May 2013 21:03:57 -0500
>> From: Dave T Nelson <dtnelson at us.ibm.com>
>> To: reflector at tvbf.org
>> Cc: reflector-bounces at tvbf.org
>> Subject: Re: REFLECTOR: Performance
>> Message-ID:
>>
>> <OF65167550.45874A96-ON86257B67.000B2B13-86257B67.000B58D7 at us.ibm.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> 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>
>>
>> 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
>>> 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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>> Message: 2
>> Date: Thu, 09 May 2013 21:12:39 -0500
>> From: Kevin Baker <flykb at verizon.net>
>> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>> Cc: "reflector at tvbf.org" <reflector at tvbf.org>,
>> "reflector-bounces at tvbf.org" <reflector-bounces at tvbf.org>
>> Subject: Re: REFLECTOR: Performance
>> Message-ID: <2FD2DF54-EC23-4B3D-8B24-6669FDA3DDCE at verizon.net>
>> Content-Type: text/plain; charset="utf-8"
>>
>> 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> 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>
>>> 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> 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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>> ------------------------------
>>
>> Message: 3
>> Date: Thu, 09 May 2013 20:22:54 -0600
>> From: Scott Derrick <scott at tnstaafl.net>
>> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>> Subject: Re: REFLECTOR: Performance
>> Message-ID: <518C59FE.40508 at tnstaafl.net>
>> Content-Type: text/plain; charset="us-ascii"
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>> Message: 4
>> Date: Thu, 9 May 2013 21:45:31 -0500
>> From: Rene Dugas <renedugas at gmail.com>
>> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>> Subject: Re: REFLECTOR: Performance
>> Message-ID: <F8774F3B-9B29-4684-9223-81BB618A81EC at gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> Brian, I did oil studies to show air disturbance from IO-540 down exhaust
>> exiting about three inches. The air disturbance for each side was about 14
>> inches in diameter. I've never gotten around to building tear drop fairing
>> but I'm certain they would help. Exit out the back would be even better or
>> through the prop like my outboard motor. I know I got carried away.?
>>
>> Sent from Rene's iPad. A pleasure. Go Apple.
>>
>>
>> On May 9, 2013, at 11:23 AM, Brian Michalk <michalk at awpi.com> wrote:
>>
>>> I still don't understand the drag mechanism for normal angle of exhaust
>> being a drag.
>>> Does anyone know where I can find NACA or other research on this?
>>>
>>> On 5/9/2013 11:07 AM, Richard J. Gentil wrote:
>>>> Geoff,
>>>>
>>>> If you make the exhaust change I would be very interested in your results
>> since mine currently exit straight down.
>>>>
>>>> Richard
>>>>
>>>> Sent from my iPhone 5
>>>>
>>>> On May 8, 2013, at 10:59 PM, Geoff Gerhardt <geoff.gerhardt at gmail.com>
>> wrote:
>>>>
>>>>> Scott,
>>>>>
>>>>> Thanks - that was the insight I was looking for and what I suspected. I
>> would actually prefer to have the normal, shorter wing - I'd love the 15kts
>> in speed and would gladly live with a little higher stall speed.
>>>>>
>>>>> Now, given that, I wonder if there's anything I could do that could
>> improve my performance. The two things that I'm considering are changing my
>> exhaust config from exiting straight down to exiting inside the cowling at
>> the prop. I've heard some folks state they have seen significant
>> improvements with that mod. The other was an intake ram scoop - would that
>> give me more MAP at altitude and a little more power?
>>>>>
>>>>> Thanks for all the performance comments/comparisons...keep them coming.
>>>>>
>>>>> Geoff
>>>>>
>>>>> On Wed, May 8, 2013 at 8:31 PM, Scott Baker <scottb33333 at gmail.com>
>> wrote:
>>>>>> I notice that several responders are giving numbers for a Velocity
>> Standard RG, while Geoff's aircraft is a Velocity 173 (aka LW 'Long Wing').
>>>>>> Velocity Standard models, with their smaller wings and reduced drag,
>> are faster than their 173 brethren ... by 15 knots on average (with
>> comparable engines and propellers).
>>>>>> The factory V173FG trainer is hard pressed to see 145KTAS in cruise. I
>> think the RG version cruises between 155-160KTAS (about 15knots faster than
>> the fixed gear model).
>>>>>> These numbers are pretty close to what Geoff is reporting for his
>> aircraft.
>>>>>> Scott B.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 5/8/2013 10:38 AM, Geoff Gerhardt wrote:
>>>>>>> Folks,
>>>>>>>
>>>>>>> I'm getting pretty consistent performance out of my 173RG over the
>> last 8-9 months since initial flight testing. My
>> question to you guys is, are the performance numbers I'm seeing typical, or
>> should I be seeing better performance? Normally, on a cross country, I'll
>> fly b/w ~8-12,000', ~60deg LOP which typically has me going 150kias at
>> 8-8.5gph. Full power, 160kias is about my max speed.
>>>>>>>
>>>>>>> I have a fixed-pitch Catto prop (66x74, design target 200mph @
>> 2800RPM). When I'm doing 160kts, my prop is spinning at ~2800RPM. That
>> tells me that I have the power to spin the prop, but may have air frame drag
>> that's keeping me from seeing the 200mph predicted by Catto at 2800RPM.
>>>>>>>
>>>>>>> I have a standard 200hp, Lyc IO-360, Lightspeed EI on one side, Mag on
>> the other. Timing as per spec for both EI and Mag. About 90hrs on the
>> engine (rebuilt). Compression/oil consumption is normal. Very stable
>> performance from the engine.
>>>>>>>
>>>>>>> My plane is fully finished and pretty tight. Main/nose gear doors are
>> not hanging out and are reasonably well tucked in when the gear is raised.
>> Main wing angles of incidence are spot on, no rudder trimming was necessary
>> to center the ball - she flies nice and straight.
>>>>>>>
>>>>>>> The factory predicts I should be able to cruise at 175kias - that's
>> just not possible with my current setup. Can others with Std Velocities
>> relate the performance you are seeing? Is this as good as it gets, or does
>> anyone have suggestions for things to check to see if I can eek out a bit
>> more speed?
>>>>>>>
>>>>>>> Thanks.
>>>>>>>
>>>>>>> Geoff
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
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>>>>>>
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>>>>
>>>>
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>>>
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