REFLECTOR: Performance
David Rene Dugas
renedugas at gmail.com
Fri May 10 10:12:26 CDT 2013
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-----
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> 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>
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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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