REFLECTOR: Performance

Grover McNair grover at mcnairperformance.com
Thu May 9 13:43:20 CDT 2013


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

 

  _____  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Brian Michalk
Sent: Thursday, May 09, 2013 12:24 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Performance

 

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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