REFLECTOR: Early model Velocity RG Engine Cooling (Now - which performance mods)?

[Dave T Nelson]

I've got a STD-RG, Lycoming IO-360 and an MT prop.  I started off with
armpit scoops feeding into a tops-down plenum, along with a single nose
mounted oil cooler.  Intake air was off a second scoop mounted on the right
wing.

My situation was that I built my plane while sharing my shop with a good
buddy who built a really nice Cozy 3 place.  We got them both flying at
about the same time, and spent many happy years racing (and bragging).  I
still say his plane was the slow ugly one.

Anyway, the main thing(s) you do to make these airplanes go fast are all
about weight and aerodynamics.  Power increases don't get the same bang for
the buck.  I focused mostly on drag reduction... really clean gear doors,
clean canard/fuselage interface, minimum cooling drag, and clean exhaust
system.  The last two are the most important.

The armpit scoops are a bit of an aerodynamic disaster... they are all too
big.  If you tuft or do an oil study on them, you'll find that the bulk of
the air is getting pushed back out of the scoop because of the inherent
flow resistance of the  tubes taking the air to the top of the plenum, the
flow through the plenum & engine, and the output behind the prop.  An oil
study will likely also show nearly dead air at the output (right behind the
prop).  The total square inches of inlet are too great, and so is the total
square inches of outlet.

Many of my initial mods were in trying to clean up the cooling and intake
air..  I made several different styles of cooling air intakes, each smaller
than the last.  Nothing worked particularly well.  Eventually, after
developing significant cooling issues (which turned out to be an engine
issue, not an aerodynamic problem), I went to the rooftop NACAs.  As I
said... they work fabulously.  I take my induction air off the right NACA.
There are no external protrusions on my plane.

The exhaust changes were probably the most speed gain.  I've gone from the
original rear exiting 2 in 1's that exit through tubes attached to the
lower cowl, to the "straight out the bottom" types you see on many XLs
today (which were by far the worst performers - a real disaster), to what I
have today - a one-of design of my own that keeps the entire exhaust inside
the cowl and exits aft of the prop.  That was a big gain!

OK, performance... I see around 185 knots true +/- at around 25 squared...
middling altitudes... at around 10 - 11 gallons / hour ... cold air, down
low, with a light plane is better still.  It's not as fast as I'd like, but
I'm not done trying.  The next effort will be a complete cowl redesign to
get rid of those awful turns where the cowl angles in just aft of the last
cylinder.  All the attached air detaches at that point...

Hope this helps.  What numbers to you see?

Dave

Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering



----- Message from "Richard J. Gentil" <richard at naples-air-center.com> on
Tue, 20 Nov 2012 10:38:47 -0500 -----
                                                                    
      To: Velocity Aircraft Owners and Builders list                
          <reflector at tvbf.org>                                      
                                                                    
 Subject: Re: REFLECTOR: Early model Velocity RG Engine Cooling     
          (David Smith)                                             
                                                                    


Dave N,

Which go fast mod have you done and what speeds are you getting? (Please
mention the engine and prop combo you are running.)

Thanks,

Richard

Sent from my iPhone 5
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