REFLECTOR: Performance

[Dave T Nelson]

Richard, I can't point at any NACA or other research, but I changed from a
"straight out the bottom" to an enclosed aft firing exhaust on my 200 HP
STD-RG.  I picked up at least 10 knots, really more like 15.  I did it
because all of my EZ friends, and especially the guys I know that race, had
done it and claimed great results.

Clearly shooting the exhaust out the bottom creates a big plume of
disturbed air... I've struggled as to exactly how the force of that "drag
plume" is translated back to the aircraft... but it sure worked for me.

Here's a picture of my exhaust.  Yes, I do get soot on my three bladed
prop.  No, I've never seen any damage issue to the prop from the hot gas
(after about 400 - 500 hours).

(See attached file: IMG_1042.jpg)

Dave

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


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.

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