From: "Finn Lassen finn.lassen@verizon.net" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Intake design
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
References: <list-12952244@logan.com>
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Date: Fri, 13 Sep 2019 10:39:09 -0400
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Thanks Lynn.

Given that I only have about 12" from engine block to plenum wall and 
shooting for maybe 7,500 RPM, is the distance from the bell mouth to the 
wall (1.25" with 1.25" runners) more important than keeping the runners 
as long as possible?

In other words, I could have 10.75" runners with a 1.25" distance from 
wall, or 11.50" runners with 0.5" distance from wall or anything in between.

It's for the Renesis engine.

BTW, I intend to 3D print the mouths, so I'll have to look up the ideal 
shape you and Charlie are talking about. (I guess a teardrop with a hole 
in it, but I'll look it up.)

Finn

On 9/12/2019 9:15 PM, lehanover lehanover@aol.com wrote:
> The rotary and most other engines are a collection of small engines 
> sharing a crank shaft.
>
> So, the rotary is two engines with about the same intake system. On 
> the dyno and on the flow bench, the biggest
> influence on performance is the shape of the intake horns. Should look 
> like a trumpet bell. The higher the RPM
> the bigger the diameter of the bell. Because: airflow into the bell 
> comes from all directions. A straight tube is the worst. Air flows up 
> the sides of the tube and has to make a 180 to enter the tube. Air has 
> mass and the 180 serves to choke off part of the tube. (As though the 
> tube developed a smaller diameter). So, a big radius allows
> for a slower turn in that 180 and flow rate increases. You can find 
> flow going the wrong direction just inside the bell on poor designs. 
> The best design was on old SU carbs where the bell looked like a ring 
> slit into two pieces and mounted on a flat surface. Cheap and the very 
> best design. I will try to find pictures and post them.
>
> Best is a large bell shape and a taper to the port size. The tuned 
> length is for one RPM. The exact length you choose may be great or 
> just short of great. Anything will be better than a stock air filter. 
> Allow at least the diameter of the interior of the bell as a distance 
> to any structure like a tube wall or a flat sided filter box.
> A flat sheet with holes the size of the bells is fine. In very few 
> cases will both housings be putting out best power at the very same time.
>
> Round tube on a flat side like a "D" shape works well. Anything flat 
> must be thick and stiff or it will die.
>
> Lynn E. Hanover


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    <div class="moz-cite-prefix">Thanks Lynn.<br>
      <br>
      Given that I only have about 12" from engine block to plenum wall
      and shooting for maybe 7,500 RPM, is the distance from the bell
      mouth to the wall (1.25" with 1.25" runners) more important than
      keeping the runners as long as possible?<br>
      <br>
      In other words, I could have 10.75" runners with a 1.25" distance
      from wall, or 11.50" runners with 0.5" distance from wall or
      anything in between.<br>
      <br>
      It's for the Renesis engine.<br>
      <br>
      BTW, I intend to 3D print the mouths, so I'll have to look up the
      ideal shape you and Charlie are talking about. (I guess a teardrop
      with a hole in it, but I'll look it up.)<br>
      <br>
      Finn<br>
      <br>
      On 9/12/2019 9:15 PM, lehanover <a class="moz-txt-link-abbreviated" href="mailto:lehanover@aol.com">lehanover@aol.com</a> wrote:<br>
    </div>
    <blockquote type="cite" cite="mid:list-12952244@logan.com">
      <meta http-equiv="content-type" content="text/html; charset=utf-8">
      <div>
        <div class="userEdit" style="font-family: arial, helvetica,
          sans-serif; font-size: 10pt; color: #000000;">
          <div><span style="font-family: arial, helvetica, sans-serif;
              font-size: 10pt; color: #000000;">The rotary and most
              other engines are a collection of small engines sharing a
              crank shaft.??<br>
              <br>
            </span></div>
          <div><span style="font-family: arial, helvetica, sans-serif;
              font-size: 10pt; color: #000000;">So, the rotary is two
              engines with about the same intake system. On the dyno and
              on the flow bench, the biggest</span></div>
          <div><span style="font-family: arial, helvetica, sans-serif;
              font-size: 10pt; color: #000000;">influence on performance
              is the shape of the intake horns. Should look like a
              trumpet bell. The higher the RPM</span></div>
          <div><span style="font-family: arial, helvetica, sans-serif;
              font-size: 10pt; color: #000000;">the bigger the diameter
              of the bell. Because: airflow into the bell comes from all
              directions. A straight tube is the worst. Air flows up the
              sides of the tube and has to make a 180 to enter the tube.
              Air has mass and the 180 serves to choke off part of the
              tube. (As though the tube developed a smaller diameter).
              So, a big radius allows</span></div>
          <div><span style="font-family: arial, helvetica, sans-serif;
              font-size: 10pt; color: #000000;">for a slower turn in
              that 180 and flow rate increases. You can find flow going
              the wrong direction just inside the bell on poor designs.
              The best design was on old SU carbs where the bell looked
              like a ring slit into two pieces and mounted on a flat
              surface. Cheap and the very best design. I will try to
              find pictures and post them.?? ?? ?? <br>
            </span></div>
          <div><br>
          </div>
          <div><span style="font-family: arial, helvetica, sans-serif;
              font-size: 10pt; color: #000000;">Best is a large bell
              shape and a taper to the port size. The tuned length is
              for one RPM. The exact length you choose may be great or
              just short of great. Anything will be better than a stock
              air filter. Allow at least the diameter of the interior of
              the bell as a distance to any structure like a tube wall
              or a flat sided filter box.<br>
            </span></div>
          <div><span style="font-family: arial, helvetica, sans-serif;
              font-size: 10pt; color: #000000;">A flat sheet with holes
              the size of the bells is fine. In very few cases will both
              housings be putting out best power at the very same time.<br>
            </span></div>
          <div><br>
          </div>
          <div><span style="font-family: arial, helvetica, sans-serif;
              font-size: 10pt; color: #000000;">Round tube on a flat
              side like a "D" shape works well. Anything flat must be
              thick and stiff or it will die.</span></div>
          <div><br>
          </div>
          <div><span style="font-family: arial, helvetica, sans-serif;
              font-size: 10pt; color: #000000;">Lynn E. Hanover</span></div>
        </div>
      </div>
    </blockquote>
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