From: "James Osborn" <flyrotary@lancaironline.net>
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Date: Thu, 24 Jul 2014 10:18:31 -0700
Message-ID: <CAF_F+MVbbZvUmJwNtxVqPt0RDe+tpPPdnpcKaRFSUAriQg8kvQ@mail.gmail.com>
Subject: Re: [FlyRotary] Re: Rv7 renises p port
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Charlie said:  Ice sails, desert sails, and now, even unlimited class
sailboats can sail faster than the wind. 'Negative slippage'. :-)

I don't think the analogy quite applies here.  For those types of crafts it
is the wind that is doing the powering.  While it is true these types of
craft can sail faster than the wind, but not while pointing straight into
it!  By definition to cruise in an airplane, the prop has to be generating
some kind of thrust and therefore could never go faster than "the wind" -
the only wind it sees is the relative wind that is generated due to its own
thrust (in cruise).  In a descent, sure negative slippage is a fact.  And
slippage has to increase greatly in a climb.  I guess I am arguing that the
only way you could see zero or negative slippage in cruise is if either
your blade cross section is asymmetrical (it usually is right?) or if the
pitch number used in the calculation is not really right based on the kinds
of factors you outlined Charlie.

Supposing that we have a typical non-symmetric blade cross section, an
accurate pitch based on the chord line of the cross section, and I suppose
a twist that is correct for the cruise RPM.  What then would be considered
a good or reasonable slippage in cruise?  I saw 3% thrown out there.  And
if your prop selection is good for all those conditions (in other words as
efficient as possible), is this the slippage you expect?  I am just
wondering if you can use a slippage calculation to judge efficiency
(roughly).

-- James

On Wed, Jul 23, 2014 at 7:59 PM, Charlie England <
flyrotary@lancaironline.net> wrote:

>  Ice sails, desert sails, and now, even unlimited class sailboats can
> sail faster than the wind. 'Negative slippage'. :-)
>
> A more significant point might be that pitch numbers are virtually
> meaningless, unless you're comparing two props from the same prop maker
> with the same blade plan form. Even then, it just tells you which has a
> finer pitch than the other.
>
> Variables can be: whether the pitch is measured on the back side of the
> blade or through the chord line, where along the diameter the pitch angle
> is measured (due to blade twist), and no doubt others I'm not smart enough
> to think of at the moment.
>
> Bottom line is that unless there's an identical airframe flying an
> identical prop, the pitch number isn't a reliable indicator of speed.
>
> FWIW,
>
> Charlie
>
>
>
>
> On 7/23/2014 7:45 PM, James Osborn wrote:
>
> I don't know jack about slippage, but I think it is the percentage
> difference between actual distance traveled and theoretical distance
> traveled if your propeller corkscrewed through the air with no thrust.  I
> found a prop slip calculator online and for 86 inch pitch, 2.85 gear ratio,
> 7000 rpm, 180 mph, I get 10% slip.  Granted the calculator was for boat
> propellers, but I don't think it matters as long as the units are correct.
>  There has to be some slip because there would be no thrust otherwise.  So
> what is considered a reasonable or good amount of slip?  Using Bill's
> numbers 86 inch pitch, 2.85 gear ratio, 7000 rpm, 200 mph, I get 0% slip.
>  That can't be right!
>
>
> On Fri, Jul 4, 2014 at 7:19 AM, Bill Bradburry <
> flyrotary@lancaironline.net> wrote:
>
>> Christian,
>>
>> It seems that you have a lot of prop slippage at cruise.  I think that at
>> that prop rpm you should be getting 200mph if you had no slippage.
>>
>> Bill
>>
>> -----Original Message-----
>> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
>> Sent: Thursday, July 03, 2014 4:01 PM
>> To: Rotary motors in aircraft
>> Subject: [FlyRotary] Rv7 renises p port
>>
>> Well hi all
>> Just thought I'd throw out there the mods I,ve done to the renises in an
>> rv7'.
>> Well the p ported engine is now back in the plane and running well, over
>> the
>> standard short manifold that was originally in the plane I have gained
>> around 400 static rpm, same prop and gearbox combo, 2.85 ratio, this
>> equates
>> to allot more hp at takeoff, just shy of 2300 prop rpm, I'm running a
>> prince
>> p tip prop at 68" x 86" pitch,
>> At 8000 ft it is turning 7000 at 180 mph tas which is an improvement of 25
>> mph on previous tests, . So next plan is bigger prop and less pitch to let
>> it rev to 7500 in strait and level.
>>
>> Cheers
>> Christian
>> Rv7 renises Aus
>>
>>
>> Sent from my iPad
>> --
>> Homepage:  http://www.flyrotary.com/
>> Archive and UnSub:
>> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>>
>>
>> --
>> Homepage:  http://www.flyrotary.com/
>> Archive and UnSub:
>> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>>
>
>
>

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<div dir=3D"ltr">Charlie said: =C2=A0Ice sails, desert sails, and now, even=
 unlimited class sailboats can sail faster than the wind. &#39;Negative sli=
ppage&#39;. :-)<div><br></div><div>I don&#39;t think the analogy quite appl=
ies here. =C2=A0For those types of crafts it is the wind that is doing the =
powering. =C2=A0While it is true these types of craft can sail faster than =
the wind, but not while pointing straight into it! =C2=A0By definition to c=
ruise in an airplane, the prop has to be generating some kind of thrust and=
 therefore could never go faster than &quot;the wind&quot; - the only wind =
it sees is the relative wind that is generated due to its own thrust (in cr=
uise). =C2=A0In a descent, sure negative slippage is a fact. =C2=A0And slip=
page has to increase greatly in a climb. =C2=A0I guess I am arguing that th=
e only way you could see zero or negative slippage in cruise is if either y=
our blade cross section is asymmetrical (it usually is right?) or if the pi=
tch number used in the calculation is not really right based on the kinds o=
f factors you outlined Charlie.</div>
<div><br></div><div>Supposing that we have a typical non-symmetric blade cr=
oss section, an accurate pitch based on the chord line of the cross section=
, and I suppose a twist that is correct for the cruise RPM. =C2=A0What then=
 would be considered a good or reasonable slippage in cruise? =C2=A0I saw 3=
% thrown out there. =C2=A0And if your prop selection is good for all those =
conditions (in other words as efficient as possible), is this the slippage =
you expect? =C2=A0I am just wondering if you can use a slippage calculation=
 to judge efficiency (roughly).<br>
<div class=3D"gmail_extra"><br></div><div class=3D"gmail_extra">-- James<br=
><br><div class=3D"gmail_quote">On Wed, Jul 23, 2014 at 7:59 PM, Charlie En=
gland <span dir=3D"ltr">&lt;<a href=3D"mailto:flyrotary@lancaironline.net" =
target=3D"_blank">flyrotary@lancaironline.net</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-=
left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;p=
adding-left:1ex">
 =20
   =20
 =20
  <div bgcolor=3D"#FFFFFF" text=3D"#000000">
    <div>Ice sails, desert sails, and now, even
      unlimited class sailboats can sail faster than the wind. &#39;Negativ=
e
      slippage&#39;. :-)<br>
      <br>
      A more significant point might be that pitch numbers are virtually
      meaningless, unless you&#39;re comparing two props from the same prop
      maker with the same blade plan form. Even then, it just tells you
      which has a finer pitch than the other.<br>
      <br>
      Variables can be: whether the pitch is measured on the back side
      of the blade or through the chord line, where along the diameter
      the pitch angle is measured (due to blade twist), and no doubt
      others I&#39;m not smart enough to think of at the moment. <br>
      <br>
      Bottom line is that unless there&#39;s an identical airframe flying a=
n
      identical prop, the pitch number isn&#39;t a reliable indicator of
      speed.<br>
      <br>
      FWIW,<br>
      <br>
      Charlie<div><div class=3D"h5"><br>
      <br>
      <br>
      <br>
      On 7/23/2014 7:45 PM, James Osborn wrote:<br>
    </div></div></div><div><div class=3D"h5">
    <blockquote type=3D"cite">
      <div dir=3D"ltr">I don&#39;t know jack about slippage, but I think it=
 is
        the percentage difference between actual distance traveled and
        theoretical distance traveled if your propeller corkscrewed
        through the air with no thrust. =C2=A0I found a prop slip calculato=
r
        online and for 86 inch pitch, 2.85 gear ratio, 7000 rpm, 180
        mph, I get 10% slip. =C2=A0Granted the calculator was for boat
        propellers, but I don&#39;t think it matters as long as the units
        are correct. =C2=A0There has to be some slip because there would be
        no thrust otherwise. =C2=A0So what is considered a reasonable or go=
od
        amount of slip? =C2=A0Using Bill&#39;s numbers 86 inch pitch, 2.85 =
gear
        ratio, 7000 rpm, 200 mph, I get 0% slip. =C2=A0That can&#39;t be ri=
ght!</div>
      <div class=3D"gmail_extra"><br>
        <br>
        <div class=3D"gmail_quote">On Fri, Jul 4, 2014 at 7:19 AM, Bill
          Bradburry <span dir=3D"ltr">&lt;<a href=3D"mailto:flyrotary@lanca=
ironline.net" target=3D"_blank">flyrotary@lancaironline.net</a>&gt;</span>
          wrote:<br>
          <blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8=
ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-sty=
le:solid;padding-left:1ex">Christian,<br>
            <br>
            It seems that you have a lot of prop slippage at cruise. =C2=A0=
I
            think that at<br>
            that prop rpm you should be getting 200mph if you had no
            slippage.<br>
            <br>
            Bill<br>
            <div>
              <div><br>
                -----Original Message-----<br>
                From: Rotary motors in aircraft [mailto:<a href=3D"mailto:f=
lyrotary@lancaironline.net" target=3D"_blank">flyrotary@lancaironline.net</=
a>]<br>
                Sent: Thursday, July 03, 2014 4:01 PM<br>
                To: Rotary motors in aircraft<br>
                Subject: [FlyRotary] Rv7 renises p port<br>
                <br>
                Well hi all<br>
                Just thought I&#39;d throw out there the mods I,ve done to
                the renises in an<br>
                rv7&#39;.<br>
                Well the p ported engine is now back in the plane and
                running well, over the<br>
                standard short manifold that was originally in the plane
                I have gained<br>
                around 400 static rpm, same prop and gearbox combo, 2.85
                ratio, this equates<br>
                to allot more hp at takeoff, just shy of 2300 prop rpm,
                I&#39;m running a prince<br>
                p tip prop at 68&quot; x 86&quot; pitch,<br>
                At 8000 ft it is turning 7000 at 180 mph tas which is an
                improvement of 25<br>
                mph on previous tests, . So next plan is bigger prop and
                less pitch to let<br>
                it rev to 7500 in strait and level.<br>
                <br>
                Cheers<br>
                Christian<br>
                Rv7 renises Aus<br>
                <br>
                <br>
                Sent from my iPad<br>
                --<br>
                Homepage: =C2=A0<a href=3D"http://www.flyrotary.com/" targe=
t=3D"_blank">http://www.flyrotary.com/</a><br>
                Archive and UnSub:<br>
                <a href=3D"http://mail.lancaironline.net:81/lists/flyrotary=
/List.html" target=3D"_blank">http://mail.lancaironline.net:81/lists/flyrot=
ary/List.html</a><br>
                <br>
                <br>
                --<br>
                Homepage: =C2=A0<a href=3D"http://www.flyrotary.com/" targe=
t=3D"_blank">http://www.flyrotary.com/</a><br>
                Archive and UnSub: =C2=A0 <a href=3D"http://mail.lancaironl=
ine.net:81/lists/flyrotary/List.html" target=3D"_blank">http://mail.lancair=
online.net:81/lists/flyrotary/List.html</a><br>
              </div>
            </div>
          </blockquote>
        </div>
        <br>
      </div>
    </blockquote>
    <br>
  </div></div></div>

</blockquote></div><br></div></div></div>

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