X-Virus-Scanned: clean according to Sophos on Logan.com From: "Charlie England" Received: from mail-yh0-f46.google.com ([209.85.213.46] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTPS id 6996211 for flyrotary@lancaironline.net; Wed, 23 Jul 2014 22:58:53 -0400 Received-SPF: pass receiver=logan.com; client-ip=209.85.213.46; envelope-from=ceengland7@gmail.com Received: by mail-yh0-f46.google.com with SMTP id a41so1461114yho.5 for ; Wed, 23 Jul 2014 19:58:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=message-id:date:from:user-agent:mime-version:to:subject:references :in-reply-to:content-type; bh=EaU3lp+EwSX/6spRCVU6RidIXGGUF4qhaKH12I3h84c=; b=x9ezJuPgm8ym0R6Ur9JXZNz4iBP32nyIGlcGERewZBAOOMPdreFr9Ue/nQaiWxvQNA YMpTHAITxkcFjfniMumjxGbpRvcFAK7HmIpkonm8CTtXvoSjBVY/coJbL5i6Eeo7Mtxk 4u25b1iEUa9CDXttl6S1lhkO3z0F/Ak3aeAoOdy/r3TF9iPsMnhvaDCtVFaM2gW74XpK e1xL4ip4emyuMyoyoiVOYdXc5T0pqymNMQBiUBjdUo+0mqDGrww/n6MjYLMsAOWoxtTJ pRLEH2Do/SEbsO3xZxgzcxF3sSIJFVyiNgFHLfbj689i8M9vWySOo8VkzWogGCuIK8uY s5Og== X-Received: by 10.236.133.165 with SMTP id q25mr7992640yhi.62.1406170696374; Wed, 23 Jul 2014 19:58:16 -0700 (PDT) Return-Path: Received: from ?IPv6:2602:306:25fa:d179:2ddc:2932:ca01:9f4f? ([2602:306:25fa:d179:2ddc:2932:ca01:9f4f]) by mx.google.com with ESMTPSA id n68sm11303433yhe.23.2014.07.23.19.58.14 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 23 Jul 2014 19:58:15 -0700 (PDT) Message-ID: <53D0767D.5030308@gmail.com> Date: Wed, 23 Jul 2014 21:59:09 -0500 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Re: Rv7 renises p port References: In-Reply-To: Content-Type: multipart/alternative; boundary="------------030007040601040705050407" This is a multi-part message in MIME format. --------------030007040601040705050407 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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 > > 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 > > --------------030007040601040705050407 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 8bit
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
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