X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.120] verified) by logan.com (CommuniGate Pro SMTP 5.3.9) with ESMTP id 4498825 for flyrotary@lancaironline.net; Fri, 08 Oct 2010 16:49:24 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.120; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=1.1 cv=UAZ0ep3suvkVn+xl78ZyFqEJZfCyw4fsauT9kMdOA88= c=1 sm=0 a=8S8fuD5XrasA:10 a=rPkcCx1H5rrOSfN0dPC7kw==:17 a=3oc9M9_CAAAA:8 a=ayC55rCoAAAA:8 a=aHY6q_TptCOuUQUsdqMA:9 a=6LKpO8gYRn_b0uMoh4wA:7 a=7CsKNwarSlS51TUOFXIjYnJ5INwA:4 a=wPNLvfGTeEIA:10 a=U8Ie8EnqySEA:10 a=ivMjd3Y9LmCn8tYG:21 a=U3Uhx63Z_n0mmnJp:21 a=Ia-xEzejAAAA:8 a=xpiEdjyoMjYjKpiNdu0A:9 a=2vz2xmmitYPyVsZ41noA:7 a=flTLe9z49ATCaGixFWA0SmyVeNAA:4 a=EzXvWhQp4_cA:10 a=JE2_UPv0sgigJFxFdTUA:9 a=d-HiJqM5egwEc8v5Wbp04NYpAEsA:4 a=KQqxNPgzF0kA:10 a=ucH7BwLj_I8A:10 a=tOQuWktmHWURPFkL:18 a=rPkcCx1H5rrOSfN0dPC7kw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 174.110.167.5 Received: from [174.110.167.5] ([174.110.167.5:57867] helo=EdPC) by cdptpa-oedge04.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id A7/9B-03860-1B38FAC4; Fri, 08 Oct 2010 20:48:50 +0000 Message-ID: <49956DBA670E47B7842FC0ABB8847DEA@EdPC> From: "Ed Anderson" To: "Rotary motors in aircraft" References: In-Reply-To: Subject: Re: [FlyRotary] Re: Prop Chord vs RPM Date: Fri, 8 Oct 2010 16:48:42 -0400 MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_NextPart_000_001F_01CB6708.AA108600"; type="multipart/alternative" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 This is a multi-part message in MIME format. ------=_NextPart_000_001F_01CB6708.AA108600 Content-Type: multipart/alternative; boundary="----=_NextPart_001_0020_01CB6708.AA108600" ------=_NextPart_001_0020_01CB6708.AA108600 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Lynn, I've looked into trying to calculate such several times and after = getting a headache each time I gave up. Prop calculations makes duct = calculations appear simple {:>). Having said that here is one equation = (below) that relates Thrust "T" and propeller diameter "D". There are = only three other significant factor in the equation. There is the speed = of the air stream into the prop disc "v" and the acceleration imparted = to the air stream by the prop "Dv" - air density is what it will be and = you can't affect that (except by where you fly). =20 so if you look at the factors one could conclude that Prop diameter = appears to be the most signficant factor (at least in this momentum = equation). The Thrust is directly proportional to the square of the = diameter. So if all else is equal then a 74" dia prop would produce = 74^2 =3D 5476, whereas 76 " dia prop would produce 76^2 =3D 5776 or approx 5467/5776 =3D 0.9467 giving approx 5% more thrust for the = slightly longer prop. I went from a 68" prop to a 76" prop when I switched from my 2.17 to the = 2.85 gear box. I was very impressed with the change in take off = performance. So comparing the two (Yes, RPM went down a bit on the prop = with the 2.85 so in real life the comparison is skewed), but in any case = at the same PROP rpm. The 66^2 =3D 4356 going to the 76 gave me 5776, comparing thrust for the two 4356/5776 =3D = 0.75 or a gain of 25% in thrust for the same prop rpm - now that will = get your attention. =20 However, this equation clearly does not take prop chord into effect and = based on the simple chart of three data points - it would appear to play = a major role in static rpm and thrust.=20 =20 From: Lehanover@aol.com=20 Sent: Friday, October 08, 2010 1:54 PM To: Rotary motors in aircraft=20 Subject: [FlyRotary] Re: Prop Chord vs RPM In a message dated 10/8/2010 11:48:42 A.M. Eastern Daylight Time, = eanderson@carolina.rr.com writes: I did a plot of chord of the three props mentioned recently. The = props were of 74-76 inches in dia and made by Catto (2) and Performance = Prop (1). Note my Performance Prop was shorter only 74 compared to Sams = and Dennis Catto Props. When mine was 76" in dia my static was lower = than 6000 which would have all three props pretty much on a straight = line. I don't know if one could make much of a linear relationship = between prop chord and rpm based on just three data points, but thought = some might find it interesting. And now how about the thrust for each diameter and blade chord and = pitch. What is the most effective prop for the most common diameters? Lynn E. Hanover ------=_NextPart_001_0020_01CB6708.AA108600 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Lynn, I've looked into trying to calculate such = several times=20  and after getting a headache each time I gave up.  Prop = calculations=20 makes duct calculations appear simple {:>).  Having said that = here is=20 one equation (below) that relates Thrust "T" and propeller diameter = "D".  There are only three other significant factor in the = equation. =20 There is the speed of the air stream into the prop disc "v" and the = acceleration=20 imparted to the air stream by the prop "Dv" - = air=20 density is what it will be and you can't affect that (except by where = you=20 fly). 
 
 
 
so if you look at the factors one could conclude = that Prop=20 diameter appears to be the most signficant factor (at least in this = momentum=20 equation).  The Thrust is directly proportional to the square of = the=20 diameter.  So if all else is equal then a 74" dia prop would = produce 74^2 =3D=20 5476, whereas 76 " dia prop would produce 76^2 =3D 5776
or approx 5467/5776 =3D 0.9467 giving approx 5% = more thrust=20 for the slightly longer prop.
 
I went from a 68" prop to a 76" prop when I switched = from my=20 2.17 to the 2.85 gear box.  I was very impressed with the change in = take=20 off performance.  So comparing the two (Yes, RPM went down a bit on = the=20 prop with the 2.85 so in real life the comparison is skewed), but in any = case at=20 the same PROP rpm.  The 66^2 =3D 4356
 
going to the 76 gave me 5776, comparing thrust for = the two=20 4356/5776 =3D 0.75 or a gain of 25% in thrust for the same prop rpm - = now that=20 will get your attention. 
 
However, this equation clearly does not take prop = chord into=20 effect and based on the simple chart of three data points - it would = appear to=20 play a major role in static rpm and thrust.
 

Sent: Friday, October 08, 2010 1:54 PM
Subject: [FlyRotary] Re: Prop Chord vs RPM

In a message dated 10/8/2010 11:48:42 A.M. Eastern Daylight Time, = eanderson@carolina.rr.com=20 writes:
I did a plot of chord of the three props = mentioned=20 recently.  The props were of 74-76 inches in dia and made by = Catto (2)=20 and Performance Prop (1).  Note my Performance Prop was shorter = only 74=20 compared to Sams and Dennis Catto Props.  When mine was 76" in = dia my=20 static was lower than 6000 which would have all three props pretty = much on a=20 straight line.  I don't know if one could make much of a linear=20 relationship between prop chord and rpm based on just three data = points, but=20 thought some might find it interesting.
 
And now how about the thrust for each diameter and blade chord and = pitch.=20 What is the most effective prop for the most common diameters?
 
Lynn E. Hanover
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