X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail-bw0-f226.google.com ([209.85.218.226] verified) by logan.com (CommuniGate Pro SMTP 5.3.3) with ESMTP id 4152123 for flyrotary@lancaironline.net; Thu, 04 Mar 2010 10:59:59 -0500 Received-SPF: pass receiver=logan.com; client-ip=209.85.218.226; envelope-from=lehanover@gmail.com Received: by bwz26 with SMTP id 26so705229bwz.27 for ; Thu, 04 Mar 2010 07:59:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:date:message-id:subject :from:to:content-type; bh=bk5ZKKMowuFz+bioWY9NJ7UjudpxiWPj8tB0IZOs3tE=; b=MDRY9WbwdLoSUZzTxRcgfyilZWNfKZ0OdGp4EYRbmxgNQPha7NiMKqEIGyRi6gavjT 6xaRLtV/n7Ler2WIWNMJn003h4BtIjrigi5hlEFpK5Cw2l8Ko3NFeP9zym97fqjPZSgJ lstsN1jYk8f6M+JTwqx/2Nh5A8ruVp4aNosxc= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type; b=M7F8bAOInQlYY/p6VOBr4M45ItGyUk6d6oBWaDcLwrW3WL1ncDK+1iKc6e5AkIDasR zyPDUILlac7sqW410VzT55ImI7Dt4jZfbHcCk0H9NxR1HotY1gg06/9WZF8Oz9S2vI3I Pl3rdN3Jrv4bxWfyOQjPN+0vHLIDpH40+6sqE= MIME-Version: 1.0 Received: by 10.239.189.13 with SMTP id r13mr998758hbh.92.1267718362039; Thu, 04 Mar 2010 07:59:22 -0800 (PST) Date: Thu, 4 Mar 2010 10:59:22 -0500 Message-ID: <1ab24f411003040759g4381a4e9x50a81b4d73c5b5fc@mail.gmail.com> Subject: Static thrust From: Lynn Hanover To: flyrotary@lancaironline.net Content-Type: multipart/alternative; boundary=001485f626c8a508000480fbae80 --001485f626c8a508000480fbae80 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable But, wait isn=92t that also where Thrust =3D Drag? Does that mean if thrust= =3D zero, then my drag is then also zero (not likely {:>). Sure enough if you look at the formula for Thrust T if the factor DV goes to zero then the whole equation T =3D 0 because every factor is multiplied by Dv (zero in th= is case). So I must be missing something because clearly my drag at cruise is not =3D 0. Arrrggg! Never have felt that I understood this prop stuff. Ed Fixed pitch propellers designed to fly, just don't work well on the ground. Airflow over the front of the blade exceeds the speed of sound long before the prop tips reach that speed. Prop drag goes up sharply before the tips get close to that speed. Light plane propellers perform better once some speed has developed. Over powering a prop makes it cavitate. That is the blade stalls for lack o= f adequate air inflow. Once the plane is moving, relative air speed over the blades, Alters the angle of attack and the stall is defeated and RPM drops as more work is accomplished by the prop. The cruise prop is more likely to stall as the blade is formed with a high angle of attack. A climb prop is less likely to stall as the blade is forme= d with a shallow angle of attack. Propellers designed for static and low speed thrust have wide blades with thick high lift airfoils. They have many blades 5 to 7 blades. In some case= s two propellers in a counter rotating assembly will be used. The leading propeller may have fewer blades than the trailing propeller. The leading propeller may be turning at a higher or lower RPM than the trailing propeller. The two propellers will have different angles of attack. You can fire up your fully loaded airboat and drive it across 100 yards of dry grass to the water if your 550 is running well. The airboat prop might not get your plane above its stall speed. So, no nee= d to go there. Measuring the static thrust of a plane with a spring scale or similar, will get you the static thrust for that minute of that day.........and not much else. Lynn E. Hanover --001485f626c8a508000480fbae80 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable

But, wait isn= =92t that also where Thrust =3D Drag? Does that mean if thrust =3D zero, th= en my drag is then also zero (not likely {:>).=A0 Sure enough if you loo= k at the formula for Thrust T if the factor DV= goes to zero then the whole equation T =3D 0 because every factor is multi= plied by Dv (zero in this case).=A0 So I must = be missing something because clearly my drag at cruise is not =3D 0.=A0 Arr= rggg!=A0 Never have felt that I understood this prop stuff.

=A0

Ed
=A0
Fixed pitch p= ropellers=A0designed to=A0fly, just don't work well on the ground. Airf= low over the front of the=A0 blade exceeds the speed of sound long before t= he prop tips reach that speed. Prop drag goes up sharply before the tips ge= t close to that speed. Light plane propellers perform better once some spee= d has developed.
=A0
Over powering= a prop makes it cavitate. That is the blade stalls for lack of adequate ai= r inflow. Once the plane is moving, relative air speed over the blades, Alt= ers the angle of attack and the stall is defeated and RPM drops as more wor= k is accomplished by the prop.
=A0
The cruise pr= op is more likely to stall as the blade is formed with a high angle of atta= ck. A climb prop is less likely to stall as the blade is formed with a shal= low angle of attack.=A0
=A0
Propellers de= signed for static and low speed thrust have wide blades with thick high lif= t airfoils. They have many blades 5 to 7 blades. In some cases two propelle= rs in a counter rotating assembly will be used. The leading propeller may h= ave fewer blades than the trailing propeller. The leading propeller may be = turning at a higher or lower RPM than the trailing propeller. The two prope= llers will have different angles of attack.=A0
=A0
You can fire = up your fully loaded airboat and drive it across 100 yards of dry grass to = the water if your 550 is running well.
=A0
The airboat p= rop might not get your plane above its stall speed. So, no need to go there= .
=A0
Measuring the= static thrust of a plane with a spring scale or similar, will get you the = static thrust for that minute of that day.........and not much else.=A0=A0<= /span>
=A0
Lynn E. Hanov= er=A0
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