X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 23 Feb 2009 18:16:32 -0500 Message-ID: X-Original-Return-Path: Received: from web36902.mail.mud.yahoo.com ([209.191.85.70] verified) by logan.com (CommuniGate Pro SMTP 5.2.12) with SMTP id 3511955 for lml@lancaironline.net; Mon, 23 Feb 2009 12:21:46 -0500 Received: (qmail 3637 invoked by uid 60001); 23 Feb 2009 17:21:47 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:MIME-Version:Content-Type:Message-ID; b=cT1K18levMqJklaT1q3mq+aTyt2niO36gCE2FAoyisMkgdY0ZRYY+wlgYO0x3Pmlq1jBShL5Hykfpbx9qB8rdhQFzAQmZa9+9aMvxtu+Rhm3mX2eAJY6omm2MgBxKuIZXPoU2LSXM1HaM3z36bu8ay4lcfByv+jnMFjTaHBSDRM=; X-YMail-OSG: lgXhFE0VM1mSLvrYwArmiKzQv.nxTBMBiSEIY2w3C2X6KT3lxHGN6AMh8btPTVZfsU7gb9Ppl5ok41m9xANQ2CdVnbsMa9n._.V4u.7O2Ua2f6qSpIj0gzKuLacmsxLzMMsWxVgTbaakeJQ2RgXeaqyCMckhlVQA8YfW_1hYwQlenBlrvTsj7Nd7RYzt1_BL3dbTcEFYmRBhiIamc.Qb371F5O1uwaQ- Received: from [149.32.224.34] by web36902.mail.mud.yahoo.com via HTTP; Mon, 23 Feb 2009 09:21:47 PST X-Mailer: YahooMailRC/1155.45 YahooMailWebService/0.7.260.1 References: X-Original-Date: Mon, 23 Feb 2009 09:21:47 -0800 (PST) From: Chris Zavatson Subject: Re: [LML] Re: FW: 360 in a small-tail LNC2? X-Original-To: Lancair Mailing List MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-673570608-1235409707=:2758" X-Original-Message-ID: <580126.2758.qm@web36902.mail.mud.yahoo.com> --0-673570608-1235409707=:2758 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Come on guys, the relative angles of wing and stab (with or w/o elevator de= flection) do not drive longitudinal stability.=A0 That angle simply determi= nes the trim airspeed for the configuration.=A0 Note that stick forces shou= ld not be confused with stability.=A0 Stick forces can be made light or hea= vy independent of stability.=A0 Testing of stability is actually done stick= free - i.e. no hands on the controls.=0ADriving parameters for static stab= ility are=A0primarily:=A0 Lengths of the mean aerodynamic chords for the wi= ng and stab, their relative distance to each other, the location of the CG = relative to the MAC.=A0 To=A0actually determine the proper stab angle.=A0 Y= ou also need pitching moment data for the airfoil sections, lift slope curv= es,=A0your desired trim airspeed, and=A0the wing down wash angle.=0ADynamic= stability gets a lot more complicated in a hurry.=A0 Items such as aircraf= t mass moments of inertia are needed.=0AThe overall=A0recipe for best speed= is to set the angle of the stab such that no elevator deflection is needed= at the target speed.=A0=A0Set the CG aft until either stability becomes an= d issue or the tail is flying at zero angle of attack.=A0 Since we have all= glued our stabs in place at one angle or another, the drag of counter weig= hts sticking out in the airstream is pitted against trying=A0to decrease th= e down force on the tail.=A0 Flap position has a big influence on pitching = moment of the section (especially our NLF section) and therefore determines= how much work needs to be done by the tail.=A0=0A=0AChris Zavatson=0AN91CZ= =A0=A0=A0=0AL360std=0Awww.N91CZ.com=0A=0A=0A --0-673570608-1235409707=:2758 Content-Type: text/html; charset=us-ascii

Come on guys, the relative angles of wing and stab (with or w/o elevator deflection) do not drive longitudinal stability. That angle simply determines the trim airspeed for the configuration. Note that stick forces should not be confused with stability. Stick forces can be made light or heavy independent of stability. Testing of stability is actually done stick free - i.e. no hands on the controls.

Driving parameters for static stability are primarily: Lengths of the mean aerodynamic chords for the wing and stab, their relative distance to each other, the location of the CG relative to the MAC. To actually determine the proper stab angle. You also need pitching moment data for the airfoil sections, lift slope curves, your desired trim airspeed, and the wing down wash angle.

Dynamic stability gets a lot more complicated in a hurry. Items such as aircraft mass moments of inertia are needed.

The overall recipe for best speed is to set the angle of the stab such that no elevator deflection is needed at the target speed. Set the CG aft until either stability becomes and issue or the tail is flying at zero angle of attack. Since we have all glued our stabs in place at one angle or another, the drag of counter weights sticking out in the airstream is pitted against trying to decrease the down force on the tail. Flap position has a big influence on pitching moment of the section (especially our NLF section) and therefore determines how much work needs to be done by the tail.

Chris Zavatson

N91CZ

L360std

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