X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 02 Mar 2012 07:54:16 -0500 Message-ID: X-Original-Return-Path: Received: from imr-ma02.mx.aol.com ([64.12.206.40] verified) by logan.com (CommuniGate Pro SMTP 5.4.4) with ESMTP id 5423569 for lml@lancaironline.net; Thu, 01 Mar 2012 12:35:58 -0500 Received-SPF: pass receiver=logan.com; client-ip=64.12.206.40; envelope-from=rwolf99@aol.com Received: from mtaomg-db01.r1000.mx.aol.com (mtaomg-db01.r1000.mx.aol.com [172.29.51.199]) by imr-ma02.mx.aol.com (8.14.1/8.14.1) with ESMTP id q21HZ59d015671 for ; Thu, 1 Mar 2012 12:35:05 -0500 Received: from core-dqb005c.r1000.mail.aol.com (core-dqb005.r1000.mail.aol.com [172.29.212.209]) by mtaomg-db01.r1000.mx.aol.com (OMAG/Core Interface) with ESMTP id A06D1E000091 for ; Thu, 1 Mar 2012 12:35:05 -0500 (EST) X-Original-To: lml@lancaironline.net Subject: Balancing L360 Ailerons (again) X-MB-Message-Source: WebUI X-MB-Message-Type: User MIME-Version: 1.0 From: rwolf99@aol.com Content-Type: multipart/alternative; boundary="--------MB_8CEC5E8C63EB746_19C4_47B3E_webmail-d036.sysops.aol.com" X-Mailer: AOL Webmail 35647-STANDARD Received: from 216.207.126.66 by webmail-d036.sysops.aol.com (205.188.181.89) with HTTP (WebMailUI); Thu, 01 Mar 2012 12:35:05 -0500 X-Original-Message-Id: <8CEC5E8C6306EE2-19C4-12788@webmail-d036.sysops.aol.com> X-Originating-IP: [216.207.126.66] X-Original-Date: Thu, 1 Mar 2012 12:35:05 -0500 (EST) x-aol-global-disposition: G X-AOL-SCOLL-SCORE: 0:2:427599744:93952408 X-AOL-SCOLL-URL_COUNT: 0 x-aol-sid: 3039ac1d33c74f4fb3494756 This is a multi-part message in MIME format. ----------MB_8CEC5E8C63EB746_19C4_47B3E_webmail-d036.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Jim Nordin=E2=80=99s excerpt from the Lancair 320 build manual says it pret= ty clearly. What it leaves out is that the linkages need to be disconnecte= d from the aileron. Leave the pushrod mounting bracket attached to the ail= eron but don=E2=80=99t connect a pushrod to it. Don=E2=80=99t even have a = bolt installed in the mounting brackets, as you want to be flutter-free eve= n if that bolt were to fall out somehow. =20 The essential purpose of balancing the aileron is, as was mentioned previou= sly, to have the inertial reaction of the aileron to wing flexing be in a d= irection to not amplify the wing deflection. Okay, let me say that differe= ntly. Wing flexes up (maybe due to a gust) and the aileron lags behind due= to inertia. If the aileron is heavier BEHIND the hinge line, then when th= e wing flexes up, the aileron will be deflected trailing edge down due to i= nertia. This increases the lift on the wing, causing more wing deflection.= The wing eventually springs back, and when flexing downwards the trailing= edge deflects up, reducing the lift loads and amplifying the elastic respo= nse of the wing structure. =20 =20 On the other hand, if the aileron is heavier AHEAD of the hinge, then when = the wing flexes upwards due to a gust, the inertial reaction of the aileron= is to deflect trailing edge up, reducing the lift and therefore reducing t= he structural flexing. =20 When the center of mass is AT the hinge line, the inertial reaction neither= amplifies nor reduces the additional lift which caused the flexing. This = is called =E2=80=9C100% mass balanced=E2=80=9D. =20 If your ailerons are not balanced, the self-amplified flexing can grow cata= strophically. Fast. That=E2=80=99s flutter. But there is some structural= damping in the system which keeps this from happening. But damping decrea= ses with airspeed, so you will eventually get to an airspeed where flutter = will happen. But that=E2=80=99s above redline speed, sometimes a lot, but = sometimes a little. (Depends on the airplane.) =20 When you have more engineering resources at your disposal, you can measure = the structural damping and allow a little less lead to be used. You basica= lly allow a little amplification =E2=80=93 not too much =E2=80=93 and let t= he existing structural damping keep flutter from happening below redline sp= eed. But you are essentially guaranteed to be free of flutter if the ailer= ons are 100% mass balanced, so that=E2=80=99s what homebuilders do. =20 Using the wing to hold the aileron while measuring the balance point is con= venient, but there cannot be any friction. You can do the same for the ele= vator. A little tough to do with the rudder, as the airplane would have to= be on it=E2=80=99s side. But a better way is to take the surface off the = airplane, insert the hinge pins, and use some kind if =E2=80=9Cknife edge= =E2=80=9D to support the hinge pins. This gives a virtually friction-free = condition. But if the hinges are low-friction enough, you don=E2=80=99t ne= ed to do that, and if the aileron hinges had that much friction, you=E2=80= =99d probably want to fix it anyway. =20 As to whether the aileron should stay in position due to friction when you = place it somewhere other than in-trail, well, when the system is fully asse= mbled it doesn=E2=80=99t matter for flutter. It only matters for handling = qualities. - Rob Wolf ----------MB_8CEC5E8C63EB746_19C4_47B3E_webmail-d036.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="utf-8"
Jim Nordin=E2=80=99s excerpt from the Lancair 320 build m= anual says it pretty clearly.  What it leaves out is that the linkages need to be disconnected from the = aileron.  Leave the pushrod m= ounting bracket attached to the aileron but don=E2=80=99t connect a pushrod= to it.  Don=E2=80=99t even h= ave a bolt installed in the mounting brackets, as you want to be flutter-fr= ee even if that bolt were to fall out somehow.
 
The essential purpose of balancing the aileron is, = as was mentioned previously, to have the inertial reaction of the aileron t= o wing flexing be in a direction to not amplify the wing deflection.  Okay, let me say that differently.=   Wing flexes up (maybe due t= o a gust) and the aileron lags behind due to inertia.  If the aileron is heavier BEHIND the hinge line, = then when the wing flexes up, the aileron will be deflected trailing edge d= own due to inertia.  This inc= reases the lift on the wing, causing more wing deflection.  The wing eventually springs back, and when f= lexing downwards the trailing edge deflects up, reducing the lift loads and= amplifying the elastic response of the wing structure. 
 
On the other hand, if the aileron is heavier AHEAD of the= hinge, then when the wing flexes upwards due to a gust, the inertial react= ion of the aileron is to deflect trailing edge up, reducing the lift and th= erefore reducing the structural flexing.
 
When the center of mass is AT the hinge line, the inertia= l reaction neither amplifies nor reduces the additional lift which caused t= he flexing.  This is called = =E2=80=9C100% mass balanced=E2=80=9D.
 
If your ailerons are not balanced, the self-amplified fle= xing can grow catastrophically.  Fast.  That=E2=80=99s flu= tter.  But there is some stru= ctural damping in the system which keeps this from happening.  But damping decreases with airspeed, so y= ou will eventually get to an airspeed where flutter will happen.  But that=E2=80=99s above redline speed= , sometimes a lot, but sometimes a little. (Depends on the airplane.)
 
When you have more engineering resources at your disposal= , you can measure the structural damping and allow a little less lead to be= used.  You basically allow a= little amplification =E2=80=93 not too much =E2=80=93 and let the existing= structural damping keep flutter from happening below redline speed.  But you are essentially guaranteed= to be free of flutter if the ailerons are 100% mass balanced, so that=E2= =80=99s what homebuilders do.
 
Using the wing to hold the aileron while measuring the ba= lance point is convenient, but there cannot be any friction.  You can do the same for the elevator.  A little tough to do with the ru= dder, as the airplane would have to be on it=E2=80=99s side.  But a better way is to take the surface of= f the airplane, insert the hinge pins, and use some kind if =E2=80=9Cknife = edge=E2=80=9D to support the hinge pins.&= nbsp; This gives a virtually friction-free condition.  But if the hinges are low-friction enough,= you don=E2=80=99t need to do that, and if the aileron hinges had that much= friction, you=E2=80=99d probably want to fix it anyway.
 
As to whether the aileron should stay in position due to = friction when you place it somewhere other than in-trail, well, when the sy= stem is fully assembled it doesn=E2=80=99t matter for flutter.  It only matters for handling qualities= .
 
- Rob Wolf
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