Return-Path: Sender: (Marvin Kaye) To: lml Date: Fri, 28 Feb 2003 07:51:22 -0500 Message-ID: X-Original-Return-Path: Received: from imo-m07.mx.aol.com ([64.12.136.162] verified) by logan.com (CommuniGate Pro SMTP 4.0.6) with ESMTP id 2039532 for lml@lancaironline.net; Fri, 28 Feb 2003 00:07:47 -0500 Received: from Sky2high@aol.com by imo-m07.mx.aol.com (mail_out_v34.21.) id q.138.1bd1f9c7 (3842) for ; Fri, 28 Feb 2003 00:07:42 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: <138.1bd1f9c7.2b90489e@aol.com> X-Original-Date: Fri, 28 Feb 2003 00:07:42 EST Subject: LNC2 Torque issues - I was slightly wrong again X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_138.1bd1f9c7.2b90489e_boundary" X-Mailer: 8.0 for Windows sub 821 --part1_138.1bd1f9c7.2b90489e_boundary Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable Maybe I would be better off to research things before I try to rely on my=20 memory. I said: <<2. The enormous diameter Lancair 320/360 wing-spar main-spar attach bolts=20= -=20 These bolts main function is to act in shear so as not to allow the wings to= =20 fold up (or down).=A0 They also function in tension to add some rigidity to=20= the=20 main spar, but they are not torqued to the bolt standard since it would crus= h=20 the aluminum bushings, plate and surely the pre-preg glass structure.=A0 I=20 don't remember (and I don't have a build manual handy) on the suggested=20 torque.=A0 This value would be sufficient for the required rigidity and the=20 size would be apprpriate for the shear load.=A0 I think someday that I will=20 clip the safety wires and re-check the torque of these bolts that I have not= =20 twiddled since 1995.>> Well, these are merely 1/2 inch fine thread bolts with a range of 40 to 57=20 foot pounds. I am pretty sure (notice no longer absolutely sure) that 40=20 foot pounds would not crush the bushings, thus not the glass either. I stil= l=20 cannot find any Lancair torque recommendation for these bolts. Anybody abl= e=20 to chime in as to the right torque? Then, (blush) I went on to say: <<3. The four AN4 bolts used in shear to hold the forward main gear mounting= =20 plate to the 1/2 inch (?) phenolic block Hysoled in as an aft main spar web=20 (and also covered with x layers of glass.=A0 We know we could tighten these=20 bolts to their book torque value, but we don't know what value would cause=20 the phenolic (or glass) to compress.=A0 We don't know whether their size was= =20 chosen merely for their shear resistance value or for their tension value.= =A0=20 We know their shear value is improved by the friction between the plate and=20 the block.=A0 This is known as the creak-torque value.=A0 We just don't know= the=20 number.=A0 The same is true for the rear spar.=A0 One thing I know from=20 experience - Glass moves.>> The book torque value for these bolts (1/4 fine thread) is a mere 4 to 6 foo= t=20 pounds. =20 Gulp, Dan forgive me! =20 I have definitely tightened these bolts far beyond 6 foot pounds. So, the=20 question is this: If these bolts are dramatically overtightened and then loosen (probably by=20 material compression) to some value that is too tight (still greater than 6=20 foot pounds), are the creaks caused by this condition? Another words,=20 movement between the plate and the phenolic at 6 foot pounds would cause no=20 creaking as would overtightening so no movement could occur? =20 Does anyone out there care? Does it matter that a hangar neighbor suggested= =20 that I just squirt some graphite between the surfaces or wear ear plugs? Ar= e=20 you all deaf and don't hear any creaks? =20 Finally, I am not adverse to proper torque values if some engineer recommend= s=20 them. I do have both inch-pound and foot-pound torque wrenches. My Honda=20 motorcycle service manual has torque values (Newton-Meters, of course) for=20 each area of assembly it references and I use those values when I work on th= e=20 motorcycle. I am happy to do the same on the airplane (hoping there is=20 something more than just book values for the many special cases). Now excuse me as my nurse is delivering my regular medication and I have to=20 put my arms back in the straight-jacket. Scott Krueger N92EX --part1_138.1bd1f9c7.2b90489e_boundary Content-Type: text/html; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable Maybe I would be better off to research things before=20= I try to rely on my memory.

I said:
<<2. The enormous diameter Lancair 320/360 wing-spar main-spar attach=20= bolts - These bolts main function is to act in shear so as not to allow the=20= wings to fold up (or down).=A0 They also function in tension to add some rig= idity to the main spar, but they are not torqued to the bolt standard since=20= it would crush the aluminum bushings, plate and surely the pre-preg glass st= ructure.=A0 I don't remember (and I don't have a build manual handy) on the=20= suggested torque.=A0 This value would be sufficient for the required rigidit= y and the size would be apprpriate for the shear load.=A0 I think someday th= at I will clip the safety wires and re-check the torque of these bolts that=20= I have not twiddled since 1995.>>

Well, these are merely 1/2 inch fine thread bolts with a range of 40 to 57 f= oot pounds.   I am pretty sure (notice no longer absolutely sure)=20= that 40 foot pounds would not crush the bushings, thus not the glass either.=   I still cannot find any Lancair torque recommendation for  these= bolts.  Anybody able to chime in as to the right torque?

Then, (blush) I went on to say:
<<3. The four AN4 bolts used in shear to hold the forward main gear mo= unting plate to the 1/2 inch (?) phenolic block Hysoled in as an aft main sp= ar web (and also covered with x layers of glass.=A0 We know we could tighten= these bolts to their book torque value, but we don't know what value would=20= cause the phenolic (or glass) to compress.=A0 We don't know whether their si= ze was chosen merely for their shear resistance value or for their tension v= alue.=A0 We know their shear value is improved by the friction between the p= late and the block.=A0 This is known as the creak-torque value.=A0 We just d= on't know the number.=A0 The same is true for the rear spar.=A0 One thing I=20= know from experience - Glass moves.>>

The book torque value for these bolts (1/4 fine thread) is a mere 4 to 6 foo= t pounds. 

Gulp, Dan forgive me! 

I have definitely tightened these bolts far beyond 6 foot pounds.  So,=20= the question is this:

If these bolts are dramatically overtightened and then loosen (probably by m= aterial compression) to some value that is too tight (still greater than 6 f= oot pounds), are the creaks caused by this condition?  Another words, m= ovement between the plate and the phenolic at 6 foot pounds would cause no c= reaking as would overtightening so no movement could occur? 

Does anyone out there care?  Does it matter that a hangar neighbor sugg= ested that I just squirt some graphite between the surfaces or wear ear plug= s?  Are you all deaf and don't hear any creaks? 

Finally, I am not adverse to proper torque values if some engineer recommend= s them.  I do have both inch-pound and foot-pound torque wrenches. = ; My Honda motorcycle service manual has torque values (Newton-Meters, of co= urse) for each area of assembly it references and I use those values when I=20= work on the motorcycle.  I am happy to do the same on the airplane (hop= ing there is something more than just book values for the many special cases= ).

Now excuse me as my nurse is delivering my regular medication and I have to=20= put my arms back in the straight-jacket.

Scott Krueger
N92EX




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