Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Wed, 26 Feb 2003 22:44:45 -0500
Message-ID: <redirect-2038357@logan.com>
From: Sky2high@aol.com
Subject: Further to torque issues
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Dan, et al,

The purpose of torqueing down a bolt to a "specified" value is to provide a 
preload in excess of the actual tension loads to be placed on the bolt.  The 
bolt is rated and sized to meet or exceed either the tension loads or shear 
loads to be placed on it.  Let's discuss three different situations and the 
importance of torque.

1. Engine cylinder head bolts - sized and torqued to exceed the worse case 
tension load placed on them by the Newtonian reaction of the regular 
explosions occurring in the cylinder.  We would not want them to be under 
stressed since each explosion would be "working" the stretch of the bolt.  
Also, the bolted together metal should not react by compressing under the 
bolt tension preload.

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

3. The four AN4 bolts used in shear to hold the forward main gear mounting 
plate to the 1/2 inch (?) phenolic block Hysoled in as an aft main spar web 
(and also covered with x layers of glass.  We know we could tighten these 
bolts to their book torque value, but we don't know what value would cause 
the phenolic (or glass) to compress.  We don't know whether their size was 
chosen merely for their shear resistance value or for their tension value.  
We know their shear value is improved by the friction between the plate and 
the block.  This is known as the creak-torque value.  We just don't know the 
number.  The same is true for the rear spar.  One thing I know from 
experience - Glass moves.

This is fun, but I gotta go take care of the dogs - in response to the 
leak-torque (arm twisting).

Scott Krueger
N92EX

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<HTML><FONT FACE=3Darial,helvetica><FONT  SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=
=3D"Arial" LANG=3D"0">Dan, et al,<BR>
<BR>
The purpose of torqueing down a bolt to a "specified" value is to provide a=20=
preload in excess of the actual tension loads to be placed on the bolt.&nbsp=
; The bolt is rated and sized to meet or exceed either the tension loads or=20=
shear loads to be placed on it.&nbsp; Let's discuss three different situatio=
ns and the importance of torque.<BR>
<BR>
1. Engine cylinder head bolts - sized and torqued to exceed the worse case t=
ension load placed on them by the Newtonian reaction of the regular explosio=
ns occurring in the cylinder.&nbsp; We would not want them to be under stres=
sed since each explosion would be "working" the stretch of the bolt.&nbsp; A=
lso, the bolted together metal should not react by compressing under the bol=
t tension preload.<BR>
<BR>
2. The enormous diameter Lancair 320/360 wing-spar main-spar attach bolts -=20=
These bolts main function is to act in shear so as not to allow the wings to=
 fold up (or down).&nbsp; They also function in tension to add some rigidity=
 to the main spar, but they are not torqued to the bolt standard since it wo=
uld crush the aluminum bushings, plate and surely the pre-preg glass structu=
re.&nbsp; I don't remember (and I don't have a build manual handy) on the su=
ggested torque.&nbsp; This value would be sufficient for the required rigidi=
ty and the size would be apprpriate for the shear load.&nbsp; I think someda=
y that I will clip the safety wires and re-check the torque of these bolts t=
hat I have not twiddled since 1995.<BR>
<BR>
3. The four AN4 bolts used in shear to hold the forward main gear mounting p=
late to the 1/2 inch (?) phenolic block Hysoled in as an aft main spar web (=
and also covered with x layers of glass.&nbsp; We know we could tighten thes=
e bolts to their book torque value, but we don't know what value would cause=
 the phenolic (or glass) to compress.&nbsp; We don't know whether their size=
 was chosen merely for their shear resistance value or for their tension val=
ue.&nbsp; We know their shear value is improved by the friction between the=20=
plate and the block.&nbsp; This is known as the creak-torque value.&nbsp; We=
 just don't know the number.&nbsp; The same is true for the rear spar.&nbsp;=
 One thing I know from experience - Glass moves.<BR>
<BR>
This is fun, but I gotta go take care of the dogs - in response to the leak-=
torque (arm twisting).<BR>
<BR>
Scott Krueger<BR>
N92EX</FONT></HTML>

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