|
|
Maybe I would be better off to research things before I try to rely on my memory.
I said:
<<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.>>
Well, these are merely 1/2 inch fine thread bolts with a range of 40 to 57 foot pounds. I am pretty sure (notice no longer absolutely sure) 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 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.>>
The book torque value for these bolts (1/4 fine thread) is a mere 4 to 6 foot pounds.
Gulp, Dan forgive me!
I have definitely tightened these bolts far beyond 6 foot pounds. So, the question is this:
If these bolts are dramatically overtightened and then loosen (probably by material compression) to some value that is too tight (still greater than 6 foot pounds), are the creaks caused by this condition? Another words, movement between the plate and the phenolic at 6 foot pounds would cause no creaking as would overtightening so no movement could occur?
Does anyone out there care? Does it matter that a hangar neighbor suggested that I just squirt some graphite between the surfaces or wear ear plugs? Are you all deaf and don't hear any creaks?
Finally, I am not adverse to proper torque values if some engineer recommends them. I do have both inch-pound and foot-pound torque wrenches. My Honda motorcycle service manual has torque values (Newton-Meters, of course) for each area of assembly it references and I use those values when I work on the motorcycle. I am happy to do the same on the airplane (hoping 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 put my arms back in the straight-jacket.
Scott Krueger
N92EX
|
|