lml@lancaironline.net Mailing List Archive

I'm confused but I don't understand where the higher numbers are justified. In the Lancair manual the replacement nuts MS21042-5 show 60-140 range of torque (inch-lbs) depending on shear/tension. That's only 5-10 ftlbs. The material specifications are 160,000 psi tensile strength and 450F. I agree Grayhawk's SAE grade 8 specification would suggest a much higher torque value (20-28 ft-lbs) is applicable for a 5/16 bolt also 160,000 psi rating but there are also footnotes showing 50% reduction for lubricated fasteners (wax etc).

But MS manufacturers of these nuts show a maximum torque of 60 inch-lbs (Spiralok). Another aerospace manufacturer talks about clamping (I believe this is a clamping connection) where there must be a smooth flat surface which is questionable here. Coastpac writes that in clamping situations use 85% of ultimate tensile strength:

For applications requiring high installation torque values and using standard NAS bolts: achievable torque is

dependent on plating, length of thread engagement, class of mating threads and lubricant (if any). For maximum fatigue

resistance and clamping force in the bolted assembly, we want to produce a level of installed tensile stress that is just below

the yield strength of the bolt material (typically around 85% of the ultimate tensile strength).

The manufacturer goes on to suggest a 5/16 bolt would torque to 330 in-lbs for 160k tensile bolt--a much higher figure than shown in the Lancair default schedule. So, it appears 60 in-lbs is on the low end but is the default Lancair value but a higher number seems to be more reasonable for this application. I'd like some additional thoughts from the experts please. Main gear fork attachment hardware is a key element in safety and the lack of any specific torque value leaves the builder to se the default schedule. I note that the nose strut bolts where the tow plate is attached is indicated at 10-12 ft-lbs by Lancair which is higher than the default schedule.

Paul

Legacy RG 186

On 2011-01-10, at 12:10 PM, Sky2high@aol.com wrote:

5 lb feet does not sound like enough torque for this application where one is definitely concerned about tension as well as shear. Check again. Even a mere 1/4" grade 8 bolt is 13 and 5/16 is 27.

Grayhawk

PS: I'd make the sucker tight so it doesn't fret or move in cross wind landings or bumpy surfaces.

In a message dated 1/9/2011 4:57:24 P.M. Central Standard Time, paul@tbm700.com writes:

i did the product upgrade with hardware from Lancair. The original bolts were rubbing the new Desser tires. When I removed the forks I found a small amount of what appears to be corrosion, possibly some fretting. A few of the bolts were not very tight when I removed them. On the Legacy manuals there are no special TRQ for these bolts so I used the table value of around 60 in-lb. I will retorque after a few landings. I suggest checking these for torque if you have this Type II gear because the mating surface is slotted to allow the tire to toe-in and this fork could rotate about the strut if the bolts are not secure.

Paul

L2K-186