[Blain]

One of the "Take aways" from reading this forum for hours and hours is the no riveted part should have unnecessary stress. Torsion, shear etc.

Like many others I managed to get my -8 rudder leading edges to come together with quite a bit of "persuasion".

All I could think of while riveting this together was "Vibration, crack, zipper, Rudder stuck".

I suppose if there had been any history of this Vans would correct the proceedure.

Any old airframe guys out care to comment?

Blain

 

[paul330]

I wouldn't count myself as an old hand as I am still building - albeit getting close to finishing.

My feeling is this: if you get the bend on the leading edges close, then any tension is not critical. The fatigue issues you allude to really apply to highly stressed parts of the airframe. There simply isn't any load on the join of the leading edges.

 

[DanH]

One of the "Take aways" from reading this forum for hours and hours is the no riveted part should have unnecessary stress.

You appear to be referring to preload and/or residual stress. If so, the takeaway is wrong.

Preload is a standard engineering tool to combat fatigue in bolted assemblies, while residual material stress can be used to combat crack formation. Two very common examples are connecting rod bolts (the bolt is tensioned to a stress higher than will be applied by the recip forces of engine operation) and shot peening of connecting rods (a residual compressive stress is created in the material surface by beating it with steel balls). Successful application of the principle means cyclical stress is eliminated, reduced in amplitude, or at least made non-reversing. No cycles, no fatigue.

Long term application of steady, non-cyclical stress below the elastic limit generally does no harm, at least at normal temperatures.

 

[Blain]

You appear to be referring to preload and/or residual stress. If so, the takeaway is wrong.

Preload is a standard engineering tool to combat fatigue in bolted assemblies, while residual material stress can be used to combat crack formation. Two very common examples are connecting rod bolts (the bolt is tensioned to a stress higher than will be applied by the recip forces of engine operation) and shot peening of connecting rods (a residual compressive stress is created in the material surface by beating it with steel balls). Successful application of the principle means cyclical stress is eliminated, reduced in amplitude, or at least made non-reversing. No cycles, no fatigue.

Long term application of steady, non-cyclical stress below the elastic limit generally does no harm, at least at normal temperatures.

Dan, good explaination. Long story short, build on? BTW, I substituted the monel rivets with a longer reach. Seemed to pull the sheets together better and I expect the monel to be stronger?

Blain