Originally Posted by Low Pass
So, we trust the tie down to be good for holding the plane to the ground in conditions that may lift it off the ground. Why can't we trust the tie down point to hold a comparable load in the reverse direction?
The issue does not seem to be the ability of the threads to carry the load, it is how the load is carried into that thread. Jacking under a tie down eye generates a bending load on the joint. A short spherical end with a matching cup on the jack carries the load with minimal bending. Just be sure there is a "fence" in case it wants to slip. There is a lot of wobbling potential with the plane on jacks this tall. The jacks should be very stable, and able to carry some side loads without deflection or tipping. Look at how the multi-thousand dollar jacks are made. They address the issues. Not saying they are required, just an example of a good design.