FYI on Grove spring gear:

Regarding the Grove 7075 spring gear questions (discussed earlier), and whether the Grove specified preformed gear is really appropriate for Kitfox 3 & 4 aircraft (some say it’s too stiff and won’t deform in a crash). I called Grove and got some insight into their design criteria for the Kitfox.

They size their Kitfox -4 -1200 gear for tail wheel operation. It is sized so that during a 3 G landing, which they qualify as a “hard landing”, but not a “crash landing”, the 7075 aluminum spring gear will be subject to a bending force maximum of 46,000 PSI. At this PSI level, the gear will flex, but not permanently deform.

For 7075 gear with their level of heat treating, the yield pressure is about 63,000, which would occur at what they guess to be about 5.5 G’s, a true “crash landing” where you want the gear to deform and absorb the impact energy. At this pressure, the 7075 will bend and permanently deform, but won’t actually break (that’s why the use it). Interestingly, using 7075 Aluminum allows them to make a lighter gear as the same size gear made of 2024 aluminum yields at 43,000 psi.

If bent badly, they can strengthen the gear up to 3 times, but after that it has permanently lost some of its spring and should be replaced (it could break on crash too).

I also asked them about this special spec Kitfox-4-1200 gear when used in Tr-gear applications. In this application, the mains are under somewhat less load then in tail dragger configuration, so this also supports my contemplation that in using this gear, at least in Tri-gear application, the gross weight of the Kitfox-4 could be safely increased to 1250 lbs if other modifications are also made (upgrading the tail feathers).

What do ya think?

Roger