This photo shows the retract mechanism frame bolted to a honeycomb former in the fuselage using ~3mm cap screws retained on the back side of the honeycomb core former by washers/nuts. Here’s the problem…. A honeycomb core is not very strong (it doesn’t have to be strong since it’s only a core; it’s job is to keep the spacing between the two skins just like the foam in foam-core wings). If you put a bolt through it and tighten it down, it will locally collapse the core. The retract frame is positioned on the front side of the former which results in shear loads being transferred to the former. As such, you have to tighten the bolts (or hysol the frame to the former) to prevent the frame from moving). The normal solution for this problem is to change the mount so that the former is not loaded in shear or by installing inserts in the former to better distribute the shear loads. This wasn’t done and thus it would be expected that the former will be damaged and/or the landing gear will come loose.

The photo also shows how top of Strut 1 is slotted onto a rotating axle to retract the gear. A ~3mm bolt is used to attach the strut to the axle. Once again, all vertical landing loads are transmitted through this bolt. Additionally, although Strut 3 allows the gear to be pushed rearwards, the retract unit is locked in the fully down position. Any rearwards movement (over-travel) of the struts will place high stresses on this bolt and the retract mechanism and can result in wear and binding.

The photo also shows the tubes (which receive the rear wing spars) attached to the front side of the former. The tubes are attached to the former with a couple of layers of carbon fiber. Unfortunately once again, the load path is compromised because there is very little contact area between the tube and the former. Typically, the tube would be embedded in the former and there would be a layer of CF on each side of the former to reinforce the joint. FEJ is relying on the small honeycomb doublers installed in the wing root to transfer flight loads to the fuselage skin and then to the former.

Regards,

Jim