scsmith
Well Known Member
Wing tape saves the day!
Well, fortunately, the wing tape makes it a tiny bit harder for the wings to fall out if the pin is not in Anyone who tries to pull the wings off with the tape still on knows this. But you are right, once there is flight load, the spars are going to be very difficult to separate. It could happen though.
For those that don't know, the PIK20, like the Libelle, uses a spar engagement design where each spar stub has a pin in the end that plugs into a socket in the opposing wing root rib. Those connections carry all the wing bending moment. Then there is a single removable wing pin that just keeps the wings from separating. There are two additional pins in each root rib that plug into the fuselage to hold the fuselage onto the wings.
Other gliders have different arrangements, some with two removable wing pins, where the pins themselves carry the actual bending moment.
I preflighted a Pik-20D glider and found that the mainpin was only inserted about half way. Wouldn't go any further into its bushing. The mainpin is supposed to go all the way through the spar extensions of both wings to prevent them from coming apart, but because it'd only engaged with one wing the result was functionally equivalent to having no mainpin at all.
I disassembled the glider and found that a 1 inch long piece of garden hose used to protect the brass bushing in the starboard wing from scoring from steel pins in the trailer hadn't been removed last time it was rigged.
On the previous day the aircraft had flown a 200km cross country. When I revealed my discovery to the previous pilot he went white as a sheet, considering the implications of the fact that nothing was preventing the wings from coming off. To this day I have no idea why it didn't kill him in a launch accident. I can only guess that flight loads caused the wings to bind up on their mountings on the fuselage. Might have been amusing if they'd fallen off as soon as he stopped rolling after landing
- mark
Well, fortunately, the wing tape makes it a tiny bit harder for the wings to fall out if the pin is not in Anyone who tries to pull the wings off with the tape still on knows this. But you are right, once there is flight load, the spars are going to be very difficult to separate. It could happen though.
For those that don't know, the PIK20, like the Libelle, uses a spar engagement design where each spar stub has a pin in the end that plugs into a socket in the opposing wing root rib. Those connections carry all the wing bending moment. Then there is a single removable wing pin that just keeps the wings from separating. There are two additional pins in each root rib that plug into the fuselage to hold the fuselage onto the wings.
Other gliders have different arrangements, some with two removable wing pins, where the pins themselves carry the actual bending moment.