Tool for "easy" bungee install

[Turbo 162]

The pictured tool greatly facilitated the installation of new bungees on my Avid.  The tool is a wooden gantry that stands on top of the seat tube, is stabilized above by a strap to a structural tube, and supports a block and tackle with 6:1 purchase.  Additionally, a small fairlead and clamcleat are used to quickly secure the line.  For line I used green paracord.  I used parts from my collections of yahtie and windsurf stuff.  In order to grip and stretch the bungee, I used a small camcleat mounted on a bent piece of 1/8" aluminum.   In mounting the bungees I was able to pull each wrap tight with the block & tackle setup.  Vicegrip pliers were particularly useful for clamping already-tensioned bungee cord to the landing gear on the bottom.  They held well and were easy to put on and take off.  For each wrap I tried to stretch the bungee as much as I could, so that in the final wrap the end loop would start off already through the aperture in the bottom of the airplane.  I then simply fed a 12-15" piece of paracord thru the eye of the bungee, tied a simple loop knot in the other end, and attached it to the block.  After lifting with the block & tackle, and maneuvering it onto the hook with a screwdriver, I simply untied the loop and pulled the paracord piece out of the eye.  Done!  Solo! (Jimmie Durante would wag his substantial nose and say "hotcha!".)

Some other comments are in order.  Out of curiosity I stretch-tested a plain hardware-store bungee (Installed on the plane by a previous owner) for comparison with the Mil-spec Type-1 3/8" bungee cord sold by Aircraft Spruce & Specialty.  I was gobsmacked at the difference!  The Mil Type-1 bungee is about 3X stiffer, and will go up beyond 120 lbs per strand, whereas the hardware store stuff more-or-less stopped stretching around 35 lbs.  The Mil Type-1 stuff will stretch to double its 0-tension length.  Whatever you do, DON'T USE THE HARDWARE-STORE STUFF!.  My calculations indicate that 7 wraps of the Mil Type-1 bungees can handle a 3-G landing at my TOGW of 916lbs, but the outward gear deflection is almost 19 degrees from the 0-G gear position,  and the average bungee cord stretch is more like 5 inches!  This analysis even modeled the inward roll of the contact patch relative to the wheel as the gear splays out.  I was unable to stretch either bungee to failure, but would love to know how much tension they can take!  Online one can find many purveyors of different kinds of bungee.  If you insist on wandering off of the righteous path, I heartily recommend stretch testing, followed by analysis.  Avid's recommendation for the safety cables is to allow 3".bungee deflection.  I'd go to 5", or maybe leave them off like Joey did, just adding a bungee inspection to my pre-flight inspection list.  If you, like I, bought your bird used, I would definitely take a careful look at the LG bungees.  Are they single-flecked (hardware-store) or double-flecked (type-1)?  Is there adequate deflection capability in the safety cables?  (My airplane was a double whammy on these questions, and I needed to have my seat tube repaired after a hard landing.)