29 April 2017

Interior. Seatbelt/Harness fitting fun.

My safety harnesses, obtained in September 2015 and installed in March of 2017, came with end fittings.  They are all  3/16" thick with 1/2" diameter bolt holes and 1.875" wide strap slots.  That thickness is appropriate for the shoulder harnesses, however it is too thick for the lap belts, the latter of which needs to be 1/8".

Additionally, the 1/2" diameter bolts holes are too large for the AN4 bolts (which are 1/4") called out for on page 42-06.  So I had my friend fabricate for me bushings with dimensions:  0.252" ID, 0.5" OD and 0.202" L.  The bushing were pressed into the end fittings (left) and attached to the F-01406E Shoulder Harness Lugs using the AN4-6A bolts and associated hardware (right).


Here are the shoulder strap end fittings in place.


The end fittings are too long to work for the crotch strap (it places the strap above the rectangular cutouts in the F-14110AB Crotch Strap Brackets, shown two images below).  So I tried drilling a hole to make it sit lower.


However, the end fitting is just too thick and creates too much space between the two Crotch Strap Brackets.


I purchased end fittings from Aircraft Spruce for the crotch straps which have 7/16" bolt holes, 2" wide slots for the strap and were 0.091" thick.  My friend made bushings for me with dimensions 0.315" ID, 0.4375" ID and 0.202" L, to fit the AN5 bolts called for on page 42-02 which have a 5/16" (0.3125") diameter .


With the crotch strap folded over on itself, it's unreasonable to use all four screws on the Crotch Strap Brackets as the thickness is too great and the brackets have an excessive clamping force on the strap, preventing length adjustment.  I deemed this acceptable and moved on.


For the lap belts, Crow provided replacement end fittings, which were not black anodized.  They had slightly narrow 1.5" wide slots for the strap and were 1/8" thick with 1/4" bolt holes.  Because this 1/8" thickness is precisely what the F-01480 Seat Belt Attach Lugs are designed for, the end fittings will not freely rotate about the bolt (the end fittings should be 0.091" thick with a 1/8" bushing).  That's okay.  I adjusted the angle of the end fittings to align close to what it would normally be when the occupants are strapped in.

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