wandersen
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I finished up welding the front seat Skybolt shoulder harness riser.
I'm motivated to get a good shoulder harness anchor installation as I've lost friends in aircraft accidents (note the plural) where there were no shoulder harnesses installed.
Here is the FAA guidance on retrofitting Shoulder harnesses to certified aircraft.
http://www.gpo.gov/fdsys/pkg/FR-2000-06-14/html/00-14910.htm
This indicates that you should do a pull test equivalent to 9Gs. Alpha harnesses (supplier for aftermarket shoulder harnesses for Bonanzas) indicates to do a 500lbs pull test on their installation (this begs the question on what you react the 500lbs against...).
Below are the pictures of the front shoulder harness riser I've welded to the fuselage. Both the 3/4 and 7/8" tubing are 0.049" which is likely overkill (and heavy - I'd do 0.035" next time.). The attach points will be the triangles welded to the base of the front seat (ala Firebolt.). The shoulder harness pull will want to tip this whole riser assembly forward. The diagonal members are welded on to help prevent this. Areas where the welds would be in tension have a 0.035" finger doublers. If the diagonals are at a worst case 25 degree angle, the diagonal tension at 500lbs pull (one side) would be 500lbs/sin(25deg) = 1183lbs (tension). This should be fine. The Firebolt plans call for the shoulder harnesses to pass over the intercostal which is way too low on the back. This is just asking for a spine compression injury.
For the rear shoulder harnesses, I will attach using the tabs welded at the corner of the intercostal well behind the rear seat. (tabs ala Firebolt plans) The Firebolt plans show a fully welded riser with bracing located within the turtledeck. This gets the shoulder harnesses up high enough but IMO is way too heavy and overbuilt. My thinking is that I don't need a full braced riser of 4130 steel. The geometry is much more favorable than the front seat shoulder harnesses. There will be some compression loads at the rear of the seat, but not nearly 500lbs. Maybe something on the order of 500lbs * sin(30deg) = 250lbs compression. I should be able to react this load with the turtledeck bulkhead material. Anyone have thoughts around this, pictures?
Thanks.
I'm motivated to get a good shoulder harness anchor installation as I've lost friends in aircraft accidents (note the plural) where there were no shoulder harnesses installed.
Here is the FAA guidance on retrofitting Shoulder harnesses to certified aircraft.
http://www.gpo.gov/fdsys/pkg/FR-2000-06-14/html/00-14910.htm
This indicates that you should do a pull test equivalent to 9Gs. Alpha harnesses (supplier for aftermarket shoulder harnesses for Bonanzas) indicates to do a 500lbs pull test on their installation (this begs the question on what you react the 500lbs against...).
Below are the pictures of the front shoulder harness riser I've welded to the fuselage. Both the 3/4 and 7/8" tubing are 0.049" which is likely overkill (and heavy - I'd do 0.035" next time.). The attach points will be the triangles welded to the base of the front seat (ala Firebolt.). The shoulder harness pull will want to tip this whole riser assembly forward. The diagonal members are welded on to help prevent this. Areas where the welds would be in tension have a 0.035" finger doublers. If the diagonals are at a worst case 25 degree angle, the diagonal tension at 500lbs pull (one side) would be 500lbs/sin(25deg) = 1183lbs (tension). This should be fine. The Firebolt plans call for the shoulder harnesses to pass over the intercostal which is way too low on the back. This is just asking for a spine compression injury.
For the rear shoulder harnesses, I will attach using the tabs welded at the corner of the intercostal well behind the rear seat. (tabs ala Firebolt plans) The Firebolt plans show a fully welded riser with bracing located within the turtledeck. This gets the shoulder harnesses up high enough but IMO is way too heavy and overbuilt. My thinking is that I don't need a full braced riser of 4130 steel. The geometry is much more favorable than the front seat shoulder harnesses. There will be some compression loads at the rear of the seat, but not nearly 500lbs. Maybe something on the order of 500lbs * sin(30deg) = 250lbs compression. I should be able to react this load with the turtledeck bulkhead material. Anyone have thoughts around this, pictures?
Thanks.
