I am modifying the front seat-back and safety harness system for a Cozy MkIV and need assistance in determining what and how much material to use.
On the standard Cozy MkIV, the shoulder harness anchor points are attached to a composite cross-beam that extends from one longeron to the other, at shoulder height.
I have modified my project, resulting in a shallower fuselage. As a result, my seat backs rise above the longeron level by about 8".
My design intention is to keep the longeron-level composite cross beam as the anchor points for the shoulder harnesses, but loop the harnesses up and over the seat backs.
I will use an inverted-"U" or "A" shaped seat back, composed of composite box-beams 2.5" wide, 3" deep. The "U" or "A" seat-backs will extend from the floor, up through the longeron-level cross-beam, and up 8".
The box-beams will use a 3/8" H-45 (3#) Divinicell foam core, with a 1 ply BID internal layup, and 2 ply BID external layup, at +/- 45 degrees. On top of that I will lay up E-glass roving for a cap, with another 2 ply BID layup at +/- 45 degrees.
This is a design that is employed in several car-seats. However, I do not have the experience to determine how thick the composite layers should be. I would like to avoid going overboard on
Design Loads:
I am using the FAR 23 guidelines to determine the static load requirements for the seat.
FAR 23.785a specifies a occupant weight of 215 lbs, with a 1.3x safety factor.
FAR 23.561 specifies a static load (in the foward direction) of 9bs. Using the 215 lbs passenger w/1.3x safety factor, that corresponds to 215 x 9 x 1.3= 2515.5 lbs.
Taking this a step further -- if we presume a 2.0 safety factor to account for homebuilt composite construction variances, and assume that the shoulder harnesses restrain 70% of the load in a forward deccellerating crach, then the static load requirements for the shoulder harnesses (combined) is 215 x .7 x 9 x 2.0 = 2709 lbs.
So... The seat back needs to withstand 2709 lbs static load, and each anchor point (2 anchors) needs to withstand a 1354 lb static load.
Please see the attached diagrams and advise. Thanks. Steve
On the standard Cozy MkIV, the shoulder harness anchor points are attached to a composite cross-beam that extends from one longeron to the other, at shoulder height.
I have modified my project, resulting in a shallower fuselage. As a result, my seat backs rise above the longeron level by about 8".
My design intention is to keep the longeron-level composite cross beam as the anchor points for the shoulder harnesses, but loop the harnesses up and over the seat backs.
I will use an inverted-"U" or "A" shaped seat back, composed of composite box-beams 2.5" wide, 3" deep. The "U" or "A" seat-backs will extend from the floor, up through the longeron-level cross-beam, and up 8".
The box-beams will use a 3/8" H-45 (3#) Divinicell foam core, with a 1 ply BID internal layup, and 2 ply BID external layup, at +/- 45 degrees. On top of that I will lay up E-glass roving for a cap, with another 2 ply BID layup at +/- 45 degrees.
This is a design that is employed in several car-seats. However, I do not have the experience to determine how thick the composite layers should be. I would like to avoid going overboard on
Design Loads:
I am using the FAR 23 guidelines to determine the static load requirements for the seat.
FAR 23.785a specifies a occupant weight of 215 lbs, with a 1.3x safety factor.
FAR 23.561 specifies a static load (in the foward direction) of 9bs. Using the 215 lbs passenger w/1.3x safety factor, that corresponds to 215 x 9 x 1.3= 2515.5 lbs.
Taking this a step further -- if we presume a 2.0 safety factor to account for homebuilt composite construction variances, and assume that the shoulder harnesses restrain 70% of the load in a forward deccellerating crach, then the static load requirements for the shoulder harnesses (combined) is 215 x .7 x 9 x 2.0 = 2709 lbs.
So... The seat back needs to withstand 2709 lbs static load, and each anchor point (2 anchors) needs to withstand a 1354 lb static load.
Please see the attached diagrams and advise. Thanks. Steve
