I installed a 4 point harness is my STOL 750.  The discussion is here.  I designed a transverse tubular mount to achieve the optimal mounting angle and use the original Zenith mounting brackets to make it easier to retrofit (I was installing this in my completed airplane).  Joe Harrington has the lightest solution with a single cable mount for each side running back through to near the rear of the fuselage and mounted to a single attach point on each side - that would be easy to do during a build, but difficult to retrofit.

I used Crow Enterprises, "inverted Y" harness which is the same as used in many Van's RV's.  They're great to deal with and will customize it as you want - I wanted "pull up to tighten" lap belts and "pull down to tighten" shoulder belts.  The rotary latch works great and has a provision for a 5th belt should you decide to add one later. Haven't priced them lately, but they're probably about $325/pair and great quality.

While most seem to install shoulder harnesses to whatever convenient transverse support member that is above their shoulders, I did a great deal of research and found that the FAA and most auto racing safety regs recommend that the shoulder belts angle back upwards from the shoulder at no more than 30 degrees (from a horizontal line extending back from the shoulder) for optimal restraint.  Although better than nothing, the more vertically they mount (greater than 30 degrees), the more the tendency is for the belts to pull back laterally as you are thrown forward and not restrain you.  If mounted behind you and between -10 and +30 degrees relative to the shoulder, the inverted Y belts tend to "cinch you in" as you are thrown forward and restrain you better.

Bottom line:  The design and installation of the mounting point(s) is equally important to the choice of belts!  An excellent article on shoulder belt installation is located here.

John

N750A

I recommend installing and using the fifth (anti submarining) strap as well. That is the one that comes up between your legs and attaches to the buckle on the bottom side of the buckle. In my "big iron" flying days it was commonly called the crotch strap. The belt does indeed help to prevent you from submarining (sliding forward under the lap belt) but it also does another important function. Early in my airline flying a check pilot had me get into the seat and fasten the belts. Then he stood behind my seat and sharply jerked the shoulder harness straps. That pulled the center mounted buckle up into my gut just below the ribs and it was like somebody had punched me there. Then he had me adjust the crotch strap a lot snugger and jerked the harness again. No discomfort, no punch in the gut. It was a very graphic demonstration of the value of the crotch strap.

As long as we are discussing the seat belts I throw out the following advice I have picked up over the years. The belts are intended to keep you from moving around a lot during crash loadings and turbulent flight. To accomplish that they need to be tight. The tighter the better. As a matter of fact, the lap belts in serious aerobatic planes have a ratchet mechanism to crank the lap belt tight to the point just short of pain. The less slack there is the less you move around when outside forces are trying to move you.

So, in the world we normal people fly planes in, that means I pull the lap belt straps as tight as I can for takeoff and landing, the two times when we are most likely to encounter strong forces. I loosen them a bit for the rest of the flight but for takeoff and landing I get them just as tight as I possibly can, there is no such thing as too tight unless you have a ratchet. Also, I use the shoulder harness and/or crotch strap (if installed) very snug for takeoff and landing as well. The shoulder/crotch straps can be loosened up or even removed if desired for cruise flight but they are on and quite snug for all takeoffs and landings. The lap belt should be uncomfortably tight for takeoff and landing and on pleasantly snug the rest of the time The less you move around during a crash, the less you will be hurt. This applies whether you are a pilot or a passenger and in all types of planes, private planes, airliners, whatever. End of lecture..............

I'm reviving this topic, as I'm curious to know if anyone has installed the 5th-point ("crotch") belt on a 750.  I'm very interested in a few pictures on how they (structurally) tied this belt in to the seat framing structure.  I have some ideas on how to build this up (via the AC 43.13) but I was hoping to see it in an actual installation.