Fri May 30 2008

Fabricating F-916C spacers

I haven't gotten much done on the plane the past few days because I've been trying to decide what to do with the seat belt system. I'll get to that in a minute. For today I just fabricated the F-916C spacers. Here I'm cutting them all to 1 1/4 inch long.

They came out fine.

OK, here's the scoop on the seatbelts. I'm planning on doing aerobatics including negative Gs and sustained inverted flight in the RV. It occured to me that a failure of the seat belt system could result in a very bad day. It's possible I could fall right through the canopy or lose control of the aircraft. It's also possible that my grip on the stick could cause me to over-G the airplane and pull the wings off. Based on all that, I decided to put in an auxiliary lap belt. But how to do it?

After posting the question on Van's Airforce, I only got a couple of responses. One fellow has a secondary lap belt that is attached to the same brackets as the primary belt system. I've gotta admit, this never even occurred to me. I was thinking of how to install a completely secondary system. But the most likely failure point of a seat belt system is probably the latch, so using a secondary lap belt attached to the same brackets as the primary probably achieves 90% of the safety of having a completely independent system.

That said, after mulling it around for a while, I decided to add a bunch of structure to allow for completely independent brackets. It'll add a few pounds and several hours of work, but I think the reassurance will be worth it. Like my friend, Brent, said...when it comes right down to it, there's just a single AN-4 bolt holding you in your seat. I believe the redundancy will make the effort worthwhile.

Soooo....This is what I'm going to do. You can see the line of force that the primary belt system has (red line). I'm going to install brackets with a lien of force as shown with the magenta line. I've already orderd four more F-716 ribs (two L and two R) and some aluminum sheet to fabricate cross ribs with. For the brackets themselves, I'll run out to Home Depot and pick up some sheet metal from the aviation aisle. This is what you'll see me working on for the next few entries.