Good wiring practices

[jiott]

If you do a search you will find quite a discussion on seat pans and support blocks. Apparently there were some instances (mostly on earlier models I think) of seat pans front and/or back support lips breaking during turbulence and heavy pilots and then falling down and jamming the control rods under the seat. This is very serious, so I glued some support blocks that just barely touch the seat bottom when installed normally and would prevent any jamming of the rods. This was not my idea, but was picked up from others on the forum. It was simple and easy to do. I have not heard of this problem for quite a while now, so probably the later models have the seat pan reinforced adequately. Anyway, for me it was good cheap and easy insurance.

[Av8r3400]

If you do a search you will find quite a discussion on seat pans and support blocks. Apparently there were some instances (mostly on earlier models I think) of seat pans front and/or back support lips breaking during turbulence and heavy pilots and then falling down and jamming the control rods under the seat. This is very serious, so I glued some support blocks that just barely touch the seat bottom when installed normally and would prevent any jamming of the rods. This was not my idea, but was picked up from others on the forum. It was simple and easy to do. I have not heard of this problem for quite a while now, so probably the later models have the seat pan reinforced adequately. Anyway, for me it was good cheap and easy insurance.

We just had this happen to a brand newly born IV-1050 on my airport field, on the plane's first flight! The seat pan relaxed down and the aileron control was jammed. Luckily the pilot/builder had a lot of Avid and model 3 experience, so was able to rudder the airplane around and made a successful landing on the grass. Everyone walked away unscathed (except maybe his shorts...).

Definitely good advise to block the seat in some fashion to keep it from jamming the controls.

[David47]

If you do a search you will find quite a discussion on seat pans and support blocks. Apparently there were some instances (mostly on earlier models I think) of seat pans front and/or back support lips breaking during turbulence and heavy pilots and then falling down and jamming the control rods under the seat. This is very serious, so I glued some support blocks that just barely touch the seat bottom when installed normally and would prevent any jamming of the rods. This was not my idea, but was picked up from others on the forum. It was simple and easy to do. I have not heard of this problem for quite a while now, so probably the later models have the seat pan reinforced adequately. Anyway, for me it was good cheap and easy insurance.

Yikes !. I'm now putting seat blocks or similar support under the seat pans. Thanks Jim and av8r3400 for the heads up.

[Dave S]

Following the initial seat pan failures in the early days.....there have since been changes that will prevent this even if the seat pan cracks.

1) Some time ago, John McBean started selling poly storage bins that could be riveted to the bottom of the seat - these bins are quite close to the structural tubing under the seats so if the seat comes down - it will come to rest on the belly tubing, not the controls. We retrofitted these to our plane and the geometry solves the concern - and makes a wonderful place for spare parts and tools.

2) Although I haven't personally seen one of the new seat assemblies, I believe currently the seats are made one piece with the buckets part of the seat pan resulting in a similar situation to #1 above - protecting the controls.

3) I have seen the current construction of the seat securements which includes tabs welded to the tubing the seat pan rests on so the seat can be very securely screwed to the airframe. In the early days, the seat pans were secured with nylon ties run through slots cut in the edge of the seat. This refinement, although seemingly minor, I believe is a very important improvement - both for the seat pan security and ease of removing and replacing the seat pan. FWIW - one of the early failures, memorialized in the NTSB files, was linked to a situation where no securements were used at all on the seat pan - the pan was simply dropped into place, the aircraft hit a pothole in the sky, seat pan came up and went back down, broke etc.. Our airplane, being an early, pre Mcbean S7, did not have this refinement; however, we went with hockey stick tape and plain clamps at the correct places around the pan, which is also very secure....but...this is bit of a pain because a person has to get to both sides to do the screws/nuts/washers.

4) The butt-blocks which have been mentioned are a great idea for otherwise un protected controls - simple and easily made gremlin proof.

The old style seat pans are still out there so well worth thinking about.

[jiott]

Dave, glad you spoke up about all the improvements. I really believe the new SS7 model is practically immune to this old problem, and wouldn't want folks to get the wrong idea about the safety of the recent designs. As I said earlier, I have not heard of this problem on the SS7. When I built mine, the SS7 was still fairly new and some of these stories of the older models were still fresh in my mind, so I opted for the insurance.