GATVC; seat & harness, wheels & brakes, & instrument panel

[JimCrawford]

Progress on the harness installation.
This is pretty well complete and ready for a write-up as a mod for the LAA. It will need formal stress calculations but the 'back of envelope' sums show this simple arrangement to be so overfactored that you would better worry about where the engine and fuel tank are going to end up before the security of the harness becomes a concern.

I found the following in Darrol Stinton's "The design of the aeroplane" and it illustrates an important point: The shoulder straps are to prevent you striking the instrument panel with your head, not to hold you into the seat. The latter function is performed by the lapstrap.

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Any significant downward angle on the straps only serves to compress the spine and reduce the effectiveness with regard to resisting forward motion. I'm not sure how the Nipper got a public transport CofA with the original lower longeron arrangement. The top longeron mod and this aft top longeron mod don't have this problem.

Nuts and bolts:
This is the set of parts for the harness end.
The two stainless steel straps serve to adapt the cable thimble to the harness attachment. The spacers prevent the straps from binding on the cable or the harness plate. This area might need some adjustment for different harness styles.

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The assembly:

P1050020harnesspartsassembled.jpg (73.17 KiB) Viewed 5858 times

and finally the harness in the fuselage. The bungee will eventually attach to the seat and prevents the harness from dropping into the fuselage through all the cross bracing wires

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See you at the rally??? I'll be the one photographing Nipper details! (prob Sunday only)

Jim

[JimCrawford]

Hi All,

I need clarification about the seat assembly. In Drawing 11, cockpit and canopy details - top left corner, There is a view on K which shows the wrap around strap (part F46) which secures the aft edge of the seat pan to the fuselage cross member. How many of these straps are needed? The drawing doesn't say and there are four bolts indicated across the back edge of the pan. My aircraft only has two straps fitted, to the outermost bolt holes. Is this correct or should there be 4? If so I'll need to get hold of another 2. Without the 2 innermost straps and without the seat back attached via the piece of angle across the back, the seat pan flexes slightly in the centre of the back edge as there is no support there. This area would be supported if there were 4 straps. Alternatively the angle may stiffen it sufficiently.

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I hope someone can help with this detail.

I'm in the process of fitting the seatback. Because it is full depth with only the strap slot to see down the back, it is hinged to the pan at the bottom edge so that it can be easily moved forward to get access.

Jim

[Neil Spooner]

Hi Jim,

I only have two, the alloy angle that runs all the way across gives sufficient support as the seat back is screwed via 6 screws to a couple of plates welded to the upper cross tube. Having the seat back hinged is a good idea, but I wouldn't leave out those 6 screws.

My a/c is fully inverted, and I use that facility a lot. My upper harness is fitted to the cross tube that supports the seat back, and runs over the top of the seat back that is raised by about 5". The shoulder harness gives me a lot of support as well as the lap straps when inverted. I also have a secondary lap strap. When I had my "outfield" landing and came to a very sudden stop, the seat back failed as the straps went tight, but still prevented me getting anywhere near the 'panel. The seat back failing gives a progressive deceleration to the upper torso.

I would recommend fitting a perspex inspection hatch at the tail end of the fuselage to inspect for foreign bodies before every flight.

Neil

[JimCrawford]

Thanks Neil, that sorts out the straps.

Re the angle and seat back, plan A;

1. delete the angle.
The four hinge positions at the four bolt positions are made by replacing the bolts with eye bolts. The seat back lower flange will be built up to supply all the seat pan stiffness required.

2. delete the 6 bolts on the seat back.
If the seat back flange is supplying all the pan stiffness, via the 4 hinge bolts, then these 6 bolts on the seat back can be replaced by a couple of Dzeus fasteners. This location now only serves to give a little lateral support to the seat back and to prevent it flapping about. If the bolts were to be retained then they would have to have captive nuts because the full depth seat back prevents access. I'd prefer Dzeus fasteners because folding the seat then becomes so quick that you would do it on a DI.

Many thanks for the gen

Jim