Seat Belt - Part 1

This blog will cover installation of the seats belts

Overview 
The seat belts used are Christian 2'' aerobatic 5 point harness out of the the storage box.

Spinal Compression
This is a touch pad for the aviation governing bodies in Australia especially loads that result in spinal compression by the shoulder harness that must be transferred into the aircraft structure.

Got it wrong
Lucky boy...!

Note: The FAA requires a minimum 9 g design load with a 60/40 split is applied the lap and shoulder straps to estimate loads. A design load of 10g with a 1.5 safety factor was used in the basic calculations. 

Revised factory roll bar and lightweight seats

The current aircraft features new seats and roll bar design that address the issue. I chose not to address this issue before installing the roll bar as a lot of work was being done by the factory will be duplicated but the shoulders harness are now a unique issue to this project.

The supplied with this kit were manufactured from vacuum formed shells with a filler sandwiched between the two halves, well that my guess as when cutting through the white filler its smelt like an automotive filler, this method is used to create vanity and baths and appeared familiar to me. What this meant that the seat belt did not have a definable load carrying characteristics and if quizzed I needed a plausible defence.

Seat Belt Attachments

Welding a new spreader bar into the existing roll bar was examined but as it cannot be removed easily and a TIG welder in a country town is a hard to find, especially if they have to come a remote airfield for two small welds.

A shoulder support was developed consisting of two [2]  1'' x 1'' x 0.625'' 2024-T3 RHS riveted to an 0.080'' plate fixed to the existing seat bracket. A folded 20 x 65 x 0.080'' 2024-T3 angle was riveted to the top side to carry the belt loads into the RHS. The RHS frame was stabilized using the roll bar spreader and a commercial 20 mm saddle clamp. 

Finally the seat was bolted at four [4] places to the RHS using M6 rivet nuts installed into the RHS and fixed with Unbrako dome head screws using 1/8" x  30 - 2024T-T3 aluminum washers.

Shoulder support for pilots seat

The shoulder harness frame was attached to the main spar using two brackets fabricated from 0.08'' 2024-T3 aluminium sheet riveted to the existing frame with five [5] 5 mm od pop rivets.

Note: Building a seat frame was not the original intent but that is where it landed

Both lap belts were attached to the face of the main spar using existing mount holes at a rib attachment. Lap attachments were fabricated from 50 x 50 x 3 6061-T6 aluminum angle. Next three [3] of the 4 mm rivets were removed from the rib attachment. The centers were marked onto the angle and drilled, fitted to the spar then each hole was reamed using a tapered reamer and battery frill secured with AN3 bolts.

Pilots lap belt attachment to main spar

Finally the crotch strap was fitted using a tapped hole now located in the rear seat spreader with the belt feed through a slot provided in the seat. 

Note: The rear attachment was required as there was not enough length when attached at the front as previously decided.

Rear Seat
A slot was cut thru the bulkhead to allow a 22 x 3 mm 2024-T3 bar to be installed. This was fixed at the rear using 7 x 4 mm rivets pitched at 20 mm.  A 0.020'' 2024-T2 doubler plate was installed to tie the attachment to the rear baggage compartment bulkhead.

Shoulder harness stiffers baggage compartment.
Stiffeners fabricated from 0.020'' 2024-T3 sheet

and the channel is factory longitudinal member

The front bulkhead was reinforced using a fabricated 60 x 12 angle from 0.032'' 2024-T3 sheet. This was then profiled and riveted to the top side of the existing bulkhead with a 0.040 2024-T3 doubler located at the front to increase the bearing area and reinforce the exit point.  

A 6 mm stainless steel bow shackle is installed to allow attachment of the seat belt harness. A quick release attachment was fitted to allow removal of the seat with the shoulder harness.

Rear seat attachment lap belt

Both lap belt attachments were fabricated from 0.080  - 2024 T3 sheet profiled to the drawing and with a suitable offset. The completed brackets were fixed to the stringers using 3.2 mm pop rivets. This attachment is similar to the current factory attachment method.

After installing the baggage compartment cover the harness attachment were inserted then bolted together using spacers at the belt attachment. 

Harness attachment
A major problem designing any connections is eccentricity but in any mechanical structure we use thicker plates with aircraft it needs to be light as practical.

To allow the misalignment to be accommodated, forged 6mm bow shackles were fitted with a weight penalty of about 12 grams each.

Happy days !

Always look at the bigger picture before setting off
Spot the deliberate error!

To tidy up this mess it was decided to remove and create a new skin with the gain being it allowed access to finish the mounting of the battery and pump. Originally it was intended to mount the shoulder strap in a completely different manner but this change allowed the relocation of the hydraulic pump - more later

Comment
Rear seat will be removed when the aircraft fly's to provide access for adjustments to the propeller controller as is now located in the place of the hydraulic pump.

Its done - Its done - Its done
 have mountings......!