Repair revisited

This blog cover the additional work done to the repair damage created in transit from the airshow.

Overview

Best not talked about

Final inspection of the repair displayed unacceptable gaps between the skin and the rib at two locations.

Initially packers were added but the realization was reached that application of rivets created all types of issues

I had been too optimistic after the repair and now had to accept this task was at the limits of my ability but it had to be fixed to my satisfaction.

Rework
A lot of time was lost rethinking on this issue and putting pride aside this was as a tough job as this builder has ever undertaken. 

After a lot of soul searching it was decided to remove the tabs that were creating the issue's and rivet new ones on. This position was reached after fitting the skins to both sides, inspecting the fit it was concluded the core of the issue laid in the curves.

With the rib exposed the curved tabs were removed and dressed then a replacement set fabricated. To allow the component to be fitted the side was cut creating tabs on the mating faces and these were then drilled allowing three [3] rivets to be installed at the top and bottom with a couple in the middle. 

The original full length stringer doubler was replaced with two [2] 0.025'' 2024-T3 custom folded channels. These were tapered on the flanges and staggered to each other to create a smooth path for any loads to transfer between members. The flanges were riveted to hold the assembly straight while lining up the members.

New outer flange

Top fixing of new bulkheads

With the part ready the tab was slid between the bulkhead web and skin and with the location marked onto the web, next the holes were drilled and all the components clecoed to the bulkhead and then riveted. The operation was repeated until all bulkheads were modified, finally the skins were fitted but it was difficult to drill the align ribs for drilling from the skin side one skin had to be off to allow the necessary drilling to be undertaken. 

To create access the damaged port skin was cut open near the rib and fitted to the starboard side and that access allowed the operation to be repeated on the starboard side.

This is one idea that allowed the positioning of the rib correctly for pre-drilling

The jig was manufactured using the damaged skin, match drilled using the new skin and fitted to the aircraft, holes for the rib could be drilled, position checked
through the whole process.

Note: Each check involves the installation and removal of one of the side skins multiple times not to mention the installation of both skins to confirm alignment which consumed the better part of each day given to each task. A jig was developed as a result of the time lost doing this and not begin able to reach the rib to control its position for drilling

Blue Stuff
The aircraft was leveled using the water tubes  at points along and across the fuselage plus the the elevator stab with a small amount of weight applied on the elevator stab to tweek the alignment before riveting with the final task to pull rivets.

Note: Both skins are clone's of the original factory skins with all factory pre-drilled holes reused.

Mid-night and the lower skin's are installed
with the next skin to be installed for riveting

The final task next week is one final check, remove clecos and fill all the empty holes with pop rivets. 

Comment
How a small amount of damage in real terms had cost the builder 75+ hours of work. rework and more rework is hard to fathom. That this much time could be consumed and not achieve perfection is beyond me but the task was like a game of chess, every move had significance with unseen consequences and with each move, options reduced in a game with no visible guidelines.

The description of the work is at best in this case an overview and dose not go close in covering the time lost in fitting, re-fitting, checking and re-work.

Ready to close

Air Show Aftermath

This blog is to be a honest account of the history of this exercise - this is the bad but with a happy ending - read on.

Factory repair scheme

On return from AUSFly 2015 the fuselage was unloaded from the return trip with all seemingly OK until the fabric strap used to hold the fuselage at the rear was removed and the damage to rib 9 and the port skin was uncovered. Without the boring detail the rear was located at the rear of the trailer for the return trip and it can be concluded at the additional acceleration collapsed the rear support allowing the rib to ride on a hold down strip and the rest is history.

Happy Days at AusFly

The factory was contacted and the repair scheme above was received within 48 hours and the parts were manufactured, alodined and dispatched with the supercharger upgrade kit.

While this was inconvenient and not a task I would willing seek out, it was one of the reasons I chose to build a conventional aluminium factory kit.

It can be repaired in the field with basic tools and should be part of any builder selection criteria. While it may grant bragging rights to have a kit built using the latest honeycomb graphite composite remember that you have to maintain it - a point to consider

The Repair
Rib No 9 was a total loss and Rib 8 had a couple of small creases and it was decided to remove it on spec. Once removed the longitudinal channel was straightened as much as possible and the new channel slipped over it and match drilled and clecoed.

Next the damaged rib was cut out using aviation snips and trimmed back to the underside of the longeron leaving the existing attachment brackets in-tack. The scrap for the No 8 rib was used as a drilling jig for the lower attachment but the damage to the No 9 rib precluded this approach.

The new rib was trial fitted and aligned to the channel doubler. When satisfied the first mounting hole for the No 9 rib was drilled - re fitted and all other holes match drilled. This was repeated for the other side then the flange's at the center tab. 

Next the No 8 rib was installed using the pre-drilled mounting holes as the starting point then all other holes were match drilled.

The channel was now reinforced with a length of aluminum angle and the tabs to attach the rib to the channel were pre-drilled to mount to the rib's, then the assembly match drilled. A single counter sunk 3 mm rivet was installed to secure the assembly. 

This operation was repeated at the next rib.

The sides were match drilled into the rib flange on each rib and cleoced. All bulkheads were fully riveted using 3 mm x 8 pop rivets at each attachment point including two rivets into the flanges.

The next task was to fit the undamaged skin on the starboard side to check alignment. This was slipped  under the side skin and wrapped around using the two remaining drilled rivets to meet the lower channel.

A number of the other ribs had holes drilled using the skin to assist in this task. The lower flange is highly mobile and this resulted in the rivets location 2 - 4 mm from the flange of the rib and I suspect that they were not exactly in the correct alignment but in the case of the No 9 rib it had little give at this point so the alignment had been set at assembly

Repaired No 9 Rib

 New Skin
The factory supplied two new skin's and one was placed on a flat table laying on 6 mm aluminium foil insulation that proved perfect for this task by allowing the drill to clear the skin and the cleco to bite at the hole created in the foam insulation effectively locking the job as the cleco's were added.

The damaged skin was cut to allow it to lay flat with weight applied and the holes traced around the sheet. 

The holes for the connection at the channel will be matched drilled at installation

Next working week we close the rear to allow the tail to be fitted. 

To at least make me feel better when the liquid level was checked on the tail plane, it was perfectly level with the fuselage - all well that ends well.

Back were it all started