Filling Rivets

This blog is this builder's final words on filling rivet heads, not sure that is is the best way, it is just a way. The final test will be when the paint is applied but the primer used currently worked correctly with no apparent issues but will be the biggest test. 

Overview
The decision to fill the rivets was one of just visual finish as explained in the previous blog on filling the rivets.

Installation
The first method tried was body filler, it proved difficult to fill the rivets due to the air trapped inside the stem creating hydraulic lock, West Systems 105 could be inserted using a syringe, but lacked viscosity and this was an issue not to mention the need for small batches as both types have to be catalyzed before use. The excess of West Systems was hard to remove, and the builder considers this not an option.

Next, automotive spot putty, while easy to inject with the syringe, once cured it proved not to bond into the rivet opening and popped out easily when trimming, so the failure rate was high.

In desperation, a waterbased acrylic filler was tried [No-More Gaps family], and this worked well in all locations and proved to trim easily with a sharp blade, but the builder was worried about the temperature that the wings would reach in the dark camouflage.

It was decided to try Parfix Urethane Sealer Adhesive, this proved to work well in all respects and would be used again at the start. 

The viscosity that gives it its useful properties creates an issue with the syringe keeping the needle on. Fitted the needle once as tightly as possible by winding it onto the syringe spigot and when not in use, inserted a length of safety wire and placed in the fridge.  

Filling the syringe was the other issue, drilled a 3 mm hole about halfway up the barrel, then filled to that hole before inserting the plunger as this allows the plunger to contact the filler providing a more accurate delivery.

Note: Prepare about four [4] syringes so if there are any issues replace it with a clean assembly

The urethane should be applied as outlined in the previous blog, then allowed to dry for a minimum of 24 hours; longer will be better. The reason is, while small in volume it's thick and therefore slow to cure. 


Additionally, Urethane could be used on rivets that had small dishes or imperfections by applying a light coat onto the existing adhesive and allowing it to fully cure and dressing with the foam adhesive pads.

A word of warning, clean all material that is inadvertently applied as this material requires mechanical removal when cured, have a top-grade thinner available with clean rags when applying. It would be best to wear disposable gloves as it sticks to the skin just as aggressively and is difficult to remove - guilty OK.

Note: A Dremel Motor Tool and 1200 grit foam pads were purchased in bulk a long time ago but came into their own for this task. The best technique was to run the foam side across the dome of the rivet with the body of the chuck placed on the skin with a tool speed of 8-9 thousand rpm. This helped prevent excess pressure, do not go above 10000 rpm as the abrasive action can be destructive.

Tools
Mini Drill 1200 grit grey abrasive pads were used sourced from Allied Express but keep the rev's down as they can shift metal in the higher rev range

A Dremel motor tool with the accessory extension shaft is a must-have for this job, in fact, it has proved invaluable for many tasks.

Comment
Be careful about what you chose to do...!

Looking back it would now it would take about 40 to 50 additional hours to fill and prepare the rivets for painting but to get here this time took a lot, a lot longer, but that is the underlying story of this build,. 

The finished look, however, made up somewhat for the lost time - just!

Oh, nice men have come with a new white coat, not my style though.

Wing Faring

This blog covers the fitting of the wing fairing.

Overview
After the disaster fitting the elevator faring the builder was determined not to repeat that event.

Installation
The first task was to mark out on the fuselage/wings all those locations were a hole cannot be drilled. Once done the factory fairing was fitted and the location of the first holes determined.

Tape to mark areas not to be used for a fixing

At this point, a Cleco was fitted and the next position determined, this process was repeated along the top side. Once completed, the lower flange was secured ensuring the fairing laid as naturally as possible on the wing. The final task was the nose and the underside of the rear faring from the flap back.


Note: Two additional screws could be added by reusing fixings on the main longerons fitted to the fuselage side. An M3 flush rivet nut was installed into a strip of 18 x 100 x 0.025" of 2024-T3 aluminium, then removing the rivets either side of the mounting hole to secure the aluminium strip with two [2] new pop rivets. The M3 screw is then inserted through the remaining hole to pick up the rivet nut.

At the rear, two [2] of the rivets for the last flap were secured the lower flange of the faring. To locate the hole a piece of cardboard of fixed to the top side of the skin and the hole located using a round jewellers file, finally, the outside edge was secured in position using a piece of gaffer tape for the next operation.

With the fairing reinstalled and secured with Clecos, the cardboard template is fitted to the top side of the faring using the gaffer tape as a hinge, next the holes locations are transferred to the faring top side and drilled.

The faring detached and the two rivet holes drilled to accept an M3 rivet nut. Finally, the fairing was secured using M3 x 12 S/S  Hex Socket Flanged Button Head Screws. A flanged head screw allows a reasonable clearance hole to installed in the faring.


Comment
Faring fitted as supplied and this was a surprise considering its size but maybe even this builder has learnt from some of his previous grievous errors.

Factory Tucano

Hydraulic Pump Relocation

This blog covers the final relocation of the hydraulic pump and accessories.

Overview
The decision to move the hydraulic pump to the baggage compartment was a matter of convenience and it met the factory request that the COG moves to 18% over the 16% allowable for this model. While it worked, it reduced the size of the compartment but the thought of building a battery mount through the original access hatch was not the first choice.

On the visit to the factory, this was discussed with Franco were it was explained that the relocation of the battery behind the rear of the baggage compartment was an access issue. At this point, Franco showed a new compartment opening that was twice the size now making it possible, the builder returned with a new frame and doubler's to upgrade this aircraft.

Installation
The modification was covered in a previous blog - click here

With the access created the pump/battery was relocated and covered in a previous blog - click here

The final task was to connect the hydraulic lines that were now cut short for the baggage compartment, both plastic return lines were lengthed by trimming in the seat area and adding connectors to reach the new location.

A length of 6 mm od [white] line was purchased but when the connection was tried it would not work but investigation showed that the material selected while dimensional correct it was harder, preventing it from installing correctly. 

A solution was found by heating a T fitting with one of the nipples installed and using it to heat form the flair and this allowed installation to proceed.

The final task was to trim and install the S/S lines on the pressure side and this has been covered previously. The biggest issue is the connections are rigid and can create twisting of the S/S lines, if not done carefully. With the lines installed in the seat area, a nut was fitted and the fitting installed, if found that the alignment was incorrect the nut was re-adjusted, the process repeated until correct the fitting aligned with its location on the pump with the nut nearly fully tight.

The fitting was then tightened and installed using liquid Teflon to seal the threads of the retainer nut.

All lines were secured with aluminium clamps lined with gaffer tape to help reduce chafing in service and secured using M3 S/S cap head screws

The hydraulic pump is mounted on isolators

Center tray is removable to allow access to the cable
and for inspections

Trial fit of all that stuff

Comments
This arrangement created an 18% COG while allowing the lightweight batteries to be retained, as the combined weight of the pump/batteries is equal to the factory battery of 5 kg.

The hose runs are a result of the relocations undertaken and the personal choice of the builder, done again with full access a different run may have evolved, on a positive note this location provides excellent access to the pump and fittings.