Farings Rear

This blog covers the finishing up of the factory rear fairings.

Overview
With the painting next the rear fiberglass was finally dressed up and installed with the correct screws along with all those final adjustments.

Installation
The lower rudder fairing lights were connected via a four [4] pin plug mounted onto the first bulkhead after the fin attachment. To do this the cable in the fairing was drawn out and connected to the plug and then feed back in into faring then the faring was secured with a  flat head M3 screws.

The elevator faring were next and again secured with the M3 pan head socket head screws with the rudder stab fairings fixed with flat head phillips M3 screws.

Next was the dorsal fin here a couple of holes were re-established using a hole finder and after a series of adjustments it was screwed to the back of the fuselage using M3 flat head screws.  The connecting cables from the the stab and trim tab had previously been connected and it was a matter of checking and fixing the dorsal fin.

Finally the rudder stab fairings were installed. As these have to be removed at the 100 hourly to inspect my nick in the spar they were fixed using M3 pan head screws with an incorporated washer. The starboard faring required some more modifications at this time as it did not fit a cleanly.

.
Note: All Rivet Nuts were re-tapped with a M3 tap to improve screw installation and avoid cross threading  

Fixing holes
Some of the holes had to be relocated, tuned pick a word this is one reason floating nuts exist. When required the correct center was marked onto the surface with a biro in the form of a cross. Next a small amount of Plasti-Bond was mixed and the hole filled then a strip of peel applied across both sides and the mixture squeezed between the fingers and set aside to cute.

When cured the new hole center was re-established and drilled with a 2.5 mm drill before sanding. Once shaped the hole was enlarged with the Dremel motor tool as described previously.

Priming
With this done they were removed and all holes in the fiberglass enlarged to about 3/16'' using a conical grinding stone found in the Dremel kit, this gave a clean hole that could not be achieved with drills. 

All fairings were primed using rattle pack bumper bar primer and left to be sanded just before painting

Comments
With the rudder and elevator stab fairings I would not remove the waste to the factory line just straighten both edges equally on both sides as the extra material would allow the fixings to be installed in a flat area the faring. Allow the faring to lie naturally as mine needs a push and shove to line up as pressure was applied before drilling mounting holes.

Note: Pressure was applied when drilling the hole to flatten out the curve and the movement when tightening up the screws created variability creating hole movement, in fact they fit differently every time if only a little. If riveting consider fixing the lower flange and then drill and fix the upper the upper.

The rivet nuts are a mixed blessing as without them the M3 large head screws could not have been used but they make the installation the holes more difficult. There biggest downside is the hole locations are more critical even with 5 mm hole but I was thinking floating nuts when doing the hole filling.

Pop rivets would be the quickest but there are reasons on this project and screws do allow you to adjust pressure obtaining a neater fit.

Above all make sure you mark out the ribs and spar before drilling.



. 

Rivets

This blog covers the filling and polishing of the rivet heads

Overview
More time has been spent  trying to find a quick method of filling rivet heads. While there are a number of clues to be found on the WWW it would be easier to join the Illuminati that find a definitive method.

Regardless most methods required some sort of epoxy was used so that is were the builder decided to start. This builder tried Plasti-Bond, two part epoxy [thick stuff] and West Systems initially.

Construction
A series rivet heads were filled using a mixture of West Systems Epoxy and slow cure hardener. These were mixed in small batches of about 8 cc with a pinch of blue chalk dust added for colour, this was found to be critical to allow you to see runs in artificial light. While a good number of nice rivet fills are achieved over fills were common with the inevitable runs. 

The best technique was inject the epoxy into the rivet opening with enough resin to form a mucus before moving to the next with the results varying from wonderful, to well a mess. 

A Black Duck

This worked well in the horizontal or near horizontal but for verticals the builder waited for the epoxy to thicken for the more horizontal rivets. 

Once cured the real work begins removing the waste. This was sliced / scraped off using a 18 mm box-cutter blade with the rear end best for scraping. 

Holding a 18 mm box cutter blade [it must be sharp] in two [2] hands, bend it using the base of the curve to slice the waste off then and finish rivets by polishing with a softened 800 grip wet and dry.

All these tasks require 110% from the person applying and removing the epoxy and that's just not possible for this little black duck...!

Note: softened paper by soaked in warm water and detergent until it just turns into a soft cloth like material. 

Alternative approach
Halfway through the fuselage there had to be a better method and the idea of using an acrylic sealant filler was examined. 

A syringe was filled with grey acrylic and a 1/2'' dosing needle fitted after grinding off the sloped opening. This was inserted and the acrylic injected slowly while moving the needle out, once reaching the opening swirling to create a cone like covering over the opening in the rivet - this is important to create a seal.

Note: Best profile is like a choc top on top of the rivet head

This material must be fully cured and this will take 24 hours and even better give it a week - firmer is better.

All the tops were removed using a curved blade as described previously. This may require a few passes to cut down to the top side of the rivet. 

Grind needle end square - Acrylic must
cover the full opening of rivet head plus a bit

If you have clean rivet tops this works well but in my case a number had rims formed by the tool and the blade could slice off the smaller once but the larger one's were removed with a Dremel fitted with a 120 grit click and lock sanding disc.

Note: Set the Dremel speed to about 10K and be very gentle using the outside edge applied at a slight angle to the rivet head








Comments
This may or may be a good method but it is quick and simple compared to using epoxy. One issue is temperature as Dark Green can reach temperatures nearly equal to a black and this will be critical on the top side of the wings. 

The acrylic is used on the fuselage is good for 70 - 80 C but a little investigation shows that Selleys 3 : 1 is rated at 90 C and this will be used in future.

Small scale tests show this combination it is happy to have acrylic primer and paint applied over it but this is a suck and see job. It will in the end be a good idea or a sea of tears - we shall see will we not.

Rudder Wrap Up

This blog covers the final assembly of the rudder and fin

Overview
With the elevator stab fitted it was time to reinstall the rudder and fin

Fin Attachment
The front attachment was upgraded to a similar specification as the new model by the addition of two [2] AN3 bolts. These and the original mounting bolt were secured to a series of floating nuts riveted to the original bulkhead, this was done for ease of assembly.

The outer floating nuts were tight at installation
requiring custom fitted bolts

Fin was fixed using a series of AN3 bolts at the
eight [8] factory fixing points

Lower fairing covered in previous blog
Nice small detail using a piece of scrap

The electrical for the top flashing beacon and the trim motor drawn through and connected  under the nose area of the fin with access is gained via removal dorsal fin.

  

The gap between the fuselage and fin was filled using silicon. Masking tape was fitted on both sides and a bead of silicone applied and then smoothed to shape allowing the tape to be removed.                                                                                                                                                                              Painter tape was used to give a fine edge

Rudder Installation
With the fin installed the final task was to fit the rudder. This only required two [2] pivot bolts to be installed and while this had been done before it proved to be a hard task to fit the nuts. 

In the end a washer was tacked with super glue and supported on the spigot on the hole jig allowing the nut to be rotated with enough pressure to engage the bolt allowing a ratached ring end and spanner to complete the task.

Next the rudder cables were pulled through and connected to the rudder horn secured using a D shackle to the horn. 

Rudder horn

Finally the electrical cable for the tail light was connected to the fixed plug inside the fuselage and then feed back into the faring allowing it to be fixed to the underside of the rudder.

Lower fairing fitted

Refitted the rear fairing between the fin, elevator stab and fuselage - this is not a standard factory part.