Sunday, February 7, 2016

Starting the fuselage - tailcone

As with the other components, the fuselage build begins with a lot of cleaning, deburring, test-fitting and priming of parts.  Something that became obvious right away is that there are a lot more pieces in the fuselage, and many of them look very similar.  I got in the habit of taking a photo of the the individual components in each labeled bag provided by the factory, so that I would be able to identify the pieces after the labels were removed - this ended up being very helpful when the actual riveting began.
Test fit of the tailcone assembly prior to priming

Test fit of the step brackets.  The test fit identified a few edges that needed to be trimmed
back to allow for proper fit, as well as some holes that needed match-drilling.
All the various channels for the front seat backrest (Bag 38).
Photo helped identify the channels during actual assembly.

Primed fuselage components - a lot of different channels

The fuselage build begins with the rear cone.The Sling 4 fuselage instructions are not quite as mature as those for the wing and empennage, so ensure you look at the more mature Sling 2 fuselage instructions as well - not everything is the same between the Sling 2 and 4, but reviewing the Sling 2 instructions will provide a little extra guidance.  First component riveted is the tailcone assembly.  I riveted the fuselage ribs at the same time using the provided jig.  The longerons were then clecoed to the tailcone bottom skin. Riveting the longerons was one of the areas that the current instructions are wrong.  The instructions for the Sling 4 indicate that all the longerons are to be riveted to the bottom skin, whereas the Sling 2 instructions correctly indicate that the outer longeron should not be riveted at this time since the lower side skin overlaps it for final riveting.  I had to drill out a number of rivets due to this mistake in the instructions.  The instructions also call out for the tie-down ring to be installed on longeron 8 before attaching the rear fuselage assembly - however, I was unable to do it in this order, so I drilled out the longeron 8 rivets and attached the tie-down ring after attaching the rear assembly to longeron 8.

Installing nutplates on tailcone rib 9.
Tailcone ribs 7, 8 and 9 riveted.
Riveting fuselage ribs using the supplied jig.

Riveted fuselage ribs all lined up.

Longerons clecoed to the tailcone bottom skin

Longerons riveted to the tailcone bottom skin.  Note that the outer logeron rivets needed
 to be drilled out as those holes are also used for attaching the side skins

Instructions call for the tie-down to be riveted to longeron 8 before attaching the tailcone
assembly.   However, the assembly does not fit over the riveted longeron 8 - easy
 to fix by drilling out the longeron 8 rivets, attaching longeron 8 to the tailcone
assembly, and then re-riveting the tie-down.
Having sorted out the tailcone floor instructions, the tertiary structure of the tailcone was then built.  Ribs were clecoed to the tailcone, using zip-tied upper longerons to keep the structure stable.   The front and rear lower side skins were then clecoed in position after attaching the rear assembly doubler (not described in instructions, but obvious where it goes - see also the Sling 2 instructions).  The step brackets were then installed.  Holes for the step brackets were not pre-drilled in my longerons, so it took some careful drilling to line up longeron holes to the step brackets.  The side skins were then riveted on.  The support channels for the luggage floor were also riveted at this stage.  The tailcone was then set aside while I await replacement components for the updated parachute box location.

Clecoing on the tailcone ribs

Clecoing on the lower side skins of the tailcone.

Installing the right step bracket.

Front of the tailcone looking towards the rear.

Riveting the tailcone skins.

The luggage floor assembly support channels (below the skin in the photo) were clecoed
and riveted while the assembly was in position in the tailcone to help ensure proper
alignment during final installation.  Note that the luggage floor was not riveted
to the tailcone during this step (that will happen later).


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