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Final Assembly -- What Comes First?

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cwilliamrose

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I thought I'd start a new thread on this subject since we have at least three airplanes in final assembly right now. Two of those, a Skybolt and an Eagle, are being assembled a little differently than what I have done in the past. The other, an AS2, seems to be being done as I normally did it.

When I was ready for final assembly the wings were completely assembled with ailerons and the wires attached. The fuselage was also completely assembled with all the panels attached, the tail feathers installed and rigged. I also fully install the engine and prop and leave it as it was for last test run. The wings had already been on the airplane and fully rigged with any rigging washers noted and the wires loosened X-number of turns from their fully tensioned positions.

The reason for doing this is that I am lazy. Very lazy actually. I don't want to have to install ailerons after the wings are on the airplane, it's easier to do that with each wing resting on a workbench or saw horses. I can flip the wing upside down or stand it vertically as the need arises. Installing the wires to the wings is easier when the wings are off the airplane and for the same reasons. Once you get ready to hang the wings installing the two mounting bolts and the wire attach clevis pins at the fuselage gets your wing in place quickly and with minimum aggravation. The ailerons, having been previously rigged, just need to be attached to the torque tube and slave struts.

Assembling the fuselage to completion is much easier without the wings being in the way. I always had the fuselage assembled and basically ready to fly when I hung the wings on for the last time. You also put the wing fabric in less jeopardy if all you're doing is sticking the wings on and installing fairings. No need to be dealing with fuselage panels, canopies, etc when all that stuff could be done before the wings are installed.

There are about 100 ways to do this final assembly step and there are many reasons why someone might chose a different approach (like having a three-piece top wing) but from my experience things go much smoother when the sub-assemblies are as complete as possible. I have always done the build off-airport which is one reason to deal with complete sub-assemblies -- it makes transport easier because there are fewer loose parts to deal with.

The sequence of events for an S-1 or S-2 Pitts/Eagle goes something like;

1) Attach the top wing to the cabanes (2 bolts). No scaffolding required, just have someone steady the upper wing until step 2 is complete.
2) Attach the flying wires to the fuselage (4 clevis pins). The top wing now has a limited range of motion.
3) Attach the I-struts to the top wing (4 bolts total w/washers left slightly loose).
4) Attach the lower wing (4 bolts total).
5) Attach the landing wires to the upper wing fittings (4 clevis pins total).
6) Attach the I-struts to the lower wings (4 bolts total w/washers left slightly loose).
7) Snug up all the wires to their previously tensioned positions. Snug up the I-strut bolts.
8) Install the slave struts (previously rigged).
9) Connect the pitot and static lines plus any wiring, fuel lines, etc. If you have upper wing fuel/smoke lines or wiring it might be easier to deal with that stuff before the lower wings are in place.
10) Check the wing rigging. No need to level the airplane for this step as it was already done, you're just looking at tip incidence, the top wing's flatness, confirming wire tensions and checking that the clevis forks have full wire engagement.
11) Check the aileron rigging and confirm there are no clearance issues at full travel.
12) Install fairings and javelins -- both previously fitted and finished.

Notice no fabricating, fitting, painting, etc. All that is already done. After completing step 12 there's not much holding you back from the first flight.
 
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