Center Section Spar

Section 8.1    Installing Main Spar

June 13, 2002     -  Chapter 8.1.1 - "Spar Positioning"                                           

This section was done during our visit to the factory's Head Start program.  First you cut a 3" wide by 6" long hole for the main spar in the fuselage along the engine/firewall bulkhead to where it lays on top of the of the gear bulkhead.  It's critical that the spar be set square and level, with the same sweep on both sides.  To accomplish this we leveled the plane and then placed the spar in the cutout (seen in picture below) and leveled it.  Then we measured the distance from the spar hardpoints to the nose on both sides to make that they were equal, and the plumb and level on the outside hardpoints.  The spar was shimmed as necessary to obtain good alignment, and then match marks were made for shipping.

Center Section Spar Fitting

27 July, 2002     - Chapter 8.1.2 - "Spar Installation"                                             

We completed this section in one long evening of work.  We used the marks made with Frank during Head Start (and a leveled aircraft) as a starting point, re-verified the plumb-ness of the the outboard hardpoints, the level of the spar, and the sweep to the "nose bolt hole".  Actually, this part was difficult due to the double edge sword of getting the fast build fuselage as we don't have nose bolt hole, and locating the center of the nose is consequently very difficult.  But, we satisfied ourselves that the positioning was correct and after scuffing the firewall and the spar, we smeared structural over the spar and the gear box tops.  Then we carefully slid the spar back in, realigned it with our marks, checked level with both our "Smart Tool" and and a water level, check the plumb one more time as well as the sweep (serious business, this), and it was permanently set.

Spar Cut Out

Preparing the spar for bonding

Section 8.2    Lay-Ups

31 July, 2002     -  Chapter 8.2.1 - "Lay-Ups"                                                              

This is a roddy good section, with plenty of good acting as they say in Python.  Actually, this is better suited to Princeton basketball, because there are tons of layups to be done.  The first is to bid the top and bottom of the spar to the firewall, and the little chamfered openings on the back of the firewall.  Of course the usual rules apply, scuff up target areas first, the glass bubbles to create a radius, apply the cloth, then peel ply.  Since there are 2-47" bid on top, 2-41" bid on bottom, and 2-9" bid on both sides of the back (and, oh did I mention, BID is cut at a 45 degree angle on the cloth following the thread line...) this is a tedious and time sucking task.  Easy, yet laborious, just the sort of thing I'm really good at. {wink}  The best thing I can say about this evening's work is "it's done".

Spar Bond - Rear Firewall

Spar Bonding - Fore Firewall

After these initial layups, the work moves on in earnest.  Next we made two foam pieces for each side of the spar out of 3/8" foam, one to go on top of the gear bulkhead (6"x4 1/2") and one to mate the gear bulkhead to the top of the spar (6"x10 1/2").  Once they were approximately sized, we cut the top of the gear bulkhead to the same height as the bottom of the spar so the foam laid in there nicely, and then beveled the edges of the diagonal sheet to rest well in it's position.  Then I covered the foam with micro (a step not mentioned in the manual, but always a good idea) and bonded them into place with micro (the manual says to duct tape them into place, but the tape wouldn't stick worth a d@mn for me, so I went this route instead).  Then all of the mating surfaces were well scuffed and they layups began (on plastic first, since there were many to do, and most of them were triaxial cloth).  Here's what they look like.

Spar Foam Reinforcements

Layups on Plastic

First we laid 4 plies of 6"x8" BID inside of the support from the top of the lower spar to the bottom of the upper spar.

Spar Foam Inner Layups

Then we laid the sets of TRIAX on the top of the support.  First was 2 layers of 7"x8" from the firewall to the top of the spar, then 2 layers of 7"x25" overlapping the first up to about 6" above the spar and running just onto the gear bulkhead by about 2", the 2 layers of 7"x33" overlapping the second and running all the way down the gear bulhead and over the main gear bolt holes.  Then 1 ply of TRIAX (4"x12") was run down from the bolt hole to on top of the floor duct, and another 1 ply (also 4"x12") of Triax was run from the bolt hole diagonally lapping onto the fuselage side.

Spar Foam Outer Layups

Finally, a 2" wide piece of BID was laid up onto each of the fuselage-to-spar inside and out over a radius of micro.

~  End of Chapter ~ End of Section   ~