Home [ Up ] [ Building The Skelton ] [ Skinning Fuselage ]

   Building the Skeleton

My method of building the skeleton was to build only the bulkheads then assemble everything in the jig.  I've seen other methods where many of the sub components were built independently but I couldn't see how I could do it that way and have everything come out straight.

First I built the template that would be used when setting the curve in the top longerons.  I used the full scale drawings on the plans to lay out the line.  I then used a saber saw and carefully followed the lines to make the cut.  It came out pretty good.  I used the wood from the side of the fuselage shipping container as template. 

 I mounted some plywood to the jig as a temporary workbench

After cutting the template, it was time to start forming the longerons.  The longerons are the basis for the shape of the fuselage so I spent a fair amount of time trying to get this right.  Like the plans say,  I put the longerons together and clamped them down at 29.75 inches back.  There is a change in the plans that called for the bend to be 2 3/16" vs. 2 1/4" on previous plans.  Total spread between the longerons at the end is now 4 3/8"

NOTE:  Mark the longeron stations prior to bending the longerons.  It's tougher to measure after they are bent.

This is the start of the bending process.  A second person makes it easier

Next it was time to use the template and bend the longeron curve that will form the curve for the exterior skin around the seating area.  Again, I tried to use care in bending them accurately.  The key is to bend them a little at a time and check with the template frequently.

It was difficult to bend them by myself but when Beth came out to help hold things in place the job was complete in about 10 minutes.

Use the template and check your status frequently when bending the longerons

The laser level pointing towards one of the uprights

Now it was time to mount the firewall.  I got hold of a laser level and set it up level next to the jig.  I calibrated the height of the level by setting a ruler on one of the horizontal members and checking the ruler.  After a little adjusting I got the level set for 3" (arbitratury height)

 

I then pointed the level at one of the uprights that holds the firewall and marked that point as the 3" line.  I then measured up 21.25" for a total of 24.25" from the crossmember to the top of the firewall. I also pointed the laser level at the 2nd upright and marked that one in the same fashion.

After clamping the firewall in place I used a plum bob dropped from a center mark at the top of the firewall and  adjusted the center of the firewall to a center point marked on the jig.

Plans slide out for viewing...

Now that the plywood is off the jig, I've lost my stand to hold the plans.  I decided to utilize some of the space under the workbench to hold the plans.  I built a frame and nailed some plywood on top then attached it with some drawer sliders.  It works pretty slick and allows me to get the plans out of the way when I'm working.

...then slide in for storage
 

After the firewall is secured it's time to lay down the longerons and secure the bulkheads.  I spent a fair amount of time ensuring the bulkheads were centered in the jig. The aft bulkheads (F-611 & F-612) have to be supported with some wood and it's important to ensure that the height of the bulkheads is correct.  At this point the longerons have to be notched so the F-611 will fit between the longerons.

At this point I was more concerned that all the bulkheads would be flush with the longerons when the bulkheads were in the correct position.  So far everything is working out as the pictures show.

As the picture on the right show, I've got some more trimming to do on the F-612 in order to get the tailwheel mount to fit properly.  I'll probably have to trim off the tabs on each side of the mount but I don't think that'll be a problem when the skin is installed.  What's one or two rivets between friends.

 

Here are some various pictures of the bulkheads installed.  If you're looking for detail it might be hard to see.
  Now the fun starts.  Jigging the F-604 (main spar bulkhead) and the F-605 (rear spar bulkhead) is a critical part of ensuring that the wing fits properly.  The position of the bulkheads in the jig, the height of the bulkheads and the angle of the F-604 (it's not plumb vertically) are all important factors.  At this point, the construction manual starts to get pretty sparce with the details so pay close attention to the plans.  I can't begin to count the number of hours I sit there staring at the plans while the TV in the garage goes un-noticed.

In the photo at left you can see that the F-604 is in place and secured with some wood bracing so it doesn't move.  Even with the bracing, I measured things at least a dozen times. 

 

Outside intersection gussets drilled and clecoed in place

 Once I felt comfortable that everything is in the jig properly,  I started to build the bracing that would hold the firewall and the F-604 together.  My process deviates from the plans slightly.  The plans suggest that you install the rear bulkheads and secure the longerons.  I felt comfortable that the bulkheads and longerons were all set correctly and decided to build from the firewall on back.  The rear bulkheads are clamped in place so I can check to see that everything is going together like it's suppose to.

Inside intersection
  Here is the bottom (top in the jig) longeron ready for drilling.  Here is some pictures of the top longeron (bottom in the jig) also

   

  This longeron runs at an angle from the firewall to the F-604.  You want to make sure when drilling the longeron to the WD-603 that you measure correctly.  It's easy to misdrill and have a hole with an edge distance that's not acceptable.  You'll note that the one on the right is close.
 

The F-602 vertical rib requires quite a bit of cutting, filing and fitting in order to fit properly.  The object is to cut the proper slots so when the skin is installed, the longeron and the F-602 provides a smooth even surface.
  The middle longeron that runs between the firewall and the F-604 is a little tricky to make at one end and requires a support bracket on the other end.  I needed to do some grinding and sanding on the support bracket so that when the skin is applied there is not interference between the bracket and the skin.  The longeron, once again, needs be flush with the firewall.

 

At the opposite end of the longeron discussed above, you need to cut the angle and bend the angle so the proper "joggle" is formed.

Since taking these pictures,  I've dilled a hole at the end of the cut to keep any cracks from propagating.
  The last piece to be made is the F-684 gusset.  This gusset needs to be formed so it attaches to the outside of the longeron but inside the WD-603.  The plans do not show it, but to get a proper fit, I had to cut the bracket to achieve a compound bend.
  The F-695 installed (gray piece)
  The plans were vague to me on how to secure the J stringer to the bulkheads.  Here is the technique I used.  I cut a little tab on one end and slit the stringer on the other end to it would be flush with the skin.
  The stringers need to be cut to fit around the rear bulkheads.
  The picture on the left shows the bulkhead not quite touching the string.  This is a problem because the bottom skin won't lay flat.  I was going to cut the bulkheads when I realized I had a little play where the bulkhead attaches to the longerons.  I was able to move the bulkhead enough get it to touch the sting. (not shown)
   
  I cut the J stringers so they did not protrude through the bulkhead.  Just a cosmetic thing since it is secured the same way.

The picture on the right shows the J stringers fit to the rear bulkhead and the tailwheel weldment attached.
  The F624/F622 intersection gave me fits.  The picture on the left shows my second attempt and it's still buggered up pretty bad.  The picture on the right shows my third attempt that I was satisfied with.  Lots of scrap parts on this exercise.
  The arm rest installed and leveled.  The picture on the right shows the angle that has to be made to secure the arm rest to the bulkhead. 
  More pictures of the firewall weldments and gussett plates.
  The baggage ribs and bell crank support rib.  Also shown on the left the is angle that sits on top of the baggage ribs for the baggage compartment floor to rest on.

The picture on the right is incomplete.  The is an angle piece and a doubler plate that is not installed.
  Nutplates installed on the spar bulkhead.  The extra holes were due to installing the nutplates vertically.  I wasn't sure but if I had left them installed vertically they might have interferred with the spar.  
       
 
 

After lots more careful measuring, I secured the F-605 (rear spar bulkhead) to the longerons.  Notice that the F-605 sits ON TOP of the longerons at this point. It's important that the measurement from the firewall to the F-604 is held to 29 15/16th at the top (bottom in the jig).  The bottom (top in the jig) measurement will be 29.5".  This difference between the top and the bottom will set the wing incidence.
   

SEAT RIBS

  
  I started to install the seat ribs and discovered a small problem that caused some concern.  There is a slight gap (1/16" - 1/8") gap at the bottom (as installed in the jig) of the 604 where the seat rib attaches.  Not all the ribs have this gap however,  I've measured numerous times and the dimensions from the firewall to the F-604 are correct.  This bulkhead is not plumb (and it's not suppose to be)since there is about a 9/16" difference between the top and bottom measurements of the F-604 to the firewall.  I'll do what I what I have to do to make this work but it's a little irritating.

  I drilled the seat ribs to the F604 to see how the rear flanges of the seat ribs lined up.  As you can see from the picture on the left, things didn't line up well at all.  After further investigation, I've come to the realization that I made a mistake when building the F-605 (rear spar bulkhead).  The height from the jig to the top of the F-605 should be 23.82" (a bit more than 23 13/16ths. Why do they call this dimension out in decimals?  Who has a tape measure that reads in decimals?)  Although I checked this dimension when I installed the bulkhead in the jig originally, I obviously didn't check it close enough since the current measurement from the jig to the top of the F-605 is 24 1/16".  That's a difference of about 1/4".  Guess what the distance is that I'm off between the top of the seat rib and the flange of the F-605 (at left)?  Yup,  you guessed it 1/4"!!  I then measured the side of the F-605 and compared it to the plans.  It would seem that I screwed up and built the F-605 1/4" to tall.   Plan #26 calls out a dimension of 22 13/16 from the top of the bulkhead to the bottom left side of the F-605a.  Guess what mine measures..........Yup, 23 1/16".

So what does that mean?  I have to order 2 F-605d channels and rebuild the sides of the bulkhead.  Not a big expense in $$ but it'll definitely cost me some time.
 

I took an idea from Mark Phillips and used this method to cut and re-attach the rib (F-619's) for easier installation of the control rods.  Although this method is a little heavier than just using a piece of aluminum sheet I like it a little better.  Besides, I couldn't find a piece of scrap sheet laying around.