THE FUSELAGE LONGERONS

 

 

I decided to include the F-786B and F-786C skin stiffeners in this section.  The reason is that these “J” section stiffeners run from the F-706 bulkhead all the way to the rear of the aircraft which qualify them to be longerons.  Anyway the first thing to do to these parts is to cut them to length.  Per drawing 18, the longeron drawing, the two F-786B “longerons” get trimmed to 88 7/16” and the two F-786C “longerons get trimmed to94 5/16”.  After the parts are trimmed to length, the ends get trimmed to fit under the forward and aft bulkheads of the rear fuselage.  Photo at left below shows a typical end trim per the drawing.  I marked the part and then I drilled a 3/16” hole where the two lines meet.  I then cut the material on the line with a Dremmel tool.

 

F-786 typical end trim Using a Dremmel to cut away material

 

The photo at left below shows the left F-786 longerons after they were drilled up.  There is nothing special here.  These parts were straight forward.  A centerline the length of each longeron is mandatory if you want to maintain edge distance from both the edge of the part and the radius of the angle.  The right photo below shows the right longerons in place ready for drilling.

 

F-786B-L and F-786C-L cleco’d in place F-786B-R and F-786C-R ready for drilling

 

The photo below left shows the left longerons from the outside.  The installation of these longerons is covered in the “Rear Fuselage.”  The photo below right shows drawing #17 hanging from the end of the storage rack.  This drawing has a full size bending template for the upper longerons, F-718-L and F-718-R.  There are some fairly detailed instructions in the plans as well as some photos to show how to bend the angle.

 

Left F-786 longerons, external view Drawing #17

 

The photo below left shows the L angle that is destined to become one of the upper longerons.  This step in the assembly is a little bit intimidating because if there is a major mistake made, I will have to order another angle.  Aurora, Oregon is a long way from Ft. Lauderdale, Florida and a mistake will cause a delay and an expensive shipping charge.  I was extra careful starting with trimming the L angle to length.  This is one time I studied the plans for a while.  I also studied the drawing (below right) and when I actually started the bends, I took my time.  The drawing is #18.  It shows the typical complete longeron, but not full size.  The scale is 1/8, but it is a very useful drawing.

 

L angle that will become one of the  longerons Drawing #18

 

The first order of business is to trim the L angle to length.  I clamped the tape measure to one of the two angles so that it did not slip off (left photo below).  The length of each L angle is 173 3/16”.  The photo below right shows the mark I placed on one of the longerons.  After I cut this L angle to length, I double checked it.  I then used it as a measuring tool to mark the second L angle. 

 

Tape measure clamped to a “longeron” 173 7/16” exactly

There are three more marks that need to be put on the longerons.  They are the spots where the bends begin and end.  These marks must be on the longeron before the bending starts.  That is clearly spelled out on drawing #18.  Photo at right shows one of the marks.  This happens to be where the bend begins.

  Mark shows the beginning of the bend

 

After the longerons were cut to the proper length, I had to set up a vice for the bending the longerons.  Since I did not possess a vice strong enough (I considered using the plastic vise I have but I nixed that idea early) I had to make a trip to, you guessed it, Lowe’s.  I purchased a good sized vice and mounted it to the Black and Decker work bench (left photo below).  I set up one of the adjustable roller stands to support the longeron during the forming process.  The picture at right below shows the bending process is ready to begin.   Notice that I started the longerons on the 11th.  The picture below right was taken on the 13th.  If I had realized that it was the 13th before I started I would have waited another day.  I am very superstitious.  I want to go back to the vice mounted to the Black and Decker workbench for a moment.  The work bench moved around as I was bending the longerons quite a bit.  Hindsight being 20/20, I would mount the vice to something heavier next time.  I actually "knew" that at the time but I wanted a good excuse to use the Workmate as a mount for the vise.  I am sure that I will eventually mount the vise to the Home Depot work bench.

 

Vice mounted to B & D workbench L angle ready to become a longeron

 

In the picture at left below you can see that the bend on the right upper longeron is taking shape.  This is a simple process, this longeron bending.  You take a fairly heavy dead-blow hammer (Lowe’s), hold pressure on the longeron to the side you are bending and smack the angle with the hammer as near to the vise as you can.  As you do this all you have to do is to keep this thing from twisting as it is bent.  A lot of double checking and a great deal of patience is required for the successful completion of this step.  The right picture above was taken at 8:15 in the morning.  The right picture below was taken at 1:20.  It shows one longeron completed.  Just so you know, I did not stop for lunch.  This step can not be hurried.  The second longeron goes much quicker, but still a lot of care has to be taken to make sure these parts have the proper shape.  I used drawing #17 for a template bending the first longeron.  I removed the drawing from the storage rack and placed it on the floor for this.  The plans are a little more elaborate than that but this worked well.  I used the right longeron as a template for the left longeron.

 

RH upper longeron taking shape RH upper longeron completed

 

To the left is a photo taken of both longerons after the bends were completed.  I was satisfied that the longerons were a mirror image of each other, as close as possible for me anyway.  This method of forming is extremely crude but with patience it does work.  Any other way of forming these parts would require some sort of expansive tooling, which would be beyond my budget.

Both longerons after bending  

The next task was to drill the longerons to fit the rear fuselage.  The left photo below shows the longerons in place ready for drilling.  The tape at the front of each longeron was put there so that I did not poke myself in the eye as I was working.  The photo at the right shows the left longeron drilled and cleco’d in place.  It also shows that I had levels on the rear fuselage assembly the entire time I was drilling the longerons.  It is hard to see but I had another level on the F-714 aft deck which was clamped into place at this time. 

 

Longerons in place Levels in place for the drilling process

The picture at right shows the level on the F-714 aft deck, which is clamped into place here.  The plans have you use plum bobs on the bulkheads to keep the rear fuselage in alignment but even though I purchased 2 of them (Lowe’s of course) I decided to use levels instead.  If the front is level and the rear is level then the unit is more than likely not twisted.

  Aft level on the F-714

 

After the longerons were drilled to the skins I checked that the assembly was still level (left photo below).  Actually, I had the levels in place the entire time and I checked quite frequently.  This is a major step in the assembly process and I didn’t want to make any mistakes.  I didn’t mention this before but I aligned the top of the longerons (horizontal legs) exactly with the top of the skins.  The next step was to locate the F-714 to the longerons.   The first step to locating the F-714 was to notch the longerons.  This notch was to allow the horizontal stabilizer aft supports to protrude through the longerons (lower right).  The way that I marked the longerons for these slots was to place the F-714 in place without the supports attached.  I then scribed lines on each longeron where these slots are located.  The picture was actually taken after the process was complete.  I forgot to take photos while step this was in progress.  Notice the centerline on the longeron.

 

Longerons drilled to the skins Notch for H.S. aft supports

The picture at lower left shows the F-714 attached with 1/8” clecos.  It also shows that I have attached the F-709 bulkhead to it.  I did this several weeks prior because I could not see any reason for waiting.  The photo below right shows the F-714 removed and the longerons are now completely drilled to the rear fuselage assembly.  These parts need to be primed and the rear fuselage needs to be assembled before I go any further with the upper longerons. 

 

F-714 located to the longerons Longeron drilling complete

The first step towards assembling the rear fuselage is to attach the skin stiffeners (longerons).  I decided to back rivet as much of the rear fuselage as I could.  The problem was that I could not hold the parts together while I riveted them together.  I gave this some serious thought and I came up with a simple solution.  I cut 4 8” wide strips of 5/8” plywood, 48” long.  I then set my table saw blade to a height of approximately 5’16”.  With the blade set to this depth, I could cut a groove in each plywood strip.  I then took one of the strips and routed out a section for the back riveting bucking bar to fit in.  Picture at lower left shows the 4 strips of plywood laying on two 8 foot 2X4’s which are laying on 2 sawhorses.  The grooves allowed me to put clecos in the parts and still have the sheet metal contact the wood and thus contact the bucking bar (picture at right below). 

Grooved plywood back-rivet bar holder Cleco protruding into groove

 

I back-riveted the skin stiffeners (longerons) on.  The left photo below shows the lower right aft side skin stiffener after it was riveted in to place.  The picture at right below shows both of the left stiffeners are now riveted in place. 

 

F-773R and lower skin stiffener F-773L and both skin stiffeners

 

After I riveted the side-skins to the bottom skin and added the bulkheads (see “Rear Fuselage”) I turned the fuselage upside down on two sawhorses.  I needed one more sawhorse and it had to be adjustable so I improvised.  I clamped another of the plywood strips across two adjustable rollers (that are normally used in conjunction with a table saw or chop saw).  See photo lower left below.  I clamped the right forward side skin in place and after I cleco’d it to the aft side skin, I leveled the plywood/roller assembly to the rear sawhorses with help from a long L angle.  See photo at right below.  I used the angle to line up the sawhorses visually.  Since the garage is sloped towards the door and the middle sawhorse is not adjustable, a fore and aft level was useless.  With the longeron resting on the plywood/roller assembly, I began drilling the holes in the longeron to match the holes in the skin, being careful to keep the skin aligned with the upper edge of the longeron.  I repeated this process for the left forward side skin to longeron assembly.  (Remember that fuselage is upside down.  Right is left and left is right.)

 

Right forward side skin clamped to longeron L angle used for fore and aft leveling

 

The photo at left shows the left forward longeron in the preparation stage of drilling to match the left forward side skin.  The skin is cleco’d to the rear fuselage and the longeron is clamped to it.  This assembly was very flimsy at this point and thus vulnerable to twisting.  I constantly checked the lateral leveling at all three supporting points, two sawhorses and the adjustable  rollers that support the front.  

 I  also  occasionally checked the longitudinal alignment.  The longitudinal check was not as critical as lateral leveling as far as twist was concerned because I kept the upper edge of the skin aligned with the upper edge of the longeron as I drilled.

 

Next I decided to drill the F-721B-L and the F-721B-R to fit the longerons.  These two parts hold the main bend of the longerons in the proper shape.  They help form the cabin area of the fuselage.  I removed both longerons from the rear fuselage assembly and carefully drilled one F-721B to fit a longeron per the plans and the drawings.  Then I aligned the two longerons to match at the rear and I clamped the two longerons together so that the vertical legs of each angle were exactly in line.  Actually I aligned the longerons at the rear by simply clecoing them together through the F-714 attach holes.  You can see the 1/8” clecos in the photo at right below.  After carefully checking the two F-721B canopy decks to make sure that the rivet pattern was exactly the same, I drilled the left longeron from the right.  The photo below left shows the two longerons cleco’d together as the F-721B holes were being transferred from the right longeron to the left. 

 

Drilling the left longeron from the right Keeping the rear of each longeron aligned

 

The next step was to counter-sink all of the rivet holes where the longeron attached to the rear fuselage skins.  I clamped both longerons together in a vice and counter sunk the holes on both at once which was a time-saver.  Then I etched, alodined and primed the longerons.  The photo at right below shows the longerons strapped to the top of my car for transport to the hangar for priming.

 

Countersinking holes Transporting the longerons

 

The photo below left shows the longerons after I primed them.  I also primed the forward fuselage side skins at the same time along with some smaller parts.  The photo at below shows the longerons and the side skins after they were transported back to the garage.  I really miss my paint booth but with my added duties taking on two facilities in separate cities,  I don’t have time to build another one.

 

Longerons and forward side skins Longerons and skins back at the garage

 

8 days after the two pictures shown above were taken, I was in Kitty Hawk, North Carolina for three days during the Centennial of flight celebration.  What an event this was.  On the last day several people gave speeches in the rain, including the President of the U.S. who gave a non-political speech about the wonders of aviation.  After the speech George had Air Force One over-fly the monument.  What a tribute that was.  A friend of mine got a picture of Air Force One and the Monument in the same shot.  What am I rambling on for, back to the fuselage.  On Christmas Eve day I did get back to the longerons.  I re-installed them and added the center fuselage assembly.  Again I was careful to keep everything level.  See the Center Fuselage file for a description of the next step of the fuselage construction. 

 

Addition of center fuselage Another view of the center fuselage

 

After the center fuselage was installed, the next step was to trim and drill the F-786A-L and F-786A-R skin stiffeners.  I trimmed the stiffeners to size, made a centerline on each one and then drilled one hole for a cleco at bulkhead F-707.  I cleco’d the 2 top skins, F-7112 and F-775, into place before any further drilling.  The forward of the two aft fuselage top skins keeps the F-706 and F-707 bulkheads properly spaced.  The aft skin keeps the F-707 and F-708 properly spaced.  I drilled the holes in the stiffeners through the skins.  I finished drilling the holes in through the rear top skin, F-775 to the stiffeners two on the date the photos were taken.  I had to stop at this point and did not get back to this step until March 29, 2004.  (See “Rear Fuselage Top Skins.”)

 

F-786A-R in place Both F-786A stiffeners in place

 

It is the end of March, 2004, the 29th to be exact.  A look in the fuselage top skin section will show a picture of me drilling the rest of  the holes in the skin stiffeners.  As I was preparing to prime these parts I noticed two double drilled holes in the right stiffener.  (Ignore the fact that the stiffener is not identified correctly in the picture.  This really is the F-786A-R.)  I made a repair angle from one of the scraps of stiffener material I had left from trimming the stiffeners to the proper length.  The repair is shown at lower right.

 

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F-786A-R with one of the double drilled holes F-786A-R and the repair angle

 

The photos immediately below show the shoulder harness brackets in place.  After these parts were located, I etched, alodined and primed 57 individual parts.  See “Rear Fuselage” for photos concerning this priming operation.

 

Shoulder harness bracket Both shoulder harness brackets drilled

 

The picture at left below shows F-786A skin stiffeners or should I say upper center longerons, after they were riveted in place on the rear top skin.  The photo below right shows these two parts cleco’d to the forward top skin from the outside.  See the top skin section for details of the next step in riveting these two “longerons” in place.

 

F-786A –L and F-786A-R attached to rear skin View of the two F-786A cleco’d in place

The fuselage longeron fabrication, modification, preparation, and assembly is now completed.  On to the “Center Fuselage” assembly.