Mulliken's Sequoia Falco F.8L

Rear wing spar and trailing edge ribs

Finally time to glue the rear wing spar in place.  You would think once was enough, but I had to learn all over again that when gluing a tapered joint, it may clamp nicely dry, but when wet with glue, it is prone to slide all over the place.  Thus my first attempt on the right side ending in an aborted takeoff.  I had to pull the spar and wipe the glue off, and since this stuff starts to set right away, it was a bit of a struggle.  The worst part was the joint on the fuselage frame.  It was the first to be mated, and it is a big joint.  It was almost too strong to separate without breaking something, after only 10 minutes of curing.  But, I got it all cleaned up, and sanded everything down once again.  Next time, I used 1/8" wood alignment pins on all the joints.  I also stapled plywood to the ribs to stabilize them, making it easier to push in the pins.  Again on the right side, one pin broke off when I was inserting it.  I found out the pins go in better when they are sharpened on one end.  Here is a view of the left wing showing the ply reinforcing, and the glued in rear spar.

Now that the rear spar is in place, the trailing edge ribs can be installed.  Most of these are in the ailerons and flaps, so there are only three on each side that are actually glued to the spar, two on the inboard end, and one outboard.  The ailerons and flaps are still all one piece, including the trailing edge strip.  I've attached the aileron/spar assembly to the wing spar with the hinges in order to get the trailing edge strip in place for gluing these ribs in place.  This picture shows the outboard trailing edge rib clamped in place. It's great to see some skin in the wing area!

Getting through the logjam

Since I last posted, I have spent a lot of time with the hinges on the flap control tube.  Of course there have been many interruptions due to harvest and other life events.  The wedges that fit these to the #2 rib are critical, because if they are off the hinges will bind.  I had to do them over once.  Finally, I had everything working and in place.  Still, I spent last week measuring and remeasuring to be sure the assembly was in alignment.  A long pause in work is not good.  It takes a while to get back in the swing. Finally, on Saturday (three days ago), during a snowstorm, I decided it was OK.  That day I glued in the #2 ribs.  I think the snowstorm helped me focus, since the stuff outside that needs doing is not going to get done for a while.

The photo shows the rear spar and the linkage arm that operates the flap hinge.  The rib is still not glued to the rear spar, but it is glued to the main spar, so this is commitment.  Because of the outboard ribs, it is no longer possible to remove the black tube,  which lowers both flaps as it turns on its hinges.

Yesterday I glued in the #3 ribs, and today the # 2 1/2.  The 2 1/2 is covered with plywood on both faces, and forms the outboard face of the gear well.  This completes the intermediate ribs.  Now the torque tube is really hemmed in.

The next step is to glue the rear spar in place.  In an earlier post, I said I would be sanding the rear ends of the ribs to fit this spar, which runs at an 8 degree angle to the main spar.  I've made every effort to sand this angle as I placed the ribs, so there will be just some final fitting before gluing in the spar.  After the spar, there are just 3 trailing ribs on each side, because the ailerons and flaps already contain most of the trailing edge ribs.  Light is at the end of the rib tunnel!

Intermediate ribs #1 and #14

These ribs are now attached to the aft face of the main wing spar.  Again, alignment is critical, since the aft ends of these ribs will be fixed to the rear wing spar, and that in turn will set the alignment of all the other intermediate ribs.  Here's a shot inside the #1 ribs from the inside of the wheel well.  The horizontal piece of plywood with the curved edge is the #5 fuselage frame, which is fixed to the inside of this rib.  To hold the rib against this frame, I used two threaded rods running through the jig centerboard, thus clamping both left and right ribs to the frame.  A lot of things had to line up.  I wasn't satisfied with the first attempt, so had to pull everything apart, wipe & sand off the glue, and try again.  It went better the second time.

The #14 ribs were easier to clamp in place.  I just clamped the aft spar against the main spar with the rib in between.  None of these ribs are attached to the rear spar yet.  After these joints cure, I will remove the rear spar, check all the rib chord lines against the lower jig line, then replace the rear spar, and sand the aft end of the ribs to fit the angle of that spar.  Then the rest of the ribs will be ready to attach to the main spar.

Wing intermediate ribs and flap control torque tube

We've had a lot of rain, but fortunately minimal flooding.  This means some time available in the shop.  These ribs are all clamped in place, and since I took this picture a day ago, the ribs have been sanded so the chord lines align with the lower jig string.  For some reason, the ribs as they were manufactured were such that they are canted upward when clamped in place.  They all had to be trimmed slightly with the sanding wheel.  It's nice to see these all in place. It no longer requires much imagination to see a wing shape here.

The flaps are controlled by a DC gearmotor which is attached to a torque tube that runs between the flaps.  There are cutouts in the ribs to allow the tube to swing through.  The torque tube pivots on hinges bolted into the rib at station #2.  The tube is at a 5 degree angle to the ribs because of the wing dihedral.  In this photo, one can see the flap end of the tube, the hinges, and the 5 degree wedges of spruce that are used to mount the hinges so that they do not bind.

The next task is to trial fit the aft wing spar.

Leading edge ribs installed

The ribs forward of the main spar are all in place, as well as the leading edge strips.  The alignment and dimensions all check out, so before long, I'll be putting in the trailing edge ribs, as planting time on the farm allows.

My current fun task is to put in the corner blocking on the center ribs.  These help to distribute loads to the skin.  At the same time, I'm framing up the access doors forward of the main spar.  There are four of these.  The photo shows the door for access to the landing gear hardware and a grease zerk.  There are also two doors for the aileron bellcranks.

Leading edge ribs

The ribs on the left side are now glued to the main spar.  Both ends of the ribs had to be sanded to an angle: 3 degrees on the leading end, and 1 degree on the spar end.  In addition, the chord line had to be maintained, while keeping the proper measurement between the leading edge strip and spar at each station.  After taking off the clamps, I was disappointed to see a 2 mm dip in the leading edge line near the middle.  Then it occurred to me the main spar might have some sag, since it is supported only on the ends.  I stretched a string, and found 2 mm sag, which I corrected with a 2 x 4 prop.  A few ribs are a mm or less too short, so I glued in some shims on the leading edge.  After sanding this down, the leading edge strip will be ready to glue in place.

 

The tips of the ribs are supported with a temporary board on the back side of the jig (lower surface of the wing), and with blocks of pine glued to the board so the ribs can't be pushed to one side or the other.  Without this support, the ribs could be quite easily broken until the leading edge strip is glued in.

Alignments

Well, the wing spar is back in the jig, and has been for about a month.  A friend from Wisconsin who is really good with a pencil and a saw came down for a week and we had a good time and got a lot done.  Since then, I've installed the intermediate ribs between the main and front spars, and am fitting the leading edge ribs on the main spar.

  
The yellow hardware is the landing gear.  The jig supports alignment strings at the leading and trailing edges of the wing.  Everything at this point is about alignment.  Of course, by now the position of the front spar relative to the main spar is completely determined by the landing gear.  If those are off by a bit, the gear will bind in its bearings, and we can't have that.  Also, the spacing between the spar faces needs to be 340 mm with a sub-mm tolerance.  All of that worked out fine.  But in addition to THOSE requirements, the chord line of the # 4 rib should project upwards to the leading edge alignment string.  In the photo below, I have arrows showing the alignment string (it is monofilament line), and the #4 intermediate rib chord line.  The ruler clamped to the rib just instersects the string, so this is good to go.

Sitting in the Falco

This is a bit premature, but we have the main spar and front spar aligned with the landing gear, so it was just too tempting to sit in there and play with a stick.

Here's another view of the gear and spar conjunctions:

Now these are ready to put in the jig.

Drilling guides

I'm drilling some holes in the fuselage frames and spars for the rudder cables, battery cables, and other stuff.  Some of the holes go at an angle, so my drill press is not much help.

For the smaller holes, the portable drill guide works fine.  This has an adjustable base, so it can be set for small angles.

The drill guide has a 3/8" chuck, so for bigger holes, I used an idea in the latest EAA magazine.  To drill a 1/2" hole, I started with a piece of 3/8" pipe, and drilled it out with a 1/2" bit.  Then I welded up a "C" with two bolts and a piece of scrap, and brazed the pipe in place.  Next, I cut out the pipe so it would fit over the spar.  Mark and pilot drill the holes on both sides of the spar.  Insert a 1/2" bit backwards in one end to position the guide at the correct angle (15 degrees for this one), and start drilling through the pilot hole on the other side.  In the picture, it looks like one long drill bit, but it really is two bits.  Kind of reminds me of a magic trick.

Aligning fuselage frame #3

This frame is glued to the front face of the forward wing spar.  Since this spar also carries one end of the landing gear pivot shaft, I've clamped the forward spar to the main spar using the landing gear pivot hardware for alignment.  Next, I leveled the main wing spar, and checked for vertical on the #4 fuselage frame center line, since that frame is now glued to the main spar.  Finally, I attached a plumb bob at the center line on the top of frame #3, and clamped the frame in place with the plumb bob over the front spar centerline after making sure that centerline matches the spar centerlines.

After double-checking all of this, I'll drill holes for dowel alignment pins so all of this can be unclamped and reclamped for gluing.  Also, there is a cavity between the frame and spar that needs to be varnished.

The gray metal gadget is a drill guide to assist in getting the dowel alignment pins square.

The view here is from aft.  You might wonder why the forward spar is clamped behind the main spar.  It's just that this turns out to be a convenient arrangement for aligning the landing gear hardware, and everything else is relative to the gear.  There's no chance I'll forget to put the front spar in front eventually.

The #3 frame carries the base of the windshield.