Flaperon Build Manual Update

Everyone is interested in reducing build time and building a better product.  I’ve been able to do that with flaperons, used on our Belite ultralight aircraft.  The time required to build a flaperon structure is now down to less than four hours per flaperon!

This assumes an easy to build wooden jig, which will hold all the ribs in place.

This is an update over our earlier manual, published just a few weeks ago.

These techniques may be applicable to building control surfaces (elevator, rudder, stabilizer, etc.) on your favorite ultralight aircraft.

At Belite Aircraft, here’s how we do it.

Table of Contents
Section A.  Specifications. 2
Section B.  Materials. 3
Section C. Preparation. 5
Section D: Build Jig; Test Fit Ribs and Bushing/Droppers. 6
Section E: Glue the Main Spar. 8
Section F:  Glue the Leading Edge, False Ribs. 9
Section G: Balsa Parts. 11
Section H: Trailing Edge. 13
Section I: Trim aluminum placement. 17
Section J:  Trim and sand glue. 17
Section K:  Apply sealant to wood. 18
Section L: Covering. 19
Section M:  Check Fit to wing assembly; install control horns. 19
Figure 1.  Completed Flaperon on an ultralight plane.
Section A.  Specifications
·         CHORD:  12” (0.305 meter)
·         LENGTH:  105 ¼” ( 2.673 meter) (span of single flaperon, excluding mounting horn extension)
·         AREA (per flaperon):  8.77 square feet (0.815 square meters)
·         WEIGHT:  dependent on amount of paint and glue.  About 4.5 pounds.
·         RED LINE Vne:  80mph.  Do not use these flaperons on aircraft exceeding 80mph.
·         CAUTION:  62mph is top of green arc.  Keep flaperons centered (0 degrees relative to chord of main wing) and make only slight movements at 62mph and higher.
CERTIFICATION STATUS:  NONE.  THESE FLAPERONS ARE UNCERTIFIED.  Use only on experimental or ultralight aircraft, at your own risk. 

Section B.  Materials

·         MAIN SPAR:  0.875” x 0.035” 6061-T6 round aluminum, one piece for each flaperon.
·         LEADING EDGE:  0.500” x 0.035” 6061-T6 round aluminum, one piece for each flaperon.
·         TRAILING EDGE: 1.125” preformed 3003 aluminum (Aircraft Spruce PN: 03-48900), one piece for each flaperon.
·         MAIN RIBS:  Precut 1/8” Birch Plywood, qty 28 (14 per flaperon) (must be trimmed by user)
·         FALSE RIBS:  Precut 1/8” Birch Plywood, qty 56 (28 per flaperon) (must be trimmed by user)
·         NYLON BUSHINGS:  fits over main spar and in flaperon droppers.  Qty 6. (must be fit by user)
·         MACHINED ALUMINUM DROPPERS:  fits to nylon bushings, allows attachment to your wings.  Qty 6.  Machined from aluminum.  Parts are “heavy duty”, having replaced an earlier design which wasn’t as beefy. (must be deburred by user)
·         CONTROL HORNS:  One for the left and one for the right dropper.  Made from welded steel.
·         LONG RIVETS:  Qty 8, use four to connect each control horn.
·         SHORT RIVETS:  Qty 16, use four to connect each trim plate
·         ALUMINUM TRIM PLATES:  0.016” thickness, Qty 4, fit around flaperon droppers
·         BALSA WOOD:  used to create rounded end on far end of each flaperon. You should have two pieces 14” of 1.25 x 3/8” balsa (approximate size).  Makes two end caps, one for each flaperon.
·         NUTS, BOLTS, and WASHERS (used to attach flaperon to wing).  Qty 12 of each.
·         BLUEPRINTS in electronic form – you print.  We can email these to you.
·         MANUAL (this document) in electronic form – you print.  We can email this to you.
·         GORILLA GLUE
·         WOOD SEALANT such as exterior polyurethane or spar urethane
·         FABRIC COVERING and associated materials (fabric glue, primer, paint…)
·         CLEANING SUPPLIES (sandpaper, scotchbrite, acetone…)
·         TOOLS (normal stuff like clamps, pliers, aviation metal snips, riveters…)
You will need a work area, completely flat, allowing you to build a flaperon.  A minimum size of 18” by 10 feet is recommended.
In the event that you have any shortages, you MUST notify us within 14 days of receipt of this kit.

Section C. Preparation

a.       Ensure that your work area is absolutely flat and big enough (10’ x 18”).
b.      Read these instructions through at least three times before doing anything.  Ensure you understand everything before doing anything!
c.       Remember, you are building a LEFT and a RIGHT flaperon.  Please don’t build two left flaperons (or two right flaperons).
d.      Remove plastic film from INSIDE of trailing edge material.  Leave film on outside.
e.      Clean up all aluminum using scotchbrite and acetone.
f.        Trim and sand all plywood parts to finished shape.  (Remove the excess tabs).  Check that they fit over the spar tube, and that the leading edge tube also fits in the front notch of the rib.  Sand as necessary.  We like using a round drum sander, such as are commonly used with a Dremel or electric drill.
g.       Ensure that nylon bushings fit over spar.  Ensure that they also fit inside machined droppers.  Sand inside and outside of nylon bushing as necessary.  Final fit should be ‘butter smooth’.  Absolutely no friction allowed.  Flaperon dropper should flop and swing under its own weight.  IF YOUR NYLON BUSHINGS ARE “OVERSIZE”, YOU MAY NEED TO MOUNT THE NYLON BUSHINGS IN A DRILL CHUCK AND TURN THEM DOWN TO THE CORRECT DIAMETER USING A MILD RASP OR SANDPAPER.
h.      BEFORE YOU GLUE ANYTHING, make sure the surface is roughed up with sandpaper and absolutely, completely clean with acetone.  This is absolutely necessary to get a good glue bond to aluminum.
i.         A note on Gorilla glue:  Our design has all of our ribs ‘locked’ in place by design, and the glue further immobilizes them.  This is true in our flaperons, and also in our wing design.  We use Gorilla glue in some locations because it adheres to materials extremely well, and because it is not used as a structurally critical bonding material.  Also, Gorilla glue expands enormously, so use sparingly.  Read the instructions on the glue container.  We like to have water available in a misting bottle, so that it can be sprayed lightly on components which are to be glued.


Section D: Build Jig; Test Fit Ribs and Bushing/Droppers

a.       DON’T GLUE ANYTHING until specifically instructed.
b.      Build a jig from wood which matches the blueprint.  It’s just a flat board with a block glued wherever a main flaperon rib goes, as shown here:
The wood jig which speeds up flaperon assembly time
c.       Slide all of the ribs, false ribs, bushings (with droppers) onto the spar.  Sand out the holes in the ribs as required.  Remember, each rib has a top and a bottom, because the flaperon airfoil is not symmetrical.
d.      Using the blueprints and your jig as a dimensional placement guide, determine where to place all parts.
Sliding the ribs over the flaperon main spar on the wood placement jig
Lightly clamping the leading edge in place (note clamp in top left corner)

Section E: Glue the Main Spar

a.                   MAKE SURE you have all parts slid over the spar and properly oriented.  If you forget them now (or have them upside down) it is very hard to fix later.
Applying glue to the main flaperon spar
b.                  GLUE:  the main spar to the main ribs.  We use a glue syringe and minimal amounts of Gorilla brand glue.  MAKE SURE that everything is absolutely square.  Spray the assembly with water and then roll the spar around  so that the glue distributes around the spar.  (The clamps holding the main spar to the leading edge  must be very loose to allow this rotation).
Note that no glue is applied to the main spar short ribs around the flaperon droppers.
The main spar has been rolled around.  Note that the gorilla glue is now evenly distributed.

Section F:  Glue the Leading Edge, False Ribs

a.       Now it is time to glue the leading edge as well.  Apply some Gorilla glue to each leading edge location, as shown here.
Leading edge of flaperon, with Gorilla glue applied.  Note that there is no glue on main spar by flaperon dropper.


b.      Roll the leading edge around, so that glue is forced downward between the ribs and the leading edge.
c.       Apply clamps throughout the assembly, so that leading edge is firmly held in place.
Clamps hold the leading edge firmly in place.
d.      As the glue sets, it will foam and look like this.
Glue setting on main spar and leading edge of flaperon

Section G: Balsa parts

(NOTE:  If your spar, or trailing edge, or leading edge extend beyond the outside rib, trim them flush using a band saw (or hacksaw).  Sand smooth.  DO NOT trim off the main spar on the inside rib – you need this ‘root’ section to install the control horns.   You’ll need to do this so that you can glue on the end rib balsa block.
a.       The four end cut balsa blocks are slightly oversized.  Each will need to be trimmed exactly to correct width (use a table saw) and then glued in place.  Two of them will need to have slots added at exactly the right location to match up with the flaperon dropper area, as shown in the photo below.
Balsa block in place, with slots cut to match flaperon false ribs
b.      They are then glued with a waterproof wood glue and clamped in place.  Also note that the end of the flaperon will have a balsa end cap block glued in place.  You’ll want to trim that part first.
Gluing a block in place, not also gluing the end cap balsa in place
c.       Sand the end cap to a smooth, aerodynamic form.


Section H: Trailing Edge

a.                   Using a flat pliers, smash the trailing edge material so that it matches with the locations of the main ribs.  See the photos.  Don’t use a pliers with serrations, as it will scratch your aluminum.
Trailing Edge smashed using flat pliers; fitted over rib.
b.                  ENSURE that the insides of the trailing edge are substantially roughened, wherever it mates with a rib.  You’ve got to do a good job of roughening, so that the trailing edge will remain glued in place.
Trailing edge being fitted to flaperon
c.                   Clamp the entire trailing edge in place at every rib location, then fill the entire trailing edge with expanding foam.  It will expand and set and glue the trailing edge to the ribs.  Allow to thoroughly set (24 hours).
Use a clamp at every rib location on the trailing edge.  Ensure the clamps don’t move while the foam is setting.
d.                  Remove the plastic film from the trailing edge and remove excess foam as well.  Trimming with an exacto knife works well.

Section I: Trim Aluminum Placement

a.                   Each flaperon is trimmed at two locations, using aluminum trim pieces:  at the two locations where the flaperon droppers are attached.  The trim pieces are precut.
b.                  ROUGHEN and CLEAN the underside of the aluminum trim sheets, so that the glue will adhere underneath.
c.                   Drill and rivet four locations on each tab.
Aluminum flaperon trim sheet, drilled.  (NOTE trailing edge is filled with foam.)
Aluminum flaperon trim sheet, drilled  (Note trailing edge is filled with foam that has been trimmed)
Aluminu flaperon trim sheet, riveted to leading edge
Clamping and gluing down the trim sheet
Aluminum trim sheet, glued in position.  (Note trailing edge is filled with foam.)
d.                  ABSOLUTELY, POSITIVELY DO NOT allow glue to get close to the nylon bushings and droppers.

Section J: Trim and sand glue

a.       Sand off all excess glue.  If you were neat with your glue application, this is not a big problem.


Section K:  Apply sealant to wood

a.       Spray or brush on two coats of a good weather resistant wood varnish on all wood surfaces.
Protect the wood by giving two coats of varnish.

Section L: Covering

a.       Cover with lightweight dacron fabric, prime, and paint.  These techniques are covered on numerous other websites.  We use Stewart Systems.

Section M:  Check Fit to wing assembly; install control horns

a.       After you have assembled the wings, clamp the flaperon droppers to the wing assembly to check fit.  Slight adjustment of wing rib placement may be done to compensate for fit.
b.      BEFORE INSTALLING CONTROL HORNS, ENSURE that wings, when folded, allow control horns to overlap.  This is a tricky and critical step.  Slight offset of control horns allows this.  This means you must build the wings, and test fit wings on the fuselage, before installing control horns!
c.       After test fit is complete and perfect, install control horns using four rivets per horn (supplied) and 3M 2216 glue (not supplied).  Control horns are to be placed 90 degrees perpendicular to flaperon chord.
View of uncovered flaperon in test fitting to wing.
Another view of uncovered flaperon.
Closeup of center attachment on test fitting
Another closeup of test fitting.
Quartering view of full left flaperon.
Root of right flaperon after installation.

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