Left Wing: Install Vortex Generators

I completed my last assembly task on the left wing before I move it back on the stand and duplicate efforts on the right wing.  Vortex generators were installed to reduce the stall speed of the airplane which will reduce landing approach speed and likewise reduce landing distance.   I've been told the S7 is better capable to produce 3-point landings with VGs, as well.  The VGs were positioned such that they have the best ‘bite’ at the airflow when the wing is at the stall angle of attack; not too far forward or aft. The manufacturer recommended that the leading edge of the VG be aligned at the 7% wing chord position.   This results in the VG functionally positioned at the 9% position.  The average wing chord for the S7 is 60 inches, so I used 4.2 inches as my setback position from the LE spar. 

Here is a Stolspeed VG

Here are the VGs placed on the precut advesive pads.

It was helpful having the wings off when doing this because then the wing root was exposed.  It was a simple matter of running a string line from LE to TE spar to determine the chord line and then using a triangle square transferring the 4.2" measurement to the top of the wing.  This location mark on the wing was then carried down to the outboard end of the LE spar and a string line run through the two marks.  This line was then projected across the tip wrap area and terminated shy of the wing tip fairing.

Here is the template used to get the correct angle on successive VGs.  The 60 mm template was used for the first 3' on the outboard wing and then spacing was increased to 90 mm up to the wing root.  The manufacturer recommended this placement so that the outboard wing would not stall first and, presumably, not result in loss of aileron control.

Left Wing Root Skins Fit-Up

The root skin consists of three pieces.  The skin is riveted on with exception to the aft piece which is screwed on for internal wing access.  Here are three pieces clecoed together.

I taped the assembly in-place where optimum, i.e. where holes centered on fuel fittings and skin centered on root rib.

 I then transfer drilled into the root rib and clecoed as I went.   I also fit-up the fuel sight gauge mounting bracket.

Here is a closeup.

I'll final assemble after painting.

Left Wing Gap Seals

The gap seals were cut to length to fit between hinges and then mitred at 45 degrees using a disk sander.

Next, holes were drilled every 8-9" while maintaining specified edge distances.  A dremel drum sander was used to notch areas where underlying bolt heads on TE spar were located which would have precluded seating of seal.

Using a 4' level, I struck a line corresponding to the top of hinge elevation.  The top of gap seal matched this line.

Two-way tape was used to adhere the gaps seals while transfer drilling was done into the TE spar.  Clecos were used to hold piece during drilling.

Following deburring of holes, I then riveted gap seals to trailing edge spars.  Next, using a block plane, I then trimmed trailing edge of gap seal to create a 0.06" air space between gap seal and flap/aileron.

Here a completion pics.

Hard to see, but bolt heads underlie the covering on the TE spar.  These areas were notched on the gap seal.

The mitred ends were constructed to facilitate potential bolt removal.  The rivet holes were located 1/4" from bottom of gap seal rather than along centerline so that the pop rivet gun head would fit unobstructed.

Gear Leg Reinforcement

I've been told that the existing gear leg shaft in fuselage socket connection is the achilles heel of my vintage plane design.  A hole is drilled and a single bolt extends through the socket and shaft.  Over time, repetitive landings on rough ground and especially with bigger tires tends to over-torque the gear shaft causing the softer socket metal hole to wallow out.  The factory has since corrected by welding steel reinforcement "patches" where the bolt goes through.  I decided to address this potential problem now and avoid headaches later, especially since I plan rough field landings with bush tires in the future.  Several guys had purchased steel shaft couplings for added reinforcement.  I wanted to avoid the extra weight and purchased aluminum two-piece collars with cap screws.  I could not find an assembly long enough, so I purchased two collars and had them welded together.  Here are the collars as-purchased.

Here is an installed 1-3/8" welded double collar installed over the gear leg socket.  The gear leg shaft is inside the socket.  A longer bolt now runs through the entire shaft, socket and collar.  I applied JB weld epoxy to the inside bearing surface of the collar before tightening down the 4 cap screws.   I also stripped all of the paint from the socket bearing surface, before installing the clamps.

Left Wing Construction: Attach Flaps/Ailerons, Wing Tip Fit-up

I got the control surfaces attached to the left wing.



Here is a closeup of one of the hinge points.

Next, I needed to fit-up the wing tip assembly.  The wing tip inside edge overlaps the rivet centerline by 5/16" so need to have a way to transfer hole locations onto wing tip.  I drew 2" line segments from hole locations to transfer to wing tip when put on wing.

Here is the final trimmed wing tip with minimum edge distance maintained from aileron.

Here is a rib section riveted to the aft end of the wing tip.  The aft end of wing tip is set flush with aileron aft edge in aileron neutral position.

The aileron neutral position is established by placing the wing spars on a linear piece of wood with shims of similar thickness.  A shim is also place under the aileron aft edge.  This results in the bottom of wing spars and bottom of aileron aft edge all in same plane or neutral position.

Here you can see trailing edges of tip and aileron matchup in neutral position.

I located holes for the nav/strobe lights.  I will utilize a single bolt, nylock nut and larger washer to fasten to wing tip later.

Cowling Fit-up and Final Install

The fiberglass cowling consists of upper and lower pieces that need to be trimmed to fit. Both pieces need to be centered and set 1/2" behind the spinner dome backing plate.  I used scrap wood as spacers seen here.

First off, I needed to trim the aft edges of the upper and lower cowls to fit and match the boot cowl joggle.

I used a Dremel cutoff wheel for a lot of the trimming and drum sander for edge contouring.

Here the lower cowl is trimmed to match the boot cowl and spinner dome plate.  For the latter, I wanted a  smooth drag-free contour transition.

Here is the oil check/fill access door installed.  It is recessed into the cowl.

Once the cowl pieces are trimmed, everything is taped together and holes are drilled and clecoed where the 1/4 turn fasteners and receptacles will be located.  Note the smooth transition from spinner dome backing plate to upper cowl.

Both cowl pieces were PPG epoxy primed in the paint the booth.

Here are completed pics of the cowl assembly with Superflite urethane top coat paint and quarter turn fasteners installed. 

One modification I did was obtain a tubing bender and bend/realign aluminum carb. overflow drain tubes so that they would daylight through the bottom cowl opening, as opposed to drilling holes for their exit.  This way, lower cowl slips on and off with ease.

Aileron and Flaps Final Construction

Hardware was installed on the covered and painted flaps and ailerons.  Shown here is a flap and aileron with attached horns.

Next up is assembly of the aileron spade assembly.  This feature is used to reduce stick forces and create something similar to "power steering".

The aileron must be balanced in the static position, so a counterweight is fastened to the aileron spade.  I'm told the weight also dampens out oscillations in the aileron.  Two aileron hinge points are placed on the sharp edge of two pieces of horizontal angle iron.   Weight is added or subtracted until the aileron is parallel with the angle.

I obtained lead shot from a local gunsmith and used it as raw stock for forming the counterweight.  I wanted to over-cast material rather than the alternative.

This pic shows one of the balance points.

I melted down the shot and used Altoid cans as a form.  This was much more cost-effective then obtaining lead sheet or plate, which Rans suggested.

Here is my smelting setup in my paint booth.  Lead fumes were exhausted by fan and I wore a supplied-air mask.  Lead fumes are extremely toxic. 

Here are the two resulting lead ingots.  I spooned off a lot of impurities resulting in these 100% beauties.

Here is the first balance trial, which was way too heavy.

Realized after the fact that I casted them way too thick so used a block plane to mill off material.  After many iterations here is a perfectly balanced aileron.  When I got close to balancing, I filed and sanded each ingot with successively finer grits.  I then dimpled the bottom side with large drill bits to remove material and nail the balance point.

Final counterweight attached to spade.