|The start: Cut-out completed ... trial fit of the Center Wing Spar
| I cut out the Template directly from the plans (vs tracing the drawing).
Checking to see if the template was 14-inches from the bulkhead and square to the center line. Turns out the template was shifted by 1/8 to one side ... more later.
holes were drilled to ensure that no cut would pierce the Side Rails on
the bottom of the fuselage. The extra clearance on one bottom
rail and lack of clearance on the other rail hinted that the template
was slightly off center relative to the side rails.
cuts made with 4-inch angle grinder with thin metal cutting
blade. Great care required since the grinder has a tendency to "grab" and
jump forward. Cutting backwards avoids this problem. Note:
holes drilled at all corners. Usual tin snips and files required
to finish the cut-out.
Red line at right indicates the furthest safe distance for the cut to avoid cutting into bottom rail angle.
|Testing fit of Center Wing Spar
in rough cut-out. Before the spar would fit, the top edges of the
left and right cutout had to be filed for an enlargement of 1/4-inch
and 18th inch respectively.
The tops of the two slots are a 4 and 9/16ths from the Side Rail.
|Testing fitting ... bottom view.
The very bottom cut-out slots for the lower spar cap angle were widened slightly for easy of sliding the Center Wing Spar through the cutout.... see next image.
|Another view of t
|Fit at the bottom of the
spar. Notches are for bolt heads Plans show the skin to be
flat. Should tapered spacers be inserted where the AN bolts go
through the lower spar cap into the bottom rails?
|Used many levels to check the positioning of the Center Wing Spar.
to ensure the spar is perpendicular to the side rail. Note: this
test is not the best because the bending of the side rail introduced
some distortion that prevents the rail from being flat on top.
Eye-ball check proves OK. The wing spar barely peeks above the Horizontal Stabilizer Spar at all points.
|Checking for Center Wing Spar alignment or parallelism using a digital level:
HorzStab: .0 degreesAt one time, the Horizontal Stab and Rudder were
Side-Rails: .1 degrees
WingSpar: .1 degrees
Motorbox: .2 degrees
off by 3.5-degrees (tilting to the left). I replaced the C-to-D skin to resolve the problem.
Note:When checking the center wing for alignment, I discovered a problem. The rear fuselage was canted to the left by an angle of .69 degrees. That doesn't sound like much, but it translates to 1 inch off at the "C" Bulkhead. It's hard to measure that small of an angle. To determine the angle, I solved the right triangle using trigonometry ... 82-inches, 1-inch, and 90-degrees (two sides and one angle).
At every stage of building, I ran a line from the rudder to the center of each section as it was added (and it was always straight), I'm at a loss how this lack of alignment suddenly appeared. I have countless photos attesting to good alignment.
The solutions rejected: reinstall the rudder, shift the center wing ... leave as-is and add trim after the first test flight.
Simple solution: slide the fuselage D-to-C skin further into the C-to-B section while shifting the rear fuselage to the right. The left side was slid forward 7/8-inch and the right side 9/16-inches. Then back-drill new holes into the C-to-B skin. This adjustment leaves sufficient clearance from the old holes so that the C-to-B skin can be trimmed leaving only the new holes.
The only impacts: Slightly shorter control rods and some trimming to fit the canopy; and, a slight forward shift in CG which will be more than offset by moving the seat backwards.
The effort was extremely easy to do.
Center Wing on Workbench
The Center Wing Spar was removed from the fuselage to begin the build process. The workbench is a level and flat surface for precision work. Once the installed skins need to be trimmed ... then it's back to the fuselage. That will require disassembly of one side .... NOTE: small machinist's square center bottom. This was used to square up the flanges to 90 degrees.
|While I built-up ribs for the outer panels, I decided to buy factory ribs from Hummel:
- Better uniformity (very nice)
- Large lightening holes will ease access
The edge holes for mounting have been punched EXCEPT the upper and lower holes. This allows one to match drill the holes in the rib to the spar cap angles by back drilling from the spar to the rib. After that, you back drill the holes from the rib to the spar web.
Blue Sharpie pen marks center line.
Note: I built the outer wing panels using built-up ribs. I created countess drill guides for the connection between the built-up ribs and the spar before I was satisfied. It was interesting to find that the Factory holes exactly matched my holes on the outer spar web (I tried a test fit just for the heck of it).
small angle with a .016 spacer is clamped to the top spar cap.
Also, a scrap of sheet metal is slide under the spar. The rib
(note blue center line) is ready to be slid into position. The
angle on top will ensure the rib is flush with the top of the spar.
A small LED flashlight from Sears (pink in upper left) was used to center the rib before drilling through the spar cap holes into the rib.
|A 4.5-inch angle grinder with a thin cutting blade was used to cut off the top-center spar
cap angle. Care must be taken that the angle grinder doesn't
"grab" and run into areas you don't want to cut. As the aluminum
heats, the gap of the cut tends to close and pinch ... care is
needed. A jigsaw would be safer.
|A laminate cutter is used to
complete the cut out of the spar web. The highly tempered
aluminum is easily cut. One rib and angle mod was removed for
knuckle and elbow room.
I left the spar cap in place to use the alignment mark on the top of the spar cap. Once the alignment was complete ... I could remove that section.
bought a new set of plans at a very reasonable price from Hummel
Aviation (my old plans stopped at page 18) ... there are 29 total pages.
One mod removed a small portion of the 3/8ths-inch Carry Through Plate. I traced the edge pattern on some scrap mylar from the mylar plans also purchased from Hummel.
Sharpie pen was used to trace the outline ... which has been adjusted slightly once the rib was installed. The cutting is a job for tomorrow. Wonder how much weight this will remove?
|Center Wing Nose Skin
In the meantime, check this link:
On SmugMug, you must move your cursor to the very bottom of the window to see the comments for the image.
Rear Spar for Center Wing
Warning: a temporary angle was used which shall be replaced before flight.
| The mid ribs for the Center Wing have been installed with two short scrap angles for location of the fuselage cutout.
The drawing above is from Page 1 which shows the side view of Bulkhead C1.
At the point where the angles touch the fuselage, a small hole was drilled (both sides).
Then a tempered steel rod was inserted (piano wire from any hobby shop).
on the drawing above, measurements were made to ensure proper location
of the rear spar. All dimensions are approximate
3.25 in. 3.0 in. =Height above fuselage
4.60 in. 4.8 in. =Distance from Bulkhead C
Tomorrow, I will enlarge the two holes and install the actual rear spar.
While the plans called for "Tabs", I decided to use "Flutes"
Bulkhead C1 temporarily resting in place ... CenterWing on workbench
Note: click for enlarged view ... temporary handle Cliqo'ed and Clamped
|Finished bulkhead resting in place against the Rear Spar
Final trim, bending adjustments and riveting will be completed after the skins have been installed and the Rear Spar is firmly fastened in place.
It is expected that adding the skins will move the Rear Spar backward .016 inches and may its height may vary from it's correct clamped position.
|Scrap aluminum was used to form
a pattern. A light-leakage test was made to confirm a tight
fit. The indentations for flutes in the form were not required as
the bend angle is modest.
Once the flange reached the "wavy" state, the bulkhead was removed from the vice. Flutes were formed used fluting pliers. Back to the vise for more forming ... removed ... then the flange was bent to the correct angle by fitting in place and using pliers and fluting pliers as required. Final light test.
Spar Support Angles
Not having any .062 on hand, I bought the set.
NOTE: Extra length for a repositioned wing.
|On the original plans Morry had
just one support from .062 angle. It attached at the top of the
spar and you had to twist it to get it to fit or almost. When we bowed
the side rails, it made this a wider angle. The lower support was added
with the carry thru stiffener. Both of these are available from Hummel
Carpet protects the aluminum from dents and scratches due to dropped tools.
|Interior, left side looking forward from the Spar Carry Thru to Bulkhead B.
Note how flush the Hummel produced angles are to the mating parts. Also note that the where the angles overlap Bulkhead B, they just manage to miss the flutes!
On the far left below the upper angle is the Center Wing SparAttachment flange where I used flutes instead of tabs.
|Exterior view of right side of fuselage showing the Clecos holding the Spar Support Angles in place.
|At Oshkosh 2015, Hummel Aviation
had a set of construction photos for the UltraCruiser. This photo
shows the Spar Support Angles were either trimmed just short of
Bulkhead B flanges or they were sandwiched between the bulkhead flange
and the skin. By not overlapping the flange, the angle will lay
flush to the skin.
Most builders are overlapping onto the flange.
I considered allowing a friend with a mill to remove .020 from the angle where it overlaps ... that would still leave .042.
|Some nice work by another builder on the Spar Support Angles and the elevator controls.
An alternate method for the upper Spar Support Angle is shown in this image ... it appears that flutes at 2-inch spacing were made to enable the angle to match the curvature of the fuselage.
I was satisfied with a straight angle ... it only pulls the skin in about 1/8-inch ... not noticeable ... and this area will be hidden behind the wing fairing.
New Plans include small drawing for the Trailing Edge
Almost too simple of a part for inclusion on this webpage ...
Initial Bend by 4-foot Bending Brake:
Calibrated Pressure for Final Bend:
|The bend must be adjusted to
exactly match the width of the rear spar. Failure to do so will
result in a convex or concave surface on the trailing edge. (If
the bend is incorrect, on can easily spread or narrow the opening to
install; BUT, the surface will be distorted.
I made the part slightly over size. After sliding into place, position the top so that it matches the aileron. Drill and Cleco.
Then adjust the bottom so that the top is in line with the surface of the wing and the bottom is flat. Drill and Cleco
|Build the ribs AFTER completing the installation. They can be custom fit to any slight anomalies from the plans.
When the Center Wing is installed back on the fuselage, the inner end will be trimmed per the plans and fit to the fuselage.
The upper and lower forwarded edges will be trimmed while ensuring proper hole-to-edge distance.
|Aileron folded up vertically. Ribs not installed.
Wing Root to FuselageI decided to save weight by eliminating the beautiful wing fairings. Instead, I am connecting the wing skin to the fuselage using .016-inch angles. This is a viable option if the wing skins have been carefully trimmed to fit the fuselage. The factory designed wing fairings can hide a lot of sins :-)
(Alternate to Wing Fairings)
|The arrow points to the skin overlap of the Trailing Edge on top of the small fairing that I have designed.
Note: I expect this change to impact drag and the handling. The junction of a wing to the bottom of a round fuselage may cause undue interference of wing and fuselage.
This change replaces many very large fairings with small 3/4 x 3/4-inch .016 angles.
|vs. The wing root fairing per the plans. Image from Snyder's Blog. Nice work!
It's a huge piece.
Hummel Aviation notes that the wing fairings stiffen the fuselage.
|Trial scrap aluminum piece cut to fit fuselage.
|Under view of cardboard trial piece taped to the bottom of the wing.
It extends nearly to the center line.
Gaffer's tape holds parts in place.
|Rough patterns. Actual piece was rough-cut even larger to allow positioning and marking for final trim.
|The Support Angle is formed using pliers. Very little bend is required. Trial piece lies on the table just to the left. Very easy to do.
The trial piece demonstrated the need for a narrower and wide flanges on the angle. The wide side keeps the flange flat while the narrow flange minimizes distortion of the other flange.
Below: two views of installed angle.
Tape tabs were used to indicate position of the Support Angle.
|Inside view of installed Wing Root Fairing.
(Holes along edge will be trimmed off when the fairing is trimmed to size.)
|Root Fairing nestles nicely into Trailing Edge.
|Bottom view of the trailing edge, new added Root Fairing and fuselage belly looking towards the rear. Perhaps this added part should be call the Trailing Edge Extension.
Trimming still required.