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Note:
Check out some additional information at the Weed Wacker downloads
page.
|
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All
of the wood (except for the wing sheeting and
the firewall) in the Weed Wacker was cut from Douglas
fir 2x4s on a table saw, then cut to length on a band
saw.
The
angle pieces were used as the corners on the fuselage,
the sticks were used as the diagonal braces in the
fuselage and the tail sticks were used in the outline
and internal bracing of the tail feathers.
The
main spar is a one-piece 10-foot strip of Douglas fur.
The aft spar is the same, only smaller. We made the
ribs by first cutting the outline on a piece of a 2x4
using a jig-saw, then cutting the shaped 2x4 in to
3/16" slices on the table saw. There is no
dihedral in the wing.
The
only problem with this system is that you have to find
wood with very few or no knots. A knot in a spar could
lead to wing failure when you least expect it.
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Here
is the side of the Weed Wacker's fuselage.
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Here
is the plan view of the Weed Wacker.
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Fuselage
Structure
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The basic fuselage
structure is just that, basic. The angle pieces go on
the corners and the sticks go in between, at 45-degree
angles. As you can see, the tail surfaces are an
integral part of the fuselage. The stabilizer passes
through the aft fuselage, while the vrtical fin sits
directly on top of the stab. The firewall and gear
plates are reinforced with 1/2-inch plywood, to
complement the usual 1/4-inch x 7/16-inch sticks. All
of the joints in the fuselage are made with either 5
or 30-minute epoxy. The wing is attached to the
fuselage with four vertical sticks, which are made out
of main spar stock. The four Sticks are glued to the
spars and fuselage corners. Next, holes are drilled
and dowels are inserted through the sticks and into
the spars. The fuselage corners gain additional
strength from the plywood walls of the bomb bay, so
this area of the plane is really heavy-duty.
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This view shows how the
angle and bracing look from the front (or back). |
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This is the system that we used for the whole
fuselage: Angle on the corners and sticks in between,
at 45-degree angles. We built the basic frame of
our fuselage in one night. Once you have the
system down, it is just a matter of mass-producing
parts and gluing them in.
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Wing Structure
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The wing structure is simple, and
easy to build. All spars are full length, one-piece
sticks. There is a main spar, an aft spar, and three
small non-load-bearing spars in the leading edge.
There is no dihedral in the wing. All of the spars are
milled out of Doug fir 2x4s, and the ribs can either
be plywood or slices of a Doug fir 2x4. The leading
edge sheeting, as well as the trailing edge sheeting,
is made of 1/32" thick lite-ply. The ailerons are
built just like miniature wings, with ribs and spars.
The trailing edge of both the ailerons and the wing
have a tapered piece of Doug fir to attach the TE
sheeting to. All structural joints in the wing are
made with epoxy. The aileron servos are mounted in the
rib bays in front of the ailerons.
The Weed Wacker's landing gear is made of music-wire,
electric-fence wire, and door-springs. The tires
are 6" foam. The music-wire is bent to
shape, then welded at all intersections. The
springs hold tension between the main gear without
being completely rigid. Electric-fence serves as a
connection between the springs and the music-wire.
We designed the gear to be very similar to the
Design used on some old full-scale tail-draggers.
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THE SECRET NUMBERS (magic?)
| Detail |
Dimension |
| Wing |
| Wing span |
120" |
| Airfoil |
Clark-Y |
| Wing chord |
21.25" |
| Rib length |
approx. 21.25" |
| Distance between ribs |
7.5" center-center |
| Rib stock |
3/16" thick |
| Main spar length |
120" |
| Aft spar length |
120" |
| Main spar stock |
1 5/8"h x 7/8"w |
| Aft spar stock |
1"h x 1/2"w |
| Main spar location (%chord) |
center is at 5.31" (25%) |
| Aft spar location (%chord) |
15.5" from LE to center of
spar (72.94%) |
| Aileron span (%wing span) |
23.5" (19.58%) |
| Aileron chord (%wing chord) |
5.5" (25.88%) |
| Aileron airfoil |
Symmetrical |
| Aileron location |
Outboard |
| Fuselage |
| Fuselage (fuse) length |
88.5" |
| Firewall (FW) height |
7.25" |
| Firewall width |
7.25" |
| Firewall stock |
1/2" plywood |
| Fuselage taper begins (measured
from FW) |
43.5" |
| Fuselage width at rear |
2.125" |
| Fuselage height at rear |
4.25" |
| Main spar vertical location
(profile view) |
On top of the fuselage |
| Main spar horizontal location
(profile view) |
24.06" from FW to center of
spar |
| Trailing edge (TE) distance from
firewall |
40" |
| Landing gear distance from
firewall |
20" |
| Landing gear width (%chord) |
approx. 37" (31%) |
| Landing gear height |
w/out wheels, 11" |
| Wheel size |
6" |
| Hatch #1 distance from firewall |
1.25" |
| Hatch #1 width x length |
5 3/8" x 11 3/8" |
| Hatch #2 location |
Between the spars in the center
rib bay. |
| Hatch #2 width x length |
6 3/4" x 10 3/8" |
| Tail feathers |
| Horizontal stabilizer (stab.)
span |
37.75" |
| Horizontal stab. chord |
8" |
| Stab. horizontal location |
TE of Stab. is flush with rear of
fuse. |
| Stab. vertical location |
On top of bottom angle pieces |
| Elevator span (each) |
17.5" |
| Elevator area (each) |
76.75in^2 |
| Vertical fin height |
20" |
| Vertical fin area |
150in^2 |
| Vertical fin max. chord |
14" at base |
| Vertical fin horizontal location |
TE of fin is flush with rear of
fuse. |
| Rudder height |
20" |
| Rudder chord |
2.75" |
| Tail-wheel size |
2" (foam) |
Note:
Check out some additional information at the Weed Wacker downloads
page.
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