Weed Wacker Drawings
 


All of the wood  (except for the wing sheeting and the firewall) in the Weed Wacker was cut from Doug 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 doug 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.

Here is the side of the Weed Wacker's fuselage.

Here is the plan view of the Weed Wacker.



Fuselage Structure

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.

This view shows how the angle and bracing look from the front (or back).


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.  




Wing Structure

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.



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)


Questions? bjshowman@weedplane.com

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