1. Overview of enlarging the turtleback
Over the years several builders have used larger canopies than the one called for in the Cozy build books. Typically, builders modify the canopy to be 1.75” taller and 2” wider (the so called Texas Canopy). This requires modifying 4 of the turtleback template on drawing M-29. The only template not modified is the J5 firewall template.
J1 and J2 are the simplest to modify since only simple additions to the plans templates are required and both have the same dimensions.
J3 and J4 will need you to take measurements to determine how much is need to raise and widen these templates.
Other builders tips are:
Use ¾” thick wood for the templates since they will stay straighter.
Use MDF as it will make a better jigs.
Shelving brackets will hold the jigs in position better than bondo.

2. Basically, the goal is to determine two things: 1
Basically, the goal is to determine two things: 1. How much to raise (height) the jig by. 2. How much to increase the width by.
The jigs will need to be enlarged from 18”x40” to the amount you increase the turtleback by. In Wayne’s case by another 1.75x2 or 19.75”x 42”
To determine how much to raise each jig (template M-29):
On your workbench, use the left edge of the workbench as the firewall reference for the J5 jig.
Use the bottom edge as the reference for the top longerons.
Draw a 46-inch line along the bottom edge of the table. (The turtleback is 46 inches long.)
Lay out the locations of the J4, J3, J2, and J1 jigs.
Mark out vertical lines (90 degrees) at each jig position.
On the J2 line, measure up 1.75” (or to whatever height you want to raise it to) and make a mark. (1 to 2 inches is the recommended range.)
Draw a line from the J2 mark to J5.
Measure the lengths needed for raising J3 and J4. The is the extra lengths you’ll use for extending the “leg” of each jig.
46”
Workbench top
40”
26”
12” J5
Firewall J4 J3 J2 J1
M-Drawing
Workbench
Measure
these lengths
1.75”
Add length to “leg” of each jig J5
Firewall J4 J3 J2 J1
Tape extra piece of paper to M drawing

3. L C Determine how much to widen each jig:
On your workbench, use the left edge of the workbench as the reference for the J5 firewall jig.
Use the bottom edge as reference for the fuselage centerline.
Lay out a 46-inch line along the bottom edge of the workbench. (Or use same one from Step 3!)
Lay out the locations of the J4, J3, J2, and J1 jigs as per Step 2. (Or use same ones. Just extend the lines to 22 inches long.)
Decide how wide you want your canopy to be at the J1 jig. (Plans is 36”. I went 2 inches wider to 38”. The widest you can go is to the longerons.)
Divide that width by 2 and make that mark on the J1 and J2 lines. (The J1 and J2 jigs are identical.)
Set the width of the firewall on the J5 line. (I didn’t raise or widen J5. I kept it per plans width of 31.50”.)
15.75”
19”
19” (one inch wider than plans) C L J5
Firewall J4 J3 J2 J1

4. Determine these widths
Set nails at J1, J2, and J5 marks.
Loft the curve by bending a flexible stick or metal ruler through the nails.
Measure the widths for the new J3 and J4 jigs.
For Jig 3 and Jig 4, subtract the plans widths from the new widths measured here. This is the extra width you’ll add at the top of each jig to widen it.
Nails to hold flexible ruler in place
Determine these widths
19”
19”
Workbench edge C L J5
Firewall J4 J3 J2 J1
M-Drawing
Tape extra piece of paper to M drawing
Add width to the top centerline of each jig C L

5. For the J1 and J2 jigs (identical):
(20) Draw centerline on the jig board.
Place M-drawing flush with centerline and flush with bottom edge.
Now…
Move M-drawing outboard until “leg” matches new width.
Move M-drawing up until “top” matches new height.
Transfer the curve from the M-drawing onto the jig board.
Jig 1 and Jig 2 are identical. Make one, trace it onto the other.
On mine, my turtleback is 2 inches wider and 1.75 inches higher. So I went “out” by 1 inch each half and “up” 1.75 inches each half.
Move M-drawing
“up” and “out”
“Up” by 1.75”
“Out” by 1 inch each side of centerline. (2 inches total)
M-drawing
Jig 1

6. (27) Draw centerline on the jig board. Now…
For the J3 and J4 jigs:
(27) Draw centerline on the jig board.
Now…
Position M-drawing until “leg” matches new width and “top” matches new height.
Transfer the curve from the M-drawing onto the jig board.
Match centerline to centerline
M-Drawing
Set new “leg” flush with bottom edge of jig board enterline to centerline