Chapter 18 - Section 1

Building The Turtle Back Form


What's Up?

In this chapter, we will be building the canopy and the turtle back (i.e. the enclosure that keeps us out of the wind when flying). I have intentionally delayed the shaping of the nose until now so that I will have a continuous flow from the nose all the way to the back of the plane.  






Purchasing the Turtle Back (TB)

As suggested by quite a few Cozy builders, it is a worthwhile consideration (time savings & economics) to buy the TB, IF you do not plan to increase the size of the TB to accommodate taller/larger occupants. Since I am 5'7" and Susann 5'5", I do not see the need to build a larger TB. So... I purchased the TB from Featherlite (a recommended supplier per plan). My only concern is cosmetic. Some Cozy builders reported (and supported by Nat) that if I do not raise the front of the TB about an inch, I may end up with a dip at the joint between the canopy and the TB. I will probably want to adopt this modification when I get there...    


Establishing the Center Line of the Turtle Back

The TB arrived in about a month after I placed the order. It's not constructed out of the normal foam and glass (as we are familiar with) but out of honeycomb materials. Its surprisingly light with many sharp edges - guess how I came to that conclusion. The inside surface is peel plied and took me a good 1 1/2 hours to get it off. My initial measurements show its about 1.5" longer than plan dimension. I decided to square it up (and trim to length) before I proceed with add-on work.


My first effort was to determine its center line location. I laid the turtle back on a couple sawhorses and had it leveled fore and aft, and side to side. Then I took a measurement between its sides and dropped a plumb line down the middle. I repeated the same at the back of the turtle back. With a straight edge, I joined the two mid-points  








Squaring Its Edges

I drew out the TB dimension on my work bench using the front edge of the bench as the starting point. Then I placed the TB on top of the pattern. I dropped a plumb line down from the TB and lined up to the pattern (on the work bench). Note the 2 plumb lines lining up to the center line on the table...


Next, I transferred various dimensions from the work bench onto the TB. Dimensions include the front edge, the end (46"), the future cut lines (17" and 27 1/4" respectively) and TB-1.


With the TB clamped on the work bench, I butt a laser pointer against the face of the work bench (right below the plumb) and cast a laser dot onto the front edge of the TB. If you look closer, you can see the laser (bottom) casting a dot at ~12:30 o'clock at the top edge of the TB. By sweeping the laser along the front face of the work bench, a series of laser dots (~1" apart) can be traced along the front edge of the TB. I joined the dots with a straight edge and lightly sanded the front edge to the line.


I turned the TB around and repeated the same process above - setting the 46" mark (length of TB per plan) and the excess. I held off trimming the TB until the last moment - just in case.



Raising the Turtle Back by 1"

I trimmed 2 slivers of foam - 46" long with 1" tall at one end and 0" at the other. I then turned the TB over and microed the foam sliver onto the base of the TB. 










Trimming the Turtle Back

Since I raised the TB by 1" in the front, the entire TB is tilted a bit. To keep the forward and aft edges vertical, I need to re-trim them accordingly. In addition, the total length of the TB was 47 1/4" which is about 1 1/4" longer than plan. The joggles at the forward end were 1" and 5/8" respectively per plan but the aft joggle was 2 1/2" instead of 1 1/4". It was obvious to me that the aft end needs to be trimmed by 1 1/4" - reducing the overall length (46") as well as the joggle width (1 1/4") to the plan dimensions.






Before I started trimming, I decided to validate my trim plan with Featherlite (Michael Dilley), just to be sure. To my surprise, Michael wasn't sure, because he had no feedback from any Cozy builder having to trim it short - and he had sold quite a few of them (about 50% of the Cozy builders, according to Mike). He basically told me that I need to make sure the aft end of the TB must line up well with the firewall. Well, I can't line it up if I do not trim it first ... I decided to search through the Cozy web and noticed Jon Dembs bought his TB from Featherlite as well. An e-mail confirmed that he had to trim his as well... That's better! Here's a picture after I trimmed ~1 1/4" off the aft end and most importantly, the firewall fits almost seamlessly!