Here's a more detailed description of the TurtleDeck and Nose Cowl modifications I made to my Four Star...

TURTLEDECK - 40 or 60 size:

To start with, I used 1/16" balsa sheeting, you can use 3/32" if you want a little more strength. Any thicker is just too much weight, andy thinner will be too fragile. You can use 1/32" light ply, but it's much harder to curve/warp than the balsa.

Just like covering, you'll need your sheeting to be a good 1/2" larger than the area to sheet. So, the widest section will need to be a good 1" wider than the widest area of the deck, which will be right where it meets the cockpit. In my case, two widths of 3" wide sheeting were enough, you can pretty much eyeball that. In the case of 60 size, you'll probably need three sheets. Just CA the 3 sheets together on a flat surface after cutting a good straight/true edge on each sheet. sand one side very flat/smooth before starting to sheet it down in one piece. My finished piece was 6" wide and the length was 1" longer than the distance from the cockpit former to the last former of the deck (where it meets the tail).

Next, glue a few small stringer strips of about 1/8 x 1/8 balsa down onto the fuse inside of the deck, spanning between each of the formers. This gives you something to glue the edges of the sheeting to. You need to sand-notch the sides of the base of the formers where they meet the fuse, so that when you sheet over them down onto the 1/8" strips, they will meet flush to the sides of the fuse. Otherwise, your sheeting will be thicker/wider than your fuse and you'll have a stepped edge where your sheeting meets the fuse sides.

The depth of your sanded flat-notches in the formers should be equal to the thickness of your sheeting. Also, the 1/8" strips should be set back into the fuse, the same amount (1/16"). This all gives you one constant, true edge down the length of your deck to which you can glue the edges of your sheeting and end up with a smooth, flush joint where it meets the top edge of the fuse sides.

Before actually gluing the sheeting in place, place it in position, centering it over the correct area and wet it down with water... I used a spray bottle. Make sure you have the smooth-sanded side up/out. Now you can start curving/bending it into shape over the formers. Do this step slowly, in increments. It's easy to rush it and crack your balsa sheeting. You can put rubber bands over the whole assemble to hold into relative shape & position temporarily. Now use a heat gun and gradually apply heat to it to dry/warp it into it's new shape.

Once dry, take it back off and it will be warped in the right direction/angles. If needed, you can now wet it down again (off the plane) and repeat the procedure by applying pressure to it to increase the curvature until it gets closer to the actual shape of the turtledeck. Just keep increasing the warp and test-fitting it onto the deck until you're close. You'll never get it warped to the actual shape, but you can get close enough that the CA will be able to hold it into final shape when you get to that point.

Place it back onto the plane and mark the sheeting where the edges meet will meet the sides of the fuse on one side. Take it off and cut a good straight edge to that side.

Put it back on and line the new straight edge into position and tape it down securely. Wrap the sheeting tightly over the formers down to the opposite side and repeat the procedure for that side. You should now have deck sheeting that is curved properly and the proper width, but a little longer than needed.

Now you're ready to glue. Position it properly over the turtledeck formers, and start CA'ing it down one side, from cockpit to tail. Once one side is done, stretch it tightly over the formers down flat to the other side as if you were applying your covering. Lifting it back up a little at a time, repeat the gluing procedure down the second side/edge of the deck. I avoided gluing the sheeting to the actual ribs and formers except for the two ends. This keeps you from getting a polygonal-faceted curvature and lets the sheeting bend/curve into a more natural/smooth shape.

Now that you're glued into position, CA the edges all the way around the entire deck again, ends included. Now you can use an X-acto knife to trim the excess off of the two ends where they overlap the first and last formers of the deck. If you have any untrue/flat areas in the deck, you can fix them to some degree by sanding and/or re-wetting them to get them back into proper form. This should produce a smooth natural curve over the formers without flat spots from gluing to the stringers.

That's about it. Let me know if you need further clarification on any of this. Sorry I didn't take any photos of this procedure, I'll do that the next time I guess.

BALSA COWL:

For the most part, the walls of the cowl were about 3/8" inch to start. You shave and sand a good bit off to get the conical shape, so it ends up more like 1/4 inch or less when it's shaped.

Also, you use a lot of 1/2 to 3/4 triangle stock to support all the wall joints, on both sides of the firewall and inside the cowl. The triangle stock lets you cut down the boxy corners right into the wall joints to get your conical shape but still have the triangle stock inside the cowl to maintain wall thickness at the joints. It's very important to put the triangle stock in behind the firewall too. You'll need it for support but mostly so you can actually start carving your conical taper in a couple inches behind the firewall (in the ply walls). This gives a longer, more gradual taper to the nose.

Make sure you mount your engine with a prop and spinner back on it first. The mounting should be not quite 90 degrees (about 10-o'clock) since you've got to keep the muffler about 1/8 inch from the outside of the cowl. Note: I used a one-piece "circular" Dave Brown fiberglass mount with blind nuts into the firewall.

Spot glue 1/16" inch balsa spacers to the back of the 2-1/4" spinner (not the stock 2" spinner), and then a 1/8" ply "ring" to the back of the spacers. This sets the exact position and angle of the end of your nose to be clear of and square to the spinner when done. (NOTE: These instructions are for a 40-size plane, you may have to increase some sizes, like the spinner size, to meet the larger dimensions of a 60-size plane.)

Build your cowl box walls out to the ring and glue them to the ring, adding the triangle stock inside the cowl at the wall seams. You'll have to leave the last side open (where the engine sticks out) and pull the prop/spinner/engine.

Piece in small wall sections on that side now, building "around" where the cylinder comes out. Be sure to leave some clearance for the throttle linkage, access to the needle valves, etc. You can leave the motor mount in for most of this, so you can keep putting the engine back in to check fit with your final 4th side.

Once you have it all built up and roughed in, you can start carving/sanding your conical shape in. After that's looking pretty good, recheck your engine fit and fine-tune the opening for it to make sure you can get to everything and your muffler is clearing the outsed of the cowl wall. Seal/fuelproof the inside of the cowl, give it your final sanding and you're good to go!

That's about it, I'd be happy to answer any specific questions you may have if/when you give it a shot. The same techniques could be applied to a variety of planes. Actually, the article I used was on making the cowl for a 4Star OR a Tiger, which is another fine bird of the same style and performance envelope.

Good luck,

Tom

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