insalacosm

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Hello - I'm getting ready to scratch build a turtle deck for my Proctor Mini Antic and was hoping for some guidance on how to design it so it looks right. The width at front and back will be established by the fuse width at those points and the height will be established from what looks right, but the challenge is establishing the curve for all formers and the sizes of the intermediate formers. Does anyone know a proven technique for designing turtle deck formers?

My build log can be found at: http://www.rcuniverse.com/forum/m_8270605/tm.htm

thanks
Steve

All Day Dan

My Feedback: (5)

Steve, I use AUTOCad for this. Use the ellipse command. The fuselage widths are the first and second points and the height is the last. The shapes have always come out right for me. I don't know how to do it any other way except by eyeball guestimates. Dan.

Laird SS

It's not too hard to do with lofting and intersection curves in SolidWorks. You can even create intersection curves on planes that aren't perpendicular to the centerline of the fuselage.

insalacosm

My Feedback: (1)

I checked and it looks like there are free trial versions of at least AutoCad.
thanks

bkdavy

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Look for a program called DeltaCad. I use it. The unregistered version will do everything except some of the printing functions. Its cheap to register. I use it all the time. It has the ellipse function and like Dan Reiss, its always worked for me as well. You can also do elliptical arcs rather than full ellipses.

Brad

deckerv

My Feedback: (21)

A totally manual way to do it would be to use a foam block, shape it the way you want it with a lot of sanding, and when you're happy with it, mark where you want the formers and cut the foam there. You'll have the outline of the former you'd need to make

kdc

The other manual way to do it is like wing ribs-cut a front and rear template and sand a stack of balsa to the tapered shape.
Or plot the formers same as wing ribs were plotted-front former and rear former shape on a piece of paper and put radial lines in and divide into equal sections.

But the easiest is to measure the width of each former and use a compass to form a semi circle. Judge where the baseline of the semi circle is to be placed and this is the same for each former only the radius is changed as appropriate to the width.

BMatthews

Everyone has offered you tools to do the drawing with but it seems like you are looking for help in what to actually make it look. But that is purely a question of artistic taste and it'll vary with each person.

As a basic option I'd suggest pure circular arcs of slightly less than the full 180 degrees. And a side view that has the deck top stringer path near to level and curving in a smooth manner to mate to the leading edge of the stabilizer at the leading or the trailing edge depending on the sort of look you're after.

Using CAD form an arc that is maybe 150 to 160 degrees and just make it the same all the way back. The other option is to have the deck taper to a flat just at the leading edge of the stabilizer. From there you'll want to draw up a nice looking side view and then from the height and width at each station do a circular arc with the radius needed to achieve the height and width. I know that most CAD programs have a circular arc tool that lets you set the radius based on three points. That's the one you want to use.

insalacosm

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Thanks everyone for the tips. I spend a few days just studying the plans and drafting a few ideas. I noticed that the early aircraft used circular curves more than elipses, so I ended up just using the approach BMatthews suggested and I did everything by hand / trial and error. I drew a line from the top of the LE of the horizontal stab to the height at the end of the turtle deck, and then drew an arc that connected the height to the width of the fuse at that point. It was fairly straight forward to make a few formers so I cut a few out of paper to prove that this looked okay and it did! I made a couple refinements to height so the pilot doesn't hit the underside of the wing and now I'm ready to cut some ply formers and start building the turtle deck. The next challange is hatching the forward cockpit area and designing the cowl...

Thanks again everyone for the inputs.
Steve

insalacosm

My Feedback: (1)

It took a few attempts but I think I have a good design laid out for the turtle deck and the hatched cockpit area. Not sure yet how I'm going to do the cowl, but that will come later. I decided to stick with circular arcs for the turtle deck formers to make the design easy, and as it turns out, I believe early aircraft used circular arcs rather than elipses.

The first step I took to design the turtle deck was to determine the height at the front where the cockpit hatch will butt up against. Once I established this height, I drew a line to the top of the horizontal stab and then this gave the height of each former. Since the width of the fuse where I'll place each former is fixed, I had the three points (height and width) needed to draw an arc to connect the three points. I'm not sure if it has any significance but the radius of the arc neded up being pretty much the same as I went down the fuse.

I first drew the turtle deck formers on paper, cut them out, and placed them on the fuse to make sure things lined up okay. Fortunatly it looked good but I decided to lower the height slightly so the pilot's head wouldn't be sticking into the upper wing. I then redrew the formers with the new height and determined the radius needed for each former. I then drew the formers on a plywood sheet and cut them out with my scroll saw.

I needed to notch the formers for the stringers and to do this a friend recommended that I glue a strip of sandpaper to the bottom of a stinger and sand the notches. I didn't have patience for the glue to dry so I used four cut-off disks on my dremel to cut the notches to the right width. It actually worked out really well although I probably cut the notches deeper than I wanted. I used my little clamps to hold the dremel in place and I used the on/off foot pedal I have for my scroll saw to turn the dremel on. This made the setup a lot safer since I had to press the pedal to get the dremel to turn on.

Below are pics of the dremel setup, a close up of a couple formers, and the formers drying in place. Also is a pic of some goodies I received from Proctor today which included cockpit trim, instrument dials, and the Jenny Engine kit. I'm not sure how the engine kit will become the beautiful dummy engine I saw online, but hopefully it will work out okay. It's really involved and I even need to wind my own springs!

Tomorrow I'll add the turtle deck stringers and will start on the forward hatch area.

Thanks again for the help. I'll probably ask for help again when I need to design the Jenny style cowl since I'm at a loss for how to proceed with hatching it for an electric setup.

Steve

insalacosm

My Feedback: (1)

Here are some pics of the completed turtle deck. I think it flows into the horizontal stab nicely should serve it's purpose of imitating the look of the Curtis Jenny. I'll continue to post progress on my build thread at: http://www.rcuniverse.com/forum/m_8270605/tm.htm

BMatthews

The deck is looking REALLY nice. As you say this sort of design was quite common in many of the early and WW1 birds.

Nice job!