I have been messing around with designing my own plane. I am just doing a one-off design so I am just using paper, pencil and calculator. I thought I'd toss this out for folks to chew on, spit out or enjoy. Below is an equation that describes a turtle deck former (90 deg to datum). It's basicly an upside down parabola. I graphed the equation and it looks OK. Think it will work?

f(x) = h - [4h(x-w/2)^2]/w^2

h = max height
w = max width
x = ranges from 0 to w

I have not tried the first turtle deck former that is usually angled back, but one needs to modify h to:

h = (a^2 + b^2)^0.5 a=distance back horizontally, b=max height vertically (see picture below)

I attached a Maple 8 plot of the first equation (h = 7 cm, w = 8 cm). Looks like a turtle deck. Now I need to cut it out. I suppose basic math does have purpose????

buh???!!!!!!!!!

i usually use a much simpler method- i glue in place the first turtle deck former and the last one, then i put a straight edge across the top of the two and measure the height where i need the other formers to go. simple and workable for single curve designs

I agree, measuring is much simpler and should produce a nice turtle deck. One question comes to mind, how do you get the first turtle deck former drawn? How do other people draw their turtle decks???

I go one more..

With Autocad, I draw an ellipse about the rigtht size, chop in half, then plot it out (1:1) onto cardboard, and use that as my 'template'. Resize (rescale) the ellispse as needed..

The nice thing about an ellipse, is that the mid points; the 'quadrant points' will be 'tangent' to the sides of teh fuse, and blend nicely to teh built-up box fuse.

(The parabola you've posted looks like it starts off already at an agle, and in my opinion, would look funny. No smooth transition from vertical flat to curvy..)

just my $0.02 worth....

Dr - You are right, I think blending at the fus is going be awful!!!! What's wrong with me? I will look at an ellispe since it should blend much better. I suppose I got too caught up in just being able to do this that I actually forgot what I am trind to do, produce a good looking turtle deck!!!!! Best $0.02 worth I've received in a long time. Thanks.

dr_wogz has it right....ellipses are the way to go. You NEED to get yourself a CAD program and spend the time to learn the basics. You'll never look back! If you don't have one, there are free downloads of TurboCAD that are excellent.

The 1st photo below shows the rear section of an autogyro that I drew up in T/CAD which has half-elliptical rear fuse bulkheads. Once you're happy with your side and top view fuse contours, you draw ellipses at the necessary stations with the major and minor radii matching the appropriate height and width.

The second plane was designed exactly the same way. How did we get along before CAD??

You are right about the time spent learning how to use CAD will pay off in the future. I just like messing around with math (do some here at work) so I just wanted to see if I could use it for something useful. I took your advise for using an ellispe and starting with:

x^2/a + y^2/b = 1

came up with:

f(x) = (h^2 * (1 - [(x-w/2)/(w/2)]^2))^0.5

h = max height
w = max width
x = ranges from 0 to w

I have attached a plot with h = 2 and w = 3. Looks much better this time. Thanks folks!

Man, that is cool....you be's the math expert!

I was fooling around in CompuFoil this morning and got it to loft a "wing" with elliptical "airfoils." The "root airfoil" (half ellipse) has a thicker % than the "tip airfoil" just for giggles and I had C/Foil loft a set of "ribs" on an elliptical planform (to get a set of bulkheads that will give a curved fuselage turtle-deck profile) with the "spars" (stringers) placed at the same % of chord so that you don't have to manually draw in all them stringers in CAD. I imported the resulting "ribs" as a .dxf into T/CAD and here's what I got. The span, chord and spar locations can all be changed as desired and C/Foil will happily loft all the necessary "ribs" (bulkheads.) That's gonna be good tool on the next airplane I do with a turtle deck. Should save some time!

DICKEYBIRD - This is what I think the scratch building community, if you can call it that, should be doing. Looking at ideas they have seen and apply them to their own projects and then take it one step further. I like your idea. I got to get started in CAD.

Any one want to coment on using french curves to get these drawn?!?!?

OK mwright, here ya go! http://www.al-ki.com/tcad/download.php#HatchPatterns This is a FREE download of T/CAD 4 It is a full featured version with everything that the commercial version had at the time of release except the raster/vector convertor (which wasn't too shiny anyway) The same site has a FREE download of the entire manual set in .pdf format as well. So get on with it man....just do it!

OK Doc_Wogs:

I'll bite on that one. Yea I use french curves. And triangles and "T" squares and pencils and erasers, Lotsa erasers LOL. I think CAD is for sissies Very Much L-O-L. I have a background in engineering. I spent lots of time in the drafting room. I find I can bdraw things faster than CAD.
But then I am and old fart. And a pig headed Coal Honkey that is too stubborn to change my ways. I have T Cad on this machine. I may someday open the files even.
I am planning to do a airobatic plane with a big thick tapered wing. With a ROUND fusalage. For a 60 size motor. I want a slower airobatic plane with sane control surfaces. I have a Sig Somethin Extra, but I want something saner first. I have a few Sig canopys that I will use as the focal point. It is where I am gonna start.
Anyway i Have to clear off the drawing table (aka my desk) and have at it. It will have a turtle deck and I will do it the old fashioned way(aka the hard way). I am just collecting ideas now. I will soon start making drawings( I mean mistakes)

Mark Shuman