I've been trying to design a three surface airplane using a book by Andy Lennon as a guide. My understanding of aerodynamics is limited, and my math skills poor,.. ( a perfect recipe for success? )

The book shows how to find 1/4 mac for a tapered or a swept design but not the combination. I need to determine the 1/4 mac of the tail plane in order to find a ballpark for the np and cg.

I've made a conceptual drawing and need to determine if its viable.

I looked at the 1/4 mac calculator in the sticky, it can't be used because I'm unsure how to determine the sweep of the tail plane as it was purely random. The drawing program being used is an older version of MS Paint so there is no way to figure the angle of sweep even if I knew the formula.

I need some kind of illustration.

Mick

I didn't check all the stickies, but this will handle swept and tapered.
http://adamone.rchomepage.com/cg_calc.htm

There is more than one way to skin a cat.

This application is an easier way to find np and CG. You don't need to know the angles. You only need a yardstick or tape measure OR simply type in what you plan to build.

http://adamone.rchomepage.com/cg_calc.htm



edit....... didn't look at the answer you already got. It's a good one...

One way to do it without math. Cut a templet out of the left or right half tail plane. Use heavy paper or cardboard. Then put 3 small holes on the perimeter at different locations. Then suspend it on something with a pin. Make sure it hangs free. Draw a vertical plumb line from each of the three holes . Where the lines intersect draw a line parallel to the fuse. The MAC will be on that line 25% back from the leading edge.

The examples in the book don't include a wing that is both swept and tapered, that's true. However, the system he shows works exactly the same for a combination. However, the final result Andy was working toward is gotten by simple measuring the spans, chords, sweeps and moments as shown in the diagram on the linked website above. However, it's easier to do when you start from the sketch you made when laying out your own design as you're choosing those measurements, aren't you. What sticky? Using the application linked above doesn't require you to provide any angles. Sweep is dealt with by the application. You simply decide how many inches back the swept tip will be for your design, just like you have to decide what your root chord is going to be, the tip chord would be, the half spans, etc.