Hello everybody! I am building Cassutt 3M, and i want increase rudder area, because i plan to fly mostly aerobatics. Raising rudder/ fin for 2 inches is common way to add area for Cassutt pilots that use their plane for aerobatics, but i want to add little more area just for looks.... Our Finnish aviation officials need some kind of proof that modifying rudder is safe and tailpost/ frame will can take that bigger load. If i calculate new load for this bigger rudder and hang that load weight at tailpost/ hinges , i can build it. I will add third hinge and aerodynamic boost for it. New rudder area will be approx 30% bigger than original and deflection angle is 20 degrees. Original rudder area is 2.6 sq/ feet. I tape new lines that look good (for me) at original tail. My plane and tail pictures are here; CASSUTT RACER OWNERS FORUM • View topic - Finnish Cassutt My humble question is how i can calculate this new rudder? How can i find force that affect my hinge/ tailpost? I got only basic mathematical skills....so is there some relative easy way to calculate it? Cheers --Vesa--

Look for a NACA paper on flap effects. A rudder is just a flap, you know. It will have a chart that gives an equivalent angle of attack of an airfoil for a given flap deflection and flap chord/wing chord ratio. From there, you can find the coefficient of lift for that equivalent AoA, allow for aspect ratio, factor in the area, and find the force.

Your regulatory agency may also require you to demonstrate that the vertical tail and rudder be able to withstand a horizontal gust of some defined magnitude. Be sure to ask them for a specific list of test cases, and get a clear understanding what combination of calculations and/or test will be needed to satisfy them. You can work backwards from there to determine what kind of math you'll need to do. The book "Design of Light Aircraft, by Richard Hiscocks, gives a great introduction on how to calculate these loads with relatively simple math. Shipping a book to Finland might be expensive, but would be worth checking into.

http://www.lightaircraftassociation....15 Example Aircraft Loading Calculations.pdf Good outline on the procedure based on Hiscocks book.

That is good. If you can follow along with this example, you should be able to substitute the load values prescribed by any of the common airworthiness standards.

I should be fine with that example calculation. This site is valuable source of information and full of skilled people that shear it.... You help to get my plane airborn with modÂ´s i really want, so: Thank you all!