- Oct 18, 2003
- Saline Michigan
Hmm, the basis for FEA and CFD are both integral calculus in two and three dimensions. Failure to understand both the basis for these solvers and how they work easily becomes a GIGO exercise. Many's the time in my career where I had advanced degree engineers doing FEA/CFD in support of my product and gotten answers that were clearly wrong. Got to the point where I would rarely do a new product without having them also do a current product in exactly the same way for their own comparison. Picked up a lot of factor of 2 and factor of 10 errors that way. Reliance upon them with understanding the basis of the analysis is likely to be troublesome.We haven't done any specific calculations on the exact magnitude of the aerodynamic forces acting upon the aileron but I imagine that they will be pretty minor as the top speed will only be 54 knots. Most of our current dimensions are purely conceptual and are either based on similar aircraft, trends in design, or some basic calculations. Since I'm still a junior in high school, my math knowledge (and that of my team) is limited to that offered by a precalc class but I'd be more than willing to jump ahead and learn some new things if needed. Teaching myself calc (or other advanced math) though would be pretty inefficient and I was hoping to be able to get a closer estimate with some fluid analysis (still need to figure out how that works). Either way though, if you know any equations or can refer me to a textbook which goes over such calculations that would be great. I'll also look into using diagonal ribs or wires to improve torsional rigidity. Thanks for the suggestions!
Much of airplane design can be done without much more sophisticated work than Excel. You can get spanwise loading, shear, bending, and torsion, brace reactions, etc through Excel. Theory Of Wing Sections by Abbott and von Doenhoff will give you chordwise airloads and control surface lift and pitching moment increments for deflected surfaces. I suspect emulation (yeah, Monkey-see, Monkey-do engineering) of successful designs in your desired speed and wing loading range will go a long ways. It will also serve as a check on the sizes of your spar tubes - compare to similar UL wings.
Two issues you do want to make certain you are OK on is bending strength and compression strength of the wing. If you start with your inboard anchor and strut mount as fixed points, and then start accumulating lift from the tip in a piece wise fashion, you can build up your shear curve and bending moment curve. The vertical reactions at the inboard anchor and strut mount will be equal to the lift that the wing makes on that side. Since the inboard anchor is just a couple bolts aligned fore-and-aft, no moment is carried at the very anchor, only shear. If you get this far, you have one more thing to check out. The braces are angled in, so go to that pre-calc class (mostly trigonometry, right?) and you will figure out that load in the strut is the vertical reaction divided by the angle of the strut from horizontal. Then you can figure out that the load in the strut times the sine of the angle from horizontal is the compression that the spar that strut is attached to will see. Elastic buckling of that spar must be prevented - that is usually picked up in a Junior year mechanical engineering design class. MSMD engineering will give a check here too. Look up Euler Buckling for basics.