Wing compression strut parts 2
by, 02-03-2011 at 01:20 PM (4135 Views)
Well I have finally got back to work after 3 months working ? Well I mean on the plane. Actually I'm not building a Piper clone airplane. I'm building a small part of the 13 rib metal wing. Like eating an elephant. So this is the first time I attempt to post pictures and I'm not sure how it will go. As to my earlier blogs I was attempting to decide how to build a light weight wing for my attempt at building a 150 horsepower 1320# gross weight supercub clone. I finally decided on recreating the PA-18 13 rib wing as per the drawings on Christian Sturms site: supercubproject.com The parts I build for this project will follow those pages in the "drawings" section of his site (the "drawings" button is in the upper right hand corner of his home page). Once you get to the drawings page enter 10062 in the search box for the first part we will discuss. So in my first blog picture (remember you can blow it up by clicking it a couple times)
are parts in various stages of completion so that you can see my thinking. Note my favorite flyer in the cage (we have cats unfortunatly) At 14 years old she has lost her medical but still flys some (ultra light catagory only) Figuring the order to make any parts is half the work usually and actually the challenging part. After you've figured out how then stamping widgets is anti climatic. In the picture you see 3 drawings from Christians site (10072) Drag strut front foot, (10062) rear drag strut foot, (10021) "N" strut gussets. Diagonally in the picture is an actual drag strut with the front foot clipped on to it. I cheated a little on this as I ordered, from Dakota Cub, 1 ea foot front and rear foot and drag strut tube, drag wire pull and nipple etc so that I would have a pattern to decide how to layout tooling and then check the quality of my work. In the second picture
you see the rear foot (10062) in various stages of completion. The triangle piece of flat aluminum is the first blank which was derived from a paper pattern. After making the first blank the rest were scribed around it to mark the rest of the aluminum blanks. I used one of those 30" shear/brake/roll that Harbor freight sells and my brother owns to cut the blanks. I did one with hand shears just to prove it could be done. It turned out fine but the shears tended to curl the blank slightly. A whack with a board brought it back into shape. Note the finished (factory) piece sitting on a blank (bottom left of second picture) to mark lines on the blank to center the bending board on. Two centering lines were scribed on each blank (flop the pattern piece over to make second mark and don't worry about width of marks just align the edges of blank and mark. You will center wood form between the marks, distance between the marks doesn't matter). In the third picture
the blank is centered under the bending board (7/8 wide piece of scrap finish wood (home depot 1" finish? measures 7/8") with the bottom edge "broke" by hand with a piece of sandpaper for the "radius" edge). The previous center scribed lines are used to eyeball the board to the center of the blank. Pressure is brought on the board by the milling quill being lowered onto the top of the board and locked. In the forth picture
a scrap of .032 4130 steel is squeezed under the edge of the aluminum and while pressing in it is tilted up a bit,presseng in again and then a second thicker piece of steel is pushed under that one and it's bent some more (repeat lifting and pushing in on the "wedges") until the side reaches about 45 degrees. At this point the blank is turned around and the other side is bent to 45* also.
In the last picture the milling vice (between the jaws) is positioned under the quill and the partially bent blank is placed between the soft jaws on top of a scrap 3/4" square tube (to keep the bottom of the part flat while you finish bending it since there is a hole in the center of the vice), the quill is lowered for top pressure on the board and the vice jaws closed to complete the two side 90* bends. Top pressure is needed while bending to keep the bottom (center of the part) from taking a curve. Some repositioning of the "X" axis of the milling table vice is needed while tightening the jaws. Note: cut your blanks so that you are bending across the grain. The blanks are 5052 aluminum from onlinemetals.com. About $20.00 for all the feet needed and the "N" strut gussets. The two certified pieces were 7 an10 dollars respectfully. Practice makes the pieces bend up perfectly on both sides so they match. For production, do several parts 1 step at a time on all parts before moving to next step. Works out to about 10 minutes a piece total/part once you've done a couple practice pieces. Finish corners on a belt sander. A slot has to be milled on the bottom like in the factory piece. I will use a ball end mill but corner holes could be used and maybe a dremmel tool or small hacksaw blade with file finish. So if you have followed so far does my description and pictures lead you to think you could build these pieces for the Piper wing?? Suggestions to improve (this works but maybe someone has a better way)? Thanks