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Design => Stunt design => Topic started by: Motorman on April 11, 2020, 07:56:17 AM
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Are you using a CAD program, or pencil & paper to do your design. It matters because you use different methods.
John Miller
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If I design a root rib is there a trailing edge taper and rib spacing that will make the thickness taper come out right if I'm reducing the cord of the root rib at each station at the printers or, does the thickness just work itself out no matter the taper, aspect ratio or rib spacing? But do you want to have the same % thickness at the tip as you do the root?
Thanks,
Motorman
I may be the odd man out or just the odd man, but I have never designed a plane that had a tapered TE. I still used the old fashioned stacking method to cut ribs on my last two but I will be going with foam in the future.
IMHO I don't think that the small amount of airfoil distortion from keeping the TE untapered on the normal 3/8 thick TE has much effect. There are at least 103.5 other things that are more important.
Ken
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The USA-1 has a tapered leading and trailing edge on both the wing and stab.
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WOW! Remind me to stay away from USA-1
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Thanks,
Motorman
[/quote]If I design a root rib is there a trailing edge taper and rib spacing that will make the thickness taper come out right if I'm reducing the cord of the root rib at each station at the printers or, does the thickness just work itself out no matter the taper, aspect ratio or rib spacing? But do you want to have the same % thickness at the tip as you do the root?
Thanks,
Motorman
Pick your airfoil, such as a NACA 0018 for a flapped plane. By the time you add a decent flap it will be a 15% airfoil. The tip airfoil is often a modified and slightly thicker version of the root airfoil.
Draw the top view of the wing, locating the root chord of the airfoil, the position of the tip chord of the tip airfoil, and connect them with the leading edge and trailing edge. Draw a line from LE to TE for each rib position.
Do the same thing with a front view to get the thickness at each rib station. This will give you the dimensions to figure a percentage reduction from rib to rib(if the ribs are evenly spaced each one will be the same percentage smaller the the previous rib).
To do it yourself:
Make the drawing of the root rib using one curve ahead of the spar, and another behind the spar. I usually just draw the top half and mirror it for the bottom. Do the same thing for each rib, stretching the curves to fit the length and thickness. Print each rib onto label paper and cut out of balsa.
If you can cut foam or no someone who does you can cut a wing panel out of foam. Then slice it into pieces with a vertical cut at each rib station. Use the chunks as a template to draw each rib onto balsa and cut out.
In the end you might find it easier to use foam for the wing and cover it with silkspan or carbon matte and iron on covering. It'll end up weighing the same with a lot less work.
Phil Cartier