camber calculations

[NEonGhOsT]

how is the radius calculated from % camber???? just a question I had....

[coachchuckaahs]

Using circle calculations, readily found by Google:

R=h/2 + c^2/8h

Where R is the radius, c is the chord, and h is the height.

The percent camber is h/c x 100

Coach Chuck

[Tom-TTom2015]

Dear Coach-

What’s the best way to make a ~6.5% camber? Cut from an old CD? Thanks

[coachchuckaahs]

Tom:

Just saying 6.5% camber does not mean a whole lot. You cannot calculate a radius with just the percent camber. You also need the chord length. Then calculate the diameter or radius, and either find something with the right radius, or make a template.

I make templates by drawing in software (I use Microsoft Publisher), print it out, then use 3M77 glue to glue it to a substrate. My preferred substrate is 1/8" acrylic sheet, but you can also use aluminum flashing, or in a pinch for a one-off cut you can use a cereal box. Once glued to the substrate, cut the curve with appropriate tool. For plastic, a band saw followed up with a belt sander. For aluminum or cereal box, scissors work fine (probably rough on scissors for aluminum).

Coach Chuck

[dbailey]

if you have access to a 3dprinter, try having your teammates that are doing the Engineering CAD event model a fixture in OnShape and print them out. Note: using "them" because they will have different radiuses for different chords. Or... you can have a constant radius across ribs of different chord, and have variable % camber.

[bjt4888]

So, Coach Chuck's method is the best way to draw arcs of specific % camber height for specific chord measurements, but I take more of a Luddite's approach.

A string taped at one end to the workbench with a pencil attached at the other end, at the radius desired, can draw an arc. I then measure the arc height for the desired chord and redo the arc drawing, using a different length of string, changing the radius, till I get what I want.

I never bother with getting the % arc equal for all the rib lengths for a tapered wing or rotor. This is just too insignificant of a performance factor.

I then cut out the arc from the piece of paper and trace onto 1/16" or 1/8" plywood and cut the ply with a scroll saw (a very fine tooth handheld coping saw would work too). Then sand the arc very smooth so that the blade cutting the ribs slides along the edge well.

Coach Brian