My current blade design

[Running Blue]

Here's a simple how-to guide for a quick and dirty set of props.  Hopefully this will be simple enough that someone can jump right into without too much theory behind them.  My goal is to illustrate that the blade design can be as simple or as complex as you care to make it.  If you have some grasp of the basics you can improve the efficiency that much more.  

This is my current set of blades and have been flying for a few months now and seem to catch the wind as well or better than other blades I've experimented with in the past.  The idea came to me during a free afternoon and I had all the materials on hand - an 8' 2x4.  I'd been flying an 8' dia set built from Hugh's plans but my backyard isn't well suited for these blades, not enough clear wind and way too much turbulence.  I had promised the 8 footer to a friend in the country who could take advantage of their size and I wanted to throw something up on the gennie in the meantime while I took the time to build another set.  As usual, projects get put off but I've been very pleased with this prop.

At this point you may want to figure an angle of attack into the blade tips.  To do so you'd want make a mark of say 1/8" down from the topside of the tip on the trailing edge and then measure your 1/4" thickness below that.  If you want to get more precise you could figure the angle from the leading edge sloping down to the trailing edge.  3 or 4 degrees of attack seem to be common angles.  I didn't put that into my blades but they seem to spin fine.  Providing an attack angle should improve performance.













Thats basically all this design needs aside from sanding out the grinder marks and a good finish sealer and/or paint.  There's plenty of improvements one could make to these blades.  Tapering towards the tip an rounding the edges could increase speed at the expense of torque.  If you do taper these make sure you plan it before you start carving the twist and airfoil.





But that's basically it.  Another "temporary" project that's still flying.

[hiker]

thats about the way i make my blades--heres a 2b4 and a 2by 6 blade...

[Running Blue]

Hey Hiker,

Nice pic, is that smaller blade walnut?  Really nice finish on it, I normally use plenty of paint to cover mine up!  Are these blades pictured for a 2 blade prop with that square hub?  I've been looking at adding more blades to mine, maybe a 6 or 8 blade to catch as much wind as I can.  Looks like your lumber is extra thick to start with.  I've been looking at doubling up a couple 2x6's to gain that thickness for a deeper angle at the root.  I've figured that 8 blades of 2x6's on a 48" diameter prop will cover 50% of the swept area.  Ought to give great torque to start up early, the real challenge will be in optimizing the airfoil and attack angle for higher speeds.  My gennies so far have been converted higher voltage industrial motors that put out charging voltage at lower speeds.  It'd be nice to take full advantage the gennie's higher output capability but I just don't have that kind of wind.

By the way, I've always enjoyed your wilderness shots.  They let a midwestern city boy like me dream of the great outdoors.

So many projects, so little time,

-Blue