A Can Prop for NoCals

Everyone knows about Plastic Props.  Many people know about carved wood props.  There is another type of prop that you can make that is a) light weight and b) effective.  I call these “Can Props” because they are formed on a can.

I have experimented off and on with these for years – and they still challenge me (probably because I don’t do them enough).  These are often seen on indoor models (Limited Penny Plane), but also some of the top scale modelers make these for their large models (Free Flight, of course).

A couple years ago, I did my Cessna Turbo 195 and asked Don Slusarczyk what to use for a prop and he suggested a 10″ diameter 15″ pitch prop and gave me instructions on how to make it.  It wasn’t too hard to make (wet formed balsa) and it works great.  Later I asked him what kind of similar prop to use for an Embryo and the pattern he recommended (7″ diameter 15″ pitch) worked well again.  Of course, matching the rubber to the prop is essential.

So I started to make this prop for a WWII NoCal where the prop diameter is limited to 7″ by rule.  I finished this prop to be used on my B.A.T. Monoplane Dimer, but was told to check the rules (one piece props only for Dimers!)

Regardless of what I put it on, here is a short segment on how I built it.

This is my first attempt on the prop for the Cessna.  Don provided the design for the fixture to set 15″ pitch.  Note the bracket at the hub to hold the prop spar (1/16″ dowel).  Also, this initial prop used an aluminum hub whereas the second Cessna prop used a one-piece spar.

For this new prop, I laid out the prop design on a plastic cup.  This is 18 degrees off vertical.  This cup is my Template – I take a second cup and slip it over this and trace the pattern on the second cup.  In that way, I do not have to continually lay out the design on a cup.

I use these cups from Walmart.  They are small.  This bag of 80 cups cost about $4.

Here is a single blade set up in a new fixture that was based on the old fixture but was designed for a fatter aluminum tube hub.  The hub was drilled for 1/32″ wire and that wire slips into a vertical tube to positively prevent rotation.  More in the next photo.

This is the back side of the same blade.  I used standard round toothpick as the primary spar.  Rather than cut the blade to fit the spar, I sanded a flat on the spar and glued it to the blade.  This method necessitated a tubing hub as shown.  The blade was very flexible, so I added a 1/32″x1/16″ stiffener to the back side of the blade.  I sanded it thinner.  The toothpick spar is being glued into the aluminum tubing with Canopy Glue.

Gluing to the cup/blade is nearly impossible, but Loctite makes a product that primes the plastic.  There is science behind this, but I won’t attempt to explain it – just know that this works.  The “Activator” is the key – I am pretty sure the glue is just CA.  Without this glue, I couldn’t glue the toothpick or the stiffener to the blade.

The finished prop comes in under 1 gram.  By the way, that is just flat black Design Master sprayed on the blades.  I haven’t yet tried this prop on any plane, but am confident that it will work for indoor models.  I anticipate having to match rubber to the prop and maybe trimming some of the prop away.

 

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1 Response to A Can Prop for NoCals

  1. LR says:

    There’s an Excel spreadsheet (maybe more than one) for optimizing this sort of prop. Info here:
    http://dcmaxecuter.org/building_tips.shtml

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