The Carbon Fiber Construction Of Large Propellers

Props for your little RC airplane or drone are effectively consumables. They’re made of plastic, they’re cheap, and you’re going to break a lot of them. When you start swinging something larger than 12 inches or so, things start getting expensive. If you’re building gigantic octocopters or big RC planes, those props start adding up. You might not think you can build your own gigantic carbon fiber propellers, but [Tech Ingredients] is here to prove you wrong with an incredible video demonstration of the construction of large propellers

The key ideas behind the build are laid out in a video demonstration for building a single prop. The base begins with a CNC wire cut foam air foil. This foam airfoil is first modified for the attachment point by cutting a plug out of the root of the airfoil which is filled with epoxy.

With the skeleton of the airfoil complete, the build then moves on to laminating the foam core with carbon fiber. The epoxy itself is West Systems Pro-Set laminating epoxy, although we suspect the ubiquitous West Systems epoxy used for all those live-edge ‘river’ coffee tables will also work as well. This epoxy is spread out on a table, the carbon fiber laid over it, and a second layer of carbon fiber (check ‘yo biases!) laid over that. This is wrapped around the foam core, then cured with an electric heating pad.

Of course, this is only a demonstration of making a single blade for a prop. The next trick is turning that single blade into a propeller. This is done with a cleverly machined hub, attached through that epoxy plug placed in the foam core. The results are just as good as any large prop you could buy, and this has the added benefit of being something you made, not bought.

This is really a master class in composite construction, and well worth an hour’s of YouTube viewing. You can check out the intro video below.

11 thoughts on “The Carbon Fiber Construction Of Large Propellers

  1. Good and detailed outline of a working process if one is avoiding vacuum bagging.
    (being picky: he could have been more generous in filling the voids when using the excess epoxy (or added some spheres to the extra at that point); and again more generous when doing the fill coat)

    Testing the props: nice way to have A vs B data, but… the tests show them pulling still air through the props. As a prop, it’s not that same as real-world performance when the thrust is pulling a machine through the air. However, as a hovering drone with a prop working as a rotor… I don’t know. Could be perfectly valid for that.

    1. As long as you’re moving relatively slowly (i.e., a fraction of the speed of the blown air), the rotors on a multi-copter are essentially operating in still air, so his bench test is a reasonable approximation to the environment in which they will operate. This is why he can come up with 8% as the ideal pitch. The same most definitely does not apply to props in moving air, such as on a fixed-wing airplane, where the ideal pitch varies with airspeed.

  2. On fixed wings I have used end-grain hard balsa plugs, recessed a bit so the head of the bolt will be below the top surface of the wing. The plug needn’t be so wide, maybe 1/2 to 3/4 inch in diam depending on the bolt diam. 1/4-20 nylon bolts have worked well in my 2-meter hot-liner sailplanes with these plugs. I’ve not tried this it on rotating wings, though, so interesting adaptation here.

  3. “With the skeleton of the airfoil complete, the build then moves on to laminating the foam core with carbon fiber. The epoxy itself is West Systems Pro-Set laminating epoxy, although we suspect the ubiquitous West Systems epoxy used for all those live-edge ‘river’ coffee tables will also work as well.”

    For the record the Tg of West System epoxy is much much lower than that of the Pro-Set epoxy, same manufacturer but pretty substantially different products. On a hot day in the desert West System epoxy will get pretty soft. West System for boats (and furniture) Pro-Set for aircraft

    1. Depends on the airfoil and the Reynolds Number.
      What’s optimum for a small (light) drone vs. a larger (heavier) drone, and blade air speed (inboard through outboard)?

      I have a hard time believing that such a simple airfoil with the same angle of attack inboard to outboard will be anywhere near optimum.

      1. It’s not an optimum propeller. But the losses from a good but sub-optimal propeller can be compensated for with reduced weight and larger diameter. Meanwhile the home-made solution is also quieter and trades more build time for lower cost so can be a better solution for a hobbyist.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.