Auto Feathering Rubber Band Propeller

Welcome to my first upload!

This variable-pitch propeller was inspired by a comment from my grandad while we were building a rubber band-powered Spitfire (1/20 scale – specifically this one: Sky High RC Spitfire XIV Kit). He wondered aloud, “I wonder if you could make one that could change pitch?” – and so, this project was born.

The propeller is based around a 38mm hub and designed for 1/20th scale aircraft. It incorporates two slots for compression springs which serve dual purposes: returning the blades to a feathered, low-drag position, and providing counteracting force during the flight profile. Think of it as a dual-rate spring system – one spring enables the transition from fine to coarse pitch, and the other completes the move to full feather. You’ll need to tune this according to your rubber band’s tension.

I used springs from this assorted set: Amazon Spring Assortment – specifically the 0.5/6/10mm springs. One was widened slightly to fit around the base plate shaft, and the other sits on the back plate shaft between the pitch and drive collar.

At 100% print scale, the parts have a very tight fit. You’ll likely need to sand components to achieve smooth operation. If you’d prefer easier assembly and don’t mind a slightly looser fit, try scaling down the propeller blades by 2–5%, and scaling up the pitch and drive collar by 2–5% in your slicer.

From my experience, cycling the mechanism through its full range of motion 20–50 times dry helps bed everything in. Afterwards, lubricate the components – I used petroleum jelly, but any PLA-safe lubricant should work fine.

The drive shaft I used is available here: Free Flight Propshaft – Vintage Model Company. Make sure to bend the end into a tang at as close to 90° as possible. If it’s off-angle, the pitch/drive collar can bind and prevent the automatic feathering from functioning properly.

One accidental feature is that if you twist the blades past their normal fine pitch, the base plate will pop out. Additionally, the clip holes in the Spinner can be used as view windows to check for correct engagement of the blade dogs into the pitch collar prior to fully seating the base plate.

The blade pitch dogs are an interference fit on the radial axis to ensure tight and symmetrical movement. You’ll likely need to file the chamfer on the dogs until the blade can reach the full feathered position. A small bump in the spinner-blade interface prevents the blades from over-centring.

Note: The blade profile has been done mostly by eye and is not yet optimised. Feel free to remix and improve it – here’s the Onshape link to the full model.

The Spitfire is still under construction, but I’ve tested this propeller on a simple foam sheet plane. I haven’t done like-for-like performance comparisons yet – so for now, consider this experimental.

I'd like to see people Prints, Experiments and Tests. I currently consider this a BETA 

Auto Feather Demonstration

Auto Feather Demonstration 

Dismantling Demonstration