Prop Spar Load Tests

Spar undergoing a 400 W equivalent load test

We tested the prop spars at 400 W load (our design climb power), and 800 W (close to maximum output -- we did not stress to 1000 W since we'll be gaining more strength from the stressed skin of the propeller).  We had two sets of prop spars with different weights, and the lighter ones were indeed more flexible, but withstood the test, so we'll be using those in our first propeller using this style of spar, in order to save some weight.

The prop is tested by putting water bottles onto the spar at regular intervals, with each having the equivalent weight to the predicted weight distribution for the prop load for that section of the prop (we divided it into 10 elements).

To give you a sense of scale, 300 W of thrust from the prop is about 36 Newtons (8 lbs, or 3.7 kg).  That is the predicted power for level cruise for DaSH v5 for the max weight (90 kg) pilot.  The higher loads scale linearly with that, so 800 W would be 96 Newtons (21.6 lbs or 9.8 kg).

An example of load distribution for a prop

(our current prop design is 175-14-400, but has similar load distribution)

(175-14-400 means it is designed for 175 RPM at 14 mph forward speed, and 400 W climb power)

Installing the prop hub clamping system for the load test

Clamping base in place to ensure a stable base

Adding weights to the prop spar

Adding the final weights for a test

Example of deflection for a 400 W test

400 W test

800 W test

Deflection for 800 W test

Note that actual deflection will be less than this on the real prop because we'll be gaining a lot of strength and stiffness from the fiberglass and carbon fiber (at root) skin covering of the foam prop.