What difference does a stiffer prop make?

Hi Everyone -

Yesterday I was doing some bench testing with the Multistar Viking 2208 2600 Kv motor, and by mistake made an interesting discovery😏  You can read more about that testing on this blog post.

One of the props I tested was the 6x4 KMP prop which I discovered sometimes have a bit of a quality control issue which I wrote about in this blog post.

Essentially, here are pictures of the two props when I bent them, first the bad prop.

This is the good prop, I had to push on the hub to get it to bend this much, so it is the stiffness it is supposed to be😊 

As I was doing the testing, I saw the "bad" prop laying on my very clean, well organized work bench...NOT!!!😬😳😵, anyway, I assumed it was the good prop and put it on and did a test.  Then as I as changing it out for another prop, I was surprised how flexible it was and realized my error.  I dug the good prop out of my flight box where I had left it after some field testing and put that on and retested that😉  These numbers are using the Turnigy AE-45A ESC with custom settings of 22.5 degrees timing and 24 KHz of PWM (pulse width modulation) frequency on 3S.

"bad" prop results

50% throttle - 17.6A/216W producing 555 gr/19.6 oz of thrust;

100% throttle - 38.4A/434.3W producing 955 gr/33.7 oz of thrust.

"good" prop results

50% throttle - 15.2A/184.4W producing 585 gr/20.6 oz of thrust;

100% throttle - 36.7A/428.1W producing 1065 gr/37.6 oz of thrust.

I had always known that more flexible props were inefficient, but due to my error and having received on bad prop from Banggood, I am now able to see clearly the difference as these props are identical other than their stiffness.  It is fairly easy to see that the flex in the prop not only produces less thrust, but causes the system to work much harder by drawing more amps to produce this thrust.  Then as the throttle setting/RPM get higher, there is an even larger difference in results.

Over time as I have experimented with props, the stiffer the prop normally results in better power and efficiency as well as a prop that runs more quietly, but nice to see numbers that back that up😊

Park Jet noise...the "other" sound of freedom😎

Cheers,

Scott