E-Props seem to be the new rage

The E-Prop folks seem to be very set on what they want the WOT rpm to be.

A 912UL with the new 3 Blade e-Prop is powering my 1991 RANS S-12.

Because I have a first generation 912UL, the prop flange holes did not mate with the e-Prop I bought. They had a solution that worked fine. It is a combination drill block and plate called the ADU-4. The only problem with that was that it was required for me to source six prop lugs. That was quite a job but I got the steel lugs from Warp Drive and then a Good Buddy of mine machined them to proper length and removed the threads. (NOTE: The guys at Warp Drive were extremely helpful even though I wasn't buying their prop).

After getting all the details accomplished I finally dialed in the pitch e-Prop suggested and it was RIGHT ON. 

First flight was 13 August 22 and through 20 Oct 22 (76 days) I logged 30 hours on the new prop. My gearbox ratio is 1:2.27. Here are some of my observations:

1. Definitely seems quieter. I say "seems" because I did extensive noise monitoring with a Decibel Meter I bought. I did these tests with the 75" 2 Blade prop at a variety of RPMs and then replicated the same dB monitoring profile with the new 3 Blade e-Prop. Basically the dB Meter registered the same noise levels for the e-Prop as the 75" incher and in one or two spots even showed HIGHER dB. But there is no doubt to the human ear the noise is lower. It is lower in the cockpit and lower to bystanders on the ground. At idle, I can actually hear the gears in gear box. I won't go into all the dynamics of this because there is another guy on Rotax-Owner who posted the results of noise level experiments the Army did for helicopter tail rotors. Read that because I think it is right on.

2. Unexpectedly, I received a dramatic increase in efficiency. Here's what I mean. My typical cruise in the S-12 with the 2 Blade was to set the engine to 5100 rpm which would yield about 80 mph. After installing the 3 Blade e-Prop that same RPM setting (5100) gets me 87 to 89 mph. Climb seems pretty much the same.I made sure not to change any other instrument or engine factors during this process. So, I think the increased cruise performance is valid. That's ~10% better. The throttle response is so much smoother, too. It feels like a turbine. It really changed the character of the aircraft. I think you can tell I am extremely impressed.