Using CTUN.ThH to compare prop efficiency

I’ve been comparing props. I’m not unsatisfied with the props that came with my copter - but I’m curious about possible differences.

Today, I did two 10-minute loiter flights to test two different props. The difference in current consumption was pretty small - perhaps not outside the margin of error.

I got the idea to look at the CTUN.ThH graph - to see if there was a notable difference in throttle required to hover. There was - but other than seeing the difference, I really don’t know if it’s meaningful.

Would anyone have any thoughts on what such differences in throttle to hover might indicate about the props?

BTW - the props requiring less throttle to over also made an uncomfortable screeching sound - I’m guessing prop imbalance causing motor bearing noise. The props have spin-on hubs. (same style as the 3DR Solo) I’m not sure how to approach balancing them. I’d appreciate any suggestions - but I’ll google for answers as well.

Thank you!

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watching with interest Joe

Not sure I can give you a great answer on measuring prop efficiency (although measuring flight duration with the same battery and charge state would be a good clue).

I did create a topic on prop balancing that you may find of interest:

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Great video Yuri - Thanks!

I was thinking about the weight of the solvent issue all the way through your video - I’m glad you mentioned it.

My searches today found the “tape” method - and it seemed like the “flying off” issue might be a concern. Perhaps less so on larger props that turn slower.

Acetone based paint (nail polish) on sanded plastic prop blades seems like an issue only if the plastic won’t handle the acetone. I imagine some latex house paint might be an option.

I did find both the balancer you’re using - and the appropriate threaded rods required for the spin on props to use as spindles - both on order via eBay.

I did do a duration per discharge calculation - the Master Airscrew props, that require less throttle to hover, will loiter for 4.71 minutes per amp-hour. The stock props flew 4.52 minutes per amp-hour. So that’s consistent with the Master Airscrew prop requiring less throttle to hover.

Once I get these props properly balanced, I’ll test them all over again. But the difference in performance is so minimal, I’m thinking either set will work out the same on any given mission.

Once again - many thanks for your helpfulness! Got any links to your videos of your autonomous lawn mower?

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I’ve also got those Master Airscrew props on my EDU-450. I haven’t gone through the same calculations you have, but anecdotally I’d agree the flight times are better and yes they are noisy. The vibration levels are low, in fact I think they are even lower than my original blades, but that sound is not great.

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Thanks Allister - I appreciate the extra input! I wouldn’t worry about the noise so much if I hadn’t noticed that the motors also seemed warmer than normal. I’ve ordered the gear I need to balance these spin-on props. I’ll sleep better once I know they’re balanced!

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We have a great deal of natural cooling here (and more to come over the next few months), so I haven’t noticed the motors getting warm. I have checked.

If the props are out of balance there should be a vibration issue and I’m not seeing that in the logs. One thing I noticed was it seemed like the molds for the props are old. The edges aren’t crisp. There was little bits of plastic left over from manufacture. I cleaned up a lot of that and it helped, but the props come to a pretty thin trailing edge so I didn’t get too aggressive. That said, if you do find a balance issue I’ll probably check mine just to be sure.


Admittedly I have little multicopter experience, but the Master Airscrew props I used on my Copter build exceeded expectations. Again, anecdotally, you’d be hard pressed to find better performing props at that price point.

My YouTube channel has plenty of autonomous mower content.

Interesting question regarding hover throttle. I think this parameter first of all shows in what part of its power band your copter is.

If the system is kept identical, same KV motors, same type and pitch prop, just bigger prop diameter, this would reduce hover throttle and the later setup would usually be more efficient.

Lower in the power band ecalc indicates motors to be less efficient, however prop diameter seems to be the main driver of efficiency and would outweigh this in most cases.

However, it is easy to imagine a larger prop, giving more lift, therefore reducing hover throttle, but actually drawing more amps at hover due to other design issues of the prop, for example energy that is wasted due to an inferior prop-tip design and resulting parasitic turbulences.

Another example is 2-blade vs. 3-blade prop, where the 3-blade could easily require lower hover throttle, while being less efficient.

So I would not think hover throttle is a reliable indicator of efficiency. The small flight time difference and relatively large hover throttle difference during your tests also indicate a rather random correlation.

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Thank you Snakeeater - your comments align well with my suspicions - which are considerably less well informed. The only variables in my two test flights were the props. Everything else was constant.

Interesting about 3-blade props. Multi blade props on full scale aircraft - and FPV racing quads - are used to improve efficiency. So I assumed a 3-blade prop might work better on my copter. But when I tested a 3-blade prop - I didn’t find this to be the case - and it introduced other problems.

Now - if I can only find a 10x4.5 carbon fiber 2-blade prop…

Thank you for your comments - I appreciate them!

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Did you ever try APC props?

APC Propellers | Quality Propellers that are Competition Proven

I’ve used them a bunch on my planes. They’re good for that. Pretty rugged and seem to run smooth. The only issue I’ve had was with their folding hub design. But I’ve never tried them on a multi rotor.

They make regular non folding as well:
Multi-Copters/Drones Archives - APC Propellers