The most efficient propeller | Less blades is better?

Support my work / pawelspychalski
Why two bladed propellers are more efficient that 3 or 4 bladed ones? And why can't we have a propeller with only one blade? After all, it should be the most efficient one, right?

[@SbangFPV]

4:09 So, Drag caused by the vortexes > Thrust generated by the blade? I noticed it yesterday on my 7” Ruxus. My Tri-blade was hovering at 20% throttle whereas when I switched to Bi-blade, hover thrust went up to 30-31%.

[@MCsCreations]

Great explanation, Pawel! Thanks! 😊 Stay safe there with your family! 🖖😊

[@minaexperiment]

Good explanation. I tried some APC 7x5 on my Apex instead of the HQ 7x4x3 and they seem a little more efficent but more vibration. One plus is that they have less drag so the wind did not affect my quad nearly as much but it also does not corner as good. I would like to try the 7x6 but i cant find a store in EU that has both the E and EP versions. Shipping from APC is like $30 not including taxes! so not worth it unless ordering bulk.

[@Vousie]

I've been using Gemfan 7042 bi-blades on my quad. I have only used these so far though so I don't know how they compare... I have been wanting to try out some tri-blade props though.

[@minaexperiment]

@@Vousie The gemfan biblades are good as long as the quad is not too heavy or have high kv motors as they are pretty flexy so they flutter when pushed hard. Gemfan tris are one of the most efficent triblades for 6" and 7" atleast. APC biblades are very stiff so they feel very nice in the air but made of nylon so they will break on impact. Not good for close quarters freestyle but nice for freestyle in the open and cruising.

[@Vousie]

@@minaexperiment Thanks. How would I tell if the blades are fluttering?

[@minaexperiment]

@@Vousie The sound when they flatten out will not be like the usual clean prop sound, they will sound "bad". I never tried it but read on youtube ppl who tried the gemfan 2 and 3-blade and said that the 2-blade was too bendy with powerful quad. The blades flatten out at high throttle, loosing thrust and making awful sound. If they work for you then its no problem but if you notice they make a bad sound on punchouts and high throttle situations i would consider the the gemfan 3-blade. They are very good.

[@Vousie]

@@minaexperiment Thanks.

[@raptor8177]

Thank you . This information was welcome

[@FPVUniversity]

You are very welcome

[@BBFPV]

How is your counter rotating quad? It should improve the efficient

[@lcprivatepilot1969]

I want very much to add a 3-blade prop to a 125-HP Piper Tomahawk, for 2 primary reasons … ramp appeal/novelty of having one on a Tomahawk and reduced prop noise.

[@pzukowski1001]

Hi why did WW2 planes have these gigantic 3 and 4 blade propellers? Is it because of the low RPM of the engines?

[@FPVUniversity]

Physics. If you have torque to spare, you have to have more prop to push the air. So you either make it bigger in diameter or add more blades.

[@KAKA-qh5ql]

Is flight efficiency better if the air is hot or cold?

[@FPVUniversity]

I believe it's higher in colder air but don't quote me on that

[@admiralgoodboy]

Do ringed propellers cancel out such vortex's?

[@Riketta]

What about 1-blade propellers in RC-modelling? We have less forces to break fastening of propeller or engine shaft. Might it be better for long range FPV for example?

[@FPVUniversity]

I don't think that's a good idea and it's complicated and very precise thing. And still, thrust vector not bein coaxial to the shaft will cause problems.

[@brezovprut4431]

What about EDF's? If EDF trades efficiency for its size (using lots of blades to get enough thrust in small form factor), can proper duct design compensate that penalty at least to be 80-90% efficient from non-ducted props?

[@FPVUniversity]

That's the whole idea of the duct: if duck walls are close enough to the propeller tip, then voxtex will not form, or vortex size (and energy sucked by it) will be reduced. This is why EDF fan blades have completely different shape

[@frankyfrench5279]

and on multirotor were blade speed is changed in control loop, the prop with least mass to accelerate and decellerate should also be more efficient than heavy prop, were more energy is wasted in breaking accelerating.

[@FPVUniversity]

Yes, but to be precise, it's not about mass but the moment of inertia

[@scotthealey1887]

if wing tips have winglets to reduce the vortices, why dont propeller tips and winglets?

[@FPVUniversity]

Some have. There is a problem with propeller winglets: centrifugal force would deform them if they are of any meaningful size

[@papagamersother5814]

Winglets help reduce induced drag on a wing, as props have a high aspect ratio the induced drag is negligible, that why you don’t see gliders with winglets (so often), same happens with props, the have a high aspect-ratio, there are a few engines with options for props with “small” Winglets (that to be honest, look like they have been bent or scraped), as mentioned, if they are to be anything useful they would have to be bigger, causing other issue s such as deformation… hope this helps.

[@divingfalconfpv4602]

Great video. Love the info.. For the biblade or tris more efficient. I always tell people it depends. Test them.. I have one drone the tris seem more efficient to equal across whole throttle range in testing. Other drones where bi more efficient. AnOther bi or tri depending weight and how fast I'm flying. If I'm cruise at 50mph the bi seem to edge out tri. I think if going slow my tri usually do better and going faster bi seem to win. So depends.. 🤣

[@papagamersother5814]

Good explanation, now I have a question for you. Considering the drag caused by the Leading edge and the drag caused by the material itself. The propellers are finished and coated in order to have a smooth surface, agreed? Yes. Now there is a Propeller from HQprops, model Skitzo 51433, the Part the blade (upper) that produces the Lift is smooth, the lower part is porous, like you feel the “sandy” feeling. Would that reduce efficiency? Cause again, that will not make the “fluid” (air) flow as it should to reach the trailing edge in a uniform manner, and yes might be disturbed by the porous surface. Does that affect the efficiency?

[@cedricgrandseigne]

that's funny, in the industry, you do the exact opposite: after a certain speed, air is detaching from the extrados (upper part) generating turbulence. to delay this detachement, you create micro turbulence thanks to roughness that will suck back the air on the extrados. done right, it reduces drag, and increases efficiency, but to be clear, the "roughness" size depends on the speed (Reynolds number to be precised), so roughness would have to evolve along the span of the propeller as the root is at low speed, while the tip is at very high speed.

[@papagamersother5814]

@@cedricgrandseigne very knowledgeable, So this specific propeller that I mentioned, The Skitzo, with the Intrados “sandy” is indeed somehow more efficient. Amazing explanation, thanks!!! When I first touched it, I thought that would be an issue, as of my understanding was that the more smooth the blade was, the less drag, the more efficient. Thanks for your explanation.

[@FPVUniversity]

The thing with fluid dynamics is that "common sense" does not always work with them. We have no idea if that increases drag without being able to compare with "smooth" version.

[@cedricgrandseigne]

@@papagamersother5814 I don't know what they had in mind, but I'd say it's not very useful on the intrados in term of drag, there's much more to gain on the extrados. it won't be a problem either ;-)

[@marcbjorg4823]

Anyone that tells you that a two blade propeller is more efficient than a multi blade propeller needs a shrik

[@tedarcher9120]

It is more efficient. Problem is that it has to be twice as long which is often not possible

[@BrainDeadEngineering]

So agree with this ! 2 blade is superior!

[@ourchannel8215]

yes...im try using 2 prop 6045 can fly 7minit,6055 prop just 2minit 😅

[@mihdd]

The need of a counter weight does not sound very efficient. I am not convinced this time.

[@prophetsnake]

Fewer. The word is fewer.

[@FPVUniversity]

That's great! Thanks

[@andriy1000]

No, it didn't