Quiet propellers

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Phil, I almost posted that! It should be interesting. E-props should play with the design…it might give them an idea.
Bill

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They look cool too😄

Awesome news! This technology also claimed to see an increase in thrust fire a given power level! Which is fantastic given it could promise to increase range while also being quiet.

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That’s what I was thinking too. Increase range for electric that really needs it, and increase fuel efficiency for those on 2 stroke, and… reduce noise, count me in. Hopefully we can generate some noise around this. Probably a bit heavier but it seems the benefit will outweigh the weight increase. Did anyone contact E-PPG? They probably know but would hurt to help propel the topic.

If they were on an X4, it probably wouldn’t fold down without removing them, but still I would
love to get a set of these.

E-Props response:
In fact… Toroidal Propellers are not new.
This “invention” was already patented in 1932. :smile:

Thanks to MIT for re-confirming that when you put more blades on a propeller and make it rotate slower, it makes less noise !

Connecting the blade tips together doesn’t do much, and mechanically, it’s almost impossible on propellers that actually pass power.

It is really not interesting for paramotors - sorry for that.

Connecting the blade tips together does at least three things: 1) it reduces tip vibration, 2) It turns two short blades into one long blade, 3) It prevents tip vortices from the prop tips. These are all beneficial to reducing noise, which would be the most important factor to me (and should be for any PPG pilot). Noise is also the single most important factor to us continuing to fly with the freedom we enjoy in today’s world. I see a lot of “won’t work” posts all over the PPG world, but the fact is that there are still significant advances that can be made even in established technology.

There is no doubt that manufacturing is the primary reason for E-Props response. They simply are not tooled for such a departure from their current manufacturing process. Manufacturing is a challenge. The props would be significantly more expensive. Developing the process to produce robust toroidal props in our scale would be a risk for any established company. That said, it will be done, and it will be significant when it is.

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I agree
Aluminum casting should not be too costly. Most of the money is in the reusable mold.
Possibly 3D printed if we can make stronger materials, CF embedded nylon wont cut it,I think🤣.
Cheers

just in this context: don’t let petrol ppg people ( most in facebook) confuse you…

the fact is: a modern eppg only needs around 4 kilowatts when cruising (38 km/h and 120-135 kg total mass).
10 kilowatts of starting power is perfectly sufficient if you use a 140 cm / 3-blade propeller.

thermals eppg need about 3 kilowatts to search for thermals or a maximum of 7 kilowatts to climb well.

On the other hand, oldscholl petrol ppg with 125 - 130 cm 2 blade propellers need around 6-7 kilowatts in cruise flight and around 12-14 kilowatts to take off safely and easily.

That means you can achieve a lot just by adjusting the propeller size, number of blades and speed. it is only rarely done in the gasoline ppg scene, with the exception of the xc, pylon experts have been working with optimizations for a long time.

to think that a toroidal propeller shape, is a game changer für ppg and eppg … purely the total surface would make up more than 20% of the total area of the circle. Areas of 5-10% are efficient, depending on the speed and desired pitch speed or cruising speed. the induced drag of modern propellers such as e-props is extremely low today. using small micro copters as an experiment for toroidal is nice, but extremely far from meaningful research. in the air mass movement as soon as it gets much bigger other laws apply. in ship traffic, we now know that only a very small type of boat can use it sensibly, even only in a very specific speed range. when flying eppg you need a large range of 30-60% power and 80-100% for take-off.

Finally, in general: projects of rc flight models or drones are often used as a comparison to eppg.

at eppg you usually have a total weight of over 100 kg because you have the pilot with you…

if you were to build an rc flight model so large that it weighed a total of 100 kg, it would also need a drive like eppg.

therefore, often hearing “my rc model with an 8 kilowatt motor is extremely powerful” is meaningless in the context of eppg because the model usually weighs less than 20 kilograms.

i have been flying rc models for over 35 years and eppg for 10 years. they are 2 completely different worlds.

I admit that I am a petrol pilot. My understanding though is that eppg has the same problem that the noise annoys non-pilots on the ground. All noise is a waste product from an inefficiency of some sort. eppg still has the same problem that there are tip vibrations and tip vortices on the propeller tips. This causes noise, and it is possible to design a propeller in a way that reduces these noise sources.

For the record, I do not think the toroidal designs shown by MIT or shown in historical patents would work optimally for PPG. I do think that a CFD-designed 4 blade prop with joined tips has a lot of merit in our domain and has a lot of potential to reduce noise … petrol or electric.

Current PPG props have a lot of optimization potential.

I mostly agree with you.

what i would like to mention is the fact that there is a very large number of eppg concepts that have known for over 10 years how to reduce noise very well and increase performance overall.

Systems that only have a maximum propeller speed of around 2100 at take-off and fly at around 1500 rpm when cruising are extremely quiet and yet powerful because the pitch speed matches the airspeed very well.

with petrol ppg, over 2500 rpm can often be “heard” extremely clearly when starting.

if you are familiar with blade tip speed and frictional resistance, you will immediately recognize what it is all about. martin hepperle presented this graphically in an easily understandable way a decade ago. I’ve linked this quite often, so I’m deliberately not doing it here anymore.

the air centrifugal effect also occurs less with a significantly lower speed. measurements with smoke and slow-motion cam have shown me the edge curve differences. That’s why I only use propellers that are ground to almost zero at the tips, like the speed models in the competition. the trailing edge also has a constant 0.3 mm. however, this is only possible in individual production with prepreg cfk. series propellers cannot be designed in this way since most customers handle the material very roughly.

the most important point when it comes to noise is still the turbulent air of the pilot and frame etc. it is only possible to fly extremely quietly by using spacers. the pipes etc. should also be streamlined and not round.

if you do all this, you can fly extremely quietly and efficiently if you want to. (you don’t have to).

the shape towards the rear is also very important. a standard ppg is like a school bus. a pod harness with an optimized form at the rear can be seen like a porsche with a drag coefficient.

it’s not just theory, me and a few other pilots have been implementing these options for many years. it is therefore clearly documented both in noise measurements and telemetry of the performance data.

Interesting stuff.

Actually, these 8 blade seem more promising.

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found this explains things better:

We used to fly with bent blade tips in the early day of the activity (90’s). If you freeze video at 0:14 take a look at my propeller tips😃 Early Paramotor Days in the US. - YouTube

You stopped using them, so were they not really worth the effort?
Too costly?
Were they very much quieter?
Thanks in advance. Sorry for all the dummy questions.

It was a Japanese PPG and the company (DK), closed shop after a couple years. They were ahead of their time and the activity was in its infancy. The propellers were called “Whisper props” and the sound generated by the tips was more rounded/muffled. Nobody knew much about those designs except the manufacturer and nobody really cared then as long as we could get off he ground😆
The story reads roughly that way: DK still exist but is not involved into the PPG business anymore. They were the inventor of the Karaoke system found in clubs and bars. They sold the factory leftover Paramotor parts to a UK businessman who basically used the DK design as a base for his own product. The company is Parajet.
I asked DK to come to the US. at the time and I became their representative for a short while. They had a few importers after me and finally called it quit.
Here’s a video of myself in Florida where I flew the first DK “Wisper” in the US. In this case “Whisper” was the name of the machine not the propellor. My small PPG was called the DK “Beat” and had the "Whisper Props).
The guy at the beginning with the white T-shirt in the video was I believe the last US. DK importer. DK was manufacturing its own wings as well. The gliders at the time were pretty lousy at best compared to today’s but the fun and excitement was the same😃

In the next video section (white T-shirt an pink helmet), I was flying my DK “Beat” in New Jersey whee I was teaching PG/PPG to my students. The wing designs had already improved - was under an ITV entry level model rated ACPUL-A if I recall correctly (the EN certification had not been put together yet). There were no PPG wings at the time. Everyone was Paramotoring with free-flying Paragliders. Actually, most PG gliders today can be flown as is with a motor. To obtain the DGAC certification, all the manufacturers have to do is add risers with trimmers and pass the DGAC flight tests. I just got a BGD “EPIC2 Motor” a few weeks ago and some of my PG studends have the exact same wing but only has the EN-B certification because their gliders do not have risers with trims. The motor risers are slightly fatter/wider. When I fly the cliffs free-flying all I have to do is keep the riser links at the same level (PG default setting for most wings worldwide), that’s all.

I dragged my DK “Beat” all over place. In the Mexico section of the video you will see a couple guys with the"Beat" as well. I was the Dude with the funky suit and Star Wars helmet😄 We all had high shoulder attachment points and the torque effect was not felt much.

The end of the video was one machine I built and still is to date, the lightest Paramotor ever flown. Split “A” risers had not yet been invented to pull “Ears” - we had to grab the outside “A” lines as high as possible and yank them down. I was the only one who could do that with a motor because the risers were connected directly to the Paragliding harness - the real thing! Nowadays, the geometry is totally different to compensate for the weight of the motor😫 My “Bug” (name I gave to the motor) was light enough to use standard PG harness connections without tilting backwards and having the thrust pointing to the seagulls. I also had a dorsal reserve parachute container, and a fleet of safety feature part of the harness made by SUPAIR.
BTW, the ubiquitous low side bars riser attachment points everyone worldwide uses now had not been invented yet and everyone was flying with high riser connection points which minimized greatly the torque effect and increased stability. The sown side was that the PPG was over stable and not as fun if you liked to pull heavier turns. Actually, many new PPG pilots should be using high riser connection points for peace of mind but it is impossible to find machines made that way anymore, except for trikes.

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Wow, that is interesting. Thank you for the cool story.

(Actually, many new PPG pilots should be using high riser connection points for peace of mind but it is impossible to find machines made that way anymore, except for trikes.)

Hmmm, doesn’t Nirvana still make machines like that? Or is that different again?

Maybe they do have higher connections but they would be one of the few if there are any others. We used to fly with “J” canes - called “J” canes because they looked like the letter “J” upside down.
If you enlarge the photo from the Cradle Of Aviation on Long Island, New York, you will be able to see the “J” canes over the dummy’s shoulders and where the risers were connecting to the frame. The machine was 82lbs dry and had a Japanese Zenoah general purpose two stroke motor. The propeller was inside a protective cage. The guy who built this thing, copied the original French version from the company LaMouette which was using a different motor at the time.

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