I've noticed it's very difficult to get accurate flight data for comparing different props, power systems, torque fins, etc., and their effects on efficiency. Even with the electric setup and the instant feedback in power consumption it provides, the weather variable makes getting useful data hard and confirming results that much harder, as there are only so many zero-wind days and even on the zero wing days with the sun set so there is seemingly no effect from thermals there is still a surprising amount of variability. I have found that day-to-day weather changes efficiency around 5-10%, and most changes in props and power systems, etc., only have around a 5% effect, so it can get lost in the noise. I've found myself on nice days testing something and getting a surprising result, then landing and running back to the shop to quickly swap out a part or grab a completely new setup with just the one variable different, and taking off again because at least the weather can't change too much in the 10 minutes between the two tests. So by the time the evening's over, I'll have 2 or 3 units out in the field that I have to take back to the shop. The point being, it's really hard to make the incremental changes of that 5% improvement here and there when weather changes make the noise floor so high.
With all my measurements I always did two flights 15 minutes apart. First with our standard prop and then immediately after with the prototype. Same engine, same glider, same conditions
Zip-line drones use a 3 bladed prop of different diameters to spectacularly reduce noise. I think this is the most important thing to grow paramotoring and the most likely end or reduction to the business. A sound test of a 2 blade prop with a 2 to 3cm radius difference should make balancing manageable.
Very interesting. I worked in R&D the cycling industry and love that Scout keep pushing the boundaries in efficiency through experimentation. The mk x prop with the softer elastomer is great for someone like myself who likes beach flying.
After flying 3 bladers for year, I flew 2 blades for the last 14 years, now my new 80" 3 blade E prop is SO much smoother....., on a plane but props are props.
Solid development effort. An exotic design I would like to see tested would be a hollow blade that has a port at the root that sucks messy air from there and ejects it at the tip in a way that will negate tip vortices or allow higher tip speeds.
Dji made something interesting with their props years ago, take a look at them. It’s a long blended winglet, Boeing 787 like… it even ends with a sharp tip. Those props are way quieter.
Hi Miro, I love your videos they are always very insightful. You are doing an amazing job of R N D in Paramotor. Keep up the great work. 😊. Hopefully one day we share the sky together. 🪂🛩️
I heard aircraft engineer said: winglet does really improve the wing efficiency, but only as well as a wing itself would do if it would be longer by half of the winglet length...
One-third of the length. Actually. Span has the greatest effect in reducing downwash. Because it acts on a larger volume of air. Picture a cylinder, diameter equal to span. Now imagine a longer span. How does the volume of the larger cylinder compare? A small change in span results in a large change in air mass deflected downward/a direction. Air mass being deflected generates the force that is lift/thrust. The more mass, the less velocity is required. Less change in velocity equals less angular deflection. So the wing does not generate as much downwash.
The loss of engine RPM with heat during climb with the fat chord blades would be caused by the exhaust heating up. The tuning of the exhaust on a two-stroke is dependent on the exhaust gas temperature because the speed of sound increases with increasing temperature, so the resonant frequency will probably increase. The other problem with operating right on the peak power point is that it is an unstable point because any increased load pushes you down the power curve rather than up which would be the case if you were operating beyond the peak power point. It's a negative feedback slope which generates the engine speed stability.
I wonder if its different in the US and Europe. Here in the US, 140cm props are the standard and probably 70% of new paramotors run it. 130 was the standard up until about 3 years ago and has been replacing the 125cm with a slow phase out starting ~15 years ago. Great work on the prop! I hope to try one some day!
Amazing Miro, truly amazing! You and your team just keep trying to make these incredible machines more efficient and fun. Thankyou for “failing 5 times to set scene 1” 😄 this is why I chose Scout! You guys are unreal 👌🏽
Again, another great educative video from Scout! It's Milo's dedication to teach people all about paramotor design that made me buy a Scout Enduro with Atom 80 engine. It's a pity that his vario-prop is not available for the Atom 80 😢
Use an electric drive system to help you evaluate props. You will be able to see extremely subtle variations and performance with high accuracy. Especially if the system will let you log volts, amps, RPMs, etc
I love to see what you tested/tried for our hobby and share with us all! Thank you so much!!! One question: Why not run full throttle at let's say 6800rpm instead of 8600? Same power, less rpm, less consumption, less heat, less stress on all parts?
I make props for FLPHG and i have found that a prop prop that has a pitch that is higher at the root and lower at the tip gives great performance. props i make are 54"dia root 23" and tip of 20" one thing i have noticed is that my prop pull air in from the tips and act like flat winglets.
Interesting video, goes to show that there's still prop re-thinking associated with very low speed flight. Almost no propeller expert has done exhaustive repeatable prop design work to fly at 25/30mph, perhaps RC prop design offers useful correlation. Experience leads me to state the following re powered para props; - longer props are more efficient than shorter props, almost w/o limit or exception - persistent prop tip speeds above .4 Mach, is annoyingly noisy - prop blade pitch exceeding 14deg@.75r results in thrust/drag tail chasing (under 12deg is preferable) - 3+ prop blades are theoretically advantageous in pusher apps where prop blade shading is significant; also more blades at finer pitch is preferable to more pitch on fewer blades.
Have you tested adding stators or flow straighteners behind the propeller? They are used in some hovercraft and airboat designs and claim increased thrust and efficiency. I could see how they could also help with paramotor frame rigidity. A con being increased weight but that may be offset with the gas savings.
No. They gained slightly less than 15% lower INDUCED drag by increasing the wingspan 30%. (They would have 41% greater efficiency from the same span increase, with a traditional elliptical lift distribution). What is remarkable, is their increased span (used inefficiently). does not increase the wing root (cantilever beam) bending-moment. Therefore the structural weight remains the same. So it's 15% better at the same weight. Not 15% better outright. Propellers cannot be made 30% larger in diameter. Diameter bogs down the engine and reduces power output. It also pushes the propeller tip speed supersonic. Which is loud. And relatively inefficient as well. The diameter is fixed at some ratio, or fraction, of mach 1.
@@EllipsisAircraft Dude, u have been reading too much technical literature. Decrease the induced drag of the prop and u can use that extra torque to create more thrust. Same diameter but greater pitch or chord. Noise will b reduced also, another energy gain. It is all about induced drag reduction, which is proportional to the lift coefficient. Those paramotor props operate at high alpha ie high lift coefficient. The induced drag is a big chunk of total prop drag, so the gains are greater. Redesign the prop, apply the Prandtl-D twist schedule and see what happens. Caveat: I did not design a prop or fly a paramotor.
@@donlawrence1428 At the same diameter, twisting the blade with additional washout INCREASES induced drag from the optimal. You have to increase diameter to attain any induced drag reduction. The (second, revised) Prandtl lift distribution is substantially LESS efficient at the same span.
You can use the large prop if you reverse the engine by placing it behind the prop so that the prop thrust blows on the engine. This will provide a lot more cooling. This is what we do in drones. This could be done by mounting the motor in front of the vehicle, or it could be mounted in back with the proper mounting structure, which would also reduce the sound for the pilot, since the thrust blows the sound away from the pilot. We are developing a full scale electric Blade Runner style flying car called the Sky Chaser. See our icon for project details.
You are going to NEED a variable pitch prop, to maintain full power, for maximum climb rate. Anything else is window dressing. As the engine heats up, and starts to lose power, the prop would de-pitch, and maintain peak power RPM. Having the pitch increase from there, as you reduce throttle, will get you SIGNIFICANT gains in fuel economy. You can use electronic systems which are similar to RC variable pitch system, or you could use an aerodynamically controlled system, like the Aeromatic prop, from decades past. The only thing it's REALLY missing, is altitude compensation. Ah. there it is. You're talking about your variomatic. That is only RPM dependent pitch, and it needs to have an aerodynamic (load) dependence, in order to hold the engine at peak power, instead of having to set the rpm above peak power rpm, to account for heat sag.
I forgot to mention, Bowers says it will reduce noise. The washout formula is used to reduce computer fan noise on the International Space station. It can be found here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-5SFGhojA-vI.html
I tried to have more efficiency on small quadcopters, only fixed pitch props available. Given the same diameter and number of blades, the only night and day factors seem to be the weight and the rigidity of the props. The lighter and more rigid it is the better. But first of all, the props must provide proper amount of lift for the weight.
Tried it all? But did you try the Prandtl washout twist? The claims are: less drag/torque, lower power consumption, and less noise. If you're still experimenting it would be interesting to see the results.
Look at the the work of Al Bowers (ret. NASA Armstrong Chief Scientist) on Pradtl wing; instead of elliptical lift, look at the bell-shaped lift profile of the 1933 Prandtl wing. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-bCwtcDNB15E.html The whole video is worthwhile, but this URL goes directly to his application of this work to propellers.
Have you thought about tubercles? I’ve seen some work with wind turbine blades replicating the tubercle structures on the forefins of a humpback whale…. Reduced noise and increased efficiency… I think it is something about reducing span wise flow and increasing vorticity to promote attachment. Could this be a number 11?
I fly an e-prop 3 blade 155 cm at 2000/2100 rpm, with an old hirth engine. many times quieter than the Polini with 150 prop and the Cosmos with 160 prop
Out of curiosity, in the classical props any reason why winglets design for propeller was not studied in your experiments? Technically there is a considerable noise and drag reduction. Checkout eVTOL propeller designs.
Very simply. Every time I did two measurements: new prototype and our standard prop as reference. Two flight 15 minutes apart. All variables the same (temperature, pressure, humidity, weight, same engine, same glider).
By annoying part I mean the typical 2 stroke engine sound of high and monotonous pitch. Most people do not mind white noise - it is similar to wind blowing trees. If you record the sound and do a spectral analysis maybe?
We have used an aerodynamically heavier propeller that stopped the fully open engine at 7500 rpm. With your prop at 7500 rpm the throttle is not fully open, that’s a different scenario
Every time I did two measurements: new prototype and our standard prop as reference. Two flight 15 minutes apart. All variables the same (temperature, pressure, humidity, weight, same engine, same glider).
This RU-vidr has tested a large number of designs of boat propellers. Including a Prandtl design which performs very well: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-kyjCwyfnrU8.html
14:29 bro there are so many uncontrolled variables in your experiment that it could be 20%+ better and your data might show a 20% decrease. I urge you to consider static testing, it’s at least a good starting point.
Every time I did two measurements: new prototype and our standard prop as reference. Two flight 15 minutes apart. All variables the same (temperature, pressure, humidity, weight, same engine, same glider).
Have you tried specifically a Prandtl foil? The Sikorsky looks by eye to be similar. But Prandtl propellers are known to be high efficient and low noise. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-w-dk1NpVNNI.html
@@SCOUTaviation Great. Al Bowers at NASA has done a lot of work on Prandtl wings. At 39 minutes he discusses Prandtl propellers: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-w-dk1NpVNNI.html He points out that most of the noise comes from the tip. And if you unload the tip it reduces the noise. And reduces the torque required for a given thrust. He quotes a 15.4% improvement, see the slide showing the graph.
2 comments, thus-far: 1. WHEN switching from a 2-blade prop to a 3-blade design, THEN one should be reducing the chord significantly, to keep the wetted-area similar? Also, at higher-altitudes, more-blades is apparently better, resisting loss-of-thrust as the air-density drops ( I don't know if you'd find that at 8,000' altitude, which is the safety-ceiling for no-supplemental-oxygen, ttbomk ) 2. the Darth Wader should have altered only 1 thing: 7800rpm max-power operating duration. It *should* have extended that. Nothing else that I can think-of.. --- Back to watching the video.. ( : --- "seconds to climb 100m" depends entirely on air-density, air-temperature, AND humidity! --- I don't understand why you weren't using a genetic-algorithm in OpenFOAM? Let IT find the optimal thickness/chord/pitch/distribution-of-force ( which should be elliptical? ) --- Ah, you've got the "toroidal propeller".. Please go watch videos on the Sharrow propeller: *nearly all* the noise from the normal prop is from cavitation! The Sharrow isn't cavitating: it's silent.
I just realized: The optimal-prop-diameter, in that context, is ergonomic: a 7' tall Dutch person could use a larger-diameter prop on their back than could a dwarf, right? Therefore, there ought be multiple prop-solutions, using a diameter powerlaw, so you fit the tallest people, the 5'9" average-men, the 5'4" average-women, & the 4'11" short women, & then each of them has a prop that works *for them*, & all get to fly with efficient props! _ /\ _
dumb idea that fan would need quite a few HP at 8,600 rpm . Make up a dummy hub / model aeroplane electric motor and you will see that the guy who recommended the extra cooling fan . obviously hasnt a clue .
have you considered a clutched (say) 2 meter diameter propeller along with a more regular size? The large propeller would be locked in the horizontal position during takeoff / landing, and the clutch would engage the larger prop at altitude.
@@turkeyphant two propellers. One clutched so that it does not spin during takeoff. You engage this while in the air (and potentially disengage the smaller one).
Hmmm. Sounds like you did not take into account the bad laminar flow, a Paramotor Prop is facing. You may not optimize prop design by conventional means. Rather, build a prop more robust against vortices. But I am afraid, that was impossible. Anyhow. You did nop see big improbevements with any of your designs. What did you expect? Conventional props work quite well in measn of efficiency, so any improvement must stay in the few per cent range. And that's what you did measure.
Dear Miro. I love your approach. You have refused to copy all other messing manufacturers, which copy one anothers, all doing the same gross mistakes. One only note about this video. I have introduced on my belt reduced nanotrike engine a customized increased reduction ratio matched with higher pitch. And my prop is spinning at max 2500 revs Min. I have achieved a level flight at a consistent lower rpms. You have mentioned the same test with 3.45 reduction ratio, and you have had no significant improvements in noise or fuel consumption. But you didn't say anything about climb ratio. Why?? According to my experience, you should have improved it. Isn't it? Kindly.
With every prop I measure max climb rate and cruise consumption. With the 3.45 I measured noise levels as well. Unfortunately, it did not perform better in any of these parameters
toroidal props have been around for decades, nothing new, they are a gimmick. the "efficiency" gains are not what people claim. people take the data from the paper out of context and make claims the paper does not support.
Thank you! People are so freaking gullible just because they look cool and they haven't seen it before. They think it must be new and amazing. No, all of these designs were explored heavily in the '40s and '50s and discarded because they were inferior to traditional designs
