Bob27

I had a prop strike once. I was running this electric system you see in the picture and like a noob I had no cage on it.(first big mistake) I stood it up outside(like how it is in the picture) I put my left hand up against the center intersection of the arms to prevent it from coming back on me, and I used my right hand to articulate the throttle. My intent was to just spin up the 4 motors at ~5% throttle to make sure everything was working. My initial throttle was a bit more than I intended or was prepared for. The unit started to come back on me and in the confusion I accidentally increased the throttle from my initial ~20% up to about 50 or 60%.(65+ lbs thrust). From my perspective the top right propeller impact my right hand, except it slipped right between my ring finger and pinky finger impacting the overbuilt 3d printed throttle. Thisdistributed the force of the strike over my palm. The force was still so hard that my entire palm was slightly swollen for the next week and bruised for a while afterwards. On top of the throttle taking the impact, the prop strike also disconnected the electric throttle cable which brought the other motors instantly to a stop which saved me from any other injury. I honestly believe that there was divine intervent involved as if the prop struck even one or two millimeters higher or lower I would have broken or completely lost a finger and had the throttle cable not popped out, the throttle would not have cut out and the bottom props could have contact my feet or the remaining top propeller could have contacted my neck. Instead I had a bruise palm and the top layer of skin removed from my ring finger where it contacts with my pinky finger. Just to put the cherry on top I only needed to replace $50 in props and plug back in the throttle cable and the unit still works just fine. My mistakes: First I was running it without a cage. This is about as stupid as it gets. My hand placement holding the unit back was not good and there was no good place to brace it(once again, never should have run it) I hadn't even finished securing the carbon fiber motor arms to the metal cage, so they could have come loose and caused even worse injury. (I hope you all are seeing just how stupid this whole situation was) Even today I still get something like PTSD whenever I am within 10 feet of a paramotor running at high throttle, and because of this experience I won't fly anything but a flat top paramotor or a skytap as I don't trust the cages enough on the other brands.

You could put a rock on one side of your cage to create the same force of torque, but your not loosing energy to it. Actually the standard APD 24s 300a esc is $1500usd and on top of this they had APD upgrade the heatsink and and a few other components for better performance. So I would say at least $1600 or about £1100. That still doesn't cover the BMS(£150), aluminum battery pack case(£150), battery pack assembly cost(£200), other electric systems such as throttle, display,flight controller, etc(£100), and the motor/battery mounts(£100). At this point we are easily up to £3650 just for the power system to replace a £2500 engine. Trust me, I have built two E-ppgs already (actually just finishing up the second) and I know how amazing it is that they have reached the price point that they have. Except it's like pushing a trolley up a ramp, over 50% of the resistance is due to pushing it up the hill, the rest is due to metaphorical bearings resistance.

I would disagree with all of this. I am helping a different company design an electric paramotor that will be a direct competitor with the SP140 and Thomas Brandstetter who I previously mentioned his reply to my question (holds the E-ppg world record) is not affiliated with them either. So neither of us have a reason to blindly defend them, but I will say they did a great job at designing the SP140. I know you still don't understand it and I can't make you, but us electric paramotor designers understand that lower rpm systems are inherently quieter and more efficient with the sacrifice of torque felt at the frame which can be counteracted by weight shift and a variety of other methods. This was not a mistake on the part of OpenPPG. Not sure where you are getting this, there are only two other E-ppg currently on the market capable of 4kw cruise. This means the SP140 is incredibly efficient. Also makes no sense. A reduction drive reduces the rpm and allows for bigger props, so If it was about getting rid of a reduction drive they would be using a smaller, less efficient, louder, and higher rpm prop. Instead they are using a very large and high pitch 3 blade just to improve efficiency and in turn they are spending a ton more money on one of the highest power motors available (mad M50 40kv motor to be exact). OpenPPG has done an incredible job at getting such a tight profit margin to allow this to be by far the best bang-for-your-buck E-ppg on the market. They are using a good well designed motor, high quality motor controller(apd 300a esc), molicel P42A li-ion battery packs(one of the best li-ion cells out there), a good frame, one of the best throttle systems on any paramotor in the world. It may not be to the quality level of a rolls-royce, but it is still an E-ppg that will last a long time and leave the buyers happy. You got that right. Primarily difficult as it increases weight and rotational mass which leads to a bad throttle response Looked into this, but there are legitimate safety reasons why it is not done and as mentioned previously, it would lead to an increase in weight and cost. For some reason people can't get their head around this, the torque you are feeling in the frame is not a waist of energy. It is equivalent to pushing a heavy shopping cart. You feel it "pushing back on you" because you are putting energy into it, but just because you feel it doesn't mean that it's wasteful. Anyway, finding a way to cancel that torque (and gyroscopic precession) would be very nice.

I can totally understand that. Can we agree that to get 10 horsepower worth of energy out of a 100% efficient propeller we need to put 10 horsepower of energy into it?(that's the definition of 100% efficient). As you may know the equation for horsepower is foot pounds torque x rpm x 5252 = horsepower. This means that if a 100% efficient proper needed no torque it would be creating infinitely more energy than you are putting into it. (1000rpm x 0 ft-lbs x 5252 = does not 10hp (10hp @ 10,000rpm = 5.25 ft pounds torque)) So mathematically you can see that to not break the laws of physics, a 100% efficient propeller would need to convert torque to thrust by some means. Infact the best modern airplane propellers are exceeding 90% efficiency which means that scientifically speaking 90% of their input torque needs to be converted into thrust.(10 hp input equals 10,000rpm x 5.25 ft-lbs torque x 0.9 efficiency x 5252 constant = 9 hp energy output.) I hope this can help you see that from a mathematical and physics standpoint that torque needs to be converted into thrust to have a net power output. If this was not the case explain how a windmill produces torque to drive a generator. The way that a windmill takes energy from moving air to generate torque is the same process, but in reverse that a propeller uses torque to make air move. For all I know, that could be to do with the inverse torque curve of electric (in comparison to IC) in the attempt to avoid the need for a reduction drive... It certainly sounds like it If you read carefully what he said, you will see that he was specifically referring to ICE paramotors for the quoted section. Suddenly I find myself distrusting the man, he is over-egging his sales pitch to the point of giving himself away with this statement! An absurd thing to say Think about it, you yourself said larger propeller is more efficient, so why have almost no ppg manufactures gone to a 140+ cm props? He isn't wrong, most paramotor manufactures in the past have been more concerned about the torque and size than noise and efficiency. It's just one trade off they have decided to make.

I got a reply back from the foot launch E-PPG record holder. Here was my question: "I have noticed that most E-ppgs tend to run around 2300rpm at the prop compared to the ~3000rpm at the prop of most ICE paramotors. I know this helps with both noise and motor efficiency, but I was curious if their is any efficiency gained or lost from running a higher pitch, “thicker” 3 or 4-blade prop at lower rpm compared to running a “skinnier”, lower pitch 2-blade at higher rpm." His response(his native language is german): "in europe, the highly efficient eppg with 2200-2300 rpm are only operated briefly for start-up. (2300-2400 for heavy trike). in an efficient climb it is around 1900-2000 rpm. in the level around 1500 -1600 rpm. Depending on the trim speed of the wing, 3 blades are usually best with a circular area coverage of around 5.5% and a pitch speed of approx. 55 -6o km / h at full throttle. in the level, the pitch speed is the ideal value for maximum efficiency. petrol ppg have never really been interested in noise reduction or efficiency. with a few exceptions. At the moment, however, a very clear trend can be seen with some manufacturers to limit the speed to a maximum of 2200 rpm and to increase the prop diameter to 140 cm. the first are already flying and are extremely quiet and very efficient. it’s going in the right direction with some. I think it’s very good." In your diagram the drag vector is for both the drag caused by the boundary layer, tip vortexes, etc and the other part is drag caused by the lift. Even if the propeller is 100% efficient most of the drag will still be present when thrust is created. Imagine it like a glider climbing at an angle. If it doesn't have any power input, it will eventually run out of airspeed and stall. That glider angle is the pitch of the propeller and the gravity pulling it down is the drag on the paramotor that the propeller is creating thrust to push against.

I am not great at articulating my words as you have seen, but let me try to explain. I think that I could best tell why the torque is required rather than the physics behind how it works. I hope we can agree that if you put 10 foot pounds of torque into the propeller, the cage will have 10 foot pounds torque in the opposite direction(back to every action has an equal and opposite reaction). I hope that you also understand that torque x rpm= power So to begin, an typically paramotor with a large and efficient wing and a medium-light weight pilot requires about 2 kW (2.68 horsepower) constant energy to stay in the air. A paramotor propeller is typically about 50% efficient so we will go with that number. So because of the prop efficiency we will need to put 4kW power into the propeller. At 4kW engine power the average paramotor propeller will spin at about 1800 rpm. If we run the math we get that the propeller is receiving 5.36 horsepower (4kW) at 1800rpm and 15.6 foot pounds torque. This also means that the torque at the frame is 15.6 foot pounds. If we then go back to our 50% propeller efficiency we can see that of the 15.6 ft lbs torque, 7.8 ft lbs torque is used to fight drag, but the other half is used to move the air to create thrust. This also means that even if the propeller is 100% efficient we would still need 2kW and 7.8 ft lbs torque to fly. If it required no torque to fly with a 100% efficient propeller, then you would be getting 2kw energy out of a propeller that you are putting no energy into which is impossible. This also means that if you swap propellers to create the same thrust at say half the rpm with equal efficiency, you will need double the torque (5.36 horsepower @ 900 rpm = 31.2 foot pounds torque vs 5.36 horsepower @ 1800 rpm = 15.6 foot pounds torque. It doesn't meant that it's any less efficient, it just means that you are exchanging rpm for torque. (By the way, I never told you this, but i think your profile picture is fascinating)

For everything action there is an equal and opposite reaction (basic physics). To generate thrust a propeller pushes air backwards. In turn the air pushes back on the propeller trying to slow it down. The engine then uses it's power to spin the propeller. This means that you could have a 100% efficient paramotor propeller and as long as it is pushing air there would still be torque at the frame. If this was not the case then propellers would be perpetual motion devices. Is that an educated guess or have you something to link to that shows it to be true? I just sent a message to the man who currently holds the world record for foot launch E-PPG on this topic. He often builds his own propellers and tests everything, so I Will be interested to hear actual numbers.

It is not wasted energy. The output of an engine comes in torque and rpm. So if the gear reduction changes by 30% to drop the propeller rpm from 3000 rpm to 2300 rpm the torque output will be increased by about 30%. The prop size pitch, blade count, and width can then be increased to provide the same thrust at a lower rpm, but but at a higher torque. Your still putting the exact same power into the propeller and getting nearly identical thrust out and with nearly identical efficiency, but one side effect is the paramotor will torque more. I was referring more to the lower rpm combined with increased pitch and blade "thickness". Of course going to a large prop will definitely help with efficiency, but most people will tell you that it gets pretty hard to foot launch with anything much bigger than a 140cm prop. Naturally this would be mostly based on height of the pilot, but a 160cm prop foot launch PPG would not work well for most people. At the expense of efficiency. Not true. Go look at any well developed paramotor and do some research into their power systems. If you look, you will notice with few exceptions that they all have motors wound to peak at almost exactly 2300 rpm, and they almost all have 140 or 150cm 3 or 4-blade, high pitch props. This is the recipe that has been discovered for creating the most efficient E-ppgs. I am personally most familiar with the motor side of this as that is what I work on. From a motor standpoint, that 700 rpm drop give us an extra ~4% efficiency. So even if the propeller might be 4% less efficient (which it's not) and cancel out the efficiency gained from the motor, most electric manufactures would still opt for the lower rpm system.

This is true, modified tips can significantly reduce propeller noise and slightly improve efficiency. I have personally modified the tips of propellers on radio control helicopters, drone, and airplanes and have had success with reducing noise. I would love to see propeller manufactures like helix and e-props at least test some new tips of various angles and shapes, but I can see a few reasons why they may not be practical for PPG use.

They already are. All 40 units of batch one where pre-ordered months ago and they haven't even shipped yet. There are now at least a dozen people waiting to preorder the batch two sp140 and for everyone who pre-ordered there is at least one more person that has the money ready, but is waiting to to buy when they are in stock Meant to say 1,000 hours. Apparently one zero is a big difference. That being said the Average gas PPG only lasts 500 hours with engine rebuilds an proper maintenance, so even if the electric components are good for 1,000 hours it would be a big improvement. That would take some doing... I would think higher pitch/broader chord would give away some aerodynamic efficiency and static thrust for a given diameter. These are things that could be done with an ordinary IC powered paramotor but we don't see it... why is that? It doesn't give away almost any efficiency for an ICE paramotor but for an electric it's actually more efficient as the winding in the lower KV motors tends to be about 3-5% more efficient. Now these could be done with an ordinary ICE paramotor. As mentioned before the biggest reason it's not done is that in increases torque (by about 30%), it often requires a bigger prop which may not fit in a standard paramotor frame, and other than noise there isn't really any advantage for an ICE paramotor. a tiny portion of noise will come from this, but it's not that much. About 80 percentage of all propeller noise comes from the tip, so if you really want to reduce noise you must prioritize this. The only way to reduce this noise is to reduce the speed that the tip of the prop is traveling.

They don't need to. If an electric lasts twice as long as the best gas paramotors, they only need to last 100 hours. That's not hard as long as you get a quality motor with reasonable phase currents and a good motor controller. Prop noise is primarily based off tip speed. So if you can get a 140cm high pitch 3-blade spinning at a low rpm you can significantly reduce prop noise for a given thrust. It will increase torque, but we could possibly bring the noise low enough that with say a 10kw power limit it would be quiet enough that hearing protection would not be needed. Most motor controllers have a capabilities such that they go into a regenerative breaking mode such that when the throttle is not applied the motor will come to a stop rather than freewheeling. This would allow for a glide more efficient than any paramotor engine with a clutch.

You definitely have a point. At this point I don't believe electric is for most people, but I think it's perfect for a few people. The sacrifice that comes with electric is a much more limited flight time, it requires ~4 hours to charge back up, and it doesn't go well with water(we are also trying to fix this) But, electric has a ton of benefits include a much quieter cruise, silent and more efficient glide, operating cost as low as 55 cents per hour, no mixing fuel, no maintenance, no vibration, very linear throttle control, no oily messes, the paramotor will last longer, and a lot more. I imagine electric being perfect for people coming from paragliding that won't use very much flight time and don't like the loud engine noise, those who are not mechanically inclined or have time to do all the maintenance on a gas paramotor, people who fly in more noise sensitive areas, those who can go fly once a week on the way home from work but only have 45 minutes anyway, or those who live on a property where they often fly shorter flights from their house. So for me personally, electric would be perfect.

You don't need to wait. The Exomo, Paracell, and OpenPPG SP140 can all handle a realistic 40+ minutes with some reserve and in perfect conditions over an hour. Or if you want to wait, I am currently helping another company who is developing a new foot launch E-PPG that is looking to have a peak flight times around 75+ minutes.

I don´t believe they ever saw production. As far as I know the last update anyone had from them was in March of 2010 or almost exactly 11 years ago. If you still want an electric paramotor I recommend looking into the OpenPPG Sp140 or the Exomo. The SP140 is the absolute best bang for your buck, but the Exomo is made from higher quality components(imagine Honda vs rolls Royce) Also which country you are in could change things as the SP140 is a high enough voltage that it is not legal in many countries.

A buddy of mine has a thrust tester that you fasten the frame to.

I am also using a 130 helix.

during the one thrust test we did with it, we saw roughly a 13% increase in thrust over the stock engine. (As a heads up, I am not the best at describing obscure parts of 2 stroke ports) I did many modifications to the engine. Here are some of the modifications I can remember right off the bat: widened intake port window, exhaust port raised to give 5 more degrees blowdown, reshaped transfer port ¨intake¨ window for better flow, lightened piston, all ports polished with ¨texture¨ then added to the intake and transfer ports, Piston windows opened and smoothed, all sharp edges of port windows smoothed to lengthen piston ring life, thermal ceramic coating added to cylinder head, piston crown, and exhaust port, exhaust port rounded for better piston ring life, and any other place where something could be reshaped within reason for better flow or extended piston ring life it was done. There are still some modifications I would like to do. For example my dremel tool couldn´t fit in to alter the transfer port windows which I would really like to open up and reshape. I would also like to either make a new expansion chamber or modify a 125cc 2 stroke motorcycle expansion chamber to use for this engine. The stock one is so tamely tuned that it is nearly useless, so a new one should give at least 20 percent more thrust with the only real limit being how much cruising efficiency I am willing to sacrifice. I would only recommend modifying your engine if you are experience with porting 2 strokes. On every step I did, I could have destroyed the engine if I made a mistake. One must also have a vast understanding of their working principles in order to optimize one without throwing any part off balance which would quickly destroy any performance that you may have hoped to gain.

What elevation are you at? I am at 4500 feet elevation and our thrust tests are coming back as roughly 30% lower than what we get at sea level.

I recently ported and polished a radne 120 along with ceramic coating the cylinder head and piston. I also removed some access casting material saving about 200 grams of weight. During a thrust test it came in at 85lbs (38kg) thrust, but I am 5000 feet above sea level. Based on other engines we have tested at both 5000' and sea level, this would equate to over 110lbs (50kg) measured thrust at sea level. I still haven't tuned the carb after porting the engine so I expect it is capable of even more than that. I am going to switch to a Minari 200cc or electric so my ported radne is for sale.

The atom 80 has a little bit more thrust than the racket, but not much and I think it is a little quieter. Other than that, they are nearly identical in every other category including weight and fuel consumption. The one advantage of the Radne is that it is very reliable and needs less maintenance than the atom 80 due to the lower power to displacement ratio, But the atom is also nice as you don´t need to deal with the decompression valve and i think it is a little more consistent in performance. If cost is not an issue an atom would be a good upgrade, but if your radne is working good, I would probably stick with it.

Have you ever tried an electric unicycle? I have been riding cheap ones for almost six years now and I recently had the opportunity to have a few months with a kingsong 16x and a few weeks with a Gotway MSX. The kingsong was awesome as it had nearly a 100 mile range, could do 30 mph and with my usage, I could go weeks without charging it. The Gotway was a whole new level. I personally hit 40 mph on one of them and could cruise up fairly steep roads at 30mph. I will say it was one of the coolest and strangest sensations I ever had standing upright with my hands free and my feet inches off the ground doing 40 mph and having only thing holding me off the ground be a single 20 inch tire tucked between my legs. I actually ended up selling the kingsong previously mentioned for a buddy of mine to someone who does hike and fly paragliding, but instead he would ride the unicycle up to where he would launch, place the unicycle in his back pack, fly down, and repeat. I still haven´t tried it yet, but it´s on my bucket list.

I'm quite interested with this build and I can't wait for more updates. I have been thinking of doing something like this except building the engine nearly completely from scratch. What I want to build is an opposed piston ~150cc paramotor engine with comparable power to a vittorazi moster. The hard parts would be making the dry sump oil system, super charger, and gearbox to connect the two crank shafts together. Theoretically it would have the advantages of a 4 stroke such as no fuel mixing, quieter(no expansion chamber), cooler operating temperature, broader power band, longer lasting spark plugs, and high fuel efficiency. It would also have many advantages of a 2 stroke such as being more simple without a complex valve train, comparable or better power to displacement ratio (more efficient scavenging, running a 2 stroke cycle, supercharged), and it should be cheaper to produce than a 4 stroke. Anyway, I have been researching into different ways I could make it and was curious if you would have any suggestions.

Will you fly at high elevation or will you plan on flying tandams at any point? If the answer to either of these is yes, I would recommend a vittorazi moster 185 or equivalent power. Your at a weight where you could go with a vittorazi atom, but unless you really need the extra flight time, I would probably stick with the moster. Other possible engines would be the Minari F1 if you need a bit extra power and don't need a clutch, or maybe an eos 150 which is somewhere between the two vittorazi engines in power.

Interesting. As someone who has built an electric paramotor and is building a second one, I just want to know more about the E-ppg that they are using. So if someone new all the details that would be awesome. I am looking for things like battery energy, battery configuration (number in series and parallel), cell size, cell chemistry/manufacturer, motor manufacturer, motor kv, frame, battery cell weight, prop size, prop pitch, total unit weight, and basically everything else. Even if anyone has part of those specs, it's not too hard to fill in the missing puzzle pieces.

I finally got to thrust test the modified paramotor engine the other day. We were able to hit a peak of ~85 pounds thrust at almost 5000' elevation. This means at sea level it could get a little over 120 pounds thrust. On the other hand one of the stock engines typically run around 75 pounds of thrust at our elevation or a little under 110 at sea level. I think the next modification I will try is a custom tuned pipe. I'm hoping with a new pipe I can get ~15 pounds more thrust.