I’m starting on a build project for an electric self-launch system for paraglider soaring. The goal of the project is to have a motor system that can be used with my existing wing and can get me from a flat, open field up into the lift band of a soarable ridge. With that in mind, these are my design goals for the project:
2000’ total altitude gain
Minimal impact on the handling of the paraglider with the power off
I’m basing it on the Nimbus project that has been flown successfully by a couple of people. I think there is someone else here on the forum who is working on one as well. It’ll be a single motor, direct drive setup, probably using 18s lipo for power.
Right now I’m playing with some power system calculations in eCalc. Since my target parameter is really altitude gain, I’m thinking that I should be optimizing the system for specific thrust (grams of thust per watt)? Climbing slowly isn’t an issue as long as I have the power to climb to 2000’, and if I can make the whole system lighter as a result that will be helpful. Based on eCalc, it looks like the best way to increase specific thrust is to keep RPM down by increasing prop pitch and/or adding blades. A single 30x20 prop looks like a good configuration according to eCalc but I’m skeptical of eCalc’s aircraft performance calculations. It is showing a 390 FPM climb rate, but my beer math says that much thrust (26 kg at 22 mph) should barely produce a climb at all. Do any of you have any experience with eCalc vs real world values on an ePPG system?
Well, I solved my own question. My drag settings in eCalc were all wrong. Once I got that corrected, it looks like my best setup is:
Neumotor 8057/75 swinging a 39x18 prop powered by 18s of 22000mah Bonka cells. That draws ~250 amps (for ~15 kW of power) and gives me ~41kg of thrust at min sink speed, resulting in a ~400 fpm rate of climb to ~2000’ AGL before I run out of power. That seems like more realistic performance and matches my beer math calculations pretty well.
if you use a 30 inch propeller and a high speed. then the system is in an unbelievably bad efficiency compared to the paraglider total weight. differently explained: in order to climp with 0.5 m / sec you need surely 10 kilowatt. if you use a 50 inch propeller you only need 5-5,5 kilowatts for 0,5 m / sec. just as a pure example of efficiency and physics. e calc is very good and also very accurate.
Yeah, I realize it’s not the ideal setup for maximizing flight time, but I’m also trying to balance motor-on performance with motor-off performance. A big prop needs a big cage, and both will add more drag. What I really need is the smallest motor and prop combination that will give me a workable climb rate to 2000 feet. Ecalc is predicting a 34x18 will climb at 250 fpm. I might try that first, as it should be a little more motor friendly. The 39x18 is a little more efficient, but it is starting to push the motor a bit and ecalc is predicting an 80C case temp.
here as an example how to solve it: with the impress 3 without motor I have a sink rate of 1 - 1.1 with the frame and propeller is the rate of descent at 1.1 to 1.2 in a standard paramotor usually at 1.4 - 1.6. the rechargeable battery (8.5 kg) is exactly where else the water ballast is, therefore the zero balance remains unchanged. The motor is near on the back. the 5.5 kg for the drive incl. Regulator, angle adjustment and housing can not be felt by thermal flying. the propeller weighs 360 grams. As a rescue system, a 135 kg parachute is installed laterally and a second system up to 140 kg in front of the abdomen in the competition pod. everything weighs 22.5 kg. Normally you do not need 2 rescue systems. I do it anyway because I fly with it in very hard thermic. With only one rescue system and a new lightweight pod harness, 18kg is realistic. The maximum height with me as 85 kg pilot is about 800 meters above ground. the level flight without thermals is about 20- 25 minutes.
That is very nice! Where did you get the propeller? I have been looking for a large folding prop like that but I haven’t found one yet. Is that the one that was used on the Flytec e-drive?
Cost is also a concern on this project I know it’s less efficient, but running a smaller prop on a smaller, higher kV motor makes more sense for my bank account when I can get a motor for $450 and a prop for $140. According to eCalc, that should be enough to hit my target altitude on 18s of Bonka 22000 cells.
Hi, Thank You. I build everything myself what I need. the propeller in the picture is from 2017. currently i’m flying a new one that has even better performance and is extremely quiet. in facebook you can see all the pictures of the propeller construction. I make everything as simple as possible … the autoclave is a wooden box and a 30 euro heating foil and a thermostat. The vacuum makes a household machine with which you otherwise vacuum vegetables or meat. high tech can be cheap. yes, I understand that many have too little money. I work myself mostly 300 hours extra per year to be able to pay for the parts I have to buy. but I have the time to work because I have to drive with e-ppg not many hours in the car to the mountains in order to fly. It is always important if you start an eppg project to check it makes sense. There are certainly many hundreds of projects that are in garages and do not work. that is even more expensive. Of course, your project can work if you can fine tune it. it’s just hard to get around the phsyik. as an example: if you have a diameter of 1.3 meters, the pitchspeed can be considered ideal from 1.5 to the airspeed to move the air volume and generate the thrust. if you only hold 1 meter, the pitch speed must be increased to produce the same thrust. The ratio is 2.0 or more. the efficiency drops very much. here if you want to see other things from me: https://www.facebook.com/thomas.brandstetter.54/media_set?set=a.2659026050782798&type=3Redirecting...
The motor I use is the same for all concepts. it is a hacker qsl 150 with 3.5 kg. In 2016, I was working closely with eppg on the coordination (revolutions, turns, etc.) for eppg in cooperation with the company hacker motor gmbh in germany.the motor is also installed in e- Trial / motocross bikes, e-karts and industrial machines as well as man-operated drones. depending on the application of course with different speeds and stator height. sometimes , I supply other diy eppg crafters with it. It also flies 1 piece currently in the US and about 20 in Europe. As esc I use since 2012 MGM HBC industry series. For the mgm esc, the wireless cockpit has also been developed. the next weeks, I present everything on my facebook page. There you can see the composition exactly if you like.
That’s great! Do you find torque to be a problem with the pod harness setup when the motor is running? It looks like most of your designs are based on traditional paraglider harnesses that wouldn’t have any torque compensation.
yes i know it’s the myth because of torque. I have a king 3 cylinder paramotor with a pagojet frame. he is 25 years old. even back then, the designers knew how to bend the push rods asymmetrically and shorten them on one side to be able to fly perfectly straight ahead. all others in europe have had a constructive torque compensation since around 2000. but yes there are manufacturers who are doing it wrong or very bad, even today 2019. in a system that is designed for thermal flight, the thrust goes to the cfk molding on the body of the pilot then goes to the straps. At full throttle, it is noticeable that there is a single torque that is immediately used positively. the direction of rotation when circling can then be used without much brake. at the level flight and thermal search with less than 30 kg thrust you feel nothing at all. A lot of it also makes that the propeller does not have a large mass of only 360 grams. most of the mass is in the center. therefore, there are no mass forces like classic ppg. but yes if you eg. with a dudek snake size 15 flies and powermotor is a constructive solution for torque compensation makes sense. I do it differently when I fly fast little wings. then I use a counter-rotating sytem with 2 propellers. But that’s another story that I tell later on my page and show there.
Thanks for the info. I’m thinking about locating all the batteries (approximately 7.5kg) on one side of the frame to add a bit of torque compensation, but I’m worried that it will adversely affect the handling with the motor off. What do you think?
I’ve thought about (and looked at) the remotely-operated electric winches, but I don’t think it would be that practical for this area. The number of 4000’ fields around here are slim, and the ones that are in proximity to soaring terrain AND lined up with the wind direction are almost non-existent. There are two guys here who have winches already, and nobody (to my knowledge) has successfully winch-launched to a successful soaring flight in this area. For flatland flying, I think a self-towing winch would be the perfect solution to what I’m after, but this area is far from flat.
I like the idea of being able to pull the self-launch rig out of my car, gear up, and take off leaving nothing but the car behind. The number of launchable/landable fields around here for a motor are probably 100x the number of towable (for soaring) fields.
Neumotor 8057/75 75kv motor
APD HV_Pro 20S motor controller (pricey, but it seems like the lighest, smallest, and most reliable option)
JC superprops 39x18 prop
18s Bonka 22000 25c cells (3x 6s 22000 packs)
That is giving me 15278 watts and 47 kg of static thrust (39 kg at climb speed), and 389 fpm of climb to 1800 ft. Total weight for the power system is 11 kg plus wiring. I can definitely do a little better in performance with a better prop… those calculations are for a XOAR wood prop, and that seems to be about the worst option available on eCalc. Almost any other prop option should net me another ~200 ft of altitude gain, with lower temps and current as well. I have yet to find an efficient 39x18 prop off the shelf
For those of you with eCalc, here is the setup. The drag calculations are set for min sink speed (22 mph) at a 7:1 L/D.
hi, for the motorless flight you need a balanced system. if you want to calculate the minimum torque in the climb just do it like all motor pilots in the world. when the propeller rotates against the clock, hit the right leg over the left. When he turns his left leg over his right leg. in hot spirals, playground fast turning is the standard way with the legs to support the curve side by shifting focus. with many pilots this always happens automatically. you do not even think about it anymore. you do it. It is also possible with the pod harness.
Project update: After going back and forth on frame material I got some 1" aluminum EMT conduit. It’s 6005, roughly 27mm OD with 2mm walls. It seems plenty strong, it’s light, and it’s cheap! It can also be easily bent with a conduit bender. I’m going to bend up a frame in a day or two to check fitment on my harness.
I’m still waffling on battery choice… 3 6s 22000 mAh bonka packs in series (two on the right frame arm, one on the left) is the best setup from a cost and power density point, but it means that I’ll have 250 amps running through 4m of 8 AWG wiring and I’ll have 2.5 kg more on the right side than the left. Splitting the batteries evenly between the two arms (3 6s 13000 mAh packs in series on each arm, with both arms running parallel into the ESC) gives me more like 125 amps running through 2m of wiring and the whole setup will cost more and weigh more per wH. If anyone has an alternate suggestion, I would love to hear it. Ultimately I need to get 66 volts to the ESC, I need around 1.5 kWh of power, and I would like to keep the weight of the batteries balanced between the two arms.
Can someone post the part number for the switch used on the openPPG power system?
Are you saying 4 meters of wire between the batteries and ESC or between the ESC and the motor? Are you familiar with voltage spikes from induction caused by long wires. You will burn up your ESC if the wires between the batteries and the ESC are too long. Search induction on this forum for more details.
4m between the batteries and the ESC. I am familiar with the voltage spike effect and have already budgeted in a cap board built by APD to deal with the problem. If I can find a way to locate all the batteries in one spot I’ll mount the ESC next to the batteries and extend the motor wires, but with the mechanical setup of my frame I’m not sure that is possible without making it seriously un-balanced.
So this is an interesting development. I started playing around with prop sizes in eCalc, to see what was the true optimal configuration for my motor and batteries. Until now, I was basically limiting myself to what I could buy off the shelf. I came up with a 36x24, instead of the 39x18 that I was planning on using. eCalc seems to think that it will net me another 500 feet of climb with slightly less amps. I went through the different options for manufacturers who actually make props that big, and settled on a Fiala E3 Electro, which actually gives it even more of a performance bump. I sent Fiala an email, and they say that they can build that prop and ship it to me for $170 USD, which is only $5 more than that 39x18 prop was going to cost! With less weight and power off drag to boot! With that prop the system becomes efficient enough that I can downsize to an 18s 2p 10000mah pack setup and still hit my 2000’ altitude goal (at almost 500 FPM). That brings the total weight of the rig down to 13.2 kg including batteries!
Try it on the ground before you fly. At this pitch on the propeller it may be that the esc explodes after 10 seconds. Building a system that has no much enough torque (Neumotor 8057/75 with 16 poles ) causes the peaks of the phase currents to rise extremely. Most hobby model construction esc burst outright. only meant well
