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.
Right now my tentative power system plan is:
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
Thanks for the info! Is that because the eRPM is too low compared to the total power? eCalc is showing me 4360 RPM at full charge, full throttle at 250A 66V (eRPM 34880 I think?). I’m going to use an APD HV_Pro 20s 300A.
Ah ok. I do not know the apd. but the specs are reading well. it is in the price range of mgm. the individual parameters I do not see on the website, like all the security features or settings. but if he is approved for man flying ultralight vehicles he will have it too. whether the cuurents go over the permissible esc range you can read then in the live monitoring at the test. my tip: if the peaks of the phases over 150% of the max. I would not fly the setup. it then has a bad efficiency. (pulls the drive 200 A and the phase currents are, for example, 60% gas travels over 300 A peak per phase) then you need either a motor with more torque or less pitch on the propeller. But what does that mean you probably will not get enough push.
I got a reply from APD, and this was his response:
“There will not be issues running the HV Pro at that RPM. Definitely keep an eye on the thermal performance, as 252A for 5 mins will make for a toasty ESC.”
It looks like with forward airspeed the motor should prop should unload down to around ~200 amps, and then as the battery discharges a bit it should sag further to around 180 amps, so I think the ESC cooling should be adequate. At any rate, I can limit both the battery current and the phase current using the ESC configuration tool if current draw is a problem. Right now eCalc is predicting a 623 FPM (2.7m/s) climb rate at full charge, full throttle, so I don’t think being underpowered is going to be an issue!
A quick aside on the prop pitch thing: I was running a fixed wing UAV development program for a while and we ended up settling on that same 3:2 diameter to pitch ratio for maximum endurance. That is usually about the highest pitch you can get without stalling the prop blades at zero airspeed. Pushing the pitch higher will continue to increase the specific thrust (grams of thrust per watt) even higher, but weird things start happening when the prop disc is stalling, or stalling unevenly with uneven airflow. 3:2 seemed to be the magic ratio for that vehicle, and it seems (according to eCalc) to be the magic ratio here as well.
Does that mean 22 x 14 would be the optimal pitch for the open PPG X4 if the motor Kv was set for that prop?
It might… although depending on the power capacity of the system, voltage, and kv of the motor a larger or smaller diameter with that same 3:2 ratio might be the most ideal for maximizing endurance. It would be something to look at in eCalc. All I know for sure is that maxing out the power system on that UAV project using a 3:2 ratio prop gave us a pretty insane climb rate (for a 4.5 lb fixed-wing UAV) and also well over an hour of flight time on a 3S 9000 mAh lipo.
you write about a rate of climb of 2.7 m / sec? and have a static thrust of max 47 kg at around 15 kilowatts. From experience I would increase the power to max. climp at 1.5 m / sec. unless you only have 40 kg as a pilot. The technology is so far today that 10 kw / 50 kg thrust are possible. Of course only with minimum 125 cm propeller. then he agrees pitchspeed also perfect. at 39 inches, he is definitely too high in any case. A movement of air masses can only be changed with a small diameter by increasing the flow velocity.
the reason why calculations of model airplanes can not be used e-ppg has the following points: a plane can be flown faster by more engine power. a paraglider always trimmspeed. he puts more power into more height. that has a problem though. at a certain level, the angle of attack becomes so great that the wing begins to brake and can no longer transform all the energy into altitude. how can that be? this is because of the motor thrust of the pilot with the eppg pushed forward. this changes the angle of attack of the wing. but the direction of flight remains the same, the angle of attack changes. the trim speed drops by 3-4 km / h. I fly and build model planes for 35 years. own constructions up to 5.5 meters span electric driven already in the middle of the 90’s. Therefore, I know the performance charts with watt per kilogram, etc. very well. Since 2014 I record everything concerning eppg from the index of performance. drive unit and the relation of the different wings. I tell you so that you may understand that I do not just want to write something but you want to clarify the basics so that you do not build a project that can not then meet the expectations. not because you have done it badly. no it’s about physics and aerodynamics that set the rules.
There are wings that can convert engine power almost 100% in height. these are eg. the kougar 2, doberman, dudek wasp, some of ozone. But that is only possible because the area is very small. The profile is very thin and a reflex profile. the disadvantage is for eppg that there are no wings for everyday life. You have to have a lot of experience with it in turbulent conditions. I fly myself a kougar 2/20 for fun flying. There are also 2 lines EN-D wings which have a very high power output. but I know that 90% of the pilots can not start this on a meadow with a motor. Also, these have no engine approval.
I think my static thrust at full throttle, full charge is more like 55kg, hence the high climb rate number. I realize that climbing that fast is probably not a realistic number, but I figure I can overbuild the system and then throttle limit the ESC, or go down a bit in battery voltage to keep it at an efficient level if it really performs like eCalc says it should. Before I started using eCalc my rough estimation was that with around 45kg of thrust I can climb at around 2 m/s, assuming a 105kg all up weight and a 7:1 L/D ratio. eCalc matches that reasonably well, once I adjusted the drag numbers in eCalc to give me 15kg of drag at 22 mph.