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.
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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.
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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.
@bratwurst I wonder if the reduction in trim speed under power is why most paraglider tow straps activate the speed system when the tow line is tensioned? Maybe it would be best to climb power on with a bit of speed bar applied? I am going to be using a normal free-flight wing.
the consideration is right the trimmer or accelerator to open something. In terms of reality, however, there is no advantage because the air resistance rises to the square. therefore eliminated the advantage again.
Makes sense. So are you suggesting that I target a maximum climb rate of 1.5 m/s for maximum altitude gain?
I suspect we think completely differently. I take real values for thrust, climp rate, etc. confirmed by hundreds of flights. I do not know where you got your calculations to the climp rates? there is no software in my opinion that can calculate that someone would have to do something like that to program. But apart from very few, there are no people in the world who would have integrated the telemetry data into a software?
many times I have talked to people who said they could build a software on the office calculator that can calculate an eppg incl. wing. Nobody can build such a software without key figures and basis values as a basis. so yes people ask me if people want a sink / glide polarity of a paraglider if I make it available to them with my logged data.
In the case of airplane wings, of course, you can calculate and make simultion calculations since the values have come to a database for many years and the values have been evaluated. For many decades, the large corporate gliders have accurately measured in flight. this is still done with new developments as it was before. only the effort is less because many meters are easier and in the file format already processed.
So with 46kg of thrust at 35 kph, 105kg total weight, and 7:1 lift to drag ratio, what do you think the climb rate will be?
I still need to know is the thrust with 46 kg as worth of a motor on a test bench? or is the thrust of a test stand where a dummi simulates the pilot and frame and cage? it is about if it is with dummi and frame / cage is the output value is real. and always by about 15% less than the value without losses through pilot and frame, cage. I will give you a example: wing 24 m2 projected area or size “M” low EN-B classe. Temperature 20 degrees Celsius. Height 500 meters msl starting point. Moisture average. wind max. 10 kph. 1.3 to 1.4 m / sec. constant climp rate. it now depends on whether the 35 kph for the propeller are positive or negative for pitchspeed on. then possibly also 1.5 or 1.2 m / sec. possible. I measure the pitchspeed always in a fixed distance of 3 meters and in 1/3 of the diameter of the prop. if then at the stand about 52-57 km / h at full throttle, it is very good.
I made my first tangible progress on the project today (besides staring at eCalc and spreadsheets for hours). I got an appropriate conduit bender and experimented with making the 53- and 73-degree bends that I need for my frame. After the first attempt, I was able to make consistent bends to +/- 1 degree of my target, and the tubing is coming out pretty nice. Maybe not as nice as using a real tube bender with the appropriate dies, but it is not kinking and is only slightly flattened, probably about the same amount as with a tube bender on a stand.
facts about 16 pole motors. with about 2.6 kg mass.
the short-term load if not too much torque is required is approximately:
15 kw / 10-20 seconds
10 kw / 30 -60 seconds
6 kw / with very good additional cooling continuous operation
4 kw in the normal design without additional cooling.
as soon as the load is above average the propeller has too much pitch it can be that you have to accept about 30% less continuous power.
as a simple explanation: at 15kw, the engine generates a heat of around 1.5 kilowatts! That’s more than 10 strong soldering iron. this heat must be removed. due to the design and few poles that is not constructively possible.
at zb. 42 or 48 pole motors allow continuous power of about 2 - 3 kilowatts per 1 kg motor weight. because the diameter is larger and therefore the radiating surface of the copper turns is larger. also the amount of air due to the centrifugal effect. the peak power for start or short full throttle passages is about 4 kw per kilogram.