Ranger electrically powered?!?

Discussion in 'Electric Propulsion' started by erkki67, Jul 26, 2019.

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  1. Aug 25, 2019 #101

    BJC

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    From the original post:
    The premise of this entire thread is questionable, if I’m accurately understanding Fritz’s Ranger concept, which I like very much.

    As others have noted, an airframe whose energy source is electric batteries needs to be light, streamlined and have a L/D much better than the majority of “low and slow, fun flying, open seating” airplanes such as the Ranger may be.

    Battery powered airplanes that may be useful for comparative purposes - the Song, the ALPHA ELECTRO, the Monet - are all powered gliders.


    BJC
     
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  2. Aug 25, 2019 #102

    12notes

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    50kg batteries is 110lbs, not 100lbs. 24 hp is 18kW not 15kW. I don't think it's realistic to take the smallest motor available for an airframe then reduce the power 17%.

    18kW for 5min = 1.5kW h
    75% power* for 1 hour = 13.5kWh
    15 minute reserve = 3.4kWh
    18.4 kWh/50 kg = 368Wh/kg battery needed.

    You can do these calculations, from now on, it's up to you to do them. Until you use realistic numbers and calculate a realistic energy density, you haven't found the solution.

    Look, there are small airframes that can get about an hour of total flight time on electric power. Pipstrel, for example, is not run by morons, they have engineers with education and experience in both aircraft design and electric motor technology, they're getting about everything they can out of it, and that everything is about an hour. The battery density just isn't there for any more endurance without an extremely specific motor-glider type airframe. Small manufacturers have claimed larger endurance, but their actual flights (not extrapolations from short flights theorizing future modifications) are all about an hour. It's just where the technology is, and battery technology does not advance very quickly.

    * - Spacek's cruise power for the 24hp, since it's their least powerful engine, reducing this isn't realistic - https://www.sdplanes.com/sd-1/engines/se-24-24hp-4stroke/
     
  3. Aug 25, 2019 #103

    GeneG

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    I totally agree with the Pipestrel thought.

    Lets see:
    18.5 Kw for 5 min - 1.5 Kw
    13.5 Kw for 30 min = 6.75 Kw
    13.5 Kw for 15 min reserve = 3.4 Kw
    11.65 Kw / 50 = 233 Kw/Kg Meets the battery specs and may interest an experimenter. That is my thought.
    And yes, I do calculate using real world numbers, just trying to provide info to others.
     
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  4. Aug 26, 2019 #104

    litespeed

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    Thanks for the informative posts gentlemen.

    This helps give some perspective to the thread.

    I do however note that a electric engine can be a much better match for a prop when chosen carefully. We can design the engine and prop to work more efficiently for thrust per available KW to suit the desired airframes speed and mission profile.

    So it is possible to get a the same performance from less Kw compared to a gas engine and off the shelf prop. How much better is the question and that comes down to optimising the design of the engine and prop as a system to suit the airframe. Just like we do when we run a redrive on a gas engine to gain more thrust.

    So a ideal electric system will use less power.
    Add the reduction in frontal area drag and some reduced cooling drag that can be possible and we gain a little more. Even better would be a inflight adjustable prop designed for the system used.

    Would this add to a 15% reduction?- not likely but a reduction that would help.

    But once again, we need a slippery machine that is optimised in all aspects to be a realistic real world electric flying machine.

    That will never be the Ranger.
     
  5. Aug 26, 2019 #105

    erkki67

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    Electrically powered engines will be interessting the day it can keep aloft aircraft like the Ranger, for at least 2h, for the same weight of a equally powered gasoline engine.
     
  6. Aug 26, 2019 #106

    Tiger Tim

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    Maybe it’s just because I haven’t had breakfast yet but I’m struggling with this one. Assuming in all cases the prop will see a combination of torque, RPM, and airframe drag why is it that a gas engine can’t be optimized as well as an electric motor?
     
  7. Aug 26, 2019 #107

    emir_82

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    That energy density meets the cell level specifications but not at full battery pack level. You have to add the weight of connections between cells, cell holders, connectors, cables, bms and housing.
    A proper estimation is 150-180Wh/kg with the vtc6 cells.


     
  8. Aug 26, 2019 #108

    GeneG

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    Reference please.
     
  9. Aug 26, 2019 #109

    litespeed

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    Hi Tim,

    I may not have explained it well.
    For any given airframe that has a gas engine its drag is greater than an equivalent power electric engine. A combination of much smaller frontal area and overall cooling drag. Especially if it is faired to suit the electric compared to a larger fairing for a gas engine.

    A good example is a Cri Cri , an electric one the same power will have less drag.
    So we gain the ability to have slightly less power for the same performance, assuming it is the same weight.

    The cooling drag is far lower because we can have much more direct airflow paths and the amount of heat given off per kW produced is lower than the gas engine, which puts a large amount of its energy into heat.

    So the prop may consume say 15kw but a gas engine has much higher cooling needs for the same absorbed power at the prop. At any given speed the prop does not care if the engine is gas or any other source, only that it consumes XPower for the revs.

    The drag reduction is the trick, no magic and all standard aircraft theory. Less drag equals better performance or less power for the same performance.

    Now the second part is the ability to design a electric engine to produce its power at exactly the desired speed for your airframe and provide a prop to perfectly suit its needs. In reality props tend to be certain available specs, so easier to tune the motor to the prop.

    With a gas motor we don't have that ability due to power curves, that's why we often have less than perfect prop/engine combinations. And often use redrives to overcome this power curve issue.

    A well designed electric does not need a redrive. The ability to tune the electric means we can get much closer to an ideal setup.
    We must remember the electric might be absorbing its 15kw at the prop but nothing is a free lunch and in reality the electricity it uses is always greater than 15 kW. A bad setup it might be 20 kW as there are no load losses involved. A really optimal setup it might be only 17 kw that is drawn from the battery.
    We also find that many use a electric engine that is much larger, heavier and as such has greater no load losses. Some use 1 kW at no load and some a lot more or less. Some will be far more efficient at our max required power others at less than our max required power.

    We could potentially design a electric that provides it max efficiency at our designed cruise speed or even its minimum sink rate for the airframe.

    That's the second trick that can mean a given system uses less electrical power from its batteries than another electric setup will at the same absorbed power from the prop.

    This is where systems thinking comes to the forefront of design. At the user end it really means we want the maximum amount of thrust for the absolute minimum amount of electrical draw. Thrust is what we are after, a optimised electrical system can give much more thrust per kW in power used than a poor system.

    That is why the big boys like EADS and Pipestrel spend so much time playing with their systils, changing motor kV windings, design of flux, props and controllers.

    Then we get into props, potentially we can have a much lighter prop as we don't have the big harmonic issues caused by the power pulses of a gas engine.

    It is all about small increases in efficiency in many areas that electrical can provide for a perfectly designed power system over a gas one and over a poor electrical setup.

    I hope that explains it but its late 2 am. So it might sound gibberish.

    A perfect gas engine for any given airframe does not exist, we essentially just use what's available or that we can cobble together.

    But we can optimise as close as perfect with electrical, the costs of development are many orders of magnitude smaller and possible even with basic small cnc, access to electronic parts and you can make a controller.

    I am happy to redo so it makes more sense when I am awake if needed.
     
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  10. Aug 27, 2019 #110

    emir_82

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    I don't know what you mean with reference. That is what happened to me in my battery pack design for the sailplane project.
    Its very simple, you have to add the weight of all components related to the battery and divide the total energy by that amount.
     
  11. Aug 27, 2019 #111

    GeneG

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    To interconnect 10 leaf cells you would need 27 inches of buss bar I used aluminum for a weight of .24 pounds
    To connect to controller and motor I used 19 feet of 6awg copper which weighs .8 pounds
    A suitable mounting made of 8 feet 1/16 6064 aluminum would weigh .5 pounds
    adding in total 1.64 pounds.
    When we are talking about 110 pounds of batteries this is rather insignificant.
     
  12. Aug 27, 2019 #112

    Pops

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    Where I live the grid power goes off often for a few hours or for days. I have a small 2K system that I use to operate a large 24 volt DC freezer and all LED lights in my hanger. When the grid power is off it feeds to my house for everything except for the central AC and the blower motor on the NG force air furnace. So I have a back up NG heater in the house that uses no electric and will heat the house and a large window AC unit that will cool 1/2 of the house and run on the inverter and ceiling fans in all rooms. All of the lighting for the house and TV's are LED's. Also low drain refrigerator in the house and another in the hanger that I also insulated on the outside to reduce the watts used to 1/2 before insulating. My normal grid electric bill is about $32 a month. The solar system and reducing the watts used is saving us a good $100 a month. Been using the solar system for about 7 years. NG well about 300' from the house and we use well head NG with a BTU 1/2 between NG and Propane. I heat and cool a 2400' house and a 3K' hanger/workshop.
     
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  13. Aug 27, 2019 #113
  14. Aug 27, 2019 #114

    12notes

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    The individual battery pouches of the Nissan Leaf 40kW/62kW battery have a energy density of 224Wh/kg. The battery modules (which I think is what you're calling cells), contain 8 pouches per module, and have an energy density of 189Wh/kg.

    55 individual pouches weighs 50.3kg, and provides 11.3kW, but you'll need a lot more to connect and mount these, as they are literaly just pouches with flaps for contact points.
    6 modules weighs 52.2kg, and provides 9.9kW, plus the interconnections and mounts you mentioned. These can be stacked and have convenient holes for mounting and electrical connection bolts.

    It's much wiser to use the module, as they would be much easier to work with, connect, and mount, plus also have the cooling and vibration dampening built in.
     
  15. Aug 27, 2019 #115

    stanislavz

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    Do you know size of them ? Looks like leaf is better and better for conversion.. Especially on power density level.

    Ps, wrap them around fuselage with tape.
     
  16. Aug 27, 2019 #116

    12notes

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    Specs are in one of the previous links.

    That's a bad idea, unless you like fire.

    Quite honestly, I don't think you're going to be able to safely mount and connect these for less than the 15% additional weight the modules add.
     
    Last edited: Aug 27, 2019
  17. Aug 27, 2019 #117

    stanislavz

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    it was a joke :)
     
  18. Aug 27, 2019 #118

    GeneG

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    I have not been able to determine from the info provided exactly how the modules are packaged in the 62Kw pack. The modules pictured are the 40Kw ones, but looking at the cutaway of the battery assembly they look different. you may well be correct and I am still seeking info. Reliable info is hard to find.

    LG Chemical has announced that they will be producing 300Wh/Kg modules next year, but until they appear they are vaporware.

    Envision AESC's NCM 811 Batteries To Exceed 300 Wh/kg In 2020

    My thoughts are that using the modules is the way to go as interfacing and mounting them is straightforward and should be rugged and reliable. Using Tesla
    modules, for instance, would require water cooling.

    As far as catching fire, out of the millions of these cells produced, none have ever caught fire, and indeed there are videos showing people shooting them with no ill reaction. Safety is one of the reasons I am looking at them.

    I have been researching Pipistrel's technology and haven't determined what battery they are using, but they claim 270Wh/Kg. Seems pretty high. They're using the Siemens SP55D electric motor which is also being used for the new Colt LSA.
    Still working on that.
     
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  19. Aug 27, 2019 #119

    12notes

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    I recall reading that the 62kW battery uses the same modules as the 40kW, but with 36 modules instead of 24. That may have been speculation, I'll check my web history when I get home, most likely we'll have to wait until someone tears one down.

    Batteries improving 3% per year averaged over 5-10 year spans has been fairly accurate of energy density since the 1960 (obviously not exactly 3% every year). Using this as a predictor, then we should be at 294 kW/h in 2020, so 300Wh/kg is entirely a believable claim. Especially since it's from a company that is already manufacturing battery packs for Nissan and is building a massive factory to supply Nissan with these batteries based on established lithium ion technology, and not a lab, small company announcing a partnership with another small company, or start up looking for investors.

    They are quoting the energy density of the individual battery pouches, not the actual packaged battery. I don't think a battery package exists that gets as much as 200Wh/kg. Large numbers of pouches, high discharge rates, individual cell power management, and mounting require wire, structure, cooling and electronics. Leaving that out sounds better, but doesn't really represent the true situation as it adds quite a bit to the weight.

    There was a Leaf that caught on fire in Texas a few years back, but the insurance totaled it and no investigation was done.
     
    Last edited: Aug 27, 2019
  20. Aug 27, 2019 #120

    GeneG

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    That is why I an struggling to get reliable data to work from. I believe that we are on the cusp of technology that would enable experimenters to begin work.
    One of the reasons I like the LG technology is the ease of use for builders as well as safety.
     

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