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  #11  
Old 07-17-2021, 05:57 PM
Norman CYYJ Norman CYYJ is offline
 
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Maybe the new RV15 is electric. We will soon know.
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  #12  
Old 07-17-2021, 07:37 PM
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BillL BillL is offline
 
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What voltage is the Zero? It looked like 48vdc? Is that right? That will require big heavy wires, and expensive drive inverter. Silicon follows amps not power.

300 vdc, switched reluctance motor designed with water flowing through the rotor and in the stator jacket. Running maybe 10,000-14,000 rpm with a belt drive. The electric motors have not gotten going yet, at least not publicly. The original Prius had optimized all these items for automotive. 100+kw water cooled inverters in the size of a normal starting battery. None of this is outside the realm of existing technology. It seems all electric projects are just experiments - perfect for our world.

The permanent magnet (PM- IMP, SPM etc) motors are not needed (or cost effective) for aero, the PM really gives high stall torque and would provide no value (performance) for a prop. All of these would be radial gap configurations not axial.

The total efficiency of the inverter and motor should be around 90+%, so the cooling load is a lot less than an IC power unit about evenly split between the inverter and motor. Also the SR can run much higher temps than PM can due to damage of PM types. This would allow higher take off performance and still limit cooling drag.

Can some aero designers say if the RV9 wing on the RV3 would give a better lift drag profile more suitable (low) electric power? Or would we still need a more glider like wing?
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  #13  
Old 07-17-2021, 09:24 PM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by BillL View Post
What voltage is the Zero? It looked like 48vdc? Is that right? That will require big heavy wires, and expensive drive inverter.
The Zero SR/DR used for teh Xenos conversion are 102 volts. Wires arenít that much larger than typical starter motor wires, and the good news is that with the battery mounted forward of the firewall (to replace the weight of the IC motor), the cables are short - in fact, in the Xenos, we use the motorcycle wiring without modification - all pretty short.

Paul
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  #14  
Old 07-18-2021, 06:54 AM
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BillL BillL is offline
 
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Quote:
Originally Posted by Ironflight View Post
The Zero SR/DR used for teh Xenos conversion are 102 volts. Wires arenít that much larger than typical starter motor wires, and the good news is that with the battery mounted forward of the firewall (to replace the weight of the IC motor), the cables are short - in fact, in the Xenos, we use the motorcycle wiring without modification - all pretty short.

Paul
That is much better, one does have to be very cautious about DC over 48v as it can kill people. There are certainly more details, about amps and wire size too. Not obvious, but there is a lower limit on motor wire size from a practical/mechanical standpoint to blindly pushing voltage higher. Wing and/or fuselage battery locations may drive different voltages as purpose designs emerge.

One question, since ~20khz can be used for the inverters to shape the AC motor power signal, does the Zero have shielded inverters and keep radios quiet?
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  #15  
Old 07-18-2021, 08:36 AM
g zero g zero is offline
 
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Interesting Webb site for electric motors, Plugboat dot com . Lots of non Chinese options .
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  #16  
Old 07-18-2021, 09:43 AM
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Originally Posted by BillL View Post
One question, since ~20khz can be used for the inverters to shape the AC motor power signal, does the Zero have shielded inverters and keep radios quiet?
Honestly canít tell you, but having flown Gabeís eXenos, I can tell you that I noticed no radio interference, and the BlueTooth connection from the motor to an Android phone worked perfectly as well - so it canít be a complete interference generatorÖ.
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  #17  
Old 07-18-2021, 03:52 PM
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Honestly canít tell you, but having flown Gabeís eXenos, I can tell you that I noticed no radio interference, and the BlueTooth connection from the motor to an Android phone worked perfectly as well - so it canít be a complete interference generatorÖ.
If the radio is clear then they did a good job on the EMI!!!
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  #18  
Old 07-18-2021, 05:46 PM
AeroEngineer AeroEngineer is offline
 
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Like Canadian Joy said: If you place the batteries to roughly match the weight of the current engine and fuel tanks, then you keep the re-engineering (and re-building time) to a minimum.

But, like Warren (Gasman) said: The energy density of batteries is much lower than that of fuel. The range of an electric airplane will be a small fraction of the range of a similar hydrocarbon-powered airplane (as will the endurance, unless you fly at ultralight/glider speeds, like 40mph).

- - - - - - - -

Let’s do a back-of-the-envelope calculation. Say that you burn 5 gph while you cruise. (That might not be exactly right but it’s gotta be within like 30%, right? Especially if you don’t mind slower speeds like you said). In the engines we commonly see on most single-engine airplanes, 5 gph probably gets you somewhere around 100 to 125 hp, let’s conservatively say 100. (Again, very rough ballpark, give or take like 30%). 100 hp is about 75 kiloWatts (i.e. 75 kiloWatt-hours per hour).

Most batteries can carry about 25 to 40 Watt-hours per pound, but the fancy expensive ones can do 100 Watt-hours per pound, maybe a little more. (Go to the website selling any large battery and they’ll tell you the Watt-hours – or at least the Amp-hours and the Volts, which you multiply together – and probably the weight. Most of the “lightweight” lithium-ion batteries will be in the 30s of Watt-hours per pound. This one has 42, for example). Say we spare no expense and go with 100 Watt-hours per pound. If we want 100 hp, i.e. 75,000 Watt-hours per hour, then we’d need… 750 pounds of battery per hour of flight. Compare that against the ~5 gallons (~30 pounds) of fuel that you currently need for each hour of flight.

In short: Each pound of battery only carries something like 4% (in my back-of-the-envelope estimate above. In reality it could be a little more, but still, less than 10%) as much energy as a pound of hydrocarbon fuel.

Cars work well as electric vehicles because it's possible to replace their 15-to-20 gallon (i.e. 90-to-120-pound) gas tanks with giant 1,500-pound batteries. You can't do that in an RV.

Again, this was very hand-wavy, back-of-the-envelope, “This number and that number might be off by 30% or more”… (Experts in batteries, or in the specific fuel consumption of piston engines and how it and the horsepower change with RPM… feel free to weigh in and correct my estimates). But even if we’re off by a factor of two or more, you can see that you’re not going to fly long cross-countries in an electric RV-3.

The motorgliders and ultralights currently offered as electric airplanes are designs that can fly with 60hp or less. Luckily, that’s roughly the max power output of one of the motors used in Zero electric motorcycles, so that’s what they used to power the electric Xenos and Gull and Strojnik. What do you think the climb performance of an RV-3 would be with only 60hp? Those electric airplanes, of course, are a lot slower, and have more wingspan (less induced drag), so they climb ok. Still, even at ~50% power (30hp), they need something like 200 lbs of battery per hour of flight, which is not too crazy. (… or, rather, per hour of powered flight. You can fly longer if you turn the engine off and do some soaring). Some RV-3s do carry 200 lbs of fuel, but I don’t think they could hold altitude with only 30 hp.

Some ultralights and motorgliders and LSAs and older airplanes – and some remarkable Experimentals like the Quickie – can take off and climb on a little more than 20 hp and cruise on even less than that. So now you’re in the realm of 100ish pounds of batteries per hour of flight. That’s definitely doable. But an RV needs a few times more power than that, and therefore, a few hundred pounds of battery.

(Yes, replacing a piston engine by a lighter electric motor buys you many "free" pounds for batteries... but not "hundreds". In an RV, if that difference is 100 lbs, that buys you… ~10 minutes of flight time. In an ultralight, if that difference is 20 lbs, that buys you… ~10 minutes of flight time. Again, this is all very approximate, within a factor of 2, just to get an idea of the general trends).

- - - - - - - - -

BTW, Van himself has an electric motorglider. But that kind of flying is very different from what he designed the RV-3 to do.

The RV-9, 10, and 12 are more efficient than the 3, i.e. they can fly with less power proportionally to their size. The 12 might even not be a total disaster if you put a 60hp electric motor in it, especially if you replaced the wings by bigger (glider-style) ones.

In any case… Given the energy density of batteries at the moment, there is just no way to fly an electric airplane very far. Even if you do everything you can to design an electric airplane that is optimized for range (battery weight far exceeding the occupant weight, thin low-drag wings optimized for low power and slow speeds and not capable of taking a lot of Gs), the airplane probably could not fly 300 miles or one-hour-plus-reserves (unless you “cheat” and also get some power during the flight from burning fuel).

Last edited by AeroEngineer : 07-19-2021 at 09:09 AM. Reason: Added the parenthetical about a lighter electric motor, and more links to serve as references.
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  #19  
Old 07-19-2021, 09:08 AM
rv3bwantabee rv3bwantabee is offline
 
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Great posts. Thank you all again for your inputs. The ability of batteries to store energy is truly sobering. Ten pounds for 1 KWh. 10 pounds of avgas has approx 60KWh of energy (20k BTUs per pound, 3400 BTUs = 1 KWh. 200,000/3400).

I need to find out what static thrust that eXenos is making, then set that in my 3 and see what taxi speed it will eventually get up to I believe in reduced thrust takeoffs but probably not that reduced.
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