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Electric RV3 (Zero???)

rv3bwantabee

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Hi,
Admittedly I'm hoping to get a response from Paul Dye, but others are welcome too! After years of contemplation of building an RV3 I bought a cheap flying one this spring. Try before you build type thing. I like it, but... years ago I had a conversation with Dick VanGrunsven about putting a Rotax 912 in one. His contemplative response was, "I think it would make a nice handling airplane, but you would have to makes some mods on the engine mount (placement) and cowling." Not a trivial amount of time.

My personal experience (finally) with an O-320 wooden prop powered, straight pipe exhaust, rendition is that it is enjoyable BUTT, loud. (even with a good headset. So I find myself cruising around with the rpm back around 1900. (I'm fine with the slower speed) I save the extra power for climbing over Mountains etc.

After reading about a zero motorcycle implant recently in a Xenos I am thinking why not in an RV3. So please tell me why not!

Thanks,
Bill

PS. My dad was an auto mechanic, I overhauled a vw bug when I was 14, several v8s through high school, a couple of Continentals, and Lycomings in the past few decades, but currently enjoy ebikes and a Tesla model 3. Dont really like ICE anymore...
 
Electric RV3

Haven recently purchased an Electric Jeep Wrangler and lots of friends with Tesla Cars I’ve grown to enjoy electric vehicles. Florida has some of the cheapest electric in the country @ .10 per KW . If it was the same price per mile as gas I’d prefer driving electric because of the quite factor.
I’m looking forward to an electric Fun Airplane…..1-1/2 hour battery would be great for fun play toy . I think from a W&B standpoint retro fitting an existing design like an RV might be a redesign of the wing , eliminating the fuel tank and putting the batteries in the wing along with making them accessible. From a design standpoint the W&B it doesn’t change as energy is consumed unlike AV gas .
A single Seat electric would make a fun project
 
Electric = local 45 minutes to 1 hour flight only. If you are good with this, go for it.
 
Haven recently purchased an Electric Jeep Wrangler and lots of friends with Tesla Cars I’ve grown to enjoy electric vehicles. Florida has some of the cheapest electric in the country @ .10 per KW . If it was the same price per mile as gas I’d prefer driving electric because of the quite factor.
I’m looking forward to an electric Fun Airplane…..1-1/2 hour battery would be great for fun play toy . I think from a W&B standpoint retro fitting an existing design like an RV might be a redesign of the wing , eliminating the fuel tank and putting the batteries in the wing along with making them accessible. From a design standpoint the W&B it doesn’t change as energy is consumed unlike AV gas .
A single Seat electric would make a fun project

The good news..... You would have prefect C.G. always.

The bad news..... You would be flying at G.W. always.
 
I'll toss in some thoughts - please remember they are thoughts which come from a point of contemplation, NOT a point of knowledge!

From what I can see in other electric aircraft designs, replacing the ICE engine leaves a relatively light electric motor and some still relatively light power control hardware forward of the firewall. I'm not smart enough to figure out the density of modern batteries as compared to the density of a Lycoming so this is where I fun off into "wild a$$ed guess" territory.

If we could place an O-320-like mass of batteries in the same location as a Lycoming engine we would be able to use the aircraft pretty much as-is without significant redesign of other components.

If we could take this concept a bit further and add a portion of the traditional RV3's fuel weight between the firewall and the normal location of the engine we could start biasing the aircraft's CofG forward. Moving the CofG forward would then allow us to place additional batteries in the wings aft of the spar, thus avoiding the re-engineering of the leading edge fuel tanks and their contribution to the structural strength of the wing.

Given that, as stated by a previous poster, depleting the charge on batteries does not result in a significant change in their mass, we could shift our mental gears to design an aircraft which would more comfortably fly nearer its aft CofG limit without having to fear that CofG moving too far aft as we burn fuel.

I believe it is this fundamental shift in our perception of the "normal" range for empty weight CofG which could potentially get an efficient single-seat aircraft transitioned from Lycoming to electric power. Get comfy with the airplane being closer to its aft limit when empty and observe loading so as to remain within the manufacturer's CofG limit, without fear of "burning" our way into an aft shifting CofG as we fly.
 
Just a few quick thoughts, from someone who has flown the electric Xenos, and is now adapting our own Xenos project to electric…..

Fundamentally, the weight of the battery pack, hanging from a modified engine mount, is a perfect replacement for the Lycoming - you may move it forward or make it tighter to the firewall a bit to make it exactly right, but overall, its a good trade. Most likely, you’ll make a longer or shorter cowl, and you can also change the shape of the cowl drastically - you don;t Ned that much room.

Teh Zero power package is perfect for the motor glider, which requires fairly low horsepower, and is just for getting ti up to soaring altitude and having fun for an hour.

To make an RV-3-like experience, you’d need it to generate more than twice the horsepower, which is doable, but of course, the duration will end up down around twenty minutes, and cooling the motor might be a problem. You’d also need a custom controller and different wiring to carry the increased power. I’ve heard there is a more powerful Zero motorcycle coming or available - haven’t looked into it. But essentially, more power leads to lower endurance in a pretty linear fashion.

So…..perfect for a motor glider, but for a sport plane like and R-3? “Yet”, as my Russian friends used to say….. which doesn't; really men “no”, it turns out to mean “Not yet”…..but technology is advancing, and we’re going to see more of this stuff every day!
 
Thanks for the responses. It has prompted me to dive into my dated bookshelf where I found a copy of Charles Dole’s Flight theory for pilots. In the preface to the first edition (1984) The first sentence is, “It is quite possible to fly without knowing the first thing about aerodynamics (some of us have been doing it for years.)” Hmmm. With 1000s of hours under my belt, I might could just almost be one of those pilots! So time to read up on some of the basics. Wing tip extensions?

My simple thought line was, I have a functioning airframe, no waiting for kit delivery/build. I could dive right in. Just buy a Zero and start taking things apart. I may have some spare time on my hands in the Stockton CA area in the coming months. I’ve stuck motors and controllers on bicycles and golf carts and really like the results, especially on bicycles, makes them very rideable in hilly conditions for the non purist.

Mr. Ironflight, thank you so much for chiming in, your recent article has really lit me up. A week prior to reading it I was riding a small 400cc motorcycle after a 12 year hiatus, thoroughly enjoying the winding road, and thinking how much more enjoyable it would be with a MOTORcycle. Started looking into Zeros and your article showed up. Sometimes life is really good.
 
Wingtip extensions will increase the bending moment on the wing inboard of the extension, and tend to reduce the overall level of stability. A new purpose-built wing could be made, though.

Paul's entirely right about the power issues. A Xenos has a minimum power requirement that's much less than an RV-3. Generally, successful airplane designers design the airplane around the powerplant so that things like power, wingspan, weight, tail characteristics join to become a successful overall machine.

Dave
 
Batteries

I did some envelope calc's a year or so ago on whether an electric RV was on the horizon yet. Came to the conclusion mentioned above - fine for a motor glider or other low speed (and hence low drag, low power) aircraft. But would take some fun out of the RV experience.

https://batteryhookup.com has lots of used lithium battery packs, at a lot less than new.

So some rough numbers. Lets say we want to be able to average 70 HP for 1.5 hours (so 1 hour endurance plus some reserve). 70 HP is 52 KW. So we need 78 kilowatt hours of power. But there will be around 10% loss in the motor, and 10% loss in the battery to motor controller, so we need to add 20% - 94 kilowatt hours.

I've been building up some batteries for an off grid house project. Price is coming in around $160 per kilowatt hour. So battery cost to build the above needed battery would be about $15,000 - using used / reclaimed Lithium Ion cells. Weight (of just the cells) would be 1000 pounds. Lifetime will be around 500 cycles if you always fully charge them. So far I've assembled 10 kilowatt hours of batteries and its a lot of work. New cells and/or larger cells (less assembly work) will raise the price. Going with LiFePO4 (a safer chemistry) will also raise the cost and weight.

You can see how the picture looks a lot better for something that needs less power. Half the power, half the weight, half the cost, doesn't look so bad.
 
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?
 
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 aren’t 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
 
The Zero SR/DR used for teh Xenos conversion are 102 volts. Wires aren’t 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?
 
Electric

Interesting Webb site for electric motors, Plugboat dot com . Lots of non Chinese options .
 
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 can’t tell you, but having flown Gabe’s 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 can’t be a complete interference generator….
 
Honestly can’t tell you, but having flown Gabe’s 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 can’t be a complete interference generator….
If the radio is clear then they did a good job on the EMI!!!
 
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).
 
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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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