# Is electric propulsion worth it?

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#### opcod

As question posted and comments after... Let always keep the : mission in mind. Having and old pack for a motorglider is ok just to take off and then glide. Just to get rid of the tow-plane. But on the efficiency.. the power /kg is still at about in lab of 1/6 of what gas is. Yes you can said you are green with battery.. but not efficient at all. On the r/c front.. 16yrs ago i got big Axi motor. I can just put the motor on top of a potato bag and it fly.. But for a 2min it cost about 1500$for the batt pack. To get the mission of : i can take off a potato bag.. check. Efficient .. no. Those Pipistrel is about 60k to swap the batt. All in all it cost less to swap the Rotax 912. But hey you on gas you fill and 10min your are back up. Electric.. stay on ground for the rest of the day charging. 380v are not available in America and 240 not really present at any airfield. #### Speedboat100 ##### Banned That’s why a biplane is terrible for speed. At Reno the biplane class is about 40-50 mph slower than F1 with similar airframe rules and almost 75% more horsepower. Wouldn't it be a time for a change then....a faster biplane ? Anyhow...electric can provide helluva lot more lay outs for an aeroplane....as the engines and many of then can be placed easily in a way a combustion engine never could. #### Speedboat100 ##### Banned As question posted and comments after... Let always keep the : mission in mind. Having and old pack for a motorglider is ok just to take off and then glide. Just to get rid of the tow-plane. But on the efficiency.. the power /kg is still at about in lab of 1/6 of what gas is. Yes you can said you are green with battery.. but not efficient at all. On the r/c front.. 16yrs ago i got big Axi motor. I can just put the motor on top of a potato bag and it fly.. But for a 2min it cost about 1500$ for the batt pack. To get the mission of : i can take off a potato bag.. check. Efficient .. no. Those Pipistrel is about 60k to swap the batt. All in all it cost less to swap the Rotax 912. But hey you on gas you fill and 10min your are back up. Electric.. stay on ground for the rest of the day charging. 380v are not available in America and 240 not really present at any airfield.
That is a challenge...therefore I am constructing a 40-50 kg aeroplane to be able to carry 20-30 kg of batteries for a decent and cheap flying.

Rutan was able to make a plane that carries 3 times more fuel than plane weighed empty..or was it 4 times ? The Voyager. That is a benchmark in efficiency.

#### henryk

##### Well-Known Member
That is a challenge...t
=DIANA2 glider, 180 kg empty,
+250 l of water ballast in wings...

#### poormansairforce

##### Well-Known Member
Rutan was able to make a plane that carries 3 times more fuel than plane weighed empty..or was it 4 times ? The Voyager. That is a benchmark in efficiency.
First off the Voyager had a wingspan of 110 ft..... You got a hanger that big? Even downsized it's going to be a big plane. The wings alone would weigh more than your 70 kg goal.

Secondly, using the same numbers from the para plane above, you need 200 plus horsepower on the Voyager so your battery is going to weigh about 2,000 lb for the same performance as a para plane which means you might take off and fly a part of pattern. Quadruple that to get to Max TOW and you'll get a little more. That would actually be a benchmark in 'lousy'!

#### rv7charlie

##### Well-Known Member
Mission, mission, mission.

I don't think anyone believes we can currently build a 200 mph cross country 500 mile range 2 seat sport plane. But...we *can* build 80-100 mph local fliers good for an hour + reserve. Be honest and ask yourself how you typically fly. I'd *love* to replace the Rotax 503 on my Kolb Twinstar with a couple of 25 HP electric motors (more prop disc area; better mass flow), and just enough battery capacity to keep me up for 20 minutes or so. No interest in a cross-country Kolb; I've got an RV for that. If I were to stumble upon a salvage Zero bike, I just might try it...

Meanwhile, battery tech continues to advance, probably faster than we realize, because it's happening in a steady ramp, rather than huge, newsworthy jumps. This won't happen tomorrow, but it's looking pretty good for a 5-10 year window, and will roughly double lithium's energy density. Nowhere near gasoline, of course, but a pretty big jump.

Charlie

#### Speedboat100

##### Banned
First off the Voyager had a wingspan of 110 ft..... You got a hanger that big? Even downsized it's going to be a big plane. The wings alone would weigh more than your 70 kg goal.

Secondly, using the same numbers from the para plane above, you need 200 plus horsepower on the Voyager so your battery is going to weigh about 2,000 lb for the same performance as a para plane which means you might take off and fly a part of pattern. Quadruple that to get to Max TOW and you'll get a little more. That would actually be a benchmark in 'lousy'!

I am not sure where you are getting at mr poormansairforce...but I did learn quickly...my design is now 50 cm longer than yesterday, but it is a cantilver monoplane...no longer a biplane.

I am talking about efficiency...no matter was it Burt and Voyager or just a drone carrying 5 kilo camera.

#### jandetlefsen

##### Active Member
HBA Supporter
Those Pipistrel is about 60k to swap the batt.
Are you talking about battery refurbishment? Where does that number come from? For the (uncertified) Alpha it is around 10,000 Euro.

But hey you on gas you fill and 10min your are back up. Electric.. stay on ground for the rest of the day charging.
The batteries are swappable in a few minutes.

380v are not available in America and 240 not really present at any airfield.
I've no idea about the electrical infrastructure in the states, but somehow they are building tons of electric car charging stations. Aircraft charging infrastructure is technically the same so i don't think this is an huge technical challenge. Also don't airports already use a lot of power needs and therefore have high voltage connections? This part appears to be the most trivial to me.

#### Speedboat100

##### Banned
Mission, mission, mission.

I don't think anyone believes we can currently build a 200 mph cross country 500 mile range 2 seat sport plane. But...we *can* build 80-100 mph local fliers good for an hour + reserve. Be honest and ask yourself how you typically fly. I'd *love* to replace the Rotax 503 on my Kolb Twinstar with a couple of 25 HP electric motors (more prop disc area; better mass flow), and just enough battery capacity to keep me up for 20 minutes or so. No interest in a cross-country Kolb; I've got an RV for that. If I were to stumble upon a salvage Zero bike, I just might try it...

Meanwhile, battery tech continues to advance, probably faster than we realize, because it's happening in a steady ramp, rather than huge, newsworthy jumps. This won't happen tomorrow, but it's looking pretty good for a 5-10 year window, and will roughly double lithium's energy density. Nowhere near gasoline, of course, but a pretty big jump.

Charlie
I see I might load my craft with extra batteries if and when that day comes....if it becomes too heavy I just have to "label" it experimental and register it and let someone test fly it.

I will do the R/C model of 1/3 scale at least. If it is impressive then so be it.

#### pictsidhe

##### Well-Known Member
380v is not available in America as it uses 208v and 460-480v for 3 phase supplies..
Almost all domestic and small supplies are split phase, so 230v is actually very easy to find. Granted, 230v outlets are not common. But that just needs one wiring up to the box. Most buildings would be able to have a 5-10kW 230v supply simply added. Many could go higher. If you have a $50k aeroplane, you'd be quite willing to spend$500 on the hookup.

I see topspeed is flooding the thread with nonsense again.

#### jandetlefsen

HBA Supporter
Compton Airport has a Pipistrel quick charger installed, somehow they got around the voltage issue. Those costs around $40k plus installation. #### pictsidhe ##### Well-Known Member There is no voltage issue, you just order the charger to suit your electricity supply. #### BJC ##### Well-Known Member HBA Supporter 380v is not available in America as it uses 208v and 460-480v for 3 phase supplies.. I haven’t purchased any recently, but autotransformers are (were) an inexpensive way to match European equipment to US voltages. BJC #### rv7charlie ##### Well-Known Member I doubt that they would be needed. Just about any kind of voltage reducer/rectifier/charger/etc these days will be 'switcher' based. Look at how many small device chargers are universal voltage devices now. A properly designed inverter style charger rectifies whatever AC comes in, feeds it into a (relatively) high frequency variable duty cycle square wave generator, and feeds *that* into another rectifier/filter, while varying the on-time of the square wave to attain desired average output voltage. My Miller Dynasty TIG welder has no physical voltage setting method. It has 3 'hot' wires, 1 neutral and 1 ground wire. You can wire from one to three of the hot wires to a hot circuit, of any voltage from 110V to 480V, from single phase to 3 phase, and it 'just works'. Running on single phase 110V will limit current output a bit (primarily due to limits in 110V supplies), but it will still work. 480V 3 phase works, too, and anything in between. Charlie #### Dusan ##### Well-Known Member As question posted and comments after... Let always keep the : mission in mind. Having and old pack for a motorglider is ok just to take off and then glide. Just to get rid of the tow-plane. But on the efficiency.. the power /kg is still at about in lab of 1/6 of what gas is. Yes you can said you are green with battery.. but not efficient at all. On the r/c front.. 16yrs ago i got big Axi motor. I can just put the motor on top of a potato bag and it fly.. But for a 2min it cost about 1500$ for the batt pack. To get the mission of : i can take off a potato bag.. check. Efficient .. no. Those Pipistrel is about 60k to swap the batt. All in all it cost less to swap the Rotax 912. But hey you on gas you fill and 10min your are back up. Electric.. stay on ground for the rest of the day charging. 380v are not available in America and 240 not really present at any airfield.
I think what is referred usually as "efficiency" is how much you convert from one form of energy to another, e.g chemical potential energy to mechanical energy and not how much it costs. For an internal combustion engine, the efficiency is typically around 40%, so 60% is wasted as heat. For an electrical propulsive system the efficiency is above 90% so less than 10% is lost as heat. I would say this is general knowledge, but not so obvious are the implications. There are two more facts affecting the performance: battery specific energy (energy per weight, some people are wrongly referring to this as "energy density", which actually is energy per volume) and power to weight ratio of the electric motor.

Implications:
- Wasting so far less heat, the air-frame for an electric aircraft can be made much more aerodynamic, having much less drag. The motor is so much smaller, batteries can be placed virtually anywhere (controlling COG), so the aerodynamics can be further improved. This means the aircraft needs to be built from the ground up with electric propulsion in mind.
- Power to weight ratio of a typical electric motor is about three times that of a comparable piston ICE. That means in some condition the weight of an electric propulsion system (batteries, motor, controller, all) can be less than a complete ICE system. Usually this is achieved by designing the system for flights less than 30-45 minutes.
- Efficiency of the electrical system does not change significantly with power setting. The electrical power plant is happy at 20% power setting, where the aircraft aerodynamically has the best range, endurance whatever. An ICE, piston and even worse for turbine, reducing the power setting reduces drastically the efficiency.

Concluding, the electric propulsion really shines in a sleek air-frame. Replacing an ICE with electrics in a draggy air-frame just emphasizes the low specific energy of today's batteries.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
It would be impossible to charge more than a few trainers without significant airport grid upgrade.
Doesn't make much sense for a future private Jetsetter to cruise at 300 kt only to wait 3hours in line at the airport for a charge station.

#### rv7charlie

##### Well-Known Member
It would be impossible to charge more than a few trainers without significant airport grid upgrade.
Doesn't make much sense for a future private Jetsetter to cruise at 300 kt only to wait 3hours in line at the airport for a charge station.
Mission!
You're not going to cruise anywhere at 300kt in a 2 seat general aviation a/c any time soon, and certainly not in an all-electric one. So those points are...pointless. ;-)
And I'd bet that a 'grid upgrade' would cost less than adding an approved tank/pump/payment system for a mogas supply next to the avgas & jetA tanks, which quite a few airports have done.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
I guess you didn't get my reply was a follow up after the last paragraph of the previous post 197. The mission now is trainers and ultralights not sleek long distance transportation.

#### rv7charlie

##### Well-Known Member
Well, you have to admit that making the connection would be pretty difficult, when his post said nothing about 300kts or jetsetters...

Dusan made no elaborate claims about extreme performance; he just pointed out that the much better weight/HP ratio, and radically improved conversion efficiency, and HP being unrelated to altitude, all work together to narrow the gap between IC engines and electric. Especially with a clean airframe, flown up high.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
Why would you go high on a short flight? The mission now is short range and very limited.
Works very well for RC models flown 10 minutes. I just ordered another one last night.