Electric C172 first test flight

[moocow]

They plan on 2 hours of endurance and 1 hour of charge time. Initial target customers will be FTU.

http://www.flightglobal.com/articles/20 ... light.html

[North Shore]

Apart from familiarity, why use a 172 for an electric design? They can't be that aerodynamically clean, and they weigh a bunch...you'd think that a smooth composite design would be better..

[Nark]

So they are replacing the 240 lbs of fuel, with 700 lbs of batteries. Who ever said the greenies were smart?

[PopnChipper]

I dunno Nark, this may be a good first step. You are right, 700lbs of batteries vs. 240lbs of fuel sounds pretty bad, but I am thinking that the electric motor is lighter than the internal combustion engine, changing that ratio some. Also, all the fuel lines are being removed in place of wiring. This may, or may not save. No alternator required anymore, and other accessories associated with an internal combustion. We can also talk about safety. No mixuture to worry about. No carb heat, hell, maybe headsets can get put aside as well since it would be quiet! For an FTU, or Sunday flyiers this may actually not be to bad!

PnC

[Heliian]

Ya right, we don't even have reliable, useful electric cars. I think a useful, cost effective electric plane is decades away. Diesel conversions is where it's at these days.

[TTJJ]

This article/blog explains the aircraft much better.
http://blog.cafefoundation.org/?p=1422

It is an interesting idea. The Empty Weight of 1300 lbs is about the same as a normal C-172. As it does not need refrigeration for an internal combustion engine a redesigned cowling will decrease drag significantly, requiring much less power in cruise.

And at an estimated $6.00 (Six) bucks an hour direct operating costs it is starting to make sense, even if initial costs are higher.

As to “why a C-172”? The CEO of this company was President of Cessna and has his eyes on the 43,000 or so C-172s testing their landing gear daily at an FTU near you.

Anyway, it is entrepreneurship at its finest.

It might even make the airport neighbors stop complaining about the noise, (although they will probably find something else about us that ticks them off).

[sanjet]

Ya right, we don't even have reliable, useful electric cars. I think a useful, cost effective electric plane is decades away. Diesel conversions is where it's at these days.

We got to start somewhere

[Shiny Side Up]

Personally I'd be all over this as a FTU, if they could get a little bit more endurance out of it, would be a very useable aircraft. The quoted STC of $50,000 is also very do-able. Big questions would be the service life of the batteries and what kind of maintenace schedule the set up requires. Having a fleet of aircraft with six-bladed props also just sounds cool.

[dcabrown]

If the aircraft perform as expected, for an FTU you could recover the installation cost in as little as 2 years which is a very quick payback period

(Math on that: $50/hr in savings of electric power vs fuel) times 500 hours per year of airtime at an FTU, = $25,000 savings per year. Install cost is $50,000.

The reason we dont have electric cars is because we dont have the elctric infrastructure to do it, AND we have no way of recharging cars nearly as quickly as re-fuelling. That said, similar barriers would exist for airports serving electric planes. There would need to be a way to have a bunch of 240V(?) plugs all over the place to recharge. It's a game of chicken and egg. No airport operator is going to invest in that infrastructure until there are sufficient planes that require it, but no planes will convert to electric because of the lack of infrastructire (i.e. at your destination airport) to serve them.

But if these planes can manage to recharge using existing infrastructure, this could be a game changer for the FTU's, or anyone who is ok with the initial weight penalty of the heavier batteries (which, will get lighter over time)

Great news nonetheless.

[Tim]

in addition the fuel savings, maint times would be wayyyyyy down and the amount of parts in the store room would go down.

[Posthumane]

This is indeed interesting, and doable, though I'm a little bit skeptical on their numbers. If they are using typical Lithium Polymer cells, which have an energy density of just over 100Wh/kg, then they will have about 32kWh installed capacity, unless they are using a currently unmarketed newer battery technology.

They claim that their 172 can cruise on 30.6 kW at economical cruise. This seemed a bit optimistic to me, but after running a quick back of the envelope calc it isn't that outrageous (see note below). Even if it does use 30kW at cruise, that only gives them about 1 hour of cruise time on 32kWh installed, not 2.

[Note: Required thrust can be found from weight/(L/D) in level flight. For a C172, the L/Dmax is about 8 or 9, so at 1500lbs gross the required thrust is 166 Lb (force) or 740 N. Power required is thrust*velocity, so for a C172 at L/D max of, say, 70kts (36m/s) the power is 26.6 kW. Divide by propeller efficiency (80%?) to get engine power output of 33.3 kW.]

My friend and I have done a theoretical design for this same concept, using a Long-EZ airframe cruising at L/Dmax. We figured with about 300kg of batteries and one person on board (gross wt limitations would make it a single seat aircraft) we could get about an hour of cruise after a short full power climb, giving us a 90 NM range or so. I discounted doing it on a C172 due to the draggy and heavy construction (LongEZ has a L/D max between 15 and 20 depending on who you ask). We would have liked to have started consruction on this a while ago, but we don't have the funds for the batteries at the moment. Any investors who wish to take part?

[Geo]

Posthumane: Did you note the regenerative charging during descents in the original article? That might be giving them a bit more energy available for their endurance calc. They also talk about a 6 blade prop - possibly a higher prop efficiency?

g

[Posthumane]

Regenerating energy during the decent would only net you very small gains. Not a good range extender. The 6 bladed prop would in theory be less efficient than a properly matched 2 bladed prop, but is probably required due to the higher speed of the UQM motor compared to a lycoming/continental (smaller prop with more blades to get the same thrust as a larger prop). The UQM motor was one of our top choices as well, but we planned to go with a reduction drive to be able to use a larger prop.

Charging on a 220V 30A outlet could be done in about 5 hours if can draw the full rated power from it. They talked about using solar cells on the wings. If you cover the 16.3m^2 wing area of a C172 with thin film solar cells (~12% efficiency) you could draw on average about 400W from these (assuming an average irradiance of 200W/m^2, as found in the southern US). This would require about 5 days to charge the batteries. Probably not worth it for the cost and weight.

Now, there ARE a number of other battery chemistries that have shown better energy densities compared to the ~100Wh/kg of typical LiPos. But they don't have the cycle life required for aircraft currently. Lithium maganese type LiPos can get somewhere in the vicinity of 2000 cycles if treated nicely (only discharged about 80% of the way), but a lot less if abused. Lithium Sulfur batteries have been shown to have up to 3 times the energy density, but with only about 300 cycles...

[l_reason]

I really like reading about guys that are trying to make this work. Burning $50/hr in fuel and oil plus 20 grand every 2000 hours is not going to be that hard to beat in a flight training environment. If that can be cut to 10/hr I cant wait to see what the future holds. I'm not a big fan of Diamond aircraft but with that basic design they could make a good electric trainer. Maybe even have two removable batteries between the wing spars, 400lbs each. Only 100lbs of motor and controller rather then 275lbs of O-240 engine hanging off the nose. It could also be done in a way that the batteries make up the bottom skin of the wing and changed in with another set to almost eliminate charging time.

I'll bet that there will be a few nice electric planes in ten years
http://www.electraflyer.com/electraflyerc.php

[co-joe]

I can see it now...oh you have too much "electric time" in your log book for us to hire you...you need to go out and get some piston time

[into the blue]

Exactly, co-joe! Even if this electric Cessna 172 turns out to be a marketing success, for quite a while it will probably be the largest electric aircraft an average pilot could to get some time in. It will take even more time for electric aircraft to begin apperaring in real-world commercial ops. I can see how an electric aircraft might be an attractive choice for recreational flight training, but for aspiring commercial pilots, it is certainly a no-no. Like you said, it's not likely they would be employable at all if they only know how to properly operate an electric motor (not the most complex type of aircraft powerplant, that's for sure )

[l_reason]

I can see how an electric aircraft might be an attractive choice for recreational flight training, but for aspiring commercial pilots, it is certainly a no-no. Like you said, it's not likely they would be employable at all if they only know how to properly operate an electric motor (not the most complex type of aircraft powerplant, that's for sure )

Electric or FADEC, whats the difference? Lots of aircraft have a single lever that controls thrust or power output. Most everything ever made by Boeing and Airbus work that way. I think the newer Diamond twins all have a single lever for each engine. Just like the big iron.

[Big Pistons Forever]

Whether this achieve commercial success or is another flash in the pan, will depend on the TBO of the battery pack. 5 bucks an hour for "fuel" doesn't mean anything if you have to set aside $50 an hour to pay for a replacement battery pack.

Since much smaller hybrid car battery packs have replacement costs of more than $8000, I have to wonder how much 700 lbs of exotic metals battery magic costs, as well as how long they can last given the demanding duty cycle flight operations will place on the battery. Anybody with technical expertise in this field care to comment ?

One thing I also noticed is if this conversion is to be used in FTU's it needs a belly gunk generator. I mean we can't deprive the ramp rats of all that valuable experience having to lie on their back cleaning all the crud off the belly, can we ?

[Posthumane]

BPF - TBO on battery packs can be made comparable to that of piston engines. A well treated LiPo battery pack (LiCoO2 or LiMn2O4) can have a cycle life of over 2000, as has been demonstrated. I think LiFePO4 is comparable. This is typically quoted as the number of cycles after which the battery will still have 90%, or 80% capacity remaining, depending on who's giving you the numbers. So the battery pack is still usable at that point, and has a fair amount of residual value for less weight critical applications.

A "well treated" battery pack means that it doesn't get discharged below about 20% Depth of Discharge (DoD) and often not charged above about 95% DoD. Following this limitation obviously reduces your effective capacity, but for aircraft this is not that much of an issue since you aim to have a 1/2 hour reserve anyway.

Costs for LiPo batteries can be as low as $0.50 per Wh, but for the larger high quality cells (such as those made by Dow Kokam, as will be used on the Yuneek aircraft soon) the cost is probably over $1.00/Wh in large quantities (consumer prices for these cells are closer to $2.00/Wh unfortunately). So if you require 30kWh for one hour of cruise you are looking at $15k of batteries at minimum, but probably closer to $30k. If you get 2000 cycles out of them, then you have a TBO of 2000 hrs. If you go to a battery pack twice the size, the TBO becomes 4000 hrs, but the replacement cost also doubles. This means your "battery reserve" at current battery prices is comparable to an engine reserve for a lycosaurus.

The TBO on a brushless DC motor such as the UQM is in the order of about 10000 hrs, and the overhaul consists of replacing the sealed bearings that support the shaft, so it's really a non-issue. Unless you overheat the motor, then you have to replace the permanent magnets, which is probably comparable to replacing the whole motor.

[alctel]

Interesting to see how much charge they hold during winter as well...

[Shiny Side Up]

I can see how an electric aircraft might be an attractive choice for recreational flight training, but for aspiring commercial pilots, it is certainly a no-no.

The recreational/PPL type market is a large one though so in terms of having a couple of these machines on the line at a FTU it certainly would be a revenue generator. There is no reason either why all PPL training couldn't be done on these aircraft, even for aspiring commercial pilots. I could see a license restriction though for those who did all their training on such an aircraft. If one could reduce even sligthly some of the costs of RPP and PPL training though I would be certain one could significantly increase one's market share in a particular area - especially if one was the first to put such machines on the line. Easier and cheaper to fly is a big seller - as I said before, merely the idea of a six-bladed prop would simply draw a lot of interest from a lot of the GA community.

I'm not a big fan of Diamond aircraft but with that basic design they could make a good electric trainer

I doubt that the diamond would work as well as the Cessna, if only because it leaves a lot less room for modification. A conversion of this nature would pretty much mean a ground up redesign. Part of the reason a 172 makes such a good candidate for this project is the ample room and very generous CoG limits. As it is right now, you could put two people in a 172 and 700 extra pounds and it would be within its limits. One wonders if an electric 172 will still be certified for spins...

Either way, it will be interesting to see.

[iflyforpie]

One problem will be the recharge time. You will have to have two hour breaks between flights, which will mean lower aircraft utilization and higher fixed costs. Also, can you imagine doing a cross country and having to wait to hours to fill up? What if there is more aircraft than receptacles at the electron replenishment station?

I would imagine in time that these issues might be ironed out. Another thing I am wondering is if solar cells could be used as range extenders?

[CpnCrunch]

The Yuneec's battery pack costs $20k and lasts 2000-3000 hours, so that's $10/hr which is on a par with your typical 172 gasoline engine.

http://www.wired.com/autopia/2010/10/el ... -near-you/

It also has a swappable battery, meaning you can fly all day (in theory).

The diesel/electric hybrid 172 sounds interesting, although I'm wondering how much it would weigh.

[Posthumane]

I think the Yuneec will make a better training aircraft in the near future than the C172 concept. It's a much less draggy design, and has been flying for some time now. Yuneec has a fair bit of experience in the electric market and have real world numbers to back up their claims.

When my friend and I started thinking about our project we had hoped to be the first in Canada marketing an electric conversion, but it's quite likely that someone will beat us to it. Either way, I think electric airplanes have the potential to give the GA industry a big boost.

[hawker driver]

One problem will be the recharge time. You will have to have two hour breaks between flights, which will mean lower aircraft utilization and higher fixed costs. Also, can you imagine doing a cross country and having to wait to hours to fill up? What if there is more aircraft than receptacles at the electron replenishment station?

I would imagine in time that these issues might be ironed out. Another thing I am wondering is if solar cells could be used as range extenders?

Extension cords for the circuit.