# Electric airplane build - an introduction



## piotrsko (Dec 9, 2007)

series of immediate questions: do you own the mechanics cert on the airframe, or are you going to be required to have an A&P sign you off with a 337? You do know that this is going to be a major mod, right? 

You can go over gross, but there are operating changes (another 337). what is the current empty weight?, I believe the engine is only about 300 to 350 lbs for a O-320

Please don't take this as a flame, I really would like to see this at the Reno air races.

Good luck
Pete Moore EAA 223407 chap 1361 Reno NV


----------



## crap (Dec 5, 2009)

To get a cheap, light, high performing battery pack you could just buy a few hundred of these: http://www.hobbyking.com/hobbyking/...Product_Name=Turnigy_5000mAh_6S_20C_Lipo_Pack

Just remember you shouldn't parallell the packs, it's better to take them apart and parallell the cells. Not an elegant solution but quite cheap, you can probably expect an even lower price when buying such a bulk. 
Energy density is about 140Wh/kg, power density is more than you could ever need.

Got any idea what motor and controller you will be using?


----------



## Posthumane (Feb 21, 2010)

Czesc Piotr, 

This plane is being built and registered in Canada, and the Canadian Aviation Regulations are a little bit more liberal in regards to changing powerplants in homebuilt aircraft (for example, there are multi-engine and turbine powered ultralights). While a lot of the rules are similar to the FARs, we don't follow the US system and therefore do not have the same paperwork requirements. My business partner is a flight instructor and homebuilder, and is in contact with Transport Canada as well as other related organizations regarding this project, and so far the results are favourable. We do have an AME (aircraft maintenance engineer, as they are called in Canada) on board with the project as well.

The "typical" empty weight of a long-ez is listed as 760 lbs, but that may be a bit optimistic. As you probably know, homebuilts vary significantly in empty weight depending on how careful the builder is and how many "extras" they add. I have seen airframes sans powerplant for sale which claim weights of significantly less than 500lbs, but then again, some people also have flying examples which weigh over 1000 lbs empty. That being said being said, people do also fly these at gross weights over 1600 lbs (even Burt Rutan's crew flew their plane overgross regularly on longer trips) with no ill effects, but I'd rather keep it as light as possible. They are supposed to be powered by an O-235 as per the build manual, but many people fly them with O-320s and even O-360s.

@crap:
Thanks for the link. I have considered the idea of paralleling a bunch of smaller RC cells to make larger capacity batteries, but I'm not entirely convinced that is a good idea. While cell voltage would be equal across a parallel pack, SOC and overall capacity might not be due to manufacturing tolerances, and monitoring every cell for balance is not practical when you have over a thousand of them.

We haven't chosen the motor and controller yet, as there are a few options available. I'm leaning towards something like the Powerphase 125 from UQM technologies (http://www.uqm.com/propulsion_specs.php). It can deliver over 30 kW continuous and about 80 kW for 90 sec with proper cooling at 3000 rpm, which puts into into a typical propeller speed range. Alternatively we could use a reduction drive on the prop have larger power output from that motor and a larger prop, but a slight reduction in drive efficiency due to the gear reduction. I haven't ran the calculations yet to see which option is better, as the larger prop is also more efficient.


----------



## crap (Dec 5, 2009)

I don't really think there are any downsides to parallelling lithium cells. Some chemistrys don't work well in parallell (I believe NiCd is one of them), but I have heard of no drawbacks with parallelling lithiumcells. Unless one of the cells fail short-circuit, but since you would be so far from the rated discharge currents they should hold up well. Though I still agree it would be better with fewer bigger cells... It's just hard not to love that price 

About the motor, do you have access to a mill and a lathe and other basic machines? Me and a group of others at the university are currently making a large ironless windpower generator that could easily supply you power requirement. We made some efficiency plots, not including eddy losses and bearing losses (these are pretty much negligible if wire gauge is well chosen):


















Titles are in swedish, but torque is in Nm and rotational speed in rad/s (rpm=rad/s*9.55)

The design is quite similar to this one:
http://www.youtube.com/watch?v=u0I0Tg8sxYw

Although ours is a bit more refined...

I expect one of these could weigh less than 30kg. Copper is about 6kg and magnets 1-2kg, the rest is up to you. Custom magnets could eliminate the need for a backing iron, meaning the entire motor could be made from aluminium, carbon fibre, or whatever. Our generator won't be very light, since it's going to be stationary we didn't bother. I'll still check the final weight though, and when the project is done I intend to post all formulas, results and manufacturing methods for others to use. Possibly also a mathlab code delivering plots and key values such as total copper mass, winding turns, etc, for a wide range configurations.

It should work fine with any brand brushless controller, you could even use multiple ones like this guy did:
http://www.youtube.com/watch?v=hy6jZEW9uxc&feature=related
brilliant guy by the way, I would never have thought of that myself.

just a thought, but it will require quite a lot of work ofcourse. 

cheers


----------



## Posthumane (Feb 21, 2010)

That looks like an interesting project. I think that making a motor like that is something we will look at in the future, but for the prototype I would rather stick to something commercially available as it is an additional complication that I don't really want right now. I don't have free access to a full machine shop, so I doubt we would save that much on it, and getting things like balance sorted out is not my idea of fun. 

I agree that the price of those cells is hard to pass up, as they are basically the same energy density as the larger LiPo cells, a high power density per cell, and about the same cost as LiFePO4. What I'm hoping to do is have battery stacks of about 12 larger cells (100 Ah), giving me batteries of approximately 44 V each (nominal). Each of these batteries would be removable and have its own charger/BMS built in (something I'm working on right now), which will communicate with the plane's power management system for state of charge information. I think using 8-10 of those batteries in series would give us adequate performance without crazy voltages (440 V isn't crazy is it?).


----------



## crap (Dec 5, 2009)

Understandable, you never want do build everything yourself. Building this motor would take quite some time.

440v sounds appropriate if you have a matching motor and controller.


----------



## piotrsko (Dec 9, 2007)

sorry, didn't see the CAD/WH

IMHO 350 v is kinda pushing the current state of the art DC motor and controller wise today unless you are going to go the commercial AC route.

and there are a couple of other difficulties with high voltage DC, like breaking a circuit with a couple of hundred amps. (they really tend to arc)

wondering what caused you to choose an EZ? perhaps a velocity, E-racer, or berkut instead?


----------



## Joeav8r (Jan 17, 2009)

Wow, sounds like an awesome project to me.
Espacially that you have choosen a Long-EZ for your conversion, a very special aircraft...

Since last year i´m involved in something that could be interesting for you, a member of our local group for solar-electric mobility (from the city of Erlangen/Germany) has built an electric hang-glider.

Here some tech. specs:
Two BLDC motors from Hobbyking, 8Kw peak each.
Two Jeti Spin 200 speed controllers
Battery: LiFePo 10Ah each cell , i guess there are 12 cells serial and four of these packs parallel ( I first had to ask him what is the actual configuration of the battery)

And here some pics:





































For more pictures just take a look at my Flickr page:
http://www.flickr.com/photos/[email protected]/sets/

This solution is working very well for the first version of this drive, it has a feasible rate of climb and a 10min runtime on full throttle.

The next big changes will be a direct drive with a single motor and the change from LiFePo4 cells toward LiPo cells from Kokam.

If you have any questions i can hand them over to the owner of this.

Good luck!


----------



## sunworksco (Sep 8, 2008)

If you have not already been married to the Vari-Eze,I would consider using a design that is more suited to EV build.The www.facetmobile.com only weighs 370lbs. ready to fly,in the ICE version.This design has a vast amount of space inside the wing and can support the battery pack in a way that will balance the CG and also give a lower center of gravity.The ev conversion of the Facetmobile would be even more streamlined than the ICE version because there is no need for ICE motor cooling and exhaust.All that needs to be exiting the fuselage is the propshaft so this makes the aircraft more aerodynamic than the ICE version.
I have been talking with Barnaby Wainfan about various build materials and you could build a frame from flat triangular rigid sheets of fiberglass and cover with Stitz fabric.
A Facetmobile would require a smaller motor/battery pack and the airframe build would be a much smaller investment and a safer aircraft overall.
Please PM me for more info.


----------



## piotrsko (Dec 9, 2007)

how'd you get barnaby to answer? I even used to work with his wife at Huge aircrash S&C.

A facet mobile would be better, but plans are kinda had to come by


----------



## sunworksco (Sep 8, 2008)

There are enough drawings out there and there is even an rc kit.
The design is very basic.The fellow that has the Facetmobile rc kit conned Barnaby out of some design info and did not let him know that he was creating a kit.Not a good way to introduce a new rc design!
I sent an e-mail to Barnaby and he was kind enough to reply.
I would like to hook him up with an investor.Great design waiting to go turbo fan jets!


----------



## Posthumane (Feb 21, 2010)

The facetmobile is a neat plane. I remember reading about it a while back. However, "better" is a matter of goals and opinion, and in this case I'm happy with our choice of airframe. The reason we went with the long-ez is its relatively high L/D ratio, at a fairly high airspeed. At 90 kts, different builds get between 13:1 and 18:1 (depending on how honest the builder is ). This means we can stay aloft at those airspeeds using less than 30kW. While the facetmobile uses less power, I don't think it would get the range. With an empty weight of 370 lbs and usable load that's comparable, even with the ICE out we would only have about 300 lbs for both motor and batteries available. While the time aloft might be comparable, the range would be less. Lightweight designs like that are attractive at first, but they have their drawbacks. The long-ez is also a fairly proven airframe with hundreds of them flying, and we can pick up a completed example and strip the ICE out in a much shorter time frame than scratch building a facetmobile.

It's a very cool design though, I have to admit. One of my other preferred options would have been a quickie, but it has even more weight carrying problems.


----------



## sunworksco (Sep 8, 2008)

The Quickie is very CG sensitive and small cockpit.
I'm building my Facetmobile with flat panels of www.alulight.com aluminum foam panels consisting of 1mm double-sided aluminum sheets on a 7mm Alulight foam panel.These panels will form the frame structure instead of the typical 6061 aluminum tubing.It creates over ten times the rigidity of the tubing and does not have very much of a weight penalty.Alulight foam panels are similar in structure to the bone structure of birds,lots of porosity for lightweight benefits but high-strength.A panel will actually float on water.The panels can be fastened together with 6061 extrusion and epoxy-bonding methods used by Lotus.Once the panels and extrusions have been water-jet cut the entire assembly only takes a day.The frame can then be covered in Stitz fabric and coated.You can build this for less money and be assured that it is correctly put together.


----------



## Posthumane (Feb 21, 2010)

I know the quickie is a poor conversion choice, I just like them for the cool factor and high fuel efficiency, but it is very much a point design in that it suffers in other areas because of the focus on efficiency. I'm really interested to see your facetmobile during construction and when it's finished. Are you documenting your build somewhere? What do you expect the empty weight to be when finished? I think a lot of people would have aversions to using epoxy bonded aluminum construction in a homebuild plane because it is not a conventional construction technique, but it certainly has worked in a number of sports cars.

On a separate note, we've been pondering the various components which we would like to use on our project. A quote request has been sent off to UQM technologies for their Powerphase 125 package, just to get a baseline. Does anyone have other commercially available motor packages in the 40 kW continuous, 80 kW 5 minute rating range? Low weight is key obviously.

From what I've seen, BLDC motors tend to have higher efficiencies in general compared to brushed (as expected to some extent), but brushed motors seem to offer a bit of a safety advantage in an aircraft application in that if the controller goes south you can power them for brief periods directly off the battery pack using a contactor. Does anyone have any thoughts on this?


----------



## sunworksco (Sep 8, 2008)

You may want to start out with an AC-50 motor/Curtis Controller: http://www.thunderstruck-ev.com/AC_drive_performance.htm
This is very inexpensive compared to what you are considering and you can always sell your motor/control combo and upgrade later if needed.UQM quote will be very high.Most EV motor/control components are reliable but the switches,wiring and battery pack connections are the usual suspects in failures.Pre-flight will include electrical inspections.I would consider using newer designed types of cables that carry more voltage and are lighter.
I do not have a blog set up yet but will publish the address when ready.
Here is an image of the original Facetmobile airframe.I am basically building laser-cut Alulight bulkheads,in place of the tubing, with circular cutouts to reduce weight.I will be milling,out of solid square aluminum, the 6061 case frames to slot the Alulight panels into with epoxy and titanium fasteners.These case frames will intersect and bond the panels together.This is very strong and rigid because the slotted case frames completely control the tear-out problems associated with epoxy bonded aluminum panels together.


----------



## maxvtol (Nov 11, 2009)

Can't be much help from an EV motor perspective, but I've bought many a BLDC motor for RC. I don't know how a motor's power and weight scale up from RC, but a very conservative ~2 lbs or less per 1kw for continuous power (I usually use 1/3 of max rated power) is common for motors up to 6kw max power (or 2kw continuous) on a brushless outrunner. So maybe 60lbs for 30kw continuous could be a target. 

Keep in mind the automotive motors won't have bearings to handle the radial, axial and cyclic loads of the propeller so they will likely have to be beefed up for an even heavier weight. 

This guy builds his own motor and controller for 18hp for $4200. Maybe you could hook up 2 in tandem or get him to build a custom one for you. Link


----------



## sunworksco (Sep 8, 2008)

Here are the motor/control components which are about $1500.00.
Batteries are around $3500.00-$8500.00.


----------



## Posthumane (Feb 21, 2010)

That facetmobile would be an interesting beast to fly. It looks like the cockpit would feel a bit like sitting in a cave, but that could be my perception.

I'm expecting the UQM quote to come back at around 15-20k for motor and controller pair. The AC-50 motor and curtis controller combo is appealing from a price standpoint, though I don't know if it is quite up to spec. The Curtis controller data sheet lists a maximum battery voltage of 108 V, and 550 A RMS for 2 minutes. That's about a 60kW output (the max ratings in the data sheet show 50 kVA). I would like to have 80 kW usable for 5 minutes, followed by 30-40 kW continuous. Also, I would like to run a 400V (ish) 100 Ah pack (100S1P), whereas with the curtis that would have to be split down to about 25S4P or larger cells.

Maxvtol, I think that BLDC motors do scale up fairly well with similar power to weight ratios, as the UQM one for example is rated at 45 kW continuous and weighs 90 lbs. The controller is fairly heavy though at 35 lbs, and is water cooled to boot so the cooling system would add some weight and would require additional ducting and such.

As far as the bearings on the motors go, I'm not sure if it's better to upgrade the bearings on the motor to handle the thrust/bending loads (not much radial load from a propeller, but bending is quite prevalent in pitch and yaw changes), or to go with an indirect drive system. I'm thinking the latter may be a simpler option. A belt drive reduction is simple, efficient, and can be made to withstand thrust, radial, and bending loads, and can also put the motor in a more efficient rpm range. Of course, it's one more point of complexity and potential failure.


----------



## Posthumane (Feb 21, 2010)

From your last post, it looks like you have a PMG-132 motor and Kokam cells, correct? I have heard a lot of good things about the Perm motors, though they are only 6hp continuous output correct? or is this a different motor that you have that just looks similar?

The Kokam cells seem like a good bet for this application, but the quotes I've gotten for them have not been encouraging. The cheapest place I've found so far is superlatticeinc.com which carries the 100Ah 5C rated cells for $518 a piece. Other quotes I've gotten were in the 700-900 range from resellers, and one quote direct from Kokam at $1200! That was a low quantity price of course and may be set up to discourage individual buyers from going straight to them for their cells, but even with the cheapest option a 100 cell setup would cost over $50k for us.

I'm going to try to find a source for the thundersky LCP and LMP cells and maybe buy one or two of each to do some stress testing on them. If they stand up to some abuse (which I heard the old ones didn't) then they may be a much cheaper option.


----------



## sunworksco (Sep 8, 2008)

I was only replying to the last comment about the Electra-flyer.
I am planning to use ThunderSky batteries and the AC-50 motor/Curtis controller.The ThunderSky battery pack takes up considerable space.The Kokam.com organization is definitely a strange one!This is why the cavernous Facetmobile is such a good candidate.You can store a 160 amp 120volt battery pack behind the seat.
You need to keep in mind that the prop speed is around 2500-3000rpm at cruising speed which is a very sweet spot for the motor rpm.In other words,you are over-engineering the drive-train with anything more expensive than what I am suggesting.


----------



## maxvtol (Nov 11, 2009)

Didn't visit their website before my post, but looks like Electraflyer already has a 50hp motor developed for a 2 seater, but don't know if it's max power or continuous. And they're already using LiPo so their charging system is already developed, very important for LiPo (I'm sure you're aware). Could save some development time and probablly big bucks for your size battery pack. Might be worth a call.


----------



## Posthumane (Feb 21, 2010)

The electraflyer website looks like it hasn't had any updates in the last year or so. Where did you find info about their 50hp motor? That may be the same motor as used in the Electraflyer-C which is 13.5 kW continuous, so 50hp peak would be quite reasonable.

Sunworksco, do you know what the curtis controller will handle for continuous duty, as opposed to the 2 minute rating given in the spec sheet? Also, when you say thundersky, I'm guessing you mean their LiFFeYPO4 cells? If so, the battery pack size you are planning on using will weight close to 200kg. Add 60 kg for the AC-50 motor, and another 80 kg allowance for the pilot, and you are nearing the gross weight rating of the plane without any airframe. I must be misunderstanding something. What do you expect the overall weight of your airframe construction to be?


----------



## maxvtol (Nov 11, 2009)

On the home page shows the latest news says 2 place 50hp and in one of the videos mentioned a new motor for 2 place as well as working on 100hp. I really don't know any more than what's on the website.


----------



## sunworksco (Sep 8, 2008)

The electraflyer website looks like it hasn't had any updates in the last year or so. Where did you find info about their 50hp motor? That may be the same motor as used in the Electraflyer-C which is 13.5 kW continuous, so 50hp peak would be quite reasonable.

I was answering the above commment by MAXVTOL .

Here are the specs : http://www.thunderstruck-ev.com/perm132.htm


----------



## Posthumane (Feb 21, 2010)

I found the continuous output rating in the manual for the Curtis 1238 controller that is included with the AC-50 package. Sure enough the one hour rating is only 155 amps RMS. This would definitely not be adequate for my application, combined with the low input voltage.

We did get a quote back from UQM. It was close to what I expected - 22k for the motor/controller pair, down to 20k in qty 5.

Btw, you attached the link to the Perm-132 motor. Why so? just curious.


----------

