# Aircraft use of Electric Motors, or EAV



## dark7622 (Jul 3, 2008)

Hi everyone,

I've been building a BD-4 aircraft, from plans, I'm still a long ways off from it flying but I was thinking about motors for the plane.

There is alot I am not sure about that I need some advice on.

You see it adds up, an electric motors I have seen in my research avg about 100 or so pounds. some more some less. A gas motor is alot more. Granted the battries are an issue.

A typical airplane with a 900 mile radius has 85 gallons of gas onboard (normally in the wings) it burns an avg of 8 -10 gals of gas an hour. 

85 x 6 (6lbs per gal of gas) = 510

I figured 10 25lb batteries at 250

The problem is and here is where I really lack the knowledge and where I see no info (so far) is about numbers for an eletric motor being used for flight.

You see an electric motor would have to maintain a constant speed of 4000 RPM's and a max of 7 to 8k rpm for takeoff. I'm not sure about the drain on the battries or how long this can be maintained.

I have read about AC Water cooled electric motors, and they seem better suited for this. 

Once at a crusing attitude there isn't any hills or dips or such (normally) and it's pretty easy to just stay on a constant speed, hence terrian issn't an issue. 

So here is the question

Length of time Motor can run on X number of battries and keep a 4k RPM. 

The plane its self for the payload I want, requires a 180hp gas motor, now there was a few articles I have read that Electric HP is different from Gas HP in that a 95HP Electric was like a 200hp gas, I'm not sure about this and that's another question, how do they compare, how do I figure out the numbers.

Another part of the problem is charging, many rual airports are lucky to have lights on the runways, plus they are grass runways. I'm not going to get a charge. I don't mind landing every 2-3 hours (since I would be crusing at 140mph), I only plan to stay within the region. THough how do I charge the battries. Hence I figured I could put in a small gas powered horzontal motor turning a generator to feed the battries, this could help provide the battreis with power in flight (so they don't drain as fast) as well as a way to charge the plane while I take a nap in the shade of the wing.

I'm not sure about the math of how much generated power per HP of a gas motor or how long it would take to charge up X number of battries. 

I don't think between the little bit of gas (since the small motor won't take much) the battries, the geneterator/motor, and drive electric motor that I will be saving any weight at all. The point is that the whole system is simpler to maintain, less moving parts and hence less maintance. I was even thinking that I could make the Gen/Gas combo something that can be bolted in for long trips and when I'm just joy riding I don't bother and leave it on the ground (hence less weight). 

The Gen/Gas Motor combo would be direct drive connected, a 2hp gas hoz motor direct bolted to a generator shaft, hence no loss of power with gears or belts, plus making it a solid unit. 

The prop would be a direct shaft connect, hence with a brushless motor there alot less friction. I could store 4 or so battries around the motor/gen/gas motor combo's and the rest in the mid section of the plane. 

So basically there is a lot of math that I'm just not sure how to compute or where to begin because I'm missing alot of variables. So anyones help would be great!

Look forward to hearing from everyone!


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## electric85 (Apr 10, 2008)

hey, i can't answer any of your questions but love your project!!!
i've always wanted a plane and i plan on getting one one day. always thought it would be amazing if you could build an electric plane but never thought it was possible. do you have any pictures or a website/blog? i'l love tofollow your build and ihope you work it all out and get this thing off the ground!


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## joseph3354 (Apr 2, 2008)

fantastic project! here are a couple links that may help:

http://www.airventure.org/2007/4wed25/sonex.html 

http://www.treehugger.com/files/2008/01/first_conventio.php 

good luck with your plane!!


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## d-bledsoe (May 22, 2008)

Awesome project. I too am building a BD-4 however not for electric. The BD-4 was my dads plane that we were building when i was a kid about 15 years ago. We had it all framed up and had to move. We had to take it all apart as it was easier to move that way and its sat in pieces ever since. Now i have taken the project over and hope to finish it someday.

-Derek


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## Guest (Jul 3, 2008)

You might think about an AC motor set up. Greater RPM's. Has Regen. Higher voltages which would be better. Lead batteries are going to be your biggest hurdle because of the weight. Lithium will be very expensive for what you need. Electric planes can work but you have a long road ahead. You may not get what you want but you can get an electric plane built. Don't give up if you have the funds to do it. 

Pete


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## dark7622 (Jul 3, 2008)

gottdi said:


> You might think about an AC motor set up. Greater RPM's. Has Regen. Higher voltages which would be better. Lead batteries are going to be your biggest hurdle because of the weight. Lithium will be very expensive for what you need. Electric planes can work but you have a long road ahead. You may not get what you want but you can get an electric plane built. Don't give up if you have the funds to do it.
> 
> Pete


Thanks Pete,

Yes, I know it will be costly, how costly I'm still trying to figure out, after all a used aircraft motor runs 10-12k a new one runs 25k. So is it more costly then those? Not sure yet. Battries are going to be an issue, I had hoped that with a combo (small gas/gen) that I could avoid some of the weight (by reducing battries). Or try to use the latest and greatest in batteries. I was thinking about dry cell

http://www.performancedistributors.com/batteries.htm

I think this can be done, there is a new battry coming (or came out, can't see to find where to buy it) from toshiba (super Ion) and it looks very promissing. 

WIth an aircraft motor it can cost 9-10k on each rebuild, they are costly beats. I'm thinking with the lower maintaince of EV AC motors that in the long run I would save alot more money. It's going to take me a while to get up everything. Even got a long ways to go with the plane as it is.

I'm thinking that as far as the motor/gen/gas combo goes that it won't change too much, it's all a mater of battries.

Though I would love to get some solid numbers together.


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## joseph3354 (Apr 2, 2008)

for 25k you could likely buy an ac system and a lithium pack.there are lots of lithium suppliers that can sell a good size pack for around 12k.


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## dark7622 (Jul 3, 2008)

d-bledsoe said:


> Awesome project. I too am building a BD-4 however not for electric. The BD-4 was my dads plane that we were building when i was a kid about 15 years ago. We had it all framed up and had to move. We had to take it all apart as it was easier to move that way and its sat in pieces ever since. Now i have taken the project over and hope to finish it someday.
> 
> -Derek


WOW, cool, well mine his the whole fuselage and landing gears.

I took a bit of a short cut and got it from this guy.

http://www.engalt.com/BD-4_Project.htm

though I saved alot of money since I got it from him alot cheaper then that (3500). 

I got a long ways to go, one thing I would really like to avoid is wet wings I rather have a tail taink for a small gen/gas motor then go though all the expense and time to seal a wet wing, which are so prone to leaking I found.

Where are you?


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## dark7622 (Jul 3, 2008)

electric85 said:


> hey, i can't answer any of your questions but love your project!!!
> i've always wanted a plane and i plan on getting one one day. always thought it would be amazing if you could build an electric plane but never thought it was possible. do you have any pictures or a website/blog? i'l love tofollow your build and ihope you work it all out and get this thing off the ground!


I'll be sure to start one up and let everyone here know the address when it's up.

Yea it's going to be a fun project.

Joe


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## dark7622 (Jul 3, 2008)

joseph3354 said:


> for 25k you could likely buy an ac system and a lithium pack.there are lots of lithium suppliers that can sell a good size pack for around 12k.


Well I'm hoping that by aug of 2009 that the price of barrties go down enough, I would really like to get a whole system togetehr for under 10k, I might be dreaming. 

Joe


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## Uncle Joseph (May 7, 2008)

dark7622,

I'm fairly new here, but welcome to the forum. What I'm not new to, is aviation. I'm building a Zodiac XL experimental with a William Wynne corvair engine conversion. Once the plane is flight proven, I may convert it to electric.

There are only 2 electric planes I know of right now. The original ElectraFlyer, which is a converted trike, and the ElectraFlyer-C, which is a converted Sonex Aircraft Xenos glider. You can read about both of them here: http://www.electraflyer.com/

Sonex Aircraft is also working on a proof-of-concept for their Sonex model. Also, as I understand it, if you're in the United States, you'll need an FAA exemption/approval to operate and test fly your BD-4 with an electric motor. Both ElectraFlyers had to go through this process.

Horsepower comparisons are very different between ICE and electric motors. ICEs are usually rated for peak HP under no load, whereas electric motors are typically rated at continuous HP under load. Keep in mind that aircraft and automobiles have very different operating characteristics and missions. What works on an automobile does not necessarily work on an airplane.

That said, many electric motors excel at operating at full RPM (i.e., take-off) or constant RPM (i.e. cruise speeds). In fact, many electric motors were specifically designed to operate at only a few different speeds, rather than having constantly varying RPMs (as most ICE automobiles do). 

A BD-4 is going to be a heavy airplane for a lightweight electric motor installation. Your only real choice due to weight of batteries is going to be lithium if you want any kind of range whatsoever. You may be able to start with a lead pack, but you may only get an hour of range (unlikely). FAA minimums would require you to have more on tap for your reserve.

At this stage in the game, I do not think that an AC system is appropriate. Regenerative braking will not work in an airplane. The only time it might remotely apply is during long descents or on approach to land. I suspect you'll have to "idle" the electric motor during power-off descents and approach to land in order to get similar performance as you would from an ICE airplane. This means you're never really "coasting" in an electric airplane, and regenerative braking does not apply. You might get some windmilling of the propeller to give you some regenerative braking, but that would only be on VERY rare occasions. How many times do you kill the ICE in an airplane during a descent? Never, unless it fails. Even at idle, you're getting some thrust out of the engine. Although think of the short landings you could make if the propeller not moving, or freely windmilling!

So, a DC system will be both simpler and cheaper. There are no formulas or real-world experience that will help you with range considerations and battery pack size. You will need to size your pack based almost completely on horsepower (i.e. voltage) requirements and guesstimate how many Ahs you'll need out of your batteries. Again, electric car comparisons will give you a starting point for your range estimates, but not a direct translation.

Also, if you're planning on operating any engine/motor in your BD-4 at over 4,000 RPM at any stage of flight, you'll need a reduction drive. Propellers do no work properly at 8,000 RPM (they break the sound barrier). Redrives are heavy, expensive and add a level of complexity that will at least be detrimental to performance. You should be able to run a DC motor in direct drive for the simplest, most efficient conversion. There are plenty of DC motors that will fit the RPM and power requirements for direct drive. You'll have to experiment with propellers, but I'd recommend going with the designer's recommendation to start, and purchasing your motor around that.

The other big consideration is the electric motor's driveshaft which would be akin to a car's crankshaft. It needs to be able to hand substantial torsional loads (turbulence, pulling out of a dive, steep turns, etc). Cars do not experience crankshaft forces in the same fashion as airplanes do. You'll need a motor with a robust shaft. Additionally, propeller extensions are tricky business, and you'll likely need one with most of the commercially available electric motors (unless you get one with a custom one-piece shaft long enough for your installation).

The best thing to do would be to compare a certified aircraft engine's performance and design characteristics to whatever electric motor you might consider. Heat has the potential to be a problem in the electric motor for take-off and climb, but not necessarily for cruise, descent and landing. The motor will need to be able to withstand the amp draw and voltage for climb and take-off without overheating.

All of these hurdles can be overcome with careful planning (and enough cash for the lithium batteries). I'm sure I'll have more thoughts on this later, because I've been formulating the plan for an electric airplane based on my Zodiac XL for quite some time.

Hope some of these considerations help! If you're already building your BD-4, then you're probably already an EAA (Experimental Aircraft Association) member. If you're not a member, you really should be!


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## dark7622 (Jul 3, 2008)

Uncle Joseph said:


> dark7622,
> 
> I'm fairly new here, but welcome to the forum. What I'm not new to, is aviation. I'm building a Zodiac XL experimental with a William Wynne corvair engine conversion. Once the plane is flight proven, I may convert it to electric.
> 
> ...


Thanks for all the useful advice, yes I had only been looking at auto conversions based on costs and the fact that I have worked on so many (auto motors, as a former mechanic). Hence I only knew off the top of my head the auto RPM numbers.

One thing I have not heard anyone comment on is the use of a deisl/gas motor powering a generator onboard for inflight charging and on ground charging.

With the way things are if I make a trip anywhere I can't count on being able to plug in anywhere, plus they don't have a way to charge for it either (most of the time). So I figured an onboard generator would do the trick. I don't expect it to keep the battries powered up in flight (a generator that big would be really heavy)but I would think that it would at least slow down the draw. THen while I take a nap or get something to eat at an airport where ever it might be, that it will continue to run to recharge the battries.

I figured with such a system that I could get away with less battries, how many less and where the fine line is, I don't know.

THough I have been thinking ablot about this, I think your right in getting the planes air worthiness certificate first, then switching out power plants. If I go the combo route (gas/gen/emotor) then the wet wings can still hold a limited amount of fuel for the gas/gen. I would like to see my plane fly first and then start work on retrofiting it. Hence (I know this isn't what alot of people would want to hear) but to keep the costs down and have a powerplant that won't be too painful financally to loose money on, I was planning on putting in a ford v6 3.8 with a north west areo 2 to 1 redrive including EFI. I put the costs (rebuilt motor) at 3.5k USD. That's not including prop, I would get one rated for the plane and with adjustable pitch which would be great for the Emotor. 

I'm planning on keeping the weight down as much as possible, using composits here and there and light wight metals where they can safely be used, sucha s replaing alot of the plywood in the orginal plans with lightweight composit honeycomb material (floorboards and other parts). Anyways I plan to bring the plane down to at least 200-300lbs below the orginal weight (since I'm going with an all glas cockpit that saves alot of weight too). 

Anyways, I got a ways to go, so I'm researching all I can research on the EV motor installation, I'm thinking with cars like the chevey Volt going into mass production next year, and other manufactures gearing up for mass production EV cars, that the market for high performance battries will open up and with higher production numbers = lower costs, so by 2010 we might see a very cost affective EV Plane. 

does anyone have any thoughts on the combo all together (gen/gas/emotor) and how one will effect the others?

Joe


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## enganear (Jun 16, 2008)

This is a fun thing to think about, but the electric weight / power compromise is so very bad that this will never work even with cost-be-damned best possible batteries.

No A&P would ever certify this for flight, but you will not get that far because calculations will prove the futility of this exercise long before.

Li-poly batteries and brushless outrunner motors have given electic RC airplanes the performance of the nitro fueled ICE counterparts. They have a range of several minutes before requiring recharge and have no useful payload capability.

Fun to think about, but my advice would be "don't spend any money" because IMHO, this project will "never get off the ground".

Build a ground based EV first.
-enganear


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## dark7622 (Jul 3, 2008)

A&P and expermental are two different types, no A&P is required to work on the engine since it's not a certified plane, homebuilt/expermental follow different rules.

Granted it might not be possible right now, but there is alot of work going on. Plus there are a couple planes out that are using electric motors, granted they are not flying for long periods of time. 

What I'm really thinking is this is a year 2000 20k plasma TV and I need to wait a while and the mass production of better battries and motors will make this into a walmart 2008 800 buck plasma TV.

granted I got maybe a year before I'm even ready for an engine, but it doesn't hurt to research the possiblities. Alot can happen in a year or two.

Can't do an EV car, one project at a time, what do I get with a dumb car? I'm only home on weekends since I fly out every week. save a couple bucks driving to the airport LOL, might help my wife though LOL So maybe when I'm done with the plane LOL.

Joe


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## enganear (Jun 16, 2008)

dark7622 said:


> A&P and expermental are two different types, no A&P is required to work on the engine since it's not a certified plane, homebuilt/expermental follow different rules.
> 
> Granted it might not be possible right now, but there is alot of work going on. Plus there are a couple planes out that are using electric motors, granted they are not flying for long periods of time.
> 
> ...


You might want to reference the experience of someone who tried an airboat project at: http://www.evalbum.com/1042

His range was 1 mile at 10 mph using components that typically give 30+ miles at 30+ mph in an EV.
-enganear


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## Uncle Joseph (May 7, 2008)

Getting an airworthiness certificate for an electric airplane should not be a problem. Where you're going to fall short is range...way short. Even with the best lithium packs out there, and the airplane loaded to gross (for the entire trip mind you, since you don't lose weight as you fly like you do with fuel), you might be lucky to get an hour of flight time out of it. Math and lots of calculations are in order to get even a rough estimate.

The idea of creating a series hybrid airplane is a good thought, but it's not practical, in my opinion. I'm thinking you're gonna have to load it down with so many batteries that you'll end up with a 2 seat airplane with 4 seats (or a large battery pack behind the front seats). You could theoretically make a removable battery pack as a range extender that sits in the back seats. But, if you add even a small gas/diesel generator to help charge the batteries, whether on the ground or in flight, you're essentially adding ballast. Ballast is dead weight. Dead weight = much less range/performance. I would only remotely consider the series hybrid concept if the generator was running all the time, and was in fact needed all the time. Otherwise you're going to have a huge weight penalty in batteries alone, and then you're adding the generator (plus fuel) penalty.

Many EVs gain several hundred pounds over their normal curb weight after conversion. This is simply not acceptable in an aircraft, unless you're willing to only fly one person (the pilot) and operate at or near gross weight for the entire flight. If you remove batteries to give yourself more useful load, your range will probably come down so much that the plane won't be very practical.

The whole thing is possible, but the reasons I've outlined above are why most, if not all current EV airplane experimenters are focusing on light sport type planes with very short ranges (1 hour maximum flight time).

Cowling, structure and weight and balance changes all compound with the slightest modification. For your airplane to have any sort of range, you'll need batteries in the wings, batteries in the cowling with the motor, and batteries in the back seat. Putting batteries in these locations after constructing and using the airplane with ICE is going to cause major overhauls of the wings, cowling and fuselage structure to accommodate battery racks. Plus, you'll then have another test period of 40 hours after the electric motor is installed because you'll be using a different experimental power source.


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## aeroscott (Jan 5, 2008)

dark good work on finding the hp electric / gas engine hp ratio , i hope its true . *I've*​ been working on the same thing with a *Lancair*​ 200 . if you figure on the cruse speed of 200 mph range will be very short but we can go to the lower end of the cruse speed and range will get way *better.i'm*​ planning on wing tip extensions *which*​ the factory had at 15 inches , i think i need more like 30 inches .high prop speeds are used for *convenience*​ with high speed engines . a lower speed larger prop will give higher trust but limit top speed so that needs to be *figured*​ .prop can be lighter *because*​ of less *vibration*​ .ac motors including dc *brushless*​ are more *efficient*​ and lighter then brushed .gear reduction would be needed for best weight . $50,000 for *li*​/poly is a big bight for me but in the airplane world engines coast that and more . *I'm*​ thinking of 130 mph and 25 kw /hr i hope , 30 kw pack is about 20 grand . if we get the *Stanford*​ silicon *nano*​ thin *film*​ batteries *that's*​ 10x better then we go air racing


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## Thalass (Dec 28, 2007)

I've heard of only a couple of electric aircraft (other than that Helios 
(pathfinder) thing that NASA built), which have been linked already. 

I was flicking through a magazine (can't remember which one, EAA perhaps, with a restored Tiger Moth on the cover) and I came across a few articles on sailplanes - and one in particular about a powered sailplane with a 30-1 glide ratio. And I thought to myself that a powered sailplane would make a perfect conversion donor. They're light, very aerodynamic (better than most kit planes/bugsmashers), and the motor isn't used constantly so the battery capacity is not so much of an issue. 

And if you were travelling cross-country you may even be able to recharge via solar cells, or partially at least via regen on your descent to an airport. 




As far as larger electric aircraft go, it's not really practical yet. Unless they produce a fuel efficient APU to provide the power (MrFusion, anyone? hehe) you won't see electric airliners any time soon - which is unfortunate because they would keep me busier than I am right now.


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## Vwbeamer (Jun 16, 2008)

This has to be irritating format for a post ever.


aeroscott said:


> dark good work on finding the hp electric / gas engine hp ratio , i hope its true . *I've*​ been working on the same thing with a *Lancair*​ 200 . if you figure on the cruse speed of 200 mph range will be very short but we can go to the lower end of the cruse speed and range will get way *better.i'm*​ planning on wing tip extensions *which*​ the factory had at 15 inches , i think i need more like 30 inches .high prop speeds are used for *convenience*​ with high speed engines . a lower speed larger prop will give higher trust but limit top speed so that needs to be *figured*​ .prop can be lighter *because*​ of less *vibration*​ .ac motors including dc *brushless*​ are more *efficient*​ and lighter then brushed .gear reduction would be needed for best weight . $50,000 for *li*​/poly is a big bight for me but in the airplane world engines coast that and more . *I'm*​ thinking of 130 mph and 25 kw /hr i hope , 30 kw pack is about 20 grand . if we get the *Stanford*​ silicon *nano*​ thin *film*​ batteries *that's*​ 10x better then we go air racing


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## CNCRouterman (May 5, 2008)

I would like to try to address the question of how much energy storage is needed, and electric motor sizing.

With regards to electric motor sizing, as someone previously mentioned, Aviation applications are much different than automotive, so the "rule of thumb" comparison for electric to gas pretty well goes out the window immediately. An aircraft engine will run at 75% power and above for much of it's service life, unlike a car, which will run at less than approximately 20% for almost all of it's service life ( hot rod's and teenagers' cars excluded ). So, I would suggest that you will want an electric motor that has a continuous rating absolutely not less than cruise power, and a 10 or 20 minute rating at or above take off power requirements. All of this presumes that you can cool it adequately. Cooling capacity will degrade with altitude if I remember correctly, so you have a bit more research ahead of you.

Your indicated 180hp engine, of which you will use, pretty much 180 hp for take off and climb. Presuming that you will have nominally the same ramp weight, the power requirements will be the same. So, for sizing your electric motor, you will want one capable of approximately the same output.

For energy storage, gas is hard to beat in terms of weight and volume, but that may change as energy storage technology matures. For now, your quest for electric powered flight needs to deal with currently available tech. Just like every aspect of aviation, you need to define the mission parameters, so for this exercise, you need to determine power requirements for a typical mission.

Takeoff: More power is better, but lets use 180 hp.
180 hp equals about 134 KW.

Climb will probably use the same power setting, although you might cut back to 85-90% instead of 100% so lets say climb out is at 121 KW (~90%).

Cruise is typically at 75% for standard cruise, and 55-65% for economy cruise, lets use 70%, or 94 KW.

Decent and pattern will be at reduced power, I don't know what percent that is for you, but I will guess it will be at about 30% or 40 KW.

So far, we have just looked at power requirements, now let's take at energy requirements.

Take off and climb to 5000 ft AGL at ~800 fpm from brakes off- about 7 minutes with ~1/2 minute takeoff (less I hope, but just trying to err on the high side). Let's say we want 1 hour of boring holes in the sky, and then descend to pattern alt., then land, so decent, pattern and touch down will take maybe 10 minutes?

0.5 min at 134KW= 1.1KWh
7 min at 121 KW= 14.1 KWh
*** cruise will be at power times hours, eg; 94KW x 1 hour= 94 KWh
10 min at 40KW = 6.7 KWh.

So, NOT counting cruise setting, you might need something in the neighborhood of 21.9 KWh. For an hour cruise add 94 KWhs or total of about 115.9 KWh.

For my own purposes, I generated a spreadsheet to look at some Lithium Ion packs, their output and weight, I plugged in some numbers to see what it would take to get near your requirements.

If each module is 3.2 volt nominal, and is 200 Ah at 14.75 pounds each and you built a pack of 40 modules you get:
640 volt
200 Amp hours at C1 (optimistically)
640v x 200A / 746watts/hp = 170hp 
128 Kw hr capacity
14.75#*40=2950 pounds of batteries.
40 modules at $496 = $99,200 Maybe less for a "bulk buy discount"?

I don't think that the BD-4 can carry that much in "fuel"?

Now, to be fair, those same batts are advertised to be able to output three times the current, or 600 amps without damaging the batts, and even as much as 11 times as much for short (as in 10 seconds) times, which means that you could try 1/3 the batts and still have the take off hp originally presumed at 1/3 the cost, 1/3 the battery wieght (983 pound), but also 1/3 the endurance, actually, less than 1/3 the endurance. 

So, regarding ramp weight and power requirements, it seems that they may both go up, just as EVs tend to get heavier than their IC counterparts.

There are other methods of generating electricity that may be better suited for aviation, but they involve chemical reactions and consumable anodes/cathodes or whatever-nodes, which lead to a host of other challenges that electric drive and the battery approach were chosen to avoid.

I know that there are several successful examples out there, and I know one person who has done some work in this area, although I do not recall if he provided any of the engineering for those particular examples. You might try contacting Bill Husa at Orion Technologies in Snohomish (sp?) Washington, oriontechnologies.net.

Bill could give you a better idea of what you really need to accomplish the mission.

My data is subject to fat finger errors, so please don't try to fly them without due diligence!


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## enganear (Jun 16, 2008)

CNCRouterman said:


> I would like to try to address the question of how much energy storage is needed, and electric motor sizing.
> 
> With regards to electric motor sizing, as someone previously mentioned, Aviation applications are much different than automotive, so the "rule of thumb" comparison for electric to gas pretty well goes out the window immediately. An aircraft engine will run at 75% power and above for much of it's service life, unlike a car, which will run at less than approximately 20% for almost all of it's service life ( hot rod's and teenagers' cars excluded ). So, I would suggest that you will want an electric motor that has a continuous rating absolutely not less than cruise power, and a 10 or 20 minute rating at or above take off power requirements. All of this presumes that you can cool it adequately. Cooling capacity will degrade with altitude if I remember correctly, so you have a bit more research ahead of you.
> 
> ...


Your numbers look reasonable to me. A logical analysis with real world limitations factored in. Is there a commercially available motor that would be suitable for this application? I suspect the required motor would be surprisingly heavy as well.
-enganear


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## Thalass (Dec 28, 2007)

Your numbers look pretty good to me. And support the idea that an electric powered glider would work (assuming you have the right conditions for gliding). 20kWh isn't that large, even 30 or 40kWh would not be difficult to squash into an aircraft - though there would be losses from having to distribute the batteries around the airframe.


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## CNCRouterman (May 5, 2008)

With respect, Thalass, the 42 KWh batt pack (1/3 the 40 module unit) would still weigh in at almost a 1000 pounds. That would be a LOT for a GA aircraft, the equivalent of 167 gallons of avgas, or about 10 hours endurance for many 4 place aircraft at cruise. I know much less about aircraft gliders than I do about powered aircraft, of which I am NO expert, but I would expect that adding 1000 pounds to any current 1 or 2 place motor-glider would keep it on the tarmac.

I hope that did not come across as snooty, I really do not mean it that way. I have wished mightily to do what dark7622 and Derek are actively doing, that is, build a plane. I even figured that as one of the things I would use my CNC router for, making components for my own design. However in 2001 when I started my CNC Router jobshop business, I discovered that I was woefully unprepared technically, financially, and temporally to get a startup venture going successfully AND design AND build a plane all at the same time. Just as many of us on this forum are scouring about to learn what we need to know about EVs, I have scoured and scrounged to learn about aviation. My venture into EVs is driven by practicality, or at least the proper respect for due diligence in the effort. My venture into aviation has thus far been limited to contributions to several startup aircraft manufacturers. I really can't count the work I have done for Lockheed, Sikorsky, Boeing, or Raytheon because it was simply manufacturing to specs, and it went through customers of mine as small parts of much larger projects for the famous guys. They probably do not even know I did the work.

One very valuable lesson I learned many years ago is to seek out reliable and knowledgeable people in the field of interest, and do your best imitation of an information sponge whenever you get the chance. I consider Bill Husa of Orion Technologies to be one of those knowledgeable resources in the aviation field, and for that matter, the automotive engineering field as well. He is not afraid to admit a lack of direct experience outside of his forte, or direct you to appropriate resources, or for that matter tell you why a particular idea is all wet, when merited.


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## aeroscott (Jan 5, 2008)

Vwbeamer said:


> This has to be irritating format for a post ever.


I didn't even post this , I was previewing it as a single paragraph and it posted like you see it .


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## KFRtoad (Jul 8, 2008)

CNCRouterman said:


> Your indicated 180hp engine, of which you will use, pretty much 180 hp for take off and climb. Presuming that you will have nominally the same ramp weight, the power requirements will be the same. So, for sizing your electric motor, you will want one capable of approximately the same output.
> ...
> Just like every aspect of aviation, you need to define the mission parameters, so for this exercise, you need to determine power requirements for a typical mission.
> 
> ...


I am jotting down ideas for an electric ultralight as well. The engine in mine is a 100 hp Rotax 912 . 
I thought what was important for rotating the propeller is the torque available to make it move. In that case the Rotax outputs 128 Nm at maximum power.
I believe an electric motor capable of 120 Nm is much smaller than one which outputs 75 kW but I am just guessing here. Anybody can comment/confirm this ?


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## Thalass (Dec 28, 2007)

500kg is quite a bit, but not too crazy - especially if you're removing alot of stuff. Or, even better, if you design from scratch. Though I must admit I don't work with bugsmashers, so it could well be too much for most cheap existing airframes. 


I did a bit of number crunchery, and this is what I came up with: 

640v nominal (200x 3.2v)

Pack rating = 40kWh

40000 / 640 = 62.5

62.5 x 1.25 x 1.05 = 82Ah

Thundersky 90Ah LFP batteries. 

3kg each x 200 = 600kg pack

640v x 90Ah = 57.6kWh total capacity

US$180 per cell x 200 = US$36000 - 23% (bulk discount for less than 18000Ah total (90x200cells) = US$27,720 


So 600kg, then (1322.772 lb). Yeah, it's alot. But not an impossible barrier to overcome. 

It's also not an overly insane price, though it doesn't include shipping.


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## Uncle Joseph (May 7, 2008)

The biggest hurdle with an electric aircraft, as with electric cars, is cost. One of the major points of building an experimental aircraft is that it's usually far cheaper than the equivalent certified aircraft (if you're comparing new or slightly used aircraft). If you can get the repairman certificate for your experimental, you'll be saving even more over time due to annual inspection costs.

I don't think an electric airplane is out of the question, unless you don't have the money to spend on batteries. A lithium battery pack for even my Zodiac XL is likely to cost north of $25-30k. My corvair conversion is only going to cost about $8k in its entirety. Plus, I'll have 4-5 hours of range on 100LL fuel. That $25-30k battery pack is likely to give me an hour of range, and doesn't include the motor, controller and airframe modifications required. So my $35-40k airplane kit just turned into a $70-80k airplane kit if I go electric. From a dollars and cents standpoint, electric isn't a viable option at the moment. However, I'm more interested in doing it as proof-of-concept. Once someone proves it can be done, then the practicality of making it available to the masses (i.e. cheaper, and functional to the average customer) will come to fruition.

I am starting to re-think my standpoint that the electric aircraft system be DC-based. AC would give slightly better range/efficiency (even though regen isn't that applicable in an aircraft), but to my knowledge, the wiring doesn't have to be as heavy duty. Correct me if I'm wrong, but AC systems can operate on far smaller gauges of wiring, right? This might make a huge weight difference, although I think you'll still need the heavy gauge wires connecting your batteries....

Of course, this is all speculation.


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## CNCRouterman (May 5, 2008)

Wire size is a function of amp draw, not voltage, not (directly) wattage. AC are usually higher voltage than DC for a given power category, so your conclusion that AC uses smaller wire than DC is generally correct, but it is due to the typical voltages used, not because it is AC. 

I have read of DC motors wired for "high" voltage, say 180 to 240, and I suppose that a brushless DC could run at the same voltages you would find AC traction motors running at, around 480 to 650, but this is just supposition on my part.
Since the power of the motor is basically volts time amps, and with volts at 480, it only takes about 280 amps to get to 180 hp, or 155 amps for 100hp. Either of which still require pretty good sized wire.

Regarding Torque. Just as IC motors can be engineered to deliver a desired torque at a specified rpm (within certain constraints) so can an electric motor be wound to produce a desired torque/rpm curve/line (again, within some constraints).

I believe that an electric motor could be far superior to an IC for aviation use, however, at least for now, the main problem is not the traction motor, but the energy storage medium.


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## loopfuzz (Jul 16, 2008)

I met a guy at the Arlington airshow in Washington last weekend, that is the designer of the Gull 2000 and he said he's also working on a electric version of it. Sounded pretty cool. More info about his little planes are at http://www.thundergull.com/

Christopher.


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## aeroscott (Jan 5, 2008)

loopfuzz said:


> I met a guy at the Arlington airshow in Washington last weekend, that is the designer of the Gull 2000 and he said he's also working on a electric version of it. Sounded pretty cool. More info about his little planes are at http://www.thundergull.com/
> 
> Christopher.


 very cool bird , can even be an ultralight . this would make a easy er electric as power demands are somewhat less .from sportaviation this month, the ElectraFlyer-C based on the sonari ,90 minutes cruse , 1 seat , 45 mph stall , 70 cruse . www.Electraflyer.com


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## panhandler1956 (Jul 23, 2008)

I'm really interested in this technology for aircraft applications as well.

I am currently building an RV-8 (www.mykitlog.com/owens) and although I have no interest in putting an electric motor on that aircraft with any of the current technology, I would love to covert a Kolb Firestar II (see example below) into an EV. The engines they run are 40-65hp. 
I am really keeping my eye on the electraflyer as well and I'll be at Oshkosh next week so hopefully it will be there and I'll learn more. The Kolb is very light weight, has room for a passenger (not all models) and has folding wings so you can store it in your garage. Would make a fun 'alternate' toy and a great research plateform. 

Brent
Columbus Ohio


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## Uncle Joseph (May 7, 2008)

panhandler1956 said:


> I'm really interested in this technology for aircraft applications as well.
> 
> I am currently building an RV-8 (www.mykitlog.com/owens) and although I have no interest in putting an electric motor on that aircraft with any of the current technology, I would love to covert a Kolb Firestar II (see example below) into and EV. The engines they run are 40-65hp.
> I am really keeping my eye on the electraflyer as well and I'll be at Oshkosh next week so hopefully it will be there and I'll learn more. The Kolb is very light weight, has room for a passenger (not all models) and has folding wings so you can store it in your garage. Would make a fun 'alternate' toy and a great research plateform.
> ...


I'll be at Oshkosh myself...I think I can do it (electric) with my Zodiac XL someday...perhaps I'll see you there.


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## Tom Thomson (Jun 11, 2008)

Dark
Here are some solid numbers which can be verified in any handbook.
A horsepower is a horsepower no matter if it's from a gas engine, an electric motor or an actual horse.
1 horsepower = 550 foot pounds per second or 33,000 ft/lbs per minute
1 hp = 746.5 watts
1 watt is 1 amp at 1 volt so 1000 watts = 1 kw (kilowatt) = 10 amps at 100 volts or 5 A at 200 V or any of an infinite number of combinations.

Using these relationships we can say that 100 hp for 1 hr is 74,650 watt hrs. At 180 V that's 414.7 amp hrs which is one BIG honkin battery. And while you're at it, don't forget that high discharge rates and DOD (depth of discharge) limitations both lessen the usable amp hrs of any battery.
Good Luck
tommyt


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## Technologic (Jul 20, 2008)

dark7622 said:


> Hi everyone,
> 
> I've been building a BD-4 aircraft, from plans, I'm still a long ways off from it flying but I was thinking about motors for the plane.
> 
> ...


The way you have to look at electric motors is not in a direct cost comparison to a standard aircraft motor (even the $90,000 twin turbo lancair engines).

You need torque for an airplane motor (a lot of it) and you fly at stable speeds for the most part (ideal for electric AC motors). Water cooled AC motor is a must... but shop around and price one (they are cheap for a very high power one in comparision)

You will have to go with Lithium... dry cell lead acid is out of the question for a plane. The weight will simply be too severe. 
An Electric airplane motor is possible... even preferable to ICUs... the reason is that they are far more stable at lower temps (ie. 20k feet and up). The motor will be so cheap I would build a redundancy motor behind it interlinked so you can switch in case of an emergency (private plane crashes are common). Be sure to add a small heating unit for the batteries (and enclose the batteries)

a 200 hp engine is rather small on a plane... but you'd want at least 70kw or so in an engine constant maybe something like 250kw peak... so say your plane goes 200mph (this will depend on weight... so use lithium). I'd figure you'd need about a 150-180kwH reserve if you're going all electric... if you're going to mess with a hybrid design (also better than the 1 motor design on efficency per mile) you'll need a 40-60kw generator and at least 70kwh's of lithium

Believe it or not... this will cost probably 50-70,000USD once it's all said and done... but airplane fuel isn't cheap... you'll make the difference back in 1 year of flying I'd bet.


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## knmi (Jul 22, 2008)

Nice to meet people that think outside the box. Here's 2 problems that have to be addressed:
-Long wings are effective wings thus propellers should be as long as possible. Long propeller means high tip speed (breaking the sound barrier). Ground clearance is vital and thus it too limits the lenght. I guess this is the reason why propellors swing at 2700 rpm with a diameter of say 74 inches at takeoff. At 4000 rpm you will either have a short propeller or use a reduction gear.
-The other thing to be aware of is that a airplane engine use 100 % power at take off and usually 75% at cruice speed.
On the positive side I do understand that electric motors have a high torque. Seen those huge Lycoming pistons? = high torque.
Now I have to rethink regarding my Pottier 180S homebuilt w/o engine.


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