# replacing a lightweight 50hp ultralight engine?



## wildirishtime (Nov 7, 2009)

I'm new here, howdy all!

I've been reading as much as I can, just getting started in EV.
I'm interested in replacing my 50hp ultralight aircraft IC engine
with electric. It currently runs max RPM at 6500 at the engine
with a 2.6 to 1 gearbox.

We are all familiar with the ElectraFlyer project and apparently someone
said he used a Lynch motor in a direct drive scenario but he was only pushing 18hp. 

While I realize I dont need a motor with 50hp, I'm having trouble
locating (affordably) a motor with the best power density that I 
can still get reasonably priced. Direct drive preferred but belt drive
is acceptable as I have the room.

Any suggestions on a motor? (brushless yet?) I realize batteries
are a whole seperate headache due to the weight, but if anyone
gets on a roll i'm all ears for battery recommendations too.

Take care all, this should be a fun project if I can ever get the dollars
to pencil out reasonably.

Thanks!
~WildirishTime


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## Bowser330 (Jun 15, 2008)

wildirishtime said:


> I'm new here, howdy all!
> 
> I've been reading as much as I can, just getting started in EV.
> I'm interested in replacing my 50hp ultralight aircraft IC engine
> ...


Agni 95 Series 

http://agnimotors.com/95_Series_Performance_Graphs.pdf

Check out the last graph...72V 400A = 26kw (35hp) @ 90+% eff.

I think the motor costs 1500$USD


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## JRitt (Sep 29, 2009)

lets say that you have a rotax 503UL motor putting out 50hp that weighs ~87lb and burns 6.8gal/hr (42lbs of fuel) with a 15gal tank (2hrs) and 20lbs of misc weight (fuel tank etc.) total weight ~200lbs. 

You need an electric motor that puts out 97 ft/lb of torque @2700rpm. You would need an 8" motor that weighs 106lbs, a controller that weighs 10lbs and a 120v 200ah battery pack that weighs 500lbs to fly for 1 hr total 626lbs. The extra 426lbs would exceed the gross weight of your plane even before you got in it and then you have the problem of finding space for 38 batteries 7.14" tall, 11"wide, and near 3"thick


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## Salty9 (Jul 13, 2009)

Have you checked the RC Groups site?

http://www.rcgroups.com/forums/showthread.php?t=1067435&highlight=ultralight+electric+power


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## wildirishtime (Nov 7, 2009)

I'll combine my replies to everyone into one message.

*Bowser*: How did you determine 35hp would work to replace
a 50hp IC motor? I unerstand there's some efficiencies here
I may not understand, but an explaination of why that's 
an 'acceptable replacement' would be appreciated.

*JRitt*: I'm not flying under "ultralight" weight requirements. I'll
be fine on weight and space you can leave that part to me. 
Plus no rotax 503 that I know of burns 7gal/hr they burn half that
(but if I pull it who cares!  )

Where did you come up with your figure of 97ft/lb of torque at 2700?

*Salty:* Unless I'm mistaken, the RC guys would really only be helpful
if I were flying a microlight, or even a true ultralight. I'm talking something
a tad bigger than that so I'm hoping this is the best forum, if I'm wrong let me know.

Thanks everyone! Biggest quesiton I guess I have at this juncture is that
I have a tested performer, this 50hp aircraft motor and it does great but runs
at 6500RPM turning the prop thru a reduction at around 2500RPM. So given
that, how do I figure a correct electric motor horsepower and RPM requirement
that will 'nearly meet' or 'meet' the same thrust requirements? (These are the
days I wish I had payed more attention in physics) 

~Wildirishtime


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## Bowser330 (Jun 15, 2008)

Wild, the agni weighs about 25 lbs, so with the weight savings maybe you would need less hp (guessing), plus at draws of 450A it can produce 40hp...So you are pretty close to your ICE peak hp but with much less weight...

Two of them mated together could make 80hp peak and weigh only 50lbs...

The 95 series agni also produces this peak power at the 5000rpm range...(per the graph in my previous post, "black line")

Nevermind the fact that the lithium will weigh the EV plane down, unless you opt for the more expensive A123 cells...

1 cell:
3.3V
2.3AH (capable of 50C bursts without significant damage, 115A)
70grams

Or even a scaled up version of the lithium polymer packs the RC plane guys are using...hmmm....


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## JRitt (Sep 29, 2009)

97 ft/lb at 2700 rpm is 50hp. I used direct drive because it righ inside the hi torque range of a DC motor. I just assumed you were looking at an ultralight. An AC 50 motor would also be in the correct range. Torque times RPM divided by 5252 equals horsepower


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## wildirishtime (Nov 7, 2009)

*JRitt:* Are you saying direct drive is your recommended solution, or do you mean have actually done an aircraft engine converion? You said "I used direct drive" so I just wanted to double check. 

*Bowser:* You mention two motors, is this what's referred to as 'series'? Do I hook them shaft to shaft for such a configuration ? If so, can you truely assume you can add the horsepower of each motor, or is that just a rough estimate? You mention "peak power at 5000rpm" that would be best for a reduction drive correct? If I want to go direct drive (as JRitt suggests) should I be looking for
"peak power at 2700 rpm" since that's the typical max prop speed I use now?

*Both of you: *I've never purchased a DC motor I'm still unsure if I should be looking at brushless, or which brands produce reliable enough motors that I should put my 'life' theoretically in it's hands without breaking my bank completely.

Thanks guys!
~Wild


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## Bowser330 (Jun 15, 2008)

wildirishtime said:


> *JRitt:* Are you saying direct drive is your recommended solution, or do you mean have actually done an aircraft engine converion? You said "I used direct drive" so I just wanted to double check.
> 
> *Bowser:* You mention two motors, is this what's referred to as 'series'? Do I hook them shaft to shaft for such a configuration ? If so, can you truely assume you can add the horsepower of each motor, or is that just a rough estimate? You mention "peak power at 5000rpm" that would be best for a reduction drive correct? If I want to go direct drive (as JRitt suggests) should I be looking for
> "peak power at 2700 rpm" since that's the typical max prop speed I use now?
> ...


you would need to connect the motors possibly by some type of simple gearing, I am not sure if you can connect them shaft to shaft...this is a true addition of HP, 40 + 40 = 80hp peak...check out the last graph for pictures of the rpm curve...its very flat and seems to have great efficiency at the 5000rpm range...yes you would use a reduction to get it down to your usable range...just like your aircraft ICE.

what reduction/rpm is something I am not sure about...personally speaking, wouldn't you want to make your cruising prop speed be your most efficient rpm range? when you are spinning faster you can afford to be less efficient because that happens for only short bursts...right?

So if your cruising speed is around 2500rpm prop speed then try to align that rpm with the most efficient rpm of the motor you plan to use...in the case of the the agni motor, 90+% efficiency around 5000rpm means you would use a 2:1 gear reduction to get down to 2500.


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## JRitt (Sep 29, 2009)

Ive never done an electric aircraft (but I do own a C172N). What I should have said was I used a direct drive as a solution. Actually you may have have to some sort of indirect drive to be able to handle the pulling thrust from the prop. Maybe not though.
I would start by looking at the various motors that meet your specs for continuous 50hp (or 97lb of torque) at 2700rpm (or whatever you decide you need for specs). Then look at controllers that match the motor. and last battery pack to fee it for the ammount of flying time you want.
(make sure you are near someplace to land when you run out of power )
for anyone else wondering about the RPMs needed for the plane it should be ~2700Rpm for take off and 2200-2500Rpm for cruising


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## wildirishtime (Nov 7, 2009)

Well then anyone have a suggestion on a 80-90 ftlb / 40-50hp continuous at 2700 to 3000rpm that's affordable? $4000 for a motor is nuts for my application - you can buy comparable aircraft motors for less than that, and I'm obviously not including batteries.

I realize it won't be 'cheap' but $4000 for a motor will kill my plans of economical engine replacement.

Thanks everyone,
-Wild


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## CFreeman54 (Jan 14, 2009)

I know he said he wants a brushless motor, but with proper cooling (air ducts at airspeed) and good controller at higher voltage (144V-156V?) and 
200-300A couldn't he almost get these specs out of a series DC WarP or ADC 9"? At 120 lbs. it would be twice as heavy as a good 3 Phase AC induction motor, 
but a lot cheaper. It also is pretty happy turning about 3000 rpm which might allow direct drive. You would lose a little efficiency, but with proper gear reduction, 
not much. See chart (only graphed at 72 V unfortunately): http://www.go-ev.com/images/003_15_WarP_9_Graph.jpg


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