Crominator

Greetings all,

Im in the process of designing a blended wing body electric plane. Wing span should come in around 8 ft. or so. I am hoping for around 12-17 lbs when its all said and done. Its a lifting body, so the planform area is fairly good sized. Bottom line is that this monster needs to go like a bat out of hell. There seems to be a general consensus that one needs 100 watts/lb for really good performance, so I am going to need about 1500-1700 watts. As I have been looking into brushless motors, I find that they can either do high volts, or high amps, not both (as one would expect from basic electronics). So I was wondering what the people thought in terms of taking the high voltage, or high current route. Or if there is a motor that can handle 30 cells and 100 amps that doesnt cost more than a new car, Im all about that too.

Currently, i am in possesion of a Pheonic 80, by Castle Creations (good for 20 cells, and 80 amps) which is all well and good, but Mega's website says that this 22/45/3 I have is only good for 50 amps (WEAK!) Does anyone know if the Mega is good for more current?

basically imagine that you can afford 18.5V 8000 mah lithium packs and need a motor/esc combo that could take advantage of it..... (no i cant afford the world, so keep the cost down, but lets see what's out there)

2 motors is an option as well (though I was shying away form that for budget concerns)

Thanks guys!

John

Henke Torphammar

this is a complex problem... you got many motors capable of 2kW... but not for long... pop up a knotch and there are only a fiew that can peak 3kW and run continoiusly on 2kW.

the Megas does´t work... the little sissy 12" prop would waste all the power you put in. I would go with the system Sean used in his P51... a C50 13XL 6.7:1 with a 20x15 prop (might have been 21x15 too) it propelled his 80" P51 to 125mph. You want roundcells maybe a C50 12XL on 32cells would be good.

You can also use the AXI series, AXI 5330/18 should be able to swing a 20x15 on 32cells round cells too I think. I don´t know of any setup like this, but reading the numbers it should cut it too.

eflight-ray

Are you just in the design stage of this model, or already building/built?
I have a large flying wing, 130" span, 6.5 lbs weight, and it flys on 7 cells. Admittedly it has a glider section and it flys slowly but 2Kw of power does seem rather excessive.
How about more information on what the model is and its proposed flight performance, perhaps the problem could be attacked from a different direction.

Henke Torphammar

it would be a good sportflyer at lot´s of less power... large wing and clean aerodynamics...


but the since keywords were "12-17lb" and "go like a bat out of hell" ...

Crominator

OK more on the design.

The purpose is a giant flyingwing/ blended body design that carries (and drops) water balloons. Most of my professors are telling me that a flying wing is a terrible way to go (low lift coefficients etc) but I am using the configuration just because I can, and its gonna look awesome (and conventional airplanes are boring).

Tentatively looking at 18 in root chord to a 10 in tip chord, with 36" hlf span on the wings. In the middle will be somewhat of a lifting body, around 24in span, and 40" centerline chord, tapering back to meet the 18" wing chord.
The wing sweep will be kept low (I developed an airfoil that keeps its center of pressure at the quarter chord independent of angle of attack, so its got very low pitching moment... ie. its reflexed) so my pitch control will come from the C wings. The winglets will be NACA 0009, mostly likely and be about 15% of the halfspan in height,m and the horizontal stabilizers will extend back in over the wing, but swept back at about a 25 deg angle. This should give sufficent distance from the CG for good pitch control.

I know all the structural people just had a heart attack over the C-wings. Carbon fiber nd reinforced spars all around.

I want the good performance because... well.... if you have to ask why we want it to go fast, no explanation is sufficent. I was hoping for an empty weight of around 10-12 lbs, and a loaded weight of around 17 lbs. Since its a flying wing, and a pusher prop, the props cant be much bigger than 14 inches if this plane is going to have a chance at rotating for takeoff.

The fact that its a fairly good sized plane helps me lower the minimum velocity for actual flight, but I kinda want to have my cake and eat it too by having this plane hold some pretty steep climbs. I am loathe to use round cells because they are so heavy, and the biggest batteries from Thunder-Power can dump 80-100 amps continuously. That and lithiums are 3 times as power dense. If i have to chew up all my cargo weight in Nicads, then that doesnt help me much.

I dont especially want to just design for "short bursts." I would rather, for safety, just have a system that can do 80 amps or so indefinately if I asked it too.


if you want to get feel for what the plane is going to look like, think of a giant picojet with higher aspect ratio wings, and more of a lifting body, or search for "Boeing BWB" on google and take a look at their blended body research. Add on to the a C-wing configuration, and you have my plane.

I am still in the design phase, but I am about to move into the building phase.

I might drop the wing span down to give it better manueverability, but then its gotta go faster to carry the weight.

Thanks for the help, let me know what other information you might need.


John


the big kicker is that i need to keep the prop diameter down or have 2 ft tall landing gear

Matt Kirsch

My Feedback: (21)

A very intriguiging project, for sure. Are you planning on a "scale" prototype first?

2000 Watts is obtainable, especially with LiPolys, because the ability to stack multiple packs in parallel gives you unlimited current potential. Finding something that can SUSTAIN 2000 Watts given today's practical limit of 10S LiPoly packs, might be interesting. 2000W on a single motor in bursts for aerobatic maneuvering, yes, but not a constant 2000W. For that, you'd want at least two 1000W power systems, or even 4 500W power systems.

With a 10S LiPoly, we're talking about ~60 Amps sustained current. With a 6S LiPoly, 85-90 Amps. Either way that's quite a bit of current to deal with. Even if you really only wanted about 1500W, it's still around 45 Amps. Heat dissipation will be your main concern.

Crominator

There wont be a "scale" prototype in its total definition, but a model of the full size wings with a much smaller motor flew on monday.

I am becoming more and more a fan of you 1000W dual suggestion because it allows me to retain use of some of my current equipment. Also, since its a pusher, we need to keep the prop diameter down to reduce chance of prop strike.

Thunder Power Batteries claims their lithiums can perform a 10C (10x nominal capacity) discharge without cooling (so we'll add cooling jsut to be safe). On a 6S4P pack, 22.2V and 8A, I should be able to discharge continuously at the Pheonix's limit of 80 amps.

So what we need then, is a motor that can do in essence 20 cells in series, at 80 amps continuously and we would have a fairly balanced system. Further more, thats 1800 watts, so assume 1600 of that actually gets to the prop. that should take a 16lb plane for a ride, depending on prop efficiency. Mega recommends for the 22/45/3, 16 cells max and a 10" Prop with 30 amps (max of 40). I dont buy that for a second. I have a 12" Master airscrew 3 blader turning 7000 rpm at 24V and 12.2 amps (which is when my pheonix 60 exploded) Are those figures conservative? I 've had it up to 50 amps on 16 cells before adn the motor didnt even get warm.

So what are folk's experience/recommendations with a motor that can groove with 80 amps at 24V?

thanks again for all your help

RC Extreme power

My Feedback: (24)

Inner Demon gear drive. http://www.innerdemon.com/
They make one for twin motors that I think will handle 3,000 watts (Call them)

Motor http://www.starluckrc.com/feigao540.html

The 54084 class motor is close to the Hacker B50
At a price of $110.00 x 2 $220.00 not bad
Average amp draw of motors is 55
55amp x 18.5 =101.75 x 2 =2003.5 watts
You will have to use two ESC
Hope this helps
Milton

Crominator

OOooOO. I saw a sight selling little Feigao motors. Does anyone have any history with those? Reliability? I sure dig the price tag

RC Extreme power

My Feedback: (24)

If you are talking about the IPS motor there have been a lot of good reports on it.
All the Frigoa motors seem to be holding up very well
Milton

Henke Torphammar

well I would not use the 10C continous on such a large pack... calls for trouble. Also the 80A esc WILL fry if ran at 80amps.

you do need a 10s pack if you want true 2kw through the flight. for a 3d plane the 6s4p would be great, but for continious 2kw... nope.

Matt Kirsch

My Feedback: (21)

The cells might be rated to handle 80 Amps "continuous" and so may the ESC, but in the real world, it isn't true.

What I think we're trying to say, but really haven't said yet, is that it's better to get your Watts from Volts than Amps. Volts is electric potential, like the height of a waterfall above a water wheel. Amps is the rate of flow, like how many gallons per minute is going over the waterfall. An analogy would be dropping 100 gallons of water per minute from 20 feet vs. dropping 200 gallons of water per minute from 10 feet. The kinetic energy when it hits the bottom may theoretically be the same, but you're using twice as much water, so it's less efficient in that sense.

I also analogize Volts to cubic inches in an engine. Sure, you can get 500HP out of a little 1.8L 4-banger with the cams, intake, turbos, spray, etc., but you're stressing that engine and it won't last long. 500HP from a 426 Hemi, on the other hand, is a daily driver...

Henke Torphammar

I´m stealing this to the outrunner/inrunner thread

eflight-ray

Crominator

Your description of your flying wing design rang a bell with me. Have you heard of the Horten flying wings? Originally designed around the 1930s-40s in Germany. R/C scale models have been made and flown, one even had twin model turbines, there have been glider/slope soarer versions and I am pretty sure an electric one was built and flown.
Might be worth a search on the web for information.

Crominator

Horten's were pretty neat, and Northrop was the man. In retrospect, mine wont look like either of these.


The problem is that current is a function of the voltage (and the resistance, but that being the same, its voltage that provides current, rather than the other way around. So given a motor (resistor) one can only obtain a certain current before the effort (voltage) cant force any more flow (current) through the system. Jack up the voltage, and you increase your ability to send current through the motor. So in theory, we would want the high voltage system for most possible power.

However, the motor combos that boast 40V, are only good for 35 amps. The only good reason for putting 40V into a motor is so you can provide more current.

The trend I am noticing is that motors seem to have a maximum energy throughput (energy being the product of volts and amps) so if we have high volts, we get low amps, or vice versa. So one could argue which puts less strain on the system. If my wallet is part of the system, then low volts, high amps puts less stress on the system cause its cheaper. But if 20V input wont even allow me to obtain 50 amps (1000W), then thats no good.

The Neu motors seems to have pretty good ratings, though somewhat incongruous. They claim up to 40 Cells, and 100 amps, which is like 4800Watts, but then they claim continuous 1800 with 2700 spikes possible. But at $260 a pop, might be more than I need. I could get away with 1 motor in that scenario, but we are right back to the single motor with a huge prop problem (prop strike)

Ok, so i've got 20V in a 5-6S4P lithium pack, connected to a Pheonix 80 esc. I dont want the motor to be the weak link here. We dont need something that can handle 40V or anything, but it has to suck down 100 amp spikes if I want it to. What motor do you choose? Aveox 36? (gear boxes are not an option)

Crominator

Here is an early rendering of my plane. The diseng has changed somewhat, primarily the introduction of C-Wings extending inward form the top of the winglets (acting has a horizontal tail so i can use the whole main wing to get lift.... something the Horten's didn't do)

Obviosuly the central body will be thicker to support a bomb bay system. and there will be motors

Crominator

Nevermind, its not working... just imagine the sweetest plane ever.


its cooler than that

Crominator

So here are the pics I promised...

http://www.batbuilds.com/images/proto-top-2b.jpg
http://www.batbuilds.com/images/proto-top-1b.jpg
http://www.batbuilds.com/images/body-with-props.jpg
http://www.batbuilds.com/images/proto-underside-2.jpg
http://www.batbuilds.com/images/proto-underside-1.jpg
http://www.batbuilds.com/images/proto-top-3.jpg

Peter Khor

My Feedback: (4)

Just imo ... I'm assuming it's an Engr project to see how much weight you can lift/distance? (water ballons) Best approach is to design the a/c from that requirement, and imo you will probably not need anywhere near 2kW. Speed/wow factor is neat and all ('cause I can do it), but it detracts from the objective of the excercise.

Crominator

It is in fact a sponsored project, but its an independent study with a professor that is cool enough to think that trying to think outside thw box is worth sponsoring. This however is not for a competition. This is my brain child that I have been mulling over for some time and now have been fortunate enough to find an advisor that wants to see it happen.

However, i am also co-leading a design team for the SAE West heavy lift design competition in April. That is much moreof what you speak in terms of a high lift, generally under powered application. For those you want conventional design, high lift airfoil, and even a lifting tail if you are cool enough In that case, you are absolutely right.

Rather, the design requirement for this plane 3 fold: 1) Carry water baloons. 2) Unconventional Design. 3) Be totally SWEEEEEET


Thrust covers a multitude of sin.

Peter Khor

My Feedback: (4)

Wow, not everyday I've seen sponsored academia projects that have no end goal in mind (from the sponsors)? fwiw, the 100w/lb is just rule of thumb; design and prop it correctly, you've get more performance than you'd expect, wereas 'let's cram as much power as we can' requires much less engineering.

You'd mentioned gearbox is not an option, and you intend to use in-runner motors ... not very efficient for the design that you presented.

Ayways, have fun with the project!

Crominator

I totally dig that Boeing model, though I was a little annoyed when I first saw it because they stole my idea 5 years before I had it jerks

the only thing I have heard about in runners vs out runners is that outrunners have more torque for a bigger prop. Should I be going with an outrunner instead?

Matt Kirsch

My Feedback: (21)

Direct drive, yes, outrunners have the torque advantage over a conventional motor that can handle the same amount of power, generally speaking.

The thing about conventional motors is that their torque can be easily multiplied through the use of a gearbox to match or even exceed that of a "comparable" outrunner motor.

As with everything, it all depends on what you want to do.

studysession

OK -
How do you come with needing 2000 watts?
Do you know what controller you will be using?
Do you know for sure how much voltage you will be running and what kv rating are you looking for in a 2000 watt motor?

As for Feigao motors - I have ran the L series before. Look here:
http://www.rcuniverse.com/magazine/a...article_id=467

I know it is not a plane, but they are good motors. As for Starluck - him and http://www.rc-monster.com are two of the importers for the US of these motors. I have purchased from both companies and have had good experiences with both of them.

Thanks!

Crominator

The 2000W came from the rule of thumb of 100W/lb for really good performance. so i figured a bit high for up to a 20 lb plane and went for it. I know I can get better performance of less power with the right props, but until i can get a hold of some equations and efficiency plots for the propellers, I am kinda sunk. In terms of what kv for the motors.... I have no idea. That was one of the purposes for this thread: to educate me on motors, so any information you have would be useful. Basically all I know is that Brushless motors work essentially as AC motors with stationary wires and rotating magnets. Beyond that, I have a Castle Creations Pheonix 80 and Mega 22/45/3 brushless.

Tell me all you know what kv SHOULD I have?

Thanks