Good Electric motor for large RC plane

[superart]

Anyone play with RC planes on here? Could you suggest an electric motor, or pair of motors, for a 90lb plane? Nitro or jet is not an option. Speed would be nice, but is not prime concern, but stability and minimizing vibration is. Plane will be used for an experimental recon project.

I'd appreciate a few suggestions from all price ranges.

Thanks.

[bigben2k]

How big is the plane?

[superart]

we haven't started designing it, but it will be about 90lb and have a wingspan of about 2-3 meters.

[killernoodle]

Would that be with or without the spider monkey passenger?

It would need to be a high rpm DC motor, very simple, possibly high rpm. You might want to look into battery powered dremels possibly running on more powerful/higher voltage batteries. 12v maybe? Probably not powerful enough though...

[killernoodle]

http://cgi.ebay.com/ws/eBayISAPI.dll...879404395&rd=1

[superart]

cool, but it can't be off ebay though. Im really looking for like a descriptions of what diferent types of morors there are, and what the pros/cons of them are.

Not really sure what the budget is, so im looking at all price ranges

[HAL-9000]

Originally Posted by superart

Anyone play with RC planes on here? Could you suggest an electric motor, or pair of motors, for a 90lb plane? Nitro or jet is not an option. Speed would be nice, but is not prime concern, but stability and minimizing vibration is. Plane will be used for an experimental recon project.

I'd appreciate a few suggestions from all price ranges.

Thanks.

Finding electric motors to push a 90Lb plane around won't be easy. Electric motors by their nature are heavy for their power output. Plus you will need some mechanism to control the power to them. And then the actual power supply...you will need batteries of some sort. Again, heavy will be the name of the day for any available battery technology. Not sure what would fill the bill. Maybe some >14.4v cordless drill motors and their battery packs. You'd probably more than four motors, forget about two. And unless that thing cruises really efficiently, you'll be out of juice in minutes.

As a comparison, an ultralight with a person usually weighs in at ~400 ibs. Those machines can rarely top 100MPH and usually pack ~25HP Rotax motor or something like that. 25HP equates to about 19 kilowatts...that's a lot of electric motors by comparison, even with a quarter the power (to match your aircraft's weight). I would probably not go the eletric motor route with something that weighs that much. It will be limited in endurance, which is important for recon, and cost some serious kilobucks. Go with a heat cycle motor.

[superart]

heat cycle?

[bigben2k]

90 lb is a pretty heavy plane, for that kind of wingspan. Are you sure? Is it the "recon" gear that makes it so heavy?

Did you consider using a heli instead? I was just reading about a heli mounted cam.

Helis are notorious for vibration, but they're more maneuvrable that a plane (I guess it depends on what kind of shots you're taking).

Otherwise, you're close to entering the "giant scale" class of models, which means you'd be past electric motors; you're looking at a lawn-mower grade engine!

[HAL-9000]

Yeah, heat cycle like a gasoline engine or something like that. Something like a 50cc Honda two-cycle for dirtbikes, or even better, those motors they put on "pocketbikes."

Two of those, you would be in business I think. And since you can get the whole bikes for about $500 a pop, the motors can't be more. You would need to find a prop and then apply appropriate gearing to get the prop rotational speed to match the motor's most efficient RPM for cruise. You would want that for as much endurance as possible. The prop's "exhaust velocity;" the speed of the air the prop pushes out, should be as close as possible to the cruise speed of your airframe for maximum efficiency at you desired cruise speed.

Once you know what the cruise speed you want is, you can figure how much thrust you need to push the airframe at cruise, and then you can go from there to pick the prop's size, pitch angle, and RPM to move enough air at that speed. Convert that power to watts and then find some motors that can do that. However, the motors/props combo max power needs to be about 40-50% above the cruise value for effective takeoff performance.

[superart]

yea, the cameras, and trancievers, and electronics, and computer take up most of the weight. That wingspan and weight is just an estimate, we are still in the early stages of design, but it will be a big plane.

We are considering using nitro engines, but routing the hot exhaust gasses and calculating for change in mass due to fuell burnt would most likely prove to be a bitch.

As for using a chopper, ideally this would be good, but we aren't allowed to use any kits, and designing a chopper from scratch is much much harder than a plane. Also i'm not sure but it might be against the rules.

[superart]

I have a 49cc engine on my scooter, the same type as on those pocket bikes, and it is pretty heavy. Any ideas for somethng lighter and with similar power output/efficiancy?

[HAL-9000]

Originally Posted by superart

I have a 49cc engine on my scooter, the same type as on those pocket bikes, and it is pretty heavy. Any ideas for somethng lighter and with similar power output/efficiancy?

I don't think you will do much better than that motor on your scooter. If it's power is ~7HP that will work fine for a very low speed RPV plane. You can also probably use a pocketbike's alternator (assuming they have those) to power your computer gear. As far as fuel depletion affecting CG, a 2 gallon tank on the main spar of the thing will keep the CG of the vehicle pretty stable, because your spar is where your highest incidence of lift will be, and shouldn't really effect the CG. Those values as well as CP change with extreme, like supersonic speeds, but I doubt you will encounter those issues with this plane!

The trick is the efficiency in your prop, how it is mated to the engine for your specific airframe. Yyou need to figure out how fast you want the thing to go, its drag, and weight, and then find the motor/prop combo that can do that within the spec. But as far as the power/weight ratio of your scooter motor not "feeling" like it can do that for you, find the equivalent electric motors and battery system to drive it for a comparable amount of time at a comparable power level, as your scooter motor and say, a gallon of gas, and you will see what I am saying.

So what's the scheme here anyways? You gonna fly a webcam with a Linksys WAP and a Linux laptop on board or something?

[superart]

Originally Posted by HAL-9000

I don't think you will do much better than that motor on your scooter. If it's power is ~7HP that will work fine for a very low speed RPV plane. You can also probably use a pocketbike's alternator (assuming they have those) to power your computer gear. As far as fuel depletion affecting CG, a 2 gallon tank on the main spar of the thing will keep the CG of the vehicle pretty stable, because your spar is where your highest incidence of lift will be, and shouldn't really effect the CG. Those values as well as CP change with extreme, like supersonic speeds, but I doubt you will encounter those issues with this plane!

The motor on my scooter isn't anywhere near 7hp. The poorly translated manual rates it at .5KW, which is aprox. .6hp. However, I think this should be enough, as it is rated to run with a 200lb load on land, so I think it should be able to provide enough thrust.

I relize the CG wont be effected too much by burning fuel, but one of the requirements is for us to submit a report with estimates on wieght change throught the flight.

Originally Posted by HAL-9000

So what's the scheme here anyways? You gonna fly a webcam with a Linksys WAP and a Linux laptop on board or something?

This is part of a DARPA contest. Basicly we are suposed to build an autonomous UAV. Then they give us some GPS coords to punch into the onboard computer. Then the plane is suposed to take off, fly to the points, analize what it sees, send back video, photo, and data about it, then come back and land. There will be different ctegories of things at these point, such as military, civilian, industrial, etc. When it identifies the ctegory, it needs to identify what it is. Like, for example, if it decides that the object is military in nature, it needs to analize what it is and how many are there. Is it a truck? A tank? A group of trucks and tanks? If its a group, how many are there?




We just started the design process a week ago, so we still don't have that much. More of a brainstorm right now than anything else.

[HAL-9000]

Originally Posted by superart

The motor on my scooter isn't anywhere near 7hp. The poorly translated manual rates it at .5KW, which is aprox. .6hp. However, I think this should be enough, as it is rated to run with a 200lb load on land, so I think it should be able to provide enough thrust.

I relize the CG wont be effected too much by burning fuel, but one of the requirements is for us to submit a report with estimates on wieght change throught the flight.







This is part of a DARPA contest. Basicly we are suposed to build an autonomous UAV. Then they give us some GPS coords to punch into the onboard computer. Then the plane is suposed to take off, fly to the points, analize what it sees, send back video, photo, and data about it, then come back and land. There will be different ctegories of things at these point, such as military, civilian, industrial, etc. When it identifies the ctegory, it needs to identify what it is. Like, for example, if it decides that the object is military in nature, it needs to analize what it is and how many are there. Is it a truck? A tank? A group of trucks and tanks? If its a group, how many are there?




We just started the design process a week ago, so we still don't have that much. More of a brainstorm right now than anything else.

As far as the pattern recognition goes regarding tank vs. Moped or whatever, can't help you there. However, at this link for instance http://world.honda.com/news/2003/2030305.html Honda sells a motor that generates 2.6KW at max power. Cruise wise you would want to design the airplane for about 1.7KW cruise power with that motor, which is about 3.5HP, which is something to work with. You can probably find beefier motors in 2-stroke mode. Also, boring that motor out to say 70cc is probably feasible, and motors of that displacement for the same size block are probably out there. Checking out pocket bikes I have seen 12HP total power in 110cc, which can't be literally twice as heavy as your scooter motor.

As far as size, a 90lb airplane with a 3 meter wingspan isn't going to go very slow and stay in the air, but like you said, you're just brainstorming. As far as fuel consumption goes, it is easy to figure out the fuel burn for a given speed once you know the parameters of your engine and what it takes to push the airplane at your desired speed with it. IMHO, designing the airplane is dependent on payload weight and what the vehicle must do with that payload. The parisitic weights of the computer/sensor system should be reduced as much as possible. Design those bits to your satisfaction first, and then determine the airplane it takes to carry that payload second. The necessary payload required for the mission makes the vehicle, not the other way around, so define the payload before defining the vehicle to carry it.

Depending on the paremeters, a lighter than air vehicle might be appropriate if can get the parisitc weight down far enough, and have the infrastructure to build such a craft. Such vehicles own when it comes to airborne endurance, at least in good weather. Good luck BTW, sounds interesting.

[HAL-9000]

Here's your board for yer plane:


http://www.linuxdevices.com/news/NS7968205815.html

[bigben2k]

I keep thinking about the Zenoa engines, but I think even those would be too small for that weight. ( http://www.zenoah.net/ )

Here are some other giant scale planes, but lower weight:
http://www.rchobbies.org/giant-scale.htm
(they're mostly racing planes)

Otherwise I gotta side with Hal-9000 here; at 3m wingspam, it better be moving quick, if it's going to hold 90 lbs at any kind of altitude. I'd concentrate on shaving weight like your life depends on it.

Can't advise you on the electronics, but recognition is a field of its own.

[9mmCensor]

Real world heavy lifters use 2 or 4 engines. Stick with that. Plus redundancy is nice. (flying on 3 or 2)

[bigben2k]

Originally Posted by 9mmCensor

Real world heavy lifters use 2 or 4 engines. Stick with that. Plus redundancy is nice. (flying on 3 or 2)

I can agree with that, but redundancy is over-rated; engine reliability is rarely an issue. The trick is that if one has an engine failure, the aircraft becomes very difficult to handle.

How about a front-back (puller-pusher) engine arrangement?

I'm still leaning towards doubling the wingspan though, because of that weight.

[ymboc]

I don't know how much or how big/heavy the equipment is but 90 lbs sounds overly heavy... is there nothing that can be done in terms of minaturization or minimization?

Out of curiosity just what equipment is required to be on board that makes it so heavy?

edit/related: can any of the equipment be moved off-board?