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Old Apr 17, 2005, 12:44 AM
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Winnipeg, MB
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Long Endurance/Range

Have any of you thought about possible solutions to enable a UAV to have long range and endurance? I hadn't really thought about this until recently, but it seems like it would be quite an interesting challenge.

What are some of your ideas for maximizing the endurance of a small UAV (gas/glow or electric)?
How would you implement telemetry for a long-range UAV?

I haven't thought too much about maximizing endurance; this seems like the most challenging aspect. Oviously, if the UAV is going to be venturing hundreds of miles from home the attitude reference must be able to function in IMC. So this means no infrared horizon sensing.

For telemetry, it could be possible to use cell phone technology. This would limit telemetry to areas within range of a cell tower. It could also prove to be expensive (long-distance charges).

I can imagine a ground station that periodically connects to the UAV for telemetry updates. To remain economically feasible, it would not be real-time.

What are some of your ideas?
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Old Apr 17, 2005, 04:24 AM
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look at http://www.edgerc.com/Locust%20UAV-MAV.htm
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Old Apr 17, 2005, 09:27 AM
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Ya know, endurance is one of those tricky things. Looking at the long-endurance uav's already out there, seems like some monster batteries (like the aerovironment mav) or a glider-like planform (like predator, global hawk, pointer, raven, etc) is needed from the get-go. Even our supposed high-endurance models don't seem to compare to the military or commercial requirements.

So beyond the platform design, telemetry is a beast. Without satellite links, seems like a cell phone link is about the only way for a modeller to go. LOS links aren't always feasable unless you're following your own car convoy or something. What else is there?

Dan
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Old Apr 17, 2005, 12:58 PM
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Long endurance (or long distance, not always the same thing) is definitely a challenge. NASA's Helios comes to mind, which was essentially a massive flying solar panel. It travelled very slowly, however, and worked best at extremely high altitudes. I've looked into solar and my personal conclusion just for me is that it's really not very practical for the hobbyist, at least for long distance. Aside from being expensive, solar panels are fragile, and not very efficient. There have been several solar powered r/c gliders, but none that I know of that could store enough energy during the day to fly through the night. So although solar might be a good way to augment the energy supply on an endurance aircraft, I personally don't think it's practical as the primary source, at least for someone on a limited budget.

On the other hand, solar is about the only perpetual source of energy we could expect to use, so if it's not the primary power supply then by definition any endurance aircraft is going to have to come down eventually (even a solar aircraft would as well, technically speaking, but theoretically it wouldn't have to). That's kind of a bummer, as the idea of an aircraft that could theoretically stay aloft indefinitely really is cool. (I guess a lighter-than-air ship would be the only other type I could think of. Hmm... )

The Aerosonde UAV can fly quite a ways, about 3,000 km I believe. But that's just because it has an efficient engine and a big gas tank. If you want to go that route you can basically go as far as you want, as Steve Fosset just showed with his Global Flyer. But I don't find that very challenging personally. It's like taking a gas powered boat across the Atlantic: I think it's more exciting to sail. And here's a guy trying to do just that- fly around the world in a solar powered aircraft.

Personally I'm interested in long distance/endurance electric powered aircraft. LiPolys are great but I'm looking forward to the next generation beyond that, such as fuel cells. Another thing that could extend the longevity of the flight would be the ability to detect and take advantage of thermals. Additionally, if the specific route from A to B wasn't necessarily important, the aircraft could be fed current meteorological data and have it decide which route would take the most advantage of prevailing winds.

As for telemetry, I think cellular is probably the best (though not ideal) option for the average person. A satellite phone could also be used but besides the expense, it seems to me they're all pretty heavy.

If you had enough money you could build and have launched your own CubeSat satellite. I don't know if they do geo-synchronous orbits or not, but that would be best. I think the price is anywhere from around $40K on up. Maybe if enough of us got together and pitched in?
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Old Apr 20, 2005, 02:06 AM
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Quote:
Originally Posted by LukeZ

If you had enough money you could build and have launched your own CubeSat satellite. I don't know if they do geo-synchronous orbits or not, but that would be best. I think the price is anywhere from around $40K on up. Maybe if enough of us got together and pitched in?
That's WAAAAY better that dropping my glider from a high altitude balloon. Now if I could just remember where I put my recipe for silica tiles.
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Old Apr 20, 2005, 02:17 AM
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According to the rules:

Quote:
All parts must remain attached to the CubeSats during launch, ejection and operation. No additional space debris may be created.
Darn! Some party-pooper already rained on your parade...

But a glider isn't really space debris, is it?
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Old Apr 20, 2005, 03:45 AM
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One project that I've been thinking (ok, dreaming) about for some time is an autonomous slope-soaring machine.
Assuming first that you live near some decent mountains. Give the UAV some knowledge of the terrain, a topographical map. Then give it the ability to sense wind direction and speed (fairly easy to do, even by just circling and watching GPS position).
You could launch it from a slope, climb to a reasonable altitude, and then hit the 'autopilot' switch. The plane would then keep climbing, and then pick another suitable slope which is on route to it's chosen destination, fly to it, and do the same.

With some reasonable LiPos powering the receiver/microcontroller/gps, it would appear that you could stay up as long as you have wind.

Obviously this only works where you have mountains, but that covers a fair chunk of the globe.

Any comments/thoughts?
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Old Apr 20, 2005, 12:02 PM
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Alexandria, VA
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I read someone's brainstorming about this exact idea on the sourceforge autopilot group. I did not keep up with his progress, but it sounded feasable...

http://sourceforge.net/mailarchive/f...ewmonth=200210

Dan
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Old Apr 20, 2005, 03:08 PM
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Quote:
Originally Posted by AnthonyRC
One project that I've been thinking (ok, dreaming) about for some time is an autonomous slope-soaring machine.

Any comments/thoughts?
Yeesh! An autonomous slope glider would be daunting indeed. I would think just the number of sensors would be prohibitive. Just off the top of my head...
GPS - obviously.
Altimeter - good idea, a 1 update/sec. might be a bit slow flying close to terrain.
Radar(Sonar?) Altimeter - need to know how high above said terrain you are.
Artificial horizon - with all the pitching and banking a slope glider does, would sensor drift be an issue? Could IR horizon sensing work when half you horizon is obscured by terrain features?
Air Speed - good
Heading - hmmm. slopers are mostly flying at some kind of crab angle.

...and most of all.
How does the UAV recognize slope lift.

I've been thinking of doing some research into hybrids by taking a .049 converted to diesel and mating that to a brushless generator and NiMH packs to run a small brushless DC motor coupled to a variable pitch prop. At takeoff the propulsion motor is run off the generator and battery packs. Once up to altitude, the diesel is shut down and the prop runs off the just the batteries. The generator just starts up to top off the batteries.

Dart
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Old Apr 20, 2005, 03:41 PM
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UAV's estimate the velocity of wind with respect to ground using sensed information about ground velocity (wrt to uav body) and airspeed (wrt to body).


Ram.
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Old Apr 20, 2005, 04:06 PM
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sesat,

Could you elaborate?

Dart
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Old Apr 20, 2005, 04:35 PM
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Winnipeg, MB
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Sesat is referring to the "triangle of velocities". Basically you have two vectors:
1) airspeed and heading
2) groundspeed and track

the resultant of these two vectors is the wind speed and direction.
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Old Apr 20, 2005, 04:50 PM
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Dart, I have been thinking of the hybrid route myself, but have not done any testing yet. I need a brushless motor first. I've read abou a few people who have made generators from them here on RCGroups but I don't think any of them posted performance figures.

For an endurance plane I've wondered how well it would work though. You're going to have big batteries, which means the need for an even bigger generator. Let's say I could build a rather slow flying glider UAV that can travel along at say 15 amps current consumption, including the power to onboard electronics. That's a pretty conservative figure I'd say. Let's say you wanted four hours of continuous operation from the batteries before they needed a recharge- that's still six times a day you'll have to fire up the engine. 15 amps for four hours is a 60 amp Lipoly pack. Not impossible by any means when you stack them up in parallel. But now, to recharge them? The generator is going to have to put out 60 amps for an entire hour, or some amount less for longer (I'm talking crudely here). Let's say your generator could only charge them at 1/2C, then it would need to run for two hours a charge. Six charges per day, two hours per charge, you're already up to running the engine for half of the day. At that point I start to wonder if I shouldn't have just had the engine be the primary power source to begin with.

Any attempt to reduce the number of charges per day (I'm talking about an endurance aircraft that can run for several days), will involve using higher capacity battery packs, but then that in turn means they take longer to charge.

And of course this isn't even getting into the issue of how many times a Li-Po can safely be recharged consecutively like that.

In actuality you would probably want to have two battery sets, one could be powering the plane while the other could be charging or resting. Solar could also be used to augment the available supply, but it won't help much.

At any rate, what's really needed are some performance figures from these generators. If an .049 or other small/fuel efficient engine could spin a massive brushless, or an array of smaller brushless motors, and create huge amounts of potential energy for very little fuel, then it might work.

It may also be possible to wind your own brushless motors that would be optimized for energy output. I'm not the brushless guru, but my guess is that at present, manufacturers would try to maximize the performance of their motors for the minimum amount of energy input - to the extent that a brushless can even be optimized for such things. But if so, that would be the opposite of what is desired when you're using them the other way around.

Just my thoughts on that topic. It's probably worth its own thread but I'm not going to start one until I have some numbers to show: anyone else who does, though, feel free. I'd be really interested to hear what others have found.
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Old Apr 20, 2005, 05:47 PM
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LukeZ

I was thinking more like 5Amps max to sustain flight. The variable pitch prop would be needed for efficiency. Roll the motor RPM's back and crank up the pitch. Possibly flying a powered glide flight profile. Long powered glide on the brushless, start up the generator to charge the batteries and augment power to the brushless for a climb back up to altitude. The generator would act as the starter by putting power to it.

I would be using either NiCad's or NiMH batteries because of the ability to fast charge them.

The airframe would be along the lines of a soaring glider with a big folding prop on the front. I don't know if I could get the L/D out of the standard pod and twin boom UAV configuration.

I haven't done much thinking on this. A project like this would be at least 2yrs out for me. Still trying to design and build a balloon drop glider.

Dart
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Old Apr 20, 2005, 05:57 PM
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Thanks Wowo.

One hope I harbor for long distance or long duration flying is a glider that effeciently rides thermal after thermal. A robot LSF flyer


Ram
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