Solar UAV test platform suggestions

[nschoeps]

All,

I'm part of a small University of Michigan team developing solar powered UAV platforms. Lately our aerodynamic team has been spending time making flying wings that don't fly. In light of this we need a testbed plane for electronics testing. I'm looking for recommendations, here are some requirements:

-Ability to fly 2hrs (Electric with a reasonable battery)
-2M or less wingspan
-Reasonable payload area, capable of 1.5lbs
-Must have alierons, preferred traditional tail
-Less expensive would be better for ordering multiple wing sets
-As out of the box as possible, none of us have lives as it is
-Need to decide soon (Tuesday)

I've been looking at 1.5M electric sail planes, but I'm open to options

Thank's to all!

I'll hopefully be joining your conversations on micro-controlled gyro stabilization soon.

Nick S.

[radiohound]

I'm sure many answers (more qualified than mine) will come up, but I don't think a plane meeting your requirements exists ... especially that part about two hours with a reasonable battery.

Something big enough to carry 1.5 pounds! This has to be a pretty large aircraft.

I think your window of requirements may need to be re-thunk.

I have been looking at the Super Dimona, which is a bit larger than your wing span requirements.

http://www.hobby-lobby.com/superdimona.htm

[Terry S]

I think you should be looking at a much bigger wing span to meet your requirments. I would scratch build a lightweight 3m glider and go from there.

Terry

[nschoeps]

Terry & Radiohound,

You're right, I'm asking for too much payload for a plane of that size. I think we could make do with half that for testing. I'd like to maintain <2M wing, unless it limits us from some really great aircraft. We are building our own model also.

Thanks!
Nick

[Terry S]

Do you have any figures for the AUW and flying speed range required. Do you intend to use solar power during your testing ? What type of flying do you need to perform, I guess gentle circles mainly ?

Terry

[Tuner]

Look Into Tandem Wing or Diamond Wing Designs.
http://www.rctoys.com/


Tandem and Diamond wings can acheive larger wing areas with small wingspans.

Just a thought!
Scott

[nschoeps]

Terry,

The craft should be capable of a scaled array (smaller) than what we plan to fly. We'll need to circles at first, possible tracking later. Flying speed, etc. are not critical on this craft.

Nick

[Terry S]

I designed an electric power glider about 1992 which would get you started I think. It was designed to get the most out of standard 3ft balsa so it was 3ft long with a 6ft span. It was only a rudder elevator model but you could add ailerons Im sure. In still air with a standard 540 motor and 1.2Ah cells we could get 20min flights. There are no plans as such as it was so simple, we just shared the dimensions between us plus talked it over with a beer or two and they all flew great. With a modern lipo and brushless it should carry the payload ok. I can sketch it out for you if you can work from a basic drawing, I can remember most of it as we made so many.

Terry

[nschoeps]

Terry,

I'd be very interested to see a sketch if you have the time. Our project seems to be sort of a "pet" project for three different professors here, and they all seem to want something different. I'm on the verge of just building something and being done with it. Lost foam is looking most attractive at this point for the fuselage, and wings might be ordered, might be built, that's TBD.

Thanks,
Nick

[Terry S]

Ok Nick I will do my best over the weekend and PM you.

Terry

[kd7ost]

Lost foam is looking most attractive at this point for the fuselage, and wings might be ordered, might be built, that's TBD. Nick

Lost foam is a pretty portly building technique for a marginal powered plane. Fiberglass in and of itself needs to be laid out pretty well to get good strength to weight characteristics. It would also be tough getting the foam out of small tail section areas. I would use a balsa built up fuselage. It's easy to build and rebuild. :D And it's easy to make and cut hatches, etc for equipment access.

Dan

[Terry S]

Im 100% with you Dan, built up is the bast way to get started.

Terry

[JettPilot]

Why even carry a battery on a solar powered sailplane ? Just put enough solar cells to fly in daylight, that would save a HUGE amount of weight. The motor would cut out durring turns, but who cares... With a much lighter airplane, it would require less power and you stand a better chance of success.

JettPilot

[Gary Warner]

All,

I'm part of a small University of Michigan team developing solar powered UAV platforms. Lately our aerodynamic team has been spending time making flying wings that don't fly. In light of this we need a testbed plane for electronics testing. I'm looking for recommendations... Nick S.

Why is your team (I assume it's revolving around control and embedded solutions) posting this question for the aerodynamic team? Where did these airframe requirements come from? (Students, teachers, outside people)

Someone has little if any understanding of model flight. There are flaws in requirements like solar powered, <2 meter wing span, must have ailerons, etc.

You want some good advice? Buy an off the shelf .40 sized trainer, have the aerodynamics guys put it together and have a local r/c pilot fly it (local r/c club will help) and then forget about the other aircraft requirements. If you guys are expecting your aerodynamics team to provide you with a feasible model platform with which to work with, based on the above specs, in a UAV fashion, the entire project is doomed to fail.

If you still want a platform that you describe, I have advice for the aerodynamics team too. These questions need to be answered CORRECTLY and the answers must conform to proven flight physics.

What's the all up weight with EVERYTHING?
What's the available power expressed in watts?
What's the wing loading expresses in ounces per square inch?
What will the watts per pound be?

Wing loadings can be a wind range, but the lower, the better. A model that is solar powered at 2 meters wingspan best not go over 10 ounces per square foot, and would likely need to be down to way less than 5 ounces per square foot (I'm thinking 2-3 ounces per square foot).

Watts per pound is a great predictor of flight performance. Here's some numbers at Reynolds Numbers <500k:
<5 watts per pound - few people have managed any controlled flight.
5 watts per pound - some skilled builder/plots can get it to fly, but most can't.
10 watts per pound - most experienced builders/pilots can get it to fly, but some will not.
15 watts per pound - entering what is generally accepted as absolute minimum power needed to just fly - barely.

When your aerodynamics team runs the numbers I think you'll see why I recommend a .40 sized fuel powered trainer. BTW, the average .40 sized fuel powered trainer has about 60-80 watts per pound and a 24-28 oz wing loading at 6.5 pounds (1.5 of that would be payload - 5 pound average flight weight).

Convince the aero team to move away from inventing the most spectacular flying machine made this century and move forward with the control team's goals. Part of working as a team is understanding when a part of that team is failing in a way that jeopardizes the whole project. You really need to talk to them ;) .

Gary
--

[Tophinater]

Why even go with a conventional aircraft? As far as efficiancy goes you cant really beat a wing. The controlling might be a little bit more tricky dealing with the elevons but other then that, the huge surface area, efficient design, entire foam construction, I think it would be perfect.

[kd7ost]

Yes, what Gary said.

I have had experience with local College students. A group of us have helped them with balloon flights to in excess of 75,000 feet. Something I've noticed is that very little amount of skill and knowledge passed along from our experienced group is worth anything until they've proven it to themselves. They will do things wrong all day long and are happy to do it. I think in some ways, failure while spending the whole budget is a very important part of learning. ;)

Dan

[ElectroLawndart]

I think in some ways, failure while spending the whole budget is a very important part of learning. ;)

Dan

Thank you for summing up my teaching system. I will give the people I'm teaching the information to get to the right solution but will allow them to get on and follow the wrong track until they ask for help. My belief is that you need to get on and follow the wrong path a few times so that you can recognize the smell of failure before it becomes a stench. Besides, those that don't raise the white flag might end up with breakthroughs that nobody had imagined.

Dart

[Quacker]

"...recognize the smell of failure before it becomes a stench."

Do you mind if I quote you from time to time?

[kd7ost]

Thank you for summing up my teaching system. I will give the people I'm teaching the information to get to the right solution but will allow them to get on and follow the wrong track until they ask for help. My belief is that you need to get on and follow the wrong path a few times so that you can recognize the smell of failure before it becomes a stench. Besides, those that don't raise the white flag might end up with breakthroughs that nobody had imagined.

Dart

No problems Dart,

It's frustrating for me, a non-teacher, when kids lose their electronics projects for all time because they're not open to how we find success. But I never went through a formal education beyond High school and Military Electronic schools. The rest is self taught but I fall short in many area's. The things I do succeed with are many times based on past failures as a kid. Trying to do things with what you had available, and not achieving success. I think those were the biggest life lessons I still carry with me today. I hate to have some one tell me the way to get it done or worse, that it can't be done.

And giving free thinkers a box of parts and the go ahead to make what they want can sure lead to some new developments. That's priceless. Good comments from you. Thanks for a life reminder. ;)

Dan

[Nick Reffold]

I get a bit cheesed off with teachers who set impossible tasks. I am not saying that it (solar powered flight) will never happen but it is certainly a long way away.

Have a look at the Helios project. It was launched from one of the sunniest places on earth, at the peak of the sunny season. How might it perform in northern Europe during the winter?

The governments of the world have put a heck of a lot of their taxpayers' money into solar energy and there is not a great deal of return on the investment. The problem is bandwidth. Photovoltaic cells generate currents when exposed to solar radiation at frequencies (or wavelengths) and bandwidths that are particular to the material (and doping) of the cells. The radiation can be, and is, focused using lenses to boost the output. Unfortunately, such lenses are bulky and heavy and not suited to airplane structures.

The academic exercise should be about understanding the key issues around propulsion of UAVs. It seems to me that the biggest problem in UAV design is energy density. That is storing energy for the lightest and smallest sources possible. At the moment the highest energy density comes from liquid fuels. Batteries cannot come close. The small fuel cells that are just on the horizon are more efficient in converting fuel to energy than fuel burning engines, but not by much.

Wouldn't the 'sweet smell of success' be a more effective learning strategy?

[nschoeps]

All,

Thank's for the . . . spirited response. I think we may be missing the point a bit. The real goal of this plane is to test electronics. This means solar power optimization, gps guidance and control, battery charge/discharge, telemetry, video cameras. The powers that be have dictated that it be less than 3M, sailplane-ish, with ailerons and reasonable payload. For a plane this size, they want it to fly 2hrs using batteries and SOME solar cells (not many). This is to prove the feasibility of our system. The plane needs to be a workhorse, not a performer. I have fully accepted that the aerodynamics of this project is going to be a "fail until we prove it doesn't work ourselves" type of project (Thank you Dan, you're spot on). In the mean time I'd like to learn more about stabilization systems, hence this thread.

Hope this helps clear things up,
Nick

[Gary Warner]

Ok, with the re-reading of my post and the further design criteria explained I find myself saying "don't try - it won't work". That's the wrong attitude for student to have and it's wrong for us middle-aged experienced people to convey this attitude. Understand that the older and more experienced you get, the more demands at are put on you to succeed in your endeavors. So idiotic ideas are quickly dismissed as the reality of time, money and success set in. As a student time, money and success and have less weight on the project. They still exist, just to a lesser degree.

I'd suggest an ARF sailplane from Hobby Lobby or Tower. Your aero team can just use the wings if they want to make the fuselage and tail feathers. What ever they do, I would suggest a flying version under normal R/C control first, and then one at a time, bring in the control systems. Bring on board an experienced R/C pilot if you don't already have one. A stable and proven platform should be established before integrating autonomous control systems. Any flights your group made should have the number one goal of a safe flight without significant damage, as a crash would be a significant setback and resources may not allow for restarting from scratch.

Here's an example of an automatic angle of attack project of mine. I used a large, stable and flight proven OlyII sailplane. I added the control and sensor circuits and added an on/off bypass switch on an auxiliary channel. Once the plane was stable in flight, I turned the system on and judged the airplanes response. On the first few flights, the AOA system was not allowed to stay on very long as adjustments were needed. Each flight was an evaluation to figure out what was needed to improve the flight. Soon, the AOA was allowed to operate 100% of the flight, even under winch launching. This was about a 10 flight test cycle involving 2 flight days and about 10 hours of code adjustments. And this was only one flight parameter.

The point of the example is to emphasize the need to proceed with small steps in mind. It may look like it's using valuable time, but it saves tons of time when the results of a failure would be a huge setback. Avoid the urge to put everything in the air the first flight. I only say this not because a failure would result in nothing learned, but so much more can be learned with some success. It's the 'building on success' idea that has made man and his endeavors as great as they are today. Good luck and please do share any specific issues that come up, before or during flight testing. You'd be surprised how many in this group know exactly what you are going to go through.

Gary
--

[ElectroLawndart]

The point of the example is to emphasize the need to proceed with small steps in mind.
--

Exactly. It easier and more pleasurable to eat a big, juicy steak in smaller bites than to stuff the entire thing in your face at one time. Sorry about the imagery. :D

By placing prototype electronics and programming on a larger airframe you have more flexability in design. Once you have a basic architecture than you can start optimizing the design to meet your design goals.

Tophinater brings up a good point about flying wings. The UAV group at BYU use Zagis though I doubt solar panels could provide enough energy to the direct drive motor. ...climb on batteries, sustain on solar?

If flying conditions can be "Still air only" maybe a parasol wing like a Pou du Ciel might work. Lots of wing area per given wing span on that one.

Here is a link:
http://caea.free.fr/en/coll/pou.html

Just throwing out ideas.
Dart

[Quacker]

In the spirit of invention, and in the spirit of the title of this thread, please look seriously into this very interesting solar platform:

http://home.comcast.net/~laurelsteele/hyperblimp.htm

Q

[Quacker]

PS. I have much clearer copies of these videos. Please ask and I will post or email them to you.

[Tophinater]

I doubt solar panels could provide enough energy to the direct drive motor. ...climb on batteries, sustain on solar?

Dart

I highly dout it as well. On your average noon sunny day a square meter of sunlight contains about 1000 watts of power. Even Galium-Arcenade(ya i know i butchered that) panels can only capture 12-14% of that power. Your average economicaly priced panel will maybe use 6-8% of that energy. So your looking at about 80 watts of power at best per square meter. Assuming all your panels operate at peak efficiancy(if one doesnt work well, they all dont work well). If you have an extremely light design that is very efficiant any maybe a little bit of help from some thermals you might be able to do it but it wont be cheap.

If I was to tackle this project, which I probably will in about two years when I get to ny senior project, I would go with a 72"+ wing that was cable launched and covered in polymer cells. You can find the cells at www.robotstore.com or www.jameco.com. I use them for a lot of my projects because they are very thin and flexible(to match the airfoil), light weight, and incredibly durable althought not the most efficiant. All powering the smallest and lightest low rpm, big prob spining, power setup you can build that could propell the wing.

[Quacker]

If you do a search, you will find a few very good solar flyers here at the Ezone.

[CenTexFlyer]

Why even go with a conventional aircraft? As far as efficiancy goes you cant really beat a wing.

I'm with Tophinater....

Take a look at RPFlight Systems Stinger (http://www.rpflightsystems.com). This wing is 48" and weighs a shade over 32 oz with battery. It will fly 1 lb of payload and stay in the air for 45 minutes on a 3200 mah LiPo. The larger 60" Spectra hauls 1-1/2 lbs and flies for over an hour on a 5000 mah pack. We have no problem with these very stable platforms flying "hands off" for extended periods, but do you use a thermal stabilization system to make sure. If you are developing an autopilot, one of these rigs would be ideal.

[ElectroLawndart]

Wow!

Just running through some numbers with the data from some of the solar panels that Tophinater provided looks more like an indoor model...

10" X 5.9" panel 7.2 volts at .2 amps equals 1.44 Watts for .4 sq ft.
78" wing span flying wing with about a 5:1 aspect ratio equals about 5 sq ft.
Max power is about 18 watts at 7.2 volt or about 2.5 amps.

Looks like a job for the "Modeling Science" forum. Sparky Paul should be able to help.

Dart

[sneu]

Why even go with a conventional aircraft? As far as efficiancy goes you cant really beat a wing. The controlling might be a little bit more tricky dealing with the elevons but other then that, the huge surface area, efficient design, entire foam construction, I think it would be perfect.


The most efficient planes (sailplanes) are more often than not conventional designs--IMHO there is a good reason in that they are more efficient than flying wings.

Steve

[ElectroLawndart]

The most efficient planes (sailplanes) are more often than not conventional designs--IMHO there is a good reason in that they are more efficient than flying wings.

Steve

I agree that the efficient planes are conventional designs instead of wings. But since the upper wing surface needs to be covered with solar cells there is going to be a need to have as much wing area as possible to the point of having it all wing.

Dart

[radiohound]

Just running through some numbers with the data from some of the solar panels that Tophinater provided looks more like an indoor model...

10" X 5.9" panel 7.2 volts at .2 amps equals 1.44 Watts for .4 sq ft.
78" wing span flying wing with about a 5:1 aspect ratio equals about 5 sq ft.
Max power is about 18 watts at 7.2 volt or about 2.5 amps.
Dart

The sunpower solar cells are much more efficient than the flexible solar pannels. Sunpower cells are about 21.5% efficient, but are crystalline in form, so they will NOT bend. I have seen a guy on the web that built similar cells into a balsa wing, but he must have been pretty nervous on the landings!

Here are the cells. They put out a max of about 3 watts each. Cost was about $12 a piece for minimum of 50 cells.
http://www.sunpowercorp.com/pdf/A-300.pdf
These cells have been built into composite wings using a mold. However, with some testing, they might be able to be integrated using vacuum bagging techniques, or creative film over foam designs.

With any partially solar powered glider, I think you are going to be looking for thermals to suppliment your solar power.

[nschoeps]

I appreciate everyone's input on this form. As we're a university operation , I'm sure it will be several years and several thousand dollars before we've made any progress :-). In the mean time, I've been wondering if it would be worth having a thread titled "Best off the shelf UAV platform". It would be based on the most value you get, factoring in price, payload capacity (weight and volume), camera mounting, stability, size, duration, etc. This would assume conventional power, though I'm sure there would be large differences between electric and gas aircraft. Anyone think this is too abstract a topic?

Nick

[ElectroLawndart]

nschoeps

I'd vote for kd7ost for the best IC powered UAV on this forum and workshop's Telemaster based UAV is a pretty impressive electric powered one. Those would be my votes.

Dart

[danstrider]

The small fuel cells that are just on the horizon are more efficient in converting fuel to energy than fuel burning engines, but not by much.


I thought I'd pass along a link about current fuel cell technology since it came up and I found this press release a few days ago:
http://www.nrl.navy.mil/pao/pressRelease.php?Y=2005&R=59-05r

15grams of Hydrogen, 3hr 19min of flying

I think fuel burning engines may have met their match :-)

With any partially solar powered glider, I think you are going to be looking for thermals to suppliment your solar power.
Edit: Oh, regarding this -- shameless plug -- do away with needing power during the day and save it for flying after dark http://soaring.goosetechnologies.com


Sorry for OTT'ing the thread. Continue onward!
Dan

[Tophinater]

You need to be very careful with crystaline cells, as they are extremely fragile. Even large enough vibrations can cause them crack so if you do end up using them you need to make sure you have a very rigid structure. This is why I suggested using flexible cells because you could go with lighter foam material which I think would give you a better power to weight ratio in the end of it all. Not to mention in the event of a crash or even a slight misshap you wouldnt have to worry about replacing fragile and expensive cells, unless you have grant, then go buy the most expensive you can find.

Also, what exactly makes a conventional sale plane more efficiant then a wing? They're heavier, have more drag, and in this case have less surface area for the solar cells. I just cant see why you would want to go with one other then the stabalization challeneges.

[ElectroLawndart]

Also, what exactly makes a conventional sale plane more efficiant then a wing? They're heavier, have more drag, and in this case have less surface area for the solar cells. I just cant see why you would want to go with one other then the stabalization challeneges.

I think it has to do with the airfoil types that can be used. A typical flying wing airfoil has the trailing edge reflexed up to give it a low pitch moment. This also reduces it's coefficient of lift. You can fly a flying wing with a good ole ClarkY but the elevons would be trimmed up in stable flight. Very draggy. In a conventional configuration you can choose an airfoil optimised to the flight envelope you intend to fly in and let the stabilizer handle the pitching moment. The stab and elevator is hung out on the end of a nice long moment arm to help make it more efficiant in its task.

Dart

PS - I'd also take a look at a tandem wing.

[Tophinater]

At lower speeds I can see the sail plane being more efficiant. But at a wings level flight(70-100mph) there is no need for any elevon trim or anything to keep the plane in level flight.

[ElectroLawndart]

At lower speeds I can see the sail plane being more efficiant. But at a wings level flight(70-100mph) there is no need for any elevon trim or anything to keep the plane in level flight.

I might have to dust off some of my old textbooks...so I could be completly off base here.
The pitch moment of the airfoil would stay the same reguardless of speed/Reynolds Number. A flying wing with a ClarkY airfoil will need to have it's elevons trimmed up to counteract the negative pitch moment that comes with that airfoil. Once trimmed for level flight the trim shouldn't change much no matter the airspeed. (subsonic of course ;) ) The same effect can be had by putting in wing washout at the tips. This has the added advantage of making the stall much softer.
A bigger problem with wings is the sensitivity to CG placement because of the really short pitching moment arm. In a conventional design with the elevator waaaay back there on the fuselage you have a nice long level arm to help you do the job. On a wing on the other hand the elevons are only several inches from the CG depending on the sweep angle. The design goal would be to have the CG as far back a possible and still maintain controllabilty.
Most powered model flying wings as with most models are way overpowered as compared to their full sized counterparts. Thus, efficiency is lower on the list of design priorities.

All that being said, I still think a flying wing or a tandem wing would be best for a solar powered plane because of the amount of surface area for a given span. If the limiting factor was wing area instead of span then a conventional glider design would more than likely be the best route to take.

Dart
(The views of this poster may or may not be shared with that of reality. This message is provided by Guinness Extra Stout. :D )

[hugo_vincent]

I assume you have seen the SoLong UAV, homepage:
http://www.acpropulsion.com/

Specific PDF link (warning PDF link!!)
http://www.acpropulsion.com/ACP_PDFs/ACP_SoLong_Solar_UAV_2005-06-05.pdf

They have done a 48 hour flight on solar power, charging Li-Ion batteries with spare power from the solar cells during the day, and running of said batteries at night. Pretty amazing stuff!!

[radiohound]

You need to be very careful with crystaline cells, as they are extremely fragile. Even large enough vibrations can cause them crack so if you do end up using them you need to make sure you have a very rigid structure. This is why I suggested using flexible cells because you could go with lighter foam material which I think would give you a better power to weight ratio in the end of it all. Not to mention in the event of a crash or even a slight misshap you wouldnt have to worry about replacing fragile and expensive cells, unless you have grant, then go buy the most expensive you can find.


I agree, they are fragile, and you do need to be carefull with them. However, to get a decent amount of power, one would need to go with crystaline cells. The efficiency of the flexible cells is 1/5 that of the crystaline. For instance the 26.55 square inch flexible pannel puts out 6 volts at 100mA, or 0.6 watts.

The crystaline cell I was talking about is about 25 square inches, and puts out 3 watts.

Considering output, the crystaline cell is $4 per watt output compared to the $40 per watt output of the flexible solar panel.

And the area required to generate this power is 1/5 smaller.

Yes, they will be more fragile though!

[Terry S]

Have a look at the Zephyr from the UK. It is powered by solar and batterys and flys all day. They are working on its replacement called the Mercator which is expected to stay up for months at a time.

Terry

[Tophinater]

Very true radio, but you cant just mount those crystal cells directly onto a foam air foil tho. You need to mount them on something strong, rigid, and flat. But after comparing the weight to power between each cell, I have to agree with you. Assuming you arent going with a wing design, crystal cells would definatly be the better option.

[ElectroLawndart]

Very true radio, but you cant just mount those crystal cells directly onto a foam air foil tho. You need to mount them on something strong, rigid, and flat.

How about a rigid lower wing surface and a clear upper surface with the cell mounting inside the wing rib bays? Some efficiency might be lost due to some light (IR, UV and or visible) being absorbed or reflected by the clear wing surface.

Dart

[HELModels]

Gold leaf on the ribs would help reflectivity without a big weight penalty.

Recesses could be molded into a composite wing and then "filled" with cells. Clear covering over that would restore a smooth shape.

[ElectroLawndart]

Does anybody know what the spectrum response curve is for these A300 solar cells. Do they respond to just visible light or full sunlight (i.e. visible, ultraviolet and/or both near and far infrared). Many visibly transparent materials absorb UV light. If the response curve spikes in the UV spectrum you could be losing power from the cells.

Dart

[radiohound]

Here are a couple links on people that are doing this sort of stuff.

http://www.chrisgood.com/rcplanes/solar/

http://personalpages.tds.net/~dbeck/

I don't know about the spectrum for the A300 cells, but in the 24 hour flight, the plane had fiberglass or composite covering the cells (they were built into the layup), and they seemed to work fine.

I have heard that these A300 cells are not as effected by heat as other older technology crystaline cells.

Walter