Conceptual design of a solar powered UAV, help please!!

[sligo565]

Hi all!

For my final year project/thesis I have to carry out an in-depth conceptual design study of a high-altitude (65,000ft), solar powered unmanned air vehicle. The project includes a comprehensive survey of previously conducted research and emerging technologies that will impact future projects (e.g. light-weight solar panels, batteries). The primary design parameters (i.e. size, weight, cruise speed, endurance, powerplant type, materials) also have to be determined. I’m trying to upload the back of napkin sketch I have of my UAV design but am having trouble shrinking down the file size, as I scanned it in its 10.9MB! but will keep trying. I would greatly appreciate any help you can offer with setting of out the design parameters, such as primary data calculations etc. Below are calculations on how far i have gotten with the project:

Reynolds Number: 129,788
Wing Loading: 13.82 kg/m^2
Power Loading: 35 Kg/Kw
Aspect Ratio: 19.24
Taper Ratio: 0.45
MAC: 0.836
MGC: 1.196

As you can probably guess, I am at the stage where airfoil has to be picked..only trouble is I dont know which one to pick, ive been looking at ones which work well in the 129,788 Reynolds number like the E64 and E66 of Eppler series but i really dont know how to find out the Cl max and L/D ratio of the airfoils.

If anyone could guide me in this step of the airfoil and other steps after this it would be muchly appreciated! :)

[jetblackaircra]

Not quite sure how you're coming up with these numbers. You must already have the concept. Are you limited in wing span, wing area, etc?

There are several places to look for airfoils.

http://www.ae.uiuc.edu/m-selig/ads.html

there you can find an airfoil database and a list of applications for airfoil analysis. One of the easiest airfoil programs out there is Javafoil. It is totally free and you use it online with a web browser.

http://www.mh-aerotools.de/airfoils/javafoil.htm

Do read through the information about the software to get an understanding of it. It uses a panel method code.

On the frame to the left scroll to the bottom and click "The Applet" to run it.

Let me know how it goes.

[deputybuzz]

What is the goal of yoru High Altitude Platform HAP? Besides traveling to 60,000 ft and and being solar powered.

Communication, payload, photography, instrumentation etc...?

Have you considered high speed blimp technology? If so I think I can help your project along with some contact and research information.

[sligo565]

Hi fellas,
Thanks for the replies, apologies I should have added more info when writting.

I have a conceptual design already planned out, which you can find attached in the word document.

Basically it will be used for photography/border control with the main objective of making it stay in the air as long as possible, maybe overnight flight. It will have a payload of 40kg. As this is a very basic design any critisicim would be much appreciated! I am not limited to wing span or wing area etc but i would like to keep it in and around the numbers shown on the sketch.

[deputybuzz]

My first question is why so many motors? Seems like a big inefficiency.

I would suggest considering a solar powered high speed blimp. If you would like to consider feasibility of something more efficient and easily obtainable in a smaller budget. HAP solar blimp designs could feasibly stay airborne indefinably.

Check out: www.hyperblimp.com

http://www.skyaero.net/hyperblimp/hyperblimp_future.htm

What is the altitude record for an electric plane? I think NASA's ship that broke up over the ocean in turbulence around 30,000 ft? I believe it was totally solar powered too?

[sligo565]

Hey Deputy Buzz,

The reason for so many motors is to get the thing off the ground, the pusher motor would then be switched off during flight, i can see where your coming from as this will just be become dead weight during the end of it.

I would love to have done a blimp but unfortunately I am too late in the design phase to do so..those things look really cool by the way!

To answer your question the Helios (produced by NASA) reached an altitude of 96500 ft (18 miles) quite and acheivment! But i think it broke up on a different voyage over near Hawaii, reason being that a company that makes Kevlar sponsered the Helios, meaning they had to use the material...Kevlar not being the best composite out there for this type of voyage!

[jetblackaircra]

Another good thing about three powerplants is redundancy. Especially for long missions it would be good to have a backup (or two).

Nice design, looks a lot like the Voyager (Rutan). Also looks a lot like my design for the Design/Build/Fly competition a few years back....

http://www.terrabreak.org/hangar/ou/2006.shtml

Yeah, that's me with the skinny legs and the white hat. A couple years and a few pounds ago, lol.

Since you've got the concept already, I'll keep my advice to a minimum. But, since it sounds like you've got your cruise flow conditions figured out the next step is to go through the list of airfoils for one that is well suited for that kind of flow, run it in a code like java foil (keep in mind your efficiency formulas for finite span) then optimize for your flight envelope. In otherwords, if you're getting really good L/D at cruise with a given airfoil, then go and check to make sure you can still takeoff. If not, adjust your airfoil for a compromise. Or add more power/high lift devices.

This is one way to do preliminary design. I usually make a spread sheet that will calculate all of these numbers for me and all I do is copy the drag polar and Cl vs alpha data for the airfoil and paste it into the spreadsheet. Then boom, you've got takeoff distance, max climb rate, cruise speed, endurance, range, etc.

Let me know if you need any help.

Mike

[sligo565]

well first of all congrats on the D.B.F. looks great, we had to do one aswell last semester...embarresed to show it to you after seeing yours but anyhow!

http://www.youtube.com/watch?v=kv5EkOiLRyo[/URL]

We didnt actually enter it into the competition, for reasons you'll see after you've watched it!

Im sure your able to use youtube but to the right you will see a link to the other teams D.B.F. in our class, UL DBF 07/08 Team A, lets just say they passed!

Anyway back to the question at hand, yeah the reason for a design similar to that of the voyager was, as there will be no cockpit, there will be ample storage space for batteries and avionics which can be evenly spread across the plane in the three booms.

Thanks also on the info about Javafoil, i have to say its a brilliant programme, after plugging in a few airfoils, I think the E423 of the Eppler series will suit as after putting it into Javafoil it showed that it will have a Clmax of 2.25 with an angle of attack of 12.5 degrees, this with a reynolds number of 100,000-200,000

Again thanks for all your help and I probably will have a few more questions for you at some stage!

[Carl.E]

To answer your question the Helios (produced by NASA) reached an altitude of 96500 ft (18 miles) quite and acheivment! But i think it broke up on a different voyage over near Hawaii, reason being that a company that makes Kevlar sponsered the Helios, meaning they had to use the material...Kevlar not being the best composite out there for this type of voyage!

Where did you find that Kevlar sponsored Helios? I hadn't heard that. Also, Helios wasn't produced by NASA; it was designed and built by AeroVironment. NASA did help fund its developement, though. Its breaking up had nothing to do with Kevlar being used; it was being point-loaded with a fuel cell power pod and Hydrogen tanks, when the aero-elastic wing structure was designed for span-loading. A new unstable mode got excited, and the covering tore off from the extreme flexing. No covering = no lift = crash. The structure itself actually held together surprisingly well during the breakup. The structure of Helios is very well-suited for its mission - look at how successful Pathfinder, Pathfinder Plus, and Centurion were. Without Kevlar and other flexible yet strong composites, these aircraft would have been much heavier and not have been able to do such things like climb to 96,000+ feet, or even fly off of solar power at all! How else would you get a 247 foot span airplane to weigh just over 1,300 pounds? ;)


I encourage you to keep up your solar design work. Keep researching for what is out there what people have already done, so you can work off of proven ideas, and stay away from ones that have been proven not to work. Solar aircraft are making a comeback for sure; DARPA is currently starting a program with a goal of a 5-year endurance UAV at over 60k+ feet. Solar power looks very good for applications such as those. :-)

If you have any other questions, feel free to ask; there's a vast supply of knowledge on here waiting at your fingertips.

-Carl

Edit: A quick google search after my inital post brought up the offical Helios mishap report, here: http://www.nasa.gov/pdf/64317main_helios.pdf
While it's 100 pages long, the short executive summary does an excellent job explaining the physical, as well as the root cause, of what happened. There are also pictures available if you search for them.

[sligo565]

copies of Javafoil numbers

[airboss]

nice project, wish you success. for initial launching why not lose one of the 3 engines and do a balloon lift to 20,000 ft. charging batteries on the way up? just an idea.
has anyone read the "popular science magazine" article on Nanosolar film panels? 30 cents per watt. flexible as they are printed on aluminum foil.you could cover the entire wing and fuselage with panels. use it as covering instead of films or fibers. the company is in california and producing panels now. reflective light would generate power from underside of wing and fuse too. good luck-allen

[sligo565]

Fortunately yes I have heard of the Nanosolar film panels but unfortunately trying to find a data sheet on them is near impossible! If you do come across one please send on the link!!

[airboss]

only item i could find is bandgap grading=NREL 19.6 percent CGIS lab cell-pixel. since i know someone who worked at NREL here in denver will give him a call and see if he can work out panel specs.

[zlite]

Nanosolar is a thin-film technology. As such, it's only 7% efficient (converts 7% of incoming light energy to electricity). As tempting as it may be to think about covering your wings with this stuff, you're limited by your wing's surface area and need the highest efficiency you can get, which today is still crystalline silicon (around 15% for production versions; higher in the lab)

[anoth]

Hi all,
I think I come on the forum a little bit too late, but at least for the future readers... I just wanted to point out that within the framework of the Sky-Sailor project I'm part of, we developed a really nice conceptual design methodology for solar powered airplane. You can get is as a pdf at:
http://sky-sailor.epfl.ch
It was used for our first prototype that recently flew more than 27 hours, only with solar energy, even during the night, the battery having been recharged with the sun during the day (while the airplane was in the air of course ;-) )
Very soon at the same address, a Phd Thesis with very practical hints will also be available.
Sunny greetings,
Anoth