Solar Powered UAV Project - Page 7 - RC Groups
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Feb 21, 2008, 01:49 PM
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I have been to Fairview park in Costa Mesa--a very nice field, and nice people too. I haven't had a chance to get a permit from the City Hall, which is required to fly there now, however. Also, the 400 foot ceiling is a little restricting. I do plan on getting a permit and perhaps flying there. I do know of another solar airplane that flies there, though.

Thanks for the kind words; it has been quite an exciting project. Each solar cell puts out ~0.67 volts open circuit, and 6 amps short circuit current. At the max power point, each cell is at about 0.55 volts, and just under 6 amps, so about 3 watts a piece. There are 18 strung together in series in the array, giving roughly 55 watts of power, operating at just over 10 volts.

I flew the plane last weekend again, and had some interesting results; I'll post more about it later (probably this evening) when I have some more time.

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Feb 22, 2008, 07:28 AM
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Just while the topic's active -

I happen to be a final year engineering student, and I'm looking at combining ideas from your project with the hyperblimp concept, to create an 'aerosatellite' - one that remains in the air 24/7, relaying data and live video from around 1500ft, and survives off solar cells and LiPoly batteries.

Carl, I just wanted to know a couple of things:

1. I found in the forums that your solar cells generate 3W and cost 22.50, but how much does each weigh? I'm trying to get the optimum weight-power-cost ratio, to calculate the size of my blimp. Have you got a datasheet?

2. What kind of efficiencies and thrusts were you getting from your brushless configuration? My plan was to design the blimp to operate continuously at 10m/s (to oppose wind etc), do you happen to have any figures of thrust per watt for your motor/prop configuration?

Again, congratulations on a fantastic project, and I look forward to hearing from you.

Feb 22, 2008, 09:33 PM
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1. The total encapsulated array weighs about 350 grams. Divided among 18 cells gives about 19 grams per cell. Remember this includes the encapsulation material, which isn't light. I don't have an actual number for you, but I'd guess 10-12 grams per bare cell. However, getting your hands on bare cells is nearly impossible, so you will probably have to get them encapsulated by a 3rd party.

2. I haven't measured efficiencies and thrust for the brushless setup like we did for the brushed setup, since I no longer have access to a wind tunnel and thrust stand. I have the theoretical numbers if you want, just let me know.

Also, thrust per watt isn't really an engineering efficiency, since it doesn't take into account airspeed. Static thrust is what most people use for thrust per watt, and how often do you fly at zero airspeed? (Not including hovering! ) What you really care about is thrust*velocity per watt, which is what efficiency really is: Power_out / Power_in.

Feb 22, 2008, 09:56 PM
Registered User
Flight update:

Last Sunday, I went and flew at Field of Dreams at San Pedro again. The first flight was launched with the sun behind some hazy thin clouds, and the lack of power was very noticible. However, I was able to stay up and fly several laps at low altitude. The data showed an average power of ~9 watts to sustain flight...a little worse than the brushed setup, but not bad.

Once the sky cleared, we launched again, and the plane climbed beautifully. After ~20 minutes into a solid flight, the motor seemed to lose power and the airplane slowly lost altitude. After landing, I realized the ESC had gotten really hot and desoldered one of the motor leads! I was only running ~2.5 amps through the Phoenix-10. I resoldered the lead and did a quick ground test, and sure enough, the motor got too hot to touch after 5 minutes at partial throttle! A little RCG research that night found that ESC's are actually pulsing full current through the motor during partial throttle. Full throttle current with my setup is still only 6 amps, so I was unsure of the problem. I posted a question in the Castle Creations about what happened here:
Turns out the PHX-10 doesn't play nice with very high inductance (high wind) motors due to it's slower switching high-side FETs. Patrick suggested a PHX-25, since it's more suited to high inductance motors. I have one to try but haven't had a chance to install and test it out yet. Hopefully a cooler running ESC will produce lower required flight powers!

Mar 05, 2008, 03:02 AM
Registered User

Flight update: 2 hours and 1,200 feet!

Got another chance to fly this past Sunday. Beautiful weather: clear skies and very low winds all morning. I had installed and tested a Pheonix-25 as suggested in the Castle Creations forum after desoldering the Pheonix-10 I was originally using. The tests went well; minimal ESC heating at partial throttle, hardly warm to the touch after 15 minutes of running.

First flight we launched at 10am with a very nice of these times we'll get it on video, I swear! In addition to the EagleTree Micro E-logger, we installed an altitude logger. This flight was to verify satisfactory ESC temps, so I kept it short at about 15 minutes. After landing I checked the ESC, and it was hardly warm, just like the initial testing showed. Success!! However, we failed to properly set up the temp probe on the data logger, so no actual temps were recorded. We did get some very nice altitude data, though. After the flight, I was able to overlay the altitude data with the power plot, which showed a nice correlation. It's attached below. Max altitude was ~300 feet.

The second flight was planned to be an hour duration--the longest flight to date. After launching at around 10:45, I settled back into a lawn chair to get used to flying sitting down... a strange feeling at first for those of you who have never done it before! Everything was solid; the plane handled beautifully and climbed at will. An hour came and went, and I felt great, so I decided to push on for 90 minutes or more. As you can see from the altitude plot below, I was able to climb pretty high on this flight....slightly over 1,200 feet! A 10' span wing sure looks small that high up! You'll also see at one point the plane suddenly dropped from 1,000 feet to 400 feet in a matter of seconds. The steepest descent rate was about 3,500 feet per minute! I'm a little unsure of what happened... the plane seemed to drop nose down some and just fall....maybe a large pocket of sinking air, radio lock-out, or just pilot error letting the nose fall too much without correction? Luckily I was able to come out of the descent and continue my flight. So much for flying for extended periods being boring! After things calmed from this, I decided not to push my luck too much more, so I landed after a flight time of 2 hours, 2 minutes.

We went to retrieve the flight data for the 2-hour flight, and found the logger was empty! No power or temp data to be had for this flight. Also, the altitude logger memory filled up about 80 minutes into the flight and stopped. I'm pretty sure I had a 3rd climb up to ~1,000 feet in the last 1/2 hour of the flight that was not recorded. The motor and ESC were warmer to the touch than after the first flight, but not too hot to hold my finger on them. This was the first time the motor had gotten warm at all. I may have to cut some small cooling holes to get some airflow over the motor. The spinner has a hole in the front for cooling that will work perfectly if I can carve away some of the firewall where the motor mounts up.... I'll look into it.

Lessons learned for future endurance flights:
Remember to bring sun screen.
Sit in the shade if possible.
Don't wear a black shirt in the sun for 2 hours.
(Yes, these above observations lead to me getting pretty sunburned. )
Double-check that loggers are working and are sampling slow enough to cover the entire planned flight.

Next flights:
Along with more time-building flights, I'm looking into possibly doing a cross-country flight record attempt as a stepping stone to an endurance record attempt in June. The current FAI straight-line distance record for a solar R/C model is only 30 miles. Easily covered in 2 hours. Mostly a logistics and planning issue it seems. I'll be doing some more research into this.

Any questions/comments/suggestions are welcome and appreciated!

May 24, 2008, 01:41 AM
72.450 mHz
spirko's Avatar
Great work with this aircraft, two questions if you can help:
1) where did you source the a-300 cells?
2) is there a laymanís formula for where / what capacity diodes to use so as to not ruin the solar cells?
Good luck with the record attempt next month, Iím in Los Angeles if I can be of any assistance.
May 26, 2008, 03:12 PM
Registered User

For now, PM or email me and I'll get you my contact for the A300 cells. I emailed him a few days ago asking permission to publish his info on here but he has not responded. When I hear back, I'll post it if I can.

As for the diodes, I am unfamiliar with how they are incorporated into the array. When our array was made, they were included if they were needed. Remember that we are not running a propulsion battery, so there is no current available to go back through the array if they stop putting out power.

Thanks for the offer for support. I may be asking for some observers for the attempt in the near future.

I'll be posting an update with my progress since my last post when I get some time.


Originally Posted by spirko
Great work with this aircraft, two questions if you can help:
1) where did you source the a-300 cells?
2) is there a laymanís formula for where / what capacity diodes to use so as to not ruin the solar cells?
Good luck with the record attempt next month, Iím in Los Angeles if I can be of any assistance.
Jun 20, 2008, 10:22 PM
Registered User

Update, A300 supplier info, and a call for volunteers

I haven't had much time to keep this updated lately, so here's a quick overview of progress.

Last weekend in Perris, CA, I flew for 3 hours straight with no issues. Launched at 8:35am and the plane easily climbed. Got some great data from the data logger, and it looks like the power point tracker is doing its job! Hopefully I'll get some time to post some data. Also, temperatures are under control and the cooling holes I made seem to be very effective even in 100 degree heat; right after landing the ESC and motor temps climbed 20-30 degrees, even with the motor off! Tomorrow I'll be going out and attempting a launch at 6:45, which is the predicted minimum sun angle needed to sustain flight. Adam (design partner and starter of this thread almost 2 years ago) will be flying out to CA and we'll be making an official endurance attempt at the end of next week or next weekend. Hopefully the weather cooperates for us to make an attempt while he is here!

On that note, we are in need of a couple of AMA observers for the attempt to make it official. No special status required, just be an AMA member; we already have our Contest Director who serves as the "official" observer; the FAI rules just require two more people. You would have to be present from launch (6:30-6:45am) through landing (7-7:30pm). However, you can make a flying day out of it; we don't need you to keep your eye on the plane every second of the day. Anybody interested and available should PM me for more info. The window we are looking at is Thursday, June 26th through Monday June 30th. Even if you are only available one of those days, that would be great! You'd be a part of making history.

Also, here is the contact info for our solar array supplier, now that he has given permission for it to be posted. One note that he wants to be made clear: he is very busy, and it's a small operation, so there can be a serveral month lead-time on ordering an array. With that, here is his info:

SunCat Solar is the name of the comany, and our contact in Alain Chuzel (pronounced "Allen"). His email address is ahmchuzel<at>aol<dot>com. (replace the <at> with @ and <dot> with . ) He can fabricate pretty much any size or confguration of array, given a good drawing (and enough money )

Jun 20, 2008, 10:48 PM
And You're Not
Glad to hear you guys are making progress, Carl. Good luck on the record attempt, if I was closer I'd be a spotter for you.
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Jul 02, 2008, 01:25 PM
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wish's Avatar
Hi Carl,

I've been reading this thread whit much please! I'm also planning to build a simular PV powered plane... one day...

How did the record attempt go?

Regards from Germany,

Bob Hopman
Aug 05, 2008, 10:33 AM
Professional Lurker
Magician's Avatar

7hr 13min solar flight!

Congratulations Carl and Adam! I just saw this press release for your flight of 7 hours and 13 minutes.

Well Done.

Aug 05, 2008, 02:51 PM
Registered User
Yes, the short version is we flew 7 hours 12 minutes, and the plane is still intact. Some apparent partial motor power loss plus a large sustained down-draft forced us to land mid-day; we were on track to break the 11 hour 34 minute FAI recrod! We'l try again next year.

A longer more detailed version with pics is definitely owed to everyone here. I've started writing a draft post to put up here, but working 50-60 hours a week plus being busy moving has kept me from getting it posted. Perhaps in the next week or two I'll get something posted.

Sorry again for the delay in posting results!!

Aug 09, 2008, 05:13 PM
Gary Mortimer's Avatar
Well done, look forward to the report
Aug 20, 2008, 02:19 AM
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Bilox's Avatar
I'm curious.... what is the rating of a single A-300 Solar Cell? (V, mA)

Aug 22, 2008, 04:59 PM
Registered User
Wow, I do not know how I ever missed this thread. Very awesome story you guys have here, I just read every word of it. I am a huge aviation fan and always have been since as long as I can remember however, I am not an aviation, electrical, or structural engineer by any means nor am I on the path to becoming one. But this stuff exactly always inspires me to at least try something. If I had that anything near what you have now, all I would want to do is slap a wireless camera to it with head tracking =)

Congratulations in all your efforts and I sure hope I see your names else where within the industry.

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