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Permalink Reply by Noth666 on March 22, 2009 at 4:38am

What would the weight be for the square meter of thin film? Using carbon and carbon/kevlar it is possible to build an extremely light frame to use for this kind of apps. What kind of shape do the panels come in?

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Permalink Reply by Genesis Factor on April 22, 2009 at 8:39am

Hey man, sorry for the one month later reply.

You probably don't NEED a support structure...just use the plane and make sure to secure the edges and have a replaceable protective layer over it.

solar panels, eps thin films can come in any shape you want. You can actually cut it to what ever shape you want, but you will have set up limitations (parrallel versus series)

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Permalink Reply by Michael Heartsong on July 17, 2009 at 7:51pm

Did you ever get an answer to how much thin film solar weighs per square meter??

And 8 watts per square meter seems VERY low. Do you have any information on how much power one square meter will generate?

Please reply: msheartsong8@gmail.com Thanks!!

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Permalink Reply by bGatti on March 23, 2009 at 6:24pm

It's not true that Wind Power won't work, it's just that it is extremely complicated.

A Sailboat, for example is a lighter-than-x object propelled by the velocity differential between two fluid bodies.

By extension, any object can be motivated by the velocity differential of the same fluid body, provided one can achieve a purchase on parts of the fluid with contrasting velocities. A Kite is a partial example of a airplane powered by the wind - a full example would require two kite in contrasting winds. Such a pair of kites would need aerodynamic control - but there is no fundamental reason why such a pair of kites could not exist, nor why, if they were to exist, they could not derive motivation from the relative movements between their respective adjacent fluidspace.

All the other questions are pedantic - ask the prof about the flight potential of relative air movement; at least its a suitably complicated question...

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ModeratorPermalink Reply by wayne garris on March 23, 2009 at 6:37pm

this is referred to as dynamic soaring the current speed record is like 357 mph
357 mph no power

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Permalink Reply by bGatti on March 24, 2009 at 9:41am

That's a pretty cool video,
but appears to take advantage of a single uplift. What I describe is the exploitation of two fluid movements simultaneously. Unlike in a sailboat, contrasting flows do not predictably occur close together, so I would expect two flying surfaces connected with a lengthy tether. such a pair could keep aloft and move at any altitude for any length of time, so long as contrasting movements could be found within the proximity of the tether.

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ModeratorPermalink Reply by wayne garris on March 24, 2009 at 4:01pm

no dynamic soaring takes advantage of the slow moving air on the back side of a hill and the fast moving air above the level of the top of the hill, read more here and yes contrasting flowes happen constanly over water . any time you have a mass of air moving over a surface the air close to the surface (turbulant layer) moves much slower then air further away ( laminar layer ) albatros take advantage of the to cross the ocean wile expanding very little energy .

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Permalink Reply by Alexander Athougies on March 31, 2009 at 3:23pm

Wind power (fan on nose thing) will work, but adds drag which is proportional to power extracted plus inefficiencies. Good for fast sailplanes. I think you know that you cannot have perpetual motion. NASA did however patent in the 60's a system to extract power from wingtip vorticies using windmills on the wingtips; I believe they outfitted a Piper Warrior with them.

I have been working on making a commercial solar cell unit for powering the R/C receiver and servos only. What I am trying to do is use a PIC to control cell voltage, thus the cell(s) will be at optimal power extraction, and use a MAX1771 chip or similar to output 5V@200mA from a source down to 1.2V so that the cell will provide power even when it is not in the best orientation and a standard small NiMH or LiPo cell can be used to provide backup power.

In order to fly completely on solar power, the goal is to be aware of the aircraft's total power consumption; meaning the aircraft must be designed to be super energy efficient in the areas of aerodynamics, power management, and overall weight. This is the reason I am trying to control cell voltage, aka. minimal cell area required. The aircraft will in no way be a 'screamer', however a HALO design would work perfectly, ie. Helios.

Compressed air or gas has been used in free flight modeling for years. The thing to watch is the cooling of gasses as they are expanded. For compressed air cars, see MDi from France, the tank pressures range from 3000psi on up.

What university are you at? Major?

I am a 4th year aerospace engineering major at CalPoly (calpoly.edu). I also do a lot of Electric Vehicle development and work at BatteriesPlus (batteriesplus.com) so I know my batteries. Most of the stuff I have done is High G capable sensing and data circuit integration for high power amateur rocketry.

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ModeratorPermalink Reply by wayne garris on March 31, 2009 at 4:16pm

i am not suggesting to attach an electric turbine to power an airplane , that is just silly . but however there are all kinds of examples of non powered flight . these aircraft extract there energy from wind and or solar (thermal) that is what i what mean by wind powered . when i think airplane power i think " the energy that moves it forward "
so yes a solar panel to power servos etc but the main motive force could come from wind . as can be demonstrated with many examples both natural and man made. any way back to the main subject of this post,
8watts ?that is extremely small.Genesis , i think a good question for the prof would be this , how much power is contained in a meter^2 of sunlight say @ sea lvl on a clear day with the sun directly over head ? this should give every one a good idea of the limitations of direct solar power. I say direct because after all a thermal sailplane derives its power from the sun it just has a whole lot more meters^2 of collection area.
ps Alex have you seen this? http://www.dimensionengineering.com/lvboost.htm

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Permalink Reply by Alexander Athougies on April 1, 2009 at 9:43am

within the atmosphere you should be able to get 1000 W/m^2 on the surface. With photovoltaics that would be around 150 W/m^2. That's why a heat engine at carnot efficiency (ie. Stirling cycles) would be more efficient at this point in time.

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Permalink Reply by Alexander Athougies on April 1, 2009 at 9:55am

the lvboost is basically the maxim 1771 or similar chip covered in a green heat sink and mounted. You can purchase that IC for less than $1. A better circuit will use two IC's thus creating a jump started unit that can operate down to 0.8V; see Application Note 1029 on maxim-ic.com (http://www.maxim-ic.com/appnotes.cfm/an_pk/1029).

I intend not only to convert the lower voltages of the more efficient cells to 5V but to control the power draw from the cell such that it is at its most efficient point on the I-V curve through the use of a PIC microprocessor and a rechargable battery as storage. Thus i will pull power from or dump energy to the battery to control the voltage on the cell therefore keeping the cell at the point of max energy output. It's similar to governing the speed of a diesel to the rpm of max torque or HP and using gears or a controllable pitch propeller in marine apps to access the full range of torque or HP available. See page 4 of (http://downloads.solarbotics.com/PDF/sunceramcat.pdf).

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Permalink Reply by Logan Greenlee on April 1, 2009 at 12:50pm

As an investigative exercise a few years ago I looked into building a solar powered plane that could autonomously fly around the world.

Unfortunately I found the construction of such an aircraft is not possible with current COTS technologies at the time. There are two factors that are preventing the creation of such an aircraft. The first is energy storage technology. Data on Li-S battery technology would indicate that it may be able to provide enough storage for multiple over night flights but current battery technologies lack the power to weight ratio required for such a mission. Super capacitors also provide interesting performance charachteristics. The second factor are solar cell efficiencies.

As far as solar technologies go, thin film has an atrocious efficiency rate. The best cell available (that I found) is produced by sun power. http://www.sunpowercorp.com/Products-and-Services/Commercial-Solar-.... Boeing, and most recently NASA have demonstrated cells with a 40% conversion rate. Sun power advertises a 21% conversion rate for their cells. Somewhere I have some estimates on output of these panels when configured for a small aircraft wing.

Certainly thin film is interesting from a weight and ease of fabircation perspective, but 8 W/m^2 is nothing to an electric motor.

Compressed air is interesting, anyone have the energy density of compressed air at various pressures?

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