> > Lithium Ion batteries. > > 15 minutes duration ! > The kind of a mobile gadget :-) More like "early innovators". Igor Sikorsky was a major helicopter pioneer* , and the company with his name on it has been at or near the forefront of helicopter development ever since. * http://en.wikipedia.org/wiki/Igor_Sikorsky They note that Lithium air batteries have 9 times the energy density of LiIon and claim that using them they could get 3 hours flight time (compared to 3.7 hours for the existing hydrocarbon fuelled version). [[ 0.25x 9 <> 3 but there may be more to it than sheer energy density. Lithium-air is non rechargeable, but points to the sort of energy densities that batteries will probably achieve in time. Last year? I posted re Aluminium-air batteries and proposals to recycle the used materials to reform a new charged battery and still get an acceptable price compared to alternatives. The same methods would probably apply to Lithium based batteries. Fuel cells are also targeting the 'holy grail' of direct conversio of full strength sensible purity Methanol - which would give energy densities well above even the metal-air based batteries. Itt may be "a while" yet. The original reference http://www.gizmag.com/sikorsky-project-firefly/15993/?utm_source=3DGiz= mag+Subscribers&utm_campaign=3Dcdd067a9e9-UA-2235360-4&utm_medium=3Demail notes While both the cruising speed of 79 knots and the gross weight of 2150 lbs are comparable to the S-300C helicopter, the big issue, as with electric cars, is range. The demonstrator has an expected flight time of 15 minutes (compare this to the 3.7 hrs the S-300C gets from its 32 gallons of fuel) but as battery technologies get better, this will improve exponentially. Lauder sees lithium air batteries as one of the most promising of these developing technologies. "Lithium air batteries would be lighter (because they have no anode) and provide nine times the energy density of the current batteries, enabling three hour flights and rivaling combustion engines." The problem at this stage is that these batteries are non-rechargeable, but research and development of rechargeable versions is ongoing. It's safe to say that the future for electric helicopters is bright. As battery technology matures the value of the systems showcased on Sikorsky's testbed can only increase. Although the company has chosen to use an existing airframe to showcase the technology at this early stage of development, it is already looking towards ground-up designs that will run two electric motors =96 one in the main rotor and another in the tail rotor. This approach, like electric car designs that place motors at or in each wheel, will further reduce weight and improve efficiency by bypassing the need for any conventional drivetrain. R --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .