Js3 jet catastrophic failure.

On Thursday, 13 September 2018 11:52:53 UTC+10, Emir Sherbi wrote:
I'm not prepared to go the electric method just yet as the current high energy density battery cells are dangerous when shorted, damaged in any way, run down, or indeed suffering from hidden manufacturing defects. It has been 10 years since the Tesla Roadster came out and current batteries have higher energy density but the other defects are still there. Any battery technology announced now is likely 5 to 10 years from being able to be bought commercially. I'm willing to be proved wrong on this but electric gliders need both high energy density and high power density and reasonable cycle life(at least 200 cycles depending on cost)along with resistance to catastrophic failure that results in fire.

Mike


Mike,

Today only safety is a "concern". Because we are very used to accept that if something with fuel exploded is a normal thing and if a battery catches fire its a big news story. Of course there is a long road ahead to make everything fail and fool proof.

Most of the times you will not land out at more than 100km from your home base.
For the same weight of an internal combustion sustainer system you get the self launch capabilities and a very long retrieve with electric (maybe more than 100 depending in a lot of variables).
For the life cycles, only if you land out in every flight you will get 200 cycles with very safe and proven cells. If you only self launch you can get 400 cycles or more.
Power density is not a problem for this application, neither the energy density. Of course that would be perfect if the batteries weight only 10kg, but with today's 30kg that is not much an issue.


Emir

OK Please tell us the name/part number of the cells, the cell chemistry and the manufacturer.

Mike

Samsung INR18650 - 25R 2500mAh 30A 3.7V
SONY VTC6 18650 3000mAh US18650VTC6 IMR

Depending on power needed, weight limit and money limit. Any of those.

On Thursday, 13 September 2018 12:57:27 UTC+10, Emir Sherbi wrote:
Samsung INR18650 - 25R 2500mAh 30A 3.7V
SONY VTC6 18650 3000mAh US18650VTC6 IMR

Depending on power needed, weight limit and money limit. Any of those.

Emir, those are both Li Co type chemistry. Not safe. You cannot ship on a passenger aircraft and maybe not by air at all.
Sure you get about 200 watt hours per Kg. You need about 2KW hours to launch a 500 Kg glider to 2000 feet allowing for prop inefficiency. You might want another 6000 feet for a retrieve so 8 KW hours. While the cells may have 200 watt hours/kg you'll need to interconnect them, monitor each cell and at least make an attempt to isolate cell problems. This can drastically reduce the watt hours/kg. I once discussed this with some people at a commercial drone shop (they also flew R/C and used LiPos all the time and had a professional interest for their drones) and was told Tesla had 180 watt-hour cells in the original Roadster but when all the packaging and protection was added they were 108 watt - hours/kg. the cells you mention are about 10 watt - hours each so you need 800 of them. That is a lot of interconnects. What do you think is the probability of of a badly manufactured cell catching fire? What about 800 of them?

Mike