Discussion in 'Hangar Flying' started by Speedboat100, Jul 26, 2019.
5$ to 50$ says McMaster carr
Dang..that ( li-po video ) does not look very safe.
Why lipos can explode:
I was going to the suggest the frangible door links as well. The only problem with the "melting floor" idea is making sure the opening below is big enough for the battery to clear the aircraft no matter what position it goes into.
The other issue is how to effectively sever the wiring connections. I know there was mention of a "guillotine" system for instantly de-energizing aircraft electrical systems in a crash (eliminates one of the primary sources of post-crash fire ignition) in the Army Crash Survival Design Guides. You'd just want to make **** sure that thing wasn't going to deploy except when you need it to.
I was thinking some kind of magnetic surface mount design like these little ones
But needs to be scaled massively up to 0 guage...
Probably needs and electrical engineer to figure out the details, multiple sprung bolts pushing onto a largish copper plates?
The fusible links would need a bit of thought too. Pretty sure you wouldn't want to hang directly on them... But you'd want any single one to release all the latches at once...
My thought about that would be that it's a hell of a lot more prone to failure and being a maintenance headache. But, then again, not an engineer nor do I claim to be.
Why not just use a GPU plug and socket positioned such that it can't physically disengage till the battery falls out.
Any electrical connection will require maintenance.
I kind of look at it as any resistance on breaking away could keep it attached. And flatter surfaces are easier to file and lubricate / inspect /treat for corrosion.
You'll never believe what happens when you set light to gasoline! Especially if you sort of spray it about a bit first...
I really don't understand the hysteria re. Lipos. They're fine IF DESIGNED, MADE & TREATED PROPERLY. Same as gas. Different challenges sure...
Some numbers for consideration:*
BTU /pound(combustion).. 2000............19167.......18300 ...5888 (BTU released as an explosive is 1929)
So while a LiPo battery fire may look intense is really going to be that hard to tame?
Interesting paper on LiPo safety systems.
*from various, some uncorroborated, sources.
**open air - non adiabatic for the liquid fuels.
For reference, TNT melts at around 175 degrees F but doesn't thermally decompose until 450+ degrees F. This is one reason it was so popular in artillery shells and bombs; you could melt it and pour it into a shell, bomb, etc with a pretty good margin of error that you're not going to set it off.
Especially versus its predecessors such as picric acid which can be set off by simply tightening a cap which has crystals formed in the groves from the liquid evaporating. I'm familiar with the latter because my chemistry teacher in high school had been an artillery and EOD officer in the Army and he demonstrated this using a remote control. Let's just say that the more advanced students (including myself and one of my classmates who now has a PhD in biochemistry) got to do a lot of things that in hindsight are questionable as hell.
But it made such a nice scream in the old fireworks.
Picric acid, peroxides and old land mines. 3 things I try* to stay away from.
LiPo's? There is one on the desk next to my mouse right now.
* No, make that "How much are you paying me?! - NOT enough"
The first two I try to stay away from. Old ordnance....I have an acquaintance who is an engineering prof who works on unexploded ordnance disposal technology. It comes in handy since one of my main interests is searching for military missing in action. It's fun to see how many different ways there are to neutralize the smaller stuff (land mines, hand grenades, artillery shells (<105 mm), etc).
Did you see this: https://electrek.co/2018/06/04/siem...5NZV4EwnTWLDNik_IuEy8eP54H3UorWOfEG0ZMpTL_1VE
Now a serious consideration is needed.
But we must wait until we know more to determine its cause and any mitigating factors.
It could be related to multiple reasons and until we know its only speculation.
But a very nasty way to die. Fire has always been a huge issue in aircraft, not common these days but it happens.
I will hold out until I know more.
Could you put enough shielding to last a few seconds to give the battery time to fall away, yet have the battery attached by a length of cable to allow it to hang a safe distance from the plane until it burned out before dropping it or reeling it back in? I know... weight and complexity, but it skirts the issue of dropping a burning battery on someone.
I think the battery cooling has not been arranged properly in many cases...Tesla had accomplished that.
Just my two cents.
I do really like Pazmany pl-2, especially after reading his book "Light Airplane Design". He used one idea, perfectly suited for electric flight - fuel tanks mounted on wing tips. Yes, it may be better from structural point, to build wing from batteries itself - it will make spar life easier, but from safety point - if batteries are kept on wing tips, it is safer in case of fire, on metal wing, with kind of firewall between batteries and wing. Yes, i have seen how lipo burns.
On the other side - if we think in original way - we may distribute motor and batteries, at the cost of extra 2--5 kg of wiring. Or even build batteries and motor as a power-pod, and mount it directly under or over the wing. Again, removing some strain on wind spar. And providing safe way for pilot to bail out, or release chute..
Sitting after/over batteries is absolutely no go..
And - batteries/motors are totally "easy to play" if going under 5-7kw of power and lower rpm. If we scale it up - it will have problems with cooling/emi and others nasty things.. Especially if going way other 100 Amps of current.
The idea of a pod to hold the batteries and potentially a hybrid engine for charging has merit.
Hence my thread on hybrid drives to greatly reduce the amount of batteries needed and the high voltages. They run high voltage for max efficiency due to not having spare energy from batteries to waste.
With a hybrid drive we can drop the volts down and offset with the much greater energy density of fuel.
As far as a tether goes- adds another level of complexity and the tether might get hung up and not allow deployment of the battery.
Yes, the risk of a falling burning battery is a issue but far less than that of a burning aircraft falling esp a gas powered one as they tend to spread the fire on impact.
In a pod...with cooling...and as a last resort a hatch that can be opened to jettison the batteries could be an option....and a device to control the temperature.
I had some experience in ev-world, ~ 7 years ago we tried to enter ev controller market, by developing our own 100kw ++ controller, small as a4 paper, 100mm in hight, and we spent ~ 2 years on rd, trying to make better, than big box controller from tesla roadster - but we fail. Yes, it was smaller, but had to be water cooled, had many emi issues etc...
On first teslas - all was simpler - many pcb, many igbt, all air cooled ! slower opening time - less emi, a lot of time for safety circuits to kick in etc.. Same with batteries.
But on other hand - https://openppg.com/shop/paramotors/openppg-22/
nice and briliant, on airplane - make pod in a pull push fashion, with battery in a middle, mounted under the wind for high wind design, over the wing, for low wing design. Or contra rotating propeller and twin bom aircraft.
And even in case of crash - this small propeller will do much less damage. And safety of working with 36-48 volts is much better.
But again - "normal tractor configuration with high wings" is dictated by having one big motor, impossible to divide into two smaller packs. And one or two passenger sitting together. With ev, we may and have to think different. As in pazmany pl1/2 - passengers are sitting on the top of wing, fuel is placed in wing tip = wing/fuselage have to withstand only motor and tail loads. 100 kg for motor + 200 kg for tail load ? instead of 200 kg from pilots + 100 kg of fuel.. 50% less..
Separate names with a comma.