Jan09
Dreamliner Electrical Issues
on January 9, 2013 at 10:39 amThis has implications for space transports. Even during the Shuttle program, we were always trying to figure out how to upgrade to electromechanical actuators, not only to save weight, but to eliminate the Auxiliary Power Unit that drove the hydraulics, whose hypergolic propellants made it a pain to service between flights. Modern vehicles will want to go this route, with the advances in battery and actuator technology, but there will probably be lessons learned from Boeing’s 787 travails.
I would take the weight penalty and get away from lithium ion, perhaps switching to nickel-metal hydride, or I would assume a lithium ion battery is going to overheat and catch fire – and design accordingly. It might even make more sense to use a fuel cell.
There’s probably a laundry list of reasons it just isn’t done, but I would like to at least hear the dismissal of things like just using the LOX expansion directly or the strong temperature differentials as the power source.
For that matter, where would a small engine/gas turbine and generator or fuel cell fall?
For that matter, where would a small engine/gas turbine and generator or fuel cell fall?
I believe the 787 has a Rat.
The problems I’ve heard about for Li-Ion batteries have typically been traced to one or more of:
- cheap low quality batteries. Seems unlikely in this case.
- overcharge from cheap or malfunctioning chargers.
- short circuit or other excessive discharge.
- less often, over heating.
Short of quality control or abuse, this type of battery is very reliable. But they do have a harsh temper if mistreated.
Anyone know what kind of lithium batteries are used in the 787? LiFePO4 is allegedly a “safer” lithium technology but does not have the energy density of Li-ion. I have a project that uses LiFePO4 for avionics, fuel pumps and engine starting and as I plan on being in the aircraft I have an intense interest in this.
At the current state of the art, I think I’d *really* like to have a way to quickly eject the energy storage module. That pretty much applies for liquid fuels too, but definitely for lithium batteries.
I don’t know what all the fuss is about. The president of Boeing Commercial Airplane is on record as saying: “God Himself could not crash a 787!”
What more reassurance could anyone need?
The president of Boeing Commercial Airplane is on record as saying: “God Himself could not crash a 787!”
Right! And I’m sure you have a citation for that quote.
Don’t be dense, Mr. Kent.
If you had just started typing the quote into Google, you would have gotten the joke by the time you got to the word, “not”.
My landlord years ago was a middle manager on the 777. I heard plenty of scary stories.
There are several problems with EMAs for large passenger aircraft; here’s a sample:
(1) Power-to-weight: once you get beyond a few horsepower, the overall weight of the hydraulic actuation, even including the hydraulic system, is less than the equivalent EMA (not sure about EHA). You will need high voltage electrical systems for the EMA to avoid prohibitive weight in the power wiring; 270V would be typical because you can rectify 3-phase 115 VAC direct to 270. The state of the art in 270V TRUs and batteries leaves something to be desired; there’s not a lot of it out there.
(2) Reliability: You will have to have a gearbox on your EMA if you need high torque, and that is a huge disadvantage for your PLOC; getting your PLOC up to 10e7 or higher for a typical airliner mission is just way easier with a hydraulic ram actuator. Gearboxes suck really bad.
You can work around some of this with EHAs instead of EMAs (per the F-35), but the experience base is a lot more shallow, and packaging can be an issue. More teething pains.
Launch vehicles may be a different story, since the mission duration times are much shorter, though.
Probably another of the typical Dreamliner integration and quality control issues. Lithium ion batteries can be dangerous of course. You just need to remember those burning Fisker Karmas.