Dreamliner Grounded.

[TheRobe]

I guess they thought Lithium Ion batteries were a good choice, .....based on how wonderful Nicads were?

Never failed to amuse at school when guys would argue for Nicads, half a day spent on battery overheat procedures...then when you go to a Lead Acid battery...for a tenth the cost, no inspection and deep cycles... INOP the temp guage, rip out two pages of checklist items. Now it's like car battery...either works or it doesn't.

Boeing must have some rocket scientists working there.

[Desert185]

Are you a mind reader? Were we separated at birth? Spooky...

:ok: :D

[rudderrudderrat]

Hi TheRobe,
based on how wonderful Nicads were?
L1011s had NiCad batteries.
half a day spent on battery overheat procedures
See page 25-6 of MMEL Electrical Power for "condition light" (read battery temperature)
http://www.caa.co.uk/docs/33/srg_acp_l1011_rev1_all.pdf

We never went back to Lead Acid Batteries - the battery charger technology simply improved.

[etudiant]

The Yuasa batteries are managed by a Thales control system, allegedly quadruply redundant, which is tasked with monitoring the batteries charging and discharging currents as well as its temperatures.
There are now reports that suggest both aircraft may have had used parts from a bad lot of circuit boards in the battery controller. This seems more plausible to me than two random battery failures.
The real shock imho was the poor containment performance of the design, with fumes vented into the cabin and cockpit as well as ejected battery fluid bathing much of the battery compartment. This was not supposed to happen, fumes were supposed to be vented and fluids contained.
Both the FAA and Boeing should be grateful for this wake-up call and take advantage of the opportunity to do a more jaundiced reappraisal of how well the outsourcing of critical subsystem design and assembly really serves the aircraft buyers and the travelling public.

[Slasher]

This was not supposed to happen,

And oft said by aircraft manufacturers when a brand new type has been
shoved into airline service.

[Brian Abraham]

Never failed to amuse at school when guys would argue for Nicads, half a day spent on battery overheat procedures...then when you go to a Lead Acid battery...for a tenth the cost, no inspection and deep cycles... INOP the temp guage, rip out two pages of checklist items. Now it's like car battery...either works or it doesn't.If you want to do a bit of insightful research you will learn that both Nicads and lead acid have various pros and cons. Which is best for a particular operator is for him to determine, and may be dictated by fleet size, operational environment, economics, whether the airworthiness authority allows a swap (STC perhaps) etc

Previous discussion here Battery - Lead Acid vs. NiCad preferences. [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-258591.html)

Despite misconceptions, lead acids may have a thermal runaway. Photo of such in a car.

http://mathscinotes.files.wordpress.com/2010/12/carbatteryrunaway.png.

All battery systems may be driven into thermal runaway if severely overcharged for a prolonged period at high temperatures. The lead acid battery, when driven into thermal runaway, will fail in such a manner that the aircraft is not endangered.

All battery systems in thermal runaway will produce large amounts of hydrogen and oxygen gas which must be vented outboard of the aircraft.
A nickel cadmium battery in an uncontrolled thermal runaway may get so hot that the battery separator melts causing shorts within the cells and the cell containers melt causing ground shorts to the outside stainless steel container. The result of these shorts is that the battery may catch fire, explode, or the resultant arcing may burn holes in the outer stainless steel box and surrounding aircraft structure. For this reason, the nickel cadmium batteries are equipped with temperature sensors and temperature warning systems.

The lead acid battery in thermal runaway will reach only a relatively moderate internal temperature (approximately 260° F) at which point the water in the electrolyte vaporises and the battery vents steam. As the separator is glass, it is unaffected by this low temperature. The loss of water caused by the venting reduces the conductivity between the battery plates and the battery ceases to accept further charge. The battery slowly cools.

All aircraft I flew professionally only allowed the use of Nicads, no STC being available to allow lead acid, though that has now changed.

http://www.concordebattery.com/otherpdf/finalfaapma.pdf

[RR_NDB]

Brian Abraham:

...Photo of such in a car. (http://www.pprune.org/tech-log/505466-dreamliner-grounded.html#post7639746)
The photo seems a NiCd pack. You may see cells inside and one outside the pack at left.

The lead acid battery, when driven into thermal runaway, will fail in such a manner that the aircraft is not endangered.

These batteries gave us "Fault tolerance" and "Graceful degradation". Essential characteristic of a good design.

In general we can say lead acid are less critical.

rudderrudderrat:

...- the battery charger technology simply improved. (http://www.pprune.org/tech-log/505466-dreamliner-grounded.html#post7638690)

Let´s hope for the same in 787. The less damaging scenario.

[RR_NDB]

etudiant:

The real shock imho was the poor containment performance of the design, with fumes vented into the cabin and cockpit as well as ejected battery fluid bathing much of the battery compartment. This was not supposed to happen, fumes were supposed to be vented and fluids contained. (http://www.pprune.org/tech-log/505466-dreamliner-grounded.html#post7639522)

A severe malfunction of the battery associated circuitry (charger, etc.) could explain the occurrences. This scenario certainly was not considered in the design. There are limits to redundance, etc.

I hope for the chargers / circuitry malfunction scenario. The "less damaging". If due components (not the design) less worse.

[TheRobe]

Whatever the case, LION batteries for planes are new technology...so my guess is that they will deep cycle them more often, not try to charge them so hard, go to larger capacity batteries..whatever...always a solution.

Given the hysteria, a lead acid retrofit would be an easy fix until they get the kinks out of the LIONs.

[Sciolistes]

The lead acid voltage drop off profile makes them not so useful. I guess thats why they all have nicads nowadays.

[GlueBall]

http://www.airlines-airliners.de/wracks/twa_l1049.jpg

[BOAC]

Any relevance to the thread?

[DaveReidUK]

Any relevance to the thread? None at all.

Photo is of one of TWA's Super Constellations, N7121C, damaged (though later rebuild with a salvaged forward fuselage) when a pressurisation test went wrong at Idlewild in 1959.

[GlueBall]

Thanks for the clarification. I thought it was a battery explosion. :{

[Chris Scott]

Well, anyway, it's a nice picture. I mean, a nice airplane. Er, that is... had been a GREAT aircraft, and the photographer did a neat job. Is it a plain 1049 or a Super G? Have had a soft spot for the Connie since a 749 carried me a quarter of the way round the world in 1955.

The Constellation was THE dreamliner, so Glueball is bang on-topic - pun not intended. (Too many 787 nightmare-threads already.)

[Mr Optimistic]

Over-pressurised when the front offside quarter light was open ?

[WHBM]

I'm reminded of the new London "bendy buses" of a few years ago, now gone, which came from a "world-renowned" German manufacturer.

Shortly after introduction one was completely destroyed by fire. "An absolutely unique incident" said the manufacturers' management.

Then a second was destroyed the same way "the most amazing and unrepeatable coincidence" said the same management.

Then a third one went up in flames as well. And then they were all taken out of service. And then it was discovered the issue had been identified in development, but was suppressed somewhere along the way ........

[BOAC]

when the front offside quarter light was open ? - probably the engineer going '"WTF was that bang....? I'll have a shufti.............Did your ears pop too?"

[Fly380]

You can always trust Sky news.
Deliveries of the 747 to airlines are stopped as an initial probe into the plane's mishaps points to overcharging of batteries.:ugh:

[ian16th]

Have LION batteries been used on any military a/c?

Or is the 787 the 1st application in any a/c?

[syseng68k]

Hi,

All three battery types discussed here have their pros and cons. Lead
acid are probably the most robust and some versions use gell instead
of liquid electrolyte, which makes them even safer in terms of electrolyte
spills. Major disadvantage for a/c use is the poor energy density to weight
ratio. Aircraft style nicads are also quite robust, have long life and are
lighter than lead acid for equivalent capacity. Both the above will withstand
moderate rates of overcharge with no damage at all, other than electrolyte
loss. Lithium Iron are well proven, have been in use for years and are quite
safe, despite the occasional scare story re portable computers. However,
they have far more critical requirements in terms of charge / discharge
currents, voltages and temperatures. Energy density / weight ratio is very
high for these batteries.

I don't know what the dc rail is in the a/c, but if at 270v or so, as
someone else mentioned, it becomes very difficult to ensure that individual
cells within the pack match in terms of charge / discharge characteristics.
If there is mismatch, either in capacity or self discharge, some cells
discharge faster and will take differing times to recharge. Over time,
some cells become overcharged, while others never reach full capacity. This
is exacerbated by high charge current and discharge loads, in relation to
battery capacity.

The best way to solve this is to have separate monitor and charge circuits
for each individual cell, but his becomes expensive for large groups of cells.
Users like telcos do monitor in this way to maximise battery life, but
typically in groups of 3 or 6 cells. On a 28v system, there are typically 14
cells in series, whereas a 270v system needs 135. This just makes the problem
of mismatch monitoring more difficult, especially for Lithium Iron.

Yuasa are a world class manufacturer and my guess is that there is a problem
with the charging / monitoring electronics, or cooling. That or the batteries
are being driven too close to their design limit to save weight...

[Shawn Coyle]

I had a lead acid battery do the equivalent of a thermal runaway in a helicopter. After emergency landing the air base's firemen emptyed a 6' high CO2 extinguisher on the battery, and an hour later it was still boiling. Lots of thermal mass!

[Lyman]

syseng68k

Thanks for a splendid overwiew. In an absence of reliable data, it is most welcome. My guess is that there will be no "gotchas" here, the silence from the principals is more indicative of embarrassment than the desire to protect new "magic".....

Spec. Operations. Maintenance. Safety.

At a guess, this new airplane was the victim of unwarranted excitement followed by intense worry, and an inability to accept some limitations in an ego driven project. Leading to secrecy, then desperation..

What a surprise.

It is a BATTERY. With a useful life, a performance profile that demands monitoring, and a payoff that demands attention, and 'useful insecurity' on the part of the operator/builder.

Insufficient capacity, (spec), overconfidence (ops), and fear (the tail wags the dog). No one, NO ONE, expects perfection. In a wild flurry to avoid the perception of imperfection, the project is put on the chopping block.

Nevermind, when all else fails (it might) there is the RAT.

[A33Zab]

Its just on the 28Vdc.

ACbus 230/115v

270vdc for ECS compressors; RAM fans; Hydraulic pumps and nitrogen generation system.

[Jetstream Rider]

Have LION batteries been used on any military a/c?

Or is the 787 the 1st application in any a/c?

A news source recently quoted a Boeing employee saying there was at least one (LiIon, not nesc same type) on the International Space Station, that the F35 and F22 have them and that there is at least one on the A380. They also quoted 1.3 million actual flight hours for the battery type in question, so its not all new, but has been proven in service already.

From that, I would suggest that this is either a manufacturing fault in the batteries or a problem with the circuitry/management of the battery.

I very much look forward to finding out what the probelm is, as I think most of us do!

[gums]

The B-2 uses them.

have to check, but F-22 and F-35 may also use them.

The Nickel metal hydride batteries are used in the Toyota Prius after an attempt with the Li-ion doofers. Those nickel ones don't have the energy per weight/volume, but are less susceptible to burning up when over-charged. Less charging system protections and such requirements, so easier to engineer and employ.

Secondly, although the Li-ion ones dont have pure lithium ( highly reactive to water), they can still react to water once going into the thermal runaway stage. Damned hard to put the fire out.

We don't need to go back to lead-acid or even NI-Cad, but the new Li-ion doofers seem a little too risky for the applications in aircraft.

[etudiant]

Afaik, the overall power system in the 787 is a UTX responsibility, with Thales managing the auxiliary power aspects. Thales in turn ordered the batteries from Yuasa, but deleguated the battery management to Meggits Arizona based Securaplane subsidiary, which built the chargers. Some reports are circulating that a defective batch of PC boards made in Mexico made their way into the charge controllers.
How Boeing or the FAA for that matter are ever going to get to the bottom of this daisy chain of buck passing and determine both a probable cause as well as a confidence restoring fix remains TBD.
My guess is a switch to NiMH batteries, to distance the plane from any taint of 'lithium batteries on board'.
That might mean a grounding stretching well into spring, while the new approach is certified.
Does anyone from the regulatory side have any insights to offer?

[USMCProbe]

I have always been a fan of Boeing, but I think they screwed the pooch on the 787. In an effort to reduce costs and put the screws to their own labor unions, they lost complete control of their supply chain. They outsourced not only production, but development of many components. Some of the subcontractors can handle it, some could not.

I think they will solve this battery problem fairly quickly, but I also believe it is just the tip of the iceberg.

I hope I am wrong about this last part, but I don't think so. The 787 has many features never tried before on a commercial aircraft. Maybe the B2 or F22 have some of the same stuff, but those aircraft were low production run, VERY low flight time airframes. They will never be put through the same number of cycles that 787s will in 2-3 years, let alone 20-40 years that the 787's will be in service.

[RR_NDB]

syseng68k:

However, they have far more critical requirements in terms of charge / discharge currents, voltages and temperatures. (http://www.pprune.org/tech-log/505466-dreamliner-grounded-2.html#post7643289)

The focus of the issue! :ok:

...difficult to ensure that individual cells within the pack match in terms of charge / discharge characteristics. If there is mismatch, either in capacity or self discharge, some cells discharge faster and will take differing times to recharge. Over time, some cells become overcharged, while others never reach full capacity. This is exacerbated by high charge current and discharge loads, in relation to battery capacity.


Indeed requiring a quite "complex" management. (algorithms)

The best way to solve this is to have separate monitor and charge circuits for each individual cell, but his becomes expensive for large groups of cells. Users like telcos do monitor in this way to maximise battery life, but typically in groups of 3 or 6 cells.

:ok: and why not to separate better each cell from adjacent? The weight could be similar and the volume would compensate for the better safety under higher temp cell operation, an usual condition.

On a 28v system, there are typically 14 cells in series,...

8 cells of 3,7 V ea.

Yuasa are a world class manufacturer and my guess is that there is a problem with the charging / monitoring electronics, or cooling. That or the batteries are being driven too close to their design limit to save weight...

[RR_NDB]

USMCProbe

I think they will solve this battery problem fairly quickly, but I also believe it is just the tip of the iceberg. (http://www.pprune.org/tech-log/505466-dreamliner-grounded-2.html#post7643308)

Outsourcing demands very wise managers, i agree with your concern.

[RR_NDB]

Hi, gums

...but the new Li-ion doofers seem a little too risky for the applications in aircraft. (http://www.pprune.org/tech-log/505466-dreamliner-grounded-2.html#post7643071)

I would complement:

She are wonderful but critical and requires competent management.

The model in my mind is: The problem is not with the battery.

[RR_NDB]

Jetstream Rider:

From that, I would suggest that this is either a manufacturing fault in the batteries or a problem with the circuitry/management of the battery.

(From that, I would suggest that this is either a manufacturing fault in the batteries or a problem with the circuitry/management of the battery.)

The model in my mind is: The problem is not with the battery. (http://www.pprune.org/tech-log/505466-dreamliner-grounded-2.html#post7643342)

[RR_NDB]

Bear Lyman,

Nevermind, when all else fails (it might) there is the RAT. (http://www.pprune.org/tech-log/505466-dreamliner-grounded-2.html#post7643004)

Unfortunately when the wonderful and critical battery fail she does an scandal: Heat (intense), smoke, hot and evil fluids and ultimately FIRE.

This is a very special kind of failure behavior. :E :sad: :} :mad:

[syseng68k]

The problem is that with any project of such complexity and wide range
of technologies, there's no alternative but to outsource a lot of systems
and parts. Systems get more complex and need specialist manufacturers to
build them. Engines, avionics and more have been sourced this way for decades.

Duff batch of charger control boards may be true, but where was the inspection
procedure for incoming goods ?. Why didn't the BITE / system diagnostics pick
up the fault once the kit was installed ?. How much testing had been done under
worst case conditions over long periods ? and, why wasn't the battery electrically
isolated once the temperature or charge characteristics exceeded limits ?. Duff
batch of boards from *Mexico* ?. That's ok then, problem solved, or a smoke
screen ?.

Sad day for Boeing though. As slf, always thought of their kit as first class
and teething troubles like this probably won't change that view. The 380 intro
wasn't exactly trouble free either, just for the balance :-)...

[1DC]

You talk a lot of sense syseng68k and make it easy for a low tech chap like myself to understand. Thank you for that.
I read in the paper that the 787 has four times the battery power of a 777, if that is correct why would that be?

[RR_NDB]

ian16th:

Have LION batteries been used on any military a/c? Or is the 787 the 1st application in any a/c? (http://www.pprune.org/tech-log/505466-dreamliner-grounded.html)

Boeing introduced Li Ion as the main battery (single) and for APU start for the first time to an airliner.

The toll for that is being paid. IMO not because a problem in the selected batteries. Because the more complex management she requires. I hope (and somewhat believe) a tweak in the management System will solve the problem.

But there are other possible and probable causes like defective parts or even algorithms.

[gums]

TNKs, RR et al.

We went thru this 40 years ago with the power supply system for the Viper.

The whiz kids working the flight control computers were given carte blanche. So the basic run-of the-mill folks that did the power supplies provided the specified volts and amps. They also had a simple emergency DC power system using PMG's and run off bleed air from the engine versus the hydrazine-powered "real" emergency system.

Unfortunately, the computer folks used voltage regulators that did not tolerate over-voltage, and would shut down when volts got above "x". So when an uncommanded EPU came on line, the PMG generator exceeded the critical voltage and POOF! No more flight controls. Not good.

We fixed the problem and also had newer solid-state voltage regulators that could handle 90 volts versus 37 volts +/-.

With known problems of the Li-ion batteries going out of control due to over-charging and such, my personal engineering decision would be to use the nickel-metal ones and have slightly less amp-hours, a little more weight, but be safe.

[RR_NDB]

gums:

With known problems of the Li-ion batteries going out of control due to over-charging and such, my personal engineering decision would be to use the nickel-metal ones and have slightly less amp-hours, a little more weight, but be safe. (http://www.pprune.org/tech-log/505466-dreamliner-grounded-2.html#post7643526)

The engineering task force certainly will provide options to the high rocks of the involved players: Yuasa, Thales and Boeing. From an strategical POV the issue deserve a strong and clear response. The change of the battery type has this "feature".

But there are chances the problem is simpler. I personnaly would bet in how the wonderful and critical batteries are being "managed". The engineers will have this info if not yet and in a scenario of this type the not trivial retrofit could be not necessary.

Another alternative (not immediate to introduce) would be have two options of batteries and associated devices. This would not be "free". There are reasons they specified the Li Ion as main and APU batteries.

I question why they not used two as main. With different "regimes" could be nice. In R&D we brainstorm continuously. :)

We went thru this 40 years ago with the power supply system for the Viper.

I can imagine how the problem was handled by the people involved. :)

Regards,

PS

My son (copilot during the RTW flight) made his first solo by December 16. :)

[Feline]

With known problems of the Li-ion batteries going out of control due to over-charging and such, my personal engineering decision would be to use the nickel-metal ones and have slightly less amp-hours, a little more weight, but be safe.

Gums - concur that sentiment - suspect that increase in weight may not be too much of a problem - but how much bigger would a nickel-metal battery be? Would they have the space? Looks pretty size limited from the pics I have seen :confused:

[gums]

yeah, Feline, I am not a dinosaur and flew the latest and greatest fom 1971 until they made me quit.

I also had an engineering degree and fully understood all the workings of the aircraft systems, and the software. So I'll go with the best we have, but only after we fully undrstand the risks versus the perceived gain in performance or weight reduction or......

but how much bigger would a nickel-metal battery be? Would they have the space? Looks pretty size limited from the pics I have seen

Not much different in form factor or weight. Just look at the Prius. Ten pounds on that sucker is a lot of weight fraction compared to 100 pounds on a 787. Hell, just one obese SLF would wipe out the weight savings, ya think?

I like the latest and greatest ( not to be just "cool"), but we have to make engineering decisions and production decisions. Safety is paramount, as they say.

787 is an engineering marvel from aero to mechanical to..... In the long run it's the stuff that you take for granted that bites you. And we learned that back in 1981 with the Viper power supply and computer power supply.

[syseng68k]

1DC:

I'm no expert, but the 28v battery is normally there just to keep essential
services such as flight instruments running when all other power generation
systems have failed. It would only have a fraction of the power capability
of the main generators, which may be 100's of Kva or more on a large aircraft.
If the battery is larger, then it means that there are more essential services
to keep alive, greater power consumption, or longer run time. I would assume
that the apu battery is just there for starting the apu and is intentionally
separate for redundancy reasons.

Quite interesting that they use a 270v dc bus for some systems and shows just
how much power is consumed. For equivalent Kva, increasing the rail voltage
decreases the current, which allows thinner cable to be used, saving weight.
Introduces a whole lot of problems for the designers athough and not something
you would want to get your hands on :-(...

[syseng68k]

RR_NDB, #33:

> and ultimately FIRE...

Cue Fawlty Towers sketch etc :-).

One of the things about Lithium Ion (spelling corrected, thanks) is that they
don't have much thermal mass, whereas both lead acid and nicad do and
will withstand high short term overload or overcharge because of this. While LI
batteries will take very high charge rates, the temperature must be closely
monitored to prevent runaway, which may have happened in this case.

Perhaps they should talk to laptop and cordless tool manufacturers, who have
10 years or so experience getting the best performance and life from li, with
few real problems http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/evil.gif...

[Romulus]

Perhaps they should talk to laptop and cordless tool manufacturers, who have
10 years or so experience getting the best performance and life from li, with
few real problems ...

One presumes they did, I rather doubt they started completely from scratch.

Key difference is if a laptop starts getting hot you just put it down and walk away from it, even if it happened on board an aircraft odds are you could keep it away from the fuselage until it burnt itself out, bit harder to do for a fixed installation battery buried deep in an aircraft...

[syseng68k]

The two are not the same though. Laptop batteries are made down to a price and
driven pretty hard, whereas aviation batteries are built and tested to a very
demanding spec and will be used well within ratings.

Looking at the spec for the charger, it looks like each cell in the battery is
monitored and is confirmed by the additional thin wire harness within the battery.
Not clear if this includes individual temperature and voltage monitoring for each cell.

Also looks like there is no separate charge circuit per cell, just the the single
pair for the overall cell group. While this isn't optimum in terms of battery
management, it is cheaper and less bulky. I would have thought that they would
have gone the extra mile with this, but they must have had their reasons...

[RR_NDB]

syseng68k,

whereas aviation batteries are built and tested to a very
demanding spec and will be used well within ratings.

Should be. In theory yes. In daily use you know what may happen.

A battery today is a complex device. No longer cells inside a case. Even software algorithms could be responsible for the problems. :} In 787 Batteries and Chargers (http://www.pprune.org/tech-log/505695-787-batteries-chargers.html) thread there is a graph on that (optimization).

I would have thought that they would have gone the extra mile with this, but they must have had their reasons...

It seems an absurd what we are learning on that.

[TURIN]

Quite interesting that they use a 270v dc bus for some systems and shows just how much power is consumed. For equivalent Kva, increasing the rail voltage decreases the current, which allows thinner cable to be used, saving weight.
Introduces a whole lot of problems for the designers athough and not something you would want to get your hands on :-(...


That 270vDC is actually a variable square wave AC. Boeing call it +/-270vDC. It's used to power the big motors. CACs, Engine Starters, pumps etc. It saves a lot of energy overall as it allows hydraulic pumps and such to be 'throttled' as required. Creates a load of heat though during the transforming which is why the boxes that do it are liquid cooled. :eek:

[syseng68k]

RR_NDB:

Fwics, to get the best result, each cell should be monitored for voltage and
temperature, with the sensors and ic in a single package that could be
built in to the cell during manufacture. Then, a simple serial protocol gets
the data back to the individual cell charging circuits. For any new technology
that has serious safety implications, it should be if anything overengineered
to start with, while experience is gained out in the field. Would assume that
Boeing have done something like that.

TURIN:

Square wave suggests that it's coming from inverters, not from an alternator, but
perhaps it makes sense as it's easier to rectify that to provide dc for the subsequent
motor inverters, or any other load that that needs dc voltage. Someone mentioned
1.4Mw capabilty onboard. Serious amount of power and wonder what they use
all that energy for...

[RR_NDB]

TURIN,

That 270vDC is actually a variable square wave AC. Boeing call it +/-270vDC.

400 Hz?

Creates a load of heat though during the transforming which is why the boxes that do it are liquid cooled.

:confused: This is amazing. Why the heat? Ok, losses but where? :confused:

Boeing call it +/-270vDC.

In our terminology a square wave IS NOT DC. Is AC! The household mains supply has a (sinusoidal) waveform with positive and negative peaks. And it's not name DC. Why? Simply because varies the direction of the current.

DC stands for just one direction of current flow. For example, (an analogy):

You are at FL 150 with turbulence. You may climb and descend but the mean level is 150. OTOH you takeoff and climb. There is a continuous "direction" until your cruise level despite any typical turbulence.

I am wondering why the designers used square wave. It's easier to generate (from a DC buss). Question:

What is the voltage and waveform that is supplied by the four gennies?

syseng68k

Would assume that Boeing have done something like that.

Inside Thales? Securaplane? Outsourcing has limitations on that, you know. :{


1.4Mw capabilty onboard. Serious amount of power and wonder what they use
all that energy for...

Part of it (not so small) is being liquid cooled. :mad: