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Scavenging a crashed 777: for a book

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Scavenging a crashed 777: for a book

Old 20th Sep 2014, 21:00
  #21 (permalink)  
 
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I'm talking about using the 28V AC alternators
You must be referring to the BUG's. Instead of explaining I will cut and paste.

Backup Generator Power
The backup converter gets power from only one ot the backup generators at any time. The converter changes the variable frequency power to 115v, 400 Hz ac power and sends it to the transfer buses. Power goes through the converter circuit breakers (CCB).
Only one backup generator supplies power at a time. Normally, the left backup generator supplies power to the left transfer bus and the right backup generator supplies power to the right transfer bus. If the left and right transfer buses need power, the right backup generator supplies the power if it is available.
The backup generator converter also controls, monitors, and protects the backup power system. The converter gets an input from each backup generator (BACKUP GEN) switch. When the switch is in, the converter controls the related CCB and transfer bus breaker (TBB) automatically. When the switch is out, the converter opens the CCB, closes the TBB, and trips the field of the generator. The converter causes the OFF light to come on for each switch for any of these conditions:
Switch is out

Backup generator field relay opens because of a fault

Engine fire switch is pulled out

Engine is shutdown.


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Old 20th Sep 2014, 21:10
  #22 (permalink)  
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Yes, I believe that is correct. Someone else on this forum provided me with the 300W and 2,300 RPM info. Not a lot of power, but it works for a wind-generator that they can fairly easily build - using a bike frame/gearing to get higher RPM from the windmill.

Thanks for contributing.
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Old 20th Sep 2014, 21:23
  #23 (permalink)  
 
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Originally Posted by kenpimentel View Post
re: APU
I've been told that 1,000G of fuel is about 15 hours of APU operation. If there is no ability to stretch for let's say a week or two, then it isn't worth the effort to run. Anyway, it produces way more energy than they need at this point. The only feasible long-term method is to use steam power with the APU, and I agree, it would take a huge boiler for that. I don't think anything existing on the plane could be repurposed for that.
It would take a lot of skill, and quite a few tools, to extract an APU from a ditched aircraft and get it into a runnable state, with the rest of the aeroplane fully or partly emersed in salt water.

re: RAT
Would the RAT deploy if the captain shut down the engines? He does it just before they hit the water. I think the RAT is plausibly the best thing to use for generation once they reach a little more sophisticated stage of development.
Almost certainly, unless he deliberately disabled it.

re: saltwater immersion
In this scenario, the plane is not immersed/floating in seawater. It's more like it is a powerboat blasting through shallow water/bottom as it rides up onto the shore. It isn't in the shallows for more than 5-10 seconds - so I'm going to pretend that nothing was really damaged by the saltwater except the engines.
Most stuff emersed in saltwater can be resurrected by prompt rinsing through in freshwater.

re: aircraft gennys
I think there is some confusion. I'm talking about using the 28V AC alternators that are driven by the engine as backup power. I believe these are 300W at 2300 RPM. I'm not talking about the IDG - those are heavy duty 120KVA alternators that spin at 24K.

re: power conversion/inversion
I realize the APU has to also be removed from the plane to get the output to be converted to something that will work with portable electronics and AC tools. I do have an AMT on the airplane (for a good plot reason). She will be able to use her docs on her laptop to figure out the bits and pieces.
And the large box of specialist tools to remove then modify the APU?

Why don't you just save your credibility by inventing the carriage of some equipment with an electric motor and basic servicing tools in cargo?

re: ditching?
Why is that so far fetched? If Captain Sulley could have ended the flight of his Airbus right onto a gently sloping beach, don't you think he would? Anyway, I do have a pilot who currently flies 777s reviewing the book and he didn't mention anything wrong with this scenario. I think it is because he's reading what I wrote and you're assuming something about what I wrote. Maybe I'll publish those portions on this forum if that will help.
No, I don't think he would - you can't reasonably expect to judge the stop-distance with any accuracy. I think that he'd do again pretty much what he did do - land parallel with the shoreline to create a short distance to shore.

re: charter flight
It would be a big change in the plot/characters to go with a charter flight. I'm hoping that I can use the excuse that there is an AMT on board who is headed to fix a 757 and is bringing along a decent set of tools to make sure they can.

re: hacksaw
Things get a lot more complicated without a way to cut SS/Alum up. One option is to have it in the cargo hold. I'm a sailor, and I know that whenever I travel to my boat, I'm bringing all sorts of tools/replacement parts. All it takes is for some passenger who is scheduled to spend a week on a boat somewhere in the Caribbean to be bringing some badly needed tool to the skipper.
Also remember the fire-axes in the cockpit and galleys.

re: Sat phone/406 EPIRB/GPS
These won't work as there are no satellites in the sky. Help is not around the corner. There is no rescue being staged, no one is coming for them. They are on their own.
There are always satellites in the sky.

Have you considered for example not using a 777 and using something basic (a DC3?, Islander?...) run by a small inter-island charter airline? More likely to have accessible tools as less in the way of security checks, more basic equipment relatively easy to canibalise, much less in the way of hi-tech avionics.

G
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Old 20th Sep 2014, 21:49
  #24 (permalink)  
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re: RAT
OK, it got partially deployed and it's a tangled mess. Might be something salvageable, but not initially.

re: tools
Yes, I have to accept there will be some tools in cargo. I had hoped not to use the "magic box" of cargo to solve problems, but seems this might be required.

re: BUG
I think I can use this still, at least initially. I'm not hearing any good reasons why that can't be removed from the plane and used for power generation. I agree it isn't trivial as it means the BUG Converter must also be pulled from the plane to convert the power. I'm not sure if it delivers 115v 60Hz or if it delivers 115v 400hz.

re: ditch scenario
I think it will make sense if you read it. At least I hope so. It's important that the plane winds up mostly salvageable. This seems as gentle as I can do it.

re: world
You misunderstand me. I didn't say there are no satellites in sight, I mean there are NO satellites. Neither are there any reinforced concrete runways where they are...

re: fire axes
Thanks! Those are going to be very handy. Do you know how many? Those are going to be major players!

re: not a 777
I've made the 777 a major actor in the story and it'd mean a lot of rework/research. I also need a lot of people to come to this new world (hundreds). Less than 100 won't support the long-term goals of the story.
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Old 20th Sep 2014, 23:46
  #25 (permalink)  
 
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The BUGs are still large 20kva gens, frequency wild machines that are directly driven by the engine gearbox that can provide power in tbe event of a main gen failure. The FADEC alternators are tiny units designed only to provided power to the FADEC EECs, very easy to drive by a small wind turbine, also designed to give a useable output at low rpm for windmilling air starts etc. Yes the output would have to be rectified but that only requires a few diodes.
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Old 21st Sep 2014, 00:07
  #26 (permalink)  
 
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Leatherman

Any AMT or LAME worth their salt will have a Leatherman in their toolbox. If they are not flying as a flying spanner, then they are very likely to have it clipped onto their belt. The Leatherman Wave or Supertool has an excellent hacksaw. Modern day security busybodies get very nervous letting engineers fly on planes with tools these days.

If on flying duties he or she might have a lightweight toolbox stowed in the cockpit, or a larger metal line tool box loaded into the bulk cargo.

Flying spanner - Colloquial term for an aircraft engineer employed on flying duties.

I'm a flying spanner currently on B767s but I also have B777 type rating.
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Old 21st Sep 2014, 01:21
  #27 (permalink)  
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re: BUGS
Thanks for the clarification on BUGs, I should be saying FADEC EECs. They don't seem to be well documented in my research, thanks for steering me straight.

re: Flying Spanner
Thanks for those kinds of inside terminology. I'll definitely use them.
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Old 21st Sep 2014, 02:20
  #28 (permalink)  
 
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If you have a crashed, stranded aircraft, and one pax is found to possess useful tools - then you'd better include the war between the survivors over possession of those tools. I trust you've read Lord of the Flies.
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Old 21st Sep 2014, 08:31
  #29 (permalink)  
 
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One axe in the cockpit, a second in the most rearward galley.

Also if you're interested, 2 megaphones, 4 hand fire extinguishers: probably 2 halon, 2 water. There should be a well equipped first aid kit, and *possibly* an emergency medical kit somewhere.

G
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Old 21st Sep 2014, 15:28
  #30 (permalink)  
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re: second axe
Great to know. I didn't see it on my Boeing Flight Crew Op manual. I guess some airlines might have it and others don't. Or, my document is out of date. Seems a security risk to have an axe where the public can access it...

re: LOTF
Yes, read it, I'm hoping to keep things from degenerating that far, but there will certainly be differences in opinions about how to survive and what to do with their future.

re: fire fighting
My Boeing doc says there are (777-200):

o Axe
1 cockpit
o Flashlights
2 cockpit
12 cabin (1 per attendant seat)
o Oxygen
15 small portable ones in cabin
o Oxygen mask with smoke goggles
2 cockpit
o Portable breathing equipment (PSE)
1 cockpit
6 cabin
o Fire extinguishers
1 Halon in cockpit
3 H2O
3 Halon
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Old 21st Sep 2014, 21:50
  #31 (permalink)  
 
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It's quite feasible to have a toolkit on board, you often get contract engineers flying between jobs and their tools go as freight, you might also find tools as cargo etc..

Have you thought of driving your generator by water power, if there is a waterfall or stream a wooden paddle wheel could be built to turn it.
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Old 22nd Sep 2014, 01:29
  #32 (permalink)  
 
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Have you thought about how your engineer is going to do the fabrication of turning your apu into a steam engine?

You may have a box of hand tools on board that belongs to your engineer. But to fabricate and connect things like pulleys and gears onto axles you're going to need to be able to weld. I've come up with an idea for this. You could use the aircraft main battery as a supply and the steel spring rods inside the passenger seats as the welding rods. Aircraft battery is a Nicad 24V with lots of juice, but you're going to have to watch the temperature during welding or it will explode! Then you will need to recharge it again.

The engine FADEC control alternators are your best bet. However they are bolted on to the front face of the engine gearbox at the bottom of the engine, which I imagine will be embedded in the beach! These little alternators produce quite a lot of power for their size and can power the entire engine at only 7% N2 (don't ask me what RPM the alternator is running at, I have no idea) They have two output windings, one for each FADEC channel. The output from these alternators is AC, so you're going to have to run it through a rectifier to be able to charge your battery. Like the standby TRU.

Well you did say you wanted McGyver!
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Old 22nd Sep 2014, 02:54
  #33 (permalink)  
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re: tools
Yes, they must be on the plane. You need the basic tools that will allow you to fabricate more tools. I have researched forging of stainless steel and casting of aluminum. AFAIK, those are the only two metals on the plane. I wish there were some brass/bronze or copper. I guess their must be copper in the "300 miles" of electrical cabling claimed by Boeing. I'll have to calculate what that might work out to be...

re: water power
This island is a real island and they don't have those elevations unfortunately.

re: welding
Awesome! I should have thought of that. I mean even with regular lead-acid batteries you can sort of do the same thing. The problem is that they don't like that kind of discharge. I think/hope NiCADs will handle it better. I thought the big batteries on the plane were lead/acid, so it's good to know they're not.

re: FADEC control alternators
Are these the same as the FADEC EECs? Just want to make sure. If so, I'm told they produce 300W at 2300 RPM (by a forum member). Yes, they need to be pushed through one of the TRUs to get DC.

I didn't realize where they were located. I'll have to talk about how hard they were to retrieve. Perhaps an engine is torn off the plane and more accessible...
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Old 22nd Sep 2014, 09:59
  #34 (permalink)  
 
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When I go down route I take my normal line engineer toolbox, that has pretty much everything I need including a hacksaw, files, my own multimeter, gas soldering iron, etc.
With hand tools I think you can be pretty generous with what an engineer would have, especially for a story, also if the aircraft is a charter operation they carry a fair bit of spares. The 777's I work on have a fairly big spares pack up onboard. Don't forget the big aircraft also carry a whole load of cargo, not just passenger bags. You could have anything in there.

Re generators; without wanting to dig out my training notes, am I not correct in thinking that if a motor is driven, it becomes a generator? First class and business class seats are full of electrical motors, could one of these be jury rigged into being a generator? As I said, my little gas soldering kit goes with me on flights!
For some sort of steam shenanigans, the main engines and APU also have air starters, little air turbine motors. One of these connected to a generator on one end and a spanking big kettle on the other might give you a working rotating thing of some sorts!
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Old 22nd Sep 2014, 13:28
  #35 (permalink)  
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re: tools
Thats what I wanted to hear. A reasonably well-equipped tool bag. Spares aren't probably useful unless they can be easily repurposed to do other useful things.

re: motors
From my research, it seems that a brushless DC motor may produce DC or AC depending on it's design. I think that is what I learned. For use in power generating, you need a design that produces power at low RPM (500 or so). A high RPM DC motor isn't useful unless you can gear it to get the proper RPMs.

re: turbine starters
That's great news! Theoretically, that could be removed from the APU and put on something smaller. It's probably well setup to drive with steam (once I figure out how to get a decent sized boiler together). I think I could theoretically use the carbon-fiber waste tank as long as I don't heat it with a direct flame. If I protected it with an aluminum plate from the plane, the radiant heat from the plate would heat the tank. After all, it shouldn't have to get more than 150 degrees C to produce plenty of steam. Need to work out all the math and look at the pressures it would require...
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Old 22nd Sep 2014, 18:59
  #36 (permalink)  
 
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Although making your own steam boiler is an easy way to blow yourself up. There's a lot of energy in pressurised steam and making a strong enough boiler is very difficult. That may be a plot device in itself for you of-course. ..

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Old 22nd Sep 2014, 21:24
  #37 (permalink)  
 
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Although making your own steam boiler is an easy way to blow yourself up. There's a lot of energy in pressurised steam and making a strong enough boiler is very difficult.
Can't help you with where to find the parts on a 777, but you should consider a Sterling cycle steam engine. Low pressure, very efficient, much safer. High pressure steam would be insane without purpose built pressure vessels.
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Old 23rd Sep 2014, 02:57
  #38 (permalink)  
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re: steam power
Sterling is great, maybe a little more complex to make than a simple steam turbine mounted on the shaft of an alternator that doesn't try to be very efficient - it dumps heated steam that could do more work. Until I spend some time researching, I don't really know if high pressure was required. I'm sure there is a formula that will tell me what pressure and volume is required to drive a certain horsepower motor. The little research I've done suggests it might work - without high pressures or high temps.
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Old 23rd Sep 2014, 11:05
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You also have the O2 bottles that'll take a couple of thousand psi and the hydraulic accumulators that'll take over 3000psi
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Old 23rd Sep 2014, 13:23
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How big are the hydraulic accumulators? How many gallons will they hold?

The problem with the container is that you've got to put feed water into it or you'll have a short run. It takes at least a gallon/minute to get any useful work out of steam power. If the boiler is pressurized to say 50psi (keeping it relatively safe) then I also need a 50+psi pump to inject the feedwater into the boiler. Can I assume the freshwater lines in the plane are pressurized to at least 40? Perhaps that could be how I get to at least 40psi.

It all suggests the minimum size for a boiler to produce 500W-1KW is going to be around 60G or so. Again, I haven't worked it out, but I've played with some steam calculators.
Steam Calculators: Steam System Modeler
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