Tech Q for CRJ guys & gals

[xcr600]

If TRU 1 fails in flight will DC Tie connectors 1 & 2 auto close to power TRU 1 from TRU 2? I dont think so but I have one manual that says "if TRU 1 or 2 fails the tie connectors will automatically close." It has been my understanding these are all manual tie connectors so you have to option of powering from the other TRU or the SERV TRU. Thanks

 

[Z28_Pilot]

Why don't you look at the QRH.......If it tells you to switch something manually, then do it....if not, then leave it alone!

-just my .02

-Z

 

[shamrock]

Electrical has always been my weakness, but looking at my manual it seems that if TRU 1 fails TIE 1 would close allowing DC BUS 1 to be powered from the SERV TRU, UTIL BUS 1 would be shed. If the SERV TRU is unavailable TIE 1 and TIE 2 would close allowing TRU 2 to power DC BUS 1, UTIL BUS 2 would be shed.

How'd I do?

 

[Detroitpilot22]

just pull the ADG handle

 

[=w=]

If TRU 1 fails in flight then why would you want power redirected to it?

 

[Lear70]

Electrical has always been my weakness, but looking at my manual it seems that if TRU 1 fails TIE 1 would close allowing DC BUS 1 to be powered from the SERV TRU, UTIL BUS 1 would be shed. If the SERV TRU is unavailable TIE 1 and TIE 2 would close allowing TRU 2 to power DC BUS 1, UTIL BUS 2 would be shed.

How'd I do?

DING DING DING! We have a winner! (That wasn't the Master Warning Triple Chime incidentally)

If TRU1 or TRU2 fail, its respective tie AUTOMATICALLY closes and the TIE PBA will light up to indicate this even though you haven't pushed it yet.

The only one that's NOT automatic is the ESS TIE. If the ESS TRU fails, the tie doesn't auto close because closing the ESS TIE prohibits DC BUS 1 or 2 from pulling power from the ESS TRU. There are certain scenarios (engine failure accompanied by electrical system problem) where it is more advantageous to have TRU1 powered than the ESS TRU (fault on the ESS TRU bus, etc).

Why don't you look at the QRH.......If it tells you to switch something manually, then do it....if not, then leave it alone!

That kind of robot thinking is going to get someone killed some day.

If you don't understand the systems on ANY aircraft you fly, you have absolutely NO business, that's ZERO, ZILCH, NADA business of commanding it. Knowing WHY you're about to push a button the QRH is directing you to is EXTREMELY IMPORTANT.

One of these days you'll run into a situation where following the QRH immediately and exactly as it says will get you into another problem.

I HATE training departments that make students rote memorize the answer, "Only when directed by the QRH" to an oral question that asks you when you would push a certain button...

 

[Mookie]

That tie thing is a major gotcha b/c if both ties close automatically, and you lose an essential tru, the QRH tells you to close the Esential (manual only) tie. this in turns locks out a large portion of the dc system....dark cockpit...no good.

Devils advocate though, if you talk to a fed about the alaska md 80 crash, they will tell you to follow the qrh to the letter. bummer they had to learn that the wrong way...

Mookie

 

[Puck Mugger]

Eject...

 

[ReportCanoa]

Climb to 410, and core lock it, dude.

 

[Lear70]

Climb to 410, and core lock it, dude.

"250 hours in a Beechcraft 1900 and Airline experience for the cost of 172 time. It's a no brainer." Gulfstreem is the right choice!"

And yet another PFT Tool. *sigh*

 

[xcr600]

Thanks Lear and others for the good responses that clairfies what I thought but was not sure of.

 

[ReportCanoa]

And yet another PFT Tool. *sigh*

With a dim wit like yours, I wouldn't detect the least bit of sarcasm in my profile either.

 

[Lear70]

With a dim wit like yours, I wouldn't detect the least bit of sarcasm in my profile either.

I WOULD have detected sarcasm... IF your profile on the left didn't indicate you were flying as a 1900 pilot in the right seat with 249 hours. All that points to Gulfstream and your sig fits the profile.

If you want to be sarcastic, maybe YOU should sharpen YOUR wit and figure out how to point out the difference between your profile and your sig.

 

[nethan]

I'm thinking the profile is a joke too. Scaring passengers? Come on now.

 

[Nancy Pryor]

There's no substitute for systems knowledge

Why don't you look at the QRH.......If it tells you to switch something manually, then do it....if not, then leave it alone!

That kind of robot thinking is going to get someone killed some day. If you don't understand the systems on ANY aircraft you fly, you have absolutely NO business, that's ZERO, ZILCH, NADA business of commanding it. Knowing WHY you're about to push a button the QRH is directing you to is EXTREMELY IMPORTANT.

One of the truest things ever written on flightinfo. An unfortunate side effect of the progress made by manufacturers in simplifying and automating the operation of aircraft systems has been a corresponding drop in the depth of systems knowledge taught by many flight training departments and sought by many trainee pilots. Regional airline new hires can't do a lot about the training department, but can do a lot about seeking additional knowledge for themselves. It is sad how few pilots do this these days.

If TRU1 or TRU2 fail, its respective tie AUTOMATICALLY closes and the TIE PBA will light up to indicate this even though you haven't pushed it yet. The only one that's NOT automatic is the ESS TIE. If the ESS TRU fails, the tie doesn't auto close because closing the ESS TIE prohibits DC BUS 1 or 2 from pulling power from the ESS TRU. There are certain scenarios (engine failure accompanied by electrical system problem) where it is more advantageous to have TRU1 powered than the ESS TRU (fault on the ESS TRU bus, etc).

This is an example of the level of systems knowledge a professional pilot has. Hats off to the pilots who know their airplanes this well. Systems knowledge is like auto insurance, most of the time you don't use it but one day you might really need it. Flipping through a QRH is no substitute for knowing what you are doing and why you are doing it.

 

[CptMurf]

Food for thought for any aircraft you may fly in the future....

TRUs convert AC to DC.........they are not actually powered
Inverters convert DC to AC....they are not actually powered either

Power flows through them, but not needed to operate. Your busses should be powered downstream through your bus-ties. But what do I know, I fly the SAAB!

 

[C425Driver]

If TRU 1 fails in flight then why would you want power redirected to it?

TRU 1 powers DC Bus 1. Closing the tie would allow another power source to feed DC Bus 1. It would not redirect power to the inop TRU.

C425Driver

 

[Z28_Pilot]

That kind of robot thinking is going to get someone killed some day.

If you don't understand the systems on ANY aircraft you fly, you have absolutely NO business, that's ZERO, ZILCH, NADA business of commanding it. Knowing WHY you're about to push a button the QRH is directing you to is EXTREMELY IMPORTANT.

One of these days you'll run into a situation where following the QRH immediately and exactly as it says will get you into another problem.

I HATE training departments that make students rote memorize the answer, "Only when directed by the QRH" to an oral question that asks you when you would push a certain button...

Well, I agree that good systems knowledge is essential..however..the A/C I fly has NO engineers panel and not really that many switches....I wouldn't want to be the guy (read:MacGyyver) that distrusts the EDL logic and tries to "force fix" something because I just KNOW that this BTC should've opened/closed BLAH,BLAH,BLAH,BLAH and subsiquently create a nice little fire to light my last cigarette with!

BTW - If someone ever tells me that I have NO (read:ZERO,ZILCH,NADA) business flying this A/C with them because I might not remember exactly wich BTC should open/close when YADA,YADA,YADA.......then I hope they enjoy me playing the SNL "Iceman 20 years later" skit on my laptop for them....over..and over...and over.....and over again!!

later Iceman!!

P.S. "you're dangerous"!!!!:smash:

 

[Nancy Pryor]

Food for thought for any aircraft you may fly in the future....

TRUs convert AC to DC.........they are not actually powered
Inverters convert DC to AC....they are not actually powered either

Power flows through them, but not needed to operate.

Maybe I'm missing your point here, I'm not sure, but both TRUs and inverters definitely require power to operate.

The reason is that their efficiency is not 100%, so some power is lost as heat in the operation of the transformers and rectifiers in the TRU and in the switching transistors, transformers (or other inductors) and various passive components in the inverters. Some energy is lost to unwanted mechanical motion in the transformer cores and windings also, which is why you can hear that 400Hz whine from the inverters. In the case of inverters, power is required to operate them even when the load on the inverter is zero. This is because the inverter has to generate a 400Hz AC waveform and drive its conversion transformer (or other inductive circuit) and regulation feedback loop even when there is no load connected, and this takes finite electrical energy. 100% efficiency in electrical power conversion would be nice, but various laws of physics make it unattainable in practice.

 

[Nancy Pryor]

Well, I agree that good systems knowledge is essential..however..the A/C I fly has NO engineers panel and not really that many switches....I wouldn't want to be the guy (read:MacGyyver) that distrusts the EDL logic and tries to "force fix" something because I just KNOW that this BTC should've opened/closed BLAH,BLAH,BLAH,BLAH and subsiquently create a nice little fire to light my last cigarette with!

Wasn't the discussion about bus ties? Doesn't your aircraft have bus ties? The point, which has been made by several people here now, is that a pilot needs to understand the aircraft systems so that he/she can understand its failure modes and execute the published failure response with understanding, not like a poorly trained monkey (no offense to monkeys). And sometimes there isn't a QRH page for a failure mode. Does triple hydraulic system failure on the DC-10 ring any bells? That's happened more than once, and in at least one case, thorough knowledge of the airplane and some outstanding airmanship made a big difference.

BTW - If someone ever tells me that I have NO (read:ZERO,ZILCH,NADA) business flying this A/C with them because I might not remember exactly wich BTC should open/close when YADA,YADA,YADA.......then I hope they enjoy me playing the SNL "Iceman 20 years later" skit on my laptop for them....over..and over...and over.....and over again!! later Iceman!! P.S. "you're dangerous"!!!!:smash:

Nice attitude. I think you just confirmed Lear70's observation.

 

[DorkProp]

I think what was meant by not blindly trusting the QRH is that the QRH is not the end-all, be-all manual for abnormal situations. In fact, our QRH specifically states at the beginning that it contains "RECOMMENDED" procedures. In general, it works very well. But as someone has mentioned, on the CRJ there is the potential for losing significant electrical power unders certain circumstances if the QRH is followed regarding tying the ESS DC tie. You, as the pilot, are ultimately responsible for the safety of the flight. If your knowlege of the systems leads you to believe that a QRH procedure would be detrimental to the flight, then your responsibility is to come up with another course of action. Even our Bombardier instructor pointed out the ESS DC tie issue in the QRH and showed us in the systems trainer what would happen if you follow the QRH under those particular circumstances.

 

[Erlanger]

Actually what the CRJ QRH says is;

This handbook contains suggested procedures only for quick reference. These procedures in no way supersede current procedures outlined in the approved Airplane Flight Manual and revisions thereto. In case of conflict, the Airplane Flight Manual takes precedence.

 

[CptMurf]

The reason is that their efficiency is not 100%, so some power is lost as heat in the operation of the transformers and rectifiers in the TRU and in the switching transistors, transformers (or other inductors) and various passive components in the inverters. Some energy is lost to unwanted mechanical motion in the transformer cores and windings also, which is why you can hear that 400Hz whine from the inverters. In the case of inverters, power is required to operate them even when the load on the inverter is zero. This is because the inverter has to generate a 400Hz AC waveform and drive its conversion transformer (or other inductive circuit) and regulation feedback loop even when there is no load connected, and this takes finite electrical energy. 100% efficiency in electrical power conversion would be nice, but various laws of physics make it unattainable in practice.

Brilliant babbling....My point was, that there is not a tru bus, as it were, that is needed to be powered to convert the electricity. Power through it, not to it. An inverter in it's simplest form is a circuit board with resistors wired to manipulate the electricity the way that you want to. All electronics lose energy through heat and some, such as aviation grade tru's, even use the power flowing through it to power a cooling fan (as shown below). And your right the tru will use power when the LOAD is zero, but not when there is no suppy through the tru.

http://www.craneae.com/Solutions/AEP/images/81-012-Lb_web.jpg

I didn't think we were discussing the energy necessary to convert electricity though. Why would it matter we can produce more than enough to cover the loss even on one generator.

The question was if tru1 fails can we power it trough tru2. The answer ultimately is... no, why would you? tru1 is powered by the flow through it and converts AC to DC, then sends that power to a bus downstream. The busses normally powered by tru1 should be powered through the bus-ties for your aircraft.

 

[Nancy Pryor]

Brilliant babbling....My point was, that there is not a tru bus, as it were, that is needed to be powered to convert the electricity. Power through it, not to it.

Babbling? Hmm... Anyway, thank you for clarifying what your original point was, yes, there is no TRU bus, the TRU is powered by its associated generator and generator control unit, the parasitic power dissipated by the voltage stepdown and rectification in the TRU comes from the same power source, but it is not free (see below).

An inverter in it's simplest form is a circuit board with resistors wired to manipulate the electricity the way that you want to.

Sorry, this is simply incorrect. A resistor network is a passive circuit that can perform voltage division or drop, current flow reduction and power dissipation, but in no way can it perform inversion. For inversion you need an active non-linear device, be it electronic (static inverter) or electromechanical (rotary inverter) as in years gone by. A resistor network, however arranged, cannot perform inversion. This is because it has a linear transfer function and a linear voltage gain between 0 and 1 (ignoring heating effects on the resistances), and therefore cannot transform a DC signal to an AC signal (inversion within the meaning of this context). I'd take the time to explain why, but you'd probably call that babbling - look it up with google if you're interested, or consult any decent electronic engineering textbook.

And your right the tru will use power when the LOAD is zero,

Actually I said an inverter still dissipates power when there is no load connected, but it is true that a TRU will also use some power with no load. This is mostly because of hysteresis losses in the transformer magnetic core which cause core heating, even though no power is being removed from the transformer to a load.

but not when there is no suppy through the tru.

Naturally you cannot dissipate power when there is no source of power.

I didn't think we were discussing the energy necessary to convert electricity though.

Agreed, the original question was about CRJ bus ties. The conversion topic arose because of your assertion that "Power flows through them, but not needed to operate" in reference to TRU's and inverters in aircraft.

Why would it matter we can produce more than enough to cover the loss even on one generator.

Absolutely. It's worth mentioning that to "cover the loss" costs fuel. This is because the extra energy required to make up the conversion losses has to come from somewhere, it's not free. In an aircraft it comes from the generators. The greater the load on a generator, the harder it is to turn the generator shaft. The harder it is to turn the shaft, the greater the engine fuel flow required to maintain an N1/N2 speed, and therefore a given engine thrust/power output appropriate for the conditions of flight. It's not a whole lot of fuel (I don't have numbers) but it is non-zero, and over many flights that adds up. So it is desirable to make the conversion as efficient as possible, not only because this allows the use of a smaller, lighter TRU or inverter with reduced cooling requirements, but because there are small fuel savings to be realized from a slightly reduced engine accessory load.

 

[CptMurf]

Sorry, this is simply incorrect. A resistor network is a passive circuit that can perform voltage division or drop, current flow reduction and power dissipation, but in no way can it perform inversion. For inversion you need an active non-linear device, be it electronic (static inverter) or electromechanical (rotary inverter) as in years gone by. A resistor network, however arranged, cannot perform inversion. This is because it has a linear transfer function and a linear voltage gain between 0 and 1 (ignoring heating effects on the resistances), and therefore cannot transform a DC signal to an AC signal (inversion within the meaning of this context). I'd take the time to explain why, but you'd probably call that babbling - look it up with google if you're interested, or consult any decent electronic engineering textbook.

Actually I have looked it up, here is a link to a simple tru with no moving parts, no rotary/static inverter. Obviously this is not built to run an aircraft, but it converts AC to DC just the same.

http://www.allaboutcircuits.com/vol_6/chpt_5/6.html

I believe that BOTH of us have a well enough working knowledge of the system from a pilots perspective. We have beat this horse to death. Let's leave it be, because I would believe most people in this thread would say we are BOTH babbling.

 

[PoorJetDriver]

Actually what the CRJ QRH says is;

Another problem with the QRH is it is designed to deal with single failures of components. If you find yourself having multiple failures of electrical system components you may actually have to start doing some troubleshooting and reaching back into the dusty confines of your systems knowledge for help.

 

[Lear70]

The question was if tru1 fails can we power it trough tru2. The answer ultimately is... no, why would you? tru1 is powered by the flow through it and converts AC to DC, then sends that power to a bus downstream. The busses normally powered by tru1 should be powered through the bus-ties for your aircraft.

Every aircraft is a little different Murf, as you've demonstrated. The saab gets its power slightly differently than the CRJ. IN FACT, if a TRU fails (burns out, whatever, so that electricity can no longer flow "through" it in your terms and be converted to DC), there is NO WAY that its respective DC BUS is going to get power. Period. NADA, unless ANOTHER TRU comes online to provide that power.

That's our Bus Tie, otherwise known on the CRJ as a DC TIE. It allows a DC BUS to get DC power from another TRU. It has to come from somewhere.

We're all basically saying the same thing as far as I can tell, just in different verbiage.

Thanks for the vote Nancy, although my verbiage was off because I was in a hurry this morning. It's not the ESS TRU that powers DC BUS 1 or DC BUS 2 if the respective DC TIE automatically closes, it's the SERVICE TRU.

The SERVICE TRU acts as a backup for DC BUS 1, DC BUS 2, and the ESS DC BUS. Each DC BUS has its own TRU labeled respectively (TRU 1, TRU 2, ESS TRU). Sorry for the slip if anyone is using this to study (WHICH YOU SHOULDN'T).

It's easier to see when you look at the overhead panel, I caught it when you quoted me.

 

[CptMurf]

Your busses should be powered downstream through your bus-ties. But what do I know, I fly the SAAB!

That's why I wanted to leave it here Lear. Never flown the CRJ....AVRO and SAAB, but don't know anything about the CRJ. I was just trying to help someone understand what a tru actually did. Convert AC to DC. Unfortunately, I have digressed into a discussion about how much energy it takes to convert AC to DC. But I have learned, I will now turn off the autopilot on the long legs to conserve the fuel that the servos would be using.

 

[Nancy Pryor]

Actually I have looked it up, here is a link to a simple tru with no moving parts, no rotary/static inverter. Obviously this is not built to run an aircraft, but it converts AC to DC just the same.
http://www.allaboutcircuits.com/vol_6/chpt_5/6.html

Hi again Captain Murf. Not trying to be a smart***, but just in case anyone is following this discussion and trying to absorb systems knowledge from it (and as Lear70 says, "which you shouldn't"), I just want to set the record straight on one thing to avoid confusion: what you have described above is a TRU (great link by the way), but what I was suggesting you look up was about inverters, and how they cannot be made from just a resistor network, not TRUs. Conversion from AC to DC is much simpler than conversion from DC to AC. A TRU has never required moving parts, just a transformer and one or more one-way conductors, known as diodes or rectifiers (basically the same thing). Your link describes this nicely.

I believe that BOTH of us have a well enough working knowledge of the system from a pilots perspective.

From a pilot's perspective, I agree absolutely. From a technical perspective, I didn't want to let that resistor network equals an inverter claim pass without comment in case someone absorbed that and it caused them later confusion. It definitely wasn't personal, so please don't take it that way. It's a case of "what's right" rather than "who's right".

We have beat this horse to death. Let's leave it be, because I would believe most people in this thread would say we are BOTH babbling.

Probably right about that! :laugh: Peace Cap'n.

 

[Nancy Pryor]

That's why I wanted to leave it here Lear. ... But I have learned, I will now turn off the autopilot on the long legs to conserve the fuel that the servos would be using.

Sigh. Noone was suggesting that you load shed to save fuel, just stating the (interesting to some) technical fact that drawing electrical energy from an engine driven alternator costs some fuel (first law of thermodynamics*), and the context was why we care about electrical efficiency in aircraft systems even though our generators can handle more load than we need. Lighten up Cap'n, what's wrong with a little technical discussion in a thread titled "Technical Q for CRJ guys & gals"? There aren't many technical discussions on this board, and I enjoyed this one. I wish we had more of them.

*http://www.grc.nasa.gov/WWW/K-12/airplane/thermo1f.html