Flightsim-pilot questions (Merged)

[Patrick_Waugh]

I fly a sim B206, and wondering when you would need to reset the generator, and what that does exactly.

Patrick

[imabell]

it might make it work again if it has stopped. ??

[Aesir]

Hi Patrick

Here is what my SA365 manual says:

"The spring loaded 'reset' function allows the generator to be restored after a transient fault"

In effect the switch resets the overvoltage or reverse current relay who disconnects the gen if the voltage exceeds 32v. It probably does the same in the 206.

[Arm out the window]

The generator is basically an electromagnet spinning around in a coil, as I understand it, as opposed to the old permanent magnet doing the same.
To get it working, there first needs to be the right electric current in the electromagnet coil, so if you hand propped a fixed wing with a dead battery, the alternator wouldn't work because there was no electricity to start it off in the first place.
I think with a genny reset (searching the memory banks here) it 'flashes the field', ie provides electricity to the right connections on the unit to get that initial current direction and amount right to kick off the magnetic fields that make the whole thing work as a generator - the idea being, if for some reason it's stopped working, you might be able to kick it off again by setting up the right initial conditions again.
Then if it still doesn't work, it's probably shat itself, to use a technical term!
So (I think) that's why your genny switch has three positions - on, off and reset, rather than just on/off.

[Gomer Pylot]

For what Patrick needs to know, the generator switch goes to the OFF position when a fault knocks it off, just like a circuit breaker. In order to get the generator to work again, you have to move the switch to the Reset position, then to the On position. Just moving it to the Reset, or to the On position, won't restore the generator. You have to move it to both positions, and if the fault was momentary, then the generator will start working again. Depending on the fault, it may still not work.

Edit: As far as I recall, the switch won't actually move to the Off position, you just get a generator light, and then you move the switch through the OFF position to Reset, and then back to ON. The generator may or may not be restored. If a couple of cycles doesn't restore it, then you assume it's out for good, and rely on the battery. You hope for 1/2 hour of battery. The engine will continue to run without the battery, of course, but your avionics and some instruments will die.

[Upland Goose]

Arm out of the Window.
I think you are spot on. I have always believed that it "flashes the field" as well. That is, realigning the polarity of the permanent magnet field windings.
It's possible that this would not be the case if you had previously selected the battery off - due to overtemp perhaps? Discuss.
This polarity may have been disturbed (reversed) or removed due to major fault on electrical system, which precipitated the genny dropping off line.
If you have a real "meltdown at 3 mile island" then heaven help you!
It's times like that you wish you had the simplicity of a Tiger Moth!
UG

[Patrick_Waugh]

Thanks guys. I am starting to get it I think.

I read up on alternators, and it seems the main difference between a generator and an alternator is that they create DC current differently.

The generator uses a moving coil in a fixed magnetic field (which is basically an electo magnet powered by the engine).

The alternator uses a moving magnetic field (the rotor) within a fixed tri-coil that allows it to generator AC that feeds a rectifier to convert to low-ripple DC to charge the battery and feed circuits.

Now, both require an initial electrical source to create the magnetic field used to allow it to generator current. So, I am now understanding that the reset allows you to reset the field and attempt to recreate the conditions necessary to restart the generation of electricity.

Seems there is a difference of opinion of if the switch must be manually moved, or will spring back to OFF, and then be manually moved to GEN.

Also, given the superiority of alternators to provide significant current at low engine RPM (idle) why do they still use generators in aircraft?

Finally, if your alternator/generotor fails, and you are now on battery only, and you were unable to land until the battery completely discharges, would you risk a flame out due to a lack of power to fire the ignitors?

Patrick

P.S. You guys are great for helping me.

[Arm out the window]

Units used on aircraft like the Bell 206 are not just generators but starter generators, ie they work as motors initially to spin the compressor for start, and will then come on line to operate as generators once the engine's running. There are various control circuits to make sure they do the appropriate job at the right time, as well as the switch settings called for in the checklist.
I think it must the requirements of this dual role that makes the starter generator the weapon of choice for this type of engine rather than the alternator - obviously easier and lighter to have just one unit, as well.
They do use alternators on light fixed wing, I think. Not sure about the small piston rotaries like the R22?

[fkelly]

The engine wouldn't fail with a flat battery; once it's running it's just a blowtorch with no ignition [let's ignore auto relight etc]. As long as the engine driven fuel pump can suck up the fuel the engine will run. More advanced engines with electronic fuel computers will also run as they have dedicated engine driven generators to power the computer...if they don't they wouldn't be...more advanced..

[Patrick_Waugh]

What would happen if?

If you left the generator switch in the ON position, and attempted a start (of a B206 in my case), what would happen when you pushed the starter?

I'm sim'ing this, and wanted to know.

I'm guessing that the generator switch switches between starter mode and generator mode, and so basically nothing would happen. You would hear silence instead of the starter motor.

Also, quick question. Is the gas producer gauge showing N1, and the Power turbin/Rotor gauge showing N2? Just checking my understanding.

Patrick

[rotorfloat]

Your starter would still function as a starter with the gen switch in the on position.

You are correct about the N1, N2/Nr guages.

[NickLappos]

Remember the gen switch is simply a means to ask the GCU (gen control unit) to make the machine turn into a generator. That is why the reset function works as it does, it simply asks the GCU to let the gen come on line.
Similarly, the GCU will not let it generate while it is a starter.

GCU's are clever fellows. Take care though, the Generator will pop on as soon as the starter is switched off, so the engine will see the big generator load, perhaps dragging it down.

[Ifrboy]

Nothing special will happen if you attempt a start with the gen switch switched into the on position.

The only thing that changes is that the generator will come online right after you release that starter button instead of when you manipulate the switch to the on position.

This isnt entirely without danger tho. This on its own isnt that dangerous, but it will cause an extra load on the engine and it might happen that the engine isnt powerfull enough at that speed, causing a drop in speed. This might drag the engine below the minimum self sustain speed, and if not taken care off, will give you a nice pudle of melted turbine parts.

[Patrick_Waugh]

Ok, I am getting it.

So, the main bus, and basically everything in the B206, is powered first by the battery, then by the generator (ie. engine) once the engine is fired up and the generator is switched on (and working).

Is there anything you can't turn on with the engine off? (ie. that requires the generator is powering it)?

Also, can you at least turn on the panel lights (to see what you are doing) with the battery off?

Thanks a bunch guys,

Patrick

[Patrick_Waugh]

Another Gyro question

In the B206, you have the switch on the overhead that powers the attitude and directional gyros. Is all that is required to spin those gyros up the battery on and that switch on? Or must there be engine power?

I realize that they probably would drain the battery quickly.

Patrick

[Hilico]

From earlier discussions on this topic, there's also the possibility that the quill shaft might snap - the sudden reversal of load from starter driving engine to (now) a generator being turned by engine causing it to fail in torsion.

[Dis-Mystery of Lift]

You cant turn anything on with out the battery on.This is a good thing so idle students cant leave switches on and drain the battery etc(Pays to check whats been played with before flicking Bat on) .You do have to pop your fuel Boost CB's as one works directly off the battery.Leave it on for a few days and no starty!!Do all night starts with torch in mouth to look at dials(When ground Power not around)

[helilad]

From what I remember of 206 is after start you idle at 60% for 1 min then increase n1 to 70% before engaging gene.I understand the 1 min gave the engine a chance to stabilise[without a gene load] and the reason for increasing to 70% was to avoid dragging n1 down below the min60% n1.

Any takers on this theory?

[tomstheword]

Every switch in the helicopter will work with the battery turned on.

Every switch in the helicopter will work with the battery turned off if the generator is working.

You can always wait until the helicopter is running before turning them on.

[nimbostratus]

Originally Posted by Dis-Mystery of Lift

You cant turn anything on with out the battery on.This is a good thing so idle students cant leave switches on and drain the battery etc(Pays to check whats been played with before flicking Bat on) .You do have to pop your fuel Boost CB's as one works directly off the battery.Leave it on for a few days and no starty!!Do all night starts with torch in mouth to look at dials(When ground Power not around)

In my experience it's only the Longranger that has a boost pump that is operational with the battery switched off (could be wrong though!).