Startup question: AC generators

[Snoopy]

It was said that small fighters don't have CSD. :music_whistling:

 

On the A-10 the Integrated Drive Generator (IDG), located in access N37 or N38, is a self-lubricating generator and Constant Speed Drive (CSD) assembly in a single unit.

[BlueRidgeDx]

Actually, the generators cannot shift gears.

 

Rainmaker, I concede that you know far more about fighter electrical systems than I do, but in the T-38 example I mentioned, the generator does shift. It's referenced in both the -1 and -1CL-1:

"

An airframe mounted gearbox for each engine operates

a hydraulic pump and an AC generator. A shift

mechanism keeps AC generator output between 320

and 480 cycles per second. Gearbox shift occurs in the

65% to 75% RPM range."

Also, listen to the following video:

 

 

The hum is not changing due to electrical transients, it's directly related to engine RPM because the the generator makes no attempt to maintain a fixed speed. Note the sound of the generator shifting when he crosses the threshold and pulls the throttles to idle.

 

On the A-10 the Integrated Drive Generator (IDG), located in access N37 or N38, is a self-lubricating generator and Constant Speed Drive (CSD) assembly in a single unit.

 

In case it wan't obvious, the facepalm smiley in my earlier post was meant for me, not for you. Facepalm is exactly what I did when I read what I had written, and realized that I must have been inebriated when I posted. :joystick:

[Rainmaker]

It was said that small fighters don't have CSD. :music_whistling:

 

In the case of US born fighters, this is untrue however. All current gen fighters that I can think of use CSD's.

 

 

I know what possibilities there are, lots of my curriculum is made up of electric engineering, i'm just curious what is used exactly and possibly for what reason. ;)

 

Actually concerning propagation of power, you are not correct. High voltage DC is far more efficient for power propagation (but the technology to convert high power AC to DC has only emerged a few years back, Germanies large north sea wind farms use DC underwater cables for power transmission from offshore to the main grid, e.g.). AC is easier to generate and transform, not easier to propagate.

 

 

I think in different terms, we are both trying to convey the same thing. My dumbed down "jet talk" is a little different than someone with an engineering degree would speak. :)

 

I am not sure what ranges are talked about with regards to high power AC or DC though. If I am thinking in the same ranges as you are, we have no need for voltages in a "high" region. Most voltages present are in the 115VAC/28VDC region, with some exceptions here and there.

Edited January 11, 2012 by Rainmaker

[Rainmaker]

Rainmaker, I concede that you know far more about fighter electrical systems than I do, but in the T-38 example I mentioned, the generator does shift. It's referenced in both the -1 and -1CL-1:

"

An airframe mounted gearbox for each engine operates

a hydraulic pump and an AC generator. A shift

mechanism keeps AC generator output between 320

and 480 cycles per second. Gearbox shift occurs in the

65% to 75% RPM range."

Also, listen to the following video:

 

 

The hum is not changing due to electrical transients, it's directly related to engine RPM because the the generator makes no attempt to maintain a fixed speed. Note the sound of the generator shifting when he crosses the threshold and pulls the throttles to idle.

 

 

 

-1's do not apply very well in this case just because of the broadness at which the information is given. There are aircraft that do this, but AFAIK, the shifting is down in the accessory drive as opposed to the main gen. This is how heavies and suck that do not drive off a CSD are operated. I will try and see if I can dig up some more information on this to clarify the T-38 system specifically.

[Rainmaker]

It is entirely possible that the CSD is coupled with a shifted gearbox with 2 speeds to avoid undesireable input-output RPM differential ranges in some designs.

 

 

I cannot confirm if a T-38 has a CSD or not. But we are in complete agreeance on this. The shifted gearbox is a likely possibility. In any event, the gen should not be the one "shifting", it should be another form of gearbox or transmission assembly.

[sobek]

I am not sure what ranges are talked about with regards to high power AC or DC though. If I am thinking in the same ranges as you are, we have no need for voltages in a "high" region. Most voltages present are in the 115VAC/28VDC region, with some exceptions here and there.

 

Yes, that was just an excursion. Aircraft electrical circuits are neither high power nor high voltage by power engineering standards. :)

[BlueRidgeDx]

-1's do not apply very well in this case just because of the broadness at which the information is given. There are aircraft that do this, but AFAIK, the shifting is down in the accessory drive as opposed to the main gen. This is how heavies and suck that do not drive off a CSD are operated. I will try and see if I can dig up some more information on this to clarify the T-38 system specifically.

 

You're right on all accounts.

 

Most -1's, and specifically the 1T-38C-1 are incredibly dumbed down. So without a maintenance manual, you can't get a real sense of how it works.

 

And you're right that it's not the generator itself shifting, but rather a shifting mechanism contained in the accessory gearbox. Chalk that up to me being imprecise in a room full of folks smarterer about electrical engineering than I am. ;)

[mvsgas]

:smartass:And here I thought electricians just knew how to call an AMAD bad and go back in the truck. So proud of you Rain :D

Edited January 11, 2012 by mvsgas

[Rainmaker]

:smartass:And here I thought electricians just knew how to call an AMAD bad and go back in the truck. So proud of you Rain :D

 

 

Gas....

 

Shush! :)

[mvsgas]

:thumbup:Ok