Turbofan Engine Generators

[Denholm]

Hey guys, this just has me baffled.

I'm putting together a presentation for my speech class which will be a 3-5 minute extemporaneous informative or persuasive speech/presentation. The instructor gave us the liberty of choosing our topic. So I naturally went for something I enjoyed and understood, or so I thought. I decided to make my presentation on Turbofan Engines, otherwise known as turbine engines. I managed to get stuck hard when it came to finding material for the generator inside the engine which supplies electricity to the plane. I've found scraps of information using Google and scholarly search engines, however nothing solid. As far as I'm aware the actual generator sits somewhere away from the airflow being turned by an accessory system located on one of the drive-shafts.

This is by far the best information I have found so far: http://www.globalsecurity.org/military/library/policy/army/fm/1-506/Ch8.htm
However, it's still not enough information for me to say without doubt that the above statement is true.

I'm wondering if any of you know of any pictures or diagrams showing the placement of the generator within the nacelle along with the location of the device that turns the generator? I would also greatly appreciate it if someone could try to explain just where the generator is located and what turns it. I suspect the majority of my inability to find information on the generator is due to my lack of knowing the names of the generator, location where it sits, and what turns it.

I would definitely appreciate any information.

[crazyivan]

Couldn't you say some internal parts are classified? Interesting report and good luck. Probably someone on here could answer your question.

[TheZohan]

check out this site too may help you alot

http://www.turbinefun.com/

see if that helps any

[eagl]

The generators and other accessories are usually driven by a power takeoff shaft, which is a driveshaft running from somewhere in engine to an accessory gearbox.  That gearbox may include an automatic transmission to keep the accessories turning at a reasonable speed, if the engine commonly operates in a wide RPM range.  The starter may also be in this accessory pack, and sometimes the generator does double-duty as a starter.

The T-37 starter/generator is actually housed in a "bullet nose" just ahead of the center of the compressor blades.  It is pretty much just bolted onto the compressor disc.  Send power to it below about 35% and it acts as a starter, spin it up past about 43% (if I recall correctly) and it acts as a generator.  On turboprops, the accessory gearbox may be bolted to the backside of the engine since the intake of a turboprop (PT-6 series anyhow) is centrifugal (sucks air in through a ring shroud around the intake), not axial (directly in line with the motor) so all the accessories are bolted to the intake housing and is driven by an extension of the main engine core rather than a power takeoff shaft coming out of the side of the motor.

[Casca]

Generators on transport category turbine aircraft are frequently driven through constant speed drives or CSDs.  The requirement is to keep the frequency constant when producing AC power (large aircraft power requirements are a combination 115 V at 400 hertz AC and 28V DC).  Back in the day this was done with hydraulics by putting a pump on the accessory pad that drove a motor connected to the generator.  The displacement of the pump could be varied to regulate the speed of the alternator.  Many newer aircraft have variable frequency alternators which eliminates the need for a CSD.

[Heater]

Depending on the engine  / aircraft type there are several ways of doing this... if you look at the F-15 / F-16 / F-22 these all use a PTO coupled to an AMAD (Airframe Mounted Accessory Drive) which in turn has the Generator / CSD (constant speed drive) mounted on it...

If you look at the F4 then it has the generator/CSD mounted in the nosecone of the J79 engine...

So like I said it depends on the type of aircraft and the engine used....
Take a look at this link this is the layout used ont he F-15 ...
http://www.garrettretireesaz.com/history/Gammill_history/F-15%20Project.pdf

[Denholm]

Alright, so my assumption appears to be correct. That an accessory system sits on one of the drive-shafts and the accessory system turns the generator.

TheZohan, is that diagram of an actual jet engine? If so it suggests that the high and low pressure turbines generate power. Casca and Heater, thank you for the information. However I'm trying to find information on Turbofan Engines of modern airliners, not military aircraft. Typically the engines between the two vary, as I've never seen a commercial airliner making use of afterburners (The flame version).

Thanks again guys, this certainly is helpful.

[Casca]

Casca and Heater, thank you for the information. However I'm trying to find information on Turbofan Engines of modern airliners, not military aircraft.

I was speaking of airliners.

[Heater]

Alright, so my assumption appears to be correct. That an accessory system sits on one of the drive-shafts and the accessory system turns the generator.

TheZohan, is that diagram of an actual jet engine? If so it suggests that the high and low pressure turbines generate power. Casca and Heater, thank you for the information. However I'm trying to find information on Turbofan Engines of modern airliners, not military aircraft. Typically the engines between the two vary, as I've never seen a commercial airliner making use of afterburners (The flame version).

Thanks again guys, this certainly is helpful.

No problem....

Google CFM56, CFM56 gearbox, CFM56 IDG  etc...
Here is a link with the gearbox / Generator and IDG in view.
http://www.airliners.net/open.file/1325191/L/

Again even on the CFM56 I think there are a least 2 different versions some use a CSD other use The IDG...

[Hawk78th]

....  “I decided to make my presentation on Turbofan Engines, otherwise known as turbine engines. (1) I managed to get stuck hard when it came to finding material for the generator inside the engine which supplies electricity to the plane. I've found scraps of information using Google and scholarly search engines, however nothing solid. As far as I'm aware the actual generator sits somewhere away from the airflow being turned by an accessory system located on one of the drive-shafts. (2)
.....

 Denholm,
 # 1 from above:  As you know Turbofan engines are the  " New Age" of turbine engines... where the Fan is the major thrust producer in an Aircraft Turbine engine.( as opposed to the Thrust from After Burner (after Internal Combustion that is)  The "turbine engines" can also refer to "Turboprop" engine such as they are connected to a reducing gearbox which houses the Prop shaft, hence the TurboShaft or Turboprop names given to Certain manufactures... Pratt & Whitney Canada for instance.

2)  Lets take the PW306C (<-clik it) model engine for example…. Found on Cessna Citation Sovernign  Business class Aircraft.  On the Engine’s Accessory gear box (AGB…  lower portion of the engine) it has a PMA( Permanent  Magnet Alternator) which produces AC Current for ALL of the ENGINES’s (**NOT Aircraft’s) electrical power requirements. (More on this in a minute). The AGB also has provisions for a “Starter/Generator” which produces DC Voltage for the Aircraft’s (NOT engine) Electrical power requirements. This  St/Gen will produce  electricity  for the Major systems needed inside/outside  the A/C..  AND is also used to start the Engine by Getting Voltage from the Batteries used in the start sequence… hence if you supply electricity TO the St/gen ….it’s a “Starter”… When the Engine is running , it’s now a DC GENERATOR (… by a flick of a switch from the Flight deck.)

 Back to the PMA…. This PMA does basically the same thing ( as a Generator) but it’s AC Voltage…. Powering the Engine’s EEC( Electronic Engine Control) or  FADEC in this particular engine ( Full Authority Digital Engine Control) . This FADEC is the Fly by wire “ Brains” of ALL this Engine’s power/protection.
 Without any input from a crewmember, It will Control : The performance of the engine at all  commanded Power settings; Prevents  Overtemp, Overspeed, over thrust and shares information with the Opposite engine should there be a Major fault.

 I’ll help with questions.. (in as much detail as you want)  lemme know.

  Btw I work (Sr. Inspector/Sr. Tech) on Pratt Engines for a living…. Small turboshafts / turboprops to the largest Turbofan’s that PWC makes…

Pratt Canada makes smaller Engines... Pratt US makes the Large& Military engines...  Same name, same technology, different uses/applications.

 

[Denholm]

Wow, thanks guys, especially Hawk. It puts things in more of a perspective. I do believe I have the information I'm after, now. Thank you all very much!