View Full Version : IDG vs APU GEN
silverhunter
3rd Jun 2009, 10:16
Hey all!
Can anyone tell me what is the basic difference between an integrated drive generator and an APU generator? :confused:
aidey_f
3rd Jun 2009, 10:48
The IDG normally contains a summng gear so that as the engine speed varies over a fairly broad range, the input speed to the generator (and thus the output freqency) remains pretty much constant.
The APU core on the other hand is normally connected directly to the generator, as the APU runs at pretty much a constant speed, give or take a bit, so it doesn't need the compensation for a range of input speeds.
smokin rivet
3rd Jun 2009, 10:50
An APU runs at a constant speed and therefore the Generator is mounted directly on the gearbox. An IDG is a combination of a gearbox and a generator as a whole called IDG, the gearbox in the IDG makes sure that the generator stays between a certain speed in order to keep the poweroutput within a certain range. Hope it helps
Bullethead
3rd Jun 2009, 10:53
G'day Silverhunter,
The actual generators should be or can be identical, the difference is that whereas the APU and it's generator runs at a constant speed the engines don't and some means has to there to be able to run the engine generators at a constant speed while the engine speed varies. This is necessary to keep the frequency of the A.C. power supply, from the engine driven generators, constant as the engine speed varies. As well as keeping the frequency constant the generators on a multi engined aeroplane are also synchronised when the various outputs are fed into a common electrical bus. The frequency stability and synchronisation are all handled by the integrated drive part of the IDG. Each IDG has its own variable speed drive and oil supply and controlling electronics to ensure that it all works as advertised.
Hope this helps, regards, more info if you need it,
BH.
doncas
3rd Jun 2009, 12:49
The APU generator is also a starter...
spannersatcx
3rd Jun 2009, 12:58
APU generators normally have a higher rating than an IDG as well.
Never heard of a generator that is also a starter!:confused:
Fargoo
3rd Jun 2009, 14:28
generator also a starter?rubbish!!APU,s have thier own starters. changed enough
On some aircraft types a there is a combined unit starter gennie. Obviously just not on ones you work on :ok:
Cyclone733
3rd Jun 2009, 14:39
Newer Turboprops tend to have starter/generators on the main engines. Eg Q400's and some of the King Airs.
A quick google search shows that the Dash 8 series APUs have starter/generators.
Never heard of a generator that is also a starter!
Really?
Suspect the relevant poster is truly out to lunch.
Been done on PT6A engines since....1964, just a short while ago.:rolleyes:
spannersatcx
3rd Jun 2009, 19:29
Quote:
Never heard of a generator that is also a starter!
Really?
Suspect the relevant poster is truly out to lunch.
Been done on PT6A engines since....1964, just a short while ago.
Why I should be out to lunch? I said I had never heard of a generator that is also a starter, I never said they didn't exist, I just haven't seen one in 30 years, anyway what's a PT6A? I only work on proper aeroplanes, and no that's not on a tripe star either.
boeing_eng
3rd Jun 2009, 19:57
The BAC 1-11 had the famous Lucas CSDS (Constant Speed Drive/Starter) which made a very interesting noise on change-over from Starter to Genny drive/regulator!!
SNS3Guppy
3rd Jun 2009, 19:59
Never heard of a generator that is also a starter!
You've never heard of a starter-generator? These are found on many types of turboprop and turbojet equipment.
You say you've been working on aircraft for 30 years, and have never heard of a starter-generator?????
Hard to believe.
spannersatcx
3rd Jun 2009, 21:43
Like I said I work on proper aeroplanes, what's a turboprop!:rolleyes:
nut turner
3rd Jun 2009, 22:26
747 Classic APU generator and JT9D-7 Series generators are the same and interchangeable. The JT9 used a CSD to maintain constant speed for generator output. The generator and CSD were mounted on opposite sides of the gearbox to each other. I also believe the GENX engine uses a starter/generator.
Like I said I work on proper aeroplanes...
Hmmm, proper.
What are those, then?:hmm:
ampclamp
4th Jun 2009, 00:12
Like others have said between the slanging about "proper aircraft"...(whatever they are)
An APU genny can be the starter as well.
The new geneation 737's ie -800 have a starter / generator.
An IDG is an Integrated Drive and genny in one housing.
Another way of doing it was a genny mounted on a CSD constant speed drive unit.Genny could usually be changed without the CSD but IDG changed as one unit.
On APU's, genny speed is generally controlled by APU speed which is usually constant or near to that, ie 99 to 101%.
So if a genny on an APU has frequency issues quite possible its a fuel control problem.On an main engine more likely a CSD or IDG issue as frequency is controlled by some very clever devices as engine speed varies widely.
Mostly generic comments but I'm sure you get the idea.
silverhunter
4th Jun 2009, 10:21
Thank you all!
A good bit of info there. Much appreciated.
The Boeing 787 seems to have starter generators not only on the APU but on the engines as well. So not really a foreign concept.
SNS3Guppy
4th Jun 2009, 16:33
Like I said I work on proper aeroplanes, what's a turboprop!
What's a turboprop? A proper airplane.
But starter-generators are found on turbojet airplanes, too. A lot of them. Perhaps it's just that in 30 years of working on airplanes you've moved in such small circles that your experience has been rather narrow...as evidenced by the fact that you've never heard of a starter-generator.
muduckace
4th Jun 2009, 18:52
The Boeing 787 seems to have starter generators not only on the APU but on the engines as well. So not really a foreign concept.
Yeah the 787 sounds exciting, supposed to be a bleedless aircraft from what I hear. Some sort of electric supercharger for the ACM's. Electric brakes too as I have been told.
muduckace
4th Jun 2009, 19:01
Generator output is a goal usually set to 115 VAC across 3 phases at 400HZ, load expectations are commonly 60,90 and 120kva and probably more in the future.
The comon goal in the engine CSD/GEN, APU/GEN and IDG is to maintain that 115vac at 400hz. Most are set up with mechanical devices designed to maintain general HZ compliance and are tweaked by electrical devices in the aircraft to maintain 400hz.