Hi Ian,I have a question remotely related to the B767.The new 7E7 I understand has an engine spec that calls for electric generators in the engines, as distict to bleed air power for generators in the a/c itself (and I'm already totally out of my depth, and most likely have this all wrong :) ). One of the reasons I understand is to prevent Airbus from using this new hi-tech engine in their A330 (if what you read in the industry mags is correct), and also the prevent noise.Can you tell us just how bleed air is used to power generators in the older a/c (aka B763)? I'm imagining either suction or blown air from the engines being ducted into the a/c body, and there turning turbines that in turn power the electrics and/or hydraulics. And I assume the air con paks are also somehow interconnected into this system too?Thanks,Bruce.

Well, in my time as a pilot and working with airliners, i have not heard of air driven electric generators. Most electric generators are connected to the engines through something called a CSD (constant speed drive), or IDG (integrated drive generator) for the airbus fans. These all are direct connection to the engine acessory drive. I would assume that they could drive the generators by air, but I would not be able to speculate on what the benefits or disadvantages would be.I know that on some etops aircraft, such as the 767, they drive extra hydraulic pumps with air, so that may be what they are doing. That is all that I can help. Sorry, i don't have any more info

Thanks.What had me asking this question (and I know absolutely nothing about airliners, which is why the question) was an article on the early planning for the 7E7. The engine specs, as discussed in the article, were what got me wondering, as apparently bleed air is not to be used for "aircraft power" (the article implies that it is for most current day jets); in favor of generators in the engines. Of course this approach requires a different concept in airliner system design, which was touted in the article to prevent Airbus from using the still-to-be developed engines for any of their current models.I guess the question could be more accurately rephrased as "what's different about the new 7E7 power systems compared to current day conventional airliner systems" . :) Thanks for your reply.Bruce (who's license and system knowledge is strictly limited to a 172 :) )

I did glance at the 7E7 site, Bruce... and what I think they meant was that the bleed air system (or perhaps the Cabin Pressurization system) was not to be powered by the engines (i.e. there was to be no engine bleed system). As Al(?) says, Main Electrical Generators are usually driven by the engine's Accessory Gearbox (which is attached via driveshafts and other geaboxes to the N2 engine rotor (or N3 rotor on Rolls Royce engines)...i.e. mechanically connected, certainly not driven by bleed air).As they say in those cookery classes, here is something I prepared earlier (for the 747-400).... It shows some of the things coming off the Accessory Gearbox.http://members.ozemail.com.au/~b744er/GearboxTutorial.JPGSome 767's do have backup (hydraulically-driven) generators, called HMG's (I don't think these are modelled in PIC). This is not to be confused with the RAT which produces hydraulic pressure.... and, by the way, you can't use the RAT to power the HMG's ;-) (the RAT only powers specific parts of the hydraulic system... not the parts which include the HMG's).Hope this makes sense.Cheers.Ian.

Hi Ian,Thanks for the clarification. And a fascinating diagram.The IDG anf the Dedicated Alternator- do they both drive the electrical system?I'm also interested that it seems that the engine starter connects to the N3 (RR) via this same gearbox.Thanks again, you must have an inexhaustive supply of photos and charts!Bruce.

"The IDG and the Dedicated Alternator- do they both drive the electrical system?"No, Bruce, the Dedicated Alternator is only a source of power for the EEC's (Engine control computers). This ensures that whilst the engine is spinning, power is being provided for engine control even if you lose all normal electrical power on the aircraft... even battery power. An excellent safety feature. Indirectly, the Ded Alt also provides power to it's corresponding thrust lever potentiometer... or RVDT (Rotary Variable Differential Transformer, as we call them)."I'm also interested that it seems that the engine starter connects to the N3 (RR) via this same gearbox."You'll probably find that all jets are like this. On two spool engines, it will be the N2 acc gearbox, of course.Cheers.Ian.

I can't ever remember you being stumped Ian. But you could use some work on your computer repair skills. Bummer man, was sorry to read that one...Mike

I have an XT you could borrow, Ian...DS CVA3339 / UKD149System: Attlon 900 McW Hamster/Gerbilized Quantum Accessible 55Gig Iodized-Encrusted Four-poster with Mega-brill Farzenhuuven http://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

"I can't ever remember you being stumped Ian. But you could use some work on your computer repair skills. Bummer man, was sorry to read that one..."Regularly stumped, Mike.... Thankfully airplanes are basically idiot-proof... and the Maintenance Manuals often go into better detail than your average computer operations manual :-) On a brighter note.... Ever hopeful, I booted up my desktop computer this morning... and it ran a lot longer than it did yesterday. In fact, long enough for me to transfer some aircraft engineer training notes to my laptop, so I'm almost back to speed. I don't know if I'm dreaming, but WinXP seems to have these amazing recovery abilities(???).Thanks for all the support, guys.Cheeers.Ian.