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Mr.Vortex
14th Mar 2011, 21:09
Hi all pprune member,

Yesterday, I have read the FADEC system in MD11. Everything seems to be OK.

However, there're one part that said the FCC send the various data such as
the N1 or EPR trim, Bleed Config, Flap position, Weight on nose wheel, GMT, and DATE.
I understand the purpose of the nose wheel and flap config but not for
GMT and DATE. Is the GMT mean Greenwich Mean Time or something else and
does the DATE mean the Dynamics, Acoustics and Thermal Environment?.
If so why the engine require those information in order to operate?

- Also, for a given throttle setting as the environment around the engine has change.
Does the FADEC advance the engine RPM automaticly according to the throttle position?
For example, if throttle is at about 80%, engine in climb rating and when the
plane climb the N1 limit is lifting and the FADEC order the engine to speed up
in order to maintain the 80% thrust rating.

- Does the FADEC manipulate the bleed valve [either LP or HP or both] in
order to maintain the minimum air pressure that the system need or the
HP valve just kick in if the anti ice is use or the N2 is drop below the setting value like the B767.

- What is the purpose of the fin that seems to be extend from the rudder to the Engine NO.2.
Is it job is to induce the laminar flow over the root of the rudder and engine cowling or does it help the plane become more stable?

Photos: McDonnell Douglas MD-11/ER Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/Varig/McDonnell-Douglas-MD-11-ER/0634602/L/&sid=85fb885ee336cac80204d9efc9014105)


Sorry for a long question and thanks for all of your reply.

Best regards

grounded27
15th Mar 2011, 05:15
However, there're one part that said the FCC send the various data such as
the N1 or EPR trim, Bleed Config, Flap position, Weight on nose wheel, GMT, and DATE.


Input in and out is what you are confused about. The FCC's sense some of this data (flap position being it"s only real job as you listed) to coordinate with other systems.

GMT is the abbreviation of what you spoke of.

If so why the engine require those information in order to operate?



The engines do not require the FCC's to operate.

Also, for a given throttle setting as the environment around the engine has change.
Does the FADEC advance the engine RPM automaticly according to the throttle position?
For example, if throttle is at about 80%, engine in climb rating and when the
plane climb the N1 limit is lifting and the FADEC order the engine to speed up
in order to maintain the 80% thrust rating.



Do not confuse thrust and N1, N1 is a fixed value, if selected it will maintain 80% N1, thrust is not accounted for as temp/alt change actual thrust. N1 is engine speed thrust is engine production.

Does the FADEC manipulate the bleed valve [either LP or HP or both] in
order to maintain the minimum air pressure that the system need or the
HP valve just kick in if the anti ice is use or the N2 is drop below the setting value like the B767.



The PSC's control bleed shift.

Mr.Vortex
15th Mar 2011, 09:10
Thanks grounded27

Now I'm confused on how the Engine trim system work. What it actually does
in flight. Does it hold the constant N1 or EPR value or doing something else?

Best regards

Joost B
27th Mar 2011, 14:00
The FADEC does not manipulate the LP or HP bleed valve on the engines but it does regulate N2 speed to maintain a compressor discharge pressure of 48 PSI. This is based on the throttle position, ambient pressure and N2 speed lever in order to enable the engine to deliver sufficient air pressure for the aircraft pneumatic system to work.

If I remember well, the N1 TRIM signal is supplied from the FCCs to compensate for slight mismatches in throttle resolver angles and still set the same thrust on all 3 engines, it only works with the levers above a certain setting. (the pilot / Auto Throttle does not have to perfectly align the levers, this is achieved by the trim signal)

The GMT and DATE are used by the ECU for fault history logging; in a backshop the ECU can be hooked up to a computer and the operating hours and fault history can be read to great detail, on the aircraft through CFDS the fault history and current faults can also be checked.

The tail engine is supported in the same way as the wing engines are mounted; by a pylon. That makes the 3 engines interchangeble (with some work) The structure you see above the "tunnel" and below the fin is that pylon structure.
It is quite a sturdy construction attached to 4 "banjo shaped" fittings that run from the fuselage and also act as the fin attachment base.
The last part is a fairing that houses the pre-cooler and pneumatic ducting that runs back to the airframe.