Question about FCU,FADEC
 

what are the. operational. differences. between FADEC and HM FCU??

FADEC is Full Authority Digital Engine Control, it calculates, controls and monitors functions of a turbine engine. Most FADEC engines have only an electronic interface with the aircraft though developmental stage engines had partial mechanical control.

FCU, I believe GE's acronym for Fuel Control Unit A hydro mechanical device later called a FMU I believe or Fuel Metering Unit which is electric hydraulic. The FMU works in conjunction with FADEC.

HM, the only thing that comes to mind is a HMU or Hydro Metering Unit, a Pratt term for their electro hydraulic fuel control.

hydro mechanical fuel control unit...... like on a 146, all swasch plates and servo pressures. No FADEC involved on that a/c

what' about the operation for accelerate/ decelerate / cruise for both hmfcu and fadec? are there any difference?

One is electronic and the other mechanical....

A FADEC system senses engine parameters (e.g N1, N2, Pc, Temp, Tq), as well as pilot demand (power levers) all electronically (transducers, tachos, LVDTs, etc) and a 'computer' or EECU (engine electronic control unit) does the maths and tells a metering unit how much fuel to give the engine.....without over-limits.

A hyd/ mech FCU senses speed (e.g N1, N2), usually by shaft driven fly-weights, and along with using 'fluid' mediums such as Pc air px or fuel px, mechanically governs the amount of fuel the engine requires...all this mechanically coupled to pilot demand. The avoiding over-limit part is more of a pilot responsibility here, as there is no computer involved.

Get a good GT engine theory book such as Rolls Royce or Jeppesen and all of this will be clearly explained.

FADEC requires HMU to control the engine.
FCU is another type of hydromechanical fuel control used without a FADEC.

Well in Helicopters anyway, don't know about them plank things.

what's engine- trimming? i heard that in FADEC u dont need to do that but for HMFCU u need to make adjustment to it.

Davis,

if you're studying this subject, you really do need to get some books on it.

FADEC is electronic, as all ready said, and a computer works everything out using programme logic and laws and keeps the engine at its optimum speed for the conditions it is monitoring. I'm talking helicopters now, but if there are two engines....each one has its own FADEC and the two 'talk' to each other to keep the two engines 'matched'.

A mechanical FCU and its associated fuel governor needs to be set up for the engine it's fitted to, by the means of control link rigging and adjustment screws which increase/ decrease certain jet orifice gaps and/or increase/decrease spring load on internal levers and mechanisms.....similar to a carburettor on a (older type) car engine. The engine(s) is(are) trimmed in flight by mechanical pilot control to the governor.

By the way........ you're welcome.

[QUOTE
what's engine- trimming? i heard that in FADEC u dont need to do that but for HMFCU u need to make adjustment to it.
][/QUOTE]

Usually a change in the AOA of veriable pitch stator blades to more efficiently compress air and prevent an engine stall RR engines rely on bleeding air. FADEC calculates this angle or need to open/close valves and sends an electrical command to an actuator, say in the case of a CF6-50 it is done mechanically off of the FCU.