EEC 737 NG

[owl-attack]

Hello All

737 NG. Engine Rating are calculate by EEC from sensed atmospheric conditions and bleed air demand


Can some one explain to me in layman terms what does Engine rating mean and why does the EEC have to calculate it? I thought engine rating where engines with 26k or 27k thrust and they were fixed when you get the aircrafts with engines fitted on them

And why are the inputs for EEC taken from bleed air demand and EEC ?


Thanks a lot

[IFixPlanes]

...737 NG. Engine Rating are calculate by EEC from sensed atmospheric conditions and bleed air demand ...
A source for this statement would be nice...

[owl-attack]

A source for this statement would be nice...

FCOM 7.15.6 Controls and Indicators on EEC light on Aft OVHD Panel

Layman terms please I am new

Thank you seniors

[Denti]

Interesting, our manual differs a bit: In the normal mode, the EEC uses sensed flight conditions and bleed air demand to calculate N1 thrust ratings.

[barit1]

The engine is flat rated at 26K or 27K (or lesser ratings) according to the customer's requirements. These are in turn determined by the airline's route structure. If less thrust is required, then the engine deterioration rate is reduced, and the maintenance cost per hour is predictably less.

But the engine is flat rated up to a specified ambient temperature (commonly ISA+15C), and the rated N1 to achieve thrust depends upon the ambient temp and pressure.

In addition, more thrust (N1) can be had if bleed air is reduced during TO. This is because EGT will be reduced at a given N1; thus the bleed data is included in the computation.

To get an idea of how N1 behaves under different conditions, see the N1 chart in the performance section of the AFM, or find a copy of the CFM Operating Instructions.

[cosmo kramer]

Actually it's (should be) basic ATPL knowledge.

If you set the thrust levers to the same position at take offs with different temperature (all other factors remaining equal), you will get different thrust outputs. Cold = more thrust, warm = less thrust.

To get e.g. 27000 lbf thust from each engine, the thrust lever has to be set differently depending on temperature.

The temperature at which the engine is "flat rated" is the highest temperature where it is able to produce the maximum thrust. Normally as said ISA + 15 degs (30 deg C ambient temperature).

Below 30 degs the engine is able to produce more than max (e.g. 27k). At 0 degs C it may be able to produce 30k (as an example only) without exceeding any internal limits, like EGT, fan speed and whatever other limit that an engineer may tell you about.

However, the max allowable thrust also depends on other things, like e.g. engine mountings (probably a lot of other things too, which again an engineer may know lots about).

So at 0 degs C, instead of exceeding max thrust, the engines has to run at a lower speed. Hence, a lesser thrust lever setting.

Above 30 degs C, the engines will no longer be able to produce max thrust. As in doing so, an internal limit will be exceeded. If e.g. EGT is the limiting factor, thrust has to be reduced to keep it within limit, hence the output will be less than max.

The EEC is, through its sensors, able to calculate what the thrust lever angle should be according to the temperature in order not to exceed any engine limits or max thrust according to above. This calculation output is presented to the pilot as the "Reference N1 bugs" on the primary engine indications display.

[owl-attack]

The EEC is, through its sensors, able to calculate what the thrust lever angle should be according to the temperature in order not to exceed any engine limits or max thrust according to above. This calculation output is presented to the pilot as the "Reference N1 bugs" on the primary engine indications display.


Thanks this is where I had some conflicting information. The first few pages of the FCOM chapter 7 (Engines) you find A/T LIM displayed in a white box on the Thrust Mode Display. The definition of FCOM for A/T LIM is:

The FMC is not providing A/T System with N1 limit values. The A/T is using a degraded N1 thrust limit from related EEC.

So as per this above definition on A/T Limit, during normal operation the A/T system uses N1 limit values ( the N1 reference bugs which are placed on the N1 gauge) from the FMC, and during a degraded operation it uses a degraded N1 thrust from the related EEC

Isn't this a conflict? Because EEC when in ON posn (which is the normal mode) provides the engines rating or places the Reference N1 bugs on the N1 gauage, but the A/T LIM defenition says A/T system takes input from EEC in a degraded mode, and in normal mode it takes input from FMC

This is where my confusion lies

Thanks a lot

[cosmo kramer]

To avoid confusion, first, with A/T LIM the EECs are still in normal mode (not EEC ALT). Not sure if you meant that or not. Anyway...

Just below the section you quoted you will find:

N1 SET Outer Knob
AUTO –
• both reference N1 bugs set by FMC based on N1 limit page and takeoff reference page
• displays reference N1 bugs at active N1 limit for A/T.

The EEC output goes through a "filter" in the FMC, before being displayed. The FMC knows what the phase of flight is, which all have different thrust limits (selectable on the N1 page in the FMC). E.g. if you are in cruise, the N1 Reference bugs automatically change to CRZ limit. If the FMC is inoperable, obviously, these limits will not be shown as the EEC doesn't know which phase of flight you are in and probably doesn't have the tables available either.

Check the FMC fail checklist. You have to set the N1 bugs manually according to the tables in the Performance inflight section.

What degraded limit is shown, I would be curious to know as well. I did have FMC fail during cruise once, in Classic, and as far as I recall the bugs stayed at the CRZ limit until manually set to G/A limit for the approach, but not sure anymore.

I guess we are moving beyond layman's terms again now. ;)

[Turbavykas]

Below 30 degs the engine is able to produce more than max (e.g. 27k). At 0 degs C it may be able to produce 30k (as an example only) without exceeding any internal limits, like EGT, fan speed and whatever other limit that an engineer may tell you about.

However, the max allowable thrust also depends on other things, like e.g. engine mountings (probably a lot of other things too, which again an engineer may know lots about).

Are you sure about this? I assume At 0 degs C engine can explode from overpressure or compressor blades will bend/fail ect. That's why it's flat rated?

[cosmo kramer]

I'm pretty sure - yes. But unable to provide any reference at all. But the engines have a huge margin. I recall reading that the engines have been run at more than 150%, but as said no references.

My previous post however, is inaccurate while trying to paint a picture in layman's term.

The N1 reference bugs do come from tables in the FMC and that only. Think of it more like interaction between the FMC and EECs. Where however, it is absolutely clear to see the EECs at work is the thrust levers themselves.

EEC Normal mode

The full rated takeoff thrust for the installed engine is available at a thrust lever position less than the forward stop. Fixed or assumed temperature derated takeoff thrust ratings are set at thrust lever positions less than full rated takeoff. The maximum rated thrust is available at the forward stop.

I hope it was clear that in the first post that lever angles vs. thrust was for explanation simplistic purposes of flat rate. One benefit of the EEC is that the lever angles remains the same with different temperatures. Hence, e.g. full forward = max rated thrust without over boost (EECs working in normal mode).

[B737NG_Pilot]

Will the FMC still be able to calculate N1 values, when climbing through a temperature inversion?

We had a A/T Lim appear to 2 different aircrafts, when climbing through an temperature inversion.

[aveng]

All engines in a series are all the same power wise. The company who owns the aircraft selects a power rating. A plug with small jumper wires is inserted directly into the EEC and this tells the EEC how much power the engine will make.

[de facto]

Below 30 degs the engine is able to produce more than max (e.g. 27k). At 0 degs C it may be able to produce 30k (as an example only) without exceeding any internal limits, like EGT, fan speed and whatever other limit that an engineer may tell you about.

Please read AVENG post :
All engines in a series are all the same power wise. The company who owns the aircraft selects a power rating. A plug with small jumper wires is inserted directly into the EEC and this tells the EEC how much power the engine will make.

Hence, e.g. full forward = max rated thrust without over boost (EECs working in normal mode).
Over boost is for PISTON engines,i thought that was basic ATPL level knowledge.:E
You will over thrust by applying max thrust(thrust levers full forward with EEC on) but you wont overspeed.

To the OP,the EEC is for fuel and engine control.
It gets info about the ambient total pressure(PT) from the ADIRUs which get them from your static air pressure port (PO) and TAT or T12 sensor.
This PT will allow the EEC to command accurate fuel for the engine.
If PT becomes invalid,your EEC will got to soft alternate mode.

For the bleed info ,the EEC gets the info from the bleed switch positions..as mentioned above,bleeds off means less EGT for the same thrust position and the EEC knows that.

Concerning the EEC engine control,its not the question for today:E

[underfire]

While everyones responses were detailed, I would look back to the OP.

Can some one explain to me in layman terms what does Engine rating mean and why does the EEC have to calculate it?

I am certain the level of detail in this thread was lost... :E

[de facto]

Engines are rated based on weight and elevator/rudder control limits which can be then derated by the owner via EEC plugs.
The top rating of the engine is the max thrust you can expect to get at fire wall position of the thrust levers...for example a CFM56-7B can provide 27400 lbs of torque up to its Tref.

EEC doesnt calculate the rating,it knows the rating already but it calculates the Max N1 TRA and provides it to the AT.

So as per this above definition on A/T Limit, during normal operation the A/T system uses N1 limit values ( the N1 reference bugs which are placed on the N1 gauge) from the FMC, and during a degraded operation it uses a degraded N1 thrust from the related EEC
Correct.
Isn't this a conflict? Because EEC when in ON posn (which is the normal mode) provides the engines rating or places the Reference N1 bugs on the N1 gauage, but the A/T LIM defenition says A/T system takes input from EEC in a degraded mode, and in normal mode it takes input from FMC
The autothrottle is providing the N1 limits if the FMC N1 data is invalid for climb,cruise and Go Around but Not for take off.
The n1 cursors can be used but are fo reference only and you would get dashes on the TMA as the FMC isnt providing the info.

[tdracer]

Lots of miss information here (mixed in with some correct information).


Most FADEC engines have multiple thrust ratings available - the CFM on the NG is no different. A 'rating plug' or 'data entry plug' plugs into the FADEC to tell it which rating to select. The rating plug is typically considered part of the engine (the rating is listed on the engine data plate - an engine company service bulletin is required to change it, which changes the rating plug and data plate) and connected to the engine by a lanyard (e.g. if a FADEC is replaced due to a fault, the rating plug remains with the engine).


The engine is flat rated for temperature up to corner point (as noted, typically ISA plus 15 - 30 deg C at sea level but decreases with altitude). However it is not flat rated for altitude - max thrust decrease with altitude.
For EPR engines, max rating EPR is basically constant at a given altitude up to corner point temperature, however N1 engines have a constant corrected N1 below cornerpoint - but we set and display physical N1 (physical N1 is corrected N1 * the square root of Theta). So, below corner point, physical N1 increases with temperature to maintain the same corrected N1 and thrust.
On Boeing installations, with the FADEC in "Normal" mode, Max rated takeoff thrust always occurs at the same throttle position - as does max climb and max cruise. Max Takeoff throttle position occurs a bit short of the max forward stop, push a bit beyond that and you get what we call 'headroom' - slightly more N1 to account for small sensor errors between engines, etc. (headroom is typically between 0.5 and 1.0% N1, depending on the conditions). The last degree or so of throttle to the forward stop will NOT increase thrust - it's basically a flat to insure that a mild throttle miss-rig won't prevent obtaining max rated thrust. Aside from the noted headroom, overboost is not possible in Normal mode (baring a major failure).


Now, with all that background to put you to sleep :E, here is the response to the original post:
The FADEC monitors ambient conditions - inlet total temperature, ambient pressure, and total pressure (i.e. temperature, altitude, and airspeed). The FADEC then calculates the correct max Takeoff, Climb, and Cruise values for the selected engine rating. It will then apply any 'debits' to those ratings to account for aircraft bleed (as communicated from the aircraft). Those values are then compared to the throttle position to determine the "Command" N1 value and the FADEC goes about controlling the engine to obtain the Commanded N1 for that throttle position.


'Alternate' mode is completely different - it's an unrated mode and significant overboost is possible.


Clear?