N1 difference

[Spin737 102]

Right, i'm not following! Its mentioning takeoff N1% adjustment for engine bleeds.

 

BLEED CONFIG - PACKS OFF at the bottom

I don't have the same manual you have, but if you're looking at the PI section, it doesn't have a TAKEOFF section because it's Performance Inflight. This is for calculations when you're airborne and something went wrong.

 

The FMC should be handling this stuff if you're simulating something weird. If the FMC is on the fritz along with whatever else is causing you mess with the PACKS, then get this book out.

 

You should not be taking off with the packs off unless you're doing something really weird on a ferry permit. At that point, you're just making stuff up.

[Driver170 42]

Here its

[Copyrighted material is not to be posted here]
PI.10.40

[Spam3d 54]

Of course they are not, still the N1 is the same for both engines anytime. A/T controls N1. What you see IRL is simply a split in all other parameters, Other than that N1 is the same for both engines.

 

 

No the N1 isnt, the Engine indications will tell you so, but the actual N1 fan speeds for different engines are entirely different, the real engine N1 is adjusted using a trim setting in the EEC unit that basically displays a corrected number to the cockpit.

[G-CIVA 62]

Vernon you really are about as dumb as they come & I knew this was coming - you have been name dropping for ages about your real world sources.

 

Why did you not quote the proprietary material that came with the product provided by PMDG?

 

Instead you hyperlink to third party documentation belonging to a real world commercial source & whether out of date or not it contravenes just about every copyright license in the book.

 

Yup I am not the forum police but things like this can become troublesome for not only PMDG but for AVSIM as a whole.  It's not smart & not clever & if you just spent just a teeny bit more time READING your source material instead of gobbing off about it like the many who have trod before you might have actually picked up something useful on the way.

 

I can feel the flames of self righteousness licking at my feet right now so I will reach for the flammazine cream & head for the door.

[badderjet 181]

No the N1 isnt, the Engine indications will tell you so, but the actual N1 fan speeds for different engines are entirely different, the real engine N1 is adjusted using a trim setting in the EEC unit that basically displays a corrected number to the cockpit.

 

That's interesting. Simply because I was very sure that N1 (especially max N1) corresponds to a fixed RPM value, same for N2. And since, as you say, the displayed N1 values are always the same, I assumed the engines would be at the same speed as well.

So you are saying at the same displayed N1 value on the EICAS the fans could in fact have different RPMs? What would be the reason for that? Or asked differently, what is that EEC trim setting for?

 

[Spam3d 54]

That's interesting. Simply because I was very sure that N1 (especially max N1) corresponds to a fixed RPM value, same for N2. And since, as you say, the displayed N1 values are always the same, I assumed the engines would be at the same speed as well.

So you are saying at the same displayed N1 value on the EICAS the fans could in fact have different RPMs? What would be the reason for that? Or asked differently, what is that EEC trim setting for?

 

 

Yep that's correct to say that each shaft has a maximum operating RPM, considered the overspeed RPM. But you have to remember that the engine only has to produce the rated thrust that its certified for, so true N1 RPM for 24K of thrust may only be 97% for eng 1 (a new fully overhauled engine) , but engine 2 is older so to get to 24K for asymmetrical thrust (As N1 speed equals thrust) it has to produce a fan speed of say 99.5%. so both are producing different shaft speeds to get equal thrust. (To be honest every engine has tons of variables that could produce different thrust, like bearing stack up, air seals etc,) The trim setting is also referred to sometimes as the 'N1 modifier', and all it does is match a set of engines together. so the EEC has a trim of -2.2 applied to ENG1, to reach correct rated thrust at full TLA (throttle lever angle) The pilot doesnt see this actual N1, the cockpit displays are unaffected. All this is done using the manufacturer data during test cell runs post build. hope that helps!

[Driver170 42]

Yup I am not the forum police but things like this can become troublesome for not only PMDG but for AVSIM as a whole.  It's not smart & not clever & if you just spent just a teeny bit more time READING your source material instead of gobbing off about it like the many who have trod before you might have actually picked up something useful on the way.

 

Shut yer gob i found it on GOOGLE

[pete_auau 1,158]

Errrr could be wrong here but its still copyright material, just because you found  it  doesnt mean the person who put there got permission  to post it

[G-CIVA 62]

I really do worry for our future ... are we really becoming this stupid?

 

I guess so.

 

Shades of Pabari Mk II & all those who trod before ... here today gone tomorrow.

 

Somebody please pass the salt.

[JRBarrett 3,070]

That's interesting. Simply because I was very sure that N1 (especially max N1) corresponds to a fixed RPM value, same for N2. And since, as you say, the displayed N1 values are always the same, I assumed the engines would be at the same speed as well.

So you are saying at the same displayed N1 value on the EICAS the fans could in fact have different RPMs? What would be the reason for that? Or asked differently, what is that EEC trim setting for?

 

There is a difference absolute maximum N1, which would be the same for all models of a specific engine, and "N1 of the day", which is calculated by the engine EEC, and varies between individual engines, based on current weather conditions (primarily temperature and pressure)

 

When an engine has undergone major maintenance, after re installation on the aircraft, it undergoes a process known as "trimming". This is performed by maintenance personnel, using special test equipment which connects to the Electronic Engine Control (EEC) or FADEC as the case may be. During a trim run, the engine is operated at full power for several minutes, then at decreasing power settings (Max N1 - 2 percent, Max N1 - 4 percent etc.) while the test equipment gathers data on the engine's performance at each setting. During a trim run, data is also gathered on acceleration and deceleration times - the power lever is advanced from idle to Max N1 very rapidly, and then from Max power back to idle rapidly, while the time for the N1/N2 speed change is measured.

 

If the data gathered during the trim run is out of spec, the maintenance personnel may make adjustments to the fuel control unit, which meters the amount of high pressure fuel being sent to the fuel injectors in the engine, then the process is repeated while new data is gathered. Once all parameters are within proper limits, the settings are strored in a hardware dongle called a "trim plug", that connects to the EEC or FADEC. The trim plug can be thought of as being similar to a computer motherboard's BIOS chip.

 

If the EEC or FADEC itself has to be replaced at a later time, the trim plug from the old engine computer is transferred to the replacement computer, so that the computer will "know" the trim settings unique to that specific engine.

 

The "N1 of the Day" for a particular engine is calculated by the EEC based on the current air temperature and pressure, and will vary between engines by a small amount, and will change from day to day based on current temperature and pressure, as well as by any fixed or assumed temperature derate that may have been entered in the FMS.

 

In other words, seeing a slight difference in current max N1 between left and right engines is perfectly normal and expected.

 

At thrust settings less than maximum, setting both engines to the same N1 should deliver equal amounts of power, but with matched N1 settings, the EGT and fuel flow will usually be different between engines, again, based on the trim settings. If the engine model uses EPR (exhaust pressure ratio) THAT will be used as the main method for the pilot to set power, as EPR is a direct measure of the actual thrust being produced at a given moment. With matched EPR settings, all other parameters (N1, EGT and Fuel Flow) will vary slightly between engines.

[scandinavian13 5,192]

 

 

I can feel the flames of self righteousness licking at my feet right now so I will reach for the flammazine cream & head for the door.

 

While I always appreciate a pointer to the manuals, and a mention that the link to copyrighted materials wasn't a good idea (I would've missed it otherwise), the post's message could stand to be a little less fiery next time.

 

Shut yer gob i found it on GOOGLE

 

And I could find someone's airport access badge on the subway system, but it doesn't make it right for me to use it. RYR's stuff is RYR's stuff and it should not be used by anyone outside of the company without explicit permission. The fact that the site is a Belgian domain, hosting an Irish airline's information should be a hint that it probably didn't get posted there in the most legal of ways.

 

 

Errrr could be wrong here but its still copyright material, just because you found  it  doesnt mean the person who put there got permission  to post it

 

Precisely.

[Driver170 42]

Good job its away then

[Driver170 42]

Talking about engine performance. Both N1 and EGT increase with OAT upto the FRT and then beyon that point N1 decreases but EGT remains constant?

[kevinh 409]

Vernon,

 

No two engines are the same. Every engine will have a different N1/N2/EGT/FF at any given power setting/OAT/altitude. When the engine is installed it will go through a series of flight tests that will determine the engine operating parameters. The lower the N1 setting at maximum power output the stronger the engine.

 

Billy Bluestar

Vernon wasn't talking about engine N1 indications, which will differ across real engines, but the thrust setting N1 computed by the FMC. The only reason those numbers will be different is a different bleed correction.

 

Yeh true, so its not a bug then with the NGX like someone explained? Need to look more into it

I was that someone and yes it still is a bug. You can't do a bleed off takeoff in the NGX as it currently is programmed.

[Driver170 42]

I was that someone and yes it still is a bug. You can't do a bleed off takeoff in the NGX as it currently is programmed.

 

Will it get programmed for the future update? Or who knows lol so what is the alternative way...