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Average Engine Working Percentaje During Takeoff?  
User currently offlineJgore From Argentina, joined Feb 2002, 550 posts, RR: 2
Posted (12 years 3 months 2 weeks 19 hours ago) and read 2024 times:

Hi everyone
Does anyone know what is the average percentage the engines are working during takeoff ? could it be 90-93 percent ?.
Thanks in advance

jgore  Smile


5 replies: All unread, jump to last
 
User currently offlineRmm From Australia, joined Feb 2001, 524 posts, RR: 1
Reply 1, posted (12 years 3 months 2 weeks 18 hours ago) and read 2013 times:

Are you talking about overall performance or N1 speed at T/O?

Rmm


User currently offlineIsmangun From Indonesia, joined Jan 2001, 117 posts, RR: 9
Reply 2, posted (12 years 3 months 2 weeks 12 hours ago) and read 1979 times:

Well, with average T/O weight of 48 metric tons (around 106.000 lbs), our planes (737-200s with JT8D-17) requires around 95% N1. But T/O with full reduction (1.94EPR or 93%N1 with OAT 31 deg centigrade) is not unusual if the A/C is not so heavy and the runway conditions not restricting.


If it's an Airbus, I'll take the bus...
User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 3, posted (12 years 3 months 2 weeks 12 hours ago) and read 1986 times:

Hola Javier,
As always, there are several correct answers to your question.

Generally speaking, when it comes to turbofan and turbojet engines, you want to use 100% of an engine's "rated" thrust for takeoff. It must be remembered that (in very simplistic terms) turbine engines are not supercharged, but rather normally aspirated - in other words, they lose power with altitude just like a Cessna 152. The percentage of N1 (on most turbofans) or EPR (many turbojets) required to obtain the engine's full rated thrust will vary significantly depending upon airport elevation and outside air temperature. For example, on the aircraft that I fly, on a cool day at a sea level airport the engines will develop their maximum rated thrust with an N1 somewhere in the upper 80's say for example 88.7%. Go to a higher elevation airport on a warm day and the N1 will be higher, for example 93.4%. (As I type this, I'm looking at the Static Takeoff Thrust Setting Chart for our aircraft. Depending on the airport elevation and outside air temperature, the N1 settings vary from a low of 84.2% to a high of 96.1%.) These numbers will, of course, vary from engine to engine, but you get my point. On most older generation engines, the flightcrew is required to come up with a takeoff power setting from a set of charts or tables. In later generation engines with DEECs (Digital Electronic Engine Controllers) or FADECs, the pilots only have to set the powerlevers into the takeoff detent and monitor things while the computer takes care of the rest.

Just to make things a bit more interesting, some aircraft have larger engines installed than they were designed for. These engines are "Flat-Rated" back down to what the airframe was designed to handle. In other words, say for example, an airplane was designed to use 10,000 LB thrust engines, the aircraft designers might specify 12,000 LB thrust engines and limit their thrust to 10,000 LBS. Why would they want to do this? Simple, remember that turbine engines are "normally aspirated" and start loosing power the moment they start to climb. By using a larger engine, the aircraft can operate at higher altitudes or temperatures before it runs out of power. (Gee, I hope I said that right - it seems awkward. Oh well, there are others who are better qualified than me to clarify this.)

On many turbojet aircraft, flight crews are also allowed to perform Reduced Power Takeoffs. This method would also result in reduced N1 or EPR indications. There are several reasons why a flight crew might want to do this and a couple of methods that they can use to do it. I don't have the time to go into this in any detail now; but if you're interested I recommend that you search the archives, I'm sure this topic has been discussed before.

Turboprop engines are similar, only instead of N1 or EPR, they usually measure their power output in Percent Torque. For those guys it's a bit simpler, they simply advance the power levers until the engines reach either their torque limit or their temperature limit.

Jetguy


User currently offlineIsmangun From Indonesia, joined Jan 2001, 117 posts, RR: 9
Reply 4, posted (12 years 3 months 1 week 4 days ago) and read 1880 times:

Just to add little piece of info to Jetguy's explanation, T/O thrust is reduced when applicable to prolong service-life, noise reduction, and probably some other reasons I don't quite understand.  Smile


If it's an Airbus, I'll take the bus...
User currently offlineMetwrench From United States of America, joined Aug 2001, 750 posts, RR: 2
Reply 5, posted (12 years 3 months 1 week 2 days 21 hours ago) and read 1842 times:

What do the Performance charts say?

Engine performance is based on "sea level, average day '70 F temp".

Performance charts are based on these ref's. The charts will compensate for say, 6,000 Ft altitude and 100 F. It might say that 93% is the target torque. In that case, 93% is in reality 100%.

Just remember that all performance figures are based on a "Standard Day". 100% doesn't necessarily mean 100%.


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