Simviation Forums

Well, i have been trying to find what the N1% for different aircraft on takeoff is, and so far to little or no avail. So i was wondering what they were for airliners, such as...

737
A320
MD90
747
etc...

No need for any fancy calculations about air pressure and aircraft weight, just plain figures!  :D

Plus how come the N1% in some instances go up to, and over 104%?

Cheers for in advance,
Luke.

I would assume it depends on your V speeds, and your payload and runway length and condition (=) FLEX or TOGA thrust setting. Maybe some other things, I don't know.

The N1 setting varies from take-off to take-off.
The FMC is the likely candidate of calculating the correct N1 setting.
HOWEVER
Since an assumed temperature derate is always desireable, the crew goes into diagrams and deliberately fools the FMC to think it's warmer outside than it really is. (In airbus this is called FLEX, and Boeins use SEL temp.)

By doing this, the FMC automaticly reduces the N1 available (since warm air makes engines less effective)
So less thrust is available at take-off, but it is still sufficient to comply with the climb profile and noise abatement procedures (need to gain altitude fast to not to disturb the poor citizens down there)

There is no general answer to your query, sorry.

All I can say is that airliners only goes "full thrust" when the runway is badly contaminated, but they will try to avoid is as much they can.

Regarding 100% N1+, I'm guessing that 100% N1 represents the manufacturers recommended maximum.
You can exceed this, but the engine will take far more damage. Some engines can go as high as 115%N1 and above

Might want to check airliners.net or PPruNe

Thanks Both!  ;)

I flew in a 737-800 last weekend.
The aircaft was full. It was 22 degrees OAT. The N1 was 95%.
That is an example of reduced thrust takeoff

This is a way of reducing the take-off thrust to the minimum required for a safe take-off, thereby conserving engine life and hence reducing your chances of an engine failure.
For example,
The CFM56-3 and -7 are flat rated at ISA+15C ie 30C. This means that they are guaranteed to give (at least) the rated thrust at the full throttle position when the OAT is below this temperature. Above this temperature, they will give less thrust because the air is less dense.

On occasions when full thrust would be more than is safely required eg light aircraft, long runway, headwind etc. you can choose a thrust setting below full thrust by telling the engines (via the FMC) that the OAT is much higher than it actually is. This higher temperature is called the assumed temperature.

If we fool the engines into thinking that the temperature is much higher then it actually is, by entering an assumed temperature into the FMC, they will use a correspondingly lower N1 to give the rated thrust for the higher temperature when TOGA is pressed. You may at any stage after TOGA is pressed advance the thrust levers further to give the full rated thrust again.

You find the assumed temperature by entering the take-off tables  with the actual takeoff weight, and then determining the hottest outside air temperature at which the take-off could be performed. This temperature is called the "Assumed Temperature" and is entered into the FMC The ambient temperature is also entered  and the reduced thrust take-off N1's will be computed by the FMC.

Matt