B737 Thrustrating

[deuzx]

Hello everyone!

I wonder how thrustrating is calculated on B737. If you have a 18,5 K rated engine, which N1 will be 18,5K?

What is 100% N1? Is that the thrust you have bought? (I.e. 18,5K or 20K)

If a company buys only 737s with 18,5 K engines, may they be able to drive their engines at heavier loead than a "23,5K company" would have? If you get 18,5 K when 84,6% N1, why do not cruise at 93,5% if that gives cruiserating for a 23,5K engine?

Thank you for any answer!

[barit1]

The airline has the option of buying any of several thrust ratings. There may be no difference in the engine hardware, but the derated engine will enjoy longer time on wing and lower operating cost because of the lower turbine temperature and reduced rate of deterioration. If his route system has long runways at moderate elevations, he may see no advantage in more thrust. It's an economic decision.

The N1 for a given thrust varies with OAT and pressure altitude, so 100% is a purely arbitrary number. On a given day, TO N1 may be greater or less than 100%.

Usually an operator has the option of buying a rating increase after delivery. There may be many details in this upgrade - reprogrammed engine controls, improved performance charts in the AFM, associated software changes... but it can be done.

[Igor37]

The engine rating ie 18.5K, 22K, 23.5K is the certified take off rating defined in the regulatory agency approved AFM and is usely limited to 5 min . As said before the airline choice is economical .
Your take off N1% is the speed the engine has to be rotated to achieve this thrust rating . For example CFM56-3 22K msl standard day take off N1 is about 93.7% (packs on), and this value will be increasing with an increase in temp. or pressure alt. Your Max Cont./Climb Thrust rating, for the same engine, will provide about 20.5K (isa+10°) and your max cruise rating about 19.2K (isa+10°) .

Hope that makes sense ,

I...