KensukeAida
Topic Author
Posts: 135
Joined: Wed Oct 12, 2005 12:37 am

### 737-300 Performance Questions

Got a couple of questions about the performance of the 737-300 in order to plug them into FS2004 and get a more realistic experience. This is for a typical WN jet.

What is the idle N1 of the CFM56-3B2? (that's the 20,000lb engine, right?). I assumed 25%, but I'm not sure.

What is the average N1 speed at cruise at M0.74 at say...32,000ft and between -20C and -30C outside temp? Assume the aircraft weighs about 120,000lbs gross weight.

Note that if this is too hard to calculate, feel free to draw upon your own experience.

What is the average fuel flow at idle and at the above cruise conditions?

Thanks.

Molykote
Posts: 1239
Joined: Tue Aug 23, 2005 8:21 pm

### RE: 737-300 Performance Questions

ALT MACH TAT N1 N2 F/F
23100 0.702 7.20 83.25 92.90 3337
27100 0.749 0.80 85.22 92.70 3282
22000 0.681 6.90 82.12 92.30 3238
34100 0.751 -16.00 89.42 92.30 2923
37100 0.749 -21.30 85.61 90.10 2270
36100 0.743 -19.90 87.53 91.40 2506
33100 0.746 -13.30 84.42 90.80 2498
34100 0.750 -14.90 88.42 91.90 2846
21000 0.634 3.70 79.92 91.50 3085
35100 0.734 -19.10 87.78 91.30 2660
29100 0.735 -7.60 84.64 91.50 2877
35100 0.743 -18.00 87.63 91.60 2706

You are correct that the -3B2 is the 20k thrust variant.

A representative data set compiled at random.

You can take a pure average of these numbers or select conditions that best suit what you are trying to model. I thought it might be more fun for you to have some data to play with rather than a parameter.

As far as idle speed.... Different "idles" exist depending on conditions.
Are you looking for a (CRZ) flight idle speed?
Speedtape - The aspirin of aviation!

Molykote
Posts: 1239
Joined: Tue Aug 23, 2005 8:21 pm

### RE: 737-300 Performance Questions

Since I will be leaving my computer soon I'll assume you are looking for a "flight" idle. I am an engineer and not a pilot but I believe this parameter is around 33% N1 (and closer to 50% N2).

This is only from memory. Hopefully a pilot can correct me and provide you with better real world data.
Speedtape - The aspirin of aviation!

KensukeAida
Topic Author
Posts: 135
Joined: Wed Oct 12, 2005 12:37 am

### RE: 737-300 Performance Questions

Thanks! This is great!

And yeah. I was looking for the N1 speed of the engine while it's on the ground
with the throttle at idle.

Thanks again!

- John

Jetlagged
Posts: 2564
Joined: Sun Jan 23, 2005 3:00 pm

### RE: 737-300 Performance Questions

Ground idle N1 will be something around 23%, depending on conditions, so your estimate is not far off.
The glass isn't half empty, or half full, it's twice as big as it needs to be.

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