Khaldon
Topic Author
Posts: 4
Joined: Sat Mar 18, 2017 7:45 am

Boeing OPT

Sat Mar 18, 2017 8:12 am

Why please there is a difference between Boeing OPT MAX thrust N1 and actual airplane N1 reading for the same assumed temperature?
 
BravoOne
Posts: 2259
Joined: Fri Apr 12, 2013 2:27 pm

Re: Boeing OPT

Sat Mar 18, 2017 2:31 pm

What airplane, what engines? Come on give us a hint at least.
 
OzzyPirate
Posts: 41
Joined: Fri Jul 15, 2016 2:27 am

Re: Boeing OPT

Sun Mar 19, 2017 1:08 am

Are we talking 737? It's quite common to get a small split between the indicated reference N1 and the N1 generated by the OPT. Normally due to differences in actual ambient conditions vs. the data used for performance calculation.

For example, if we used an OAT of 18C in our calculations but the actual OAT is 15C, the reference N1 will be different for the same assumed temp.
 
skyhawkmatthew
Posts: 477
Joined: Wed Oct 26, 2005 4:42 pm

Re: Boeing OPT

Sun Mar 19, 2017 4:47 am

OzzyPirate wrote:
Are we talking 737? It's quite common to get a small split between the indicated reference N1 and the N1 generated by the OPT. Normally due to differences in actual ambient conditions vs. the data used for performance calculation.

For example, if we used an OAT of 18C in our calculations but the actual OAT is 15C, the reference N1 will be different for the same assumed temp.


This is the only time I've seen a difference between our RTOW data card and the aircraft computed N1 on the 777 as well. It's not unusual for the aircraft's TAT indication to be a couple of degrees different to the ATIS, slightly changing the computed N1 or EPR displayed. As long as it is close to the value on the card, and makes sense, there is no issue.
Qantas - The Spirit of Australia.
 
Khaldon
Topic Author
Posts: 4
Joined: Sat Mar 18, 2017 7:45 am

Re: Boeing OPT

Mon Mar 27, 2017 7:43 am

I am so sorry for the late response,

I am talking about Boeing 777-200 / 777-300
 
Khaldon
Topic Author
Posts: 4
Joined: Sat Mar 18, 2017 7:45 am

Re: Boeing OPT

Mon Mar 27, 2017 7:45 am

GE engine
 
BravoOne
Posts: 2259
Joined: Fri Apr 12, 2013 2:27 pm

Re: Boeing OPT

Mon Mar 27, 2017 10:50 am

Khaldon wrote:
GE engine


Which GE engine?
 
BravoOne
Posts: 2259
Joined: Fri Apr 12, 2013 2:27 pm

Re: Boeing OPT

Mon Mar 27, 2017 10:51 am

BravoOne wrote:
Khaldon wrote:
GE engine


Which GE engine? The 115K or?
 
mmo
Posts: 1189
Joined: Thu Apr 18, 2013 3:04 pm

Re: Boeing OPT

Mon Mar 27, 2017 12:32 pm

From what I have seen, if the OPT and actual conditions are identical then the N1 is generally within .1%. However, as pointed out previously, if the temps are higher/lower then the N1 will vary. In reality, it doesn't vary that much but it won't be exact either. To be honest, the variation has negligible affect on takeoff performance.
If we weren't all crazy we'd all go insane!
 
Khaldon
Topic Author
Posts: 4
Joined: Sat Mar 18, 2017 7:45 am

Re: Boeing OPT

Wed Mar 29, 2017 4:23 pm

GE90-115BL engines
 
BravoOne
Posts: 2259
Joined: Fri Apr 12, 2013 2:27 pm

Re: Boeing OPT

Wed Mar 29, 2017 6:45 pm

What mmo said would apply.

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