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Airbus cost index and LRC

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Airbus cost index and LRC

Old 4th Mar 2020, 08:13
  #21 (permalink)  
 
Join Date: Jul 2006
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Thank you guys, especially OPEN DES for the explanations. I finally understand it now haha.
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Old 4th Mar 2020, 10:12
  #22 (permalink)  
 
Join Date: May 2006
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I came up with 40kg/min as a fuel flow, not a cost index but evidently thatís not correct. I asked for what cost index you would use for LRC and you said 40. I can see this is getting a little frustrating for you but I appreciate you trying and your patience. To be honest, I personally am still confused. Maybe you could attach that reference you mentioned as a screenshot? The table above with the different engine types is the only one I found in the FCOM, is this the same table you are referring to?

Pineteam, maybe you can help me out and give OPEN DES a rest lol?
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Old 4th Mar 2020, 10:49
  #23 (permalink)  
 
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What you seem to be missing is that CI = 40kg/min is not referring to fuel flow per minute, it is referring to a CI of 40 which is telling the FMGC to work on 40 kg of fuel being the same cost as 1 flight minute.

The reason the table gives different numbers to the graph is that the table is making assumptions for the sake of simplicity, the big one being that the cruise level is within 1000í of optimum. If you look at the higher altitudes / weights on the graph you get a CI of 30, much closer to the 40 from the table.

Also if you look at some of the CI values for various engines youíll see that it doesnít make sense for it to refer to a fuel flow of kg/min, for example a CFM-56-5-B8 engine would be on every A320 if LRC gave 15kg/min fuel flow!

If Airbus had just avoided specifying the CI as kg/min it would be a lot less confusing. It appears they have done this to differentiate the metric from imperial aircraft.

I hope that helps. I didnít understand it either until OPEN DES explained it, but I think heís on the money.

Last edited by AerocatS2A; 4th Mar 2020 at 10:59.
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Old 4th Mar 2020, 10:56
  #24 (permalink)  
 
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To answer your specific question as to how to use the table. For an A320 with V2527-A5 engines within 1000 feet of optimum FL and metric fuel gauges, set CI40 for LRC.
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Old 4th Mar 2020, 10:56
  #25 (permalink)  
 
Join Date: May 2006
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Ok thank you all for your input and patience. So out of all that I can take away that we insert a CI of 40 in the FMGC to get LRC. I hope that’s right otherwise shoot me now lol.
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Old 5th Mar 2020, 09:10
  #26 (permalink)  
 
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Originally Posted by STLTH View Post

Pineteam, maybe you can help me out and give OPEN DES a rest lol?
Sorry, Just read your post now! xD Happy other members explained it. =)
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Old 14th Feb 2021, 05:52
  #27 (permalink)  
 
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Is this applicable for single engine scenarios as well? If we set CI 40 in a single engine situation, does the the FMGS still give us LRC for one engine inoperative?

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Old 14th Feb 2021, 16:14
  #28 (permalink)  
 
Join Date: Jun 2014
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As far as I remember, Single Eng FMGS calculations are by default at LRC. They don't use Cost Index
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