"fmgc_idle_fac" and "fmgc_perf_fac" ?

[Stu Antonio 2713]

fmgc_idle_fac=
fmgc_perf_fac=

What are those entries in the aircraft config setting?
Can't find anything in the Aircraft Options pdf....

Greets,
Stu

[Koen Meier 1315]

Those are the idle/perf values on a/c status page. You can change them in the fltsim.cfg or the a/c status page via arm in the change code.

[Stu Antonio 2713]

I see. But what exactly does it mean for the aircraft? And how do I know what to set here? For example I‘ve downloaded 2 321 liveries, one with =0, the other one with =3. Is this related to airframe age? 

[M_i_k_e_V_o_g 167]

Done by engineering.
Perf factor is shown on the ofp though, so if there is a discrepancy it is to be resolved with dispatch and changed if necessary.

Amending the PERF factor is made to account for airframe/engine specific deterioration and therefore increased fuel burn from the std. Amending or updating the IDLE factor is to adjust the FM descent profile. If it is thought to be incorrect and the aircraft is descending too early, too late etc.

[Koen Meier 1315]

in the fslabs it does affect fuelburn but irl only calculations.

[Cathal Kavanagh 47]

Quick question, should we update the Fuel Factor option on Simbrief with the value for fmgc_perf_fac= 

 

? Or should simbrief be set to a particular setting for accurate fuel burn logging from the flight plan?

[Koen Meier 1315]

27 minutes ago, Cathal Kavanagh said:

Quick question, should we update the Fuel Factor option on Simbrief with the value for fmgc_perf_fac= 

 

? Or should simbrief be set to a particular setting for accurate fuel burn logging from the flight plan?

Simbrief should be set to the perf value that the aircraft has but you might need to tweak in the end as the fuel burn isn’t entirely accurate I feel.

[Cathal Kavanagh 47]

On 10/25/2020 at 10:49 PM, Koen Meier said:

Simbrief should be set to the perf value that the aircraft has but you might need to tweak in the end as the fuel burn isn’t entirely accurate I feel.

Hi Koen,

 

Any tips on how to calculate additional fuel burn % from the FP when logging burned fuel? I'm trying to get as accurate as possible a fuel factor.

[Simon Kelsey 1086]

I have to say that as far as the IAE engines are concerned my Simbrief fuel figures are always pretty much spot on, within 100kg or so most of the time, provided the Simbrief fuel factor matches the FMGC PERF factor.

I rarely fly the CFMs so I'm not sure how it stacks up for them!

[Camille MOUCHEL 119]

20 hours ago, Simon Kelsey said:

I have to say that as far as the IAE engines are concerned my Simbrief fuel figures are always pretty much spot on, within 100kg or so most of the time, provided the Simbrief fuel factor matches the FMGC PERF factor.

I rarely fly the CFMs so I'm not sure how it stacks up for them!

i fly only CFM and the same, I did a flight from AZ to B fully managed in climb and descent and speed, and difference was within 100kg, the difference is only due to the taxi fuel, i always plan 200Kg of fuel but most of the time, i used 80-120kg so i always have in avg az surplus of 100kg when taking off

[Michael Gold 3]

On 12/28/2019 at 8:03 AM, Stu Antonio said:

I see. But what exactly does it mean for the aircraft? And how do I know what to set here? For example I‘ve downloaded 2 321 liveries, one with =0, the other one with =3. Is this related to airframe age? 

I'd like to come back to this older question in this thread -- how would one go about figuring out what value would be appropriate for the airframe you're doing a config for?

[Stu Antonio 2713]

2 hours ago, Michael Gold said:

I'd like to come back to this older question in this thread -- how would one go about figuring out what value would be appropriate for the airframe you're doing a config for?

The real perf factors of each airframe of are usually not made public by the airlines. You will have to make one up, or find a source somewhere to get this value from. Some Virtual Airlines though (ie vEZY), who have access to their real world counterparts, provide very detailed airframe configs including this values.... 

[Antti Salo 99]

Airframe age gives quite a good ballpark. For a new aircraft it will be around zero, and 20 years will add around 5% of burn. Though in reality it can vary a lot.

Even if you had access to the real world figure of a certain airframe, it probably wouldn’t be valid for too long, as IRL the figures are updated at recent intervals and for example an engine change can change it significantly in either direction.

[Dan Parkin 140]

I knew of an old airframe operated by a large UK carrier that was notorious for essentially flying sideways if was so knackered.