PFPX profile for the 747-8

[B777ER 2,484]

2 hours ago, srcooke said:

Personally I monitor several flights, if there is a discrepancy does it occur in the climb,cruise or descent phase of flight.

Be sure to use the climb/cruise/descent profiles as planned in PFPX including CI.

When planning are using PFPX online weather or that sourced from the weather engine ( PFPX online been more accurate )

Having monitored the fuel difference from the flights apply an average bias adjustment.

I too use the PFPX online wx for aloft winds forecast. I agree, much more accurate. I'll fly few more and keep track. The patch for the QW 787 just came out so I might be busy with that one as well! 

[xTiMm_ 50]

27 minutes ago, B777ER said:

I too use the PFPX online wx for aloft winds forecast. I agree, much more accurate. I'll fly few more and keep track. The patch for the QW 787 just came out so I might be busy with that one as well! 

... what? Check where you are posting 😄 

[Raphael_Chacon 42]

23 hours ago, B777ER said:

I just did an almost 10hr flight using this new profile. Was 14,000lbs under estimated arrival fuel. The winds were pretty much spot on with the forecast and followed along with the flightplan. Think there needs to be work done on this one. For those using this profile, the weights for MLW and Empty weight are different than what PMDG has in their aircraft.cfg as well. If I keep coming in under I will have to add a percentage increase in the cruise fuel bias. 

EDIT: This was the pax version profile. 

Ive performed 1 Long haul and 1 Medium Haul so far.   Figures are very precise.    Of course, i follow plan step climb, and use ASP4 weather including adding the FP to it so winds and weather becomes more precise.     I see no problem.  Are you sure its the correct template you have into PFPX folders?  Remember there were other templates before around that were actually not good, i had the issue and when revised, somehow i confused files, now using the correct file for planning, give it a check out and if possible re-download it.

About relaxing it a bit, i feel itll be a good idea.   My numbers point to point are very very exact so far that i whised they wouldnt, but i havent had any problem indeed, may be i would add some BIAS tweak if i need some...

Hope you find a solution soon.

Happy Flying! 😎

Edited September 25, 2018 by Raphael_Chacon

[Lude2Envy 11]

On 9/23/2018 at 6:59 AM, kityatyi said:

Agreed. Not only FSLabs released a PFPX profile for their Airbus A319 and A320 but also Leonardo attached a profile for their Maddog as well as Aerosoft for their CRJ.

And PMDG did for the DC-6. 

[downscc 1,327]

On 9/25/2018 at 9:32 AM, Raphael_Chacon said:

Ive performed 1 Long haul and 1 Medium Haul so far.   Figures are very precise. 

Agree... although I wouldn't use the adjective precise.  Sufficient works.  I ran a few fuel burn measurements to compare with the profile (Tip:  Use the Bias feature in PFPX) and the measured fuel burn over 6-10 min was well within 3% of the profile.  I consider that sufficient.

Keep in mind that a 14,000 variance is not necessarily a gross error.  Depending on your planned trip fuel that could be 3-6% error or less.  I haven't played with it enough yet, but I suspect the hourly rates are okay but maybe we need to add an extra 6000 lbs for start, taxi and climb.  I finished a 14.2 hr trip with fuel remaining expected to be 25000 and actual was 21000.  Don't forget, the FMS fuel remaining value does not include start and taxi.

[captainsazzman 83]

On 9/22/2018 at 12:51 PM, Olympic260 said:

Simbrief does a very good job there. I am a PFPX user my self but had no issues at all using simbrief for calculating my -8 flights.

did you make any adjustments to the simbrief 747-8 template like max ZFW, etc?

[Olympic260 415]

2 hours ago, captainsazzman said:

did you make any adjustments to the simbrief 747-8 template like max ZFW, etc?

I just made sure that the weights there are the same as the sim aircraft

[blueairone70 3]

http://airlinerperformance.net/aircraft-types/

go this site for a profile

 

 

 

[Skyrock 4]

On 10/3/2018 at 5:38 PM, downscc said:

Agree... although I wouldn't use the adjective precise.  Sufficient works.  I ran a few fuel burn measurements to compare with the profile (Tip:  Use the Bias feature in PFPX) and the measured fuel burn over 6-10 min was well within 3% of the profile.  I consider that sufficient.

Keep in mind that a 14,000 variance is not necessarily a gross error.  Depending on your planned trip fuel that could be 3-6% error or less.  I haven't played with it enough yet, but I suspect the hourly rates are okay but maybe we need to add an extra 6000 lbs for start, taxi and climb.  I finished a 14.2 hr trip with fuel remaining expected to be 25000 and actual was 21000.  Don't forget, the FMS fuel remaining value does not include start and taxi.

If you used the profiles from airlinerperformance.net, then I can tell why the difference happens.

First of all, when we encounter higher temperatures (so higher than ISA), we should burn more fuel and fly faster. This is also what PFPX takes into account when generating a flight plan. However, in the sim we are only flying faster, but we burn the same amount of fuel as we'd do in ISA+0 conditions. So whenever you are flying in regions with big temperature deviations (compared to ISA), there will be an error.

Second, the profiles seem to lack accuracy when it comes to different Cost Indexes. Maybe thats why you guys had different outcomes. For the 747-8, I figured at CI 90, the bias is around -1,1%, while at CI 15 it is -6,1, so quite a difference.

I don't know if only PMDG planes are affected or every plane, but I also noticed it on the 777. Thats why I got rid of the ISA deviation tables in the profiles for the 777, but unfortunately, I can't do the same for the 747-8 unless someone releases a .txt file which I can amend.

Check also our discussion in the PFPX forum regarding this issue: click here

Edited October 8, 2018 by Skyrock

[downscc 1,327]

42 minutes ago, Skyrock said:

I don't know if only PMDG planes are affected or every plane

I am quite positive that the fuel burn rates for PMDG aircraft include SAT deviation.  During beta we always run a few burn measurements at different conditions and the particular developer responsible for this takes a lot of pride in his rates matching Boeing, usually to within 1%.

I do not have the same confidence in 3d party data obtained by hobbyists at no cost.

If you have proprietary Boeing data with which you can make the claim that there is no temperature deviation effect then please contact PMDG via their support portal with such data.

Edited October 8, 2018 by downscc

[Skyrock 4]

12 minutes ago, downscc said:

I am quite positive that the fuel burn rates for PMDG aircraft include SAT deviation.  During beta we always run a few burn measurements at different conditions and the particular developer responsible for this takes a lot of pride in his rates matching Boeing, usually to within 1%.

I do not have the same confidence in 3d party data obtained by hobbyists at no cost.

If you have proprietary Boeing data with which you can make the claim that there is no temperature deviation effect then please contact PMDG via their support portal with such data.

I'd love to see your method of fuel burn measurements, because in my tests (described in the link) I burned exactly the same amount of fuel regardless of SAT. Or if there is a deviation in fuel burn, it's very small. My experience confirms that. Since I stopped adjusting for ISA deviations for 777 flights, my flight plans were pretty precise. Before that, whenever I had a deviation from ISA, I was always way off the plan.

So please, enlighten me on how you do that.

Edited October 8, 2018 by Skyrock

[downscc 1,327]

4 minutes ago, Skyrock said:

'd love to see your method of fuel burn measurements,

It is pretty straightforward.  Open lower center CDU and display FUEL page. Pause sim and note exact fuel and the GW value, at a given mach and temperature fly unaccelerated flight for 10 min.  Pause again and note fuel and weight.  Find equivalent lb/hr at given average weight with specified conditions.

How do you do it?

[Skyrock 4]

8 minutes ago, downscc said:

It is pretty straightforward.  Open lower center CDU and display FUEL page. Pause sim and note exact fuel and the GW value, at a given mach and temperature fly unaccelerated flight for 10 min.  Pause again and note fuel and weight.  Find equivalent lb/hr at given average weight with specified conditions.

How do you do it?

My method is the following: set up the flight sim at a random location (I used KVPS or EDDF), set the clear skies weather theme without any weather tool like ActiveSky or other tools (only P3D, nothing else except maybe AFSD, see below) and then depart with a random load (most of the time I departed with 2/3 of the MTOW). Let it settle at the optimum FL and wait until the engines are stabilized. Then you can take the bias using the bias window in PFPX. I open up AFSD for this since the numbers shown there match the performance. You can also open up the fuel page in the CDU to get the exact numbers. After 1min, take the difference between both numbers. The result is multiplied with 60. To rule out any errors, I do this test a few times.

Due to the clear skies theme, you'll always have ISA+0 and no winds, so this way there is no external influence on the performance. Write the numbers down and set the temperature to like ISA+15 (for FL330, ISA+0 equals -50°C, so in this case set it to -35°C). Wait until the engines are stable again and use the bias window again. The drag bias is constant while the fuel bias changes..

This method worked like a charm for the 777.

Edited October 8, 2018 by Skyrock

[downscc 1,327]

So, you are using PFPX bias as an indicator of accuracy of data?  Interesting.  I see why you come to your conclusions.

[Skyrock 4]

I don't need PFPX for this to see that the fuel burn is the same. Don't reduce it only to this. PFPX only provides the bias, but the fuel burn my test results is always the same.