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I'm flying the PMDG738 in P3D v4.4. I like to get my actual fuel burn to match the estimated numbers in PFPX. I'm currently using the default for that aircraft but consistently end up with less fuel than PFPX calculates.

 

To get this more accurate I have used the built-in utility to get a more accurate figure but after entering all the information provided I end up with an even worse result than with the original.

 

I'm beginning to think there must be a problem with PFPX. I'm convinced I am entering the correct actuals so why don't these improve the results. I only enter these values when the aircraft is at cruise, not climbing or descending. Is that how the utility should be used?

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Which performance file is in use Ray, using the AirlinerPerformance file is very, very accurate here.

 

The only adjustment required is to match the weights and capacities of the NGX.

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Hi Stephen,

 

The performance filename is 737-800W_B26B27_v1.00.per.

 

Are you using the same one? Or should I download the one for 737-800W on your link?

 

LATER: Downloaded that file and it's the same filename and size. So perhaps it's something else in my config.

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Yes I should think it is the same file.

 

Here is my configuration, in KG :)

 

ngx-per.thumb.jpg.45e319706cdaa3bc3533168ac8d010de.jpg

 

The use of de-rated climb, especially CLB-2 is likely to lead to greater fuel burn to cruise altitude.

 

 

 

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14 minutes ago, srcooke said:

Yes I should think it is the same file.

 

Here is my configuration, in KG :)

 

The use of de-rated climb, especially CLB-2 is likely to lead to greater fuel burn to cruise altitude.

 

Thanks Stephen. I haven't done a direct comparison because your last comment may provide the answer. Using Topcat I always go for the TO-2 option. Do you choose the same? Flaps 5 TO-2 and normal climb power thereafter? I'm wondering if I need to adjust Topcat options.

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Unless performance is required CLB-1 Ray.

 

You may find the entries in the Flight Crew Training Manual useful, section 3 & 4.

 

A note from the manual regarding reduced climb thrust:

 

"Use of reduced thrust for climb increases total trip fuel and should be evaluated by each operator."

 

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You could still use TO-2 switching to CLB-1 on the thrust reduction altitude.

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TO-1 on most runways seems a safer option. I do feel the aircraft is somewhat dawdling on its roll. What do you use as a matter of interest?

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Test flight EGPH-EGBB, FL270. TO-1, CLB-1

 

Fuel on line-up at EGPH was spot on at 9,700lbs. Fuel on landing on 15 was 5,200lbs - PFPX calculated 5,600lbs.

 

I suspect some of the difference may be the climb rates. PFPX states 250/280/.78.

 

The PMDG 738 CDU had 305kts for the climb which probably accounted for me reaching ToC later than PFPX calculated. I'll try and stick to PFPX climb speeds and see how it goee.

 

Appreciate your help as always Stephen.

 

 

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Reference my image above, set ECON climb and CI45.

 

The descent is a matter of preference, I prefer to maintain a higher speed than ECON descent will allocate.

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Okey dokey. ECON it is. Given the engines are close to idle on descent that probably doesn’t make much difference to fuel burn. Climb appears to be the key.

 

Shutdown now until tomorrow. Thanks once again. 👍

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Hi Stephen

 

Despite making changes as you suggest I continue to use more fuel than PFPX calculates. Here is the result of my latest flight from EBBR-EDDM. Actual fuel used comes from the Electronic Flight Bag log. All values are pounds remaining (sorry!) with PFPX first with actual in brackets. The first value is when lined up on the runway and the last on landing.

 

EBBR 9.8 (9.6)

SOPOK 7.2 (6.8)

ROPUV 6.5 (6.1)

UBIDU 6.0 (5.6)

MOVUM 5.7 (5.3)

DKB 5.0 (4.6)

BURAM 4.9 (4.5)

EDDM 4.4 (4.1)

 

The difference seems consistent at around 400lbs which suggests cruise burn is okay. But I'm using TO-1 5 flaps and then CLB so why this difference. And what can be tweaked to reduce the difference? Maybe it's the climb rate as PFPX has 250/280 whereas the PMDG uses 250/305.

 

How close are your actuals to the PFPX calculation?

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I don't know if you've seen some threads around, Ray - PMDG aircraft seem not to burn correctly when taking ISA deviation into account.  I.e. with low ISA deviation, they burn more, with high ISA deviation, they burn less.  I've found this on their 737, 777 and 747.

 

I have made some notes after tests I did testing their fuel burn at different ISA deviations, I can post them if you wish.

 

I have found this problem with both default profiles, and the good ones found on airlinerperformance.  Both profiles are good in my opinion.

 

With the 747, I have to adjust my cruise bias each flight depending on ISA deviation to get an accurate result with the PMDG aircraft.  Don't seem to have this problem with FSLabs A320 (mind you they built their own profile for it, so it ought to be accurate!)

 

Whether or not you're encountering this, I don't know.

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So you burnt 200lb more fuel getting to the runway, did the taxi time match ? Also the sim ground friction model will come into play here.

 

Then there is an additional 200lb difference at the first waypoint.

 

Can you post a snapshot of the current aircraft general setting.

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1 hour ago, VHOJT said:

I don't know if you've seen some threads around, Ray - PMDG aircraft seem not to burn correctly when taking ISA deviation into account.  I.e. with low ISA deviation, they burn more, with high ISA deviation, they burn less.  I've found this on their 737, 777 and 747.

 

I have made some notes after tests I did testing their fuel burn at different ISA deviations, I can post them if you wish.

 

I have found this problem with both default profiles, and the good ones found on airlinerperformance.  Both profiles are good in my opinion.

 

With the 747, I have to adjust my cruise bias each flight depending on ISA deviation to get an accurate result with the PMDG aircraft.  Don't seem to have this problem with FSLabs A320 (mind you they built their own profile for it, so it ought to be accurate!)

 

Whether or not you're encountering this, I don't know.

 

The ISA DIF thing may be making a difference to my flights. I haven't read any of the discussion. GIven the cost of PFPX and the PMDG737 it's disappointing the calculations / usage aren't more accurate. I have no plans to buy the A320. I'm waiting for Concorde.

 

Thanks for the offer of data but unless I can actually get anything to change (PFPX or PMDG737) there seems little point.

 

1 hour ago, srcooke said:

So you burnt 200lb more fuel getting to the runway, did the taxi time match ? Also the sim ground friction model will come into play here.

 

Then there is an additional 200lb difference at the first waypoint.

 

Can you post a snapshot of the current aircraft general setting.

 

On that flight I did but on others the taxi usage was fine. If the problem was that simple I'd work around it. On another flight today I ended up with 500lb less than an hour less on a flight lasting less than an hour. That's disappointing.

 

I asked earlier how close your numbers were to PFPX. That would be helpful. What do you mean by the "current aircraft general setting"? PFPX or P3D?

 

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7 minutes ago, Ray Proudfoot said:

I asked earlier how close your numbers were to PFPX

 

Pretty much exact, within kgs at TOC and TOD, the only discrepancies occurring from ATC route changes on arrival.

 

A transatlantic 744RR run yesterday EGKK-KJFK was pretty exacting also, a 1t difference to TOC where I was testing the CLB-2 difference. This 1t difference was then constant to TOD, again the differences on arrival due to ATC routing.

 

Post the changes you have made in the aircraft editor/general tab Ray.

 

 

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Thanks Stephen. Clearly we have different configurations as we use the same version of PFPX and are both running P3D v4.4 with live weather.

 

Here's what you requested. Despite changing units to Kg the aircraft weights are still in pounds. Don't know why. Changes are only what you advised.

B737_1.png

B737_2.png

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Forgive me if I've misread the numbers but for EBBR-EDDM it seems that PFPX calculated a trip burn of 5400lbs, vs PMDG's actual burn of 5500lbs (read to the nearest 100 lbs?). That's a 100lb (45kg) difference, or about 1.8%. To quote - "GIven the cost of PFPX and the PMDG737 it's disappointing the calculations / usage aren't more accurate"  Seriously ??!!

 

What's causing the bigger variance in point numbers is a 200 lb higher start/taxi burn before departure. Irrespective of how PMDG or FSX/P3D models burn on the ground or at low thrust BRU is a big airport, it would be normal practice to apply a higher fixed taxi fuel allowance at larger/busier airports.

 

As for the FSX/P3D fuel burn vs temperature issue, I did post a good while ago asking for folks wanting to help with testing revised files. I had one reply for 1 aircraft type, and didn't get any feedback on the revised performance file. It would seem that 99.9% of users aren't that bothered, which seems to be borne out by how the majority of Twitch streamers use/apply both flight planning applications.

 

Cheers

Jon

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I have flown EBBR-EDDM using my setup as posted above.

 

ATC route as flown:

 

(FPL-LHR2283-IS
-B738/M-SDE1FGHIJ1RWXYZ/LB1
-EBBR1430
-N0444F330 SOPOK UY863 ETENO Y863 RUDUS T109 HAREM T104 ANORA
-EDDM0058 ETSI
-PBN/A1B1C1D1L1O1S1 NAV/RNVD1E2A1 DOF/190403 REG/DAERA
 EET/EBUR0008 EDUU0015 EDMM0041 RVR/75 OPR///
 PER/C
-E/0201)

 

The PERF INIT page was fully configured and enroute winds and descent wind entries completed.

 

ngx-perf.jpg.5dac6533dcc127c54c5aaa13b3861a5c.jpg

 

NADP-1 was implemented as published in the charts, takeoff and climb was TO-2@32C and CLB-1

 

The differences in arrival figures were from a late descent from ATC as indicated.

 

My recorded entries in the attached PDF are highlighted yellow:

 

 


--------------------------------------------------------------------------------

EBBR-EDDM-1.pdf

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59 minutes ago, BW901 said:

Forgive me if I've misread the numbers but for EBBR-EDDM it seems that PFPX calculated a trip burn of 5400lbs, vs PMDG's actual burn of 5500lbs (read to the nearest 100 lbs?). That's a 100lb (45kg) difference, or about 1.8%. To quote - "GIven the cost of PFPX and the PMDG737 it's disappointing the calculations / usage aren't more accurate"  Seriously ??!!

 

What's causing the bigger variance in point numbers is a 200 lb higher start/taxi burn before departure. Irrespective of how PMDG or FSX/P3D models burn on the ground or at low thrust BRU is a big airport, it would be normal practice to apply a higher fixed taxi fuel allowance at larger/busier airports.

 

As for the FSX/P3D fuel burn vs temperature issue, I did post a good while ago asking for folks wanting to help with testing revised files. I had one reply for 1 aircraft type, and didn't get any feedback on the revised performance file. It would seem that 99.9% of users aren't that bothered, which seems to be borne out by how the majority of Twitch streamers use/apply both flight planning applications.

 

Cheers

Jon

 

That flight was not totally typical of the problem. Fuel when lining up usually matches that in PFPX. But thereafter I consume more than PFPX calculates. Even by ToC the difference is a few hundred pounds. The fact it doesn't worsen thereafter suggests cruise burn is okay. It's climb burn that appears out. I tend to leave taxi out / in at fixed values. Maybe I should adjust them at larger airports like EDDM although by then the 'damage' has already occured.

 

@srcooke, thanks for posting your results. Very frustrating I can't replicate them. Although I enter cruise winds (ToC) and ISA DEV I don't enter arrival winds. Interesting you use a CI of 35. I use 45. Is that a factor?

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One other thing. Assuming everyone is using the 737-800 Winglet version and engages the a/p within one minute after take-off how can there be so much difference when the sim is the same and the aircraft is the same? Only the weather and route changes but I always have less fuel than PFPX calculates.

 

And returning to my original point. Does anyone refine aircraft performance using the inbuilt utility in PFPX? I've found it makes things worse, not better. But I'm entering actuals when at cruise. Does anyone else use it and do you find it improves things?

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