PFPX Fuel calculation problem

[Ray Proudfoot 8,961]

I have the Xtreme Prototypes Lear 25 which I use in P3D v5.3HF2. For planning my flights I have used PFPX for years. It gives me everything I want.

Now to the problem which I have to post here as the official forum is now read-only.

I planned a flight from Helsinki to Frankfurt. PFPX calculates the distance as 1025nm. I have selected the Fuel Option as No Reserve but have added 750lbs. The fuel calculation comes out at 6,658lbs - 603lbs more than the capacity.

But the distance of 1,025nm is a fraction of the max range of 2,000nm in the documentation. Given I have only 2 pax I'm struggling to understand why PFPX thinks the fuel burn is so wrong.

To tweak it I opened the Aircraft Editor in PFPX and paused the flight at cruise (FL400, Mach 0.82) and entered all the data required for a more accurate burn.

But still it shows the max fuel capacity of 6055lbs is insufficient by 603lbs.

I decided to fly the route anyway and landed with fuel remaining of 1,607lbs. PFPX calculated 1,407lbs which is pretty close.

It's just the calculation for the whole route I can't seem to get accurate enough when the max range is so much greater. Fuel used was 4,354lbs. PFPX calculated 5251lbs would be used. That's a huge difference.

Anyone have any experience in adjusting fuel burn in PFPX?

[beechcaptain 105]

Sorry to not be able to provide definitive help, but it would seem that adjusting fuel bias for that a/c might do the job.

 

[Bob Scott 7,721]

Try manually setting a lower cruise level--I've seen wonky results like that when the flight level I selected was higher than what PFPX determined was the maximum, driven by performance or even by route/airspace altitude restrictions.  When it was route restrictions getting in the way, I just got rid of the affected route designator and substituted in direct point-to-point segments to the route's waypoints. 

[Ray Proudfoot 8,961]

1 hour ago, beechcaptain said:

Sorry to not be able to provide definitive help, but it would seem that adjusting fuel bias for that a/c might do the job.

 

I tried that but it made little difference. I even deleted it and still no significant change. But since posting I did some searching and found a document uploaded to the PFPX forum 3 years ago. It has lots of useful info on how to refine the tables for fuel burn.

So I shall try it tomorrow on a dummy flight simply to time how long it takes to reach a certain altitude and how much fuel was consumed.

The document is named PFPX AIRCRAFT FILES EXPLAINED.PDF.

@Bob Scott, I always stick to the altitude PFPX decides unless it’s a silly one due to restrictions. Today’s second flight was much shorter but each time I passed a waypoint I noted my fuel used compared to the calculated one in PFPX. Mine were always lower.

I agree those low altitude restrictions are a pain. I just request higher in RCv4.

[MarkW 1,493]

Ray, there is a profile on Simbrief, maybe use that as well for comparison.

[Ray Proudfoot 8,961]

45 minutes ago, MarkW said:

Ray, there is a profile on Simbrief, maybe use that as well for comparison.

I guess I have to install SimBrief Mark. I’d rather not. I’ve found the document that describes the process for adjusting fuel burn rates. Let me see how I get on with that.

[MarkW 1,493]

2 hours ago, Ray Proudfoot said:

I guess I have to install SimBrief Mark. I’d rather not. I’ve found the document that describes the process for adjusting fuel burn rates. Let me see how I get on with that.

Nothing to install, the flight planner is just a website but sounds like you have it sorted. 

[VHOJT 177]

I would definitely try manually setting a flight level and see if that helps.

@srcooke might be able to offer some assistance?

[Ray Proudfoot 8,961]

9 hours ago, MarkW said:

Nothing to install, the flight planner is just a website but sounds like you have it sorted. 

 

9 hours ago, VHOJT said:

I would definitely try manually setting a flight level and see if that helps.

@srcooke might be able to offer some assistance?

The procedure for determining fuel burn is lengthy but not particularly complicated. Firstly, no weather. Just manually setting the temp so ISA=0. Then aircraft on autopilot asap so climb rate is constant at the required speed. 300kts / Mach 0.7 during climb. Mach 0.82 in cruise. Pause the sim at the relevant flight levels and note the time it took to reach that point.

I’ll leave descent alone for now. What I can’t understand is how limited the range is. Just over half what the aircraft is capable of. And that was with five souls including flight crew of two.

One question. Does Dry Operating Weight include crew + aircraft with no fuel?

[srcooke 52]

8 minutes ago, Ray Proudfoot said:

One question. Does Dry Operating Weight include crew + aircraft with no fuel?

Yes in PFPX it does.

Are you using the Learjet 25 file that you sent me some time ago Ray ? If so you are using adjusted figures ?

Using that file and PFPX online weather at FL400, a flightplan distance of 916nm returns a trip burn of 3534lbs.

If you email me all the data that you have for the learjet plus your PFPX aircraft type performance file and the aircraft registration file you have in use I''l take a look.

 

[Ray Proudfoot 8,961]

@srcooke, many thanks Stephen. Given it’s the only Lear I have then it probably was the one I’m using for the XP version.

I’ll send you the files shortly.

[Ray Proudfoot 8,961]

It would appear the claimed range of the XP Lear 25D is not 2,000nm but closer to 1200nm. Hence why trying to plan a flight of 1025nm with weather to consider was pushing it somewhat.

I'll use the PFPX utility to refine fuel burn and stick to Mach 0.77 rather than 0.82 in cruise. Hard to get the boy-racer out of my blood!

My thanks to @srcookefor his help. 👍