Jump to content
Sign in to follow this  
Ray Proudfoot

PFPX Fuel calculation problem

Recommended Posts

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?


Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
Cheadle Hulme Weather

Share this post


Link to post

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.

 


Glenn Wilkinson

dk1xTfc.jpg                                      28.jpg

Share this post


Link to post

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. 


Bob Scott | President and CEO, AVSIM Inc
ATP Gulfstream II-III-IV-V

System1 (P3Dv5/v4/XP12): i9-13900KS @ 6.0GHz, water 2x360mm, ASUS Z790 Hero, 32GB GSkill 7800MHz CAS36, ASUS RTX4090
Samsung 55" JS8500 4K TV@30Hz,
3x 2TB WD SN850X 1x 4TB Crucial P3 M.2 NVME SSD, EVGA 1600T2 PSU, 1.2Gbps internet
Fiber link to Yamaha RX-V467 Home Theater Receiver, Polk/Klipsch 6" bookshelf speakers, Polk 12" subwoofer, 12.9" iPad Pro
PFC yoke/throttle quad/pedals with custom Hall sensor retrofit, Thermaltake View 71 case, Stream Deck XL button box

Sys2 (MSFS/XP11): i9-10900K @ 5.1GHz, 32GB 3600/15, nVidia RTX4090FE, Alienware AW3821DW 38" 21:9 GSync, EVGA 1000P2
Thrustmaster TCA Boeing Yoke, TCA Airbus Sidestick, 2x TCA Airbus Throttle quads, PFC Cirrus Pedals, Coolermaster HAF932 case

Portable Sys3 (P3Dv4/FSX/DCS): i9-9900K @ 5.0 Ghz, Noctua NH-D15, 32GB 3200/16, EVGA RTX3090, Dell S2417DG 24" GSync
Corsair RM850x PSU, TM TCA Officer Pack, Saitek combat pedals, TM Warthog HOTAS, Coolermaster HAF XB case

Share this post


Link to post
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.


Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
Cheadle Hulme Weather

Share this post


Link to post
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.


Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
Cheadle Hulme Weather

Share this post


Link to post
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. 

  • Like 1

Mark W   CYYZ      

My Simhttps://goo.gl/photos/oic45LSoaHKEgU8E9

My Concorde Tutorial Videos available here:  https://www.youtube.com/user/UPS1000
 

 

Share this post


Link to post

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

@srcooke might be able to offer some assistance?

Share this post


Link to post
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?


Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
Cheadle Hulme Weather

Share this post


Link to post
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.

 

Share this post


Link to post

@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 (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
Cheadle Hulme Weather

Share this post


Link to post

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. 👍

  • Like 1

Ray (Cheshire, England).
System: P3D v5.3HF2, Intel i9-13900K, MSI 4090 GAMING X TRIO 24G, Crucial T700 4Tb M.2 SSD, Asus ROG Maximus Z790 Hero, 32Gb Corsair Vengeance DDR5 6000Mhz RAM, Win 11 Pro 64-bit, BenQ PD3200U 32” UHD monitor, Fulcrum One yoke.
Cheadle Hulme Weather

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  
  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
×
×
  • Create New...