Ray Proudfoot 231 Posted March 8, 2018 Share Posted March 8, 2018 I have recently bought the Xtreme Prototypes Lear 25 and am flying it in P3D v3.4. I downloaded a template for the Lear 25 from this site (thanks to the author for supplying it) and I'm adjusting the Fuel Bias to try to match the calculated fuel usage in PFPX. I'm confused by one entry on the calculator. I'm entering actual fuel flow per hour (1465) but PFPX is then changing the Calculated fuel flow / hr to a smaller value. Why? If the aircraft is consuming 1465lbs per hour should that value be used in PFPX? 1241lbs/hr is considerably lower and I find I have insufficient fuel for some of my flights. Please login to display this image. Link to comment Share on other sites More sharing options...
Ray Proudfoot 231 Posted March 8, 2018 Author Share Posted March 8, 2018 Just a follow-up to my earlier post. If the fuel calculations were out by just a couple of hundred pounds on a 1hr flight I wouldn't mind. But PFPX calculated I would have 880lbs on landing and the reality was I had 350lbs with a low fuel warning light on. These Bias figures need adjusting but the values I'm entering are accurate so I fail to understand why the fuel difference is so large. Link to comment Share on other sites More sharing options...
Ray Proudfoot 231 Posted March 8, 2018 Author Share Posted March 8, 2018 No one appears to have an answer to this problem so I think I’ll just increase the fuel flow numbers until I end up with the same amount of fuel in P3D as PFPX suggests. Link to comment Share on other sites More sharing options...
srcooke 422 Posted March 9, 2018 Share Posted March 9, 2018 Hello Ray, I have never had to use the calculator with the airliners and performance files I have in use. The reduced fuel flow is offset by the calculated drag, the calculated flow been 18% less than your actual. PFPX would then use the +18% figure for its calculations based on the performance file. The result will depend on the quality and data range of the performance file. Link to comment Share on other sites More sharing options...
Ray Proudfoot 231 Posted March 9, 2018 Author Share Posted March 9, 2018 Hi Stephen, Thanks for that explanation. The performance file came from a chap in Russia and his website is all in Russian so I can't navigate around it. No email address was supplied. What is the best way of increasing the amount of fuel that PFPX will calculate? Increase the fuel flow or fuel bias? The numbers I am entering into the dialogue are accurate as I have access to all of them via various interfaces. But clearly something is wrong in the process as the amounts calculated are too low by quite an amount. LATER: The file was supplied by a chap called CoolP who I can message via this forum. I'll send him a message. Link to comment Share on other sites More sharing options...
srcooke 422 Posted March 9, 2018 Share Posted March 9, 2018 I would look at the fuel burn figures over a few flights with the default performance file, then try manually adjusting the bias figure for the percentage difference required in the aircraft settings accordingly: Please login to display this image. Link to comment Share on other sites More sharing options...
Ray Proudfoot 231 Posted March 9, 2018 Author Share Posted March 9, 2018 Thanks Stephen, much appreciated. Strange that entering accurate fuel burn figures into the interface doesn’t solve the big difference. But the definition of insanity is doing the same thing and expecting a different result. I’ll give your method a try and report back. Link to comment Share on other sites More sharing options...
Ray Proudfoot 231 Posted March 9, 2018 Author Share Posted March 9, 2018 I decided to delete all the files I had for the Lear 25 and start afresh. I must have been doing something wrong before (maybe assigning the Lear 35 instead of the 25) because this time I kept a check of the remaining fuel at each waypoint and it was around 50lbs difference. That's good enough for me. I did enter the usual data into the Bias utility though just to see what came out. A Cruise Fuel bias of 1.5% and Add Drag of 0.5% meant the supplied file is pretty accurate. Phew, problem resolved and thanks for your help Stephen. Link to comment Share on other sites More sharing options...
Skyrock 4 Posted March 9, 2018 Share Posted March 9, 2018 Looking at your picture from the first post, it appears that you have quite a difference in the speed. You preselected Mach .81 but from your entered speeds, this equals only Mach .801. Are you sure you were flying at Mach .81 the first time? This could have a huge influence on the fuel and drag biases. Link to comment Share on other sites More sharing options...
Ray Proudfoot 231 Posted March 9, 2018 Author Share Posted March 9, 2018 Skyrock, My actual Mach speed was 0.759. The problem was I was using a template for a Lear 45 instead of a 25. Once I started again the fuel calculation y PFPX was much better. Link to comment Share on other sites More sharing options...
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