El Chapo Posted January 2, 2023 Share Posted January 2, 2023 Hi, I've been struggling for a while for fuel management. I always came lower than expected, and I could'nt figure out why. Eventually, the issue seems to be quite simple: fuel flow seems bugged... When you take (left fuel flow + right fuel flow)*(time duration), you end up with approximately 50% of actual fuel consumption during that same duration. Is this a known issue? Is it an misunderstanding from my side due to units conversion? Is fuel flow not indicated in lbs per minute? Thanks Link to comment Share on other sites More sharing options...
Hiob Posted January 2, 2023 Share Posted January 2, 2023 3 minutes ago, El Chapo said: Hi, I've been struggling for a while for fuel management. I always came lower than expected, and I could'nt figure out why. Eventually, the issue seems to be quite simple: fuel flow seems bugged... When you take (left fuel flow + right fuel flow)*(time duration), you end up with approximately 50% of actual fuel consumption during that same duration. Is this a known issue? Is it an misunderstanding from my side due to units conversion? Is fuel flow not indicated in lbs per minute? Thanks Just from the top of my head - isn't fuel flow shown per hour usually? I don't know much about the Hornet though. "Muß ich denn jedes Mal, wenn ich sauge oder saugblase den Schlauchstecker in die Schlauchnut schieben?" Link to comment Share on other sites More sharing options...
Soeren_Haudrup Posted January 2, 2023 Share Posted January 2, 2023 Hi everyone IIRC the fuel flow shown on the IFEI is indicated number x 100 / hour Link to comment Share on other sites More sharing options...
El Chapo Posted January 2, 2023 Author Share Posted January 2, 2023 (edited) In that case it makes sense since 100/60 is around 2... But I wonder who invented it... On the M2000 you have it in kg/min which makes the calculation straightforward. Edited January 2, 2023 by El Chapo Link to comment Share on other sites More sharing options...
Hiob Posted January 2, 2023 Share Posted January 2, 2023 Well lbs/hour gives you the quickest estimate for the remaining time on station. 15.000 left; Bingo = 5.000; fuel flow of 5.000 lbs/hour gives two hours on station. "Muß ich denn jedes Mal, wenn ich sauge oder saugblase den Schlauchstecker in die Schlauchnut schieben?" Link to comment Share on other sites More sharing options...
Exorcet Posted January 2, 2023 Share Posted January 2, 2023 22 minutes ago, El Chapo said: In that case it makes sense since 100/60 is around 2... But I wonder who invented it... On the M2000 you have it in kg/min which makes the calculation straightforward. The Hornet has a MFD fuel page, you don't need to calculate anything at all. And why is fuel/min better than fuel/hr? You can just convert by 60 if you need the other. 1 Awaiting: DCS F-15C Win 10 i5-9600KF 4.6 GHz 64 GB RAM RTX2080Ti 11GB -- Win 7 64 i5-6600K 3.6 GHz 32 GB RAM GTX970 4GB -- A-10C, F-5E, Su-27, F-15C, F-14B, F-16C missions in User Files Link to comment Share on other sites More sharing options...
Soeren_Haudrup Posted January 2, 2023 Share Posted January 2, 2023 Hi Chapo i get your point and i guess it is mostly a thing about, what you are used to. It is not totally uncommon in military aviation to use the SI system. Afaik soviet and/or russian aircraft (among others) did this like forever On the other hand, most western military aviation and basicly all international aviation uses imperial units and naval measurements and having everyone on the same page, is not that bad either. Link to comment Share on other sites More sharing options...
El Chapo Posted January 2, 2023 Author Share Posted January 2, 2023 Usually we're flying to waypoints that are minutes away, not hours away... Link to comment Share on other sites More sharing options...
Hiob Posted January 2, 2023 Share Posted January 2, 2023 (edited) 7 minutes ago, El Chapo said: Usually we're flying to waypoints that are minutes away, not hours away... The units and gauges are probably tuned for real life operations and not for us desk jockeys... Also, fuel for ingress and egress is calculated prior to the start of the mission (bingo?), time on station can vary for various reasons (engagements, weather, adversaries) Edited January 2, 2023 by Hiob "Muß ich denn jedes Mal, wenn ich sauge oder saugblase den Schlauchstecker in die Schlauchnut schieben?" Link to comment Share on other sites More sharing options...
Soeren_Haudrup Posted January 2, 2023 Share Posted January 2, 2023 Hi Chapo I mean im not a navy guy at all, but afaik this aircraft is all about operating from a carrier, right. And simply by looking at any map, you get an estimation, what distances these guys are dealing with. I would say, we are talking about seriously long hours here and tons of fuel, but that´s just me. 1 Link to comment Share on other sites More sharing options...
Exorcet Posted January 2, 2023 Share Posted January 2, 2023 1 hour ago, El Chapo said: Usually we're flying to waypoints that are minutes away, not hours away... It depends on the mission, but minutes are just fractions of hours anyway. 15 minutes = 0.25 hours, etc. Also, the previously mentioned FPAS MFD page will tell you how much fuel you'll have when you arrive at a waypoint, so you can just bring it up instead of trying to work it out yourself. I've found that it's fairly accurate. Awaiting: DCS F-15C Win 10 i5-9600KF 4.6 GHz 64 GB RAM RTX2080Ti 11GB -- Win 7 64 i5-6600K 3.6 GHz 32 GB RAM GTX970 4GB -- A-10C, F-5E, Su-27, F-15C, F-14B, F-16C missions in User Files Link to comment Share on other sites More sharing options...
El Chapo Posted January 2, 2023 Author Share Posted January 2, 2023 In the end it's certainly a question of habit. Having worked for ever in kg/min, I did not even thought that working in lbs/hour might even be possible Fuel management on older aircraft is done at a 10kg precision after several hours of flight, without any fancy FPAS page, so I intend to reach the same precision with the F18. I'll have to adapt the math, but in the end since I now understand where my mistake come from, I will get away with it. Learning the x 1,66 multiple table should not be that hard Link to comment Share on other sites More sharing options...
Mikaa Posted January 2, 2023 Share Posted January 2, 2023 Why not just think of the fuel burn in terms of pounds per hour and decimal hours? Then you can again divide by six if you need more precision than 0.1hr. (Not to mention, most times the gauges themselves aren’t accurate enough to truly be relied upon to that level of accuracy, but I digress) IRL it’s much easier for me to calculate remaining on-station time using this method of decimal hours, but ymmv. I agree, SI units would be easier in theory, but since I’m flying in a western country, I’ve just learned to embrace the minute/hour ratios to pph for fuel burn to the point where it’s just second nature. Link to comment Share on other sites More sharing options...
El Chapo Posted January 2, 2023 Author Share Posted January 2, 2023 (edited) In fact French planes work in kg/min, so it's not really a west/east difference. It's like mbars vs inHg for altimeter settings. For me, all comes down to speed in kts and Mach. If your reference speed is 420kt for example, you are flying at 7 Nm per minute, so that airfield 70 Nm away will be reached in 10 minutes, hence your fuel on arrival 10xFF in lbs/min. Same if you fly M 0.6, it's roughly 6 Nm per minutes, so you'll reach the same airfield in 11,5 minutes, hence another fuel. If I have a TGT 100 Nm away from push point, it will be an 11 minutes flight at 540kt, 22 minutes in and out, hence my fuel. Etc... I don't see myself working in tens of hours. Edited January 2, 2023 by El Chapo Link to comment Share on other sites More sharing options...
Mikaa Posted January 2, 2023 Share Posted January 2, 2023 Well unfortunately we don’t have the luxury of changing the units on the gauges. I’m just telling you what works for me. Is it easy working with decimal hours? No, I’d be lying if I said it was… but I’ve just learned to embrace it. Move the decimal for 6 min precision, divide by 6 for 1 min precision. And yes, nm/min is also super helpful to make the calcs a bit simpler. I’m genuinely all ears if you can think of a better way to do it. Link to comment Share on other sites More sharing options...
El Chapo Posted January 2, 2023 Author Share Posted January 2, 2023 In fact I'll keep in mind approximately 3 fuel flows: in DCS max range -> FF around 30+30=60 (x100 lbs per hour) = 100 lbs/min Max performance in high altitude -> FF around 50+50=100 =170 lbs/min Max performance in low altitude -> FF around 75+75=150 = 250 lbs/min With these 3 figures I should be able to compute everything, working the small differences with % (e.g I read FF 27 instead of 30 = it's a 10% difference that I subtract on my end result). Link to comment Share on other sites More sharing options...
Bunny Clark Posted January 4, 2023 Share Posted January 4, 2023 There's usually not even a reason to open the FPAS page unless you want to know your ideal altitude and speed. The HSI will show you your estimated fuel remaining on arrival of any selected waypoint or TACAN station. If you just want to know your fuel state when you arrive at the next waypoint, a quick glance at the HSI will tell you, no maths needed. 1 Oil In The Water Hornet Campaign. Bunny's: Form-Fillable Controller Layout PDFs | HOTAS Kneeboards | Checklist Kneeboards Link to comment Share on other sites More sharing options...
jaylw314 Posted January 7, 2023 Share Posted January 7, 2023 On 1/2/2023 at 1:19 PM, Mikaa said: Well unfortunately we don’t have the luxury of changing the units on the gauges. I’m just telling you what works for me. Is it easy working with decimal hours? No, I’d be lying if I said it was… but I’ve just learned to embrace it. Move the decimal for 6 min precision, divide by 6 for 1 min precision. And yes, nm/min is also super helpful to make the calcs a bit simpler. I’m genuinely all ears if you can think of a better way to do it. Decimal hours is a pretty common thing to see in US aviation. Alternatively, there's always the E-6B slide rule calculator Link to comment Share on other sites More sharing options...
Mikaa Posted January 7, 2023 Share Posted January 7, 2023 11 minutes ago, jaylw314 said: Decimal hours is a pretty common thing to see in US aviation. Alternatively, there's always the E-6B slide rule calculator God forbid I ever have to use that thing again haha. 1 Link to comment Share on other sites More sharing options...
oldcrusty Posted January 7, 2023 Share Posted January 7, 2023 5 hours ago, Mikaa said: God forbid I ever have to use that thing again haha. I'll be damned... I found one at the bottom of my bookshelf drawer. After 40 years 2 Link to comment Share on other sites More sharing options...
Solution El Chapo Posted January 7, 2023 Author Solution Share Posted January 7, 2023 After further testing, indeed, no issue with FF vs fuel consumption, just an issue due to units misunderstanding. It all comes down to a "human/machine interface". I'd bet a lot that the one who decided to display that FF in (lbs/hr)/100 instead of lbs/min never put his pants in a real plane. Or at least not at 150ft/540kts... Anyways, thanks for the various replies and inputs, some good came out of this! 1 Link to comment Share on other sites More sharing options...
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