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Calculating fuel consuption L/min. How?

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Hello friends, I was just thinking how to calculate the amount of fuel to a sortie using mission planner flight time. I would like to take enough fuel to complete the mission, plus emergency and climbing. We usualy lose aircraft performance if we are too heavy. So, is this a good approach to calculate the fuel consuption (continuous power)?

 

Take flight endurance (continuous) in hours divide by total fuel load and then for 60. l/m = flight_endurance(h)/(fuel load(L)*60)?

 

How to calculate fuel consumption for combat power? Supose continuous is 2200 rpm and combat 2500 rpm.  

 

l/m (continuous) - 2200

l/m (combat) - 2500

 

So l/m (combat) = l/m (continuous) * (2500/2200) is a good approach? How extra % fuel considering the estimated flight time to overcome emergency, combat and climbing? 

 

Thank you in advance. I tried to be generic but I'm interested on Bf-110 performance on different fuel loadouts. 

Edited by =BLW=Tales
Spell check.

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Understand that fuel consumption varies with airspeed, altitude and temperature. Without any published performance numbers, I would do my own testing in the QMB area on a summer map. Summer because my performance numbers will be lower. 

 

If I want an idea of fuel consumption from engine start to cruise altitude, I’d start from a parked location with the bomb load I want to carry. For this first test I would only take 10% fuel. Start, taxi, and takeoff normally, then accelerate to whatever speed you typically use while climbing up to cruise altitude. After reaching that speed I would simply keep climbing until the engines quit due to fuel exhaustion. Note (use the cockpit clock) how long it takes you to pass various altitudes, pause and look at the map to see how far from the base you are as you pass various altitudes. Now I have some idea about fuel required for the initial part of the flight.

 

If you’re a SP guy that does airstarts, skip that previous test.

 

For the cruise portion (that you are trying to calculate above) you now start your test at whatever altitude you’re going to fly, again with 10% fuel, with the bomb load you plan to carry. Again use the cockpit clock or your phone’s stopwatch to time how long your fuel lasts at max continuous power (as soon as the engines sputter pause and check your time). In SP campaigns the formation should not be cruising around at max continuous power.

 

The math problem you solve is:

X liters you start with, divided by the minutes before the engines sputter equals your fuel burn per minute. For example if you start with 120 liters and it takes 10 minutes until the engines sputter, you’re burning 12 liters per minute at continuous power.

 

Repeat this airstart, but this time set combat power and check your time before your engines sputter (or possibly overheat). The math formula is the same for this test, but in fewer minutes. Using the example above, 120 liters and it only takes 7 minutes until the engines sputter, you’re burning just over 17 liters per minute at combat power.

 

Armed with these liters per minute estimates you can easily figure fuel burn in 10 minute increments, and look at the mission map to get a sense of mission duration.

 

Or...just take 50% fuel on your next sortie.:good:

 

 

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On 2/23/2020 at 5:55 PM, =BLW=Tales said:

I was just thinking how to calculate the amount of fuel to a sortie using mission planner flight time.

400 L per engine per hour and you should be fine. Don't calculate on the deciliter, you're not in the airliner business.

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S!

 

As ZachariasX wrote, I also calculate roughly 400 liters per hour (per engine where applicable) and based on missions flown before. Usually an hours worth plus some extra in case of leak or prolonged combat etc.

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@=BLW=Tales taking a cue from two guys who I admire and respect it's either 400 liters per hour or 800 liters per hour. I genuinely have no clue. 

 

@ZachariasX suggested 400 liters per hour which is ~6.7 liters per minute

@LLv34_Flanker suggested 800 liters per hour  which is ~13.3 liters per minute

 

Since you specifically mentioned the 110, I ran a test on the Rhineland summer map in the Bf110 E-2. I did an airstart at 600 meters, 10% fuel which is 130 liters, and selected a fairly common load of 2 x SC 500 and 4 x SC 50. At spawn in I pushed the power up to max continuous and waited for the "out of fuel" warning. Pause when you see the message and look at the cockpit clock. In this "dirty" trial, 130 liters of fuel lasted 13 minutes and a couple seconds. 130 liters divided by 13 minutes is 10 liters per minute or 600 liters per hour at a pretty light gross weight.

 

For the second trial the only condition I changed was removing the external stores (bombs). Surprisingly or not, the "out of fuel" message came on at the 12 minute mark. Why the discrepancy? In this trial my airspeed was steady at 420 km/hr while it was only ~370 km/hr in the previous. But the drag and gross weight numbers were lower. Puzzling to say the least, but this is entertainment software not a full fidelity aircraft simulator. The takeaway from this trial is 130 liters divided by 12 minutes is 10.8 liters per minute...round off to 11 liters per minute or 660 liters per hour...but round off to 700 liters per hour.

 

Armed with these two numbers, I would go with their ballpark number of 800 liters per hour as it gives you a cushion or reserve if you prefer. 

 

On the E-2, 50% fuel load is 640 liters, giving you a conservative mission planning time of 48 minutes (640 liters divided by 800 liters/hour equals .8 hours). 

 

MEA CULPA @ZachariasX

After carefully re-reading your post I see that you indeed said 400 liters per hour PER engine. :blush:

 

Edited by busdriver

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I use a method similar to busdriver. Select quick mission with no enemies and a standard amount of fuel that you want to test ie for the pe2s87 I used 520 litres, that spare 20 is to get the plane set up in flight and on a good course. You can then speed up the game to x8 and watch the fuel gauge. Pause the game whenever it reaches a marker ie 400ltr, 300ltr and open the map. I then use the il2missonplanner software/app to accurately record distances and time flown.  By hitting ‘restart mission’ you can change the payload but have all the other conditions identical to the first run. You can then make a detailed chart that will help make a quick reference guide. So in this example when I fly the pe2s87 I know that when I hit 200 litres of fuel I have about 100km or a little over 15 minutes to get home (but that can be extended by dropping the fuel mix- figures I have in a separate table, can’t give all the data away ;) 

E69521B9-078A-4DC8-9041-4A55FFFF7EA3.jpeg

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Test the plane in qmb. Use minimal fuel, write the liters down. Spawn, set the engine settings you want to test. Wait until the engine quits. Press finish flight and write down the mission time. There you have it. Liters/min.

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This is of limited help. A flight consists of several power ratings. You need to take off, you need to climb, you cruise, etc. You can extend your flight time considerably by reducing rpm and mixture. The longer you fly, the better your mileage as (ok, in real life) you cruise on an efficient setting. A longer flight will make the most economic part longer, while leaving the other parts the same.

 

When I said 400 L per engine per hour, this is a generous amout that works for all, even the thirsty engines and let you come home. You can fly for one hour in the Mustang burning 250 L or so. If you plan tp fly three hours, you don't really need 800 L, you can cut that a bit, depending on what you plan to do in that time. At max power and rpm, the Merlin will burn 400 L in a bit more than half an hour. How so?

 

If you are interested in fuel per hour, then you can use this rule of the thumb:

 

A 30 L engine (~36 g air per cycle) burns 2.2 g fuel per cycle. At 1 ata. At 2 ata, it burns 4.4 g plus extra fuel for the rich-rich setting, it is more than twice of that, but say double for the mix and double for the displaced volume making it 8.8 g for the 60 L of air. Per cycle.

 

At 3000 rpm i thus get 1'500 cycles per minute.

 

At 1 ata, I get 1'500 * 2.2 * 60 = 198'000 g or 198 kg of fuel burned per hour, or 198 / 0.75 = 264 L per hour

 

At 2 ata, I get four times that much, namely 1'056 L per hour !

 

So you can see, when I stated 400 L of fuel, this is flying at 1.2 ata ot maybe 45 inches. If you have the throttle full forward at 2 ata in a 45 L engine, you'll burn about 1'500 L in one hour!

 

There are people who say that the Bf-109 "can cruise at 600 km/h" (I vaguely remeber such written by someone). Now if you look at how much goes into that engine at a rating that lets it do 600 km/h, then you know with 400 L at hand, you're hopping. Not cruising. A 20 minute timer would be "inifinte" for practical purposes.

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11 hours ago, DerSheriff said:

Test the plane in qmb. Use minimal fuel, write the liters down. Spawn, set the engine settings you want to test. Wait until the engine quits. Press finish flight and write down the mission time. There you have it. Liters/min.

 

Wow...great idea. 😂

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3 hours ago, busdriver said:

 

Wow...great idea. 😂

image.thumb.png.3e4774a1e2233bc9368080f82baa52dc.pngT

 

Thats how I quickly tested many planes, takes only a few minutes, especially with the time compression feature.

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