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How to calculate your current flight time and fuel flow oscillations


Vitormouraa

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Hey guys,

 

Today I just wanted to show you a quick, easy way to have a rough idea of your current Flight Time. But first of all, I'd like to say that these methods, aren't by any means, professional ways to calculate your exact time available in the air, instead, it's just a quick way to find out your current flight time.

 

But why current flight time? because your current flight time (let's call it CFT) varies quite a lot depending on the atmosphere such as temperature, altitude, flight conditions such as speed and finally, PLA (Power Lever Angle).

 

There are two methods to find out your CFT;

 

1° Method: Take your total fuel, subtract from your bingo, then the result is divided by your current Fuel Flow (FF - pph), after this, you should multiply the result by 60 (60x). The result should be your CFT in minutes.

2° Method: Take your total fuel, subtract from your bingo to find out your usable fuel, divide by your current FF (Fuel Flow - but this time, it should be in pounds per minute of fuel ppm, instead pounds per hour pph). The result should be your CFT in minutes just like the 1° Method. This method is actually used in real life operations (TOT-BINGO)/FFppm. Also special thanks to Chicken from our Discord :) To find out your PPM is very simple, take your PPH and divide it by 60. Do the opposite to find out your PPH.

 

 

Atmosphere conditions: +15°C, 29.92 inches of mercury (standard pressure).

 

1° Scenario using the first method:

 

My flight conditions are as follows:

 

250 KIAS, 220ft altitude (let's call it Sea Level - SL)

 

FF: 8,760PPH Total usable fuel: 3,800= 3,800/8,760= 0.433*60= 26 minutes of flight.

 

 

5rkkGkd.jpg

 

 

2° Scenario using the second method:

 

My flight conditions are as follows:

 

250 KIAS, 15,000ft altitude

 

FF: 123PPM Total usable fuel: 3,800= 3,800/123= 30 minutes of flight.

 

 

IVBgCFx.jpg

 

 

3° Scenario using the second method again:

 

My flight conditions are as follows:

 

250 KIAS, 25,000 ft altitude

 

FF: 0.99PPM Total usable fuel: 3,800= 3,800/0.99= 38 minutes of flight.

 

 

HQXCwoL.jpg

 

 

-----------------

 

Important notes: As I said above, your CFT will vary as soon as you increase/decrease your Indicated airspeed, change your altitude or increase/decrease your throttle. Also, I was using Infinite fuel in order to have the same value at all times, so doing that you are actually able to see the differences. 26 minutes, 30 and 38.

 

Why does the fuel flow vary so much? Well that's because the engine has to adjust its FF in order to work properly, as you increase your altitude, the pressure decreases, and air density decreases as well, so the engine has to "trim out" the fuel flow in order to keep the engine under normal conditions, temperatures and others.

 

I did this based on the Harrier engine, but you can do this for any aircraft, as long as you have Fuel Flow meter and your usable fuel or total fuel subtracted from the bingo.

 

Never forget to calculate the Bingo fuel, you need to go home after you finish your mission!

 

Thank you guys, I hope that was useful. If you have any suggestion or correction, please let me know.


Edited by Vitormouraa
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  • 4 months later...
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  • 2 weeks later...
3° Scenario using the second method again:

 

My flight conditions are as follows:

 

250 KIAS, 25,000 ft altitude

 

FF: 0.99PPM Total usable fuel: 3,800= 3,800/0.99= 38 minutes of flight.

 

 

HQXCwoL.jpg

 

 

Small typo mistake.

It isn't 0.99PPM but 099PPM off course :thumbup:

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  • 1 year later...

Hi guys, I know I am coming late to the party and I would guess you all have figured it out by now, but the thought I throw my 2 cents in about fuel calculations in the Harrier. The calculation is always based on the Airspeed and altitude you are at so that is standard,. But I have so much to do in the harrier I need something quick. Now Vitormouraa calculations look good to me but way to much math in the head. I only care how long I can fly so try this instead, Let's say your fuel flow is 62PPM I would round this down to 60 PPM, I then multiply by (x10) ten this gives me the amt. burned in 10 minutes or you can use the full 62PPM and end up with 620 for 10 minutes or 600PPM for 10 minutes. I then multiply this by 3 to get 30 minutes and if I want the fuel for and hour multiply by (X2) two. Now at a glance you can estimate how much flight time U have at this current speed/altitude. This will only give you the approximate time you have but the calculations are quick and easy. I would not worry to much about BINGO fuel if you have to figure that out your already in trouble, but by subtracting BINGO from total fuel you can approximate your usable fuel. If you are attempting to calculate time and distance to go to a recovery base just convert your ground speed to miles per minute measure the distance off the F10 map or just estimate the distance and the calculation is easy because you know how much fuel it will cost you (approximately) because you know what 10 minutes of fuel will be..... I just trying to keep it simple, If I have figured anything wrong please let me know.

 

 

WeakLink

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  • 6 months later...

You seem to calculate things from the Pounds Per Minute (PPM) value, while I calculate from the pounds of fuel in tanks to maintain general idea how long I can operate.

 

So if I have 4300 fuel left, then I divide it with 100. So I have 43.

That means with 43 minutes at 100 PPM I am empty.

Now, I can keep the PPM under 100 fairly easily like at 80-90 PPM, so I know that I have plenty of reserve.

 

So, when I know I have 43 minutes I can use just the navigation system to check for the distance and time on target, like select the last waypoint or any waypoint near landing.

 As I know that speed in Knots equals distance in Nauticle Miles (1 knot in hour is 1 nmi). I know how far I can go in an hour.

So 350 knots is 350 nmi and if I have 43 min flight time, I know I have 3/4th of the distance to go.

If I have distance to boat 130 nmi, then I can check 350 nmi vs 130 nmi and just play the odds quickly. What is that I have more than twice the required fuel to fly there at current condition.

 

I try not to calculate fuel consumption as accurately as possible, because I like to have reserve for whatever reasons there might be. Be getting lost, to speed up, fly at lower, avoid something etc. I like to keep a 15 min accuracy for the flight time when at distance. In closer and lower fuel amounts I calculate in 5 minutes if not even less in emergency.

Like I have 800 pounds of fuel left, that means 8 minutes at 100 PPM
and I check how far I can get with my speed (ie 290 knots) so about 35 nmi. (290/60*8=38).

 

As in normal situation, I can always try to maintain 100 PPM condition. If I get below that, all is good. I can always dump the extra fuel if weight limits doesn't allow.

But I do not want to situation where I am 100 pounds on the moment I am at approach and I have 1-2 nmi to go.

And this is why I like to set bingo often to 1200, as it gives me 12 minutes at 100 PPM. And with 12 minutes reserve
I can often fly 60 nmi at 300 knots. And 60 nmi is about 110 km. So that is plenty to operate around a FARP/FOB.

 

Edit: As you can see, while your method is all fine and good for accurate calculation, I use it on Hornet or Viper as there I don't have luxury to operate from a FARP like I can with Harrier.

 

And I have custom to perform multiple sorties from a FARP with harrier, so it is constant quick attacks, returning to FARP to rearm and back to action. You learn quickly to estimate required fuel and ammunition for the sorties. Like with a Harrier a 3000 pounds is plenty for me. I know how much I can do with 4x Mk.82 and 38 rockets, and still loadt extra fuel to be able extend attack maneuvers safely. While with Hornet that 3000 is a value that I am looking for to turn from the combat zone as likely boat is at 150-200 nmi distance to begin with. So think the difference where FARP is 20-30 nmi from the action, vs that boat is at almost 10x the distance.

 

The Hornet method to provide Fuel Flow Per Hour is nice, but it is for long distances.

Like fly at 450 knots and you know you can reach 450 nmi with an hour.
 And your fuel flow tells you value x 100 that is to hour.

So value 75 tells you consume in an hour 7500 pounds, and then you reference it to your value and it reads 3000, you know you have less than 30 min flight time. So less than half the nmi your knots indicates.... So about 200 nmi.

 

So while many do say that Harrier has "short legs", it actually has far more capabilities than Hornet or Warthog as it can operate from a FARP/FOB.

A well planned FARP is easy to land, you get armed and fueled and you are heading back to action in 5 min from the approach.

How far does Hornet fly in 5 min? Exactly, not far at all...

 

 

Edit: Corrected the layout as it got broken on last edit for some reason.

And slight addition:

 

Easy way to just estimate the capabilities of flight range and time is IMHO this:

 

Check how much you have fuel. Example 4300 is converted as 43. This is same as flying with 100 FFP. So now you have knowledge that you have 43 minutes fuel to fly if your Fuel Flow Per Minute is 100.

 

Now you can take your actual fuel flow, example 72 FFP and you can compare it to that 100. That 72 is from 100 about 25% (28% to be accurate) less.

If your fuel amount gave with 100 a 43 minutes, now you can take your 25% and increase your 43 minutes by 1/4th.

That means 1/4 of the 43 is 10 minutes more, so in total about 53 minutes flight time.

 

And if you look current flight speed, you know that in an hour you can cover that distance in nautical miles. So 53 min from 60 min is about 10 minutes less, so 1/6 less. So you can take your speed like example 287 knots, round it to 280 nmi and then take 1/6 away from it so about 50. So you can see that you have about 230 nmi to fly.

 

 


Edited by Fri13
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  • 1 month later...

I've used the 1000 lb rule:

  • 1000 lbs for initial taxi and climb to cruise altitude. Less if you don't have to wait.
  • 1000 lbs per 100 miles of cruise
  • 1000 lbs per 10 minutes of playtime

With a steady left hand, these are conservative estimates with some built-in safety margin.

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  • 2 weeks later...
On 1/25/2021 at 8:38 PM, Fri13 said:

You seem to calculate things from the Pounds Per Minute (PPM) value, while I calculate from the pounds of fuel in tanks to maintain general idea how long I can operate.

 

So if I have 4300 fuel left, then I divide it with 100. So I have 43.

That means with 43 minutes at 100 PPM I am empty.

Now, I can keep the PPM under 100 fairly easily like at 80-90 PPM, so I know that I have plenty of reserve.

 

So, when I know I have 43 minutes I can use just the navigation system to check for the distance and time on target, like select the last waypoint or any waypoint near landing.

 As I know that speed in Knots equals distance in Nauticle Miles (1 knot in hour is 1 nmi). I know how far I can go in an hour.

So 350 knots is 350 nmi and if I have 43 min flight time, I know I have 3/4th of the distance to go.

If I have distance to boat 130 nmi, then I can check 350 nmi vs 130 nmi and just play the odds quickly. What is that I have more than twice the required fuel to fly there at current condition.

 

I try not to calculate fuel consumption as accurately as possible, because I like to have reserve for whatever reasons there might be. Be getting lost, to speed up, fly at lower, avoid something etc. I like to keep a 15 min accuracy for the flight time when at distance. In closer and lower fuel amounts I calculate in 5 minutes if not even less in emergency.

Like I have 800 pounds of fuel left, that means 8 minutes at 100 PPM
and I check how far I can get with my speed (ie 290 knots) so about 35 nmi. (290/60*8=38).

 

As in normal situation, I can always try to maintain 100 PPM condition. If I get below that, all is good. I can always dump the extra fuel if weight limits doesn't allow.

But I do not want to situation where I am 100 pounds on the moment I am at approach and I have 1-2 nmi to go.

And this is why I like to set bingo often to 1200, as it gives me 12 minutes at 100 PPM. And with 12 minutes reserve
I can often fly 60 nmi at 300 knots. And 60 nmi is about 110 km. So that is plenty to operate around a FARP/FOB.

 

Edit: As you can see, while your method is all fine and good for accurate calculation, I use it on Hornet or Viper as there I don't have luxury to operate from a FARP like I can with Harrier.

 

And I have custom to perform multiple sorties from a FARP with harrier, so it is constant quick attacks, returning to FARP to rearm and back to action. You learn quickly to estimate required fuel and ammunition for the sorties. Like with a Harrier a 3000 pounds is plenty for me. I know how much I can do with 4x Mk.82 and 38 rockets, and still loadt extra fuel to be able extend attack maneuvers safely. While with Hornet that 3000 is a value that I am looking for to turn from the combat zone as likely boat is at 150-200 nmi distance to begin with. So think the difference where FARP is 20-30 nmi from the action, vs that boat is at almost 10x the distance.

 

The Hornet method to provide Fuel Flow Per Hour is nice, but it is for long distances.

Like fly at 450 knots and you know you can reach 450 nmi with an hour.
 And your fuel flow tells you value x 100 that is to hour.

So value 75 tells you consume in an hour 7500 pounds, and then you reference it to your value and it reads 3000, you know you have less than 30 min flight time. So less than half the nmi your knots indicates.... So about 200 nmi.

 

So while many do say that Harrier has "short legs", it actually has far more capabilities than Hornet or Warthog as it can operate from a FARP/FOB.

A well planned FARP is easy to land, you get armed and fueled and you are heading back to action in 5 min from the approach.

How far does Hornet fly in 5 min? Exactly, not far at all...

 

 

Edit: Corrected the layout as it got broken on last edit for some reason.

And slight addition:

 

Easy way to just estimate the capabilities of flight range and time is IMHO this:

 

Check how much you have fuel. Example 4300 is converted as 43. This is same as flying with 100 FFP. So now you have knowledge that you have 43 minutes fuel to fly if your Fuel Flow Per Minute is 100.

 

Now you can take your actual fuel flow, example 72 FFP and you can compare it to that 100. That 72 is from 100 about 25% (28% to be accurate) less.

If your fuel amount gave with 100 a 43 minutes, now you can take your 25% and increase your 43 minutes by 1/4th.

That means 1/4 of the 43 is 10 minutes more, so in total about 53 minutes flight time.

 

And if you look current flight speed, you know that in an hour you can cover that distance in nautical miles. So 53 min from 60 min is about 10 minutes less, so 1/6 less. So you can take your speed like example 287 knots, round it to 280 nmi and then take 1/6 away from it so about 50. So you can see that you have about 230 nmi to fly.

 

 

 

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