Fuel Calculation

[Steve Waite]

With IF you find out what the exact specs of the simulated plane are...

Let’s just say your plane specs claim:
6000Nmls range
400kts cruise
40000ft cruise alt

You find you only get 4000Nmls

So you can try:
250kts
30000ft
Try less load, shallower climbs, slower climb rates, and so on.

Or in IF you could set the Range Parameter to 4000Nmls and leave it at 400/40000

The route is shortest possible path, same as ATC guides you if there were no other planes.

When you get to your destination and get vectored about, you spend longer in the air and use up precious fuel very quickly, compared to cruising. Add this time to the reserve fuel time.

[Dean B]

Steve,

When you say 'You can try flying at 250kts, 30,000ft...', are you saying we should adapt the way we fly our planes to match IF's fuel calculation?

If my flight dispatch dictates that for a 800ml flight I fly at FL410 with a cruise of 0.8M (around 470kts TAS or 270 IAS), for maximum fuel efficiency, then flying at 250kts (IAS or TAS?) and FL300, will vastly increase my fuel load.

As I explained, a flight from LPPT to EGLL.

VRoute calculates I will need 8340KG including a minimum landing fuel of 910KG.

TopCat calculates 8915KG - including Reserve and with 1890KG remaining.

Ideal Flight calculates 5895KG.

According to Flight Sim Commander I used 5569KG so in theory I could have made it. I would have been in big trouble from the authorities and my Co. Boss though.

Maybe a tweak to the code?

[Steve Waite]

Of course i'm not saying you adapt to fit IF, I'm afraid you're not quite getting it Dean.

The flight parameters you have set in the Parameters screen are "wrong". You have to reduce the "range" you set in the parameters page to "increase" the fuel value you get.

Do the flight and see how much fuel you use. With Ideal flight, you record what your plane "actually does" IF does not dictate the fuel.

If you fill up your tank and fly 100 miles and run out, thats your range. You may go farther if you fly slower, that's all i'm saying.

I''ve tested those fuel calculator programs and they don't work, so I wrote IF.

My test flights in the 747 are spot on, with jetstreams added in, and flights in the baron to the minute and single teaspoonful of fuel. But I don't refer to any docs, just the real values the sim produces.

Steve

[Steve Waite]

If you turn off taxi and reserve (set to zero) and then do flights by the shortest path, allowing for ATC vectoring, you will run out of fuel as you land, if the parameters are correct.

Part of the great thing about IF is you get it to record for you the EXACT performance of the simulated plane.
So you tweak the Parameters, Range, Speed, Alt, Climb, and so on.

Because you did the flight before and put those parameters in yourself, and unless you changed your engine or wingspan since last time, the fuel will *always be roughly about the same*, allowing for weight carried and winds on the day.

Because of this fact, IF will determine the fuel EXACTLY. But you have to get the params right, and when you do, THAT is the performance of the plane in THOSE conditions of cruise speed, alt, climb and so on.

Best regards
Steve

[Steve Waite]

Ideal Flight calculates 5895KG

Concept is wrong, IF does not calculate, you told it that you want 5895KG in a round about way.
Mind you, ironically, IF was closest here, but it's just a fluke.

It's no good saying the plane does 6000Nmls and you only manage 4000Nmls, and then if you do, it's got nothing to do with IF. Unless you never had real winds aloft and air density to deal with, and IF weather does that, it's the only true weather engine.

When you get it, you will be amazed that no one has thought to do it this way. You are testing a theory in a simulation of a plane and recording those facts in IF. IF shows you the exact performance of the addon. Addon aircraft manufacturers; please take note.

Steve

[Steve Waite]

VRoute calculates I will need 8340KG including a minimum landing fuel of 910KG.
TopCat calculates 8915KG - including Reserve and with 1890KG remaining.

Um, they obviously don't work then, with those diverse results

Whereas, with the routes I'm doing in IF, the ETA and the fuel come out exactly on the button! BUT only for those planes I've bothered to find the performance of, by tweaking the params after each flight.

Unfortunatly, this appears to be a hard concept to grasp initially, because it's different to normal. But once you get it, it's easy. The easiest way to get exact results. AND the way it's done in real life, here we just use a simulated aircraft in a simulated environment instead.

Steve

[Steve Waite]

After choosing the best cruise altitude and speed, load up your aircraft with an average payload and get up in the sky. When you get there, settle in to the cruise for a minute to stabilise the plane. Pull down the Alt addon menu, and choose the IF: Main menu - Fuel Report.
You will get the maximum range of the aircraft in those conditions, best to turn off winds first.
The fuel flow is recorded and range calculated against ground speed.
Use this as a good starting point for the Approximate Range value in the aircraft Flight Parameters screen.
The route distance, and hence time, is calculated for shortest path along the route, plus departure and approach vectoring (DP/STAR) as ATC would guide it.
You would have to add Taxi time, and Reserve time. Reserve time should include for any extra manoeuvres likely, as well as regular reserve time. Perhaps you have a lot of planes active at your destination so you may get delayed on approach.
If the real aircraft uses less fuel than your simulated aircraft, check the climb rates, payload, or fuel load. Often quoted range is the maximum theoretically possible, and not realistic. Often, addon aircraft have no proper fuel scalar settings and the fuel they use is almost arbitrary.

[Steve Waite]

Ideal Flight calculates 5895KG.
According to Flight Sim Commander I used 5569KG

So you can increase the Range slightly because you had 326KG of fuel left.
You do the flight again and have 3KG of fuel left.

Now you know the exact range for those conditions, but it's only perfectly accurate for trips of that exact distance, as you need the same fuel load to start with!

Now you set your taxi time and reserve time. Then when you land, you should have all your reserve left!

[Steve Waite]

big trouble from the authorities and my Co. Boss

Right, as usual, Dean's realistic view of things helps to get aspects of IF looking right.

Reserve Minutes fuel time; Choose how long the aircraft is required to be able to cruise on reserve.

Taxi Minutes fuel time; Choose how long the aircraft may be required to taxi, go around, and make any other manouvres in flight or on the ground.

All Minutes = Cruise Fuel Minutes.

You have the main amount of fuel set by Ideal Flight, that gets you from take off to landing. Remember that vectoring into and out of airports is included, calculated with respect to nominal speeds.

Then Taxi and Manuovres fuel time, 15 minutes is the default setting. You may want 30 minutes or more if there could be traffic at the destination, with possible delays.

Now we have a clear reserve setting. [rd pre8]

Thanks Dean. Can you confirm this may be a better way to think of it?

Regards; Steve

[Steve Waite]

According to Flight Sim Commander I used 5569KG

When you get your Ideal Flight assessment, you can see all the details about fuel. If you accept the assessment, the briefing and the assessment details are added to the records, where you can check back on fuel used in the past.