fuel consumption and flight planner

[jgf]

I've had problems with several add-on aircraft not having anywhere near the fuel requirements projected in the default FS9 flight planner. Recently tried a short flight, Alabama to Arizona, in a 707; the flight planner showed 72000lbs fuel required, I loaded 90000lbs. Before I'd even climbed to altitude FS was popping up the "fuel is critically low in the selected tank..." message; though the FE station showed plenty in all tanks. About halfway across Texas, 16000ft, 250kt, I ran out of fuel.

This particular aircraft was a FS2k2 model "upgraded" to FS9, but I've had similar problems with FS9 native aircraft. Is there anything I can do to have the flight planner give me correct fuel amounts?

[Capt.Propwash]

how many tanks do you have on the craft?   did any of the tanks still show FULL or 1/2 empty? Did you have your Fuel Crossfeed switch turned on?

Some planes I have learned, suck the fuel only out of the Center tank, YOU (the pilot) manually have to Feed the Center tank from the Right and Left wing tank.  (i know this sounds stupid, and it is, but there have been a few that have done this).

at the time of takeoff, till you got to your cruise altitude when you got the "LOW FUEL WARNING", were you at 100% full throttle, or did you have the throttle open just enough to sustain 250 KIAS?????? If you were at full throttle the whole time, you just
just opened the fuel valves all the way and wasted your fuel due to consumption. Nothing (that I know of) can really be done about it. other than reduce your throttle a little bit on the climb out.

[jgf]

The aircraft had seven tanks (L/R main and aux, three center);  I had removed some fuel from the wing tanks and one center tank, all crossfeeds were active.  Climb was 600ft/min, about 230kt, throttle probably around 80% (higher rate of climb or less throttle caused stall warnings;  had a full load of passengers and cargo, but well within specs, taking off a night in a blinding thunderstorm).  I leveled out at 16000ft and activated the AP,  was near the MS/LA border when I checked fuel - approx 41% remaining.   Had been getting the low fuel warning almost from takeoff.

At first I considered this due possibly to a less than optimum conversion from FS2k2, but remembered other aircraft, prop and jet, GA and commercial, with similar problems (though not as bad as this).  Though occasionally the error is in the other direction:  a long distance flight in a light single, which should have been at the limit of a full tank, saw me landing with 40% fuel remaining.  I assume the flight planner is using parameters in the air and/or cfg files to compute fuel usage;  since the amount of fuel is easily ascertained, that leaves the fuel flow scalar to tweak, but is there anything in the air file which overrides this.  (I've been using flight sim since the early days of FS98, but it's only been the past couple of years I've been learning to do things "by the book" and thus noticing inaccuracies.)

[jgf]

An instance of the default planner erring in the opposite direction.  For a flight from LaGuardia to KLAX (approx. 2100nm) using John White's L-049A (range of 3000+nm), the planner said I would need more fuel than the plane carried!  Taking off with full tanks and economic cruise I landed with 31% fuel remaining - which implies the aircraft files are correct and the flight planner has problems ...but it was dead on for a flight from Honolulu to Tokyo in a Posky 747.

So.  What to do for accurate flight planner information?

[Nav]

Coincidence, jgf! Just this afternoon, I've acquired the Abacus Constellation and started on one of my 'customary' round-world trips - the first leg being Melbourne to Cocos Islands Intl., just over 3,000nms.

Sure enough, the flight planner told me that I'd never make it! But after getting to height and settling down 'in cruise' at 240 knots with the mixture leaned off etc., I look like making it OK. Unless the winds screw me, of course!

The Flight Planner is great in most respects, but wildly inaccurate on fuel. I suspect that the fuel figures were just 'estimated,' rather than based on testing. Or maybe they just 'flew' the aeroplanes at low altitude for a short distance with mixture full rich, and then noted the amount used.

But the problem is easily solved by doing your OWN short test flight and calculation. Which adds interest, too...... After all, it's 'only a game.'

I would recommend that anyone wanting to do any 'serious' long-distance flying just checks the consumption of the chosen aeroplane in gallons per hour over an hour of actual flying, with mixture etc. right and revs at the 'correct' level.

[JerryH]

jgf, I believe part of your problem with the 707 is the cruise altitude of 16,000 feet and airspeed of 250 kts (250 KIAS?).

This aircraft is designed to fly at a much higher altitude and speed. At your flight conditions, the fuel flow rate will be excessive. I would suggest cruising at 30,000+ feet at 300+ KIAS. Climb with the throttle set at no less than 90% N1. In fact, for testing purposes you might try Full Throttle during the climb.

Rerun your Alabama to Arizona flight and let us know if it made any difference.

Regards,
JerryH

[jgf]

The flight planner gave the cruise altitude of 16k ft (it did seem low, but who am I to argue;  I've never flown anything but off the handle or into a rage).  I'm suspecting perhaps this particular aircraft just wasn't a good conversion from FS2k2;  250kt was almost full throttle and it flew in a noticeably nose up attitude (have been told many aircraft do, so didn't think it too odd at the time).

[JerryH]

I'm pretty sure the flight planner's altitude is the minimum required to clear obstacles enroute. Anything above that is your option.

[Stewy44]

A good rule of thumb when flying the tin:

Cruise FL = Trip Distance in NM

Flight - 60 NM
Cruise Alt - FL 60 (6,000 ft)

Cheers

[Nav]

Just for interest, made it to Cocos Islands Intl. with fuel in hand.

Trouble was, though, that the Abacus Connie has a suitably 'old-fashioned' autopilot. For example, you can't just tell it to take you to say 25,000 feet and level out - you have to level out manually and then 're-engage' the AP once you're 'straight and level.'

Beyond that, the model doesn't appear to 'support' GPS approaches - I had to land the darned thing manually in 5-mile visibility...........

Anyway, down on the ground, 'safe and sound.' Thankfully, that lovely Connie model goes exactly where you point it.  And I know now that it can make over 3,000nms. on full tanks.

Next stop Seeb Intl., Oman.......

[Stewy44]

the Abacus Connie has a suitably 'old-fashioned' autopilot. For example, you can't just tell it to take you to say 25,000 feet and level out - you have to level out manually and then 're-engage' the AP once you're 'straight and level.'

Beyond that, the model doesn't appear to 'support' GPS approaches - I had to land the darned thing manually in 5-mile visibility...........

Wouldn't that be realistic for most Connies?  Sounds like quite an adventure - post some pics please!

[Nav]

"Wouldn't that be realistic for most Connies?"

Yair - that's the problem, I've got lazy in my old age......

Don't do screenshots any more, but I've messaged you with my email address. Give me yours and I'll email a video. Really is, to my mind, a 'special' (meaning 'different') aeroplane.

[Gringo6]

Go over to:

"www.simviation.com/-HJG Boeing Panels" and download the "B707 Fuel Management Tutorial"

Believe this will help with the 707 flight.

Oh yes, eliminate the quotation marks from both of the above.

[Gringo6]

Since you say the airplane's fuel consumption is ok in FS2k2 and FSX it might be useful to look at the "aircraft.cfg" file of the aircraft in each version of Flight Simulator to see if they differ.

There are three places to look:

Look under [GeneralEngineData] at the "Fuel_Flow_Scalar",
is it the same for FS9 and for FS2k2 & FSX ? It probably should be.

Look under [TurbineEngineData] at the "fuel_flow_gain",
is it the same for FS9 as for FS82k2 and FSX ? Again it probably should be. While you're there look at the "static_thrust" value. Is it the same in all three versions of F/S?

Look under [jetengine] at the "thrust_scalar", is this value the same for all three? Again it probably should be.

This where the fuel flow values are set. If they are all
compatable then the problem must be with the flight planner.

[Stewy44]

This is a cool fuel planner as well.

http://fuel.aerotexas.com/