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Fuel flow question


Mud

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A have a question about the fuel flow gauge. In other planes I have flown you will notice the fuel flow decrease at the same throttle setting as you increase your altitude. Yet in the Tomcat I am not seeing that behavior.

 

What am I missing? :)

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Climb up to 40000+ and go into zone 5 you’ll see a huge decrease in FF. Also in mil as well will be around 4500 to 5000 depending on atmospherics.

 

Being in 'Zone 5' will have nothing to do with 'a huge decrease in FF' - given the FF indicator doesn't display FF above MIL.

 

It will be more difficult to see fuel consumption reduction based on altitude due to the FF non-linear indication. Above 36,000' temp remains constant so efficiency drops away with further climb.

 

Edit: - contemplated explaining SFC and jet engine efficiency varying with altitude, then decided against it lol.

Try some economy testing at different altitudes using a steady ground speed...

FF.jpg.d1b00b6a9bf450f2f0a36ffcdff9c4d1.jpg


Edited by VampireNZ

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I definitely see decreasing FF with altitude gained. It’s not as easily noticeable as in the F-18 where at mil power you’ll see 120 each engine at sea level and 32 each at FL380, but there’s a clear difference.

Also notice that on our current (incorrect) tapes the scale condenses by more than double above 5k PPH, so throttle and altitude changes cause significantly smaller tape movements when FF is already above 5k PPH.

And as noted above, afterburner is not reflected in the FF tapes at all.


Edited by SonofEil

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  • 4 months later...

By 36,000ft you really mean to say the tropopause in a std atmosphere. Because unless the earth is flat, it's altitude varies significantly. From the low side of the 20's up to the 40's depends where you are, the airmass you are in, and whether you're flying thru or across a jet stream. It varies in DCS as well, and the default mission settings are standard for pressure they are not standard for the lapse rate, for a standard lapse rate you have to set it 15'C.

 

In DCS you can vary to a small degree surface temperature and you have a lot of leeway in the pressure - those will give you your atmosphere in DCS. Regrettably there is no weather physics engine in DCS [yet] to work out rain, humidity, clouds (cloud formations like CB's, fog, stratus, cumulus), vapor effects, icing, hail, rain & winds, windshears, downdrafts.

 

It would be truly amazing for the DCS engine to actually run more than just standard lapse rates, but more like dry & wet adiabatic rates & saturation rates, A humidity model as well as pressure to make some resemblance to actual weather; but we have what we have. Here's hoping Wags sees this and chimes in letting us know what the future holds :P For a start a good vertical weather engine would be awesome! just vertical you could do so much with that, think of it - some actual procedurally generated clouds, inversions, fog, rain, icing, virga! that could actually look like clouds, not these 'things' we have now.

 

i'd recommend for testing you know what the atmosphere is like 1st for your test. either run an adiabatic lapse rate to find it, or maybe there is a module that has OAT working, either way lots of ways to do this. Or the simplest make sure you run a standard atmosphere where yeah 36000' is the tropopause, make sure you ahve set 29.92Hg or 1013.25Hpa for your pressure and 15'C as your temp and you have you std atmosphere.

 

just remember the tropopause is an optimum place for the engines [not the aircraft] as general rule, but FF is more directly related to the specific mass of the air passing thru so going higher will affect it, just with the loss that the inlet temp is no longer in your favor.

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Well an F-14 thread about fuel flow is probably not a good place for visibility, however, I like where you're going and improved weather would be awesome. It's perhaps the only thing I've missed in my transition from FSX to DCS.

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