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Hornet fuel consumption questions


Airhunter
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I recently did some comparisons between various aircraft in DCS as some people have stated that the efficiency of the JF-17 and the Hornet are quite high. To my surprise I found a very head-scratching engine economy and performance on the Hornet. All tests were at 30000ft, ISA-like conditions, full internal fuel and the default DCS loadout (pylons when applicable). The Hornet was the outlier across the board and did not even closely match the publically available and stated values I have found. It has by far the longest full AB time of all jets I have tested in DCS, much better economy and a much lower TSFC than most other comparable jets in DCS. Below are my test results.

 

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Especially in the chart above you can see the F110-GE-400/402's TSFC of 1,23 in FULL! afterburner. Publically available sources state a value of 1,74, which is mostly in line with comparable engines of similar thrust rating and size.

 

 

Below is another picture showing a fuel flow of 22200 lbs/h in full AB at Mach 1.63 and 30000ft. I think GE would've won a nobel prize by now if they managed to develop such an efficient engine.

 

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Now, other aircraft such as the F-14B, and F-16C match the stated values very well, the 16C's fuel flow matches the real, publically available FF charts mostly within a margin of +/- 5%. I wasn't able to find any publically available fuel flow charts for our F/A-18C and I do know the document designation of where to find those values, however this very document seems to be classified. Now my question to ED - since your aircraft are built on publically available data, what source or data did you guys use to model this? Could you please reference a source that would back the current performance of the Hornet's engines? If not, would you please consider adjusting these values based on public TSFC values for dry and wet thrust? Currently the Hornet is way more efficient than the Tomcat or any other comparable jet- nothing of the "short legs" the US NAVY was talking about all these past years.

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I started to wonder that those fuel flow figures for Hornet can not be right and after checking both DCS manual and NATOPS i noticed that IFEI (and ENG page) only show fuel flow of the main engine, it does not include FF for afterburner so no wonder those figures seemed so strange. :D

 

EDIT: Disregard, tested with scripted mission which calculates fuel flow and it seems like DCS F-18 does include afterburner FF as well (which also should be reported) so those figures are correct after all and indeed very optimistic. For example at sea level A1-F18AC-NFM-200 manual's (-400 engines) combat fuel flow chart gives FF of 79200lb/h and in DCS F-18's FF is 69318lb/h so pretty huge difference. And since -402 is more powerful it probably should have even higher FF at full afterburner.


Edited by Kapsu
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Isn't the fuel flow in hornet measured in lbs/min?

 

The info for F404-GE-400 engines shows about 900lbs/min at 30,000ft, MACH 1.54, Max power per engine.

 

Interestingly the charts don't go to MACH 1.6 at 30,000ft.

 

I did not neccessarily use the FF shown on the DDI page and IFE but total fuel burned over time (as you can see from my charts). Not every aircraft measures fuel the same way so I went the total fuel burned over X amount of minutes route and calculated the burn per hour manually. The DDI FF value is just a reference and "should" be in lbs/h / PPH - that's the most common one at least. Again, look at the charts and go tell me that seems even remotely right to you.

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Didn't test the Su-27S?

 

IIRC the full fuel jettison speed was between 20-30 minutes when using all fuel pumps at maximum speed to pump fuel around. And that is faster than the speed fuel was flowing to afterburners, yet the afterburner time in Su-27S IIRC was far lower than what it is possible to get pumped even to feeder tank.

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And since -402 is more powerful it probably should have even higher FF at full afterburner.

 

I wouldn't think that more powerful would always have to mean higher flow. Tech advances. Newer engine tech can produce more power and more efficiency (I.e. I'd assume the latest Raptor engines are more powerful and more efficient than the F-14's engines, though I could be wrong). For the Hornet's notorious lack of fuel and short legs.... you'd better believe they were doing everything humanly possible to produce the most economic engine for a fighter with a low amount of fuel capacity to begin with... but afterburner is still afterburner so something to look at.


Edited by wilbur81

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For your graphs, are you flying at constant speed? If not, your graph is invalid since TSFC is also depended on speed.

 

This.

 

So I did plot the FA-18's fuel flow curve vs the F-16's one. In-game DCS data.

 

Not saying what is right and what is wrong, but the DCS FA-18C's fuel flow plot seems to flatten earlier than the DCS F-16CM's fuel flow plot.

542526714_FFatMAXF16F18.thumb.png.a5065a1a877c94f4e62a3f65d2d8cf38.png

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This.

 

So I did plot the FA-18's fuel flow curve vs the F-16's one. In-game DCS data.

 

Not saying what is right and what is wrong, but the DCS FA-18C's fuel flow plot seems to flatten earlier than the DCS F-16CM's fuel flow plot.

 

I think this is completely normal since they have different engine, thus different SFC. And the design of the intake and the nozzel also affect the FF because FF = SFC * Thrust, and thrust is affected by intake and nozzel. Maybe the F-18 has a better intake than the F-16 at high speed (and AFAIK it should).


Edited by Kumabit
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You guys forget the F/A-18C is dual engine. The speeds I tested at are noted in the graphs, there is really no way to test this at X speed and full AB in most aircraft in DCS. It's either a static test with wheel chocks or max AB at X altitude and see where the speed settles. What is more worrying to me is the FF of around 22k lbs/h in the Hornet (per engine) while the Viper is getting close to 60k lbs/h at almost the same conditions. I also understand that without an exact thrust reading or graph calculating an accurate TSFC is almost impossible hence why I took the base published engine ratings for all my calculations.

 

Again, I am mostly wanting an answer from ED on what data they based this on as there isn't anything public out there in terms of FF charts and thrust profiles at X altitude. The FF values and AB times I measured were really odd and stood out from everything else out there. The base Hornet also isn't an exactly new design, it's already phased out by the Navy.

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if we assume the model is correct maybe it’s because differing pressure and bypass ratios ? Plus you have to factor operating RPM and air flow. The GE-F110 at 30,000LBS thrust vs. the F404 17,000LBS. If the F110 is moving more air it will need more fuel. Plus the F-16 seems to cruise more easily it may be at the cost of higher flow rates. Definitely an interesting finding though. I’d have assumed the F-18 would be less efficient do to weight, drag and having 2 moderately powered engines.

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You guys forget the F/A-18C is dual engine. The speeds I tested at are noted in the graphs, there is really no way to test this at X speed and full AB in most aircraft in DCS. It's either a static test with wheel chocks or max AB at X altitude and see where the speed settles. What is more worrying to me is the FF of around 22k lbs/h in the Hornet (per engine) while the Viper is getting close to 60k lbs/h at almost the same conditions. I also understand that without an exact thrust reading or graph calculating an accurate TSFC is almost impossible hence why I took the base published engine ratings for all my calculations.

 

The FF with different speed at the same altitude is NOT the same, so your FF graph is a CURVE for every aircraft and they are not the same. For your test, you need to do a integration on the FF curve with time to get the fuel consumption. Therefore, same burn time does not mean same fuel consumption.

 

And also, you can't just assume the FF is constant and times the time to get the fuel consumption. This is NOT how this work.

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  • 10 months later...

Hey guys, don't you need to know the thrust to compute SFC from fuel flow ?

Then how do you know the thrust at 30 000ft ?

 

Because the higher you fly, the less thrust you have.

And the thrust also changes with the speed.

 

So if you are taking bench thrust data, you got it wrong.

 

Hornet has the highest fuel fraction of your test and the lowest top speed.

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  • 3 months later...

So is ED looking into this?

The hornet is like a super fighter at the moment and outfuels everything without breaking a sweat. No wonder pilots are taking 10 actives in competitions like TACT and just fly around behind till the enemy is out of fuel and weapons... gg wp.

Ferry range on deck for hornet is also higher than Flanker. How is this possible?

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I think that there may be a factor that may be influencing the OP's test, in that I think the engine actually cannot get supplied with enough air at higher altitudes to use full fuel flow. It seems to lower the fuel flow and close the nozzles slightly. I think the test done at SL might yield different results, and this ties in with the criticism of the Hornet that it has trouble gaining speed at higher altitudes, and the Mach 1.8 limit due to intake design. I think the inlet design is sacrificing power for operational simplicity, more-so than the F-16 inlet does. I think this is reflected in how fast the two airframes go up high.

At the same time, I am not saying it isn't a problem in DCS, I just don't know.

 

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