[NEED TRACK REPLAY]Acceleration lower than real F-16

[oldtimesake]

Hi,

 

Try low fuel (10%) and disable fuel burn, do a 300kts - 650 kts acceleration at sea level. The DCS F-16 spends 15.1 seconds, while the real F-16 block50 spends 13 seconds.

 

Whether the thrust or the drag profile or both are broken.

 

You can guess where the real F-16 figure comes from.

 

update: track reply file here

 

https://forums.eagle.ru/showthread.php?t=252003

Edited February 15, 2020 by oldtimesake
update track replay file

[Sayuuk]

How did you disable fuel burn in the real F16?

[razo+r]

How did you disable fuel burn in the real F16?

 

There's the option to enable unlimited fuel.

[TeamMaximus]

How did you disable fuel burn in the real F16?

 

It required the use of a KC-135T that could match the acceleration up to 650 kts while transferring fuel. :smilewink::pilotfly:

[BIGNEWY]

Hi please attach a track replay and any source data that does not break our 1.16 forum rule.

 

Please note we do already have some tweaks in progress which will be added in a future patch, so it maybe already be adjusted internally.

 

thanks

[b101uk]

some observations.

 

 

most of the references for such a thing are calculated relative to some fixed values, so are somewhat notional.

 

 

likewise the second values in such charts are clearly rounded to whole seconds.

 

 

35C OAT would add 1.24sec to the time, -5C OAT would add 0.93sec to the time.

 

 

they are relative to an ISA day so 29.92in/Hg at 15C (59F), but the test itself would be done at a different positive altitude that would give a reading of 29.92in/Hg at that altitude with an OAT of 15C at that altitude which would place that actual sea level pressure at other than 29.92in/Hg and temperature other than 15C, for example the density altitude.

 

 

by using unlimited fuel, you are causing a mass penalty, as the chart data for the F-16 block 50 with the F110-GE-129 engine says it would have used 276LB of fuel to full AB from 300kts to 650kts.

 

 

 

spool time of the F110-GE-129 engine, as the charts are for 200kias to 750kias, so spooling from power levels for 300kias to 650kias would add time not in the charts or are included in the sub 200kias zone

 

if you did it at sea level (or just above on one of the maps), you are potential in ground effect unless to did some density altitude shenanigans.

Edited February 6, 2020 by b101uk

[oldtimesake]

video:

 

 

spool time is already considered. The acceleration starts well below 300kts to make sure the engine is already full power at 300kts.

 

As for the fuel burn, 276lbs fuel does not influence that much for the acceleration time. It only affects the flying weight by 1-2%. We are talking about 15% deviation in acceleration time.

[b101uk]

video:

 

 

spool time is already considered. The acceleration starts well below 300kts to make sure the engine is already full power at 300kts.

 

As for the fuel burn, 276lbs fuel does not influence that much for the acceleration time. It only affects the flying weight by 1-2%. We are talking about 15% deviation in acceleration time.

 

 

 

multiple errors in method of testing all together compound error, fuel is only one part.

 

 

Another is in the IRL charts IAS is used, because at sea level on an ISA day IAS and TAS are the same, yet in the above video they are diverged by ~2% at ~110ft, which would indicate that despite what is said it is NOT an ISA day, otherwise at ~110ft there would be no more than ~0.2% difference between IAS and TAS, a ~2% divergence between IAS and TAS would indicate there is ~1000ft difference between altitude AGL and density altitude and/or OAT differences that diverge from an ISA day.

 

 

next the methods of rounding used is not known, we do know that the second values are clearly rounded in all the tests at all the different gross weights tested they are whole seconds recorded, but we can guess that they are using the most favourable methods of rounding they can get away with when rounding down, which could be a low as <.5sec gets rounded down or a high as <.999sec gets rounded down, meaning there could be 0.5sec to .999sec error, in other words 13sec was really 13.5sec or even 13.999sec, which is more error that gets compounded.

 

 

next I don't have an F-16 in DCS yet, but the IRL tests were at 20000lb effective gross weight at the start of the test which was inclusive of fuel, but IRL there is always an amount of fuel that is intrinsically not posable to use, so to get extra fuel mass for a margin of safety things could and would be removed from the aircraft and substituted with an equivalent mass of extra fuel while keeping to 20000lb effective gross weight, which can change the AOA at a given speed to be again more favourable for the test.

Edited February 7, 2020 by b101uk

[oldtimesake]

the 13 seconds could be 12.5 rounded up, not necessarily 13+ seconds.

[The Falcon]

...and disable fuel burn...

Try not to disable the fuel burn it could be the option that breaks something

[b101uk]

the 13 seconds could be 12.5 rounded up, not necessarily 13+ seconds.

 

 

very true, but the fact that it is clearly rounded and no one knows the rounding method employed dose cast ample doubt and an amount of deviation in conjunction with other things that produce cumulative error range.

 

 

 

 

and well if we look at it objectively, the sea level 20000lb level flight acceleration times are operationally useless, when in reality if you found yourself at such an altitude and such a slow speed with so little fuel and no weapons you would do better gaining altitude and speed rapidly so you at least have glide range to play with and more chance of exiting the aircraft in a more relaxed manner of your choosing while picking an eventual crash area for the F-16 that will cause less or no notable damage on the ground, else conserving fuel at 200kts and riding it down if you knew there was a suitable place in reach, as you still have the option of ejection.

 

 

 

 

talk about useless operational data, it can only have been rounded down, lol.

[oldtimesake]

It is scalable. If your simulation is wrong in terms of acceleration at 20000 lbs , then it is very likely that it's also wrong at 24000 lbs, 26000 lbs, 28000 lbs...

 

I will ask someone to make a track replay.

[bbrz]

I have no idea how anyone can claim that the acceleration is 'wrong' due to a 0.5sec 'error'.

[oldtimesake]

I have no idea how anyone can claim that the acceleration is 'wrong' due to a 0.5sec 'error'.

 

That is more like to be a "2 second error", give or take.

 

An error of 15% in kinematic performance is not ignorable.

[bbrz]

An error of 15% in kinematic performance is not ignorable.

Testing without actual fuel burn isn't ignorable either.

[JumpinK]

And always keep in mind: It's still WIP

[bkthunder]

Guys, there are are already 2 or 3 threads about this. I reported it first with tracks and detailed performance testing. The thread was closed with a “engine is WIP” answer.

 

https://forums.eagle.ru/showthread.php?t=252003

 

P.S. the manual tat nineline is asking about was sent to him by PM and they are well aware of that (as I am sure you are too because it is *that* manual that we all know about).

Edited February 15, 2020 by bkthunder

[oldtimesake]

Thanks you for the track replay file here

https://forums.eagle.ru/showthread.php?t=252003