investigating F-16 F110 Underperforming in Mil Power

[Exorcet]

For a while now I've felt like the mil power performance of the F-16 was a little low, though I chalked it up to the DCS version being Blk 50 as the GE engines favor AB over dry thrust.

However I did finally get around to do some testing and it looks like there is a lack of thrust/overprediction in fuel flow even taking into account the F110's.

I have tracks attached, though due to forum rules I am not posting the source info. I can send it via message.

Summary of the issue:

Testing at DI 102 at 34015 lbs weight to compare to data at DI 100 at 34000 lbs weight

DCS shows increased Delta between speeds when accelerating under full mil power. This not only impacts acceleration, but climb and cruise, so the F-16 has a harder time getting to optimum altitude and uses too much fuel when cruising.

DCS fuel burn at 510 knots is approximately 4200 PPH while the actual value should be just under 3900 PPH.

Ideally some more testing is needed to see if this is more of an engine issue or drag issue, and it should be tested at more speeds, altitudes, and weights, but the condition that I did test is an important one as it's relevant to the F-16 in a CAP role.

F-16CFuelFlow_35000FT_102DI.trk F-16CMilAccel_30000FT_102DI.trk

[darkman222]

7 minutes ago, Exorcet said:

engine issue or drag issue

I am particularly interested if it turns out that the drag is the cause for that...

[Exorcet]

2 hours ago, darkman222 said:

I am particularly interested if it turns out that the drag is the cause for that...

Comparing AB to Mil in acceleration it looks like it's probably thrust. AB accel is much closer to the real jet, especially when supersonic. Subsonic accel was slightly underperforming, but that was probably because of imperfect flying when the jet is close to stall at the low starting speed.

[Lord Vader]

Hello @Exorcet

What values are you using to base your tests? In other words, where is the "(data)" entry coming from?

Please send that information to @BIGNEWYvia private messaging. 

Thanks for your cooperation.

[Exorcet]

Data has been sent.

[Exorcet]

This is still labeled as "PM Evidence" so I wanted to follow up. Do you need more source information?

[BIGNEWY]

Hi Exorcet, 

thank you for the PM, we will take a closer look, but our initial test show our data is correct. 

We will check for drag issues or other anomalies. 

thank you 

[Exorcet]

59 minutes ago, BIGNEWY said:

Hi Exorcet, 

thank you for the PM, we will take a closer look, but our initial test show our data is correct. 

We will check for drag issues or other anomalies. 

thank you 

Thanks for the confirmation. The F-16 model is quite good. This is not a massive error, and my flying wasn't perfect, so if it's deemed to be within tolerances I can understand.

[Spartan111sqn]

yes, my feeling is more in the drag, induced by AoA or stores, I do not know, but there is something, hornet RL pilot told me that with same loadout vipers and hornets (2xbags and empty pilons), both in MIL they were never able to catch them when in formation flying and accelerating in MIL.

 

Just for give you a hint.

[Furiz]

All I hear about Viper engine is that is very powerful, great acceleration etc etc, I can't speak from personal experience or give any evidence but DCS gives me the feeling that Viper is struggling with drag more than other planes.

[Alpiinoo]

The F-16 is a very good performance jet IRL. However, even with clean jet in DCS, it seems to have a low power.

Edited August 4, 2024 by Alpiinoo

[Glide]

Agreed.  Going over the top is the worst.  You bleed off all your airspeed, then pull the nose down, and wait...one second...two seconds...three seconds...for the afterburner to finally bring back some airspeed.  Broken.

[darkman222]

Yeah. How to bring attention to the slow speed handling and energy retention of the DCS F16 while people still flying circles for Tacview and complain about + or - 0,2 degrees per second turn rate difference to the EM diagrams, that made them lose the fight against a jet with a 3 deg / sec advantage.

[Stroke 3]

Generally the slow speed handling of the dcs F-16 feels bit janky.

[Glide]

I believe it's a limitation of the game though, no the model.  I believe they have it as correct as they can get it with the current engine.  Hopefully, the F4 is a window to what's coming. The Viper is still my fav.

[Stroke 3]

wdym? what limitation?

[Glide]

It's just the way the sim models acceleration right now.  I said "hopefully", but I just took the F4 for a ride over top and the acceleration was wonderful.  Gimme more of that!

[Stroke 3]

oh ok thx

[Exorcet]

On 3/21/2024 at 10:09 AM, BIGNEWY said:

Hi Exorcet, 

thank you for the PM, we will take a closer look, but our initial test show our data is correct. 

We will check for drag issues or other anomalies. 

thank you 

Any update on this?

[Exorcet]

I was sent a helpful suggestion to test the F-16 takeoff roll since there was some discussion on whether the acceleration issues were down to drag or thrust. I've done the tests and it looks like the thrust in mil power is giving expected results.

Test 1 - 34015 lbs 102 DI

Real KIAS at 2000 ft from brake release - 136

Sim KIAS at 2000 ft from brake release - ~135

 

Test 2 - 42000 lbs at 144 DI

Real KIAS at 2000 ft from brake release - 122

Sim KIAS at 2000 ft from brake release - ~120

 

Testing was done at Sas Al Nakheel in Hormuz at 10 ft MSL. Engine run to 90% RPM before throttle up to mil and brake release.

This suggests that drag may actually be the culprit, though there is a possibility that the thrust curve of the engine is correct at very low speeds and incorrect at flight speeds.

A response from ED @BIGNEWY @Lord Vader would be helpful. I have the source data as well, but following the procedure from last year will not post in forum.

[BIGNEWY]

5 hours ago, Exorcet said:

I was sent a helpful suggestion to test the F-16 takeoff roll since there was some discussion on whether the acceleration issues were down to drag or thrust. I've done the tests and it looks like the thrust in mil power is giving expected results.

Test 1 - 34015 lbs 102 DI

Real KIAS at 2000 ft from brake release - 136

Sim KIAS at 2000 ft from brake release - ~135

 

Test 2 - 42000 lbs at 144 DI

Real KIAS at 2000 ft from brake release - 122

Sim KIAS at 2000 ft from brake release - ~120

 

Testing was done at Sas Al Nakheel in Hormuz at 10 ft MSL. Engine run to 90% RPM before throttle up to mil and brake release.

This suggests that drag may actually be the culprit, though there is a possibility that the thrust curve of the engine is correct at very low speeds and incorrect at flight speeds.

A response from ED @BIGNEWY @Lord Vader would be helpful. I have the source data as well, but following the procedure from last year will not post in forum.

Hi, 

if you have new evidence we can look at and it is a public source please DM me. 

thank you 

[Spartan111sqn]

Hi, has an impact the air flow, the more AoA the less air flow in the engine, so less fuel burnt to keep the same stoichiometric mixture, when the aircraft is reducing the AoA the air flow is bigger and the engine can inject more fuel, so more power.

 

You can test it and see how at the same flight level, for example 250 kts FL300, push to pure MIL, then your fuel flow reach to a limit and as the aircraft is accelerating slowly and reducing the AoA, the fuel flow is slowly also increasing until it reach to the terminal velocity of the aircraft at that altitude and speed, then the AoA is stabilized and also the fuel flow.

 

Then maybe the feeling of the performance is not because of the engine, maybe the AoA or drag of stores are a bit exagerated.

 

dunno if I explained well myself.

Edited Friday at 08:22 AM by Spartan111sqn

[Spartan111sqn]

So, for me the behaviour of the aircraft "clean" is perfect, but seems that stores drag and AoA because of it is maybe too much and reduce more than it should?

 

I have heard that the handling of the aircraft a maneuverability for example at FL250 with 2xext+2xharms+all_pods+2,0,1 is easy..., this is why I said it about drag and AoA..., which is not the case, it feels under these conditions very short on power.

Edited Friday at 08:27 AM by Spartan111sqn

[Spartan111sqn]

On 3/7/2024 at 5:30 PM, Exorcet said:

For a while now I've felt like the mil power performance of the F-16 was a little low, though I chalked it up to the DCS version being Blk 50 as the GE engines favor AB over dry thrust.

However I did finally get around to do some testing and it looks like there is a lack of thrust/overprediction in fuel flow even taking into account the F110's.

I have tracks attached, though due to forum rules I am not posting the source info. I can send it via message.

Summary of the issue:

Testing at DI 102 at 34015 lbs weight to compare to data at DI 100 at 34000 lbs weight

DCS shows increased Delta between speeds when accelerating under full mil power. This not only impacts acceleration, but climb and cruise, so the F-16 has a harder time getting to optimum altitude and uses too much fuel when cruising.

DCS fuel burn at 510 knots is approximately 4200 PPH while the actual value should be just under 3900 PPH.

Ideally some more testing is needed to see if this is more of an engine issue or drag issue, and it should be tested at more speeds, altitudes, and weights, but the condition that I did test is an important one as it's relevant to the F-16 in a CAP role.

F-16CFuelFlow_35000FT_102DI.trk 176.98 kB · 45 downloads F-16CMilAccel_30000FT_102DI.trk 379.26 kB · 41 downloads

we would need data of AoA evolutions and Fuel flow, also with different loadouts.

[Exorcet]

6 hours ago, BIGNEWY said:

Hi, 

if you have new evidence we can look at and it is a public source please DM me. 

thank you 

Hi BIGNEWY, I do have support for the takeoff rollout but this looks essentially correct to me and I had included it to try to see if the issue here, if there is one, is drag or thrust related. I can still share if you'd like.

My primary question was on the original investigation as the thread is still labeled as "Investigating" and there was no follow up after the March 21, 2024 reply. Was the examination conducted? Was the F-16 level flight acceleration deemed correct?

 

Thanks

 

  

4 hours ago, Spartan111sqn said:

we would need data of AoA evolutions and Fuel flow, also with different loadouts.

I agree that more test flights would be helpful. I've shared the original tracks (hopefully they still work) so the methodology is there for anyone to copy.

 

For DI I've been using a spreadsheet.

F-16 Stores Drag dash1source.zip

Edited Friday at 01:09 PM by Exorcet