in roadmap DCS F16 turn performance

[feipan]

He just told you.

[Machalot]

12 minutes ago, feipan said:

He just told you.

If you're talking to me, then I think you have misunderstood either my question or his answer.  At the same airspeed the aircraft can have different Mach numbers because the ambient speed of sound is different.  That starts to matter at some point between when the flow becomes compressible and when it becomes transonic.

[Hummingbird]

13 hours ago, karasawa said:

2) The speed of sound in your reference is 333 m /s, while that in game is 345 m /s. So you should not compare the turn rate under the same mach number, but under the same true speed. 

 

Are you sure? It shouldn't be if you use ICAO at 15 deg C.

[karasawa]

5 hours ago, Machalot said:

I meant, if you match TAS the Mach will be different, and how much does that difference matter? 

About 0.03 Mach

[karasawa]

48 minutes ago, Hummingbird said:

 

Are you sure? It shouldn't be if you use ICAO at 15 deg C.

Let's pick a point from the HAF manual: sea level , 0.7 Mach , 21.7deg/sec, 9G. Question：what is the speed of sound?

 

true air speed = 9*9.8/(21.7/57.3) = 233m/s

speed of sound = 233 / 0.7 = 333m/s

10 minutes ago, gortex said:

I do a lot of BFM in the Viper and this recent OB patch has brought some performance improvements back.  What I still find is that with a clean configuration the sweet spot for turn rate near sea level is at 470-480 knots.  Any slower than that and you can't sustain g.

 

This still seems faster than the EM diagrams I've seen.  Or am I incorrect?  Are we still waiting for additional changes that might bring that corner speed down a bit?

what is your fuel load?

Edited September 21, 2021 by karasawa

[Hummingbird]

2 hours ago, karasawa said:

Let's pick a point from the HAF manual: sea level , 0.7 Mach , 21.7deg/sec, 9G. Question：what is the speed of sound?

true air speed = 9*9.8/(21.7/57.3) = 233m/s

speed of sound = 233 / 0.7 = 333m/s

 

I'm talking about DCS.

[karasawa]

Just now, Hummingbird said:

 

I'm talking about DCS.

 

That's easy. You can check tacview for true air speed and mach number, and calculate the quotient. 

[Machalot]

2 hours ago, karasawa said:

About 0.03 Mach

Ha, I'm clearly failing at articulating my question. 

 

The aerodynamic coefficients are explicitly dependent on Mach number. So at constant TAS, but with different speed of sound, the Mach will be different, and the resulting CL and CD curves vs alpha will be different. So STR will be different as well.  My gut tells me this matters, but I haven't checked the math to confirm how sensitive. 

 

(Mach also affects thrust...)

 

What I'm getting at is that it might be preferable to match atmospheric conditions as well.

Edited September 21, 2021 by Machalot

[Hummingbird]

3 hours ago, karasawa said:

 

That's easy. You can check tacview for true air speed and mach number, and calculate the quotient. 

 

Simply use the ctrl + y infobar, press it twice and you get TAS.

 

My question is why you think the speed of sound in DCS is 345 m/s at SL at 15 deg C and 333 m/s on the charts?

 

The charts show performance at ICAO, that is std atmosphere, 15 deg C at SL, where the speed of sound is 340 m/s, not 333 m/s. Furthermore the speed on the chart is listed in TMN. So I don't understand why you find the need to do any calculations.

Edited September 21, 2021 by Hummingbird

[Glide]

I love all the math.  I especially love it when others do the math.  Those of us who have detents on our throttles will have noticed that full Mil power has gone from ~11000 pph to ~14500 pph.  What remains the same, however, is that in full Mil power the jet still falls out of the sky in a turning fight.  This means you need to stay in AB if you want to sustain the rate, and it shortens the time you can spend in a turning fight.  If this is close to perfection, then I will be resetting my expectations and learning to lean on the throttle more. 

[Xavven]

2 hours ago, Glide said:

I love all the math.  I especially love it when others do the math.  Those of us who have detents on our throttles will have noticed that full Mil power has gone from ~11000 pph to ~14500 pph.  What remains the same, however, is that in full Mil power the jet still falls out of the sky in a turning fight.  This means you need to stay in AB if you want to sustain the rate, and it shortens the time you can spend in a turning fight.  If this is close to perfection, then I will be resetting my expectations and learning to lean on the throttle more. 

 

In ACM I'm in full afterburner unless in specific circumstances:

1. to avoid going over ~500 knots when already pulling max G
2. in anticipation of a descending turn that I'm beginning at high speed already, which would lead to me going over 500 knots near the bottom of the turn
3. to avoid GLOC if pilot is near it
4. to avoid a 3/9 overshoot when in or near the control zone of the hostile aircraft
5. to avoid ground collision in a descending turn close to the ground
6. when defending an IR guided missile

Otherwise, instead of MIL power, consider staying in afterburner and pulling more G.

 

Any dogfighting experts feel free to correct me. I'm always looking for advice and improvement.

[karasawa]

9 hours ago, Hummingbird said:

 

Simply use the ctrl + y infobar, press it twice and you get TAS.

 

My question is why you think the speed of sound in DCS is 345 m/s at SL at 15 deg C and 333 m/s on the charts?

 

The charts show performance at ICAO, that is std atmosphere, 15 deg C at SL, where the speed of sound is 340 m/s, not 333 m/s. Furthermore the speed on the chart is listed in TMN. So I don't understand why you find the need to do any calculations.

 

My question is that I have proven the speed of sound in HAF manual is 333 m /s and why don't you believe it? You haven't learnt physics or centripetal acceleration?

 

The data in HAF manual is based on flight test, and is converted to standard atmosphere, but it does't mention its the standard atmosphere of which year. There are slight changes over time.

 

345m / s is closer to present day atmosphere. 

 

 

Edited September 21, 2021 by karasawa

[karasawa]

9 hours ago, Machalot said:

Ha, I'm clearly failing at articulating my question. 

 

The aerodynamic coefficients are explicitly dependent on Mach number. So at constant TAS, but with different speed of sound, the Mach will be different, and the resulting CL and CD curves vs alpha will be different. So STR will be different as well.  My gut tells me this matters, but I haven't checked the math to confirm how sensitive. 

 

(Mach also affects thrust...)

 

What I'm getting at is that it might be preferable to match atmospheric conditions as well.

 

Good question.

 

Lift and drag depend on true air speed and force coefficients (witch depends on Mach number), so lift and drag depend on both true air speed and Mach number. 

 

However, Lift and drag depend on true air speed by a power of 2. Force coefficients do not vary that much (sometimes almost constant) when Mach number changes. 

 

1) Air speed remains constant but Mach number changes slightly: lift and drag changes slightly.

2) Air speed changes slightly but Mach number remains constant: lift and drag changes by power of 2.

 

So I would rather keep airspeed constant instead of Mach number, which yields much smaller error.

[Machalot]

25 minutes ago, karasawa said:

Good question.

 

Lift and drag depend on true air speed and force coefficients (witch depends on Mach number), so lift and drag depend on both true air speed and Mach number. 

 

However, Lift and drag depend on true air speed by a power of 2. Force coefficients do not vary that much (sometimes almost constant) when Mach number changes. 

 

1) Air speed remains constant but Mach number changes slightly: lift and drag changes slightly.

2) Air speed changes slightly but Mach number remains constant: lift and drag changes by power of 2.

 

So I would rather keep airspeed constant instead of Mach number, which yields much smaller error.

I agree Mach is a smaller effect in general, but there is a drag divergence Mach number where that might change. 

 

There's also the matter of reducing alpha for a given G load because CL goes up with Mach. The result is that CD goes down at approximately power 2 versus alpha.  Is this comparable to the TAS effect? Hard to say without data. 

 

I also didn't mean to say it's either/or for matching TAS or Mach; rather, we should match both. 

 

 

Edited September 21, 2021 by Machalot

[SCPanda]

On 9/21/2021 at 1:21 AM, NineLine said:

Please post your data, we certainly didn't check how it performs vs other aircraft, we checked it against available reference data with SME review, thanks.

 

Test is based on GE-129 / 24k lbs GW / DI=0, see attached.

 

While not perfect, and needs a little tuning here and there, it is much more accurate than the previous version.
 

DCS F-16C Sustained Turn Tests ED.pdf 108.36 kB · 79 downloads

Thx for sharing your test data. According to your test data, DCS F-16 with 24k lbs GW and 0 DI can achieve STR of 21.2 D/Sec at 9G at 0.7 Mach (around 437 kts) at 500ft, which is really great and realistic performance.

 

However, this graph definitely shows different results. https://dcs.silver.ru/77  Test done by @totmacher

 

According to this graph, DCS F-16 (OB version 2.7.6.12852) with 10784 kg GW (23774.65 lbs, a little lower than ED's test) and no pylons (0 DI) can only achieve STR of 18.62 D/Sec at 0.7 Mach at 1000ft. Yeah I know the altitude is off by 500 ft but I highly doubt the difference would be that big. At 0.5 mach, the STR is also more than 3 degrees per second lower than ED's test. 

 

Another thing is I have tried the new FM, our DCS F-16 with 24k lbs GW and 0 DI cannot even achieve not to say maintain 9G at 0.7 Mach. At least that's what the G number in the cockpit tells me. I don't know how ED got 9G in the test. 

 

Personally, I would love to have the STR performance indicated by ED's test data. I mean, 20.6 D/Sec at only 0.5 Mach and 5.9G is absolutely amazing. Unfortunately, it just seems not true at all. 

 

@totmacher I saw that you also noticed ED's data. Would love to have some of your input in this discussion. Thanks. 

 

[SCPanda]

On 9/21/2021 at 4:48 AM, karasawa said:

Thanks for providing the data.

 

To ED F-16 team:

 

1) Do not take the "linear approximation conversion table from HAF manual" for high-precision. We are on a regime that 0.5deg/sec error could mean big difference. The correct way is to use the law "sustained G should be inverse proportional to weight" to convert the performance among different weights.

 

Using linear approximation will under-estimate F-16's performance. 

 

2) The speed of sound in your reference is 333 m /s, while that in game is 345 m /s. So you should not compare the turn rate under the same mach number, but under the same true speed. 

 

Could be the reason ED's test is way better than https://dcs.silver.ru/77 indicates. 

[Hummingbird]

14 hours ago, karasawa said:

My question is that I have proven the speed of sound in HAF manual is 333 m /s and why don't you believe it? You haven't learnt physics or centripetal acceleration?

 

The data in HAF manual is based on flight test, and is converted to standard atmosphere, but it does't mention its the standard atmosphere of which year. There are slight changes over time.

 

345m / s is closer to present day atmosphere. 

 

 

 

 

 

Refer to here: https://www.grc.nasa.gov/WWW/K-12/airplane/airprop.html

 

The speed on the EM charts is in True Mach Number under ICAO ISA.  You even get some nice small graphs with corrections for variations in temp from std. day.

 

Std. day conditions haven't changed since 1966 AFAIK. 

 

To quote:

"The ISA models a hypothetical standard day to allow a reproducible engineering reference for calculation and testing of engine and vehicle performance at various altitudes"

 

Without this standard frame of reference EM charts would be pretty pointless.

Edited September 22, 2021 by Hummingbird

[karasawa]

2 hours ago, Hummingbird said:

 

 

Refer to here: https://www.grc.nasa.gov/WWW/K-12/airplane/airprop.html

 

The speed on the EM charts is in True Mach Number under ICAO ISA.  You even get some nice small graphs with corrections for variations in temp from std. day.

 

Std. day conditions haven't changed since 1966 AFAIK. 

 

To quote:

"The ISA models a hypothetical standard day to allow a reproducible engineering reference for calculation and testing of engine and vehicle performance at various altitudes"

 

Without this standard frame of reference EM charts would be pretty pointless.

 

Then please explain this:

 

Let's pick a point from the HAF manual: sea level , 0.7 Mach , 21.7deg/sec, 9G. Question：what is the speed of sound?

true air speed = 9*9.8/(21.7/57.3) = 233m/s

speed of sound = 233 / 0.7 = 333m/s

[totmacher]

12 часов назад, SCPanda сказал:

I saw that you also noticed ED's data. Would love to have some of your input in this discussion. Thanks. 

 

12 часов назад, SCPanda сказал:

According to this graph, DCS F-16 (OB version 2.7.6.12852) with 10784 kg GW (23774.65 lbs, a little lower than ED's test) and no pylons (0 DI) can only achieve STR of 18.62 D/Sec at 0.7 Mach at 1000ft.

 

I'am used metric system in my measures. Altitude was 1000metres (don't feet). Sorry that don't wrote that. 
Now i'am update site and you can see all data right with "imperial units"

https://dcs.silver.ru/77-1728,mach,lbs,turnrate

 

DCS data
5,000 feet MSL
Sustained Turn Rate
Reference Values (Red)
Reference - 0.79 Mach at 9G = 19.5 D/Sec
Game – 0.79 Mach at 8.9G = 19.1 D/Sec

 

My measures
3,281 feet MSL
Sustained Turn Rate
Game – 0.78 Mach at 8.93G = 19.01 D/Sec

 

The data are similar but confused by the difference in 1719feet altidude

 

Later maybe i will post data for 5000 feet (or 500 feet) altitude with TrackView track file for compare.
 

[Hummingbird]

1 hour ago, karasawa said:

Then please explain this:

 

Let's pick a point from the HAF manual: sea level , 0.7 Mach , 21.7deg/sec, 9G. Question：what is the speed of sound?

true air speed = 9*9.8/(21.7/57.3) = 233m/s

speed of sound = 233 / 0.7 = 333m/s

 

Simple, base your calculation on measured load factors, and not the calculated turn rates which are often abit inaccurate.

 

Hence why I always compare measured & charted load factors at specific speeds, never turn rates. If I want precise turn rates, I calculate it based on the actual measured load factors.

Edited September 22, 2021 by Hummingbird

[SCPanda]

40 minutes ago, totmacher said:

 

 

I'am used metric system in my measures. Altitude was 1000metres (don't feet). Sorry that don't wrote that. 
Now i'am update site and you can see all data right with "imperial units"

https://dcs.silver.ru/77-1728,mach,lbs,turnrate

 

DCS data
5,000 feet MSL
Sustained Turn Rate
Reference Values (Red)
Reference - 0.79 Mach at 9G = 19.5 D/Sec
Game – 0.79 Mach at 8.9G = 19.1 D/Sec

 

My measures
3,281 feet MSL
Sustained Turn Rate
Game – 0.78 Mach at 8.93G = 19.01 D/Sec

 

The data are similar but confused by the difference in 1719feet altidude

 

Later maybe i will post data for 5000 feet (or 500 feet) altitude with TrackView track file for compare.
 

Thank you for the clarificaiton!

 

Yes please, I would love to see your test data at 500ft and 5000ft. Thank you for the hard work!

 

Also, I see that Hornet's STR really outperforms the Viper in all speed ranges. That should explain why it's basically impossible to beat a Hornet with a Viper. 

[karasawa]

1 hour ago, SCPanda said:

Thank you for the clarificaiton!

 

Yes please, I would love to see your test data at 500ft and 5000ft. Thank you for the hard work!

 

Also, I see that Hornet's STR really outperforms the Viper in all speed ranges. That should explain why it's basically impossible to beat a Hornet with a Viper. 

Stay above 10000 ft and you can out turn a hornet easily in a 2 circle fight.

[Machalot]

2 hours ago, Hummingbird said:

Simple, base your calculation on measured load factors, and not the calculated turn rates which are often abit inaccurate.

Can you expand on this? Why is this the case? 

[karasawa]

10 minutes ago, Machalot said:

Can you expand on this? Why is this the case? 

Obviously he has no idea about the turn rate. He thinks the turn rate from manual has error can cannot be trusted.

I remember during my primary school era the math teacher always cited the speed of sound as 333m/s. 

Edited September 22, 2021 by karasawa

[Hummingbird]

4 minutes ago, karasawa said:

Obviously he has no idea about the turn rate. He thinks the turn rate from manual has error can cannot be trusted.

I remember during my primary school era the math teacher always cited the speed of sound as 333m/s. 

 

 

*facepalm*