DCS World Flight Modelling Principles

[Wags]

Dear DCS Pilots,

 

DCS World Flight Modelling Principles document: https://www.digitalcombatsimulator.com/upload/iblock/dcc/DCS FM principles plus MiG-29 P-47 F-16.pdf

 

Perhaps the least understood by customers, and the most complex task for us, is the creation of aircraft flight dynamics for DCS World aircraft. To help shine some light on this mysterious subject, our flight model engineering team created the linked document to share the sources we use, the fundamental principles behind the engineering, and the techniques we use to create and test the most accurate flight models possible.

 

It is our hope that with a better understanding of the process that you will truly appreciate the time and effort that goes into creating a flight model for DCS World and why it is not a speedy or simple task.

 

Thank you and kind regards,

The Eagle Dynamics Team

[Leaderface]

I allways wanted to know some of this stuff, so: Thanks.

It seems that (with the work over the years) you are now better guessing a flight model.

And building a plane on scale gives you data to work but accurate data of the movements of the alerons under pressure, engine data, etc. needs to be verified on the real aircraft or with the constructor or all the work might be wrong later.

And is military data, so things are not very easy to obtain.

Can you tell us how many things are automated by the flight model and how many are tunned to accomplish the experiences of the real pilots experiences?

[SVgamer72]

Amazing!

 

Thank you WAGS and ED. You made my little Grinch heart grow 3 sizes reading this post!

[cubanace]

Thank you.

[Beltza]

Great Wags, thank you.

[UrgentSiesta]

REALLY great to see nitty gritty stuff like this - thank you!

[probad]

nobody that actually needs to read this will

thats the irony

 

thanks though

[Raisuli]

I am curious why you calculate TAS using air density at a particular altitude when the speed of sound (in air) is dependent on temperature and not density.

[Davee]

I am curious why you calculate TAS using air density at a particular altitude when the speed of sound (in air) is dependent on temperature and not density.

 

Surely as I recall physics, the speed of sound is dependent on both and air density is affected by temperature? Higher temps - lower density and vica versa. So the base for calcs would be density?

[wilbur81]

Thanks guys! I hope you know that, as an avid military flight sim fan since Falcon 3.0, I have always assumed that the flight modeling was THE most challenging aspect of what you guys do... and it is what you're great at. :thumbup:

[shagrat]

I am curious why you calculate TAS using air density at a particular altitude when the speed of sound (in air) is dependent on temperature and not density.

So what happens to any fluid(gas) if its density increases? ...and if the density decreases? So how does an airfoil produce lift? Now you just need to connect the dots.

[Raisuli]

So what happens to any fluid(gas) if its density increases? ...and if the density decreases? So how does an airfoil produce lift? Now you just need to connect the dots.

 

 

I'd rather do the math.

 

 

Vsound=SQRT(adiabatic constant * gas constant * absolute temperature/molecular weight of gas)

 

 

Not seeing density anywhere in there. We're not talking about lift, we're calculating TAS from MACH, and MACH is calculated against the speed of sound.

 

 

Still confused, but thanks for trying.

[Moa]

I'd rather do the math.

 

 

Vsound=SQRT(adiabatic constant * gas constant * absolute temperature/molecular weight of gas)

 

 

Not seeing density anywhere in there. We're not talking about lift, we're calculating TAS from MACH, and MACH is calculated against the speed of sound.

 

 

Still confused, but thanks for trying.

 

They're working in dimensionless units.

[Moa]

If anyone wants to really understand the ED document or is creating their own flight model (I am) here are three books to really help get you up to speed:

 

1. Mechanics of Flight, 2nd Edn Warren F Philips

 

 

https://www.amazon.com/Mechanics-Flight-Warren-F-Phillips/dp/0470539755/

 

2. Applied Computational Aerodynamics: A Modern Engineering Approach (Cambridge Aerospace Series)

 

 

https://www.amazon.com/Applied-Computational-Aerodynamics-Engineering-Cambridge/dp/1107053749

 

3. Numerical Recipes 3rd Edition: The Art of Scientific Computing 3rd Edition

 

 

https://www.amazon.com/Numerical-Recipes-3rd-Scientific-Computing/dp/0521880688

 

 

Mechanics of Flight - gives you an understanding of aerodynamics and dynamics (the physics of motion). It includes a chapter on the equations of flight in matrix form suitable for use in a flight simulator. It goes over the such subtleties as of the differences in sideslip determined from experimental data vs that obtained from calculation (don't mix them up !).

 

Applied Computational Aerodynamics - shows how aircraft performance can be estimated without access to a windtunnel or the aircraft. ED are doing this with their CFD modelling (bravo !).

 

Numerical Recipies - shows the techniques for non-linear fitting where you can take the observed or computed aircraft performance curves and fit to get the fundamental aircraft parameters which characterise the performance.

 

Hopefully that helps jump-start anyone with the inclination to get into this stuff (there have been aerospace engineering students on these fora in the past).

 

Thanks Wags for the technical overview. It won't stop that whining noise here, but still great to see.

[Yo-Yo]

I am curious why you calculate TAS using air density at a particular altitude when the speed of sound (in air) is dependent on temperature and not density.

 

Where did you see this calculation??

[Eldur]

Thanks guys! I hope you know that, as an avid military flight sim fan since Falcon 3.0, I have always assumed that the flight modeling was THE most challenging aspect of what you guys do... and it is what you're great at. :thumbup:

 

Literally this. They really moved three steps forward with Flaming Cliffs back in the day, and have even been improving from that point on. The old SFM were kinda bland and dull, but the new Su-25 FM had me blown away and it set the standard it still holds today. I'll celebrate again when the SFMs of the AI get kicked out of the core. These improvements are what DCS really needs and there are quite some vital things like the weather that certainly need such a buff. If ED keeps making such jumps, the future will hopefully be bright.

[HILOK]

Dear DCS Pilots,

Perhaps the least understood by customers, and the most complex task for us, is the creation of aircraft flight dynamics for DCS World aircraft. To help shine some light on this mysterious subject, our flight model engineering team created the linked document to share the sources we use, the fundamental principles behind the engineering, and the techniques we use to create and test the most accurate flight models possible.

 

It is our hope that with a better understanding of the process that you will truly appreciate the time and effort that goes into creating a flight model for DCS World and why it is not a speedy or simple task.

 

Thank you and kind regards,

The Eagle Dynamics Team

 

thanks for sharing, wags. much appreciated!

cheers

hilok

[401TIGGER]

Many Thanx to you and the Team WAGs

[CobaltUK]

Books only get you so far. Time and again it seems that input from RL military pilots gets rejected as inconvenient ? Dismissing critique seems to be the preferred response.

Edited July 25, 2020 by CobaltUK

[Hammer1-1]

I remember when Lock On was the top dog on the street and how accurate that was...

[Hummingbird]

Just two notes regarding the paper and the F-16:

 

1) The paper actually shows the DCS F-16's STR being too low below Mach 0.6 (difference gradually worsens the lower the speed)

 

2) It doesn't address ITR which has been proven too low (https://forums.eagle.ru/showthread.php?t=263877) compared to the same performance manual used for comparison in the paper, i.e. 9 G's cannot be hit until 0.10+ mach later than it should.

Edited July 25, 2020 by Hummingbird

[maxTRX]

It's nice to know what devs use to arrive at performance numbers. It's even nicer to see the performance that relates to 'published' numbers.

 

I mostly fly the Hornet. Knowing how FCS works throughout the entire flight envelope is as important as fluid dynamics, etc.

 

I wonder if devs have enough info in that department.

[DD_Fenrir]

Books only get you so far. Time and again it seems that input from RL military pilots gets rejected as inconvenient ? Dismissing critique seems to be the preferred response.

 

Horseshit. Time and again ED reference SMEs, ex-pilots of the aircraft in question whose opinion they use to validate their FMs. Given that these will be a subjective evaluation is it any surprise that two pilots opinions may differ.

 

Furthermore, Wags has stated, particularly regards the Hornet FM, that some elements have to be deliberately less than accurate to protect those US military pilots who may be obliged to use the real aircraft operationally from potential adversaries using DCS to benchmark the performance of their aircraft and exploit any weaknesses.

[Volator]

Furthermore, Wags has stated, particularly regards the Hornet FM, that some elements have to be deliberately less than accurate to protect those US military pilots who may be obliged to use the real aircraft operationally from potential adversaries using DCS to benchmark the performance of their aircraft and exploit any weaknesses.

 

That's why they should have pushed the F-4 instead of the F-16 :smilewink: SCNR

[Yo-Yo]

Just two notes regarding the paper and the F-16:

 

1) The paper actually shows the DCS F-16's STR being too low below Mach 0.6 (difference gradually worsens the lower the speed)

 

2) It doesn't address ITR which has been proven too low (https://forums.eagle.ru/showthread.php?t=263877) compared to the same performance manual used for comparison in the paper, i.e. 9 G's cannot be hit until 0.10+ mach later than it should.

 

"Too low" means less than 0.5 seconds at 13 s or less than 4%?