Bf109 flight model issue.

[JG13_opcode]

And you know exactly what an aircraft's energy state is at the end of a turn, because.... why??? Because it is what the sim spit out?

Uh, yes. The aircraft's energy state at any given time is fully specified by weight (fuel remaining), altitude, and speed. For short duration maneuvers we can consider that the change in chemical potential energy due to fuel burn is constant. All that's left is speed and altitude. If you know what altitude and speed you entered a turn, and you know what speed and altitude you end up at, then you know the total amount of energy that is dissipated.

 

How did you get the amount of drag from turbulent airflow which caused the aircraft to slow down???

I didn't, because the magnitude of drag is irrelevant when considering energy states.

 

Therefore how do you know the aircraft slowed down enough (or too much) in the sim?

Welcome to my world! You just discovered why "energy retention" is a pretty worthless metric for comparing sim aircraft to their historical counterparts.

 

So how do you know the end energy state is correct at the end of the turn which all your suppositions are based upon?

If by "correct" you mean "historical", well the answer is you can't. Not unless you have some data to compare against.

 

If you use data points of real aircraft turning, to estimate end point energy losses, do you then know the angle of attack that the wing is generating throughout the turn?

Why is that important? The concept of energy retention to some people is the idea that you come out of a turn with more (or less) energy based on some mythical properties of the plane. I'm explaining to you how the math works, and I'm telling you that if you want to calculate how much energy is disspated, you don't need to know anything about drag.

 

You maybe see my point.

Honestly, not really.

[Venturi]

Uh, yes. The aircraft's energy state at any given time is fully specified by weight (fuel remaining), altitude, and speed. For short duration maneuvers we can consider that the change in chemical potential energy due to fuel burn is constant. All that's left is speed and altitude. If you know what altitude and speed you entered a turn, and you know what speed and altitude you end up at, then you know the total amount of energy that is dissipated.

 

Ok, yes, as you trivially stated... we know the energy state at any one given point with:

 

weight (you mean mass, right? I mean since this is physics. Also weight changes with altitude as gravity is a distance phenomenon),

height

speed.

 

But you state chemical energy transformation is a constant, it is not. You haven't taken into account the relative inefficiencies of converting the chemical energy into kinetic energy. 1) Engine inefficiency (varies), 2) Prop inefficiency (varies) - just try using inefficient prop settings in a maneuver vs. efficient ones.

 

You are making a simple and obvious statement but making it incorrectly.

 

I didn't, because the magnitude of drag is irrelevant when considering energy states.

 

I'm not sure where you get that supposition as the reason why you have a lower energy state at the end of the turn is because you have experienced turbulent drag...

 

Welcome to my world! You just discovered why "energy retention" is a pretty worthless metric for comparing sim aircraft to their historical counterparts.

 

Actually I believe this is a crucial metric. It is just not easily measured and/or translated into the sim. Therefore not easily comparable to real counterparts, except in qualitative terms. But that's most likely what we have right now.

 

If by "correct" you mean "historical", well the answer is you can't. Not unless you have some data to compare against.

 

I agree, it is difficult and I'm sure the devs/game engine have a way of doing so. It is probably not exact, however.

 

Why is that important? The concept of energy retention to some people is the idea that you come out of a turn with more (or less) energy based on some mythical properties of the plane. I'm explaining to you how the math works, and I'm telling you that if you want to calculate how much energy is disspated, you don't need to know anything about drag.

 

You seriously think your mathematical abilities can predict the exact amount of energy lost in a turn before knowing the final energy state of the plane? Even Richard Feynman could not do that. Turbulence is one of the great unsolved mysteries of physics.

 

Anyone can do E1-E2=Elost. That is not the point. A sim must try to predict, that is why it is a sim. Turbulence makes it almost impossible to do so unless the data is extrapolated empirically from real world tests and then replicated. This is most difficult to do in all flight conditions as tests are just data points. I would love to be proven wrong on this however.

 

Honestly, not really.

 

Hope I helped, now.   

Edited August 20, 2016 by Venturi

[JG13_opcode]

Please use quotes... this blue text inside another quote thing is harder to reply to.
 

Ok, yes, as you trivially stated... we know the energy state at any one given point with:
 
weight (you mean mass, right? I mean since this is physics. Also weight changes with altitude as gravity is a distance phenomenon),
height
speed.

Sure, mass.  Doesn't matter.  The change in weight with altitude is not significant and we can assume it is constant for this analysis.
 

But you state chemical energy transformation is a constant, it is not. You haven't taken into account the relative inefficiencies of converting the chemical energy into kinetic energy. 1) Engine inefficiency (varies), 2) Prop inefficiency (varies) - just try using inefficient prop settings in a maneuver vs. efficient ones.

 Did you even read what I wrote?  On short time scales, i.e. the duration of a maneuver, the fuel burn is insignificant, so we can assume the change in chemical potential energy is constant, and then simply ignore it.  The error will be less than 5%.  Probably less than 2%.
 

You are making a simple and obvious statement but making it incorrectly.

 No, I'm afraid it's you who is confused.

I'm not sure where you get that supposition as the reason why you have a lower energy state at the end of the turn is because you have experienced turbulent drag...

You're not reading what I'm writing.  Read the words that I am writing.
 
IF YOU KNOW THE STARTING ENERGY STATE, AND YOU KNOW THE ENDING ENERGY STATE, THEN YOU KNOW HOW MUCH ENERGY WAS DISSIPATED.  YOU DO NOT NEED TO KNOW ANYTHING ABOUT DRAG BECAUSE YOU ALREADY KNOW HOW MUCH ENERGY WAS DISSIPATED BECAUSE YOU KNOW THE END STATE.
 
I'm not sure how to put it any simpler than that.
 
You know the start and end point.  You just take the difference.

Actually I believe this is a crucial metric. It is just not easily measured and/or translated into the sim. Therefore not easily comparable to real counterparts, except in qualitative terms. But that's most likely what we have right now.

Anything that can be quantified can be translated to a computer program. That is a basic fact of life.  You can't measure energy qualitatively.  I would argue you can't measure anything qualitatively.
 

You seriously think your mathematical abilities can predict the exact amount of energy lost in a turn before knowing the final energy state of the plane? Even Richard Feynman could not do that. Turbulence is one of the great unsolved mysteries of physics.

This is the part that made me angry. Son, I do this for a living.  You've already stated that you don't have a degree in this subject matter, so why do you think you can speak authoritatively about the "unsolved mysteries of physics"?  Turbulence is not a mystery and you need to just stop talking out of your behind.  The fact that you think turbulence is an unsolved mystery of physics speaks to your arrogance and the yawning chasm that is your ignorance in this particular subject area. Yes, I do think my "mathematical abilities" are up to the task. Why? Because I went to school for it and studied hard for many years. I don't pull this stuff out of thin air.
 
What you are failing to grasp is the idea that the speed and altitude at the end of a maneuver gives you the final energy state.  This is not wizardry, this is basic first-year university stuff.  If you have historical data of a guy going "i started the turn at this speed and altitude, and ended at this speed and altitude", then you know how much energy he spent turning and you can compare it to what happens in the sim.
 
If you know the energy states at the beginning and the end, you can calculate how much was lost.  Where it goes doesn't matter.  Get that through your head.

Anyone can do E1-E2=Elost. That is not the point. A sim must try to predict, that is why it is a sim. Turbulence makes it almost impossible to do so unless the data is extrapolated empirically from real world tests and then replicated. This is most difficult to do in all flight conditions as tests are just data points. I would love to be proven wrong on this however.

Turbulence itself (like all fluid flow) is governed by the Navier-Stokes equations. The equations have no closed-form solution. What that means is an exact solution is not possible. What it does not mean is that an approximate, numerical solution is not possible.  There is a branch of science called Computational Fluid Dynamics that has taken what used to be PhD-level problems involving turbulence and shock waves that people spent careers studying, and turned them into first-year homework that can be completed in a few hours.  Turbulence is actually very well-studied.

 

If you really want to keep going down this rabbit hole I strongly urge you to educate yourself on this matter because you have some fundamental misunderstandings that are really hampering you.

Edited August 20, 2016 by JG13_opcode

[Venturi]

Your misunderstandings are really hampering YOU.

 

Can't wait to see how you'll illuminate the next issue for us.

[JG13_opcode]

Your misunderstandings are really hampering YOU.

Nah, go back and re-read the thread and you'll see that you're just in over your head. Sorry little fella. I tried my best to give a concise explanation and fill in the gaps for you but you seem intent to turn this into something adversarial.

 

Can't wait to see how you'll illuminate the next issue for us.

The discussion was perfectly civil until you felt the need to get sarcastic with me in post #83. Edited August 20, 2016 by JG13_opcode

[Venturi]

Sorry little fella. I tried my best to give a concise explanation and fill in the gaps for you but you seem intent to turn this into something adversarial.

 

 

 

Your concise explanation is E1-E2=Elost and you think that predicts turbulence and results of angles of attack? You are really something. Your arrogance and condescension in this thread is legendary. In fact, it is pretty familiar...

 

Peace, out.

[Crump]

Excellent way to handle that JG13_opcode.

 

Venturi, Total Energy Concepts for Aircraft Performance have been around for several decades.  It is proven methodology.

[Crump]

[II/JG17_HerrMurf]

Look, it's all really simple.

 

Dps+Dch=Vvvs

 

 

Where: Dps = DONT pull the stick too hard

             Dch = DONT climb too hard

and

 

             Vvvs = Victory over VVS

 

See, problem solved..................unless you encounter Vfha = VVS Flap Hanging Ace. But that is a different discussion.

 

Don't ask me to explain it. It's much too difficult for you noobs to understand!

 

Edited August 20, 2016 by II/JG17_HerrMurf

[Crump]

 

 

.unless you encounter Vfha = VVS Flap Hanging Ace. But that is a different discussion.

 

That La-5 did deploy full landing flaps at the top of zoom.  That should be a great way to quickly swap the blue for the green....

 

 

 

 

The discussion was perfectly civil until you felt the need to get sarcastic with me in post #83.

 

It gets that way when the brain gets stuck.  You should try explaining the concept of how a relief valve on the intake side of the supercharger impeller will keep a set pressure going into the manifold but will not prevent manifold pressure fluctuations on the downstream side of the impeller.  

[YSoMadTovarisch]

See, problem solved..................unless you encounter Vfha = VVS Flap Hanging Ace. But that is a different discussion.

 

Who is everywhere, unfortunately, and that's not the thing only the flaps do, I've seen those "Aces" used flaps as thrust vectoring, as insta recovery mechanism to get out of flat spin at terminally low altitude ,etc....it's insane.

Edited August 20, 2016 by GrapeJam

[Venturi]

Oh, so.... this quote from you, Crump

 

 

There is room for interpretation in the math and anybody that tells you differently is flat out wrong. That is why our sims at the training department cost millions of dollars and still cannot accurately reproduce some portions of the aircraft's behaviors/performance. http://forums.eagle.ru/showpost.php?p=2592439&postcount=111

 

is wrong then?

[Crump]

 

 

is wrong then?

 

Nope and contradicts nothing in this thread.... 

[LLv24_Vilppi]

This does not conflict with anything that has been said by JG13_opcode, and this is not a comment directed to him, but just to be pedantic, the energy of an isolated system does not change. An aircraft is of course not an isolated system, but loses energy by interacting with the material it is travelling through.

 

For you who haven't studied the matter deeply: it's called air. In my case it may contain sometimes bullets, tree branches, and occasionally intermix with dirt and water, but those cases should be handled separately.

 

IF YOU KNOW THE STARTING ENERGY STATE, AND YOU KNOW THE ENDING ENERGY STATE, THEN YOU KNOW HOW MUCH ENERGY WAS DISSIPATED.  YOU DO NOT NEED TO KNOW ANYTHING ABOUT DRAG BECAUSE YOU ALREADY KNOW HOW MUCH ENERGY WAS DISSIPATED BECAUSE YOU KNOW THE END STATE.

If I'm allowed to play an English to English interpreter just a little bit here, I think that what Venturi is trying to say is that while you can clearly calculate the energy difference between the two points, you also need to know exactly how much chemical energy was transferred into kinetic energy and in what efficiency by the engine in order to know how much energy was lost during a manoeuvre.

 

If the balance between the engine performance during the manoeuvre and the loss of energy is not correct, this might cause some unwanted behaviour in the flight model. How significant this might be, I cannot tell..

 

That being said, engine performance in different flight regimes must be a well studied problem, and there must be quite good models for that. And while we do not know exactly how the energy was lost during each exact point of time during the manoeuvre (this doesn't seem like a trivial problem), the total energy lost is then of course easily calculated. So, how critical this is for simulation is definitely arguable.

 

Just as a closing note, there is an old maxim which I've learned to cherish: "all models are wrong, but some are useful". Even F=ma isn't strictly speaking correct. We just usually can ignore the effects of general relativity in WWII context, as I believe the error won't be that significant even with the REALLY FAST Me-262

 

In simulation it is always also a balance between computational complexity (keeping those frame rates up) and accuracy and of course trying to match the performance with multiple, sometimes conflicting sources.

Edited August 20, 2016 by LLv24_Vilppi

[JtD]

I think you're thinking way too complex, Venturi. Obviously you can take mass, altitude and speed at two points and calculate the difference in total mechanical energy from that, ignoring fuel burned, changes in gravity and what not else. You'll still arrive at a figure that will be accurate enough to describe the aircrafts performance. You can fairly accurately determine drag from that, if you know thrust. And that's what matters here - empirically determined lift & drag.

 

Of course, it won't tell you anything about fluid dynamics and turbulence. But then you don't need to know them, because as our reference, we also only have tons of empirical data. It gives us the bits of the information that matter - essentially the polars that give us lift and drag over angle of attack. There's no reason to make things more complex than that.

[Venturi]

I appreciate all that, my interest and comments have been, all along, regarding the points in wing modelling when the flow is becoming turbulent. For instance a max effort 400kph turn in a Yak, versus the same in a FW. Or at the edge of a low speed stall, with full flaps in a Yak.

 

I am wondering if the engine is modelling the drag created by this turbulence, or if there is indeed any way to accurately model the drag at these times, except at an approximation. If it is significant drag (I think it must be) I do not see how it is calculated. If it cannot be calculated correctly then how is it modeled, if it is even modeled at all?

 

I do not see how a simplistic E1-E2=Eloss sort of retrospective calculation given one particular turn and set of variables can help predict that. Can you find by that the induced drag and a/c energy loss due to turbulence in that exact circumstance? If you cannot, then how can you predict the behavior of the wing, especially given all possible situations, as we have in the sim?

 

Nor do I see how a polar diagram can predict the drag imposed by turbulence, let alone with loss of lift at portions of the wing and not others (since not all of the wing loses lift at the same time and some portions may be stalling at given AoA while the wing as a whole may not be - and this induces turbulence and drag only in some areas.)

 

But ultimately I am only curious, given the multiple existing FM complaints about a/c behavior when turbulent conditions might be expected to be experienced, which might explain certain findings in the sim...

 

If you could explain to me why turbulence does not create appreciable drag in these situations, I would be obliged.

 

I have attached the combined polar diagram from naca airfoil 4412. Including drag for lift graph (green) and transition points for laminar to turbulent flow-x/c separation/transition (blue/red). As well as a combined polar graph, with moment coefficient (yellow) and Cl/AoA (light red).

 

Thanks.

Edited August 20, 2016 by Venturi

[SvAF/F16_Goblin]

Just want to chime in and say that I enjoy your discussions much and it keeps refreshing my old memory about all the math and physics

But please keep it civil and continue to educate us all in these matters.

 

Regards

[JtD]

It certainly creates significant drag, but that drag is empirically measured for instance in wind tunnels. The results are polars like the ones you posted, which include the effect of turbulence. The simulation will then use calculations to approximate these findings. How well it does - your guess is as good as mine.

 

One should keep in mind that even for a very accurate flight model, one does not need to break down the aircraft calculations to infinitesimally small surface areas, because that is insignificant. There are plenty of tests for aircraft of the era showing which wing sections go turbulent when, and data showing how the aircraft reacts to that. Therefore, a couple of wing sections will be quite accurate already - and coupled with the empirically determined aircraft behaviour, it can be accurate way beyond what you can determine in your chair at a desk looking at a screen. Without ever actually calculating turbulence.

[Venturi]

So can you explain where in the polar we are seeing drag induced by large scale turbulence at AOA beyond stall?

 

Cause I see drag for normal controlled flight, but don't see where we would go when one section of the wing is stalling (IE that cross section's polar is stalling) but not another's. Where's the drag for beyond stall?

 

I mean, I assume that as the wing begins to stall, the drag goes up, yes? Because of large scale turbulence? Isn't a loss of laminar airflow over the entire cross section a stall by definition? Isn't the condition of some wing stalling, but not all the wing, the condition most of us flying the sim are in when we are in a maximum effort turn? When we are seeing wingtip vortices shown which are also turbulence?

 

I don't see wingtip induced drag in the polar. Wonder if that's included? 

Edited August 20, 2016 by Venturi

[Venturi]

There are plenty of tests for aircraft of the era showing which wing sections go turbulent when, and data showing how the aircraft reacts to that. Therefore, a couple of wing sections will be quite accurate already - and coupled with the empirically determined aircraft behaviour, it can be accurate way beyond what you can determine in your chair at a desk looking at a screen. Without ever actually calculating turbulence.

 

Well, that is kindof what I supposed to begin with. Thanks JtD.

[JtD]

There are polars that give you drag for beyond the stall. There's some of that in the reports I've linked in this post. For instance report 627. The reports also contain some polars for the full aircraft as tested in the tunnel, also to beyond the stall. For instance report 618.

So, yes, drag continues to go up past stall.

I'd agree that a complete loss of laminar flow is a stall by definition (unless we want to nitpick details over laminar/turbulent boundary layers).

Generally, the maximum effort turn would be flown just before a part of the wing is stalling. Defects/damage excluded. As soon as part of the wing, i.e. at least one cross section, stalls, you're losing lift and adding drag, which the rest of the wing won't compensate efficiently. Additionally, you're losing controllability.

 

Wingtip vortexes have little to do with stalling, they are there as soon as you are creating any lift. They are there to because there's airflow around the wingtip, from high pressure below to low pressure above. You just happen to see them when water starts to condense or freeze. That depends on the atmospheric conditions as much as on the vortex.

 

What's included in what drag figure usually is part of the fine print in these reports. Generally, 2D data does not include induced drag (such as wingtip vortexes), because the airfoil is assumed to be infinitely long. But then, induced drag can easily be calculated provided you have empirically determined the Oswald coefficient for whatever wing form you're using.

 

(I could multi-quote for more clarity, but I hope I'm still understandable.)

Edited August 20, 2016 by JtD

[Venturi]

I'll summarize your statement.

 

1) drag from turbulence must be measured empirically, on a airfoil by airfoil basis. It cannot be calculated a priori.

 

2) drag from turbulence at AOA beyond stall is sometimes available in polars, also empiric data only (as would be expected).

 

3) empiric data on drag from turbulence is largely 2D cross sectional data, whole wing 3D data such as wingtip induced drag (and I assume other aspects on the wing surface such as bulges, pods, radiators, etc) are not always available but can sometimes be calculated depending on additional data available.

 

Yet, clearly ultimately a complete wing 3D polar up to and beyond the stall is what is ideally needed to calculate the wing behavior in the sim. Since there is washout and twist in many wings.

 

Sounds like about what I thought earlier. Thanks for the reply.

Edited August 20, 2016 by Venturi

[Crump]

Anything useful or we still feeding ego's?

Maybe once you guys figure out all your questions about "drag due to turbulence" some thing useful to your community can come out of it?

 

Of we can just go back a page to the useful stuff and skip the discourse.

[1PL-Husar-1Esk]

What is major issue almost the cheat of 109 is that you can bind adjustable stabilizer together with pitch axies and have pulling creasy aoa but never stall and stable wonder machine Check it out yourselef.

 

Btw question to Crump what it is saying about FM / physics model in general?

Edited August 20, 2016 by 307_Tomcat

[Crump]

 

 

Yet, clearly ultimately a complete wing 3D polar up to and beyond the stall is what is ideally needed to calculate the wing behavior in the sim. Since there is washout and twist in many wings.

 

It is pretty easy and accurate to convert 2D airfoil data to a 3D wing.  

 

Without that ability to reasonably predict, designing an airplane would be mysticism than a science.... 

[Crump]

What is major issue almost the cheat of 109 is that you can bind adjustable stabilizer together with pitch axies and have pulling creasy aoa but never stall and stable wonder machine Check it out yourselef.

 

Btw question to Crump what it is saying about FM / physics model in general?

 

 

Your game is not handling trim forces in the same way that an aircraft does.  To a pilot, trim is control forces but to the aircraft it is a speed, to the wing it is an angle of attack.  If you trim an aircraft to maintain an angle of attack that it cannot you will get a trim stall in reality.

 

Trim the airplane to fly at a slower speed than it is capable of doing and you will get a trim stall.

 

http://avstop.com/ac/flighttrainghandbook/elevatortrimstall.html

 

In summary, trimming does not change the wings usable angle of attack.  

[Holtzauge]

Just to add some stuff on energy retention: Attached is a result from a C++ simulation I did some years ago for the Fw-190A8 which not only shows the beginning and end energy states but the road between these. The big problem here is not only to come up with how to model the drag as a function of Cl but also as a function of Mach because you quickly run into compressibility when you point the nose down with a WW2 fighter. You can see that in the way the dive speed gets a kink down at about M=0.67 in the simulation. So not only do you need the Cl/Cd polar, you also need it for the Mach number you are traveling at. So since the polar varies during the dive due to Mach effects, you have varying atmospheric conditions due to the altitude, together with the prop efficiency which also varies both due to disc loading, advance ratio and prop tip Mach effects you are looking at a pretty complex picture.

 

So to sum up, energy retention or whatever you want to call it is not easy to model accurately and it therefore gets difficult to prove what is right or not. So in a diplomatic fashion I think both Venturi and JG13_opcode have a point here: Yes, it certainly is difficult to do, but at the same time it can be done but as usual the accuracy will depend on the assumtions made.

[Crump]

You don't need any of that.  You need some basic information about the aircraft and that is all.

Edited August 20, 2016 by Crump

[JG13_opcode]

Your concise explanation is E1-E2=Elost and you think that predicts turbulence and results of angles of attack? You are really something. Your arrogance and condescension in this thread is legendary. In fact, it is pretty familiar...

 

Peace, out.

The only one who brought up angles of attack is you.

 

To determine energy lost you don't have to even consider angle of attack.

 

I don't understand why you are so fixated on this.

[Crump]

They are fixated on it because they do not understand what your talking about JG13_opcode.  They do not see how it is possible despite the fact it is pretty standard aircraft performance math techiques.  Therefore an attempt is made to link the known to the unknown which unfortunately brings in a bunch of static as others on the board try to increase their "internet credibility" by demonstrating their knowledge.

 

Unfortunately, they do not know either so are just adding to the confusion.

 

Meanwhile, this bonfire of the vanities burns....they attack you and drown out the issue so that nothing gets resolved in the end!

 

It is very simple.  For performance purposes, aircraft are considered a closed system as Thrust = Drag in steady state flight.  Using that relationship, newtonian physics dictates F=ma and we can use the physical relationships of how thrust and drag develop to determine performance.

 

That is something you learn in a classroom and it does not take a bunch of gobbly-gook to muck it up.

[JG13_opcode]

I think that what Venturi is trying to say is that while you can clearly calculate the energy difference between the two points, you also need to know exactly how much chemical energy was transferred into kinetic energy and in what efficiency by the engine in order to know how much energy was lost during a manoeuvre.

 

Yes I think this is what he's trying to say, too.  Except it makes no sense.

 

How can these two things simultaneously be possible?

 

1)  you can calculate the energy difference between any 2 points if you know the 2 points

 

2)  you can't calculate the energy difference between the beginning and end of a maneuver (2 known points) without knowing how much chemical energy came out of the fuel and how much was dissipated against drag

 

Those statements contradict each other.

Edited August 20, 2016 by JG13_opcode

[JG13_opcode]

 

 

I do not see how a simplistic E1-E2=Eloss sort of retrospective calculation given one particular turn and set of variables can help predict that. Can you find by that the induced drag and a/c energy loss due to turbulence in that exact circumstance? If you cannot, then how can you predict the behavior of the wing, especially given all possible situations, as we have in the sim?

 

Ah, you know what?  I think I just figured out what is going on here.

 

Nobody is suggesting that you can predict some arbitrary future maneuver with only the delta-E from a single turn.  Not me, not anyone else.  I think the misunderstanding entered the thread in post #74.  The only one talking about prediction is you.

[Holtzauge]

You don't need any of that.  You need some basic information about the aircraft and that is all.

 

Well it depends on the level of accuracy you want but for the simplistic types of performance estimates you like to do then I see why you would think that.

 

It is very simple.  For performance purposes, aircraft are considered a closed system as Thrust = Drag in steady state flight.  Using that relationship, newtonian physics dictates F=ma and we can use the physical relationships of how thrust and drag develop to determine performance.

 

That is something you learn in a classroom and it does not take a bunch of gobbly-gook to muck it up.

 

Yes, I understand it looks simple to you but that is because you seem to fail to grasp that the F in F=ma is more complex to derive than you seem to think. This F is actually a function of all the factors I listed in post #111.

Edited August 20, 2016 by Holtzauge

[Crump]

And here it goes.....

 

The result is actually pretty complex Holtzauge.  It delivers a good prediction of what can be expected and an accurate relative line up of aircraft performance.  That is why it is used.

 

It is like the lift formula is very simple math.  However, the Lift formula is amazing accurate and elegant math that accounts for all lift required.

[Crump]

[Holtzauge]

And here it goes.....

 

The result is actually pretty complex Holtzauge.  It delivers a good prediction of what can be expected and an accurate relative line up of aircraft performance.  That is why it is used.

 

It is like the lift formula is very simple math.  However, the Lift formula is amazing accurate and elegant math that accounts for all lift required.

 

Well before you said it was simple. If you now say it is complex so then we agree. In addition, nothing you say here contradicts post #111.

 

 

Yes, and as I said before in post #111, the problem is deriving the F in F=ma.......

 

 

[LLv24_Vilppi]

Yes I think this is what he's trying to say, too.  Except it makes no sense.

 

How can these two things simultaneously be possible?

 

1)  you can calculate the energy difference between any 2 points if you know the 2 points

 

2)  you can't calculate the energy difference between the beginning and end of a maneuver (2 known points) without knowing how much chemical energy came out of the fuel and how much was dissipated against drag

 

Those statements contradict each other.

I think he's talking.. and then I read your next post:

 

Ah, you know what?  I think I just figured out what is going on here.

 

Nobody is suggesting that you can predict some arbitrary future maneuver with only the delta-E from a single turn.  Not me, not anyone else.  I think the misunderstanding entered the thread in post #74.  The only one talking about prediction is you.

Exactly (and that's why I wrote that I don't disagree with you).

 

But during simulation one DOES need to make these predictions as the players are not going to restrict themselves to the conditions that the published, limited empirical tests give results to. Yes, if the flight model does result in similar energy state after a similar kind of manoeuvre in the simulation as the empirical results show, one can verify that something's been done right, but that doesn't guarantee that everything else is right. After that it comes down to understanding how robust the model is. In practice, quite often, the more robust one tries to make the model, the less accurate it usually is (compared to the empirical data), and vice versa, the more accurate one tries to make the model, the less robust it usually is.

 

And going back to what I believe Venturi is trying to say (sorry mate, not trying to put words into your mouth, so please correct me if I'm wrong), in order to create a robust and accurate model one would need to be able to grasp the highly complex and chaotic nature of turbulence and other related phenomena.

 

Again, this all being said, I don't know how robust the best computationally feasible models (for commercial combat flight sim) for aerodynamics are, so I can't comment on this exact topic, but I can see what Venturi is trying to say.

 

I might be a bit incoherent in the text above, as it is rather late in Tokyo at the moment, and I am rather drunk. I'll try to edit and fix it to more coherent text tomorrow, but for the meanwhile, give a benefit of doubt

[Crump]

 

 

Well before you said it was simple. If you now say it is complex so then we agree. In addition, nothing you say here contradicts post #111.

 

It is simple.  The thought process and underlying math used to derive that relationship is NOT simple.  Why are we even talking about this??

 

Are gamers going to reinvent aerodynamics and aircraft performance math?   

[Venturi]

 

It is simple. The thought process and underlying math used to derive that relationship is NOT simple. Why are we even talking about this??

 

Are gamers going to reinvent aerodynamics and aircraft performance math?

 

And your motivations become clear once again Edited August 20, 2016 by Venturi

[JG13_opcode]

But during simulation one DOES need to make these predictions

Sure but that's not what's being discussed here.

 

The math behind the sim is off topic.