New FM excessively draggy?

[Brainless]

I'm not very experienced with MiG-21, but noticed that I need more thrust when landing, than before. May be this is normal. (p.s. Nothing is more scary for me in DCS than landing MiG-21. :shocking:).

[humptydumpty]

I'm not very experienced with MiG-21, but noticed that I need more thrust when landing, than before. May be this is normal. (p.s. Nothing is more scary for me in DCS than landing MiG-21. :shocking:).

 

Yeah noticed the speed bleed too during landings, and yes she is scary but gives the best immersion during landings :)

[cauldron]

Hi there,

as promised, I did some easy calculations and experiments. The full documentation can be found in the appendix of this post. The conclusion is that the engine of the MiG-21Bis seems to be underpowered in DCS while the Mirage 2000Cs' engine is overpowered compared to their real abilities. For more detail have a look at my research. If nobody has done it already I try to submit the problem on Mantis, although I have no track files of my experiments.

 

 

Malek,

 

Your math F=ma is not complete. You forgot that there is another force acting upon the body D Drag. Excess thrust is what you are looking for, you have mass sure but you need drag as your equation for experimental testing is fundamentally flawed.

 

 

Acceleration = Net accelerating force/mass The "net accelerating force" is excess thrust or a thrust deficit or Thrust-Drag or F(n)=T-D - given that it is flying straight and level and Lift = gravity Your starting equation should be the following:

 

Sum of Lift/drag/gravity/thrust and mass of the object due to F=ma... you have omitted lift drag and gravity from your test. It is completely invalid.

 

From there you will want to get the thrust required for level unaccelerated flight (subsonic) which is:

T[r]= W/ (C[L]/C[D]) weight divided by the ratio of coefficient of lift over coefficient of drag.

 

 

Drag = D(p)+D(i) or Parasitic drag + Induced drag -induced drag is drag due to lift for the most part, and parasitic drag is mostly due to friction but also some energy losses such as cooling losses etc. and that is subsonic nor transonic(getting close to and up to MACH 1) as we won't get into wave drag, etc that start to happen.

 

 

In short you have trivialized the all forces involved into a static thrust model of the engine - this leads you down a completely false road of experiments.

 

 

Total subsonic drag coefficient C[d] = c[d]+induced drag coefficient

 

C[d] = c[d] + ( C[L] squared ) / ( pii * e*AR )

 

Where e= span efficiency factor, pii=pii ie. 3.141559..... , AR aspect ratio

 

C[L] Coefficient of lift = W / ( 1/2*p * V(squared)*S

 

Where W= weight, p density, V elocity, S wing area

 

 

Now thrust required for unaccelerated flight so you can get to how much excess thrust there may or may not be ( mindfull this will not be static thrust ):

 

T[r] = from above ^^^

 

You are basically making a a drag polar graph. Then to compare the planes you'll need to determine their proper drag as well as the thrust available for the speed and altitude, the weight, but to get their drag you'll need quite a bit more information.

 

 

 

 

 

Your test has started you in a good direction, get some aerodynamics books:

 

I recommend:

 

introduction to flight by John D. anderson ISBN 0-07-001639-9

 

or

 

aerodynamics for naval aviators NAVWEPS 00-80T-80 ISBN 1-56027-140-X

 

or if you are of spanish incline:

 

Aerodinamica y actuaciones del avion por A. Isodoro Carmona ISBN 84-283-2227-9

 

best regards.

[Malek]

Dear Cauldron,

 

you are almost right. Yes, of course are my calculations very unprecise, I quote myself: "The results are not very precise, because aerodynamic drag is not included..." Please read the whole document. But the results are definitely not trivial, as I wrote, I did use the formula F = m*a for "laboratory accelerations" which means in a vacuum, so there is no air or another fluid which could generate drag. You probably don't know the exact definition of trivial, which means that a mathematical proof is so easy that no term operations are needed to proof it.

 

Aerodynamic Drag was obviously included in the experiments, because DCS is a realistic simulation. So the empiric experiments are correct in the dimension of the project.

 

To sum up, as I wrote several times, the laboratory speeds say nothing about the performance of the plane in real or in game, but it gives a reference point!

 

A personal remark for you, Cauldron:

They way you tried to proof me like an idiot or a liar is very unscientific. Furthermore it shows how arrogant you are, because you could have guessed from my calculations and way of argumentation that I'm still in education :smartass: and at the beginning of physics. And every academic, at least in Europe, wouldn't have used all your formulas to show what is wrong, because he had known that I won't understand them and that I won't use them. No physician is using formulas which he has not proofen by himself. So you have shown off your knowledge about physical formulas, but as well your need to be better than others.

 

If you still feel that my documentation is still so "trivial" do it yourself. :thumbup:

Edited December 23, 2016 by Malek

[cauldron]

Malek,

 

Also, the M2000c is contemporary to the F-16 and the mig-29. The M2000c is a tailless delta with vortex generators, automatic leading edge devices and an unstable center of lift, the mig-21 is a traditional delta similar to the mirage-3 and F-106 delta Dart though the mig-21 has a tail, both good and bad depending on what kind of performance you are after.

 

A more direct comparison would be the F-5, or outside DCS the Mirage-3 or mirage F-1 the Su-15 the F-4 Phantom or the Bae Lightning, the F-8 Crusader, and F-106 Delta dart. there is lots of data available for all those planes to make comparisons.

 

These are all contemporaries of the Mig-21

[cauldron]

Dear Cauldron,

 

...You probably don't know the exact definition of trivial, which means that a mathematical proof is so easy that no term operations are needed to proof it....

 

A personal remark for you, Cauldron:

They way you tried to proof me like an idiot or a liar is very unscientific. Furthermore it shows how arrogant you are, because you could have guessed from my calculations and way of argumentation that I'm still in education :smartass: and at the beginning of physics. And every academic, at least in Europe, wouldn't have used all your formulas to show what is wrong, because he had known that I won't understand them and that I won't use them. No physician is using formulas which he has not proofen by himself. So you have shown off your knowledge about physical formulas, but as well your need to be better than others.

 

If you still feel that my documentation is still so "trivial" do it yourself. :thumbup:

 

 

There was nothing rude, nor condescending in my remarks, criticism can be hard to give "gently" and hard to receive. But such a reaction as yours is not warranted. No where do i imply you are an idiot, nor a liar. The comment of "trivial" is not a mathematical one but one that you trivialised some important factors involved in your experiment that heavily influence the outcome of it, do not take it as a comment to your person.

 

You, as i said, are on the right track in testing and experiments. the formulas i used have the same math that you used, the most complicated had a squared function, multiplying and division, and writing formulas in a txt chat is not fun, and i spent quite a bit of time to try to show you some of the factors evolved, and even looked up some books for you, that can be tested for in the simulation if you want to go that way, the mig-21 and the F-5 are wholly de-classified.

 

Try not to jump to conclusions of ridicule, when you post an experiment for being read and reviewed by others.

Edited December 23, 2016 by cauldron

[Malek]

:doh: I know aswell what a M2000C is and the difference, like many of her pilots...

 

I must admit you have the ability to create relations where no ones are :smilewink:.

 

Have you recognized that the discussion is, that the MiG-21 feels underpowered since the last patch? The documentation gives some data for further interpretation.

 

For example: I compared the Fishbeds laboratory acceleration with its in game acceleration, I saw that theres a big negative difference, then I compared the M2000C laboratory acceleration to its ingame acceleration and saw that there is a big positive difference. Although the technical difference between the M2000C and the Fishbed, their acceleration differences should be in the same direction, because it makes no sense that the M2K accelerates faster than her engine technically is able to, from where should she get this additional acceleration? From the sun? Hard to explain in words...

 

Furthermore I have never wrote, that the MiG-21 should be equal to the M2000C? It was never my intention to say that the MiG should be similar to the M2000C. (Already written earlier) And btw. I know which airplanes were real opponents of the Fishbed but many of them are not in game and are for my conclusion, that those two aircraft seem to be not balanced to their real abilities, obsolete.

 

So, my suggestion is that we stay how it is. With my knowledge about philosophical argumentation and physics I'd say that my test have shown that the actual flight model of the MiG-21 is underpowered, as many feelings already have guessed. Although the documentation is very confusing, because I did it within 1 1/2 hour. The test may be very unprecise but for me still usable. To argue here about the accuracy of the test and our knowledge is sort of off topic, you have submited your concerns about the test, but as long as you don't do a more precise test which unproofes mine, it should be used to support our feelings about the FM.

 

If you'd like to continue arguing with me we can do that in private messages.

Edited December 23, 2016 by Malek

[cauldron]

I know that a M2000C is and the difference...

 

I must admit you have the ability to create relations where no ones are :smilewink:.

 

Do you recognized that the discussion is, that the MiG-21 feels underpowered since the last patch? The documentation gives some data for further interpretation.

 

For example: I compared the Fishbeds laboratory acceleration with its in game acceleration, I saw that theres a big negative difference, then I compared the M2000C laboratory acceleration to its ingame acceleration and saw that there is a big positive difference. Although the technical difference between the M2000C and the Fishbed, their acceleration differences should be in the same direction, because it makes no sense that the M2K accelerates faster than her engine technically is able to, from where should she get this additional acceleration? From the sun? Hard to explain in words...

 

Furthermore. Have I never wrote, that the MiG-21 should be equal to the M2000C? It was never my intention to say that the MiG should be similar to the M2000C. (Already written earlier) And btw. I know which airplanes were real opponents of the Fishbed but many of them are not in game and are for my conclusion, that those two aircraft seem to be not balanced to their real abilities, obsolete.

 

I'm still writing how to proceed...

 

 

1st, no one is ridiculing you, so stop being such a brat about it or you'll find not many people to even listen to you.

 

What is the basis of your "laboratory" data? your "F" in F=ma in your laboratory data is missing a lot of factors, which implies your experimental data will not give you any valid results to make any claim of under-or-over powered.

 

You could find some interesting things, like where L/D max is for each plane at different altitudes, maybe graph the the ingame curves for evaluation and interpretation, you could do a lot of interesting things with what you are doing.

 

But your premise and "laboratory" models of static thrust from the planes being the only "Force" is far from the only Force acting on the planes in your acceleration model. The game simulates a lot of things, exactly which we don't know. Your test can show a window into them if you dig deeper.

 

I'm done if you keep knee jerking into insults and feeling insulted constantly.

[Malek]

Okey Cauldron.

1. I don't feel bullied or anything why should I? But I think you and me are focusing on different aspects and then there is the cultural difference between America and Switzerland which is blocking this discussion.

2. Please read my last paragraph, which I was still writing when you posted your next reply

3. Yes, the basis of my laboratory data is F=m*a, because I just want to know how fast the mass m of the aircraft would be accelerated with the Force F in a vacuum, and because it is in a vacuum there is basically no drag, if the object isn't touching anything, which is the case in my thoughts. And you must agree that something is wrong, when the aircraft would accelerate in the vacuum with 5 m/s^2 and then it accelerates in real(ingame) with 6.5 m/s^2.

4. I don't want to find something different and do a big scientific work, I just did very quick some experiments which should show the problem.

5. Yes in my first reply I was insulting you because I thought you were as well insulting me before, probably the difference between our cultures. Later I just defended myself.

 

Can we please stop this discussion as offered earlier?

[GGTharos]

Malek, the only useful comparison is to the real aircraft data, just to be on the same page. Maybe your method can detect a potential issue, but there's no sense in reporting this without comparing to the real charts.

 

Maybe what's wrong here is that you don't realize that actual airspeed and pressure altitude will have an effect on engine thrust, thus your comparison in lacking since you don't know the actual thrust value.

 

Again, comparisons should be made against real aircraft data.

Edited December 23, 2016 by GGTharos

[Cobra847]

Let's keep it really civil gentlemen. :)

 

Your help will be really instrumental in nailing down the remaining inconsistencies.

[humptydumpty]

Let's keep it really civil gentlemen. :)

 

Your help will be really instrumental in nailing down the remaining inconsistencies.

 

Don't intend to send this off topic , but now the miggie is not getting refueled , I ask for 100% fuel for the main tank and then the grounds crew says ok and then after sometime says she is fueled but the fuel indicator has not moved at all remains in the same position.

 

I don't know if the DCS updates messed it up or what ?

[Malek]

Malek, the only useful comparison is to the real aircraft data, just to be on the same page. Maybe your method can detect a potential issue, but there's no sense in reporting this without comparing to the real charts.

 

Maybe what's wrong here is that you don't realize that actual airspeed and pressure altitude will have an effect on engine thrust, thus your comparison in lacking since you don't know the actual thrust value.

 

Again, comparisons should be made against real aircraft data.

 

 

Alright. That's true, I took the dry engine thrust as a constant, which is a big misstate by me :doh:. Okey, now I have reason for abandoning my method.

 

And I memorized to only use real aircraft charts, but I think that I won't do any more calculations in aviation until I have all mathematical tools to do them correctly.

[NineLine]

Don't intend to send this off topic , but now the miggie is not getting refueled , I ask for 100% fuel for the main tank and then the grounds crew says ok and then after sometime says she is fueled but the fuel indicator has not moved at all remains in the same position.

 

I don't know if the DCS updates messed it up or what ?

 

Might be better to open a new thread, might get lost in here :)

[BadHabit]

Just grab some popcorn and enjoy :-)

 

Sent from my HUAWEI G510-0100 using Tapatalk

[humptydumpty]

Might be better to open a new thread, might get lost in here :)

 

Yep a new thread.

[Frederf]

Based on a single-run test I did in post #8 the MiG's level acceleration has:

1. Not changed since July.

2. Meets (subsonic) and exceeds (supersonic) printed records.

 

There are of course other tests than straight and level accelerations: external stores, climbing, diving, turning, non-afterburning, etc.

 

I've also noticed a big gap between cockpit indicated and F2 indicated airspeeds with the pitot shock special option on. So what feels slow by looking at needles might not be as slow (or might be faster) than it looks.

[GGTharos]

Malek, your best tools are the real charts OR if you want to do CFDs, then do CFDs :)

Usually the real data is superior to a CFD, but a CFD can be fairly good also.

 

I just want to say that I appreciate that you tried to examine the issue with some science, which is great, and you learned something along the way which is also great :)

 

Alright. That's true, I took the dry engine thrust as a constant, which is a big misstate by me :doh:. Okey, now I have reason for abandoning my method.

 

And I memorized to only use real aircraft charts, but I think that I won't do any more calculations in aviation until I have all mathematical tools to do them correctly.