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Helyi

Weight/Drag/Inertia Mishandled?

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Am I missing something?

Has anyone else noticed there seems to be extremely limited effect of inertia on zoom climbs with respect to fuel? (However there is a significant difference to sustained turn ability, acceleration and powered [non-zoom] climb etc).

This seems contradictory to what inertia and mass would have me believe...

Same aerodynamic profile (obvious controlled variable) utilising a yak with ~10% fuel will end up at the same point as a yak with 100% fuel... In the same amount of time.

Not only that but the near empty plane seems to dive just as effectively and even appears to bleed virtually the same amount of speed off on the straight and level per second as the fully laden one.

Something does not seem right with this.
I would expect an initial faster acceleration at the start of the dive with less fuel and a slower deceleration at the top of the zoom climb as the carried inertia becomes less relevant and power:weight becomes more relevant.
(And conversely for more fuel)
This is not the case at all.

I've tried to do a few quick tests and there seems to be very very little difference between 10% and 100%.

Starting quick mission at 1500m.
Close rads.
Mixture ~Full Rich
Prop RPM - Max (2700rpm)

Accelerate to 400kph. initiate dive (picked a point on ground to aim at for each test to keep minimise nose rating/climb curve variable).

At 650kph pull smoothly to a ~50-60 degree zoom climb to minimise AOA drag.

The two 'closest' replicated dives/climbs I could replicate were :

100% Fuel - 300kph --> 400kph (Autolevel, full closed rads @ 1500m) - 13 seconds
100% Fuel - 650kph achieved in 23 seconds. (Timed from the moment the nose moved from the horizon off autolevel)
100% Fuel at 300kph - 2590m (21 seconds from time of nose crossing horizon to altitude and speed achieved)
100% Fuel at 200kph - 2880m (29 seconds from time of nose crossing horizon to altitude and speed achieved)

10% Fuel - 300kph --> 400kph (Autolevel, full closed rads @ 1500m). 11seconds
10% Fuel - 650kph achieved in 22 seconds. (Timed from the moment the nose moved from the horizon off autolevel)
10% Fuel at 300kph - 2560m (23 seconds from time of nose crossing horizon to altitude and speed achieved)
10% Fuel at 200kph - 2880m (30 seconds from time of nose crossing horizon to altitude and speed achieved)


Now the time difference could actually more be a slight difference in pulling up from the dive and slight inconsistencies holding the same angle etc. however this is both visually as close as I could get on reviewing captured video.
The differences in all the tests are marginal at worst.

For a 90% reduction in fuel this doesn't seem right...
With more fuel I would expect the heavier plane to be a reasonable amount higher than the lighter plane by the same loss of speed (2560m vs 2880m).
320m is a decent amount, but even still...
The lighter plane should have lost more inertia to aerodynamic drag than this I would have thought.

Edited by LordHelyi
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Are you sure you were at the same altitude at 650kph when initiating zoom climb? I couldn't determine from the text. 

 

Your test is overly complicated.

Much simpler test. Accelerate to top speed in level flight, lets say 500kph for yak, initiate a climbing turn, level off at 250 kph. See altitude gained

http://www.airbase.ru/pilotage/yak3/53.gif

Edited by Shifty_

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Can't argue with your data, but the extra weight of the fuel definately has some effect on handling. I went up in a Yak online yesterday, stalled all over the place, burned crazy amounts of energy and had generally miserable handling until I realised, that I had brought 100% fuel rather than my usual 55%. As soon as I set the fuel back to my usual level everything was fine.

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Perfect question shifty.
I just double checked my video recordings and the start was 2000m. The dive both 10% and 100% hit 650IAS at precisely 1000m (almost imperceptible difference in the analogue altimeter).

But before that, why a turn climb over a pure unloaded zoom climb?

An unloaded zoom climb is the perfect test of mathematical inertia and momentum. (perhaps I've answered my own question there by choosing 60 degrees... However at that constant angle I still think the amount of effort the wings would have been assisting to the energy system is minimal and its easier to hold steady than pure 90 degrees)

Since we are eliminating the variables of air resistance (Same altitudes and same initial speed - as we know air resistance is squared for a given velocity therefore double speed quadruples resistance is not a factor here) and square-cube law (same wing/aerodynamic profile by using the same plane) and lift factor.

A Yak-1's empty weight: 2,330Kg (just a quick google, exact weight isn't terribly important)
If 1L of fuel is approximately = 0.8 Kilograms (this is a pretty respectable estimation)
100% fuel = 408 L = 326.4Kg
That's 14% of the entire aircrafts empty mass! That is mathematically significant!

10% fuel is 40L (ingame readout) a measly 32.6Kg or 1.3% of it's empty weight!

So at 100% a fully laden Yak-1 = 2656.4Kg
At 10% = 2362.6Kg

That alone tells you its momentum values and an idea of its inertia since inertia is merely mass as a resistance to change in velocity.

 

Mathematically for momentum we get:

p = mv

p = momentum 
m = mass (kg)
v = velocity. (m/s)

p = (2656.4)(180.6m/s)
   =  479745.84kg x m/s!
That is *alot* of momentum.

For the unladen plane:

p =  (2362.6)(180.6)
  =  426685.56kg x m/s!

Which indicates the near-empty plane only carries 88.9% of the loaden planes momentum [or 11.1% less momentum] at 650kph.
This is really just a fancy way of saying the lighter plane is 11.1% of weight of the heavier one but its placed into pure physics form.

The difference for turn and lift capability comes from the fact that as far as fuel goes, it is absolutely dead and useless mass until the very moment it is being ignited in the engine. Of which the empty plane is carrying 1.3% extra useless mass vs 14% for the laden plane.

It *should* be useful mass for other purposes such as energy retention in a straight line but it just doesn't add up mathematically in game. It sure as hell gives you the penalty to turning and lift, but it does not provide the benefit it should in other areas.

Now, since the forces acting on the two planes are basically the same (gravity and air resistances as discussed earlier) it is clearly evident the heavier plane *should* be achieving higher zoom-climb altitudes than they are.
 

 

A quick revision of my initial numbers [i was in a hurry typing up to get out the door for work earlier]:

I correct my starting altitude: it was 2000m not 1500m.
 

 

100% fuel - exactly 900m altitude when the nose passes through horizon line.

10% fuel - exactly 850m altitude.

(this would be accountable for a marginal difference in how tight the turn at the bottom of the dive was, I'd say 50m is pretty good for manually flown!)
Either way -50m and a minor difference in turn radius should not have equated to negating a 12% difference in momentum for final achieved heights:speed ratio.



TL:DR
The 1.3% vs 14% weight differential is tactically significant and reflected well in-game. (This differential mathematically puts a value on the difference in turn capability, climb and acceleration)
The 11.1% momentum difference is also tactically significant but not reflected well in-game. (This should put a mathematical value on energy retention after dives/in zooms/in long fast turns)

The heavier plane should have achieved a higher airspeed at any given/chosen altitude you want to look at through the zoom climb and thus a higher altitude overall

The reason I chose to ignore any altitude over 200kph is because power:weight and acceleration capability [prop hanging] becomes the domineering factor and at 200kph it becomes too difficult to keep the plane from wallowing to keep a fair comparison to angles of attack/drag.

It's 01:25hrs here so hopefully I didn't mess up any copy-pasting of moving thoughts around.
 

Edited by LordHelyi

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Here is screencaps from the vids so you can side by side comparison:
I do note that the 10% vid the bottom of the dive is slightly lower and slightly faster [barely anything], but you would expect this to translate proportionally at the top as well (which it does not)

Irrespectively, I was looking for tactically significant difference in zoom climb capabilities when compared against the tactically significant impact in turn/climb/acceleration ability.

The short of this. There is no reason in a dogfight server to take anything more than the very bare minimum you think you will survive for.

Theoretically taking too little fuel should result in excessive bleeding of speed in high to medium speed turns but I'm not sure this is the case either. 

I am beginning to wonder if fuel weight is modelled as an extra 'external payload' so to speak and adds some parasitic type extra drag which it should not.


100% Fuel: Very start
http://s16.postimg.org/fa83wf203/100p_start.jpg
 

100% Fuel: Bottom of the dive
http://postimg.org/image/615xmat41/full/
 

100% Fuel: 300kph & Altitude:
http://postimg.org/image/iee6fgtep/full/

 

-------------------------------------------------------------------------------------

10% Fuel: Start
http://postimg.org/image/ubnrtdz5n/full/
 

10% Fuel: Bottom of the dive:
http://postimg.org/image/7yg16ky7v/full/

 

10% Fuel: 300kph Altitude.
http://postimg.org/image/ninex48cb/full/
 

Edited by LordHelyi

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I'll be the first to admit that math is not my subject, but, yes the game engine has problems with calculating mass, or the effects of drag or well, just about anything to do with the FM, or it has gotten the wrong inputs (garbage in/garbage out) on what to calculate in the first place.

 

The atmospherics are great, but the actual way the planes behave is just nonsense.

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!

 

 

 

Well…. I had to react, because what is wroten over there is partially wrong in my humble opinion !

 

It's not that obvious that a heavier plane will dive quicker if his engine is turned on. Thinking in term of momentum is very very misleading, so let's take a look at the acceleration of a diving plane because, well, we all know what is the acceleration !

 

The acceleration, which is the derivative of the speed, follows newton law which is :

 

m*a = [sum of difference forces]

 

With m the mass of our beloved plane, "a" her acceleration and [sum of difference forces] all the forces applied to her.

 

Ok let's say that right now we don't care about air resistance and that the plane's engine is off. We only have the gravity, the force is m*g, g being the gravity constant over the earth. Ok to simplify, let's say that the plane is aiming straight toward the ground and we don't have to deal with angles and projections. We have :

 

m.a = m.g 

so we can simplify by m and :

a = g

 

So acceleration DOESN'T depends on the masse of the plane ! Ok that's weird, if I drop a hammer and a feather, I expect the the hammer to be quicker, therefore having a higher acceleration. Well, it's because of the AIR RESISTANCE. On the moon, there is no air resistance and it's a different story :

 

 

 

Ok let's start again and call Fr the drag produce by the air on our plane. Fr depends usually on the speed of the planes but let's says it roughly constant in our problem. Now we have :

 

m.a = m.g - Fr

 

Minus Fr because it's going against the plane acceleration.

so, we have

a = g - Fr/m

 

 Oh?! What do we have? The biggest the masse is, the biggest the acceleration is ! Our heavier plane is indeed building speed quicker. And our hammer is indeed quicker that the feather. Yeah but all that is IF the engine is OFF !

 

Now, full throttle, we have a new force, the engine's one, helping us to accelerate. Let's call this force Fe and look again :

 

m.a = m.g - Fr + Fe

 

so

 

a = g + (Fe - Fr)/m

 

Ohhhhhh? What can we said now? We can't say anymore that it's obvious that our heavier plane is quicker, because if Fe > Fr, it's actually the other way !!!

 

Fe is constant,

Fr the drag actually increases with the speed. 

 

So I would say that at the start the lighter plane is quicker, having a better acceleration and then when the drag increases and at very hight speed its the other way around. 

 

BUT as stated by LordHelyi, the difference in masse is not that BIG and therefore the term (Fe - Fr)/m is quite small so I would say that in dive, full throttle the difference is very small and insignificant ! 

 

Conclusion :

 

- Its not obvious that the heavier plane dives quicker because he has a SMALLER STARTING ACCELERATION when engine is on

- The game is OK !

- Heavier plane should accelerates quicker with engine off

 

 

Moreover I doubt that flight sim developers would have made such a big mistake in their models ! 

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Well…. I had to react, because what is wroten over there is partially wrong in my humble opinion !

 

It's not that obvious that a heavier plane will dive quicker if his engine is turned on. Thinking in term of momentum is very very misleading, so let's take a look at the acceleration of a diving plane because, well, we all know what is the acceleration !

 

The acceleration, which is the derivative of the speed, follows newton law which is :

 

m*a = [sum of difference forces]

 

With m the mass of our beloved plane, "a" her acceleration and [sum of difference forces] all the forces applied to her.

 

Ok let's say that right now we don't care about air resistance and that the plane's engine is off. We only have the gravity, the force is m*g, g being the gravity constant over the earth. Ok to simplify, let's say that the plane is aiming straight toward the ground and we don't have to deal with angles and projections. We have :

 

m.a = m.g 

so we can simplify by m and :

a = g

 

So acceleration DOESN'T depends on the masse of the plane ! Ok that's weird, if I drop a hammer and a feather, I expect the the hammer to be quicker, therefore having a higher acceleration. Well, it's because of the AIR RESISTANCE. On the moon, there is no air resistance and it's a different story :

 

 

 

Ok let's start again and call Fr the drag produce by the air on our plane. Fr depends usually on the speed of the planes but let's says it roughly constant in our problem. Now we have :

 

m.a = m.g - Fr

 

Minus Fr because it's going against the plane acceleration.

so, we have

a = g - Fr/m

 

 Oh?! What do we have? The biggest the masse is, the biggest the acceleration is ! Our heavier plane is indeed building speed quicker. And our hammer is indeed quicker that the feather. Yeah but all that is IF the engine is OFF !

 

Now, full throttle, we have a new force, the engine's one, helping us to accelerate. Let's call this force Fe and look again :

 

m.a = m.g - Fr + Fe

 

so

 

a = g + (Fe - Fr)/m

 

Ohhhhhh? What can we said now? We can't say anymore that it's obvious that our heavier plane is quicker, because if Fe > Fr, it's actually the other way !!!

 

Fe is constant,

Fr the drag actually increases with the speed. 

 

So I would say that at the start the lighter plane is quicker, having a better acceleration and then when the drag increases and at very hight speed its the other way around. 

 

BUT as stated by LordHelyi, the difference in masse is not that BIG and therefore the term (Fe - Fr)/m is quite small so I would say that in dive, full throttle the difference is very small and insignificant ! 

 

Conclusion :

 

- Its not obvious that the heavier plane dives quicker because he has a SMALLER STARTING ACCELERATION when engine is on

- The game is OK !

- Heavier plane should accelerates quicker with engine off

 

 

Moreover I doubt that flight sim developers would have made such a big mistake in their models ! 

 

Nice!

and how do you explain away the matching climb figures???

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I'll be the first to admit that math is not my subject, but, ......, but the actual way the planes behave is just nonsense.

hillarious

 

Flying half of my life, and now you show up and I can through all my experience into the waste. That's kind of frustrating. I guess the FM guy (an aerodynamic engineer, who created the FMs for RoF, DCS and BoS) will not feel any better.

 

@OP: You obviously don't have too much knowledge of physics. That's no problem. But how about some studies, before you make such posts ?

Edited by BlackDevil
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Thanks !


 


 


ma = -mg + Fe - Fr


 


a = -g + (Fe-Fr)/m


 


Fe > Fr all the time because Fr gets smaller as the speed reduces. Lighter plane should be better at climbing from level flight.


However, after a zoom and climb it's not obvious which plane should be higher.


 


 


Only advantage heavier plane has is top speed. Using classic  quadratic model for air resistance Fr = a*v*v with v the speed and c a coefficient, you have : 


 


0 = mg + Fe - c*v_top*v_top  when you hit top speed no more acceleration, drag balance gravity and engine power.


So we have


 


v_top=sqrt([mg+F]/c)  The heavier the quicker. You can notice that when you are skiing with a heavier friend and he out runs you ! 


Edited by Alkyan

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So, you think that aircraft as heavily wing loaded as all these are, and as heavy as even the lightest of them are should be unstable in all flight regimes, like the planes here are?

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Until 1C/777 provides a way to log data during flight, as 1C did in IL-2 with DeviceLink, or as 1C did in CoD with C#, no one can say with any certainty how well the planes are matching the real world data.

 

Just too many potential sim pilot errors can be made during testing that can completely through off the results. A statement that is based on the hundreds of test logs people generated for IL2 (and other sims) that I have reviewed over the past 10+ years. Where most of the errors were in the way the user performed the ingame test, and not an actual error in the FM. So, until that day, any and all claims of 'testing' should be taken with a grain of salt, and as a bare minimum a track file should accompany any testing so others can review the methods used during testing. Because a simple +/- 20ft change in a 'level' flight speed test can account for some of the errors of the plane being too slow or too fast.

 

Which brings up a related point, Pilot Combat Accounts.. Pretty much worthless to say anything about plane performance.. In that in combat accounts are typically one sided stories that says more about the pilot vs pilot skill than plane vs plane performance.. That and the account typically does not contain enough information to recreate the scenario of the one plane in game to see if you can obtain the same results, let alone the other planes state.. To put that statement into perspective.. For every German pilot combat account of his Bf109 being able to out turn a Spitfire, their is a British pilot combat account of his Spitfire being able to out turn a Bf109.. Yet to this day people still think some sort of statistical average could be gleamed from pilot accounts, but that is a pipe dream, for so many reasons, but one being you never get a chance to read the post action combat reports for the pilots that were killed in action, just to name one.

 

Combined that with the fact that zoom testing was not a standard test in WWII, The standard tests were Top Speed and Rate of Climb.. I have only seen a few zoom tests, and of those, they were conducted in the field and not an instrumented test, thus not enough information to recreate the scenario in game to see if you can obtain the same results.

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Well…. I 

*snipped*

Alkyan, naturally the lighter plane will accelerate faster on initial dive since its undergoing its acceleration produced by work of the engine which is still overcoming the negative effect of drag and conversely is also true.

At the same velocity the air resistance is identical between the two massed planes so it's not that one is enduring more resistance than the other.

The problem appears to be that the momentum/kinetic energy each carries doesn't appear to be correct (I concede the tests aren't perfect since we can't set an auto-pilot to fly the exact same flight path, but its near enough)

 

Essentially, if those two planes were following side-by side or nose-to tail following a flight path to each other then we would expect to see that the planes should separate to begin with, the heavier plane falling behind.

As the dive and speed continues the heavier plane should catch up toward the bottom and then should continue to pull ahead as the climb begins.

As the climb nears the top the lighter plane should begin to make ground once more.

 

That's not what appears to happen. (time to each point in space) - The only minor difference in time to points is more likely due to error in inexact flight paths (The turn of the dive took 3 seconds @ 100% and took 4 seconds @ 10% fuel)

So in effect, the 10% plane spent longer in a state where it should have been decelerating more rapidly from less momentum yet still lost its energy at the same rate as the heavier plane.

 

If I did the zoom climb with the engine off I anticipate the results would be the same, its the energy retention that doesn't feel right.

It was a quick test and one that I think a dive to X speed to Z altitude followed by time to Y speed would indicate better.

Alternatively could just autolevel to maximum speed and shut off engines and measure the deceleration rate between the two planes also.

 

However its *over* the maximum speed that I suspect something is wrong that I was trying to measure quickly.

 

 

 

@OP: You obviously don't have too much knowledge of physics. That's no problem. But how about some studies, before you make such posts ?

 

You don't get to walk into a conversation and call people stupid and produce nothing yourself.

It's hilarious you draw some analogy to operating a piece of machinery somehow gives you innate knowledge of newtonian equations.

Until 1C/777 provides a way to log data during flight, as 1C did in IL-2 with DeviceLink, or as 1C did in CoD with C#, no one can say with any certainty how well the planes are matching the real world data.

 

Not questioning virtual performance vs real world performance by the aircraft numbers themselves.

e.g I'm not interested if the top speed of the real yak is 100kph and the virtual one is only 70kph.

or if the real yak can "zoom" from 650kph and gain 2000m of altitude but the virtual one can only gain 1500m from 650kph.

 

I'm interested in if the virtual yak's weight is not being modelled correctly against another virtual yak of a different weight.

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However its *over* the maximum speed that I suspect something is wrong that I was trying to measure quickly.

 

It's only over the maximum speed (or if engine is off) that the different weight should make a difference. Assuming physical accuracy, I believe that extra fuel should only be taken if it's planned to spend a lot of time in vertical maneuvering above the maximum speed, though IRL I think full tanks were almost always used, in order to provide for contingencies.

 

I think if the test were repeated by first reaching maximum speed horizontally, we would be able to see more clearly if there is a problem, as the weight will effect the entire dive instead of only the later part where the aircraft has passed its maximum speed (~ 550 kph?).

 

About what fraction of the dive does it take to hit max speed?

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So, you think that aircraft as heavily wing loaded as all these are, and as heavy as even the lightest of them are should be unstable in all flight regimes, like the planes here are?

First thing: wing loading has nothing to do with stabillity. Nothing at all. You are missing some basics here.

(the Eurofighter has a much higher wingloading and is unstable - ULs have a lower wingloading and are more stable)

 

Second: all BoS planes are stable. You mix up stabillity with agility.

 

Third: Agility of BoS planes are matching the data available.

 

My suggestiion: Record your flight. And then check the deflection of your controls, whenever it became "unstable".

If you are honest to yourself, you will recognize "steered instabillity". All clients have the same FM. How does it come, that some are rockstable and others are "unstable" ? Try to calm down your inputs.

 

PS: http://forum.il2sturmovik.com/topic/14275-still-enjoying-il2-bos/

Edited by BlackDevil

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@LordHelyi: just take a friend to an MP session. He takes full fuel, you take the same plane empty. This should convince you, that everything is allright. Your "tests" are not convincing, as the inaccuracy is much higher than the effect you are measuring.

 

And don't talk about inertia, if you do energy conversion (zoom climbs).

Edited by BlackDevil

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I really think the lack of axial inertia is a bigger problem but it deserves it's own post.

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You cannot say "ignore inertia" because inertia is very relevant on any object in motion.

The heavier plane should be reaching the end points before the lighter plane (up until a very critical point where the lighter one will 'catch up')

Again like I said in the initial post, after a dive over maximum speed even straight and level the lighter plane still seems to bleed speed off just as slowly (or just as quickly) as the heavier plane.
The lighter plane should slow down faster until the force the engine can provide is equal to the drag induced by the airframe.

Every kph over that point is driven by its momentum and mass and at the same airspeed it experiences the same amount of external forces against against it (air resistance and gravity).
t's not compressing/running into air in front of it any faster than the lighter plane so it's experiencing the same net negative force against it but it has more mass so those effects have less effect on it.
The heavier plane will experience higher forces for longer only simply because it is not decelerating as rapidly but its higher inertia offsets this.

The zoom climb extension i looked at it in principle as the same as the straight and level extension but with greater gravitational effect opposing the plane more directly thus slowing it down faster.
(As opposed to viewing it as rotational momentum about an axis above it like a pendulum).

Edited by LordHelyi

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What I was trying to point out, it that in a gravity field, mass is not (that) important which can be counter intuitive. So far, I'm really not convinced that there is something wrong.

Other factor are the 10% pourcent of mass difference is mathematically significant however already physically hard to observe if not in strict testing  conditions.

I'll take a closer look at your claims and tests when I'm back from work.

However I don't see how developpers of a flight simulation could have done something wrong on such a basic thing ! And if they mishandled the way gravity works, it's a miracle plane fly that well in the game ;)
 

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Alkayans formula is literally just f=ma.
Only he extrapolated out forces (Input from motor and drag) which I ignored since they are for all intents and purposes controlled variables/constants in the example.
And he was actually incorrect in saying that engine power is always greater than air resistance [it is in straight and level flight, engine power = drag at maximum speed when no more acceleration occurs], it is not however the case due to square-cube law and its exactly when we enter engine power < (less than) air resistance (when we utilise gravity to add to our energy system to overcome maximum speed) that things seem a little.... screwy... 

In an unloaded zoom climb you are also looking at engine power being less than the combination of air resistance and gravity (where wings are not generating lift to add to the energy system - this is why inertial formulas are completely relevant to the problem at hand). 

I've tried at 90 degrees and straight and level I'm not seeing much difference to my initial test.
It could be pilot error as such but I'm trying to keep the maneuvres of diving/levelling/rating the nose as clean as and consistent as possible and also flying with minimal slip induced drag.

Let me put it another way, when the wings aren't doing anything the plane is for all intents and purposes a funny-looking bowling ball moving upwards with a certain value of kinetic energy or velocity.
With the engine on it continues to have a force exerted on it (that is still less than the sum of the forces acting against it.... since our planes do not have a thrust:weight ratio > 1 ) .
So at some point as air resistance drops (due to velocity decreasing) engine capability to provide continuous force to continue the current plane of motion becomes more important than the planes ability to resist the forces trying to decelerate it ;)

As for converting energy it should still follows the simple laws of physics.
Looking at v^2 = (u^2 + 2a)d and ignoring air resistance you end up with two planes that should end up at identical heights irrespective of mass, this is no different than looking at throwing two objects up into the air with the same initial velocity in a vacuum, actually thats exactly what the formula is ;)

Of course we do have air resistance so therefore its not quite so cut and dry but for the two objects up in the air principle the heavier object of course will go higher than the lighter one assuming identical aerodynamic profiles and stability (one isn't tumbling compared to the other etc.)

It also means that from the moment those objects "leave" the reference frame (lets say its your hand throwing them) then the lighter object immediately begins decelerating faster. Thus if you pause time at any given point the heavier object should be higher and faster than the lighter object.

Now if you add in another force continuously acting on the object (lets say its the engine) then it becomes another matter and actually becomes more complicated than it first seems.
However as I said earlier that's where there is a critical point where the extra force being adding to the system from the engine is providing more effect to gaining energy to the system than the extra weight overcoming air resistance (because again of square-cube law).. In other words, the engine is becoming more efficient the slower the plane becomes (because of square-cube law of drag)..

It's this that something feels off in that the heavier plane seems to actually decelerate faster than the lighter plane at speeds it should not.

It's very difficult to test.
I'm very much trying to get to the bottom of both explanation and understanding *mathematically* however I think the answer is significantly more complicated than myself nor anyone here is able to offer particularly since we do not have numerical values for things like air resistance.


What I would expect should happen considering *ALL* of the above we have spoken about is this:
I would expect to see the lighter plane achieve a higher altitude due to the efficiency of the engine adding to the system being significantly higher secondary to thrust:weight (With the heavier plane being ahead then overtaken by the lighter plane).

With the engines off I would expect to see the heavier plane achieve a higher altitude and achieve that maximum altitude before the lighter plane.

What I'm seeing is neither of these scenario's and that seems off to me.

 

Also o7 to BlackDevil for contributing. I'd like to think we are all now having an intellectual discussion about the issue and not a slinging match.

Edited by LordHelyi

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Firstly, I don't want to say it's right or wrong. Would have to test it as well, but...

 

 

within the game there is no gravity as well as no air for example. A programmer also do not simulate gravity or air, he's always simulating the consequences of them. And each consequence is a subject on it's own, so if one thing about air / gravity is implemented and correct , it's not necessarily for all 'things" about them.

 

It's also not criticism to the developers, ok, just want to say how object oriented programming works...  :salute:

Edited by StG2_Manfred

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What you should test is no engine, same speed from a unpowered dive, level flight and check the lighter plane is the first to reach low speed. And Check both plane top speed. I don't think i sais that the engine traction is always greater that the drag, drag can virtually increase indefinitively with the speed.

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I think Alkyan I may have taken that from:
"Fe > Fr all the time because Fr gets smaller as the speed reduces."

Which is true whenever the object is below or at a net equilibrium of forces (either below maximum speed or at it), I don't believe the critical point is precisely at the planes maximum speed for the changeover from net benefit of inertia resisting deceleration to the benefit of gaining acceleration [or less deceleration in this case] from the engine... There is a point there and its at that point I'd expect to see a shift in separation of the two planes.
Since I can't fly two planes at once I was looking at separation as a function of "time" for the test (and I'd have anticipated a greater disparity between the two if things were seeming right).

​I am genuinely curious on the subject.

I'm not trying to criticize anyone or the devs (except the rudder sensitivity/curves really need fixing, requiring third-party programs to manipulate sensitivities to something manageable is a bad necessity ;)

 

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that a quote out of context. I said that when the plane was CLIMBING. Which is a fair assumption, the plane is usually slower at that point and therefore a smaller drag. Of course if the plane is climbing with a huge initial speed it's wrong. What's important is for you to change your tests. Becaus the mass effects the traction and drag, but as you said traction minus drag changes sign during a zoom and climb, be heavier is depending of the moment good or bad... Ill take a look if I can find the time.

Edited by Alkyan

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Until 1C/777 provides a way to log data during flight, as 1C did in IL-2 with DeviceLink, or as 1C did in CoD with C#, no one can say with any certainty how well the planes are matching the real world data.

 

Just too many potential sim pilot errors can be made during testing that can completely through off the results. A statement that is based on the hundreds of test logs people generated for IL2 (and other sims) that I have reviewed over the past 10+ years. Where most of the errors were in the way the user performed the ingame test, and not an actual error in the FM. So, until that day, any and all claims of 'testing' should be taken with a grain of salt, and as a bare minimum a track file should accompany any testing so others can review the methods used during testing. Because a simple +/- 20ft change in a 'level' flight speed test can account for some of the errors of the plane being too slow or too fast.

 

Which brings up a related point, Pilot Combat Accounts.. Pretty much worthless to say anything about plane performance.. In that in combat accounts are typically one sided stories that says more about the pilot vs pilot skill than plane vs plane performance.. That and the account typically does not contain enough information to recreate the scenario of the one plane in game to see if you can obtain the same results, let alone the other planes state.. To put that statement into perspective.. For every German pilot combat account of his Bf109 being able to out turn a Spitfire, their is a British pilot combat account of his Spitfire being able to out turn a Bf109.. Yet to this day people still think some sort of statistical average could be gleamed from pilot accounts, but that is a pipe dream, for so many reasons, but one being you never get a chance to read the post action combat reports for the pilots that were killed in action, just to name one.

 

Combined that with the fact that zoom testing was not a standard test in WWII, The standard tests were Top Speed and Rate of Climb.. I have only seen a few zoom tests, and of those, they were conducted in the field and not an instrumented test, thus not enough information to recreate the scenario in game to see if you can obtain the same results.

 

Hear ye, hear ye! Written like a true scientist.

 

I hate myself for quoting a complete post and replying to it with a short, simple comment, especially as it seems to be more of a general comment than a comment specific to this thread. But this post is definitely worth several thorough and thoughtful readings for anybody criticizing the flight models.

 

Important thing to notice here is that I'm not saying if the models themselves are wrong or right, that is beyond my expertise. Only thing I'm saying is that I'm not convinced most of the time by the arguments that a lot of people come up with as the arguments are so vague (from scientific point of view). I.e. non-standardized tests run in an environment they don't fully necessarily understand (the simulator itself), quoting subjective opinions of pilots, which cannot really be used as basis of any standard, as ACEOFACES explains in his post.

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that a quote out of context. I said that when the plane was CLIMBING. Which is a fair assumption, the plane is usually slower at that point and therefore a smaller drag. Of course if the plane is climbing with a huge initial speed it's wrong. What's important is for you to change your tests. Becaus the mass effects the traction and drag, but as you said traction minus drag changes sign during a zoom and climb, be heavier is depending of the moment good or bad... Ill take a look if I can find the time.

Mass has zero effect on drag, only inertia, which has a direct correlation to acceleration because it is by the very definition the resistance to acceleration and thus deceleration.

Drag remains a constant for two objects of identical size/shape/material etc. but of differing mass.

This is demonstrable by a mass in a vacuum affected only by gravity that I posted two posts ago... v^2 = U^2 + 2a x d

 

Aerodynamic stability (tumbling for example with a bullet) and Aerodynamic profile (the shape/surface area/material etc) affects drag.

 

Climbing is only part of the zoom climb towards the end (and its still an unsustainable climb but engine input [external continuous applied force, is significant]), the point where this becomes significant the heavier plane should actually be ahead and the lighter playing 'catch up' (and then consequently surpassing it).

As I said, the only way I can test that is by utilising time to x altitude as a function of that separation.

In which there appears to be little to no difference.

 

In fact the numbers do suggest it is working correctly. I am just not convinced they differences we are seeing are quite true to what you would/should see in real life.

It could also be that >650kph needs to be used to get clearer numbers.

 

Using the same videos for consistency purposes I decided to check the deceleration times.

From ~650kph as soon as speed starts to decay.

Every 50kph drop results in these times:

 

(We are still above maximum speed [Vmax] here so the engine should be doing nothing to assist arresting deceleration...)

---------------------

100% fuel

650 --> 600kph = 5 seconds

 

10% fuel

650 --> 600kph = 6 seconds (???? ill give this a benefit of some flight path error perhaps but the following number says no)

 

 

--------------------------

(We are still above maximum speed [Vmax] here so the engine should be doing nothing to assist arresting deceleration...)

100% fuel

600 --> 550kph = 3 seconds

10% fuel

600 --> 550kph = 3 seconds.

-------------------------

(We have approached and gone through Vmax, the engine is starting to slowly add to the system but it would insignificant at this point, from here on out there should be a growing inversely proportional relationship between the two planes deceleration per second... i.e. the lighter plane slowly begins to decelerate slower than the the heavier plane which should begin to slow down much more rapidly, it would be non-linear in nature)

 

100% fuel

550 --> 500kph = 2 seconds

 

10% fuel

550 --> 500kph = 2 seconds

-------------------------

100% fuel

500 --> 450kph = 2 seconds

 

10% fuel

500 --> 450kph = 2 seconds

------------------------

 

100% fuel

450 --> 400kph = 2 seconds

 

10% fuel

450 --> 400kph = 3 seconds (Critical point somewhere between 400-500kph where less drag and increase effectiveness of engine force in power:weight terms becomes the domineering force on the system)

 

------------------------

 

100% fuel

400 --> 350 = 2 seconds

 

10% fuel

400 --> 350 = 3 seconds

 

------------------------

 

100% fuel

350 --> 300kph = 2 seconds

 

10% fuel

350 --> 300kph = 3 seconds

 

------------------------

 

 

So is this correct?

Yes and no.

This is exactly what should happen (a speed that is *below* Vmax becomes the critical turning point where air resistence and the benefit of mass succumbs to the benefit of engine power to lower mass [we can demonstrate that using f=ma and f is a constant extra force applied to the system from the engine so knowing f + m you can easily see how acceleration (rather its still deceleration) is affected by the extra mass as 'f' becomes closer to the total kinetic energy (i.e. velocity) of our "system".)...

However the deceleration still seems to be too high for the heavier plane exactly where it should be performing better.

 

 

Those numbers of deceleration times actually shows exactly why I said earlier [with minor reclarification]:

 
I would expect to see the lighter plane achieve a higher altitude due to the efficiency of the engine adding to the system being significantly higher secondary to thrust:weight (With the heavier plane being ahead up until the critical point then being caught up to and then overtaken by the lighter plane).

With the engines off I would expect to see the heavier plane achieve a higher altitude and achieve that maximum altitude before the lighter plane.

 

But that's not what we I'm seeing (which is what I have been saying, that momentum does not appear to properly modelled).

What we are seeing is the heavier plane decaying its speed at the same rate as the lighter plane above Vmax and above the critical point (not correct) where the critical point is where the continuous applied force from the engine becomes significant for the reduced drag AND reduced gravity (which we should see, correctly).

Edited by LordHelyi

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Oh my.... mass doesn't change the FORCE of the drag. But mass change how this force is going to affect you. If you are very heavy, drag force will have a smaller impact on your acceleration (then speed, position), it's what I mean. I think it is very obvious in regard of my first post... It's the story of the hammer and the feather again. Acc = g + Fdrag/m.

Now I didn't have time to read your entire new post, even if I feel a bit of confusion, I can't say anything, I'll look when I'm home.

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So, you think that aircraft as heavily wing loaded as all these are, and as heavy as even the lightest of them are should be unstable in all flight regimes, like the planes here are?

 

What do you mean unstable?

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What do I mean by unstable?

 

That feeling that you are trying to balance these aircraft on the point of a pin, for one example.

 

The feeling that these aircraft are fairly weightless, regardless of the fact that they have engines/drivelines that weigh around 2000 pounds, and are much heavier than your typical modern general aviation aircraft.

 

This has been an interesting discussion, I always appreciate it when real world technical items are discussed as it's always a good day to learn new things.  However, we must remember that we are not talking about real aircraft, we are talking about representations of real aircraft that are generated by a computer program.  A comupter program that is designed to run on home hobbyist  computers, not NASA supercomputers.  Real airflow cannot be modeled in any way that is realistic, no PC has the power to do that.  So as was said before, we have pixel planes that are programmed to behave in some sort of manner that depicts actual flight, but in fact is NOT actual flight.

 

Ones and zeros gents, that's all we have here, just ones and zeros, and a simple decimal point in the wrong place, or a flawed bit of input info can throw any chance of "realistic" flight behavior right out the window.

 

And that is what a very sizeable number of people that are struggling with the "flight dynamics" of BoS are on about.

 

There are lots of players, here, and on other forums, that have a high degree of skepticism about the veracity of the BoS global FM.  Only very few of you seem to think all is peachy here.

 

Obviously both conclusions cannot be true at the same time.

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There are lots of players, here, and on other forums, that have a high degree of skepticism about the veracity of the BoS global FM.  Only very few of you seem to think all is peachy here.

I answered you, and you totally ignored that answer. And now you come with this most senseless of all arguments.

Everyone, who is not your opinion belongs to very few, and you, of course, are the speaker of the majority.

 

 

First thing: wing loading has nothing to do with stabillity. Nothing at all. You are missing some basics here.

(the Eurofighter has a much higher wingloading and is unstable - ULs have a lower wingloading and are more stable)

Second: all BoS planes are stable. You mix up stabillity with agility.

Third: Agility of BoS planes are matching the data available.

My suggestiion: Record your flight. And then check the deflection of your controls, whenever it became "unstable".

If you are honest to yourself, you will recognize "steered instabillity". All clients have the same FM. How does it come, that some are rockstable and others are "unstable" ? Try to calm down your inputs.

PS: http://forum.il2sturmovik.com/topic/14275-still-enjoying-il2-bos/

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What do I mean by unstable?

 

That feeling that you are trying to balance these aircraft on the point of a pin, for one example.

 

The feeling that these aircraft are fairly weightless, regardless of the fact that they have engines/drivelines that weigh around 2000 pounds, and are much heavier than your typical modern general aviation aircraft.

 

[sNIP]

 

There are lots of players, here, and on other forums, that have a high degree of skepticism about the veracity of the BoS global FM.  Only very few of you seem to think all is peachy here.

 

So obviously you have no idea what you're talking about. Wikipedia -> Aerodynamic stability -> read

 

Just shortly - agile plane = less pronounced stability. Compare LaGG and Yak for example - LaGG is a better gun platform, because it's more stable - but it's also a friggin brick in a dogfight. You luftwhiners have to understand that your Bfs are so nice and agile because they're less stable. And of course, all planes in BoS are aerodynamically stable, not a single one is neutrally stable or unstable. As mentioned - read the Wikipedia article above (God forbid you buy a book on aerodynamics and read it, like some of us had to...).

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Fuel has a marked effect on turns/stalls in the Fw 190. Seems to have less effect in zoom climb than I would expect. This is experience/anecdotal as I have not specifically tested it.

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Luftwhiner?

 

Me?

 

Too funny,..

 

I have tried to verbalize how these things feel to a lot of us, you chose to make it personal, Fine, I refuse to stoop to your childish level.   The majority of players are not real pilots, please understand that and stop being so damned elitist. 

 

If the price of admission to BoS is a Thrustmaster Warthog, then this sim is doomed, and all the praise by the Legion of 777 Defenders won't save it.

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If the price of admission to BoS is a Thrustmaster Warthog, then this sim is doomed, and all the praise by the Legion of 777 Defenders won't save it.

 

Many of us who plays and like the game dont have this "rubber band" issue, and we dont have a Warthog. Have you thought that maybe the problem lies with you ? :salute:  

Edited by istruba

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Oh my.... mass doesn't change the FORCE of the drag. But mass change how this force is going to affect you. If you are very heavy, drag force will have a smaller impact on your acceleration (then speed, position), it's what I mean. I think it is very obvious in regard of my first post... It's the story of the hammer and the feather again. Acc = g + Fdrag/m.

 

Now I didn't have time to read your entire new post, even if I feel a bit of confusion, I can't say anything, I'll look when I'm home.

I had assumed you meant correctly and/or its a language conversion issue for yourself.

 

However it's just when you have other people reading a discussion and may even learn something from our workings, I feel it important to keep it specific and accurate :)

I probably should have said something along the lines of "just to clarify" and then the remainder.

 

However I nor anyone else can purport to having 100% perfect communication 100% of the time. :)

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In fact the numbers do suggest it is working correctly. I am just not convinced they differences we are seeing are quite true to what you would/should see in real life.

 

I think the timing precision needs to be better in order to tell for sure. I made a little simulation (MATLAB or GNU Octave) for the Yak-1 under discussion and it looks like the difference in time to slow from 650 kph to 550 kph only differs by about 0.3 seconds. The simulation is very simple - only considering nothing more than mass and a fixed zero-lift drag coefficient - and thus doesn't match the game, but I think it gives an idea of the magnitude of the effect.

 

I used 0.025 for the drag coefficient (the rest of the parameters are from Wikipedia, this thread, and an online air density calculator).

 

Does anyone know the real Cd for a Yak-1?

 

Here's the chart from the program:

 

 

9SriAYc.png

 

 

Edited by reve_etrange

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Oops, forgot to convert kph to m/s!

 

The difference is still only about a second - it's probably less in the game due to the inclusion of induced drag and use of the correct Cd,0.

 

 

 

goB7tGR.png

 

 

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Good stuff there reve_etrange it gives a reasonable approximation of what to expect to see.

If you were to add a continual force adding to the system less than the force of the drag to the system you'd expect to see the two curves re-converge together at a lower speed after Vmax.

Difficult to get an accurate test in game though.

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I like the two graphs there, reve_etrange.  Of course, this would be assuming fuel quantity had no bearing on CG.  If the CG moved aft with fuel that would reduce drag and vice versa.

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