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[Ala13_ManOWar]

Really Herra, I'm not interested in arguing.


Please, explain you to me,

Flaps deployed, power settings unchanged, elevator and rudder trim unchanged. Aircraft's angle of attack is almost immediately reduced to 3°, but nose goes up because the aircraft starts to climb:

How in the world can nose go up while AoA is lower right after flaps deploy? How is AoA measured in Il-2? If AoA is reduced from 4º to 3º in your initial conditions, how can nose go UP?? AoA is relative to wind, you can have more or less of it nose down or up, doesn't matter, so you can be nose up with few AoA, or nose down with high AoA. In your experiment, how it's supposed to work? if AoA lowers to 3º immediately means inside Il-2 wind direction relative to wing chord (AoA definition) change instantly as you lower flaps but your aircraft still flies same direction against wind? How is it?  ??? ???

The aircraft then settles into a a phugoid mode descent where rate of descent and airspeed vary somewhat but the general trend is descending. Angle of attack varies between 2°-3° depending on the stage of oscillation.

And please, also explain this. Flaps deploy or less AoA doesn't mean ever you have to descent. Why Il-2 ends descending after a (long) while? in your logic, if you have more lift how can you descent? and while landing how can you descent but nose is up so it covers the runway sight if AoA is lower? In RL flaps deploy and AoA lowering is an aid to see runway lowering the nose, not the opposite... Explain me how on Earth works Il-2.


Anyway whatever it's the explain to you, a real aircraft just don't behave like that, so as you asked want to listen from me how RL behaves (just a comment I leave, jeez) or how you want RL to behave to match Il-2?


S!

[Herra Tohtori]

Please, explain you to me,

Flaps deployed, power settings unchanged, elevator and rudder trim unchanged. Aircraft's angle of attack is almost immediately reduced to 3°, but nose goes up because the aircraft starts to climb:

How in the world can nose go up while AoA is lower right after flaps deploy? How is AoA measured in Il-2?

I'm pretty sure angle of attack in IL-2 is measured as the wing chord's angle of incidence relative to airflow. But, even if it didn't give the accurate value, it will still tell whether the AoA is reduced or increased: And, if the climb angle is increasing faster than angle of attack is decreasing, then the net effect is that the nose pitches up relative to horizon.

Obviously, when I speak of "immediate response" I mean that the aircraft starts to react to deployment of flaps quite rapidly, which is not surprising since they are pretty large control surfaces. But since the deployment of the flaps is a gradual process, the angle of attack is also gradually changed.

If AoA is reduced from 4º to 3º in your initial conditions, how can nose go UP??

Because the whole aircraft is kicked upward by the increased lift.

AoA is relative to wind, you can have more or less of it nose down or up, doesn't matter, so you can be nose up with few AoA, or nose down with high AoA. In your experiment, how it's supposed to work? if AoA lowers to 3º immediately means inside Il-2 wind direction relative to wing chord (AoA definition) change instantly as you lower flaps but your aircraft still flies same direction against wind? How is it?  ??? ???

Didn't I already explain this? Oh, wait, you probably didn't read those posts thoroughly.

There are two things going on here: The flaps have an effect on the aircrafts rotational attitude AND linear motion.

Here's a diagram of why flaps cause a reduction in angle of attack:



Straightforward enough, isn't it? Of course, as the flaps are being lowered, this process happens gradually. These frames are separated just for illustrative purposes.

Except that is not the whole story. Even though the flaps still reduce the angle of attack - much like pushing nose down with elevator - they still cause an increase in net lift because of the change in coefficient of lift.

When you factor in the fact that the aircraft has "excess lift", it causes the aircraft to accelerate upward. This will make the aircraft's flight path angle upward.

Here is a diagram of the effect of moments and linear forces combined:




Where the aircraft's nose turns depends on the relative effects of these two things: The flaps turn the nose down relative to airflow but the increased lift causes the aircraft to climb.

If the climb angle is larger than the reduction of angle of attack, the net effect is that the aircraft pitches up relative to horizon.

In larger scale, the whole process looks more like this, which I already linked earlier:

The aircraft then settles into a a phugoid mode descent where rate of descent and airspeed vary somewhat but the general trend is descending. Angle of attack varies between 2°-3° depending on the stage of oscillation.

And please, also explain this. Flaps deploy or less AoA doesn't mean ever you have to descent.

No, it doesn't have to descend, that's just what happens when the aircraft is not controlled by pilot or autopilot system.

Why Il-2 ends descending after a (long) while? in your logic, if you have more lift how can you descent? and while landing how can you descent but nose is up so it covers the runway sight if AoA is lower? In RL flaps deploy and AoA lowering is an aid to see runway lowering the nose, not the opposite... Explain me how on Earth works Il-2.

The aircraft descends because power settings are not changed, but drag is increased due to deployed flaps. This causes the airspeed to drop. If the trim is not adjusted for the lower airspeed, the aircraft will descend.

Anyway whatever it's the explain to you, a real aircraft just don't behave like that, so as you asked want to listen from me how RL behaves (just a comment I leave, jeez) or how you want RL to behave to match Il-2?

My argument is that the fundamental behaviour of the aircraft flaps in IL-2 is not as far removed from reality as you seem to claim.

It is very possible, and even likely, that some IL-2 aircraft don't model the flaps accurately. The amount of lift and drag increase may be wrong, as may be the effect on the plane's attitude (AoA). However, that is a problem with individual flight model parametres, and you should direct your critique there. You've been making some very harsh claims on the fundamental mechanics of flaps in IL-2, which have been shown wrong by in-game data: You claimed that flaps cause AoA to increase, while in fact it is reduced.

Did you ever experiment with flaps in IL-2 using an actual indicator for what your aircraft's angle of attack really is, rather than just relying on your impression?

[Ala13_ManOWar]

I don't think it's a matter of an individual FM Herra, that the case may be at least ONE FM out there with correct behaviour inside Il-2, specially default aircraft. Not the case, every aircraft in Il-2 behaves the same as far as I have flown, that's incorrect although I get perfectly what you think to happen (I understood first time, and I knew what your explain would be to what happen).

Show me one single FM, only one, behaving correctly with flaps so I can't say it's a core design flaw as I think (that's what you're fighting to demonstrate now, isn't it?).


About your drawings they are fine for your point (although faked vectors...  ), but not the whole thing we are discussing. Now think the case, you're inside Il-2, levelled, deploy one point flaps, no power change, you do whatever you have to keep levelled, first fighting against nose up, then to prevent aircraft to descent. Final stage, same power setting, one point flap, HUD says AoA is lower like your example, you're a perfect pilot and altitude is kept same, just airspeed a bit less or even same doesn't matter, still levelled... but your nose raised against horizon... What's your explain? Whatever the explain you now perfectly what I mean, lowering flaps in Il-2 makes your nose to cover the runway making harder to land. Tell me please.

S!

[Herra Tohtori]

I don't think it's a matter of an individual FM Herra, that the case may be at least ONE FM out there with correct behaviour inside Il-2, specially default aircraft. Not the case, every aircraft in Il-2 behaves the same as far as I have flown, that's incorrect although I get perfectly what you think to happen (I understood first time, and I knew what your explain would be to what happen).

Show me one single FM, only one, behaving correctly with flaps so I can't say it's a core design flaw as I think (that's what you're fighting to demonstrate now, isn't it?).

As you've pointed out, I am not a real life pilot, and I haven't flown any of these aircraft so I don't know how exactly these planes would behave. I can only analyze their behaviour through my understanding of physics.

Since I also have some understanding of how physics simulations work (the mathematical background behind it), there is a difference between the underlying mechanics and the data you feed the simulator.


To paraphrase the great Charles Babbage: "On two occasions I have been asked, "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" ... I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question."

In other words, if the data is wrong you'll get wrong results even if the machine itself works perfectly.

In this case in particular, I feel that the equations used by the physics engine itself are likely to be correct, as it is all fundamentally well-known and understood physics. There's no need to "fake" anything.

But if the game is using incorrect flight models... well, of course that becomes difficult to analyze, especially if one has not flown these particular aircraft.

About your drawings they are fine for your point (although faked vectors...  ), but not the whole thing we are discussing.

Well, yeah, of course the vectors are just there to give an approximate idea of the relationships of forces affecting the aircraft. I'm pretty sure I could import screenshots from X-Plane with vector indicators activated, and get similar results.

Now think the case, you're inside Il-2, levelled, deploy one point flaps, no power change, you do whatever you have to keep levelled, first fighting against nose up, then to prevent aircraft to descent. Final stage, same power setting, one point flap, HUD says AoA is lower like your example, you're a perfect pilot and altitude is kept same, just airspeed a bit less or even same doesn't matter, still levelled... but your nose raised against horizon... What's your explain?

That has to do with your airspeed in the different stages of the experiment.

Since you're allowed to maintain altitude, you must indeed adjust the angle of attack so as to keep the equation "Lift = Weight" balanced.

In the first stage, you lower the flaps and that changes the coefficient of lift for the wing. With airspeed initially unchanged, your wing produces lots of lift and you must reduce it somehow to avoid climbing - which you do by reducing angle of attack with elevator.

But, since your drag is much higher than thrust (engine power unchanged) your aircraft loses airspeed, and when airspeed is reduced, lift is also reduced, and you must then start to slowly increase the angle of attack in order to maintain the lift-weight equilibrium.

However, if you look at the lift equation from earlier you should notice that the relationship between lift and AoA is linear, but lift is proportional to the square of velocity.


To put this mathematics into physical perspective:

If you're flying at 8 degrees AoA at 120 KIAS, your wing produces four times as much lift as if you were flying at 8 degrees AoA at 60 KIAS
Since doubling airspeed quadruples the lift, the wing would be producing about the same lift at only 2 degrees AoA at 120 KIAS, because 2 degrees is a quarter of 8 degrees.

Approximately speaking, that is. Things get more complicated near zero angle of attack and likewise near the critical angle of attack.

What this means in context of your example is that when your aircraft slows down, of course you need to start pulling the nose up in order to maintain airspeed, flaps or no flaps. Eventually as you slow down enough you'll need to pull so much angle of attack as the wing stalls (that's what's known as the "stall speed").

Whatever the explain you now perfectly what I mean, lowering flaps in Il-2 makes your nose to cover the runway making harder to land. Tell me please.

Well it seems to me that there are two functions to using flaps and you just need to decide which way you want to use them.

Firstly, you can use it during approach to reduce the angle of attack and improve visibility, but you must then make sure you maintain your airspeed so that you can keep the nose pushed down. In other words you need to maintain your approach speed by increasing power. The power increase is necessary because flaps increase drag - you must then add power to equalize thrust and drag to prevent the aircraft from slowing down.

Secondly, you can use it to reduce the level-flying airspeed at which your aircraft stalls. This can be useful when you are landing on a short runway because slower speed reduces the landing roll distance. Or you may want to minimize the impact velocity in a forced landing. In this case, you would be "riding the stall" at the final point of landing, at slowest possible airspeed with angle of attack as high as possible without stalling.


Speaking of landings, most of the aircraft in IL-2 are tail-draggers that would optimally be flown to a three-point landing. The nose covering the runway was a historical problem with many of the planes, to such extent that pilots started coming up with novel solutions for landing on short runways such as curved approaches, in which the pilot could maintain the sight of the runway threshold longer.


The problem with "fast approach" mode (nose pushed down to see the runway) is that you're then coming in at higher than normal approach speed and you'll have to slow down before you can touch down - or you can reduce flaps as you reach runway threshold, and then start increasing AoA to slow down.

Aircraft with tricycle landing gear or two-engine planes, such as P-38, P-39, B-25, and A-20 are of course much easier to land as the forward view down is much less obstructed. They're also much easier to land because the landing gear arrangement prevents nose-overs during braking.


By the way, an aspect of physics in IL-2 that is incorrect is ground handling. That is mostly because they never modeled static friction in, and all landing gears just use kinetic friction, sliding on the surface. The rotation of the wheels is there just for show; every plane is essentially a sled. This means take-offs, landings and taxiing are in my opinion the weakest part of the game mechanics in IL-2.


My experiences in IL-2 suggest that flaps work (more or less) like they should in these situations, but I of course have no way to compare them to the real warbirds as I never flew them.

Then again, WW2 aircraft are substantially different from modern general aviation aircraft. A Beech King Air C90GTi has empty weight of 3,150 kg and loaded weight of 4,580 kg. That's about comparable to a late-war single-engined fighter (P-51D, empty weight 3,232 kg, MTO weight 5,488 kg). A twin-engined WW2 fighter like the P-38 is substantially heavier at 5,800 kg empty, 9,798 kg MTO.

What types of aircraft have you flown? If we're talking about something like Cessna 152, that thing weighs only about 500 kg, even the lightest single seat fighters in WW2 weighed at least two times more than that and were of similar dimensions. Flaps would have a much more pronounced effect on a light aircraft than a heavy one.

[rockdoon]

im just gonna point out in my 20 hours of flight instruction (i know its not alot) in the cessna 172 it tends to pitch up when flaps are brought out, and we have to push forward on the yoke to push the nose back down, now in some larger aircraft the plane will pitch down, it all depends not all A/C work the same

[Ala13_ManOWar]

Tomorrow I'll look for time to answer.

im just gonna point out in my 20 hours of flight instruction (i know its not alot) in the cessna 172 it tends to pitch up when flaps are brought out, and we have to push forward on the yoke to push the nose back down, now in some larger aircraft the plane will pitch down, it all depends not all A/C work the same

Rockdoon, seems you still few hours and/or you didn't reach theory about it, although not sure where you are because European theory is usually way more larger than USA for example. But look at it next flight, also talk to instructor. Your nose lowers... sure it does, don't look only firsts seconds, look your nose distance to horizon (I'm sure your instructor talks you about look that, isn't it?).

What types of aircraft have you flown? If we're talking about something like Cessna 152, that thing weighs only about 500 kg, even the lightest single seat fighters in WW2 weighed at least two times more than that and were of similar dimensions. Flaps would have a much more pronounced effect on a light aircraft than a heavy one.

I'm well aware about I haven't flown anything like a warbird (except a flight in Tiger Moth  ), but mate an aircraft is an aircraft and fly the same with same physics behind. C152 is 760Kg MTOW, C172RG 1200Kg MTOW, also I have microlights licence got in Tecnam P96, supposed less than 500Kg. Every of them have it's own "flavor", but deep behaviour follows same rules. Indeed in DCS P-51 I can feel clearly that behaviour although I haven't flown any P-51... That tells me something. Not the case in Il-2.

S!

[Herra Tohtori]

an aircraft is an aircraft and fly the same with same physics behind.

That's a tautology... A feather and a football both fly with the same physics as a Boeing 747 and the space shuttle.

The slight differences in their behaviour are due to them being different objects. They behave differently because they are not the same.

If you have two different aircraft they can behave differently. That's where different flight characteristics come from. I don't see any reason why that wouldn't extend to flaps producing different response on different aircraft.

[Fresco23]

Such an intense conversation... 

[Ala13_ManOWar]

Herra mate, I was on trying to answer with drawings like you did, quote everything an explain, and so... but I have no time really nor I'm in the mood...


Still last example I gave you didn't answer really, when I told you something you bring it to what you want to understand and look for your bizarre explain. Just I try one more, but I'm not even going to answer any more, I said before and you get me answering again. No more, I can't go through a brick wall.


Mate, read carefully this time, don't change scenery I told you for your convenience, just take it as is and try to understand, I try to explain my better (I know my English not the best). For now we achieved to you recognizing AoA lowers when flaps down, but still you say that gets you to a nose up  ???. Easier scenery, your plane 100KIAS levelled flight, you know one speed is related to one AoA, the one giving you the lift you need (your weight). Now we deploy flaps, but this is a perfect plane no speed loss, so 100KIAS levelled flight say 10º flap deploy. With flaps I have more lift, so to keep equilibrium I need less AoA to get same lift I need to keep my weight at 100KIAS, forget climb or descent this is a perfect aircraft autopilot keeps you perfectly levelled all the time. Like you achieve to understand, AoA is lower with flaps deployed, so inside this second condition, would your nose be higher or lower than first condition? and remember, nose up or down doesn't means you to climb or descent, that's related to wings and AoA, still you're perfectly levelled in our perfect aircraft.

Ok, now I hope your answer would be clearly your nose have to be lower... and that doesn't means you to descent or climb, just means your nose is lower, so your nose clear more distance to horizon from cockpit. That's the clue every pilot in the world is told to look for. So, inside Il-2 now, why same speed, deployed flaps, same levelled, your nose is higher than no flaps although lower AoA as your HUD says ??? ? How can be your AoA lower being your nose higher still levelled ??? ? Find an aircraft not behaving like that and show us because whatever the logic behind (the one you trying to explain in soooo long sooo many posts) it's a miserably mistaken behaviour and never ever what really happens.


For further information please read this (many things out there, just one I think very clear and well explained),

http://www.amazon.com/Stick-Rudder-Explanation-Art-Flying/dp/0070362408

go into any pilots theory web and study it or look for an engineer and fight with him, not with me  .


This time definitely out the Man of War.

[Herra Tohtori]

Herra mate, I was on trying to answer with drawings like you did, quote everything an explain, and so... but I have no time really nor I'm in the mood...


Still last example I gave you didn't answer really, when I told you something you bring it to what you want to understand and look for your bizarre explain. Just I try one more, but I'm not even going to answer any more, I said before and you get me answering again. No more, I can't go through a brick wall.

Well I'm having similar thoughts, I'm not sure you understand what I'm saying.

Mate, read carefully this time, don't change scenery I told you for your convenience, just take it as is and try to understand, I try to explain my better (I know my English not the best).

I respect the language barrier and your English is better than my French so I'm not one to criticize. I'm pretty sure we both have a good understanding of the flight dynamics involved but just need to make sure we understand what the other is saying...

For now we achieved to you recognizing AoA lowers when flaps down, but still you say that gets you to a nose up  ???.

Flaps change the natural trim of the aircraft so that it stabilizes to a lower angle of attack. However, if that angle of attack with flaps still produces more lift than weight, then the aircraft starts to climb and it is that climbing trajectory which causes the nose to rise over horizon.

In this case, the aircraft requires manual input from the pilot to reduce angle of attack even more than where it naturally settles with the flaps down, and that's done by forcing the nose down.

Easier scenery, your plane 100KIAS levelled flight, you know one speed is related to one AoA, the one giving you the lift you need (your weight).

All right, but how does the aircraft know how much lift it's supposed to produce? Generally there must be some sort of intelligent controller onboard to artificially maintain the elevator trim so that lift and weight actually remain equal.

Now we deploy flaps, but this is a perfect plane no speed loss, so 100KIAS levelled flight say 10º flap deploy. With flaps I have more lift, so to keep equilibrium I need less AoA to get same lift I need to keep my weight at 100KIAS, forget climb or descent this is a perfect aircraft autopilot keeps you perfectly levelled all the time.

Yes, the autopilot pushes the nose down to compensate for the increased coefficient of lift. If the aircraft keeps flying at same indicated airspeed, that's what must happen indeed.

Like you achieve to understand, AoA is lower with flaps deployed, so inside this second condition, would your nose be higher or lower than first condition?

If the aircraft's trajectory is perfectly horizontal (vertical speed zero, no climbing or descending), then clearly the nose would point lower than in first flight state.

and remember, nose up or down doesn't means you to climb or descent, that's related to wings and AoA, still you're perfectly levelled in our perfect aircraft.

Ok, now I hope your answer would be clearly your nose have to be lower...

Within the artificial constraints that the nose is being actively pushed down by the autopilot or pilot, yes.

and that doesn't means you to descent or climb, just means your nose is lower, so your nose clear more distance to horizon from cockpit.

Obviously. If lift-weight equilibrium is artificially maintained, the aircraft keeps traveling in a straight line.

This whole conversation has been about why the nose goes up when you don't apply any control inputs, though.

That's the clue every pilot in the world is told to look for. So, inside Il-2 now, why same speed, deployed flaps, same levelled, your nose is higher than no flaps although lower AoA as your HUD says ??? ?

But... that's just not how it works. IL-2 flaps don't work like that. If you deploy flaps in the game and maintain level flight you must force your nose lower in order to avoid climbing.

How can be your AoA lower being your nose higher still levelled ??? ? Find an aircraft not behaving like that and show us because whatever the logic behind (the one you trying to explain in soooo long sooo many posts) it's a miserably mistaken behaviour and never ever what really happens.

Within the constraints you specified, of course the nose is lower.

No flaps, 50% power, about 70% prop pitch, 30% fuel... level stabilizer engaged, and she flies at about 310 km/h TAS at 2 degrees angle of attack.





Flaps 50%, needs a bit more power to maintain airspeed. Level stabilizer is starting to fail due to excessive airspeed for the aircraft's configuration, the aircraft is climbing at about 1 m/s but that's still level enough for demonstration purposes. You'll notice that the angle of attack indicator is showing -2 degrees...





Full flaps. Need almost full engine power to maintain airspeed, and I had to disengage level stab and manually trim the aircraft to fly level (full elevator trim down, and I still had to push on the stick to keep the aircraft from climbing). AoA indicator reads -4 degrees.






The point is that if the nose is not being forced down when flying at high speed, then the aircraft will start climbing and that's what increases the pitch attitude relative to horizon.

Flaps by themselves reduce angle of attack a bit (1-2 degrees in case of B-25J flight model in IL-2) but that alone is insufficient to equalize the lift, so the aircraft starts to climb.

If the pilot forces aircraft to level flight by righteous use of elevator, then you get results like those shown above. But you'll notice from the pictures that the elevator deflects quite a bit down even at 50% flaps, so it's not surprising that if you just leave the elevator alone the aircraft would pitch up dramatically.



The core of the argument here is that there's no fundamental "need" for lift to remain equal to weight when flaps are deployed - the pilot must take care of that (by reducing angle of attack).


Let me ask you a question.

Using this "ideal perfect aircraft" from your example. It's flying at 100 KIAS, clean configuration (no flaps, no landing gear). Trimmed to fly straight and level, but no autopilot.

Now the pilot advances throttles and aircraft starts to accelerate. Elevator trim is unchanged. What will the aircraft do?


EDIT: Added some gaps between quotes/paragraphs to make the post easier to follow.

[Ala13_ManOWar]

Said no more answer... I hate me... 

Now the pilot advances throttles and aircraft starts to accelerate. Elevator trim is unchanged. What will the aircraft do?

That's the definition of climb mate, you levelled throttle up, then aircraft uses that excess power to climb keeping it's trimmed airspeed. That's the way the wing "knows" the lift need as you say, that's the equilibrium I named couple of hundred times yet XD. Also applies to descent, you throttle down letting her alone then aircraft first decelerate a bit start descent and stabilizes at a descent rate depending on how much throttle you downed but always at trimmed airspeed, that's how you calculate where to start a descent to let you at a certain altitude keeping airspeed all the way. An engineless aircraft just descent at trimmed airspeed, doesn't falls as a stone or stalls like many people thinks. Even that glide is well measured, it's specified on manuals and big aircraft knows exactly how much far they can go engineless starting at known altitude. The wings are "smarter" than it looks like you just have to let them fly.

This whole conversation has been about why the nose goes up when you don't apply any control inputs, though.

well, not my point, I know why nose goes up, what I say is Il-2 behave doesn't match real thing, in a real aircraft you don't have to push so much even nothing to keep your nose with flaps deployed even with your new lift. Now with your answers to my "controlled scenery" I see something, nose can't go up forever like Il-2 if you deployed flaps so may be what Il-2 lacks ia a proper drag modelling? That can be the thing. I don't know about core design, what I do know for sure is it behaves far from real, and I thought this whole conversation was about you think Il-2 is perfect and the real thing is wrong  .


S!

[Herra Tohtori]

Said no more answer... I hate me... 

Now the pilot advances throttles and aircraft starts to accelerate. Elevator trim is unchanged. What will the aircraft do?

That's the definition of climb mate, you levelled throttle up, then aircraft uses that excess power to climb keeping it's trimmed airspeed.

Yep, I know the aircraft starts to climb, what I'm asking is... why?

Think about Newton's first law: "...an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force."

When in level flight, aircraft is not moving up or down. Vertical speed is zero.

To get the aircraft moving up (or down), it must experience of change of vertical velocity so that it is no longer zero.

That means there must be an acceleration upward (or downward).

When there is acceleration, there must be a net non-zero force in the direction of acceleration.


What is that force in your opinion? It can't be the engine's thrust because that's directed forward. So, please do answer: What is the force that makes the aircraft deflect upward from a horizontal trajectory?

By the way, an aircraft's trim is actually set to maintain a specific angle of attack rather than a particular airspeed. If there was some kind of inherent speed-maintaining property on aircraft they would not get into long term oscillations between airspeed and altitude. If the aircraft is stabilized to fly at a particular trim and particular airspeed, it does tend to maintain that airspeed as well but getting to that point requires usually management of both the trim controls and thrust settings.

That's the way the wing "knows" the lift need as you say, that's the equilibrium I named couple of hundred times yet XD.

There is no direct coupling between the aircraft's weight and lift. The equilibrium must usually be maintained by a pilot - otherwise the aircraft will end up in oscillating flight path (phugoid).

The wing doesn't "know" anything. It's a dumb physical object that interacts with the airflow. It just produces lift as defined by its profile, airspeed and angle of attack.

Since these parametres can be almost anything, the lift also can be almost anything; there's no requirement for it to always be equal to aircraft's weight and in fact the whole business of aviation is based on being able to change how much lift is being produced. Otherwise, maneuvering would be very tricky...

Also applies to descent, you throttle down letting her alone then aircraft first decelerate a bit start descent and stabilizes at a descent rate depending on how much throttle you downed but always at trimmed airspeed, that's how you calculate where to start a descent to let you at a certain altitude keeping airspeed all the way. An engineless aircraft just descent at trimmed airspeed, doesn't falls as a stone or stalls like many people thinks. Even that glide is well measured, it's specified on manuals and big aircraft knows exactly how much far they can go engineless starting at known altitude. The wings are "smarter" than it looks like you just have to let them fly.

Again: Why does an aircraft trimmed to fly level turn to descend when throttle is decreased? What makes it move downward? There must be a net downward force to make the aircraft's vertical speed change from zero to negative.


To shuffle the deck even more thoroughly, here's an additional question:

If a bomber is trimmed to fly level flight at some given engine power settings, and then it drops 8000 lbs of ordnance at once, will it start to climb or stay level if the trim is not changed?

This whole conversation has been about why the nose goes up when you don't apply any control inputs, though.

well, not my point, I know why nose goes up, what I say is Il-2 behave doesn't match real thing, in a real aircraft you don't have to push so much even nothing to keep your nose with flaps deployed even with your new lift.

It's difficult to quantify "how much" the nose must be pushed down when you don't really "feel" the aircraft in the game. You don't feel control forces or the lateral accelerations, so that already makes a huge difference in how the flight is perceived.

Another explanation could simply be that the aircraft are very different from what you generally fly, so they might respond differently... It doesn't necessarily mean that it's fundamentally wrong.

Now with your answers to my "controlled scenery" I see something, nose can't go up forever like Il-2 if you deployed flaps so may be what Il-2 lacks ia a proper drag modelling?

But, as I've demonstrated earlier in this thread, the nose doesn't go up "forever". The aircraft initially climbs due to high airspeed it carries from its initial configuration, and majority of the nose going up is caused simply by the trajectory shifting upwards (which happens because wing is producing more lift than aircraft's weight). When the aircraft slows down, it starts to descend but because it doesn't automatically stabilize to a particular airspeed it ends up waving up and down in a generally descending pattern.

Since the speed does reduce with flaps, the drag increase of flaps is definitely modeled. How accurately, that is a different question.


Although, one difference between modern general aviation aircraft like Cessnas and Beechcrafts, and WW2 warbirds is that the warplanes are significantly heavier in proportion to their dimensions, and have a lot higher power-to-weight ratios (and in most cases, higher power-to-drag ratio as well).

If you look at two physically similarly sized planes - like Beech King Air and P-38, roughly speaking - they would probably have about equal amount of drag caused by deployment of flaps. But, the same drag force will cause much less deceleration on a heavier aircraft, which means the heavier aircraft would carry its speed longer after the flaps are deployed... which would mean the climbing arc would be much longer as well.

I've noticed that the "nose-up" tendency of most planes tends to be much less obvious if you only lower flaps below 250 km/h or whatever is specified for the aircraft.


For what it's worth I've noticed that generally speaking, flyable AI aircraft tend to have many sorts of "weird" features in their flight models, because they're originally meant for AI use only. P-36 is one such aircraft - others include B-17, B-24, B-29, Fi 156, Fiat G.55, Tupolev Tu-2, TBF Avenger, M.S.406, 410 and Mörkö Morane... lots of weird things in these particular flight models. The official flyables usually have better flight models with less general strangeness, but it should also always be remembered that all flight simulators are approximations in the end.

That can be the thing. I don't know about core design, what I do know for sure is it behaves far from real, and I thought this whole conversation was about you think Il-2 is perfect and the real thing is wrong  .

I don't think IL-2 is "perfect" by any means, and I can't change how reality operates, more's the pity.

You were the one who said that the behaviour of flaps is fundamentally flawed (ie. going in different direction than reality), I merely demonstrated that it is not so.

There's a difference between "flaps make nose go up when it should go down" and "flaps make nose go up too much".



In the end, it's always going to be a discussion about the accuracy of flight models.