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[jg1234]

Hi folks,

My question is sort of a "what have others experienced" one so I thought the lounge might be the place to start.

I have DBW 1.71 and IL2 4.10.1 with Modact 3.06 installed. I have been playing around with a few different variants and a few different mods/flight models of the the P-36 , Hawk 75A aircraft.

I find that the nose of the plane tends to drift up and I have to apply downward pressure on the stick to keep it level. Also, when landing I find applying landing flaps really causes the nose to shoot up as well.

This behavior doesn't happen on the other planes I fly (Hurricane, FM2 Wildcat, BF 109, P-40B, SBD, Spitfire MK1) so I was wondering if this is just normal behaviors for the P-36 or if anyone else has experienced any thing similar?

Thanks in advance - jg1234

[Ala13_ManOWar]

That happens in many mods FM. Just isn't that easy to make a FM from start I guess.

Whatever, not so hard but that behaviour is seen in every aircraft throughout Il-2, nose going up with flaps, but it's a newbie mistake. When flaps applied in RL nose goes down as you need less AoA... So don't worry about it because entire simulator is faked with that and can't be fixed  . You just don't use full flaps and that's enough.

S!

[Herra Tohtori]

When flaps applied in RL nose goes down as you need less AoA...

What? The aircraft doesn't have any way of knowing how much angle of attack it "needs". It will settle on some angle of attack depending on its trim - if it's trimmed to fly straight and level, it's flying at whatever angle of attack which happens to produce an equilibrium between weight and lift.

Deployment of flaps and other high lift devices generally has two main effects on an aircraft: First, the amount of lift increases, and secondly the centre of pressure moves (either forward or backwards, and more often backwards).

The increased lift makes the plane want to climb (gain vertical speed due to inbalance; lift > weight, so aircraft must start climbing).

The shifted centre of pressure causes a moment on the pitch axis, which makes the aircraft re-orient pitch up or down relative to the local airflow. Usually flaps shift the centre of pressure backwards (trailing edge of wing produces more lift), which means the angle of attack is reduced.

But since angle of attack is measured relative to the direction of travel, it is not necessarily tied to the surface coordinates.

When flaps are deployed and trim is not adjusted, the higher lift means the aircraft will enter a climb. Because it is now traveling upward, the aircraft will stabilize itself relative to the local airflow, depending on what kind of angle of attack it wants to settle on. If the aircraft is climbing fast enough, that means the aircraft will pitch up. More often than not, flaps cause the trailing edge of the wings to produce more lift so the centre of pressure shifts slightly backwards, and that does have a tendency to make the aircraft seek a lower angle of attack (aircraft pitches down relative to its direction of movement)

Of course if there is any kind of autopilot or manual pilot onboard that wants the aircraft to stay at the same altitude when flaps are deployed, it will force the nose down by adjusting the elevator or elevator trim (to maintain the lift=weight equilibrium). However this is a controlled response, rather than automatic response of the aircraft. And, obviously different wing and flap configurations can cause different things to happen.


In a very brief test, that is exactly what happens in IL-2. I tested with a B-25, trimmed it to fly straight and level at low power setting, and it turns out it was flying at about 5 degrees angle of attack at that particular airspeed and payload. When I deployed the flaps, the angle of attack reduced, but as the aircraft started to climb, the nose actually pitched up.


I'm sure there are many FM's that are simplified or incorrectly modeled, but on a fundamental level I don't think there's anything physically wrong with this...


TL;DR: Angle of attack and pitch attitude are not the same thing and it is entirely possible for an aircraft to pitch down relative to airflow (reduced AoA) while pitching up relative to the ground (increased pitch attitude).

[Ala13_ManOWar]

Can't believe... You like to argue, isn't it?

The aircraft doesn't have any way of knowing how much angle of attack it "needs".

Mate, an aircraft "knows" the AoA she needs because velocity, or true airspeed, don't come here saying you discovered the fire.


Whatever, too long text to read it, YES, you read right what I said. Look for flight theory, I have no time to waist explaining flight basics to whom don't listen  .

S!

[jg1234]

Thanks Folks for sharing that information.

There are some good pieces of insight in there. I will fly the plane more and see what I can do.  The plane is overall great to fly.

Cheers - jg1234

[Herra Tohtori]

Can't believe... You like to argue, isn't it?

The aircraft doesn't have any way of knowing how much angle of attack it "needs".

Mate, an aircraft "knows" the AoA she needs because velocity, or true airspeed, don't come here saying you discovered the fire.


Whatever, too long text to read it, YES, you read right what I said. Look for flight theory, I have no time to waist explaining flight basics to whom don't listen  .

S!

It's less about having an argument and more about wanting to understand what you're saying, because it seems rather odd to me. It is a topic of interest to me and I always strive to know more.


My question is regarding the difference between angle of attack, and the pitch attitude relative to the horizon. It seems clear to me that while they are connected, they are not strictly speaking the same thing.

Sure, a stable aircraft will seek (or "know") the stable flight attitude relative to the airflow, and generally deploying the flaps will cause the angle of attack to decrease (in most cases at least).

But, that doesn't mean the aircraft's nose can't climb regardless, if the entire aircraft enters a climb caused by the increased lift.

I did a test in IL-2 1946 and the results were entirely expected; angle of attack was reduced, but the aircraft pitched up.


There might be some language barrier somewhere or otherwise bad communication on my behalf, but I would appreciate less condescension on your behalf. If I am being unclear or too verbose in my meaning, I can draw a picture or make a video if it would help.

[Ala13_ManOWar]

It's less about having an argument and more about wanting to understand what you're saying, because it seems rather odd to me...

I understand perfectly. Do you? Look at the Lift formula and try to guess, or read about it if you don't get it, the key is there, not just because I say,



http://en.wikipedia.org/wiki/Lift_%28force%29

But, that doesn't mean the aircraft's nose can't climb regardless, if the entire aircraft enters a climb caused by the increased lift.

More odd things just for your eyes, an aircraft never, ever climbs because "lift" but "power excess"...  What is more, during climb lift is lower than aircraft weight...  ??? ??? ???


Don't mean to sound rude, but mate, sometimes looks like some people like to argue just for pleasure. I would be glad to explain a million times to everybody, but, couldn't you just say, "mate, that's weird, you sure? How is that?". No, you start arguing trying to explain me the thing  ??? . Mate, I don't believe, I know, I passed my pilot exams once, I experienced in real aircraft, you've to understand I don't need to pass again a Principles of Flight exam by you. You "don't believe"? Fine, I'm not trying to convince you about Science is right.

S!

[snachito]

When flaps applied in RL nose goes down as you need less AoA...

I'm trying to understand as I've flown in a plane even got to fly it for a little bit (intro flight as I wanted to be a pilot till I found out the price...YIKES) and would love to fly one day in RL, so anything about flight interests me especially if I can learn something new. 

But as far as that what you wrote ^^^^^why do we need flaps to take off if in real life it makes the nose go down  in real life or is this a different scenario? 

[snachito]

Forgot to add to the OP, Trim, Trim, Trim!! I pretty much think all the aircraft tend to do the nose up thing, but right away I trim the nose down as well as keeping the little ball in the gauges when it starts to get moving all over the place. You'll notice the effect more when you drop ordinance and in the the IL-2 Jets.  I just use the hat on my joystick to trip the up/down, left/right rudder and keyboard for the ailerons.

[Herra Tohtori]

I understand perfectly. Do you? Look at the Lift formula and try to guess, or read about it if you don't get it, the key is there, not just because I say,



http://en.wikipedia.org/wiki/Lift_%28force%29

Truth be told that's a bit simplified formula, since coefficient of lift is a function of wing's profile and angle of attack. And the relation v^2 is only applicable within a certain flight regime, though it is a pretty good approximation.

Deployment of high-lift devices changes the lift coefficient (and sometimes surface area) of the wing at a given angle of attack.

So, if airspeed and air density are not changed, and the flaps are deployed - the lift is increased, and drag is also increased.

If the aircraft was previously flying straight and level, that means the sum of forces acting upon it was previously zero. Thrust and drag were equal, as well as lift and weight.

Now when the flaps are deployed, the aircraft's lift is higher than weight so it will begin to accelerate upwards, gaining vertical speed. Similarly, though, if thrust (engine power) remains constant, drag is now greater than thrust, which means the aircraft starts to decelerate.

The secondary effect of the flaps is that the aircraft's stable angle of attack is reduced. But since the aircraft's stability is determined relative to the airflow, and the aircraft is already in a climb because the higher lift from the wings caused an acceleration upwards, the aircraft's pitch attitude can still increase even if angle of attack is decreased.

But, because the drag is higher than thrust, and because the aircraft is slightly climbing, the aircraft will lose airspeed, which will reduce the lift, so the aircraft makes a brief climbing arc before it starts to descend (due to slower airspeed caused by the increased drag of the flaps).

The end result is something like this:



Obviously, angles are exaggerated and just there for illustrative purposes. Likewise the directions of the force vectors are not necessarily precise. Any feedback or pointing out errors is welcome.

More odd things just for your eyes, an aircraft never, ever climbs because "lift" but "power excess"... 

If we're talking about sustained climb, then sure. But that's assuming the aircraft is not losing any airspeed. I'm sure you're familiar with the fact that you can convert kinetic energy into potential energy. A climb is a climb, even an unpowered aircraft can climb if it has enough airspeed. It won't climb very high, but it will climb nonetheless.

Honestly speaking though I kind of disagree with that statement. An aircraft generally stays in the air because of lift, and lift is the main force that makes an aircraft climb... the engines are there to maintain airspeed so that the wings can produce the lift required to counter gravity. Apart from VTOL aircraft and very powerful military or aerobatic planes, the engines don't really contribute all that much to the vertical force component...

What is more, during climb lift is lower than aircraft weight...  ??? ??? ???

That would depend on the alignment of the thrust vector. With high enough thrust to weight ratio you can even do climbs without loading the wing at all, but that's really rather irrelevant to the situation we're discussing.

But then, lift can be lower than aircraft's weight in descent as well.

Don't mean to sound rude, but mate, sometimes looks like some people like to argue just for pleasure. I would be glad to explain a million times to everybody, but, couldn't you just say, "mate, that's weird, you sure? How is that?". No, you start arguing trying to explain me the thing  ??? . Mate, I don't believe, I know, I passed my pilot exams once, I experienced in real aircraft, you've to understand I don't need to pass again a Principles of Flight exam by you. You "don't believe"? Fine, I'm not trying to convince you about Science is right.

It's faster if I explain my viewpoint immediately and point out where I see the conflict or discrepancy. How could you respond in a relevant fashion without knowing that?

The crux of the matter here, as far as I can see it, is how the aircraft behaves as a Newtonian free-body object. The forces acting upon it determine where it moves. If the upward force (lift in this case) is higher than force of gravity (weight), the aircraft accelerates upwards, and that means it enters a climb...

[JotaC]

But Herra, Manowar is not saying the plane will not climb when flaps are enabled...

[Ala13_ManOWar]

And you still argue Herra...  ??? ??? ??? ??? ??? I won't read all that long thing.


Herra, seriously, I say again, don't try to explain it to me, I understand perfectly, I know what I said, it's basic theory you're asked for in a licence exam and furthermore I experienced inflight. Don't try to tell me how it works...

When flaps applied in RL nose goes down as you need less AoA...

I'm trying to understand as I've flown in a plane even got to fly it for a little bit (intro flight as I wanted to be a pilot till I found out the price...YIKES) and would love to fly one day in RL, so anything about flight interests me especially if I can learn something new. 

But as far as that what you wrote ^^^^^why do we need flaps to take off if in real life it makes the nose go down  in real life or is this a different scenario? 

Just for you, not for Herra as he'll still write another mile long post with his "beliefs".



It's easy mate. Think a level aircraft. There one (true) airspeed is related to one lift (your weight) and lift is related to one AoA. If you lower flaps CL changes as you rises wing curve, you get more lift, yes, but, isn't your weight still the same? You don't need more lift to support your weight... So look above formula, CL is related in basic to AoA and wing shape, you change wing shape, may be wing Area a bit depending on flaps kind, but Lift is the same (your weight) so to keep lift the same if you rises something AoA have lower to get same lift, your weight, as atmosphere density and airspeed won't change. So finally you need less AoA to get same lift supporting your same weight at same (true) airspeed. You lower flaps, you need less AoA, your nose lowers, always, in every aircraft in the World.

In RL what happens? You lower flaps, instantly nose tends to rise a bit by a tiny time, of course I didn't said doesn't happens, but nose rises because you're same airspeed and have more lift so your engine trying to keep your airspeed-AoA equilibrium instantly have excess power... your nose rises because that excess power, not lift. Then airspeed stabilizes your engine needs again its full power, in fact even more as you increased your drag with flaps. Final stage is your airspeed a bit less, but as you need less AoA to get same lift (your weight) your nose is a bit lower despite your lower airspeed means more AoA need. With full flaps your nose is a lot lower. A real example, you're in traffic circuit in your nice C152, 70KIAS, 1900rpm, you get ABEAM threshold, pre-land check, landing lights, 10º flaps, your nose try to rise just a bit then stabilizes and you get 67KIAS, 1900rpm, and your nose lower (so you see landstrip better I've to say), before flaps you had four fingers from nose to horizon and after flaps you have five.


About taking-off, think nose pointing a bit lower doesn't means "down" and doesn't means you go down with it  . Anyway it depends on aircraft, C152 for example takes-off with 10º flaps nicely, but 0º would be fine also in long enough runway. Flaps increases drag (a lot) and increases take-off run in fact, but in a medium to short runway allows you to go airborne a bit sooner so you save that distance running in ground what in RL is important for safety (if you have a puncture or blown out for example, bad deal). But as said depends, I also fly a C172RG, a way heavier aircraft, and she takes-off with 0º flaps but even more with only 10º flaps just wouldn't take-off ever in a short runway, so much drag increases... Flaps aren't always so good. In fact full flaps are dangerous in GA light aircraft if you don't deal with it correctly. Modern jets are another World, an airliner always uses flaps because they're usually so overpowered they can deal perfectly with drag increase and take-off run distance save is also important. Also with flaps you'll climb slower but more vertically, so it's useful to clear obstacles before you reach them, that's the only thing in use flaps for taking-off.

In Il-2 really use of flaps for take-off is stupid... as increases take-off distance and we don't take-off sooner with them but same speed as always and have no obstacles to clear... That's what you wanted to know, isn't it? 


Whatever, I know flying isn't nothing cheap, but if you like go for it. Think it's an inversion, not a waist, and do anything you have to do to achieve (well anything but don't kill anybody XD).


S!