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Many are having problems with the new flight model so I'm putting some thoughts down that may help. I'll be addressing them first by effect, then by stages of flight, so if you're looking for landing, go straight to the bottom .


Prop wash:
We're all familiar with this one, though it's commonly wrongly referred to as torque. This is the effect that causes large amounts of yaw during takeoff. It's caused by the rotating column of air moving backwards behind the propeller. When this column reaches the vertical stabiliser it pushes it to the side, turning the nose of the aircraft in the other direction. The pilot should use rudder to control it during takeoff. In real aircraft there is often a "Takeoff" setting for rudder trim that mostly compensates for it. You can work out this setting for your favorite aircraft and use it in the game too if your ride is equipped with pilot adjustable rudder trim.

P-factor:
This is little understood by those not familiar with the intricacies of aerodynamics. It is caused by the propeller disc not being & right angles to the direction of travel. It is most obvious at high speed and high angles, so it's biggest effect will be observed on taildragger aircraft in the takeoff roll just before the tail lifts, as this is when the propeller is at it's greatest angle from optimum and some speed has built up. On an aircraft that has positive angle of attack, the propeller blades going down have a much greater effective pitch angle (angle of attack) than the blades going up and the result is more thrust on one side than the other until the aircraft returns to neutral angle of attack. This effect will cause the aircraft nose to tend to swing in the same direction as prop wash and should be countered in the same way.

Torque:
As the engine turns the propeller in one direction it tries to turn the airframe the other way. In real life sudden large throttle movements can make wingtips touch the ground in very powerful piston engine propeller aircraft, but in the game we don't have to worry too much until our wheels are off the ground.
Once we're wheels up torque try to make a wing dip. At low speeds pilots should avoid large aileron inputs to counter this, as the dipping wing already has an effective increase in angle of attack which puts it perilously close to stall. Aileron input will only make this worse and may well initiate an ugly low speed, low altitude stall if you're just wheels up or on final approach. At speeds close to stall speed some rudder input opposite the dipped wing will quite effectively bring things back in line.
Some aircraft are designed with one wing at a slightly greater angle of attack to provide more lift on the "dip" side, thus allowing the aircraft to fly with neutral aileron trim at cruise power. On those aircraft you'll find that one wing dips at low power settings and the other wing dips at high power.

Gyroscopic effect:
This is an odd one to get your head around, though if you've played with the toy gyroscopes that science teachers love you may be familiar with it. When you apply a turning force to the axis of a rotating mass, it responds by trying to turn at right angles to the direction of the force. The greater the force or the more suddenly you apply it, the more strongly the rotating mass tries to turn at right angles. The direction of the response will be left or right handed depending on the direction of rotation. The propellers of our aircraft are very large rotating masses.
What this means for us pilots in single engine (and some twins) is sudden pitch inputs are going to induce some unwanted yaw and sudden yaw inputs are going to result in unwanted pitch. Countering this requires several strategies.
1. Be gentle with pitch & yaw inputs
2. Learn which way your aircraft jumps and anticipate it with small amounts of countering input.

Adverse Yaw:
When you apply aileron input to initiate a turn, you cause the rising wing to generate more lift and the other wing less lift. As more lift creates more drag, the wing on the "up" side is now trying to drag the nose away from the turn. This reduces turn efficiency and overall drag, increasing the energy loss associated with turning. A small dab or rudder in the direction of the turn is all that's required. Once the turn is established and you've eased off on the ailerons you should find that the rudder can be returned almost to centre.


Practical Considerations in Flight:
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Takeoff

Initially the aircraft is stopped and the undercarriage is mostly controlling roll and pitch, so the big factor is prop wash. This needs a big slab of rudder input to counter, but the rudder is not effective until there is air flowing over it. Start with brakes applied and run the throttle up. As engine power increases, so will the tendency to yaw, but the propeller is also causing air to flow over the rudder. Add rudder as necessary to control the swing. Having the brakes applied will help if you're finding it difficult, as the rudder also controls side to side brake balance and until you release the brakes this will give you brake assisted steering.
Many pilots also find that locking the tail wheel helps.

There are many different recommendations for the first part of the takeoff roll. Some find that it's best to run the throttle up slowly while holding the brakes; others find they can more easily control things if they go straight to full power. It will vary a bit with aircraft type, so experiment some and see what works best for you.

Upon releasing the brakes the aircraft will start to accelerate down the runway. In tail draggers you may find the tendency to yaw increases some as P-factor increases, then drops off quite a bit when the tail comes up. Conversely, you may find that the increasing speed reduces the need for rudder as the vertical stabiliser becomes more effective at higher speed.
A further complication in taildraggers when the tail comes up is gyro forces. If you allow the tail to come up suddenly you'll get a big gyroscopically induced yaw. You'll need to be ready to adjust the rudder to counter this. You may also find it helps to start the takeoff roll with the stick well forward and ease it back as the tail comes off the ground to control the rate of change of pitch.

The next point of difficulty comes when the wheels leave the ground. At this point the landing gear ceases to be of any assistance in controlling torque induced roll and in many aircraft you'll find that a wing wants to drop. If you're not much over stall speed, adding aileron is likely to put that wing over critical angle of attack and cause it to stall. Instead, use rudder to drag the nose to the high side wing. This will slightly lower lift on the high side and bring the aircraft back to level. Don't overdo it though or you'll have the other wing dropping.


Climb

With any luck you'll now be off the ground and in a gentle climb. Keep the climb gentle for a few seconds so that your aircraft will accelerate to best climb speed quicker. Get the gear raised ASAP and once you've got a bit of airspeed remember to retract flaps if you were using them.

If you try to keep your nose pointed at an aircraft taking off ahead of you, you'll almost certainly not be able to keep up. If he's pulling away and you need to make formation with him, let the nose fall back to level and get some more speed. Distance is usually harder to recover than height when trying to form up, so worry about matching altitude after you've caught up.

A word here on climb. If you want to convert level flight to climb at the same speed, you must add power. If you don't add power and just pull back on the stick, at best you'll climb at a much lower speed. If your cruise speed is not very fast to begin with and you don't add power, you may even end up descending after only a few seconds.
Also be aware of your aircraft's various climb speeds. Best climb speed is the speed at which the aircraft gains altitude quickest. This is NOT best climb angle, which will occur at a somewhat lower speed. Best climb angle is good for getting over high objects without taking a detour (for example a line of trees at the end of the runway), but what you gain in angle you lose in time to altitude.

Once you've selected climb power and adjusted the aircraft pitch angle so that you're climbing at your required rate, trim. Trim the elevator first so that you don't have to pull or push on the stick to maintain chosen climb speed. If the aircraft is equipped with rudder trim, trim rudder so that the slip indicator is centered. If you don't know what the slip indicator looks like in your favourite ride, or where to find it, check the cockpit reference guide kindly compiled by neural_dream. It can be found by clicking here.
Finally, if your aircraft is equipped trim ailerons to cancel torque induced roll. This must be done last as a badly trimmed rudder will also cause some roll. If you trim aileron before rudder, you're going to have to come back and re-trim aileron after you've finished with rudder.

Bear in mind that engine efficiency (and hence torque) changes with altitude, so if you're climbing or descending the torque will be slowly changing much of the time. You'll periodically find you need to re-trim for torque in a long climb or descent even if you haven't changed throttle settings.


Cruise

Not too different to climb. Most aircraft that aren't equipped with in flight trim adjustments have a cruise speed at which the aircraft is neutrally trimmed in rudder and aileron. If you're a fan of long missions you'll find them much more relaxing if you can cruise at this speed, so do a bit of experimenting and find where it is. On most such aircraft it occurs between 35% and 65% throttle. As aileron trim is subject a bit to altitude you may find the neutral trim cruise speed varies a little with altitude too.


Manouvering

The time will come for combat. I wont go into tactics here as they vary so much depending on what you're flying and what your opponent(s) are flying, but there are a few considerations that have arisen in the last patch or two.
In a turn fight you'll find you tend to be fairly slow and using high angles of attack that rapidly vary. You'll find that sudden changes in pitch are causing the nose to bob sideways a bit (gyroscopic effect), sudden roll inputs are causing yaw (adverse yaw) and that poor rudder coordination (slip angle) or sudden power changes (torque roll) are causing wings to drop away. All of these effects will require you to be active but gentle with the rudder. Until you get the hang of it you may find you're overcontrolling some, but with practice you can adapt. It may also help to play with your rudder sensitivity settings a bit. While the in game Input setup is good for this, I prefer FoolTrottel's IL2Sticks Utility as it allows you to quickly swap previously saved profiles (requires game exit/re-launch) for quick comparison. IL2 Manager also has a stick sensitivity tool built into it.
You'll also find that adjusting trim for the low speed range keeps your joystick nearer center. This is usually helpful in managing fine control inputs such as aiming.

For the boom and zoom crowd sudden changes of direction and power are not so much of an issue, but they tend to operate over a large speed range. Shots will tend to be taken at fairly high speed, followed by a sudden change in direction before extending to set up for the next pass (if necessary ). Because of the variation in speed and the difficulty of aiming when the joystick is far from center, it may prove useful to trim the aircraft for a much higher speed and power setting than combat cruise when you're in the patrol area but not engaged. While this means you're going to be constantly holding the stick & rudder off centre while on station, it can make accurate shooting much easier at the very high speeds involved in this tactic and may make that second pass not necessary. It will also mean that your controls are in their best response range should your target take evasive action at the last moment requiring some sudden hoiking around to keep the sights on him.

Should you be one of those flyers that has a very versatile flight style, you're going to need to be very active on the rudder. While rudder is not very significant as primary input, with the current flight modeling in this sim it essential for fine tuning the aircraft to manage all the side effects of the forces we have to deal with as pilots of high powered propeller aircraft.


Descent

Really just climb procedure in reverse. Set power low, trim for your chosen descent speed and keep an eye on aileron trim (if available) as altitude decreases.


Landing

Landing is commonly referred to as the most challenging part of routine flying and for good reason. A landing is very close to being a crash, particularly when landing on an aircraft carrier. The idea is to fly a gentle approach slope at a low enough rate of descent that the landing gear doesn't break when it hits the ground, then just before you touch down reduce speed and power and increase angle of attack so that the aircraft stalls and stops flying just as the wheels touch down. Very few sim flyers I've seen online do it right (including me ) with most of them opting for a somewhat higher landing speed and flying onto the runway, hoping they don't bounce high enough to cause a crash (and in a tail dragger you WILL bounce if you touch down too fast).
Because of the very low speeds involved larger control inputs are required to make small corrections. There is a strong tendency to overcontrol when initial control response is less than expected. Further, at the power settings normally used for landing fairly small changes in throttle setting mean large percentage changes in torque and consequently large roll responses from the aircraft. Again there is a strong tendency to overcontrol when reacting to these forces, particularly as they're somewhat stronger in v4.02 than we've had in previous versions.

In this version it is more important than ever to set up your landing approach with correct altitude and speed. The better your set up, the less control input you need to apply during the approach and the easier it is to get on the ground smoothly and gracefully.

Similarly, it's more important than in any previous version to understand proper throttle and pitch control during landing. Contrary to intuition, we use throttle to control glide angle and pitch angle to control speed. If you're going to land short of the runway you need to add power to flatten the glide. If you're going to overshoot, you need to reduce power to make the glide steeper. When you're too fast you need to raise the nose of the aircraft a bit and when you're too slow you need to lower it.

At least to begin with, start your landing approach well out from the end of the runway. Try to get about about 12 to 1 glide slope set up (approximately one runway length for every 100m/300ft above runway altitude) and get your speed down early. Lower flaps and let the aircraft settle in, then trim for approach speed. If Rudder and Aileron trim are available, set them up for a power setting lower than required to maintain the glide slope to minimise the correction required when you pull power off at touch down. Don't forget to lower landing gear.

As you approach the runway, watch the near end of the runway in your windscreen. If it's moving up your screen, you're descending too quickly and will need a touch more power. If it's moving down, you're going to overshoot and will need to reduce power. After making power adjustments your speed will want to vary a little, but it should settle back down to your selected approach speed in a few seconds as the glide slope adjusts.

Keep an eye on your speed too. You'll want to be approaching stall speed in the last stages of the approach. If you've got to wash off too much speed in the flare the aircraft will not want to settle on the runway. While not that critical on the big land based runways, this will result in missing the wire or missing the whole deck on a carrier. You don't want to be washing off more than 5-10mph (8-16km/h) in the final flare and touch down.
Because you're flying so slowly you need to be very careful with the controls. When you're this close to stall, any large rudder, or aileron movement is likely to make one wing stall. You'll need a fair chunk of control input to get responses, but even the slightest amount of overcontrol will cause disaster.
Similarly, large changes in power at this speed are going to cause big roll and yaw responses. Be careful correcting these and as far as possible use mainly rudder to control them. Again, overcorrecting is as bad as or worse than undercorrecting.

Just before touch down pull the nose back and ease the power off. This should be time so that the wheels touch the ground just as the aircraft stalls. The pull back and throttle down needs to be smooth, not sudden or our gyroscopic forces and torque are going to bite us. If you pull back too suddenly the aircraft will yaw, almost certainly causing one wing to stall at this low speed. Even pulling back gently you may need a touch of rudder to keep the nose straight.
Likewise with throttle, if you yank the power off you'll find wing wants to drop. A smidgeon of rudder and a smooth reduction in power will generally keep the wings level, though you may also need the slightest touch of aileron in some aircraft.

If you're in a tail dragger and you've done it right, you'll achieve a three point landing. For tricycle landing gear aircraft, the main wheels should touch first. In either configuration, if you get the landing attitude right and you're too fast the aircraft will float above the runway or even climb. If you've not pulled the nose up far enough and you're too fast you'll touch down but bounce. If you're too slow or too early you'll stall before touch down and either bounce or break something.

If you do bounce on a land airfield, don't push the stick forward. Ease a touch of power back in (very carefully and not much) to prevent the aircraft stalling before the second touch and maintain a slightly nose high attitude. Unless you've really made a botch of things in a major way, this should allow the aircraft to settle moderately gently back onto the runway.
If you bounce on a carrier you'll either miss the wires or if you catch a wire you're likely to break your landing gear on the second touch, so do your best not to bounce too much on a carrier landing. If you're going a bit fast or slow and you're not too badly damaged on a carrier approach, go around and start over. Make your decision to abort early, particularly if you're too slow.

Once the wheels are on the ground, forget the ailerons even exist. Keep the stick back and gently dab at the brakes to bring the speed down. If your landing has been a bit rough and the aircraft is rocking around, use rudder to bring it back into line. Remember that left/right brake balance is linked to rudder and try not to get too enthusiastic with the rudder while the brakes are applied .


Summary

We've got a lot of new reactions to be aware of in v4.02, but with not much practice they can all be mastered. Some of us have also had issues with corrupted patch downloads or messed up stick sensitivities, and short of the approaches posted elsewhere there's not much can be done about that, but hopefully this post will help those that are simply having difficulty coming to terms with the increased gyro and torque effects and understand better what's going on.

Some important points:

Torque and propwash are not the same thing and require different countering techniques. Even if you don't remember the names right, you will find it to your advantage to learn how to deal with each one.

Gyroscopic effects are much greater than they've been in any previous version. They will take some getting used to and may require you to adjust your control technique or stick sensitivity settings.

Learn your aircraft!! Knowing stall speed and aircraft response with and without flaps deployed and with and without a full fuel/ordnance load is much more important than previously. With the importance of these effects so much increased, there is a lot less room for fudge factor than previously. I used to find it easy to land or takeoff in situations that would be suicidal in real life, but no more.

Correct technique is much more critical than in previous versions. I'm finding this by far the most challenging flight model of any version right back to the original IL2 Sturmovik, but loving the renewed challenge so much that I've increased my offline flying just for the practice.

If I've made any errors or not been clear enough on any aspect, feel free to add to or correct my offering. If you don't find it useful, feel free to ignore it