Stall and Spin inconceivable

[chn6]

I tested the latest version of the 1.2.16, MiG-21Bis Stall and Spin still don't feel quite right, you can see my Trk and Tacview files, when a stall occurs, both sides of the wing MiG-21Bis have hardly lift poor, so the aircraft not to enter the Spin, at the same time, the aircraft can always keep unexpectedly smoothly stall.

 

MiG-21_Spin2.rar

[mytai01]

Accelerate to supersonic at sea level then pull into and hold 85 degrees nose up until you tail slide and see how the stall is then! I did it and entered an unrecoverable flat spin. However, I deployed my drag chute after entering the spin. The drag chute did not help my situation nor did it look right graphically. Both of which I doubt would be the case in real life. I've heard of Phantom pilots recovering using their drag chutes. I ejected from my MiG-21Bis before it entered the water...

[Hadwell]

yeah the drag chutes in dcs are kinda messed in general, they don't really act like chutes, more like airbrakes, like giant plywood boards...

 

and it's damn hard to get the 21 in a flat spin, since it's so long and narrow, its naturally stable. and you won't be getting it into a flat spin at 300 km/h ias... need to bring it down so the plane is stalled, but moving the control surfaces still does enough to initiate the spin....

Edited March 17, 2015 by Hadwell

[mytai01]

I kept the nose at around 85 degrees nose up after I lost all forward airspeed then entered a tail slide before tumbling around and into a flat spin.

[Nuibility]

It's a bug, again.

[Maverick Su-35S]

Stalls and Spins are overall the same for any aicraft with only slight differences!

 

Accelerate to supersonic at sea level then pull into and hold 85 degrees nose up until you tail slide and see how the stall is then! I did it and entered an unrecoverable flat spin. However, I deployed my drag chute after entering the spin. The drag chute did not help my situation nor did it look right graphically. Both of which I doubt would be the case in real life. I've heard of Phantom pilots recovering using their drag chutes. I ejected from my MiG-21Bis before it entered the water...

 

Hi,

 

 

For whoever has trouble getting out of any kind of flatspin on any type of aircraft here's what you guys should know and please read all before replying:

 

 

You ALWAYS enter a flatspin after one or both wings are stalled (a stall is only dependent on ANGLE OF ATTACK and NOT airspeed (as 99% of people try to thing) so if you don't understand this first, there's nothing to be discussed) and you HAVE or GAIN some beta angle (side-slip) which is the only further ingredient that can induces a spin, whether the beta angle comes from a rudder input or differential drag on the wings or inertia coupling (transferring alpha (AoA) into beta (side-slip) when a wing is rapidly stalled (usually at speeds higher than 600+km/h) and the plane rolls about 90 deg. in an instant so the initial angle of attack is converted into beta which can induce a spin. These are among the main reasons why stall-spins will occur.

 

Now, if for any reason you didn't have time or simply didn't want to reduce the angle of attack (pushing the stick or reducing the pull) after a wing stalled first (the MIG-21 is unique for sharply rolling you towards the stalled wing), be sure that there is a beta angle going to be created that will eventually induce a spin..., so there's plenty of time to react before reaching a high enough yaw rate to get stuck in a spin.

 

If the spin does occur, DON'T waste any further seconds and rapidly apply the correct inputs (the sooner the better)..., simply push full rudder towards the opposite direction of spin (this one's pretty logical), apply full roll control TOWARDS the direction of the spin AND NOT OPPOSITE and PULL the stick fully..., YEAH, PULL the stick completely. These inputs are the best to firstly reduce the yaw rate and ONLY after it became low enough (you should get used to this by practicing) you should push the stick forward ONLY to reduce the AoA and then start to counter the roll with ailerons then start a pull up. The reason why you should use aileron or roll inputs towards the side of the spin and not opposite (as you normally do with rudder) is because this way the AoA on each wing will be higher and will produce the drag needed to brake the yaw rates. Let's imagine: If the plane spins to the right at about 70..90 deg. AoA and if you apply right side aileron, the right aileron will deflect upwards and the left one downwards and as the left wing will meet an airflow component from the nose of the aircraft, the lowered aileron will increase the lift (but very slightly) and create some extra drag. The same thing will happen to the right wing, because although the aileron is raised the wing is moving backwards like and so it meets an airflow component coming from behind, then the raised aileron will increase the AoA and so the lift (slightly) and drag for the right wing as well.

 

Pulling the stick and NOT pushing it (as most would try to think) is first of all helping the horizontal tail (elevator) reach a lower AoA than stall (which will increase lift on the elevator) and secondly will reduce the airflow shadowing/perturbation on the rudder at high positive AoA and also helps reduce the yaw rate, because if you push the stick and it tends to lower your nose at first, it will only tend to do so in the first split second after which it will develop into an uncontrollable pitch rock oscillation which is harder to get out from because this also increases the yaw rate through a combination between the aerodynamics and flight mechanics forces that act on any aircraft, so you should most of the time AVOID pushing the stick in a spin, unless you're in a simple wing stall or the yaw rate is low enough for you to do it.

 

I know I might sound a bit difficult in the way that I explain but sometimes the best solution is to get into details a little bit, and most of the time this helps.

 

As a short conclusion, for ANY aircraft (and everyone should test this) that is found in a positive flat spin (positive AoA), the rudder should be deflected in the opposite direction of the spin (although it usually has a lower ability to reduce the yaw rate at high angles of attack than the ailerons do have), the ailerons should be deflected towards the side of the spin (stick towards spin) and the stick held full backwards. These inputs should be held until the yaw rate is low enough for you to push the stick and reduce AoA and ONLY THEN you can apply opposite roll input to counter the remnant roll rates and of course bring the rudder to null. Usually the plane should have a yaw rate of lower than 40..50 deg./s (that's 2 seconds for rotating a quarter circle) before you should attempt a nose down input, otherwise you might find yourself rocking in pitch as I already said.

 

IF you find yourself in a negative flat-spin (upside down flatspin) you should follow the same logic, which is to deflect the ailerons so that they increase AoA and drag on both wings, so in this case the stick should be held opposite to the yaw direction (as opposed to positive flat spins), rudder should be held opposite to the yawing direction as usual, but the stick should be pushed in order to achieve the same logic as for positive AoA spins until the yaw rate decreases to a safe enough value before pulling to a positive AoA recovering from the dive.

 

 

Wish you guys all the best!

Edited April 28, 2015 by Maverick Su-35S

[Maverick Su-35S]

It's a bug, again.

Not a bug..., it's the real plane!

[Golo]

Hi, ...

 

If the spin does occur, DON'T waste any further seconds and rapidly apply the correct inputs (the sooner the better)..., simply push full rudder towards the opposite direction of spin (this one's pretty logical), apply full roll control TOWARDS the direction of the spin AND NOT OPPOSITE and PULL the stick fully..., YEAH, PULL the stick completely ...

 

 

What you just said is just about completely oposite (save the rudder part) of what any manuals I red including MiG-21 say about spin recovery.

Edited April 28, 2015 by Golo

[Maverick Su-35S]

What you just said is just about completely oposite (save the rudder part) of what any manuals I red including MiG-21 say about spin recovery.

 

Would you like to contradict me? Just try your own way with ANY aircraft (F-15, P-51, A-10, Su-27, MIG-21, F-86, etc.) and try my way without what "the manual says" and see the difference. It's easy to test! Manuals are not always linked to reality and there had been many cases when the manual actually killed the pilot and they later found why it was wrong!

 

I'm a pilot and aerospace engineer and there are very few in this world to understand flight dynamics and aerodynamics so well. Even if I sound arrogant, I know what I'm saying when it comes to talk about this!

 

Don't get me wrong, and just test it!

 

 

Have a good day man! Cheers!:thumbup:

[Maverick Su-35S]

Here are some examples for what I said and after you'll see them you should understand how it works.

 

Look at this HARV F-18C:

 

 

The inputs for putting it into spin are just what you said that the manual is opposed to what I told, so therefore the manual would put you into a spin or make it much harder or impossible to recover from if you should use ailerons in the opposite direction of the spin or yaw, so when you want to enter a spin you rise the alpha (AoA) to critical or beyond and apply cross-controls (in this case he put full left rudder and full right stick). At 0:30 seconds you can see the ailerons being deflected so that the stick is towards the spin and slightly pulled and although the aircraft (typically for the F-18C's aerodynamic configuration) rolled and entered a negative spin, the yaw rate had already been reduced by then. If anyone wonders why would cross controls (for positive AoA only) put you into a spin is because the ailerons increase the yaw in the direction given by the rudder and vice-versa for negative AoA where the ailerons would increase the yaw if they are in the same direction as the rudder.

 

The cross-controls (stick opposite to rudder) can get you much quicker into a spin (at low airspeed only) as well as out from it, rather than the case when they are coupled to the same side which would get you slightly later into a spin (only for low airspeed) and would be much harder to get out. As I said, the ailerons control the yaw rate and yaw acceleration/deceleration when the AoA is far beyond the stall point, so they become more like a rudder effect at those alpha (AoA) and coupled with the elevator input they can help you increase the yaw rate of the spin or decrease it as you wish. Anyone can test it and see!

 

The way he gets it out is exactly as I've already told you: full opposite rudder and stick towards the spin, with the elevator full up or slightly up, but NEVER down before the yaw rate is low enough or you'll start dancing in pitch!

 

Another example is this F-15:

 

 

See? Same inputs to get into stall! This should tell all the logic behind. Although the F-15 didn't want to apply stick towards the spin is because the purpose of the test was to see if they can make the aircraft recover only from rudder inputs with stick neutral. The F-15 is a statically stable aircraft and it comes out much easier without stick inputs as compared to the F-18 which is statically relaxed and slightly unstable.

 

Here's another example:

 

 

Although it's harder to see the inputs (but not impossible), this F-18 did the same to get in and out of the spin.

 

Test it on the MIG-21, you'll see the same results. The MIG-21's aerodynamics and flight dynamics are the best simulated in DCS, even better than for the F-15C (tested by myself). The reason why it starts becoming almost unstable (tends to recover harder from high high positive AoA or high negative AoA) is because the leading edge root vortex that is known for all high sweep wings and delta wings, and even more for wings with LERX (like the F-16, F-18, SU-27, MIG-29), tends to move the center of lift/pressure (or CP as it's known) very much forward making the plane very less stable than it was at lower AoA. So this is not a bug as someone said, and it's tremendously realistically replicated here. If you guys don't know why it behaves like it does, simply ask and don't throw the bug issue before you are certain.

 

 

Have a good day guys! Learning is an everyday routine!

Cheers to everyone!

Edited April 29, 2015 by Maverick Su-35S
Cross control effect within a spin, detailed.

[theropod]

Another example is this F-15:

 

good examples and informations thank you!

 

off topic: i couldnt enter flat spin with dcs f-15 as shown on the video.

when they first released f-15 beta ,both flat and inverted spins were implementable and the way that the recovery was same as your information but now ,f-15 dont wants to spin anymore.

aircraft recovers the spin itself ,even cas channels closed

[Golo]

Well Ive tried it and it works, which leads me to the conclusion that spin characteristic for MiG-21 as of now are incorrect (bug).

 

MiG-21 spins are unstable and oscilatory in pitch, yaw and roll. Right after onset of the spin controls are to be set neutral and aircraft should recover.

 

If alerons are applyed into the spin oscilation are even more pronounced, if deflected oposite the spin aicraft can experience rotation along its longitudinal axis.

This behaviour acording to the manual was much better represented in version 1.2.14 before the change to FM in my opinion.

[Lunatica]

很正常吧，小展弦比的三角翼超过临界攻角后升力损失平缓，不容易造成尾旋，你后来很明显是丧失方向稳定性进侧滑然后尾旋。

Edited April 30, 2015 by Lunatica