F-16 Yaw Departure

[Hoirtel]

So I saw these videos......

 

 

When trying this myself I could not get the same result in DCS, so I don't think the FM goes this far. Not really a deal breaker and possibly to be expected from a sim but interesting to try it out. I attempted with two 120cs on left wing (tip and next rail) and one on right wingtip, I also had around 60% internal fuel and loaded the travel pod on the bottom (in video it seems like it has a small tank on the centreline). I went to 36k, 0.93 mach and roll to the right with a hard pull. I got major slow down but stayed controlled all the time. I do wonder if the this aircraft in the video is configured differently? In the HUD video you can hear the pilot talk about engaging the NPO? I'm not sure what that is...

 

Be interested to hear if anyone else thinks this should work, or is it too far out for DCS. I'm not even sure if the FM is finished yet so maybe this will come later on.

 

 

[Mover]

16 minutes ago, Hoirtel said:

So I saw these videos......

 

 

When trying this myself I could not get the same result in DCS, so I don't think the FM goes this far. Not really a deal breaker and possibly to be expected from a sim but interesting to try it out. I attempted with two 120cs on left wing (tip and next rail) and one on right wingtip, I also had around 60% internal fuel and loaded the travel pod on the bottom (in video it seems like it has a small tank on the centreline). I went to 36k, 0.93 mach and roll to the right with a hard pull. I got major slow down but stayed controlled all the time. I do wonder if the this aircraft in the video is configured differently? In the HUD video you can hear the pilot talk about engaging the NPO? I'm not sure what that is...

 

Be interested to hear if anyone else thinks this should work, or is it too far out for DCS. I'm not even sure if the FM is finished yet so maybe this will come later on.

 

 

 

I did this course at Edwards.  It's done in a D-model with a centerline fuel tank.  I think the wingtips were clean, although we might've had concrete 120s on the wingtips.  Nothing on 2 or 8.  Fuel is balanced by the IP to create a departure/spin-prone condition.  He's talking about the MPO switch (by your left knee) which is part of the Critical Action Procedures if you're in an inverted spin (MPO SW OVRD AND HOLD, STICK CYCLE IN PHASE).

 

Fun course.  Only place that lets you full stop out of an SFO.  Felt like crap the rest of the day though.

[Hoirtel]

Thanks mover! I can only imagine what this must feel like... I think I would be pretty ill at best! Ah MPO, that's something else I should learn about! They talk about this particular test being done with asymmetrical load out (similar to after using a missile) to give a similar result to high rudder input however I couldn't get DCS to do it with the asymmetrical missiles or the rudder input. It might be out of it's scope. I also don't think we can change the fuel balance. I may try with other configs but it just seems to hold steady and lose energy. 

[Machalot]

In my early days messing around with the DCS Viper was was able to get it into some yaw spins, but I don't know if they were the same phenomenon shown in the videos.  I did it by flying to high altitude at a high pitch angle, letting the speed bleed down below the stall speed, and then hitting the rudder.  In a few cases I was unable to recover before the deck even with over 40 kft of altitude to start.

[Hoirtel]

No that's not the same as the test. Transonic speed, above 35k, asymmetrical load out. Roll and hard pull - rapid g onset. 

[aSnatchyConman]

Hey Hoirtel. Some additional info (if you're interested):

 

- The loadout that's being flown in the videos is referred to as the "Sortie #6" config at Edwards. It has AIM-120's on STA 1/2/9, 300 Gallon Tank on STA 5, and a Targeting Pod on STA 5R (typically a Sniper pod because they cause more yaw instability than a Litening pod).

- The Sortie #6 config is one of the most (if not the most) unstable configs you can fly in CAT I. It's used for training Test Pilots at Edwards prior to testing brand new, not previously cleared configurations or new flight control computer software. Due to how unstable it can be, it is only ever flown w/ a spin chute on the jet (in case the pilot can't recover from the post-departure deep stall/spin). There are other configs that are flown at Edwards for training. Sortie #1-3 are used for pilot fam and training CAF pilots to recover the aircraft in a benign loading. Sortie #4-5 are used for initial Test Pilot training (at USAF TPS) and are a little bit more "sporty" than #1-3.

- In the Sortie #6 config, if you do the maneuver seen in the videos above (what is called a "slowdown turn" at Edwards), the nose will slide down (towards the earth, first video) as you depart controlled flight. If you do it in the opposite direction (to the left), the nose will slide up (away from the earth, second video). In DCS, this behavior doesn't seem to happen. The nose may move a bit, but not as it's supposed to from real-world observations. 

- Other maneuvers that are used to test departure susceptibility in this config are 1G, Elevated AoA Rolls (stabilized at 1G on the AoA limiter, ~26 AoA) and Max G Rolls (stabilized at the aft stick limiter in a turn and then rolling "over the top" while holding the stick against the aft "stop"). All of these maneuvers are done at ~35K ft and between 200-300 KCAS. In DCS, the FM doesn't seem to be able accurately recreate the Slowdown Turn yaw departure like is seen in the video, but I've been able to get a couple departures using Max G Rolls. Not quite as "violent" as what's in the video but somewhat similar.

- Another factor (which Mover mentioned above) is that departures only really start happening when the CG is far enough aft such that the horizontal stabilators lack the authority to control the jet. If CG travel isn't modelled in the DCS Viper FM (i.e. if ED assumed a constant CG), then it may not be possible to effectively recreate the behavior seen in the video (since that maneuver was done at a CG that is close to limits, ~41% MAC). Hopefully ED can improve the High AoA FM in the future. It's definitely difficult to model since most post-stall behavior is nonlinear and not so easy to approximate. 

 

Hope this helps!

Edited March 21, 2021 by aSnatchyConman

[Hoirtel]

15 hours ago, aSnatchyConman said:

Hey Hoirtel. Some additional info (if you're interested):

 

- The loadout that's being flown in the videos is referred to as the "Sortie #6" config at Edwards. It has AIM-120's on STA 1/2/9, 300 Gallon Tank on STA 5, and a Targeting Pod on STA 5R (typically a Sniper pod because they cause more yaw instability than a Litening pod).

- The Sortie #6 config is one of the most (if not the most) unstable configs you can fly in CAT I. It's used for training Test Pilots at Edwards prior to testing brand new, not previously cleared configurations or new flight control computer software. Due to how unstable it can be, it is only ever flown w/ a spin chute on the jet (in case the pilot can't recover from the post-departure deep stall/spin). There are other configs that are flown at Edwards for training. Sortie #1-3 are used for pilot fam and training CAF pilots to recover the aircraft in a benign loading. Sortie #4-5 are used for initial Test Pilot training (at USAF TPS) and are a little bit more "sporty" than #1-3.

- In the Sortie #6 config, if you do the maneuver seen in the videos above (what is called a "slowdown turn" at Edwards), the nose will slide down (towards the earth, first video) as you depart controlled flight. If you do it in the opposite direction (to the left), the nose will slide up (away from the earth, second video). In DCS, this behavior doesn't seem to happen. The nose may move a bit, but not as it's supposed to from real-world observations. 

- Other maneuvers that are used to test departure susceptibility in this config are 1G, Elevated AoA Rolls (stabilized at 1G on the AoA limiter, ~26 AoA) and Max G Rolls (stabilized at the aft stick limiter in a turn and then rolling "over the top" while holding the stick against the aft "stop"). All of these maneuvers are done at ~35K ft and between 200-300 KCAS. In DCS, the FM doesn't seem to be able accurately recreate the Slowdown Turn yaw departure like is seen in the video, but I've been able to get a couple departures using Max G Rolls. Not quite as "violent" as what's in the video but somewhat similar.

- Another factor (which Mover mentioned above) is that departures only really start happening when the CG is far enough aft such that the horizontal stabilators lack the authority to control the jet. If CG travel isn't modelled in the DCS Viper FM (i.e. if ED assumed a constant CG), then it may not be possible to effectively recreate the behavior seen in the video (since that maneuver was done at a CG that is close to limits, ~41% MAC). Hopefully ED can improve the High AoA FM in the future. It's definitely difficult to model since most post-stall behavior is nonlinear and not so easy to approximate. 

 

Hope this helps!

 

Thanks for that information. It is really interesting. I can see how difficult this sort of behaviour would be to model and the number of variables involved also make it unlikely to respond in the same way. I may try the other manoeuvres you describe, see how it responds.

[SUBS17]

You can enter this departure in DCS F-16.

[Hoirtel]

1 hour ago, SUBS17 said:

You can enter this departure in DCS F-16.

How did you do it.