investigating Spin recovery active despite pirouette commands

[Hulkbust44]

When inputting pirouette FCS commands (Full lateral left/right stick with full rudder in same direction) Spin recovery mode activates. During a commanded pirouette nuisance spin indications should be suppressed.

Funnily enough, having spin recovery activate is the closet you can get the DCS aircraft to a pirouette.

SPNAOA.trk

[wilbur81]

I may be doing it "wrong", but I get a nice pirouette by full stick aft and full rudder, not full stick left or right. At the right airspeed, she pirouettes quite nicely with full aft stick and rudder deflection without ever triggering spin mode.

Edited February 4, 2022 by wilbur81

[Hulkbust44]

1 hour ago, wilbur81 said:

I may be doing it "wrong", but I get a nice pirouette by full stick aft and full rudder, not full stick left or right. At the right airspeed, she pirouettes quite nicely with full aft stick and rudder deflection without ever triggering spin mode.

 

Can you get up her up to 45 alpha? Thing is it just turns so slow in DCS. Can't get the airspeed down either. In Wags early video on it he was spiraling down at 90kts indicated...
Depending on the alpha, the lateral stick won't touch the ailerons, input is fed to the rudders.

[wilbur81]

1 hour ago, Hulkbust44 said:

Can you get up her up to 45 alpha? Thing is it just turns so slow in DCS. Can't get the airspeed down either. In Wags early video on it he was spiraling down at 90kts indicated...
Depending on the alpha, the lateral stick won't touch the ailerons, input is fed to the rudders.

I'll just have to upload a track...

[Ahmed]

I see this is tagged as "need evidence". NFM "High AOA Flying Qualities" section has some information on it.

[Mikaa]

9 hours ago, Ahmed said:

I see this is tagged as "need evidence". NFM "High AOA Flying Qualities" section has some information on it.

Agreed. In the appropriate NFM, the subsections pertaining to Aircraft Stability and Dynamic Response, and High AOA Flying Qualities outline some deficiencies in our DCS Flight model; specifically including AOA Capability (Transient and Sustained), Yaw Rate Warnings, and Pirouette Logic. 

Some Highlights Include (paraphrased):

- Full Aft Stick input results in 50-55 degrees maximum sustained AOA (resulting in potential -18000fpm descent rates); and yaw rates during maneuvering above 50 degrees aoa can be significantly higher than desired.

- Combined Pedal and Lateral Stick inputs between 35 degrees and 55 Degrees AOA provide enhanced roll performance when compared to individual inputs in this AOA regime. These inputs can lead to excursions into the "60s" of degrees AOA, which can blanket the ADC (reading 48 KCAS in HUD).

- When AOA is above 35 Degrees, Yaw Rate warning is replaced with the Departure Warning tone (not implemented in our current model; we should hear beeps increasing in frequency depending on the Yaw Rate, starting at 40 deg/sec Yaw)

- If Yaw Rate develops at 50-55 AOA easing control stick off the aft stop should immediately reduce AOA below 50 and terminate the yaw - Sustained Yaw Rate at 50-55 Degrees AOA can lead to display of Spin Recovery command arrows.

- Pirouette Logic is engaged at <210KCAS and >25 AOA and spin display logic is modified during this maneuver to prevent "nuisance spin indications" (though at 50-55 AOA and sustained Yaw Rate the spin recovery command will engage, as written above)

 

The Attached track is my attempt to enable the pirouette logic, mirroring Wags' Pirouette video from 2018 (also attached). Although the current FM allows the maneuver, maximum sustained AOA is ~36, with transient to ~40.9 with slight stick modulation to increase yaw-roll coupling on entry (as well as to attempt to increase transient AOA above 35). AOA never even approaches 50 degrees, thus AFAIK the Spin Command should never display. Additionally, my interpretation of the above sections indicates that 50-55 degrees AOA should be commandable and sustainable with full-aft stick input, and if full aft stick and pro-spin pedal and lateral stick were commanded, a transient to "60s" of AOA should be possible, setting off both the departure warning tones and spin recovery display commands. 

 

My humble interpretation of this is that the pirouette should be sustainable with full lateral stick and pedal, and aft stick modulated to maintain appropriate AOA (Above 25 degrees, but optimally 45-50 degrees). This just isn't possible with our current DCS model. Aside from the dampened AOA capability and the lack of departure warning tone implementation, the current FM seems pretty close until you reach the edge of the envelope. 

 

 

 

F-18C Pirouette Test.trk