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[CORRECT AS IS] Strange stall behavior?


Harley Davidson

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Hey Guys,

 

 

Just posting some strange behavior I've found in the flight model. We don't have the combat tweaked for the Viper so I'm learning its flight characteristics.

 

 

I wanted to see what happens in different stall attitudes and one of the stalls was an over the top stall where the aircraft goes vertical until speed is lost and the aircraft is pulled rearward by gravity until I can get the nose down again (power off stall).

 

 

What I've noticed is the Viper will go into a "flat" stall and will drop without being able to recover. I've tested this from around 30k ft and near 15000ft it starts to propose. Power, rudder, roll etc cannot brake the stall. I tried cycling full power as the nose dropped with full stick forward and almost punched out as 8000ft was passing, I did manage to bring her back into normal flight with the thicker air density around 7500ft.

 

 

Is this normal for this aircraft? Give it a try as it is repeatable. Interesting!


Edited by Harley Davidson
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It's a normal and a well-known characteristic of the airplane. For more information look up Recovering From Deep Stalls And Departures

By Joe Bill Dryden in Code One Magazine.

 

In short full stick forward can be insufficient to recover from an AOA of about 45-60 degrees depending on the pitch rate. The airplane is naturally stable at about this AOA like a ball in the bottom of a dish. The FLCS is semi-unintelligent and commands full nose down beyond 28 degrees AOA regardless of pilot input. The airplane will happily attempt to reduce AOA with stab for nose down forever even though it may be impossible to do so directly.

 

The corrective action is the MPO switch to override control over the stabs and input stick back to increase AOA. At the increased AOA reverse input to stab for nose down. This time the pitch rate will be higher when hitting the "hill" should "break through" to reduce AOA into the normal operating range again.

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As Joe Bill so eloquently put it,

 

"the idea is not to be Joe Cool by reaching over, engaging the MPO switch, and then trying to make the stabilator actuator white-hot by wildly pumping the stick"

 

The F-16 doesn't take kindly to being handled roughly... she prefers a gentler hand. You have to get 'in phase' with the pitch oscillations e.g. pull until the nose begins to fall, then push until it starts to rise, and repeat the cycle. Once in phase, you should recover in 2 or 3 cycles i.e the "fluttering leaf" effect will stop and the nose will remain where commanded. Then it's throttle as required to reach 200KIAS, MPO=Norm, and business as usual. ;)

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Do we have any info on whether the MPO switch can be / was used to get a snapshot advantage or turn lead when otherwise not possible?

 

Again the good old argument would be: If you felt your life depended on it, would this be a viable option in the ranks of scratching, throwing dirt and spitting into the eye in a knife fight?

Lincoln said: “Nearly all men can stand adversity, but if you want to test a man's character, give him power."

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Do we have any info on whether the MPO switch can be / was used to get a snapshot advantage or turn lead when otherwise not possible?

 

Again the good old argument would be: If you felt your life depended on it, would this be a viable option in the ranks of scratching, throwing dirt and spitting into the eye in a knife fight?

MPO only gives more pitch down authority, not pitch up :)

When you hit the AOA limiter, having more pitch up authority would only have you depart controller flight, and this would be a suicide manoeuver.

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