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[CHK] Instability on rotation for Takeoff and Landing


Hawkeye91

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For some reason, when I'm rotating the aircraft for take off or trying to hold the nose off for landing aerobraking the pitch instability gets wild often times leading to a tail strike. I did a landing today where I touched down and the nose started to drop, so I raised it to 10 degrees and neutralized the stick and the pitch kept rotating until the tail scraped. Currently it feels unwieldly with its current implementation. I'm using a 7.5 mm extension, no curves, and some deadzones so I don't have any unintended inputs. Is this working as intended? is the FCS modelling incomplete or am I just a bad pilot? 

Edit: After some testing it seems that if you rotate a little above 10 by a degree or two is where the pitch stability is the the problem and at heavy weights. Often times I feel like at heavy weight I have to rotate back hard on take off to get the aircraft to start pitching up then push forward to counter act the pitch up instability that happens afterward to prevent a tail strike. I always use TEF on heavy weight Take offs.

 

Edit 2: After further testing at heavy weight, it almost feels like the emergency take off auto rotation is pitching up the the aircraft on touch down. I'll attach a track file.

JF17 Rotation.trk


Edited by Hawkeye91
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  • uboats changed the title to [CHK] Instability on rotation for Takeoff and Landing
9 hours ago, SlipHavoc said:

I've also struggled with takeoffs more than I would have expected, for the same reason.  I'll be interested to see if there are any other responses here.

 

So I've been doing a bunch of testing, and it feels like its the emergency take off auto rotation engaging even though I'm trying to rotate the aircraft. Combining the two inputs might give it that feeling of instability because you aren't anticipating the extra pitch up tendency. I attached  a track file to my original post, so hopefully @uboatssee it  😁

I believe its also happening on landing when you land at heavy weight because the nose just pitches it self up into the air if you land fast. More weight = faster approach speed = pitch up on landing from the emergency take off auto rotation.


Edited by Hawkeye91
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  • 4 weeks later...

Hi, the auto rotation function is not an emergency function, but rather to assist manual rotation by deflecting the elevator for an extra 8 degrees when main wheels are WOW and airspeed greater than 108 kts.

 

It's unlikely that the auto rotation function engages at landing, since it only re-energizes when airspeed drops below a certain threshold, but I'm still looking into the issue where static instability occurs. There'll be some small adjustments in take-off/landing roll behavior in the next update.

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EFM / FCS developer, Deka Ironwork Simulations.

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On 8/6/2021 at 7:30 AM, LJQCN101 said:

Hi, the auto rotation function is not an emergency function, but rather to assist manual rotation by deflecting the elevator for an extra 8 degrees when main wheels are WOW and airspeed greater than 108 kts.

 

It's unlikely that the auto rotation function engages at landing, since it only re-energizes when airspeed drops below a certain threshold, but I'm still looking into the issue where static instability occurs. There'll be some small adjustments in take-off/landing roll behavior in the next update.

Fantastic! Thank you for looking into it!

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  • 3 weeks later...
On 8/6/2021 at 7:30 AM, LJQCN101 said:

Hi, the auto rotation function is not an emergency function, but rather to assist manual rotation by deflecting the elevator for an extra 8 degrees when main wheels are WOW and airspeed greater than 108 kts.

 

It's unlikely that the auto rotation function engages at landing, since it only re-energizes when airspeed drops below a certain threshold, but I'm still looking into the issue where static instability occurs. There'll be some small adjustments in take-off/landing roll behavior in the next update.

Just wanted to say the adjustments to the take off/landing behavior feel great!

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  • 4 months later...

@LJQCN101 Hey, hate to dredge this up again, but it seems like the JF-17 is falling on its tail while trying to aerobrake when landing. After touchdown, if you leave the control neutral, it will continue to pitch on its own until the tail hits unless you push the stick very far forward to counter act it. It seemed like this was fixed before but now its happening again. Anything changed recently?

Edit: a quick test with a light loadout and a heavy loadout, the light loadout didn't pitch up and scrape the tail, but the heavy full loaded one did. Maybe its a weight and balance issue?

Edit 2: I've attached a second trackfile where I landed with a full heavy loadout and fuel and I made a very soft landing with a modest pitch up attitude between 8--10 degrees. I then let go of the stick while it was stable there and as the plane decelerated it pitched and back on its tail from about the most textbook landing I could make.

JF17 Landing.trk

JF17 Perfect Touchdown.trk


Edited by Hawkeye91
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