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Vertical stability problems with F-16CJ Block C

Controlling your aircraft, using the autopilot etc.

Re: Vertical stability problems with F-16CJ Block C

Postby Streak » Tue Jul 14, 2020 7:11 am

Josh,

Thanks for the heads-up. I am still somewhat confused by what you've stated though. If I provide no inputs during flight, will the aircraft settle into level flight regardless of the airspeed? Maybe I don't understand "fly by wire".

Also, what about the cosmetic problem with the external view that shows flaps extended when they are actually retracted? Is this by design?

Thanks in advance for your reply to this message.

BR

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Re: Vertical stability problems with F-16CJ Block C

Postby Thorsten » Tue Jul 14, 2020 8:44 am

If I provide no inputs during flight, will the aircraft settle into level flight regardless of the airspeed?


If you put the aircraft in level flight and let go of the controls, fly by wire will attempt to hold your current state (in the F-16 it's probably programmed to use airspeeds rather than attitude as state). So if you increase airspeed you would expect that lift changes, pitching moment changes and so you need to trim, but the controller realizes that and does that automatically to hold the state.

To a first approximation if you release controls the plane will try to continue doing what it did before, so if you let go of the stick in a climb, the plane won't go to level flight but continue to climb.

So moving the stick isn't a command to move an airfoil, it's a command to the controller to go to a certain attitude changing rate.
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Re: Vertical stability problems with F-16CJ Block C

Postby Johan G » Tue Jul 14, 2020 12:00 pm

Streak wrote in Mon Jul 13, 2020 11:49 pm:[...] when engine was starting the flaps were extended automatically for takeoff. I was not aware of this in previous flights and never retracted the flaps after gaining altitude after takeoff. [...] I have verified this with a flight where the flaps were retracted after takeoff and achieving a safe altitude.

I might have this confused with some other fighter, and it might be different between versions and blocks, but I was under the impression that the flaps of the F-16 normally are automatic and would extend and retract when landing gear extend and retract (and in some other flight regimes too of course, like in low airspeed and high alpha).
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Re: Vertical stability problems with F-16CJ Block C

Postby Streak » Tue Jul 14, 2020 2:35 pm

Johan,

You may be right but what concerns me now is that the external view of the aircraft doesn't show the flaps in a retracted state when, in fact, I have retracted them. I know that the flaps are retracted because the flight characteristics change when changing from extended to retracted. This was the original issue of this post because I wasn't aware that engine start auto-extended the flaps and I hadn't retracted them during flights when vertiical stability was erratic. Now when I retract the flaps, I try to visually verify this with an external view but when I try, the flaps appear to be in an extended state when, in fact, I have retracted them. Perhaps this behavior should be the subject of a new post instead of addressing this issue in this post thread. What do you think? Please advise.
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Re: Vertical stability problems with F-16CJ Block C

Postby legoboyvdlp » Tue Jul 14, 2020 3:17 pm

You can see on the HUD the position of the flaps. ("F20 G", lower left).The manual reference:

Image
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Re: Vertical stability problems with F-16CJ Block C

Postby Streak » Tue Jul 14, 2020 6:10 pm

Great post! Just what I needed. Thanks for the clarification! I guess I'll visually check the TEFs when the airspeed is above 370 knots to see if they are generally retracted but still operating as ailerons.

Thank You!

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