F16 pilot excites the longitudinal mode AGGRESSIVE

Operating an F-16 on the ground or in the air - from the engine start sequence, over replacing a wing, to aerial refueling procedures
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saberrider

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Unread post17 Jul 2018, 07:39

In this video look like TO ME the F16 pilot excites the longitudinal mode more than he need it ,also TAPPING THE rudder BESIDE the ARI imputs.My qwestion is why ? For the photos or because he fly to slow and must do this https://www.youtube.com/watch?v=UXAgW24deIE .https://www.youtube.com/watch?v=Rta-qvvfi_U
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MVSGas

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Unread post17 Jul 2018, 08:00

Without having cockpit video or flight data recorder information, we have not way of knowing that the pilot did or did not do and what the FLCC was doing or not. We would be guessing at best.
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vilters

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Unread post17 Jul 2018, 15:14

Most F-16 pilots never touch the pedals in flight because the "ball" is centered by the FCS.

There is sideslip "adverse yaw" when aileron banking at slow speed, and the FCS "steers" the rudder to keep the ball centered.
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ygbsm

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Unread post17 Jul 2018, 16:51

vilters wrote:Most F-16 pilots never touch the pedals in flight because the "ball" is centered by the FCS.

There is sideslip "adverse yaw" when aileron banking at slow speed, and the FCS "steers" the rudder to keep the ball centered.

Sorry for the pain of calling you out...but you ain't ever flown 'em. How many dudes who have know they see a ball off to left all the time (can any engineers answer why?) and put in rudder trim to compensate.

Just keepin it real from time to time...
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tjodalv43

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Unread post17 Jul 2018, 18:13

Yep, one of the first things I do after the gear light goes out is reach back and put in some rudder trim because it’s usually off to the left, moreso once you start hanging stuff off 3 & 7. FLCS def doesn’t center the ball for you. If you’ll be spending much time trans to super sonic you’ll probably have to retrim the rudder for that speed too.
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saberrider

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Unread post17 Jul 2018, 21:08

ygbsm wrote:
vilters wrote:Most F-16 pilots never touch the pedals in flight because the "ball" is centered by the FCS.

There is sideslip "adverse yaw" when aileron banking at slow speed, and the FCS "steers" the rudder to keep the ball centered.

Sorry for the pain of calling you out...but you ain't ever flown 'em. How many dudes who have know they see a ball off to left all the time () and put in rudder trim to compensate.

Just keepin it real from time to time...
can any engineers answer why? I BELIEVE that the trimm is necessary because the torque of the engine at mill power and hard turning mostly to the left put some asymmetric stress on a one side than another side .I read somewhere some pilot help the turn by applying ruder for some degree and work fine until IS fade out by FLCS. But ++ vilters++ is a pilot and know better.
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35_aoa

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Unread post18 Jul 2018, 02:59

Every jet I've ever flown needs some amount of rudder trim to perfectly center the ball. Goes for single engine (Viper and Goshawk) as well as twin engine (Hornet and Super Hornet).......same for FLCS vs FA-18 CAS (our version of FLCS). Sometimes it is due to external stores causing the effect, sometimes it is just an old jet that could best be described as "bent", that needs trim even completely clean. Flying around tactically, it isn't normally significant enough to warrant attention, other than maybe flying "double ugly" drop tanks (a legacy Hornet thing), or some weird asymmetric stores configuration. But just going from point A to B cross country, or certainly when you are low on gas trying to optimize fuel to get home, I will carefully trim the rudder(s) to ensure I'm not creating excess drag needlessly and burning extra fuel in the process. Yes RSRI (Rolling Surface to Rudder Interconnect in the FA-18) or ARI (Aileron to Rudder Interconnect) or whatever else, depending on manufacturer terminology, will generally keep the ball close to centered in turns, but if you are yawed in straight and level flight, it is never going to correct for that. The only other rudder "trimming" feature I know of in FBW 4th gen jets is post departure they will generally have some ability to null out any yaw rate or beta dot in order to facilitate a more timely recovery. This is only functional in the Viper, IIRC, when in an upright departure........hence the "IF IN INVERTED DEEP STALL-RUDDER OPPOSITE YAW DIRECTION" CAP. In the Hornet, this feature was added to address the "falling leaf" departure mode we struggled with in the early years, to much success (many other FCS software changes also contributed to that success).
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tjodalv43

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Unread post18 Jul 2018, 14:42

35_aoa wrote: The only other rudder "trimming" feature I know of in FBW 4th gen jets is post departure they will generally have some ability to null out any yaw rate or beta dot in order to facilitate a more timely recovery. This is only functional in the Viper, IIRC, when in an upright departure........hence the "IF IN INVERTED DEEP STALL-RUDDER OPPOSITE YAW DIRECTION" CAP. In the Hornet, this feature was added to address the "falling leaf" departure mode we struggled with in the early years, to much success (many other FCS software changes also contributed to that success).

The the yaw-rate limiter in digital FLCS of Block 40s and onward actually works inverted too so opposite rudder isn’t required. The note you’re referencing applies to analogue FLCS jets like you noted though.
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35_aoa

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Unread post19 Jul 2018, 05:12

tjodalv43 wrote:

The the yaw-rate limiter in digital FLCS of Block 40s and onward actually works inverted too so opposite rudder isn’t required. The note you’re referencing applies to analogue FLCS jets like you noted though.[/quote]

Nice, makes sense......I only ever flew block 15's so we didn't have all the cool modern day stuff.
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vilters

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Unread post23 Jul 2018, 13:03

Ha, nice;
In those older blocks the pilot was only in the FCS rudder loop till about 25° AOA.
From 25°AOA till 29°AOA, the FCS gradually removed the pilots inputs and at 29°AOA the piot was completely out of the FCS loop. FCS would automatically control rudder with anti spin inputs.
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saberrider

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Unread post24 Jul 2018, 07:18

I believe that limit ( 25AOA for rudder deployment to start the dumping ) is still available in later variant just because shape of the a/c it's the same and will work just fine .

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