JF 17 Authority

[PatatOorlog]

Hey guys, So i fly the jeff on a daily basis and i would like to know what you guys think about whether or not this is realistic.

My main questionable ability of the jeff is being able to have full control when still at 70 - 130 knots whilst pulling 32 - 40 aoa

 

Here is a demonstration: JF 17 Is The Most Balanced UFO - YouTube

 

Then i would also like to mention the snappiness on the rudder, its feeling like it always has full authority, no matter at what speed.

I just find it weird, not really a bug report just a quick message whether or not this is realistic. if it is well so be it 

I attached a tacview ( Regular dogfight)

 

Jeff.zip.acmi

[LJQCN101]

The relaxed static stability (RSS) characteristics of the JF-17 enables the aircraft to create positive pitching moment up til around 60 degrees AOA with full elevator deflection leading edge down. Surely you can still pitch-up the aircraft at 70 knots, if the AOA is less than 60 degrees. (Just watch how the elevator stays at neutral position when holding the turn at 27 degrees AOA, and think about how the aircraft would behave when the elevator fully deflects.)

 

The F-16 is known to be able to do the same. I'll post the Cm curve of F-16 for example, as a typical characteristics of an RSS aircraft.

 

The main reason for the AOA limiter to exist is that:

1. Nose-down pitching moment plummets as AOA increase above 30 degrees.

2. Directional stability becomes negative (unstable) at above 27 degrees. Try staying at an AOA region between 30-45 degrees (using EFCS) and notice the wing rock aggravating. Any side-slip created would further decrease the ability for the elevator to generate nose-down pitching moment.

3. Rolling while pulling (and even worse if kicking the rudder into the roll) at the same time risks overshooting the AOA limit due to a phenomenon called inertia roll-coupling, to where the nose-down pitching moment created by the elevator is not enough to suppress the rapid pitch-up. Kicking the rudder at around AOA limit would especially be very dangerous, which is why the F-16 imposes an rudder authority reduction law to prevent the pilot from making rudder input at high AOA, but JF-17 doesn't have such features. As a basic rule, you're not allowed to pitch and roll the aircraft at the same time for more than 360 degrees bank changes consecutively, or making bank to bank pull & roll for more than 180 deg bank changes.

 

 

Your video just demonstrates the typical relaxed static stability characteristics, which other RSS aircrafts such as F-16/Su-27 also possesses, but with less inertia.

 

For more info try the three EFM & FCS demonstration videos at:

 

Edited September 29, 2021 by LJQCN101

[LJQCN101]

As for the yawing moment coefficient (Cn) created by the rudder, it remains pretty much constant from 0 to 35 degrees AOA, and then plummets into approximately 0 at 60 deg AOA. No magic included.

 

 

As mentioned above, the directional stability (Cn-beta) become negative (unstable) at above 27 degrees, which also means you'll get less yaw dampening moment to counter the yawing moment created by the rudder, hence more sensitive rudder.

Edited September 29, 2021 by LJQCN101