What surfaces move if you fly straight and apply rudder?

[saberrider]

Only rudder is moved or the flaperons along to the rudde to give you level turn?Talking about F16 only.

[saberrider]

I asked this questions because in the sim flaperons go up and down 3degrees with rudder apply for yaw . Thus the real F16 get it for your knowledge?

[rheonomic]

Roll and yaw axes are coupled, so if the rudder moves and you want to maintain the same roll attitude you have to move some other surface to counter the roll induced from the rudder deflection.

[saberrider]

Roll and yaw axes are coupled, so if the rudder moves and you want to maintain the same roll attitude you have to move some other surface to counter the roll induced from the rudder deflection.

This axis coupled will be just in control laws for the F16?

[sprstdlyscottsmn]

No. It is the same principle as differential horizontal stabilizer deflection. You are generating a force above the CG. That will make it want to roll in the direction force is applied. The distance above the CG is less than the distance behind the CG which means the roll coupling is less strong than the yaw itself. Also, with yaw, one wing temporarily is move faster than the other and makes more lift causing it to roll. With swept wings, the forward wing now has a lower sweep angle and thus makes more lift causing it to roll. Both of these rolls are in the opposite direction of the "above the CG" roll and will become the dominant force in roll as well.

[johnwill]

I could be wrong, but I believe the aileron-rudder interconnect (ARI) on the F-16 is a one way device. Meaning application of roll command will directly go to the ailerons (and horizontal tails) and a portion of that command (function of Mach and AoA) will go to the rudder to minimize sideslip in the roll. Same as turn coordination in a mechanical flight control system. But pilot application of rudder command does not go to the ailerons to minimize roll during a sideslip. During structural flight test of F-16, many steady sideslips, rudder kicks, and rudder reversals were performed to verify design loads on rudder and vertical tail throughout the entire flight envelope. In all those maneuvers, it was necessary to apply roll commands to maintain a reasonably wings level attitude.

[saberrider]

Johnwill,Thank for this answer. You know at which point rudder became ineffective(max .speed)?

[johnwill]

Rudder effectiveness is reduced due to structural flexibility. At high airspeeds, supersonic, flexibility of the rudder and vertical tail reduces the effectiveness of rudder in the same way as aileron loss and eventual reversal. That is the primary reason for the ventral fins being added - provide more directional stability at those conditions. This effect does not happen at one point, but is gradual as airspeed and mach increase. As mach increases, the center of pressure on the tail and rudder moves aft, which increases the twist on the tail fin. The effectiveness never goes to zero or reverses.