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BAN ALL RUDDER PEDALS!!!!!

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  • #16
    Originally posted by 3WE View Post
    I'm also thinking some C-130- (and/or pilot-) bashing is in order given the nice barrel roll that was once done in a 707 and it lived to fly another day (as did it's pilot).
    Well maaaaaaybe...

    But: in spite of its dramatic appearance, the 707 barrel roll, if flown properly, did not push any of the aircraft's limits - very different from the maneuver that's the topic of this thread. In fact it had almost a completely opposite purpose: the barrel roll was intended to look cool, but keep the aircraft well under control. The intent of the C130 maneuver was to push the aircraft as close as possible to the point where control would be lost.
    Be alert! America needs more lerts.

    Eric Law

    Comment


    • #17
      Originally posted by Evan View Post
      They usually do in normal attitudes. When you get into a slip in a power-on scenario (I think we can assume a commanded slip in level flight is a power-on scenario) you will get some degree of rudder float, increasing from the neutral position with the increase in slip angle. Therefore, as the slip angle increases, the pilot has to apply less pedal force to maintain the angle and the angle also begins to swing out at a faster rate. Eventually it reaches a point where the rudder force needed to maintain the slip and the rudder float meet. At that point you can maintain the slip with no pedal pressure at all. Beyond that however, you get into rudder force reversal... this is where you must maintain opposite pedal force against the slip to maintain it. If you fail to do this, you will get into extreme slip angles, a nose-up pitching tendency, AoA issues and a wing stall / spiral / public-funded military asset writeoff... all rather quickly.
      ???

      Ok, you have rattled off a procedure and not said one single word as to why or the mechanism behind all of that. You turn the vertical stabilizer caddy-whompass into the relative wind and the rudder-action reverses, but only when the engines are running????

      You know, sort of like avoid AOA's greater than 15 degrees PERIOD.

      Never mind that it's because around 16 degrees, the airflow becomes turbulent and you lose lift and ailerons tend to become ineffective.

      Any Gabriel (the Aeroengineer) comments?
      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

      Comment


      • #18
        Originally posted by 3WE View Post
        ???

        Ok, you have rattled off a procedure and not said one single word as to why or the mechanism behind all of that. You turn the vertical stabilizer caddy-whompass into the relative wind and the rudder-action reverses, but only when the engines are running????
        .
        The mechanism is pretty simple. First of all, the actual mechanism that moves the C-130 rudder is relatively primitive: a direct, hydraulically-boosted mechanical linkage. That leaves it susceptible to rudder float. When the aerodynamic forces working on the vertical stabilizer are off-centerline, as in a slip, they will reduce the rudder forces the pilot needs to overcome to increase the slip angle and the pilot will feel this. That's known as rudder float. Here is a description of how that works:
        If the rudder angle required to maintain a given sideslip angle is greater than the float angle for that amount of sideslip, then pedal forces must be applied to keep the rudder from returning toward neutral. As sideslip angles increase toward the higher angles, there is a tendency for the rudder to float out more rapidly less pedal force is required to hold the rudder deflection. A point is finally reached where the rudder angle required to hold the sideslip angle and the rudder float position are identical. At this point the rudder stays where it is with no pilot force on the pedals. In effect, the rudder is balanced with zero pedal force. The term “rudder lock” is sometimes applied to this point, but this is misleading because the rudder is not actually locked. It does require force on the opposite pedal to return to a normal flight attitude, but the rudder will readily respond to that restoring pedal force.

        Beyond this point, the pilot must apply opposite pedal force to restrain the rudder from floating further out. This is rudder force reversal, also called rudder overbalance. It is not fin stall, because the airplane remains directionally stable and will return to straight flight if the rudder is returned to neutral and the wings are leveled. Getting into rudder force reversal requires abnormally high sideslip angles, which are prohibited by the flight manual. Rudder force reversal is preceded by heavy, unmistakable buffet on the vertical tail (but not fin stall) that usually begins between 16 and 24 degrees of sideslip. A noticeable reduction in rudder pedal force starts at about 17 degrees of sideslip. Further increases in sideslip produce large yawing transients and a reversal of pedal forces. If the pilot lets the rudder float and does not reduce the sideslip, the aircraft will yaw out to a sideslip angle of 40 to 45 degrees. The nose-up pitching tendency that occurs simultaneously can cause one wing to stall. The airplane is now in very serious trouble! Both lateral and directional stability have been lost and recovery is problematic at best.

        Susceptibility to encountering rudder force reversal is greatest at low speed and high power (usually 75% power or greater) with flaps extended. It has never been reported in a power-off condition. Power effects on the wing and fuselage of the C-130 reduce the directional stability level sufficiently so that rudder force reversal occurs before fin stall. Recovery from a rudder force reversal condition requires returning the rudder to neutral and can be assisted by rolling wings-level, pushing the nose down to decrease angle of attack, and reducing power; but only if altitude permits.

        Some of that description is specific to the C-130.

        Another thing to consider as long as we are talking about S_ _ _ L is that at high sideslip angles the airspeeds become erroneous...

        Comment


        • #19
          Originally posted by elaw View Post
          Is it written somewhere that maneuvers performed by test pilots should always progress as predicted in advance and have a happy outcome? My understanding of tests like these are that they're often performed to find out where "the edge of the envelope" is, and if you never go past that edge, how exactly do you know where it is?
          It's called a wind tunnel. You don't find this out with real pilots in a real plane. As a test pilot, you get to the imminent signs of danger and then you recover.

          Comment


          • #20
            Originally posted by Evan View Post
            It's called a wind tunnel. You don't find this out with real pilots in a real plane. As a test pilot, you get to the imminent signs of danger and then you recover.
            Then why do ANY testing with actual airframes?

            Comment


            • #21
              Originally posted by Evan View Post
              When you get into a slip in a power-on scenario (I think we can assume a commanded slip in level flight is a power-on scenario) you will get some degree of rudder float, increasing from the neutral position with the increase in slip angle. Therefore, as the slip angle increases, the pilot has to apply less pedal force to maintain the angle and the angle also begins to swing out at a faster rate. Eventually it reaches a point where the rudder angle needed to maintain the slip and the rudder float meet. At that point you can maintain the slip with no pedal pressure at all. Beyond that however, you get into rudder force reversal... this is where you must maintain opposite pedal force against the slip to maintain it.
              Whaaaaaaaat?????? If that is correct, then the C-130 could never* be certified for civilian operation under any category.

              (*Never means except waivers, exceptions and AMOCs).

              --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
              --- Defend what you say with arguments, not by imposing your credentials ---

              Comment


              • #22
                Originally posted by Evan View Post
                Here is a description of how that works:
                [INDENT]If the rudder angle required to maintain.....
                Do you have the source of that and the link to it?

                --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                --- Defend what you say with arguments, not by imposing your credentials ---

                Comment


                • #23
                  Originally posted by Gabriel View Post
                  Whaaaaaaaat?????? If that is correct, then the C-130 could never* be certified for civilian operation under any category.

                  (*Never means except waivers, exceptions and AMOCs).
                  I have a Lockheed document. I'll have to PM it to you. But just Google 'rudder lock' and ignore all the gust lock hits. Or here: http://www.aero.polimi.it/~chimetto/...06Sideslip.pdf

                  Occasionally [in an extreme sideslip maneuver] an airplane will exhibit a characteristic called "rudder lock" where the force on the rudder pedals reverse as the rudder deflection approaches its maximum deflection. The rudder will tend to "float" all the way to maximum deflection without any further effort by the pilot.
                  This is, of course, an attitude outside the manufacturer's operating envelope. I'm sure it is not certified to be flown this way any more than it is certified to be flown straight into the ground.

                  Comment


                  • #24
                    ....and if people like Chuck Yeager hadn't stepped past the line we would all be still flying around in prop aircraft taking two days to get from Heathrow to Sydney.
                    To set a safe limit you have to step over the line to see what happens and formulate a procedure to get out of the situation developing.
                    You can see WHAT happens in a wind tunnel but you can't learn HOW to get out of it.
                    If it 'ain't broken........ Don't try to mend it !

                    Comment


                    • #25
                      Originally posted by Gabriel View Post
                      Whaaaaaaaat?????? If that is correct, then the C-130 could never* be certified for civilian operation under any category.

                      (*Never means except waivers, exceptions and AMOCs).

                      In spite of the word "lock", I'm not really seeing verbiage that says that the pedals don't swing back the other way nor indications that the rudder does not function.

                      Given a fat-ass airplane slicing sideways through the air, perhaps it's a crazy random swirl that hits the rudder just right when you are really slipping and there is a loss of back pressure, even though the vertical stabilizer as a whole is still pushing towards straightness as any good weathervane should?

                      Even the lowly 172 has warnings (but not prohibitions) in the POH against slipping with full flaps that can result in elevator oscillations.

                      Maybe it's something to do with aircraft with the designation of C-1xx?
                      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                      Comment


                      • #26
                        Originally posted by brianw999 View Post
                        ....and if people like Chuck Yeager hadn't stepped past the line we would all be still flying around in prop aircraft taking two days to get from Heathrow to Sydney.
                        To set a safe limit you have to step over the line to see what happens and formulate a procedure to get out of the situation developing.
                        You can see WHAT happens in a wind tunnel but you can't learn HOW to get out of it.
                        Let's not confuse Chuck Yeager boldly going where no man has gone before with routine certification test piloting.

                        As I said, absolute envelope limits on an aircraft like this can be established in the wind tunnel. There's no need to risk lives nor aircraft to verify this. Finding the limits of controlled fiight without exceeding them is another story. From the incident description, my best parlour-guess is that this was a steady sideslip test to determine the following:
                        Steady Sideslip Determine the gradient of rudder deflection per degree of sideslip, and aileron deflection per degree of sideslip for one flight condition. Secondary objectives are to determine the amount of bank angle required to maintain a constant heading during the sideslip, to measure any pitch trim change that might result from the sideslip, and to identify any region of the flight envelope where "rudder lock" is present.


                        As long as a test pilot knows how to recognize "rudder lock" and is trained and vigilant and prepared to recover, this is not a reckless procedure. It sounds to me like the pilot(s) here did not fit that description due to "poor procedural guidance".

                        Comment


                        • #27
                          Originally posted by 3WE View Post
                          In spite of the word "lock", I'm not really seeing verbiage that says that the pedals don't swing back the other way nor indications that the rudder does not function.
                          If you look closer you will see this verbiage:
                          The term “rudder lock” is sometimes applied to this point, but this is misleading because the rudder is not actually locked. It does require force on the opposite pedal to return to a normal flight attitude, but the rudder will readily respond to that restoring pedal force.

                          Comment


                          • #28
                            Short version: Rudder force reversal in not acceptable. (the little point is a period)

                            Long version:

                            § 23.177 Static directional and lateral stability.
                            (a)
                            (1) The static directional stability, as shown by the tendency to recover from a wings level sideslip with the rudder free, must be positive for any landing gear and flap position appropriate to the takeoff, climb, cruise, approach, and landing configurations. This must be shown with symmetrical power up to maximum continuous power, and at speeds from 1.2 VS1 up to VFE, VLE, VNO, VFC/MFC, whichever is appropriate.
                            (2) The angle of sideslip for these tests must be appropriate to the type of airplane. The rudder pedal force must not reverse at larger angles of sideslip, up to that at which full rudder is used or a control force limit in § 23.143 is reached, whichever occurs first, and at speeds from 1.2 VS1 to VO.
                            [...]
                            (d)
                            (1) In straight, steady slips at 1.2 VS1 for any landing gear and flap position appropriate to the takeoff, climb, cruise, approach, and landing configurations, and for any symmetrical power conditions up to 50 percent of maximum continuous power, the aileron and rudder control movements and forces must increase steadily, but not necessarily in constant proportion, as the angle of sideslip is increased up to the maximum appropriate to the type of airplane.
                            (2) At larger slip angles, up to the angle at which the full rudder or aileron control is used or a control force limit contained in § 23.143 is reached, the aileron and rudder control movements and forces may not reverse as the angle of sideslip is increased.
                            (3) Rapid entry into, and recovery from, a maximum sideslip considered appropriate for the airplane may not result in uncontrollable flight characteristics.

                            § 25.177 Static lateral-directional stability.
                            (a) The static directional stability (as shown by the tendency to recover from a skid with the rudder free) must be positive for any landing gear and flap position and symmetric power condition, at speeds from 1.13 VSR1, up to VFE, VLE, or VFC/MFC (as appropriate for the airplane configuration).
                            [...]
                            (c) The following requirement must be met for the configurations and speed specified in paragraph (a) of this section. In straight, steady sideslips over the range of sideslip angles appropriate to the operation of the airplane, the aileron and rudder control movements and forces must be substantially proportional to the angle of sideslip in a stable sense. This factor of proportionality must lie between limits found necessary for safe operation. The range of sideslip angles evaluated must include those sideslip angles resulting from the lesser of:
                            (1) One-half of the available rudder control input; and
                            (2) A rudder control force of 180 pounds.
                            (d) For sideslip angles greater than those prescribed by paragraph (c) of this section, up to the angle at which full rudder control is used or a rudder control force of 180 pounds is obtained, the rudder control forces may not reverse, and increased rudder deflection must be needed for increased angles of sideslip. Compliance with this requirement must be shown using straight, steady sideslips, unless full lateral control input is achieved before reaching either full rudder control input or a rudder control force of 180 pounds; a straight, steady sideslip need not be maintained after achieving full lateral control input. This requirement must be met at all approved landing gear and flap positions for the range of operating speeds and power conditions appropriate to each landing gear and flap position with all engines operating.

                            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                            --- Defend what you say with arguments, not by imposing your credentials ---

                            Comment


                            • #29
                              Originally posted by Gabriel View Post
                              § 23.177 Static directional and lateral stability.
                              (a)
                              (1) The static directional stability, as shown by the tendency to recover from a wings level sideslip with the rudder free, must be positive for any landing gear and flap position appropriate to the takeoff, climb, cruise, approach, and landing configurations. This must be shown with symmetrical power up to maximum continuous power, and at speeds from 1.2 VS1 up to VFE, VLE, VNO, VFC/MFC, whichever is appropriate.
                              (2) The angle of sideslip for these tests must be appropriate to the type of airplane. The rudder pedal force must not reverse at larger angles of sideslip, up to that at which full rudder is used or a control force limit in § 23.143 is reached, whichever occurs first, and at speeds from 1.2 VS1 to VO.
                              [...]
                              (d)
                              (1) In straight, steady slips at 1.2 VS1 for any landing gear and flap position appropriate to the takeoff, climb, cruise, approach, and landing configurations, and for any symmetrical power conditions up to 50 percent of maximum continuous power, the aileron and rudder control movements and forces must increase steadily, but not necessarily in constant proportion, as the angle of sideslip is increased up to the maximum appropriate to the type of airplane.
                              (2) At larger slip angles, up to the angle at which the full rudder or aileron control is used or a control force limit contained in § 23.143 is reached, the aileron and rudder control movements and forces may not reverse as the angle of sideslip is increased.
                              (3) Rapid entry into, and recovery from, a maximum sideslip considered appropriate for the airplane may not result in uncontrollable flight characteristics.
                              Interesting, but this goes against the aerodynamic behavior of rudder control systems that are prone to reversal. As I said back there, the C-130 has a relatively primitive reversible control system (designed in the early 50's!). Most modern transport aircraft have fully powered irreversible rudder controls. Perhaps this FAR was written after the C-130 was designed. And perhaps we need to use bold type on part that says "appropriate for the airplane". Slideslip angles where reversal can occur are prohibited in the C-130 flight manual.

                              Comment


                              • #30
                                Originally posted by brianw999 View Post
                                ....and if people like Chuck Yeager hadn't stepped past the line we would all be still flying around in prop aircraft taking two days to get from Heathrow to Sydney.
                                To set a safe limit you have to step over the line to see what happens and formulate a procedure to get out of the situation developing.
                                You can see WHAT happens in a wind tunnel but you can't learn HOW to get out of it.

                                Originally posted by Evan View Post
                                That's all based on what I know of the C-130 in general and perhaps the AC-130J has some modifications that effect the onset parameters (such as twice the power?) and I'm not saying this is what happened here, I'm merely illustrating the difference in skill and knowledge that a test pilot who is pushing to boundaries must possess. In other words, that's what test pilots are for.

                                I think people are really starting to mix up the different objectives of "testing" an aircraft.


                                Chuck Yeager was a test pilot in an experimental airplane, designed to push the envelope and learn about airframe and engine design. Similar goes for test pilots of brand new aircraft designs. I believe testing of a new aircraft of a KNOWN aircraft design has different objectives.


                                I am guessing, they are going to put the plane through all different types of maneuvers, not to test the design, but to test the actual airplane to make sure it is not defective and performs per the manufacturing specifications. In this case, a "test" pilot flying a a perfectly good aircraft, lost control outside the parameters of the testing and subsequently recovered in such a way as to irreparably damage the plane. This is a pretty serious problem and royal screwup. It should never happen, and frankly points to serious and costly problems that should have been rectified by procedure and training.

                                Comment

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