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Thread: Loss of Control - inadvertant spins

  1. #21

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    Wolfgang (Stick and Rudder) said most of those turning final spins are because the pilot thinks the ailerons are the bank control. So they get slow on base to final and then rapidly try to unbank from the turn with just aileron and that draggy down going aileron drags the wing back into a spin.
    Should have used plenty of rudder to unbank when flying slow with the stick back.
    (sort of what Cub Builder said)

    I say don't overuse the rudder (skidding) while banking into the turn. But banking into the turn usually isn't the problem. The problem is getting out of that turn because after some time the aircraft slows and the pilot has a lousy pitch sight picture so gets near stall. Best to lead with top rudder getting out of that turn. But most lead with aileron.
    Last edited by Bill Berson; 07-10-2018 at 05:10 PM.

  2. #22
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    Quote Originally Posted by WLIU View Post
    I fall into the camp that observes that too many pilots rely exclusively on what they see on the panel and not enough what their senses are telling them. I am introducing an acquaintance with a Cessna background to a Pitts that has nothing in the panel other than airspeed and altitude. Right now, when I give this young man the airplane I always feel that I am sliding off my seat to the right. A sample of one, but I think a symptom of what "modern" training produces.
    ...
    Tape a sheet of paper over the panel glass and listen to what your butt is telling you.

    Wes
    Prior to solo, I have always had my students fly around the practice area (first) with my coat covering the panel, asking them to hold a specific airspeed in slow flight. I'd periodically lift the coat from the airspeed momentarily to let them see how close they were, usually within two to three mph. Later we'd fly the pattern several times with the coat over the panel (full stop-taxi backs only). This assures them (and me) that they can fly perfectly well by looking outside and paying attention to feel and sound. Even prior to that, I've had them sit limp in the seat while I flew, first, in coordinated flight, then with the ball off to both right and left, differing amounts, while looking at the ball and ensuring they can actually feel the side forces. Included in this would be having them sitting tensed up while I do the same thing, to show how little you can feel under those conditions. Then, of course, it's their turn.

    Another thing to help them is to be sure they understand to use a light touch on the controls, so they can feel what's going on.

    All of the above is so they know how to feel and see and hear what the airplane is telling them.

    Larry N.

  3. #23

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    Quote Originally Posted by Joda View Post
    Huh? An airplane is not a boat. You don't steer it with the rudder. You bank the airplane to redirect the lift vector so it will turn. You use the rudder to keep the airplane coordinated (i.e., the ball in the center, not slipping or skidding). The rudder is not turning the airplane. The wings are. Read the FAA's "Airplane Flying Handbook" (FAA-H-8083-3B), starting on page 3-10. The section titled "level turns" will give you the whole scoop. One quote from the handbook that is germane to this discussion:

    "The pilot uses the rudder to offset any adverse yaw developed by wing’s differential lift and the engine/propeller. The rudder does not turn the airplane. The rudder is used to maintain coordinated flight."

    Note that it specifically states that the rudder does not turn the airplane.

    Getting back to spins, others have already stated that you can enter a spin from either a slip or a skid. If the airplane is coordinated during the stall, it won't spin. If it's uncoordinated, it may spin. Keep the ball in the center and all is well!
    Agreed, "The rudder does not turn the airplane." In post #5 the young chap flew right wing low in straight flight. This is one of the most common errors CFIs see with students while climbing out on takeoff. The rudder is used to counter engine torque and P factor, etc. to avoid yaw or slip. If the wings are level, rudder must be applied to resist the heading change of the skidded turn. Level the wings and hold heading with the rudder will keep the ball centered and errors are more easily seen than by looking at the ball or yaw string or felt in the seat of your pants.

    In turbulence the ball swings from side to side faster than the footwork can handle. Large aircraft have yaw dampers to counter the yaw. The light plane pilot can counter the heading swings with rudder similar to a yaw damper and smooth the ride. Countering the turbulence that raises a wing with only aileron adds adverse yaw that amplifies the heading swings in turbulence. The side to side yawing motion is what generally makes passengers airsick.

    I would be happy to give a more detailed explanation of the flight dynamics if you are interested. Summery, use ailerons to hold the wings level or at the desired bank angle and rudder to eliminate yaw. Yaw (heading change) with wings level should be countered with rudder.

    If you can agree with that next discussion should be how insufficient rudder use (just opposite the common explanation of too much rudder) can lead one into the fatal turn to final and that can be followed by how aileron effectiveness at high AoA can lead to loss of control as in the video of post #15. Notice that the rudder is centered as the loss of control continues to impact.
    Last edited by jedi; 07-10-2018 at 08:28 PM.

  4. #24

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    I agree the pilot in post #15 should have been holding some right rudder to offset the high angle power factor (p factor or whatever you call it)
    Instead he was likely holding some right aileron to prevent left turning which stalled the left wing first. His first reaction was full right aileron which was the worst possible reaction and made it yaw left violently.

    So with insufficient right rudder up to the event he was not coordinated. The power was perhaps the cause of the left stall break.
    Last edited by Bill Berson; 07-10-2018 at 10:43 PM.

  5. #25

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    Quote Originally Posted by cub builder View Post
    No doubt many will disagree with this statement, so I'll put it out here for discussion. I was taught 40+ years ago when I was learning slow taildraggers: "In normal flight, use the ailerons to roll the plane level. In high angle of attack situations, use the rudder to control the roll of the plane as the aircraft will respond quicker and hard aileron inputs can trigger a stall as is demonstrated in the video." Before criticizing the statement, I would suggest trying it... at altitude.
    That is true of most airplanes, not just slow taildraggers (ref: USAir Boeing 737, Flt 427 rudder hardover). As AOA increases there is a point where rudder becomes more effective for rolling the plane and can overpower the ailerons for roll control. In fact, some refer to that as "crossover alpha" or "crossover speed" and most CFI's will touch on that concept with students when performing slow flight but there is not a lot of emphasis and it's one of those things quickly forgotten after the checkride.

    I have had aircraft do a spin entry from coordinated flight in an accelerated stall. That comes from the wings being less than identical in either shape, drag or rigging. In an accelerated stall, usually one wing will give up first causing an immediate hard roll, and the plane will spin without any additional input to intervene.
    If there is no yaw when the plane stalls, the plane won't spin. Any of the factors you describe (and many others) can impart a yawing moment and yaw is what causes the spin. I'll bet you may have done the old exercise of stalling a plane and holding elevator backpressure to prolong the stall while keeping wings level with rudder only. Any misapplication of rudder will result in a spin.

  6. #26

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    Quote Originally Posted by cub builder View Post
    Here's a good stall video for you experts to analyze. VIDEO
    There are several factors that eliminate me as an expert - including
    • I have never flown that make/model of airplane
    • I do not know how the airplane was loaded
    • I do not know what atmospheric conditions existed at the time
    • etc.

    I will note some of the things I see in the video:
    • there is counterclockwise rotation around the longitudinal axis (initially)
    • before the aircraft strikes the ground, there is clockwise rotation around the longitudinal axis
    • there is counterclockwise rotation around the vertical axis
    • the airplane is held in a high angle of attack; exceeding critical AOA

    Here is what I surmise:
    • There was no spin
    • The pilot could have lowered the angle of attack, breaking the stall
    • The pilot could have used (more?) right rudder to stop the rotation around the vertical axis


    IMHO

  7. #27

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    Quote Originally Posted by FlyingRon View Post
    Touching down doesn't involve stalling an aircraft. It's near impossible to stall most aircraft with the mains on (or just above) the runway.
    No longer generating enough lift for (level) flight does not equate to a stall.
    I don't know about that Ron. When I was a Guard pilot checking out in the Bird Dog, they had to show me the "Army Way". I was getting an add on FW designation to my RW. I had an FAA com/inst (basic requirement) and was in a FW slot. I was getting instruction from a former USN Neptune pilot.
    Norm didn't like my grease jobs and showed me the right way. Stay at least 3 feet off the RW and when the stick hits the rear stop, let her drop. The bottom dropped out. Sure felt like a stall to me. Every other pilot in the unit did it the same. There were reports of the A/C light between the MLG ocasionaly getting busted.

  8. #28

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    When I was learning to fly in the J-3, my CFI had me do a lot of slow flight practice. 15 to 20 minutes at a time. I'm talking slow, right at the stall. One day he showed me accelerated stalls. Shallow turn, close to stall, ailerons neutral, stick back to the stop. apply bottom rudder until back to level flight. The Cub wanted to roll out opposit the turn and would go into a bank the other way if you let it. I would think that the inside wing would stall first and that wing would drop. Anybody?

    A late friend instructed in B-24/B29's. He told me that stalls in a sixty degree bank were in the syllabus. All crew members were on board.

  9. #29
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    I can guarantee a birddog is not stalled with the main gear on the ground, PERIOD. Running out of lift does not equate to a stall. The Birddog will quite happily takeoff from the three point attitude.

    What happens with high AOA's and slow airspeed is the combinatino of the decrease in lift and HIGH amounts of drag. This means you drop and slow down even faster, but it doesn't mean you're stalled.


    Again, to spin you need to be:

    1. stalled.
    2. have an assymetric angle of attack.

    Note that some of the stall/spin mystique comes from the fact that people think that all lift goes away when you stall. In fact, the lift vs. aoa curve is pretty symmetrical. What enables a spin is that before the stall an increase of AOA makes more lift, after an increase of AOA makes less lift. This is what allows the spin to self sustain.

  10. #30

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    Um, no. In a spin the entire wing is generally on the back side of the L/D curve and there needs to be a sustained yaw input. That can be due to engine and propeller forces (power is destabilizing). It can be due to my foot holding the rudder pedal full forward. It can be to an under-trained pilot holding some unintentional rudder input during an intentional or unintentional slowing below the wing's critical AoA.

    The "asymmetric angle of attack" is what we do to execute a snap roll. We put the wing just on the plus side of the L/D curve and then add max yaw. One wing remains at max lift driving the rotation, the other wing goes to be on the "back" side of the L/D curve generating drastically less lift and much drag. Having one wing driving the rotation is why snap rolls rotate so much faster than simple "slow" rolls. As I think about this I will agree that a unintended spin can be entered by flying uncoordinated so that one wing stalls before the other. But if the resulting unintentional attitude allows an increase in airspeed, the accident pilot likely gets into a spiral. Still not a good place to be.

    One factor that likely leads to failure to recover from unintentional spins is a pilot attempting to put the nose down rather than removing the yaw input, and maybe adding power, which is a pro-spin input. 99% of the well known emergency spin recovery methods (PARE, Beggs-Mueller, Finagin) start with pulling the throttle hard against the idle stop, and applying anti-spin rudder input. This is counter-intuitive to the typical modern trained Cessna/Piper/Mooney pilot. But its the quickest and most effective way to start an emergency spin recovery.

    Some homework - Go up to a high altitude, slow the airplane into a stall, add and hold rudder. Push the stick forward while holding rudder. Observe that the rate of rotation increases and no recovery occurs. Pull the stick all of the way back. Observe that the rate of rotation slows. Now add power. Observe that the spin changes pitch but no recovery occurs. Reduce power to idle, move stick to neutral or simply release, apply and hold anti-spin rudder. When the rotation stops release the rudder input, move the stick to allow the airspeed to increase to 100, and return to level flight. This exercise is used to introduce new acro students to spins. It demonstrates that exit from a spin can only occur when power is reduced and anti-rotation/spin rudder input is applied.

    Now we know that for the first two rotations of a spin we are in the incipient phase and immediate anti-spin control inputs combined with pulling the power will get us flying again quickly and with minimum loss of altitude. Which is to say that a spin entry during the base to final turn need not be guaranteed sudden death, but too few pilots have the knowledge and understanding to react promptly and correctly.

    Which is another long way to say that our current training is deficient.

    Best of luck,

    Wes

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