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6 Answers

Why “Flat spin” is most hardest to overcome even though it is only involved in yaw movement?

Asked by: 9874 views Aerodynamics

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6 Answers

  1. John D Collins on Oct 13, 2013

    In a flat spin, the rudder and elevator often do not have sufficient air flowing over their surfaces to change the yaw or pitch to one needed for recovery.

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  2. ccwebb on Oct 14, 2013

    A true flat spin is near unrecoverable because the CG is too far aft thus unable to get the nose down, no matter what the controls are set to.

    Even though it’s Wikipedia, the middle section speaks nicely about flat spins.


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  3. Florian on Oct 17, 2013

    For answering this question, imagine that the plane has zero forward speed (quite unlikely, but helps to understand why it’s the more critical spin).

    That pretty much means that the plane is plummeting straight down, and if you’ve done an upset recovery training before, that’s not even too far fetched. Also, let’s imagine that the aircraft is actually not rotating around the spin axis, but really just plummeting down in a straight line.

    The key here is the horizontal stabilizer. You’ve learned that the angle of attack is the angle between the relative airflow (which comes straight up in this case) and the chord line. Assuming an aircraft with no angle of incidence of the horizontal stabilizer and at 0° pitch during the spin (the most extreme flat spin imaginable), your angle of attack would therefore be 90°. It’s quite obvious that a 90° AoA is about as stalled as it gets (try generating lift by blowing air perpendicularly onto a flat plate). That means that your horizontal stabilizer and therefore elevator are unfortunately useless, so you can’t recover purely by means of self-induced aerodynamic forces.

    However, it’s a different story when the aircraft is, let’s say, 50° pitch down. Your angle of attack is now “only” about 40°, which means your conventional stabilizer is still stalled, but odds are that only the airflow on the tips of the horizontal plane is stalled but there is still some airflow over the center of the plane, therefore giving you some limited pitch control. Therefore you can “push” the yoke forward (or, if your aircraft has good spin recovery characteristics, not pulling the yoke as hard will already do the trick) to pitch down further to decrease your AoA and transition back to normal flight. When speeding back up, the airflow over and therefore effectiveness of the rudder/vertical stabilizer increases and you can stop the yaw around the spin axis.

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  4. Brian on Oct 17, 2013

    “A true flat spin is near unrecoverable because the CG is too far aft”

    The CG is only one of more aspects than I can list that play a role in the spin game. If you read Stall and Spin awareness by Sammy Mason you’ll read a part where he talks about a canopy change made to an aircraft he was spin testing. That was the only change made and resulted in a punch out due to an unrecoverable flat spin.

    When the aircraft flat spins the center of lift (center of pressure, or CP as is more commonly used when you don’t talk to the FAA experts…) moves forward. The result when is, when CP moves up to where the CG is, the spin becomes perfectly stable. Combine that with an aircraft who’s relative wind is straight up, and you have absolutely no conventional aerodynamic method for recovery.

    Interestingly, the best chance you have to recover is a foot from impact. Air density plays a major role in what little influence the control surfaces have. What’s unrecoverable at 20,000 feet may very well be recoverable at 5,000 feet. However, if perfectly stable, the only recovery method’s are punch out or deploy a drag shoot designed to pull the tail of the aircraft vertically and put it into a normal spin.

    Hope that helps, for what it’s worth that book Sammy wrote was an incredible, and very easy, 150 page read.

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  5. Randy on Oct 24, 2013

    There have been a few times when I thought I might die during my aviation career. One time was during a “spin training” session with a young student. Well, we were both young at the time. I used to teach all my students how to get into and out of spins. It was legal at the time. Do not think that you cannot get into a flat spin with your weight and balance within in limits in a Cessna 150. It happened to me and a student many years ago. We were adding and reducing throttle at the apex of the stall to get a counter-torque effect to help us spin quicker to the right. Yeah, not the smartest move. We went flat while adding power. What save our souls is that I had the sense to climb to over 6000′ agl prior to our spin session. There were 3 distinct moments when I thought to myself that we might impact the earth on our way spinning down. I can’t tell you the rate of descent, but it wasn’t extremely fast. The control surfaces had no force on them, they felt as if we were in a hanger. I could hear the elevator hit the stops…”clung” through the empennage. I’ve heard that once before airborne, different story, not relevant. I’ve been in hundreds of spins, but only one flat spin. I’m writing this for only one reason and this is, if somehow you find yourself in a flat spin, and there will be no mistake, you will know that you are because you will hear no air-rush, your controls will be static, and you will be looking at the horizon and not the ground, add full power and push the yoke forward. That should “tip” you over into a normal spin. That’s what save our lives that day. We recovered around 1500′ and went around at least a dozen times. This worked for me for an upright flat spin. I cannot guarantee it will work for you and I do not recommend trying to get into one without parachutes, an aerobatic aircraft and an experienced aerobatic instructor…of course.

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  6. John on Nov 15, 2014

    That’s ingenious, Randy. The propwash gave you the airflow you needed for the elevator, similar to how a tailwheel airplane can lift its tail while you’re sitting on the ground with the brakes set and throttle open.

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