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Thread: Stall Characteristics

  1. #1

    Stall Characteristics

    Our little group has a 1973 Sundowner 180hp.
    3 of 4 of us are students working toward our Private and while doing
    our Power Off Stalls the plane wants to drop hard to the right.
    Has anyone had any experience with this problem in the Sundowner??


  2. #2

    stall characteristics

    The plane is out of rig. To find out if it is the wing or rudder out of rig, try this test in the air: Set up cruise flight, straight and level. hold the ball centered and let go of the yoke, keep the ball centered by using the rudder. If the plane starts to roll right away, the problem is in the wing rigging. Note which way it rolls for the mechanic. Then hold the plane level with the yoke, and put your feet flat on the floor. If the ball moves, the rudder rigging is off, again note which way, and how much ball deflection for your mechanic. Note if the yoke is level too.

    Most often, the misrigging will be spread between the wing and rudder. Also, check that your gauges aren't off level. Your instructor should be able to help you through that. The easy way is to hold level on the attitude indicator and not see the D.G. turn. Then cross checking the attitude gyro with the turn coordinator.

    With the plane rigged, these things stall very nicely, straight forward with the nose bobbing. Mine was a violent tuck and roll until I rerigged it.
    I chewed through my restraints for this?

  3. #3
    Well, the plane MIGHT be out of rig. More likely, though, is that all of you aren't "stepping on the ball". Keep the ball centered throughout the pre-stall and the wing shouldn't drop.

    Best regards,

    Steve Robertson, CFI SEL/MEL
    N4732J 1967 Super III

  4. #4
    Joe and Steve are both correct.

    A properly rigged plane (of our models) will just bob its nose and descend, if the ball is kept centered during a power-off entry and stall. Most newcomers, in part due to nervousness, will be stabbing at the rudder pedals while trying to keep the ball centered. This will induce PIO. In short order the pilot 'gets behind the ball', and the plane rolls. But the roll is not violent; you just pretend that it is a descending steep turn, and fly into and then out of it.

    As we have written so often, the (properly rigged) plane will not spin without being forced into it as described in the A1CE TCDS. It will instead enter a spiral dive. The spiral dive is not as disorienting as a true spin, but it DOES require prompt recovery, as IAS will increase much faster than it will in a spin. My Sierra will hit VNE within five seconds of entry into a nose-down spiral dive, and that's with a 2G recovery applied. I have not had it beyond VNE, and don't intend to. Here is a link to an FAQ with more info on the subject. You can learn a lot about the handling of these planes by searching on 'spiral dive', 'spins', etc. on this BAC website.;id_cat=8#416

    Almost every one of these planes that I come across are out of rig; some much more so than others. Most need their control cables re-tensioned; or need flap adjustment; or have loose aileron hardware or misadjusted ailerons; or have misadjusted rudder trim/nosewheel centering; or a combination of all these factors. You can't rig anything correctly if the cable tensions aren't right. Varying air loads will be 'slapping' the control surfaces, as the loads change, making it impossible to keep them where they need to be.

    Almost anyone can check for play in their ailerons (loose bushings and rod ends). I try to shoot for no more than one-eighth of an inch of free play at the aft edge of the ailerons, and less is better. Then have someone 'lock' one aileron to the adjacent flap with their fingers and hands. Try to move the opposite aileron up or down. It is quite common to be able to move the other aileron an inch or more. It's not possible to properly rig or fly the plane with that kind of slop in the system.

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