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Thread: Aft C of G

  1. #41
    PerryB's Avatar
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    Quote Originally Posted by bob turner View Post

    I own a Decathlon - not quite the same. I am not wild about multiple turn spins, so will be doing no exploratory testing. Just wondering if these fine airplanes can go flat?
    Bob, I've spun a 150 Decathlon many turns, many times and often with an adult male in the rear. By 3 turns it's as wound up as it's going to get, and I've never had it try to flatten out. Because of the way I was taught, I always recovered with positive/assertive control inputs, but I think if you just let go of a Decathlon it'd fly itself out of a spin. I don't know how the airspeed would stack up, but I think it would stop rotating and start flying on it's own fairly quickly.
    After Monday and Tuesday, even the calendar says WTF !
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  2. #42
    mvivion's Avatar
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    Quote Originally Posted by bob turner View Post
    No - I rarely do more than 3/4 of a spin.

    But I have heard stories of folks who like to count the turns - I understand the impulse to make/break records (yesterday I did 42 Stearman landings) - but my impression is that after two or three turns a spin will tighten up.

    We had a Citabria fatality last month - extremely experienced instructor; object of the lesson was CFI spin certification. I have heard almost nothing - one pilot suggested a low level engine failure and an unsuccessful landing - but I initially wondered if it hadn't spun in?

    I own a Decathlon - not quite the same. I am not wild about multiple turn spins, so will be doing no exploratory testing. Just wondering if these fine airplanes can go flat? Pretty sure a Cub can get into a difficult-to-recover spin with a heavy guy in the back. Not gonna try that either.
    Bob,

    I was advised by a guy who would know as I was becoming familiar with aerobatics to remember one thing about spins: Any airplane MAY become unrecoverable in a spin. As Pete noted, pay careful attention to the pitch attitude. If it starts to go flat, recover immediately. Unless you’re flying an aircraft certificated for flat spins.

    Spins deserve a great deal of respect. Pilots often fail to exhibit that level of respect, and sometimes pay a heavy price.

    MTV

  3. #43

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    Thanks for that - my feelings were gut instinct, and now they have at least some basis. I also got some input via PM.

    Ten turn spins are not necessary or productive, and may not be safe.

  4. #44
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    I’m going to resurrect this thread regarding “excess stability.” The comments about it don’t make sense in my planes (plural) so I asked a very close friend, a Professor of Aerospace Engineering at a large university about stability, controllability, maneuverability, etc. with respect to my own airplanes. My Rev is a good example to start with. On paper the CG sits comfortably within the CG envelope. Flown empty I describe it like trying to balance on ball bearings. This plane is not excessively stable. In its forward limit its anything but. Clearly what I perceive as stability improves with weight added aft. It could be argued that maneuverability is at its peak but in this example that isn’t a good thing. Controllability is more difficult to understand. The plane responds to pilot inputs but the pilot has to make constant corrections. What a design engineer and a pilot define as controllability may not represent the same thing. My Cessna’s tendencies are along the same lines although not as dramatic. The concept that airplane stability improves as CG moves forward until it becomes ”excessively stable” doesn’t prove up in my experiments. I’ve read several papers about it and talked to the smartest guy I know about it. All we can come up with is that the paper description and pilot description don’t reconcile, and that’s probably semantics.

    I was in FSDO a couple of weeks ago talking to a couple of inspectors and mentioned that every flight in my Rev brings another adjustment, so every flight I’m a test pilot again. CG was a large part of the discussion. It’s an interesting process. They reminded me why STCs are time consuming and difficult to get. Certificated guys operate within limits that somebody else explored and defined. Experimental guys don’t have that luxury. I have a new perspective on the process.
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  5. #45

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    Are you possibly confusing stability with speed of response?
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  6. #46

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    pa11driver
    I missed your post (#1 earlier. I used to load as you do most all the time. But now would have to to say "it depends". Times I tend to load tail heavy, going into a short/new strip that I need hard braking, or if I have long legs to fly hoping to increase my airspeed. I will try to load front heavy for taking off on rough stuff so I can get the tail up, or knowing I am going into rough air.

    I enjoy threads like this that help explain some of the terms and theories.
    DENNY

  7. #47

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    Stewartb
    How much dihedral did you dial in?
    DENNY

  8. #48

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    I don't drink milk.

    Quote Originally Posted by cubdriver2 View Post
    Hold a gallon of milk at arms length in front of you, now hold it close to your chest. Which is easier

    Glenn

  9. #49
    cubdriver2's Avatar
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    Quote Originally Posted by arnold bronson View Post
    I don't drink milk.
    It also works with oil and Johnny Red with a handle

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  10. #50
    stewartb's Avatar
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    Quote Originally Posted by DENNY View Post
    Stewartb
    How much dihedral did you dial in?
    DENNY
    Standard Supercub, if memory serves. Jeez, that was two years ago but it clearly has typical Cub dihedral. This is a W&B issue. The Flight Standards guy was interested and helpful, but that was not what I was at FSDO for. Weight aft is a normal thing for most of us. This Phase 1 testing isn't my normal operational profile so the CG is not a problem as much as an opportunity to learn new things. And new respect for test pilots.
    Last edited by stewartb; 11-07-2018 at 07:59 PM.

  11. #51
    BC12D-4-85's Avatar
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    Both PA-12's I flew had what I'd call neutral stability (https://www.boldmethod.com/learn-to-...y-in-aircraft/). If disturbed in flight they would take off on their own up/down/sideways. Took constant minor corrections to maintain desired flight. One I owned had an O-360 and CS prop and was forward CG...still went looking when it smelled something. Wheels, skis, floats didn't matter. Not bad just different than the others I owned or had experience in.

    Rigging was about 0.75* dihedral for the one with extended wings and 1* with factory wings. 2.5* wash on both.

    Gary
    Last edited by BC12D-4-85; 11-07-2018 at 07:44 PM.

  12. #52
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by DENNY View Post
    Stewartb
    How much dihedral did you dial in?
    DENNY
    standard 3" at spar attach

  13. #53

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    Quote Originally Posted by cubdriver2 View Post
    It also works with oil and Johnny Red with a handle

    Glenn
    OK I'll try the Johnny Red

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