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Aileron Flutter

Discussion in 'Jabiru' started by Outback, Apr 22, 2010.

  1. Outback

    Outback New Member

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    Have any other Jab owners experienced aileron "flutter". In my J430 I find the ailerons vibrate in mild (actually very mild) turbulance. At times times this flutter is quite violent and takes a fair bit of holding by the control stick.
    My ailerons are set correctly as per instructions from Jabiru. The trailing edge of the ailerons can be moved about 4mm while the cockpit end of the cable hasn't moved - this is due to slop between the inner and outer sections of the cable. I hope it not cable ware as the aircraft is virtually brand new - only 35hours.
    Any ideas?

    Garry
  2. facthunter

    facthunter Well-Known Member

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    Ideas.

    No, but I would investigate it further, sooner rather than later. How does it respond to airspeed changes?. Is there a recommended.setting for droop?. Nev
  3. icebob

    icebob Active Member

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    sounds more like cable tension issue.

    Bob.
  4. Tomo

    Tomo "Young Enthusiast"

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    What it could be is your ailerons are in such a neutral position they get a wiggle up.

    I've had the same problem (soon as it happened I landed and checked it out though, it had just been adjusted previously).

    When banked, or had pressure on the ailerons it would go away. To fix it we just dropped them down a bit, so they aren't just trailing in the 'no load' area.
  5. XP503

    XP503 Active Member

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    Is dropping the ailerons a good idea?
    Adds unnecessary drag and effectively gets rid of the washout that's been designed into the wing.
    The ailerons shouldn't flutter at all maybe the cables need to be tightened....
  6. icebob

    icebob Active Member

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    The other thing it could be is if the cable runs through a pulley and that pulley is frozen then the cable wears a flat spot and the cable gets loose. don't know the system so only guessing.

    Looks like you may have to physicly check the whole ailron system, yuk!:yuk:

    Bob.
  7. Captain

    Captain "THE RAT"

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    That is not normal and is the type of issue that needs to be investigated and cured.

    Very concerning that it takes a fair bit of holding.

    Have you checked all of the hinges? And also check the clamps thru the inspection opening at the end of the cables inside the wings, or anywhere else where a bolt, or the wedges, or the inner brackets on the back of the seats have come loose?

    The 4 mm of movement is about what I get, but have you used a fair bit of force there to see if the outer cable is slipping at either end? The outer cable clamps would need to be pretty loose & noticeable to do that.

    And is the bellcrank still tight on the rear of the tube to the stick?

    I'm no expert, but I do have one and have built one so I hope this helps.
  8. Relfy

    Relfy Aviator

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    I'd do as per the previous posts but i remember when i was at the factory a while back, they were trouble shooting a jab with the same problem and I recall it came down to either an unbalanced prop that can get a type of harmonic resonation going through the outer wing and aileron or the aileron adjustments were out and it needed more washout.

    Give them a ring. They should set you on the right track pretty quickly.
  9. Tomo

    Tomo "Young Enthusiast"

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    Yes, you don't won't drag, but they do have to be in a certain position I found out.
  10. Outback

    Outback New Member

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    Thanks to everyone who have replied.
    Both ailerons are now drooped as per specifications. Jabiru told me to place a straight edge along the underside of the wing and the trailing edge of the aileron and there should be a 4mm gap where the trailing edge of the wing meets the leading edge of the aileron. This is to pre-load the ailerons. It looks a bit strange to see the ailerons drooped below the flaps.
    The cable has no slack in the wing, the bellcrank is free and there is no restrictions anywhere in the system.
    I do have a Patroni 3 blade ground adjustable prop and have checked that each blade has exactly the same pitch.

    Garry
  11. Tomo

    Tomo "Young Enthusiast"

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    Great you got it sorted mate, exactly the same problem I experienced once.

    Technical term called 'aileron snatch' I have been told, interesting stuff!
  12. Outback

    Outback New Member

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    Thanks Tomo, but the problem is still not solved. I just pointed out what has been done to resolve the problem.
    I'm currently waiting for more information from Jabiru. I'm told that VH-BNP (the Jab they use for publicity etc) had the problem and it was necessary to put some small trim tabs on the ailerons to load them up.
    Gee, I am impressed by the response to my problem. Again, thanks to you all.

    Garry
  13. dazza 38

    dazza 38 Well-Known Member

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    Hi Garry, im glad your on to it, control flutter, can be very dangerous.Im sure you well aware of this, i just posted this for everyone else, for new guys who might never have heard of flutter. Its has ripped planes apart. Their was a Grob, years ago i remember that crashed due to aileron flutter. Cheers
  14. Modest Pilot

    Modest Pilot Member

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    Each Jab aileron cable run has two 90 deg turns. Each 90 deg in a Teliflex cable gives about 15 thou slack. Guys in the U S A have been running the cables down the wing struts in J230/J250 and that halves the slack as there is only one turn. (see recent Kitplanes articles) The later J230 lends quite well to this setup. The J230 was flutter tested for the ARB (U K) at 160kn with electrically driven offset weight in the wings so I guess that any flutter is not divergent; still it is a nuisance; and I have yet to fly a J230/J250 that does not vibrate to some extent in this area.
  15. Tomo

    Tomo "Young Enthusiast"

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    Yeah ok.... I followed BNP home from Temora.... nice aircraft.
  16. xair1159

    xair1159 Member

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    Do not take this problem lightly and find a cure before flying!

    There was a recent AD on Zenith 601 aircraft involving aileron flutter which was found to be partly caused by incorrectly set control cable tension. See http://www.lightaircraftassociation.co.uk/engineering/Airworthiness/SAFETY ALERT - 2009.pdf

    For the effects of flutter have a look at this

    Other possible fixes are mass balancing which is awkward to build in or reflexing the aileron to give some aerodynamic pre-load, which is much easier if it works. This type of problem is usually sorted by careful flight testing by pro test pilots, not really a DIY job.

    Nick
  17. Outback

    Outback New Member

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    Good news! Problem solved. Firstly, I agree with Modest Pilot that from my experience too most J230/430's have some degree of vibration in the ailerons (more than any GA aircraft I have flown). So the changover point from a "vibration" to a "flutter" is pretty subjective.
    Jamie and Rod at Jabiru were very helpful and supportive (as they were during the construction phase) and after consideration suggested:
    1. Carry out the 4mm adjustment to the ailerons as per a previous post. This pre-loads the ailerons and they are now drooped down below the flaps.
    2. Place tape between the trailing edge of the wing and the leading edge of the aileron. This prevents airflow in that gap that can create vibration. This gap was pretty snug.
    3. Pull the cables tight in the cockpit where they come through the wing to take up any slack. Tie them together. Mine had about 10mm of movement in the wing.
    4. If the above dosn't fix the problem, put a small tab pointing down on the ailerons.
    Well I didn't have to do step 4. On 2 test flights to-day in calm conditions then moderate turbulance, the ailerons didn't move in straight and level flight. There was no vibration/flutter at all at any time, inputs were smooth...and no, the airspeed was not reduced by lowering the ailerons.
    Thank you for all the responses...they were appreciated.
    Garry

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