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Thread: weight and balance datum

  1. #1
    Junior Member
    Join Date
    Oct 2008
    Location
    canterbury,kent
    Posts
    16

    weight and balance datum

    Hi Guys,

    Just fitted a new but heavier engine and now trying to do the weight and balance and get aircraft into cog.

    Previous owner a little unsure and said reference front of wing but no levelling reference just on level ground. Whilst this works for a cog point I feel it is not what I was expecting and the aircraft would fly very nose heavy and well out of cog.

    I would have thought the aircraft should have the boom level, this would put extra weight on the front wheel when measuring and the aircraft would be out of cog, as expected, and brought back into balance by placing the battery for the electric start as necessary.

    Can someone let me nw the official levelling reference

    Thanks

    David

  2. #2
    not real name 500 Club
    Join Date
    Feb 2007
    Location
    Wick
    Posts
    956

    weight and balance datum

    The manual states that the a/c should be on level ground. The Cof G datum point is the leading edge of the wing.
    What engine are you fitting as a matter of interest - an electronic ignition 447 or a 503 or ..... ?
    I would also be interested to see deatils of the new engine mounting arrangement that has been approved by the LAA for another member.

  3. #3
    Junior Member
    Join Date
    Oct 2008
    Location
    canterbury,kent
    Posts
    16

    weight and balance datum

    Thanks for the reply, I will have to check my weight again and ensure ac on level ground.

    The engine is a four stroke 508 Rotax but is much heavier and I have had to do loads of tests and also put in place the boom modification, make different engine mounts and engine frame.

    I will use in competitions so would not recommmend the engine change otherwise, too expensive!

    I still have the flight testing to do which might be interesting with all the changes.

    regards

    Hadders

  4. #4
    Senior Member 500 Club
    Join Date
    Dec 2006
    Location
    Northants
    Posts
    880

    weight and balance datum

    david,
    While not knowing the Sluka be aware that there is sometimes a difference between the actual CG and the measured due to a convienent way of defining it in practice.
    If the factory uses a method and then flight tests for approval it is then established that the figures work against this method so everyone uses them with confidence.
    The actual CG point will move over a large range when statically measured on the ground depending on the attitude of the plane but these factory methods are a lot more practical to use and as long as they can be repeated the result will relate to a known flying condition.
    You will not be in the Sluka for Popham then!!
    Mick

  5. #5
    not real name 500 Club
    Join Date
    Feb 2007
    Location
    Wick
    Posts
    956

    weight and balance datum

    Has anyone put a 503 in a Sluka yet - dual ignition would be nice.

  6. #6

    weight and balance datum

    I hate the 'all three wheels on a level surface' idea. Try finding a level surface on a grass airfield / farmers barn! - and then are your tyres inflated evenly, have tyres been changed for larger ones on the mains, has the suspension sagged etc etc. A datum level that can be verified with a spirit level is so much better. Even slight pitch attaitude cahnges shift apparent Cg a long way with high wing microlights with all the empty mass collected on the boom.

    However I supose if it is near enough and inside the limits done this way the best you can then it should be Ok for flight test - when the real Cg position should become apparent by pitch stability and trim cues.

    Shoot for as far inside the imits as you can without major buggeration and modification hadders and you shoudl be good to go.

    Dont the LAA have the weighing info on file??

    Paul

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