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  1. #11
    Senior Member 500 Club
    Join Date
    Dec 2006


    Hi All,
    Square tubes are easier to machine and fix things to but round tubes are lighter and probably better in twisting loads.
    Boom tubes are usually driven by availability of material I suspect.( the Shadow one is a water drain tube from the local power station I am told)
    If you find another replacement boom for your plane it needs to be the same material , size and manufacturing method to be successful as an easy solution otherwise the tests and paperwork would go on for some time and even then it would need some providence I suspect.
    The approved LAA mod should be good because it effectively replaces the front of the boom with another inside and increases the support for the front wing through bolt.
    You should consider this at an early stage even before you can see the cracks as its a known problem.
    It might be good for a few of you to get together and produce the fix collectively to keep the price down.
    Extra brakes might be possible but do not dismiss the small drum brakes as they are more efficient for the likes of planes than the discs but its all down to weight.
    The engine change was a 508 fourstroke which is only practical for competitions due to its availability and fuel performance.
    There is no reason why you cannot fix a 503 but the only advanage of the duel ignition is down to the removal of the points, it actually works better as a single spark.
    Hope this helps

  2. #12
    Junior Member
    Join Date
    Oct 2008


    Hi Roger,

    I have recently had the boom modified as I have added a 508 engine. The work I had done was more than necessay ie a slightly longer sleeve. I had the boom sleeved with a piece of sluka original boom, split and cut and and new saddles and new bolts(2) made. We reammed out the front holes to accept the new saddle. The sleeve was pop riveted all over to keep in place as requested by LAA. Because I also had made different engine mountings the whole lot was then load tested to cater for a heavier 508 engine. The loads for a 447 are much lighter in both weight and torque.

    Give me a call if you want some information or email.


    david 01227 700441

  3. #13


    Square tubes don't have anything like the tortional strength of round ones, If you can find a Spectrum, check the tail and see how easy it is to twist

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