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  1. #1

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    need to add weight question

    I need to add weight to the tail of my newest addition cox .09 medallion powered, can i add weight to the bottom of the elevator next to the fuselage,without hurting flight cariteristics?Or add the weight on the fuselage as shown in pictures?
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    Last edited by jayseas; 01-21-2014 at 12:14 PM.

  2. #2

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    There should be no appreciable difference either way.

    Personally, I'd stick the weights to the fuse.

    Greg

  3. #3

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    Thanks Greg.

  4. #4
    JohnBuckner's Avatar
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    Just curious where exactly is the CG without those weights and have you flown that ship yet?

    John
    \"Keep your controllines tight\"

  5. #5

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    Cg is about 1" forward of the l/e. Haven't flown ship yet.

  6. #6
    JohnBuckner's Avatar
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    Ah yes thanks. I am thinking perhap shortening the nose maybe useing a smaller tank or box tank possibly even recessing the tank into the wing. Just a thought.

    John
    \"Keep your controllines tight\"

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    Quote Originally Posted by JohnBuckner View Post
    Ah yes thanks. I am thinking perhap shortening the nose maybe useing a smaller tank or box tank possibly even recessing the tank into the wing. Just a thought.

    John
    Wow, that's a very nose heavy model.

    Perhaps adding 1/2" -3/4" to the tail moment?

    Greg

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    I have added 1.5Oz to the tail, the c/g is now 1 1/4" aft of the t/e of the wing.I will go fly like this and see how she does.Ship weighs 11.5 oz total.

  9. #9

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    Is your CG 1 1/4 aft of the leading edge? If so, I wouldn't start out with it that far back. Maybe 1/2 to 3/4 in at the most.

  10. #10

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    I would not glue the weights onto Elevator, because the Elevator can break off at fuse Joint easy after hard landings.
    I also would split the amount of weights in half and fix it on left and right side of the fuse.

  11. #11

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    I did split and and attach the weight to the fuselage.

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    It's not suprising that it's come out nose heavy, that's a long nose moment and a short tail moment. If it were me I'd probably shift the engine back a little if I could, ditch the spinner (too much weight out on the nose) and maybe go to one wheel, or none if you fly off grass.

    The lighter the better!
    Go knife edge your cub!

  13. #13

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    Probably a good idea to ditch the spinner but not much weight there, but it all adds up i suppose.If i have to i can shift the eng aft some and go with a different shape tank.But first some flight test.
    thanks guys for ally your comments.

  14. #14

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    Yeah, be sure to let us know how you go!

    Incidentally, what size tank is that?
    Go knife edge your cub!

  15. #15

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    tank is a 1 1/4 oz

  16. #16

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    Quote Originally Posted by jayseas View Post
    I need to add weight to the tail of my newest addition cox .09 medallion powered, can i add weight to the bottom of the elevator next to the fuselage,without hurting flight cariteristics?Or add the weight on the fuselage as shown in pictures?
    Hi Jayseas, I have a different approach and I hope I'm not too late.

    I think a better solution would be to saw the fuselage off, in front of

    the tail segment, make the cut 45 degrees, not 90 degrees. Then

    splice in a fuselage extension, bringing the elevator hinge line back

    to the neutral point of your pushrod. You'll still to have to add tail

    ballast, but maybe only 1/3rd as much. The prior suggestions that

    have you relocate the engine further back is also a good Idea.


    Frankly I think the best plan of action is to cut away the wing, stab

    and elevator ; and build a new fuselage with the relocated engine

    and lengthened tail moment. This way you may not have to add any

    weight; resulting in a lighter and better flying model.

    An easy way to determine nose and tail moments is to locate the

    components on the 3/8" fuselage sheet, that is, place the engine,

    fuel tank, completed wing, and empanage into postitions that render

    the balance at approx. 15-20 % of the wing chord.


    Just looking at your model, it's difficult to determine span and wing area.

    It looks as if you based your model on a Ringmaster Jr, which has 195sq"s

    wing area. If you can keep the total ready to fly weight under 12 ozs,

    you will have a nice flying airplane. There's lots of weight saving things

    you can employ on your next model. Leave off the landing gear, spinner,

    use a lightweight covering, and finish. Also, hook up a Balloon tank, which

    feeds at regular atmospheric pressure, not a pressurized bladder. Good Luck;

    Tony

  17. #17

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    Tony alotm of what you save makes sense but leaving of landing gear and such i can't do. i fly alone.I will fly as is first to see what's up.But as you stated. i will keep the cutting the fuselage in mined.Thanks

  18. #18

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    Well it's been awhile but, what i ended up doing is shortened the nose went to a 1 OZ tank, pushed tank and eng back 3/4" With 1 oz of weight to the tail.CG is just shy of 3/4" aft of l/e.
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    Last edited by jayseas; 03-01-2014 at 02:24 PM.

  19. #19
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    Congratulations Jayseas shortening the nose was the most obvious first step and glad to see you took that step. Now that brings us to the next obvious question since I still see lead peeking out from under that tail, Where does it balance now??

    John
    \"Keep your controllines tight\"

  20. #20

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    Quote Originally Posted by JohnBuckner View Post
    Congratulations Jayseas shortening the nose was the most obvious first step and glad to see you took that step. Now that brings us to the next obvious question since I still see lead peeking out from under that tail, Where does it balance now??

    John
    .CG is just shy of 3/4" aft of l/e.

  21. #21
    JohnBuckner's Avatar
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    Excellent now its back into a reasonable range. I may I would like to talk about main gears. I understand why you have the mains so far forward in an attempt to protect the prop and possibly prevent flop overs, Heck in the days of the old timers before there was much RC a lot of airplanes did this too and for the same reasons.

    But do understand and this applies to RC also that when the mains of a conventional gear (tail dragger) is so far forward from the CG that this will promote landings that are what I would characterize as 'boingers' or crow hopping. The very best place for the ease of landings is for the wheels footprint to be exactly under the CG as many early American full scale gliders. But of course this makes it hard on propellors so somewhere just forward of the leading edge will actually improve your landings with minimal flop overs.

    Moving those wheels back and say getting rid of that plastic spinner which always looked cheezy to me anyway should just about eliminate the need for that pesky lead peeking out from under that tail.

    John
    Last edited by JohnBuckner; 03-01-2014 at 07:42 PM.
    \"Keep your controllines tight\"

  22. #22

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    Smile

    Hi John, the ideal location for a wheel is not directly under the CG!

    The ideal location for a wheel or wheels or even a towhook is 15 degrees

    in front of the CG.This has been a known trim for quite a few decades.

    I first heard about the 15 degree location in 1958 when I built my first

    A1 Nordic glider . I then noticed that most of the top stunt flyers located

    their landing gear very close to that same 15 degrees.

    Tony

  23. #23
    JohnBuckner's Avatar
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    I was talking of the wheels foot print in relation to the the CG and was not talking about towhooks at all. Now in terms ease of landing and the least tendency to porpose or bounce a CG wheel is indeed the best location and I learned this in the late fifiies and sixties flying a number of wonderful and rather vintage for the time old ships even then such the Baby Bowlus, Pratt-Read and even a Leister Kaufman, full scale ships and all had the single main gear very close to the CG.

    The further you move that main gear forward (taildragger) the more directionally unstable the airplane will become and the more pronounced will become the tendency to bounce on anything less a perfect touchdown. Now Obviously you must have the main gear further forward than a glider to keep the propeller off the ground.

    Also my whole point is the OP's gear is excessively forward and simply moving it back a little would eliminate that lead!

    John
    Last edited by JohnBuckner; 03-01-2014 at 10:51 PM.
    \"Keep your controllines tight\"

  24. #24

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    Thanks for your comments guys. i like the way the plane looks with the wheels set forward,also with ground i have to fly over and land on it helps to keep it from flipping over on takeoffs and landings.I agree the big red spinner has got to go, it's being changed to a smaller yellow one.Again thanks for all your comments, i don't post often, but when i do i get get some good advice from the site.
    jim


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