Thread: Silly girl wants to enlarge GUILLOWS plans!!!!

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  1. Silly girl wants to enlarge GUILLOWS plans!!!! 
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    Sort of a newbie but have experience with aircraft mechanics and airframe work. I have two plans from GUILLOWS a Spitfire and a Mustang both with about a 17 inch Wingspan. I am flying a hobbyco nextstar 40 right now for training and have plans for a ZIROLI P-47 THAT i want to build up in the future.

    Do to some obscene quest on my part I would like to enlarge the guillows plans to a much larger size and build those to see if I could get them to fly better and at giant scale. I know this seems like a Fools errand but I would like to do it anyway just as a project.

    First I would like to know what enlargement size would be possible since I would like to get the plans up to giant scale size and what thickness of wood would I have to use in the bulkheads to get it stiff enough for the new scale?

    Any help would be appreciated and snickers and gaffaws will be respected since I know this isnt something a sane girl does.

    thanks Alexandrea

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    Farmville, VA
    Hello Alexandrea,
    Many of us designers are undertaking those "fools errands". Your concept sounds like it could be fun. For the most part, I would start by swapping the balsa frames in the fuselage with Liteply in 1/8" thickness. Balsa should be fine for the wing ribs. In general, Basswood strips (or Spruce) would be a reasonable substitute for the balsa stringers.
    Assuming you are planning on a Gas engine, there will be a weight and balance issue as a result of the rather large weight of these engines relative to the power. Locating as much of the control system in the rear fuselage as possible will be a big help. I prefer to put the fuel tank on the CG to help avoid a noseheavy condition.
    The structure will need reinforcement around the stress areas, such as sheet balsa fill behind the engine, and beefing up the landing gear mounting system. A little to much here will be much better than too little. The same is true of the wing center. The loads of a heavy model will require thicker material, and likely some doubling of the spars.
    As far as enlarging the plans, I use a copy shop such as Kinko's, where they have copy machines with 36" wide paper. You will probably have to run the plan through in sections, and enlarge them in several steps to arrive at a final size. By way of example, I find that a wing with about 1200 square inches of area is just about right for my Zenoah G-26. If you multiply the 17" span by the average chord, this gives you the area of the small model. Divide this area into the area of your desired size, and take the square root of the result. This will be the enlargement factor to go from the small model to a "biggie".
    Good luck, Dave
    Dave Robelen

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    Thanks Dave I was thinking I would have to use stiffer balsa in certain areas but didnt realize that the CG and other areas would have to be done.

    this silly girl thanks you alot,


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    Marysville WA
    Why do you call yourself a silly girl? I LIKE THE IDEA!!!!!!! Actually, I've taken plans I received in magazines and blew them up. As Dave suggested, use light ply instead of balsa for framing and so on, you should be fine. Just remember to make sure the plane is balanced at the point shown on the plans when you get it finished and it should be a flyable plane. What I would recommend you do is PICK DAVE'S BRAIN ANY CHANCE YOU GET ON ANY QUESTION YOU HAVE. I don't think he will mind too much, since he was also encouraging you on this "little" project. The only thing I see as a problem is the engine cowling and cockpit canopy. You might want to see if you can get the plans CLOSE to a size of a comercially produced kit. That way, you can buy ready made ones. It's either that, or you will have to make something yourself, and that's no picnic. Good Luck

  5. The idea is gorgeous! 
    Hi Alexandrea...

    Do you know this link ?

    there you can find many plans, a little larger than the 17 inches Guillows... (and sometimes less scale...) dating from the same era in fact...

    Well MANY people have scaled these plans up...

    Just one suggestion: you might consider using a "better" airfoil when scaling up. The "simplex" airfoils used in Guillows 17 inches small models are almost the only good ones for this size. Aerodynamic performance depends on something called "Reynolds number"...17" Guillows fly at low Reynolds and at a low Reynolds, simplex airfoils are the best... but for a 30" wingspan model, the "Reynolds" gets bigger and then the "simplex" airfoil isn't the best anymore... But for larger models, there are better airfoils...

    Tell me if you want to know a little more about it...

    See ya.


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    Huntington Beach, Ca. USA
    look at top flight kit for the 40 or 60 size engine to get a better idea of what sort of wood, control surface and engine placement. I believe you can view their plans online if you can't find one locally.

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    hawkestone ontario canada
    go for it it works just fine as long as everything changes the same amount

    As you increase size you change the spars from balsa to stronger material and don't increase the dimension of the spars as much as the scale.

    For example double the span, change to spruce main spars and increase the width but not the depth. The strips forward of the main spar stay 1/16 balsa since they were that thick more for handling than flight load.

    Triple the original span and you again increase spar width but not depth and you start adding shear webbing + sheeting the part of the wing forward of the spar with 1/16 balsa creating a "D tube" structure that is very strong and resistant to warping.

    Changes to the fuselage structure get even more complicated... as you get larger you change to sheeting the whole fuselage and the sheeting becomes the main structure. 1/16 balsa skinned fuselages are good without much other support for up to 4 times the original size of the Guillows plans if going electric powered. Glow or gasoline engines impose more loads requiring additional stiffening.

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