Calculation question: for a wide cockpit is it correct to consider the wingspan only the sum of the wings lenght?

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Arnaldojrbr

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And here a NACA 2412 section (1.75 m chord), terribly drawed, just to give an idea about the position of the wings.

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dog

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Dec 29, 2019
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radfordc


Exactly THIS i'm talking about! If a guy can make a junkyard fly, with all his drag and mess... Why I can't? It's ugly, terrible drag, have a plastic chair as a seat... but it flies! Amazing isn't it?
the sunshine clipper aprears to be moddled on
a clasic flying boat ,the sikorsky s 38, and could be called an SSS,single seat sikorsky.
the design of these types of craft,explicitly states
that how you arrive is vastly more important than
when
Arnaldojrbr :like the renders of your project
 

wsimpso1

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Hmm. I do not get it. You have a 70 kg boat hull, which already weighs more than the fuselage on my 200 hp 2150 pound gross 200 mph airplane, and then you need to add an internal structure. Usually a boat hull is already a pretty substantial structure unto itself... Then you are adding an upper set of structure, which will add a bunch more stiffness unless it all is just hinged and latched to the hull. I would revisit the boat hull and see how much structure it really needs added to the hull.

Next, that is a mighty skinny looking tube being used as an aft fuselage. Lots of pod and boom LSA's with empty weights and power around yours with either bigger tubes aft than that or with fabricated booms of large cross section at the fuselage and tapered towards the back. The empennage pulls down and applies lateral loads and is going to be partially washed by the prop too. Enough stiffness as well as enough strength is going to be needed in those parts.

Then the choice of airfoils... 2412 is thin, which forces structural weight up over a 15% to 18% thick wing. the 2412 hits min drag at 2 to 4 degrees angle of attack. How did you select this airfoil? Usually wing area sets takeoff and landing speeds - so you figure out what speed you want to get off the water, which is some modest amount above stall speed and thus CsubL for takeoff is some modest amount below stall CsubL0. Adjust wing are until you like things, then you go to your estimated cruise speed, pick off CsubL. That is where you want either lowest Cd of the foil or highest Csubl/Csubd from your foil. Then go pick a foil that does all of that.

Billski
 

Arnaldojrbr

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wsimpso1


then you need to add an internal structure. Usually a boat hull is already a pretty substantial structure unto itself... Then you are adding an upper set of structure, which will add a bunch more stiffness unless it all is just hinged and latched to the hull. I would revisit the boat hull and see how much structure it really needs added to the hull.
I think that i need a "skeleton" cause the engine, the wings, the tail and the seats needs to be anchored in the fuselage and i coudn't think in any other way to do that. The engine weights a lot and need to "rest" in the floating surface, the wings needs to be attached to the body and so on... I have the impression that I'm over estimating this structure but I have no idea at all. Any feedback from you will be very appreciated!

Next, that is a mighty skinny looking tube being used as an aft fuselage. Lots of pod and boom LSA's with empty weights and power around yours with either bigger tubes aft than that or with fabricated booms of large cross section at the fuselage and tapered towards the back. The empennage pulls down and applies lateral loads and is going to be partially washed by the prop too. Enough stiffness as well as enough strength is going to be needed in those parts.

I fixed it! Below is my new sketch from the metallic structure, please take a look at it and tell me any impressions that u had. As I said before, any feedback is appreciated!

Then the choice of airfoils... 2412 is thin, which forces structural weight up over a 15% to 18% thick wing. the 2412 hits min drag at 2 to 4 degrees angle of attack. How did you select this airfoil? Usually wing area sets takeoff and landing speeds - so you figure out what speed you want to get off the water, which is some modest amount above stall speed and thus CsubL for takeoff is some modest amount below stall CsubL0. Adjust wing are until you like things, then you go to your estimated cruise speed, pick off CsubL. That is where you want either lowest Cd of the foil or highest Csubl/Csubd from your foil. Then go pick a foil that does all of that.

Being sincere with you, I choose the 2412 because it's very similar with the Clark Y and this is the easyest airfoil to build! I downloaded the xfoil and a couple of other software but I'm still learning aerodynamics, so mess with things like that is the same to give a Iphone for a caveman. I tought the same about the thickness of the airfoil (too thin). If you have any suggestion...

One more time thanks Billski for the precise comments and the guidance!

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mcrae0104

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Oct 27, 2009
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4,240
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CO
I fixed it! Below is my new sketch from the metallic structure,
Three things to consider with this tail design:
  1. You might want to consider a triangulated truss design. (Yes, there are trusses with verticals only, called Vierendeel, but that’s a different story.) The tail structure you have is essentially a tripod with some stiffeners (the vertical members) that help prevent buckling. Will it work that way? You will need to determine the flight loads and analyze it (or build and test one) to know.
  2. The top tube of the tripod terminates in a T-intersection. That transverse tube it terminates into will be in bending in reaction to the tripod. Either this tube will need to be beefy enough to react that force, or you may consider altering the geometry to receive the tail reaction differently with some kind of truss structure (triangulation). Depending on the magnitude of the loads and other design constraints, a beefier tube may or may not be preferred (based on weight or perhaps other considerations).
  3. You will need some way to keep the tail post vertical when a horizontal load is applied to it. Look at other tube fuselage designs for some ideas about ways other designers have addressed this. (Related: consider the twisting the tripod will experience when a horizontal force is applied midway up the tail post; a triangulated tail section would help address that also.)
it‘s great that you’re getting into SketchUp to model your ideas, but really, these structural pointers are downstream from some of the bigger picture concerns of designing an aircraft (e.g. desired payload & performance). Do get a copy of the Raymer book, and consider the weight issue of utilizing an existing boat hull and adding a second structure. You will need a decent grasp of statics to design the structure; if books are your thing, there are lots of them, but I suggest Jeff Hanson’s YouTube statics course as a good starting place.
 
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