Sussing out fuselage 'Cone' plans

mastermalpass

Elite member
In designing the fuselage of a rather round plane, I've come to real sticky spot in the process - flattening the fuselage pieces into shapes that I can cut out of a flat piece of foam, to then bend into a connical shape. I've tried a few different things, but so far what I'm drawing up just doesn't feel right to me.

Before I delve into what I've tried, I want to mention an important requirement; I do not want to rely on software where I build a 3D model and then 'unwrap' it into a 2D shape. I want a physical approach that will allow me to draw out plans using a pen, a ruler and maybe some string.

I did find a method used by sheet metal cutters for designing cones but, I find the instructions hard to follow. So many google results for 'How to flatten a cone' lead to how to do such a thing in Solidworks, that I'm having a hard time finding any other 'analogue' approaches to this problem.

So, to start, I have a blueprint, I have some steps that I've measured out into segments, I have the cross-sections between these segments and from those I have the circumference of the trailing and leading edges of each segment..

1650550514037.png
1650550607932.png


So, I have all my lengths figured out. The issue now is drawing the shape. If I draw the leading and training edges straight and parallel, then I end up with a piece that can only be bent into a straight cylinder that slopes at the join, rather than a cone. Using the technique linked above, I drew triangles that would help me gauge the 'slope' of the cone I wanted to form:

1650551101445.png


Here's another problem - the plane I am desinging is taller than it is wide. So I've ended up with two reference triangles for each segment. I decided on picking the shortest one as it has the steeper slope and it's probably easier to squash a steeper slope to shallower angle than going the other way around. Back to the method linked above, I drew circles centered on the 'apex' of the 'cone', one reaching the trailing edge and then another reaching the trailing edge minus thickness of the segment. As I know of no tool for 'Adobe Illustrator, please cut me a slice of this circle which will have the same arc but be exactly 255mm long', I just drew another line over it then stetched and bent it until it was within 1mm of the desired length.

1650551245975.png
1650551713506.png


I tried this again with the second segment and now I have a couple of shapes... Am I confident in them? Nope! 😂I mean, the desired thickness of segment B, if fitted in the middle of the two lines, apparently places these lines too far apart for that same distance to link them at the ends and so I'm going to get a crooked cone. This could just be the result of tolerance stack and when it comes to working in real life, I will be sanding out such imperfections anyway, but at this stage, am a little unsure if I am going down the right path.

1650552336306.png

So, in case I am about to waste a lot of time, I was wondering if anyone had any methods for preciecly measuring out a fuselage piece, or if the only way forward from here is trial and error.
 

Hondo76251

Legendary member
Im kind of a pencil and paper, trial and error builder myself. I prefer to spend more time cutting and gluing vs planning. It looks to me like youre on the right path far as i can tell, just tweak the fit and fishish as you go!
 
Yeah I'm thinking if you're planning to just have skin pieces that you bend and glue together, it sounds too messy a process for me. I don't know how I would ever do it in 2D on paper. I imagine a big room full of NASA engineers in the 60s drawing that sort of thing. In white shirts, black ties, short hair and thick-rimmed glasses. I think if you used formers to wrap around, you might have more success. At that point you can trim each skin piece until it does what you want when you wrap it. Wrapping first with a piece of cardstock can be helpful, but that gives you an approximation of the inside of the foamboard skin, not the outside. :unsure: It all sounds really hard to me. I like angles. :D
 

cyclone3350

Master member
Im kind of a pencil and paper, trial and error builder myself. I prefer to spend more time cutting and gluing vs planning. It looks to me like youre on the right path far as i can tell, just tweak the fit and fishish as you go!

Dito's here. I use drafting vellum paper for making precise patterns. It is durable, and very transparent. I rough cut out a pattern & tape it over my formers. I then trace out the exact outline to be cut. This may take several steps if there are compounds in the bend s & curves, but works for me. Art suppliers & Hobby Lobby R some sources for this. Post # 33 here: https://forum.flitetest.com/index.p...cub-and-time-to-change-my-avatar.68115/page-2 will give some ideas on this method.
 

SSgt Duramax

Junior Member
In order to get the curvature you want, you may have to do several smaller pieces as opposed to one larger one.

I usually just wrap printer paper approximately around where I want it to lay, then roughly trace out the shape I want a little larger than I need it, then cut it down accordingly.

You could also find a papercraft model somewhat similar to yours and see what they do there.
 

mastermalpass

Elite member
Yeah I'm thinking if you're planning to just have skin pieces that you bend and glue together, it sounds too messy a process for me. I don't know how I would ever do it in 2D on paper. I imagine a big room full of NASA engineers in the 60s drawing that sort of thing. In white shirts, black ties, short hair and thick-rimmed glasses. I think if you used formers to wrap around, you might have more success. At that point you can trim each skin piece until it does what you want when you wrap it. Wrapping first with a piece of cardstock can be helpful, but that gives you an approximation of the inside of the foamboard skin, not the outside. :unsure: It all sounds really hard to me. I like angles. :D

See now, I imagine a plumber in a t-shirt working on his garage floor like Colin Furze.

1650634228467.png


Looks like I may have to trial and error it then. Just did a test print of my two shapes... They are way off. 😂
 

Tench745

Master member
I don't know about accounting for the different height and width of the fuselage, but if you're just joining a pair of circles you can use a cone-calculator.
http://www.gardenendeavors.com/rack/conepage.html This is the one I have used in the past. The page walks you all the math, but if you scroll down there is a calculator you can just plug in numbers for the diameters of the two ends and the height you want. Then it will spit out the radii you need to draw for the flat pattern and the angle for how much of the circle to cut out.
 
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SSgt Duramax

Junior Member
I'd like to see @Niez13 way in on this too.
Yeah, or someone who regularly does it. I would like to learn more. I've picked up a few tricks here and there, but some folks can hammer them out like no ones business. I understand to a point some of them wanting to keep it underwraps to a certain extent, like John overstreet, but certainly someone will post it up for us peasants. Until then, I am guess and check, but my problem is, if there is a curve or something I really want I will either carve it out of XPS or print it.
 

SSgt Duramax

Junior Member
I honestly wasn't sure if this was going to work, but the F-106 semi plans I am following, there is an interesting curvature that lines up and it forms a concave compound curve in the fuselage section. I think you could do the same and achieve convex.

One caveat- I defoamed my paper "rasterize" style then super 77'd the new paper patterns over it. This is far more resilient than DTFB paper, and I do see the paper wrinkle a little bit when I do it, but when I mold the fuselage out the wrinkles disappear. This leads me to believe that the paper on the DTFB is a limiting factor and that the paper would infact wrinkle if it were just plane DTFB. This has yet to be seen and I haven't experimented with it yet.

Part of me when I come up with a new idea says someone has already tried it, and it probably isn't worth pursing (everytime I say I have an idea, someone quickly points me to where someone has already thought of it) but I will be trying it. I do know you really don't get wrinkles using the "rasterize" method, and that is super awesome.

Just gotta learn how to make my own skins.

Edit, I havent glued it on yet, but this is how it looks.

20220422_154811.jpg


Sure, I knew I was just reinforcing what you said about the Overstreet.

If you plan on being famous as a Real Player you better copyright your plans. Make people ask permission. ;)
I know people.
 
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Ratcheeroo

Legendary member
So I would guess that they are unwrapping 3d models,if I had the ability to do that with software then I would go that way. Point of the thread is that is there another method other than that and besides trial and error? There is no easy way out , I have used all the suggested things posted, :LOL::LOL:. Some to good success, some not. Called scratchbuilding:ROFLMAO:
 

Tench745

Master member
Another way to do it is to make a spine of some sort (box, x, sticks, whatever) and put formers over it. Pad out the formers with some foam and then wrap paper around the formers, marking where the center of each former touched the paper. That paper can now be taken off, trimmed to the lines, double checked on the plane, and then used as a pattern. I like to mark a centerline on the paper, trace both sides, then fold the paper in half along the centerline and compare the two sides I traced to make sure it's symmetrical. Repeat for each set of formers.
 

Tench745

Master member
Another option is the "rollation" method. This also uses formers and is similar to the above method, but instead of wrapping the paper around the formers you roll the formers along a flat surface.
See attached videos by Ron Covell for a better explanation of rollation.
 

Niez13

Elite member
In designing the fuselage of a rather round plane, I've come to real sticky spot in the process - flattening the fuselage pieces into shapes that I can cut out of a flat piece of foam, to then bend into a connical shape. I've tried a few different things, but so far what I'm drawing up just doesn't feel right to me.

Before I delve into what I've tried, I want to mention an important requirement; I do not want to rely on software where I build a 3D model and then 'unwrap' it into a 2D shape. I want a physical approach that will allow me to draw out plans using a pen, a ruler and maybe some string.

I did find a method used by sheet metal cutters for designing cones but, I find the instructions hard to follow. So many google results for 'How to flatten a cone' lead to how to do such a thing in Solidworks, that I'm having a hard time finding any other 'analogue' approaches to this problem.

So, to start, I have a blueprint, I have some steps that I've measured out into segments, I have the cross-sections between these segments and from those I have the circumference of the trailing and leading edges of each segment..

View attachment 224442 View attachment 224444

So, I have all my lengths figured out. The issue now is drawing the shape. If I draw the leading and training edges straight and parallel, then I end up with a piece that can only be bent into a straight cylinder that slopes at the join, rather than a cone. Using the technique linked above, I drew triangles that would help me gauge the 'slope' of the cone I wanted to form:

View attachment 224445

Here's another problem - the plane I am desinging is taller than it is wide. So I've ended up with two reference triangles for each segment. I decided on picking the shortest one as it has the steeper slope and it's probably easier to squash a steeper slope to shallower angle than going the other way around. Back to the method linked above, I drew circles centered on the 'apex' of the 'cone', one reaching the trailing edge and then another reaching the trailing edge minus thickness of the segment. As I know of no tool for 'Adobe Illustrator, please cut me a slice of this circle which will have the same arc but be exactly 255mm long', I just drew another line over it then stetched and bent it until it was within 1mm of the desired length.

View attachment 224447 View attachment 224448

I tried this again with the second segment and now I have a couple of shapes... Am I confident in them? Nope! 😂I mean, the desired thickness of segment B, if fitted in the middle of the two lines, apparently places these lines too far apart for that same distance to link them at the ends and so I'm going to get a crooked cone. This could just be the result of tolerance stack and when it comes to working in real life, I will be sanding out such imperfections anyway, but at this stage, am a little unsure if I am going down the right path.

View attachment 224449
So, in case I am about to waste a lot of time, I was wondering if anyone had any methods for preciecly measuring out a fuselage piece, or if the only way forward from here is trial and error.
So what you have going there is actually not very far off. The side view, cone, angle view is a what I always do for perfect circle to circle formers along the same center only. That is where it gets different. So unfortunately, I have no idea how to find the shape of the skins from non-circle to non-circle using CAD 2D software. However, there are a few tips and tricks to create skins for either circle to circle or non-circle to non circle.

Circle to Circle

The first thing you want to make sure is that both formers/circle are along the same centerline. From there you can create the side/cone/angle view. Now you know exactly how big the hypotenuse for the cone is, but more importantly the radius for a circle you can draw and cut out to wrap around the former. Also you can measure the distance of the skin/cone(It will be a smaller radius and will line up with the former in front of the other former). Then, using paper you can cut out the whole circle and wrap it around the formers. Make sure the skin/circle piece is in the right spot and mark the top and bottom where the two pieces will meet. Also, make sure to mark a center point on the top and bottom of all my formers so I know where to mark. This will create a seem on the bottom. When you actually mark where the two ends meet, to create the seamline, bring the skin/paper back to where you cut it on the paper, draw a line to center of the circle and it should be a 90 degree angle. Then just cut it out of foamboard, mold it, glue it, and you're finished.

Non-Circle to Non-Circle/Perfect Circle

When you have two formers that are not perfect circles there is not too much to do besides cutting and trimming. Using the side view you find out how long the piece should start out as. Then, wrap the paper around the former and trim using the tips below. I sometime use one piece of paper to find the shape. Sometimes I use ten or more, just depends on the piece.

Former Tricks to Create Skins

So anytime I mention a former, it always is glued to a box spar, or T style spar to make sure the former is straight and in the right spot. This makes it a million times easier to draw and trim skins. One thing I also do is at sections like the tail of the aircraft for the T spar, I use it for creating skins, then cut it out once I know the skin is good. That way the rear of the aircraft is light, but still easy to make. This is the easiest way to create good looking skins that will be relatively easy to make.

For all the formers I put on a plane before skins they always account for foamboard(5mm usually depending on the brand). However, the trick is to cut a strip of 5mm thin piece of foamboard that you can wrap around the former to make it act like a skin piece is already there. Then the paper is basically exactly what the skin will be.

When creating skins with wrapping paper around two formers and trimming, use a flashlight. By shining a flashlight on the other side of the paper, you will see exactly how far off the paper is from the edge of the former.

Last tip is to be creative. If you can think of another way to do it, try it.

Hope this helps, let me know if you have any questions.

(Also, I am building 48 inch Albatross DVA as well so we can fly them in formation at FF).
 
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