The Fi-1 vintage Swedish sailplane

[Don Boose]

This is a wonderful story (except for the part about the fragility of on-line resources) with fascinating images. A glimpse into aviation history and modern aircraft restoration.

Don

[Leif Ohlsson]

Thanks, Don - it is a fascinating story, isn't it! Back now to the reworking of Aaron's Fi-1 model:


Fuselage with full set of inner parts

I had some basic ideas about the fuselage which called for some modification of Aaron's original design:

• Aaron's design of the fuselage is excellent for this model, since it is made roughly the same way as the original ply laminations. As we have just seen, they, too, had to be applied in comparatively thin stripes. But I wanted glue strips, instead of the tabs of the original model. This is easy - you just copy, e.g. the front outline of a section, offset it the width of your intended gluestrip, and make the tabs manually.

• However I also wanted to make a complete interior - not that all of it will be visible, but as it turns out, it is just as easy to make a complete interior as a partial one, once you've decided to make gluestrips. Here's my basic idea: If you can make a gluestrip of, let's say 5+5 mm width, why can't you make a gluestrip which is equal to the entire width of the section you started with, minus the space at the end where the next section's tabs will end up?

• Third and final point is that I always thought gluestrips - and inner parts - should run the opposite way of the part they are closing, if you see what I mean. If the outer shell has a joint at the bottom (like Aaron's design of the Fi-1), the inner sections should join up at the top. In other words, the two layers are displaced half a round.

Here's the result for the Fi-1 outer and inner parts, painted and unpainted version, all in one composite image:



What you see is Aaron's fuse parts and paint pattern overlaid on a textured version (ply with a small metal nose-cone "bowl").

The tabbed pieces sticking out upwards constitute the inner shell. Individual parts serve as 1) gluestrips joining two sections; 2) inner patterned parts; and 3) closing strips for the outer parts - three functions in one. Which isn't too bad, when stated this way…

[A teaser here: What's really wrong with this picture? Find the answer - which is also a reminder to myself to do something important still remaining to be done - at the end of the next post.]

[murphyaa]

Aargh. I always hated cliffhanger endings.

[Wad Cutter]

Leif. there are times my minds eye is blind and this is one of those times. Maybe once I start building more of these type of fuselages it won't confuse me. The fault lies with me and not you or your build. I always look forward to your ideas and builds and then have to wait for the next part. I guess it's the way you write that I enjoy weather I understand or not. When the time comes that I have picked the glider I want to build as my R/C aircraft, will I be able to come to you and/orr Aaron about certain concepts of building that alludes me? Such as the inside controls for the spoilers and etc. I’m not sure where to find this information. Thank you very much for another great article. wc

[Leif Ohlsson]

Hello, Aaron - hope you holler whenever I'm heading in the wrong direction in your view!. Waddie, these images sometimes look like one of those puzzle pictures psychologists use to me as well. That's why I missed the obvious - once you've seen it - point revealed at the bottom of this post. My fear now is that someone really bright will take a second or third look and say that it's really alright as it is, and why couldn't I see that? We'll see - here's one bit of not totally uninteresting theory, followed by one bit of thinking out aloud.


The principle behind the fuselage design

The main principle of the inner-outer parts of the fuselage is that the inner parts are exactly 1.6 mm shorter in rolled up circumference, than the outer parts. This is a universal truth for 0.25 mm thick paper, and valid for every size of any part which is going to be rolled up into a full circle or ellipse.

It is an example of the old paradox "If you have a string that runs all around the world, and would like to lift it one foot above the ground, all around the world - how much longer would you need to make the string?

The answer is 2 x 1 feet x 3.14 = slightly more than 6 feet. Using this formula, any inner section of a fully closed fuselage part, using 0.25 mm thick paper, will be 2 x 0.25 mm x 3.14 = slightly less than 1.6 mm shorter circumference, same for every fuse part, however large or small they are.

I came upon this method while trying to find a method of making rolled up cylinders with a full inner "ledge" formed by the inner layer, upon which the end pieces (lids) could rest. See ."Making paper cylinders with a ledge & full inner layer"


How does one glue up a design like this?

I envisage the assembly of an individual fuselage section to take place in this order:

• Draw pencil centerlines on the back of both inner and outer parts. Preshape both outer and inner parts by rolling them with a steel rod against the back of a mousepad or whatever is your favourite soft base for this kind of work.

• Glue one end of an outer parts to the center line of its inner part; apply glue only at the very end of the outer part, and when glueing it make sure it really coincides with the the centerline on the back of the inner part and is well aligned all along the part - 5 mm difference all along the fore-aft edges. This will determine the accuracy of a whole section.

• Glue the other end of the outer part, still hanging loose, against the centerline on the back of the inner part, to join up with the other end of the outer part. Press down against a large diameter tube or similar to achieve an invisible joint.

• At this point, all of the inner part, except its very center, is still unattached to the outer part. Now apply judicious strings of glue at the edges (front and back) on one flap of the inner part, and press down while, again, carefully aligning the outer and inner parts. The end of the inner part should end up exactly on the center line on the inside of the outer part. Do the same with the other flap of the inner part, which now should end up snug against its own other end.

All of this will be easier to understand when I - eventually - can illustrate it with test-build photos.

[Answer to the teaser in the last post: The inner parts will have to be flipped horizontally before grouped on a print sheet - as they are drawn now, the glue would be applied to the beautiful ply texture, while the real inside would be white. Not good. Got to remember to really do this!



In tomorrow's installment: "How to draw up a set of inner fuselage parts for any similar model".]

[Leif Ohlsson]

To my horror , looking at the image just posted above, I now see that my fear of being exposed as a pompous ass & total dimwit really were well founded. It would actually have been alright to use the parts as originally drawn! Can you see it?

Apologies for creating confusion and totally unnecessary scratching of heads. On the bright side, those of you who couldn't see anything wrong with the previous image may now give yourselves a well-deserved pat on the back! More on the bright side, this demonstrates the value of posting - you understand what you're doing better when trying to explain it to others.

Leif

[Don Boose]

And if you give the paper a half twist before gluing the ends together, it will become a moebius strip and the aircraft will sail into another dimension.

But seriously, this is a most valuable tutorial (your delightful momentary loss of situational awareness to the contrary notwithstanding) that has applicability to a wide range of models. It is well worth careful reading.

Don

[Loui]

very informatives... your Work In Progress always fascinate me. Thank you. -Loui-

[Rubenandres77]

Leif, you've made a wonderful job with the textures of this glider. It is amazing what you can do. The final result is really beautifiul! I definitely want to see more of your nice work!

[Leif Ohlsson]

Friends, you're very kind! Here's the promised tutorial. And as you will probably notice, for obvious reasons I had to change the very last caption a little bit...:


How to draw up a set of inner fuselage parts for any similar model

The inner sections of the fuselage parts were made entirely from Aaron's original parts. As such, it is an illustration of a general method which can be used when redrawing any similar model. Here are the steps:



Outer parts (above): The first steps are easy - redraw the original part, minus its glue tabs. Finish the outer parts, textured & painted versions, as described in earlier posts.



Inner parts (above): Making the inner part involves cutting up the outlines of a copy of the outer part, offset front and aft curves the amount you want for glue tabs, and the top outline 0.8 mm (standard for all parts made up of 0.25 mm thick paper).

The final result is an inner part which is 5 mm further forward then the outer part it will close, 5 mm shorter at the back (to allow for the glue tabs of the adjoining inner part); and with top and bottom each 0.8 mm closer to the centerline. This is to make the full inner part 1.6 mm shorter in circumference than its outer part. This measure is common for all parts to be joined up as a full circle (of whatever roughly circular shape), be they 20 mm or 2000 mm in circumference.

I imagine the best procedure to build up the full fuselage is to close all rings of inner and outer parts separately, and then join up these rings by pressing the glue tabs of one part into the shell of the ring in front of it (for the front half; vice versa for the rear half).

My plan for this model is to make one fore, and one aft fuselage half this way - much like your breakfast egg cut open. Any inner structure (which remains to be designed) can then be shoved into e.g. the rear part, before joining the two eggshell halves, and finally add the tail and canopy.

The principle is to trust Aaron's design to be able hold the model together, just like he and Rich already has proved by building it, and to add just a bit of inner structure, like the pilot's seat, instrument panel, and some hints of the steel-tube framework. This is the opposite of many models with very rigid and loadcarrying inner frameworks, where a perfect fit is absolutely critical. I like such frameworks, but I do not know how to design one "after the fact", which is why I'll have to find another way.

We'll see about the interior. At least this is what the plan looks like at the moment.