Lets make some tail bits.

 Acroduster  Comments Off on Lets make some tail bits.
Oct 262019
 

The plans call for square tube at a few locations. I don’t think it will be a problem to use round tubing. As usual, use what you got! I also don’t think I have enough space for the 2 central bearings, another fudge expected there.

remember: full size!
..bend some tubes..

My template has a more rounded outline at the outer elevator. Might have to redo it, since the big one has a smaller radius.

test fit, looking good.
..and preparing for the next fun parts

More FreeCAD exercises.

 Acroduster  Comments Off on More FreeCAD exercises.
Oct 122019
 

I’m trying to get the steps needed to get this fuselage shape drawn documented. This will be the part that the undercarriage has to connect to.

Insert the image
Scale it to the correct dimensions
Shift it to the 0,0 origin (just for easiness)
Draw a B-Spline curve
Do another and shift it backwards 190mm
Select curved shapes, identify the 2 lines, and voila!

The back curve should have a sharper corner, I’ll work on that. Next step is adding the leg and try the fillet parts…

And we have a leg. Next the hardest part yet, a smooth transition between leg and fuselage.

Openscad again.

 3D print, Acroduster  Comments Off on Openscad again.
Sep 232019
 

3 reasons, Ed asked my if I could do something for his latest project, and I really fancy those 1970’s looking flared undercarriage pants as well. So, bite the bullet, and do some thinkings. I found what appears to be a good starting point on github, so let’s see if we can do this. The greatest hurdle for me is the design phase, once I have the .stl file it’s simple.

The 3rd reason is that I am knackered from working in the garden today, SWMBO decided that the path that runs around the garden needs moving.

The program as is does allow multiple profiles sections, but it does divide then equally along the span. Not what I need. So we have two options, fix the code, or make the pants into multiple sections. The first method will require brain-cell activity, we go with that!

28 sept: It’s a bit of a slow week with other jobs taking priority, but things are progressing. Taking the road less traveled is definitely keeping the braincell entertained. I learned a lot the past few days. I managed to get the turtledeck drawn, and I thought it was then only a matter of printing. Oh the folly of innocence..

it really looks great, measurements are correct, just print it..
of course it does not fit in my printer, but I knew that.

..so what is the challenge? When I import the .stl the ‘skin’ is either to thin, so that the printer does not see it. (less then the 0.4 mm orifice of the printhead.), or if I make the part thicker is starts to complain in a language I do not want to repeat..

/*
Construction of the turtledeck for the SA750.
Date: 28 sept, 2019
Inspiration: https://openhome.cc/eGossip/OpenSCAD/lib-bezier_surface.html
OpenSCAD 2019.08.04
All rights as usual, do as you please, it's open source. 
*/

include <bezier_curve.scad>;
include <bezier_surface.scad>; 
include <function_grapher.scad>;

t_step = 0.01; // smoothness, might be too much for real life printing.
thickness = 0.1;
width = 0.1;
inch=25.4; // is an inch
scale=0.33; // my scale

// refer to fuse stations on full size. 
sta75= 0; 
sta100=25*inch*scale; 
sta120=45*inch*scale;
sta125=50*inch*scale;
sta129=54*inch*scale;
/*
Draw the approx formers on a piece of grid paper, and take the coordinates from there. 
*/

formers = [
//former at sta75
    [[-109,0,sta75],[-100,36,sta75],[-80,82,sta75],[-60,105,sta75],[-40,124,sta75],[-20,136,sta75],
    [0,140,sta75],
    [20,136,sta75],[40,124,sta75],[60,105,sta75],[80,82,sta75],[100,36,sta75],[109,0,sta75]],
 
//former at sta100
    [[-75,0, sta100],[-60,55,sta100],[-40,92,sta100],[-20,105,sta100],[-10,120,sta100],
    [0,150,sta100],
    [10,120, sta100],[20,105,sta100],[40,92,sta100],[60,55,sta100],[75,0,sta100]],

//former at sta120
    [[-55,0,sta120],[-30,30,sta120],[-20,43,sta120],[-10,46,sta120],
    [0,50,sta120],
    [10,46,sta120],[20,43,sta120],[30,30,sta120],[55,0,sta120]],

//former at sta125
    [[-44,0,sta125],[-30,30,sta125],[-20,43,sta125],[-10,46,sta125],
    [0,50,sta125],
    [10,46,sta125],[20,43,sta125],[30,30,sta125],[44,0,sta125]],
 
// and a fake one to get the rudder blended in.
  
    [[-44,0,sta125],[-30,20,sta125+6],[-20,30,sta125+12],[-10,40,sta129-14],[-5,65,sta129-6],
    [0,250,sta129+inch],
    [5,65,sta129-6],[10,40,sta129-14],[20,30,sta125+12],[30,20,sta125+6],[44,0,sta125]],
];

//here the magic happens.
            
    function_grapher(bezier_surface(t_step,formers),thickness); 
    
// that's all there is to it. (if only!) If only I had the knowledge I will have in 5 years today, this would be easy.

After a lot of pulling the hairs, I got the code down to the above, it works beautiful and it ‘should’ be simple to build other variants, if, but only if I can get the code to play happy with the printer. I normally slice with Simplify3D. Since I have Octopi (cura slicer) running on the printer, I want to try if that will eat it.

The other slight issue is of course that I will have to chop up the part in 2 or 3 sections, but that should not be a problem. In the end it will be covered with a layer(s) of light glass to keep it from falling apart. The whole idea is of coarse, that modelling in software is ”easier” then producing lots of dust.

That’s the theory..

29 sept: after a good nights sleep I woke up to realize I have a lot of the good stuff from Stefano. Why oh why did I not think about that? The other option is to try with Freecad, import the .stl, make it a solid and take it from there. Options, options. Then there is Solvespace, and of course all the paid for stuff that I can’t afford.

30 sept: ok, this is the reason why this does not slice well: the code likes the shape to bend in certain direction. At the tail end I try to be smart and diverge, creating a bend in the other direction. And that is what is causing the problems for the slicers.

That’s the woodwork done

 Acroduster  Comments Off on That’s the woodwork done
Sep 232019
 

The weekend has come and gone, I have a few more days leave, so lets continue to add more stringers. Bottom is done, one more side to do. I tried 2 different methods of supporting the stringers. At the bottom the more scale version, but it is a bit flimsy. The method used for the sides works better. But, since no one will see it afterwards, and since it is still strong enough, I will leave it as is. This is the end of this chapter, next I might do the stabilizer/elevator section. Did I say already that the designer specifies aluminum-tubing for this? I had the wood, and I thought this makes it look a lot more like a proper plane! It’s an experimental class plane, you are allowed to deviate from the plans!

bottom and left side

For the brazing I have settled on a 0.7mm canule, it gives me the best results (for now). Start with a bit of propane, bottle valve opened less then 5 mm on the clock face, orange valve opened to get the 1.5″ flame. Then add a bit of O2 to get it nice and hot. The flame should just be nice and blue. For the bigger jobs, you need to increase the propane a bit, but I’ve never needed more than a 5 cm flame. Most joints take around a second or 2 max to complete. As always when playing with gas and flames, you are responsible for not burning down your house!

start with a 1.5″ propane flame..
..and add some O2 to make it nice and hot.

Nice weather

 Acroduster  Comments Off on Nice weather
Sep 192019
 

There is no reason for the pics, it’s just nice weather and it looks great ๐Ÿ˜‰ Weight as you see it here is 1850 grams.

Of course I took it to our end of season do, just to show off.

if you look careful, you’ll spot the rudder. The Bucker belongs to Ed, who took this picture of these two armchair pilots..

bare side
side with stringers and fake covering.
under carriage with the printed streamline fairings.

 Posted by at 12:40 pm  Tagged with:

Stringers and other bits

 Acroduster  Comments Off on Stringers and other bits
Sep 162019
 

This is where loads of fun can be had. To the naked eye, adding a few stringers should be a 10 min job. Yes, sure, but if I can stretch it for a few days? First I added the round formers from firewall aft. They all have the same radius as the firewall, so that makes life a bit easier.

Anyway, a good day was had, and I think I have the process worked out now. As always, let the pictures tell the story.

The bending contraption, borrowed from Thomas ๐Ÿ˜‰
Difficult to see, I try to show the false formers here.
try gluing a tiny bit of metal to a 4 mm tube, when you only have 2 hands. (Note to self: don’t forget to fix the inner corner on the opposite site. )
the end result, stringer #1 done.
cockpit side
tail side, the stringers are fixed with a pop-rivet. They were also alu from what I can find. I like this better!
Even Paolo’s brazing look a mess until cleaned up, so I don’t feel too bad.
one side done..
nice job, even if I have to say so myself

when in doubt..

 Acroduster  Comments Off on when in doubt..
Sep 052019
 

…check biplaneforum.com There are a surprising amount of active builds going on, and luckily the Acroduster is alive and well. Just an example: here’s a pic of an ”original” compared to mine. Isn’t that fun!

I will have to ask the original posters if I can use their pics here, so right now I’ll leave it at this one pic.

This is a repair job, but there are so many interesting details here.
note the tabs for mounting the skins.
Mine follows the drawings, other then that, not bad!!

Looking at the full size one and the original drawings there are a number of small differences, but as each person decided how to tackle a problem differently, each solution is as good as another.

For me the pic answers these questions:

When the landing gear moves past a certain point, the bungees have to go through the bottom of the fuse. Guess what, you see little doors, which are not in the original drawings. Great idea! You might notice that the skin covering the landing gear is a narrow strip, so when you bump her down too hard, all you need to replace is the 5″ section that covers said LG.

The drawings are not very clear about how to attach the skins to the frame, all you can see is a number of crosses where bolts go. Here you see the answer: a strip is welded to the frame. This is where all the bolts go!

There is a bow for the bottom skin, but not clear how to attach it, other then to the side longerons. Here you see them connected to the heavy cross section. Simple and logical.

This is what you see everywhere, the plans were/are just a general description of the big important stuff. Everything else is left up to you, for your entertainment and pleasure ๐Ÿ˜‰

 Posted by at 6:16 pm

Every engine needs a firewall.

 Acroduster  Comments Off on Every engine needs a firewall.
Sep 032019
 

Slow day today, ran out of silver again. Never mind, Ralph from sonderlote.de is sending another load!

Anyway, stumbled across a bit of aluminum that just looked like it wanted to be a firewall. I made it the high tech way, from dxf to cnc. Of course I keep saying to myself that in order to cut alu you need the right bits and proper cooling. Never mind, it worked sort of. No damage was done to man or machine.

Blue dot is carb intake. Not planned, just sort of happened to end up there.
..and it’s a good time to check prop clearance. Looks ok, it’s about 8+ cm when on wheels.

No workies today? I officially have now joined the ever growing army of AOP’s. Not full time mind you, for starters just 2 days a week, the other 3 are needed to fund the hobby! But it is nice to have a 4 day weekend ๐Ÿ˜‰

Tail wheel support.

 Acroduster  Comments Off on Tail wheel support.
Sep 022019
 

Wanted to keep this reasonably light, not perfect scale, but looks close enough when done. I can always change it! Mounting is with 2 M4 screws.

always looks horrible before cleaning.
A bit of a departure from ‘real’, but this part does get a beating.
2 M4 nuts welded in place. Top part is also U-shaped to fit between longerons, bottom U-shaped to fit carbon part.

The seat is built from 6 alu strips going front to back and 7 crosswise. Sort of like in this test. I need to think about this a bit, the center one going to the rear will have to be somewhat special.

Seat for the all important driver.