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Author Topic: 3D Printed Rubber Powered Airplane  (Read 493 times)
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Billbo
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« on: February 23, 2020, 06:18:09 PM »

On-and-off for nearly the last two years, I have been experimenting with attempting to design, print, and fly a completely 3D-printed rubber-powered airplane.  My first attempts were with vase-mode PLA printed airframes.  A few of these actually flew, but more often than not they were usually damaged on landing.  This is because the thin vase-mode printed PLA shells that made up these planes were also very fragile.  I had slightly better luck printing smaller rubber-powered planes with HIPS plastic, but the real breakthrough came in the middle of last year, when a company called Colorfabb in the Netherlands came up with a lightweight PLA filament.  This filament actually expands into a foam plastic as it prints.  (The degree of expansion is determined by the temperature and speed at which the filament is being printed.)  The airplanes that I have printed with this filament are still mostly thin shells, but these shells have a degree of flexibility that gives my airplanes pretty decent resilience, but also makes them light enough to fly under rubber power alone.  A video compilation of some flights that I have made with the latest version of my airplane can be found here:  https://youtu.be/2k9LypU1OJI.  If you have a 3D printer and would like to try printing this airplane, I have published the design on Thingiverse, and it can be found at this link:  https://www.thingiverse.com/thing:4127098
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pedwards2932
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« Reply #1 on: February 25, 2020, 07:29:21 PM »

Very interesting.  I have made some parts for planes with my printer.  I would think the material you are using may work out to do cowlings etc.  I am going to get a roll of it to try.  How flexible is it?
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Billbo
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« Reply #2 on: February 26, 2020, 12:15:52 PM »

Here is a small video where someone prints what looks like a cowling and demonstrates the flexibility of this material:  https://youtu.be/8LUc1J48sUc.  Of course, you can make more rigid parts with LW-PLA if you add internal structure to your parts.
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fred
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« Reply #3 on: February 27, 2020, 02:01:42 AM »

Interesting experiments. There is Skilled designer builder of ..Scale..RC models.. who has experimented heavily with this stuff.
His views: It's  Pricey filament and it has erm.. reduced structural  properties.. as in a notable portion of weight saved needs go back in as
Carbon; tubes rods etc... to stop wing droop, let along  G loads. 
Material is both intriguing And disappointing. Likely there will be something better in the future.
IMO for max lightness.. One 'could' print a genuinely Scale design and subsequently use the print as a Plug
 for making a Female Vacuforming Mold for  1 MM depron.
ALFA models fashion.. Still the benchmark for Lightweight .. Scale ... RC.
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che
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« Reply #4 on: February 27, 2020, 07:23:03 AM »

There is a article in the latest Aeromodeller of a guy who's done the same thing. Might be worth comparing notes.

CHE
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Billbo
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« Reply #5 on: February 27, 2020, 11:30:00 PM »

There is a article in the latest Aeromodeller of a guy who's done the same thing. Might be worth comparing notes.

CHE

I presume that you mean someone else has also 3D printed a rubber powered airplane when you say 'someone has done the same thing'.  I would very much like to see this article, and I see that I can buy digital copies of this magazine on the Aeromodeller site.  Is this article in the February 20 issue?  Could you tell me the name of the article?  When I look at the table of contents for the February issue, it is not clear to me which article you might be referring to.  (The February table of contents in on this link:  https://pocketmags.com/us/aeromodeller-magazine/feb-20)
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Viperkite
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« Reply #6 on: February 28, 2020, 05:50:35 AM »

It's in the March issue of Aeromodeller. He is making scale jet models for edf.
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Billbo
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« Reply #7 on: February 28, 2020, 12:21:54 PM »

It's in the March issue of Aeromodeller. He is making scale jet models for edf.

Thank you for this clarification, Vikerkite.  From Che's post, I thought that the person in the Aeromodeller article had also designed and flown a 3D-printed rubber-powered flying model, and I was quite eager to see their work.  So far, I believe I am the only one who has done this, but I would still very much like to see someone else do it, or to learn about someone else who has done it.
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Billbo
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« Reply #8 on: February 28, 2020, 01:02:55 PM »

Interesting experiments. There is Skilled designer builder of ..Scale..RC models.. who has experimented heavily with this stuff.
His views: It's  Pricey filament and it has erm.. reduced structural  properties.. as in a notable portion of weight saved needs go back in as
Carbon; tubes rods etc... to stop wing droop, let along  G loads. 
Material is both intriguing And disappointing. Likely there will be something better in the future.
IMO for max lightness.. One 'could' print a genuinely Scale design and subsequently use the print as a Plug
 for making a Female Vacuforming Mold for  1 MM depron.
ALFA models fashion.. Still the benchmark for Lightweight .. Scale ... RC.

Certainly on a weight basis Colorfabb LW-PLA is significantly more expensive than standard PLA.  A 750 g spool of LW-PLA costs $51.00 (https://www.printedsolid.com/collections/1-75mm-specialty/products/colorfabb-lw-pla-filament-1-75mm-x-750g-natural), which translates to $68/kg.  This is about three to four times the cost per kg of a decent-quality standard PLA filament.  However, because of the way LW-PLA expands when printed, the price per cm^3 for LW-PLA compares quite favorably to standard PLA.  For that 750 g spool that costs $51, the price per unit volume (allowing for a .403 - .476 g/cm^3 density) is $0.027 - $0.032/cm^3.  For a $20 spool of PLA (assuming a density of 1.2g/cm^3) the cost per unit volume is $0.024/cm^3.  This means that on a printed unit volume basis, LW-PLA is only 13% - 33% more expensive than a $20 spool of standard PLA.  On this basis, I do not find the cost of LW-PLA to be excessive.

As far as the strength of this filament goes, I have found it to be the only material suitable for 3D-printing a rubber-powered free flight airplane.  I have tried printing rubber-powered planes from standard PLA and HIPS with limited success.  (The HIPS worked somewhat better than the standard PLA.)  However, my LW-PLA rubber powered planes have proven to be very resilient, and able to survive some pretty hard landings and even crashes into trees.  I have used some standard PLA printed keels and stringers to strengthen the fuselage of my airplanes, but the rest of my airframes were printed with LW-PLA, including the wings.  There was one wing I printed with a thin, undercambered airfoil that I tried (as shown in my video) that proved to be less rigid than I would have liked, but I have since changed the design of the internal spars of the wing to make the wing much stiffer.  I think because this material is so new, it will take a while for all of us to figure out the best ways to use it and print with it.  And certainly my rubber-powered airplanes are not subject to the same stresses that an aerobatic RC plane is subjected to (except perhaps for hard landing and crashes).  But at the same time, I came across this video of an RC twin engined Beechcraft that was printed from LW-PLA, and it looks like it handles the stresses of aerobatics quite well (https://youtu.be/RBhVqBZBZHU).

I believe that Colorfabb LW_PLA is an awesome material for 3D-printing flying models.  I think there is still a lot to learn about it.  I know, for example, that my print settings for LW-PLA are much different from what other people are using, and are different from what even the manufacturer recommends.  I have been printing LW-PLA in vase-mode with an 0.3 mm nozzle at a print speed of 20 mm/s, a temperature of 210 - 220 C, and a flow rate of only 35%.  Most others are printing this material faster at a temperature of 240 -250 C.  I believe that because I am printing at a slower speed with a smaller nozzle, I am getting a better heat-transfer rate to the filament which in turn facilitates its expansion.

I am really looking forward to seeing what other people can do with this material, and learning more about how others are printing with it.

 
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Prosper
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« Reply #9 on: March 04, 2020, 08:48:49 AM »

Thanks very much for this thread Billbo - what you've done is adventurous and interesting.

Stephen.
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Billbo
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« Reply #10 on: March 08, 2020, 02:07:20 PM »

Thanks very much for this thread Billbo - what you've done is adventurous and interesting.

Stephen.

Thank you for your encouraging words, Stephen.  Now that the design has been published, I am really looking forward to seeing someone else print and fly this model.  I have received some really good suggestions for things to try with this airplane from the RC groups Free Flight forum, mostly from Bruce Matthews.  One of the things he suggested was to try propellers with a steeper pitch.  The prop that I have been using (which is 3D printed), has a diameter of 200 mm and a pitch of 260 mm (which is a 1.3 P/D ratio).  He suggested trying higher P/D ratios.  To that end, I have printed two more 200 mm diameter propellers, one with a pitch of 300 mm (1.5 P/D ratio), and another with a pitch of 360 mm (1.8 P/D ratio).  I have also changed the way the wing spars are printed; the change will make the wings stronger and stiffer.  This is particularly relevant to the relatively thin, undercambered airfoil that I tried in my video.  That wing was not as rigid as the other two thicker flat-bottomed wings that I tested, and that wing ended up breaking in a hard landing.  I am waiting for a day with calmer air to fly and test these modifications, but that may take a while; after all, I am in New England, and it is now March.  I will definitely update this thread when I fly with these new propellers and modified wings.
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