Fully 3D printed sailplane model. optimized for 0.2 nozzle (weight reduction) by grafalex

Last crawled date: 3 years ago

Overview
This is same Walt's Fully Printed Glider model, but optimized for 0.2mm nozzle to reduce weight and tweaked a little bit to improve printing accuracy.
Original design looks very interesting for me, but there were too many complains that resulting plane is too heavy. So I had to redesign some of the parts, keeping overall design unchanged.
I am uploading Solidworks models so that you can add more tweaks if needed.
UPDATE 14-Jun-2015: I finished printing the fuse and installing electronic components. Resulting weight is 636g including battery. Plastic parts are 320g.
However I doubt this plane can fly, and weight is not the problem. The real problem is weight centering which is 57% of the wing horde (tail is too heavy comparing with nose). It should be 25-30% for a normal flight. In other words plane will crash right after take off.
UPDATE 29-Jun-2015: I redesigned the fuse. I moved main fuse body farther to the nose, extending overall fuse+tail length by approx. 30 mm, while keeping wing-stab distance about the same. I also reduced tail parts diameter as well as walls thickness to reduce some weight.
This all should move CG to 25-30% depending on motor and prop
I just started printing these parts so perhaps I’ll be adding more tweaks to STL files.
UPDATE 12-Jul-2015: Minor update just fixed few issues on fuse main parts.
I finished printing fuse parts - everyting fits perfectly.
Still stuck on vert stab redesign.
UPDATE 15-Aug-2015: Finished designing vert stab. I preserved overall shape, but could not reproduce airfoil. No big deal, think.
Since tail got narrower, I had to decrease rudder horn size to fix the tail. I also updated motor mount part.
I am assembling the model right now. Will post updated photos and weight summary little later.
UPDATE 25-Aug-2015: Maiden flight was not too long. Just 3 seconds :) It did a loop and crashed vertically on the nose.
It might be caused by one (of more than one) of these reasons:
Tail is still to heavy
Horizontal stab was not set correctly in idle state and cause plane constantly pitch up
There is huge backlash in stab mount. It plays for several degrees which can be too much for fully deflectable stab
I am reprenting some of the parts that were broken on crash - wing tip, wing center, motor mount. Then I'll probably investigate whether I can use bowden for horizontal stab (to reduce backlash)
UPDATE 14 Sept 2015: Second flight ended the same wayhttps://www.youtube.com/watch?v=7Otw3EAnxgw
Not sure what happened. I removed all backlash on elevator, set elevator to 3 degrees down, double checked CG it was about 30%.
I will have some consulting with r/c plane modeling gurus. Then will decide what should I fix in the model.
UPDATE 25-Nov-2015: Made another design change
Made nose even longer
changed motor mount angle to 4 degrees down to address heavy propeller momentum
few minor changes in fuse parts, mostly reducing weight
Wing parts are untouched
This should move CG closer to the nose, Now should be around 20%
I am in progress of printing these parts. Will make another attempt
UPDATE 04-Sep-2016: Finally took courage to make another flight attempt.
As suggested I went to a field with a high grass. There I tried to throw plane several times from a small altitude. I was under impression that I throw it fast enough, but video shown that speed was too small. Obviously, plane wants more speed to fly. Otherwise it falls on a left wing.
Motorized flights (thrust at 30%) were a little better, but I still could not understand how to trim it right. CoG was at 20-25%, but when I add more thrust plane raised its nose too much. Eventually I had to trim elevator until it balked to the rudder. No more room to trim. Fortunately it helped.
Finally I added more thrust and it took off!! Though, the flight was not too long. I could not turn it back. Every time I tried to turn it tended to fall. Finally it raised its nose too much, did a loop and then I totally lost control.
Another thing I found after crash is too hot motor. It definitely requires some cooling.
Here is the video of my attempts. If you feel it is boring – go directly to 1:51 for the flight.https://youtu.be/BaLBQySvFkA
Summarizing my findings:
Plane needs speed to fly, it does not glide but fall immediately
Rudder does not turn plane as it should
No motor cooling
CG is still not in place, needs to be moved a little forward.
Not enough room for elevator to move (fixing CG should help)
It looks like there is a huge propeller momentum pulling plane up and left
What next? I have to regret my followers: I will not continue working on the project. Now it is time to move on. I have plenty of other projects to work on rather than stuck on this one. Though, I will be glad to see your prints and remixes.
During the project I got plenty of experience in different areas:
how to design plane models in Solidworks
how to calculate essential plane parameters
how to select proper material to print
learned a lot of 3D priniting stuff: different slicers, nozzles, printing speeds and temperatures, and so on
how to set up a model for its first flight
I am still interested in the idea of a 3D printed plane. But next time it will be something different. I would prefer to have at least 4-channel control (add ailerons) and I like take off the ground on wheels. I have not selected a model yet but I have couple ideas in mind.
Stay tuned.
Equipment
I used these electronic components
Motor – Turnigy 2209 1050kv 28 turn 15A
Prop – selecting between 10x6 Direct drive, APC 10x5 and SF 10x4.5
Servos – Hobbyking HXT900
Receiver – Hobbyking 6 channels (plan to change it with 3 channel receiver)
ESC – Turnigy Plush 18A
Battery – Zippy Compact 1300mAh 3S
Here are my weight stats (for previous attempt)
Total for the wing, including carbon rods - 231g
Fuse printed parts – 129g
Total with electronics – 636g
I am uploading weights table as an Excel spreadsheet. Refer to second sheet for weight centering calculation.
Changed parts description (comparing to Walt's version)
Wing panels:
reduced walls thickness to 0.4mm. This will force exactly 2 perimeters (external and internal) when using 0.2mm nozzle. These 2 perimeters are sticked together very well giving extra strength (when printing original STL there was a distance between outer and inner walls and therefore printed model strength was quite poor)
added couple additional 2mm ribs every 20mm - this helps keeping wing shape more accurate, bending resistance
removed hooks to mount sections. Original hooks were too easy to break. Instead I added thickening on the top and bottom to increase gluing area
Wing tips:
It is now hollow with ribs instead of solid.
same thickening at the bottom to increase gluing area
Wing center links:
Original file had number of holes that suppose to reduce weight. But these holes require couple perimeters to be printed around them which add some weight. It appears that model without these holes and 5% infill weights less than original part with holes.
Original model had a bug around rear screw hole. I could not manage to fix it, but it does not make an impact on result quality (small piece of extra plastic could be easily removed after printing)
I added small membrane inside screw holes. It is needed to correctly print ceiling and hole above. Membrane can be easily removed with a drill
I do not like supports, but they work really well for this part.
If you do not like supports you can print this model using bridges. I added couple walls and supporting bridges at the solidworks file, but they are disabled by default. These walls should be removed after printing.
Horizontal stabilizer:
Same trick (as wing tips) worked here as well. I redesigned stab to be hollow with ribs
Fuse:
I completely re-developed fuse. My fuse version is twice lighter than original
Decreased shell thickness to 0.6mm – this is enough to keep its shape, but stay at lower weight.
Reduced main parts thickness and added big holes in order to reduce weight
Redesigned servo mount, changed servo layout so that straight carbon push rods can be used instead of Bowden.
Servo mounting holes are designed to fit HXT900 servos
Motor mount is designed to fit my Turnigy 2209 motor. Mounting holes are 16 and 19mm and compatible with many other motors
Fuse shell parts are now mounted with special hooks. No screws. For front section I designed a bayonet-like mounting
Tail body moved little further to the nose to fix CG. Fuse made little longer at the nose by 40mm.
Wing mount shifted closer to the tail (fixing CG). To preserve wing-stab distance tail was extended a little bit
Tail:
Tail diameter decreased to 20mm, thickness to 0.8mm
Tail length extended to keep wing-stab distance
Horizontal stabilizer and link parts remain the same
Spinner:
I did not have 40mm spinner, so I just designed a printable one. I took collet, spacer and nut from other broken spinner.
Even more weight reduction
There is also possibility to reduce wing weight even more. The idea is to reduce wall thickness to 0.2mm - same as nozzle size. But this required couple extra ribs.
Unfortunately I got this idea after I printed my wing. I printed couple sections (just to evaluate the approach) but not the whole wing. Wing section weights about 9g, wing tip is about 10g. This all gives projected wing weight about 150g.
Surface of the printed part is not quite smooth, so certain degree of sanding is required.
I uploaded these files with Experimental* prefix. Please send me a note if this approach works for you.