Radio controlled airplane

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montagdude
Posts: 29
Joined: Tue Jan 08, 2019 9:04 pm

Radio controlled airplane

Postby montagdude » Thu Oct 03, 2019 3:22 am

This is my first completed (well, almost) project with FreeCAD. It is a small radio controlled airplane with mainly balsa and film construction. Wingspan is 32 inches, and I'm shooting for about 8.5 ounces total weight. I have designed it with a pusher prop so that the camera can go in the front for first-person-view flying. The airfoil was also custom designed. All the parts are now done, and all I have left is to design a jig for building the wing on a workbench and transform all the parts to 2D outlines for laser cutting.

For modeling, I used the Draft -> Part workflow exclusively. It is what I'm used to, and it works well for this kind of task where you start with an "outer mold line" solid aircraft and have to slice it into parts. Lots of intersections and booleans were involved. I am using FreeCAD 0.18 (the AppImage) on Slackware64 14.2. FreeCAD was great for this project. It is getting quite good!

Thanks for looking.
Attachments
2019-10-02-231507_1600x838_scrot.png
2019-10-02-231507_1600x838_scrot.png (294.77 KiB) Viewed 3815 times
2019-10-02-231426_1600x838_scrot.png
2019-10-02-231426_1600x838_scrot.png (147.81 KiB) Viewed 3815 times
2019-10-02-231357_1600x838_scrot.png
2019-10-02-231357_1600x838_scrot.png (159.07 KiB) Viewed 3815 times
2019-10-02-231316_1600x838_scrot.png
2019-10-02-231316_1600x838_scrot.png (226.92 KiB) Viewed 3815 times
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nemesis
Posts: 347
Joined: Tue Mar 25, 2014 11:24 pm
Location: France, Lyon

Re: Radio controlled airplane

Postby nemesis » Tue Oct 08, 2019 6:45 pm

montagdude wrote:
Thu Oct 03, 2019 3:22 am
This is my first completed (well, almost) project with FreeCAD.
Nice first shot!
don t forget to show us a video of the first flight!!
montagdude wrote:
Thu Oct 03, 2019 3:22 am
transform all the parts to 2D outlines for laser cutting.
I would try with Path workbench, to localize the parts in a single wood sheet, but just for the setup, so you can then generate the dxf or svg you need
have a look here
phpBB [video]
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Zolko
Posts: 472
Joined: Mon Dec 17, 2018 10:02 am

Re: Radio controlled airplane

Postby Zolko » Wed Oct 09, 2019 10:58 am

montagdude wrote:
Thu Oct 03, 2019 3:22 am
It is a small radio controlled airplane with mainly balsa and film construction
Nice. I have a couple of questions:
  • what's the purpose of the servo on top ?
  • you didn't include some diagonal stiffeners in the wing, that's going to be problematic
  • there seems to be a week point on the fuselage at the back of the wing, where 2 parts are joining.
try the Assembly4 workbench for FreCAD v0.19
install with Tools > Addon Manager > Assembly4 — simple tutorial here
montagdude
Posts: 29
Joined: Tue Jan 08, 2019 9:04 pm

Re: Radio controlled airplane

Postby montagdude » Wed Oct 09, 2019 7:10 pm

nemesis wrote:
Tue Oct 08, 2019 6:45 pm
montagdude wrote:
Thu Oct 03, 2019 3:22 am
This is my first completed (well, almost) project with FreeCAD.
Nice first shot!
don t forget to show us a video of the first flight!!
montagdude wrote:
Thu Oct 03, 2019 3:22 am
transform all the parts to 2D outlines for laser cutting.
I would try with Path workbench, to localize the parts in a single wood sheet, but just for the setup, so you can then generate the dxf or svg you need
have a look here
phpBB [video]
Thanks for the advice! I have never tried the path workbench. I will look into it, but at this point I'm almost done laying out all the parts anyway. I will try to remember to post video of the first flight when I get it built.
montagdude
Posts: 29
Joined: Tue Jan 08, 2019 9:04 pm

Re: Radio controlled airplane

Postby montagdude » Wed Oct 09, 2019 7:14 pm

Zolko wrote:
Wed Oct 09, 2019 10:58 am
montagdude wrote:
Thu Oct 03, 2019 3:22 am
It is a small radio controlled airplane with mainly balsa and film construction
Nice. I have a couple of questions:
  • what's the purpose of the servo on top ?
  • you didn't include some diagonal stiffeners in the wing, that's going to be problematic
  • there seems to be a week point on the fuselage at the back of the wing, where 2 parts are joining.
1) The servo on top is for the ailerons.
2) Diagonal stiffeners are usually not needed for something so small and light. I'm sure it will be fine in flight. The only potential difficulty is making sure it doesn't twist when heat shrinking the covering.
3) I'm not sure which two parts you are talking about?
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Kunda1
Posts: 5945
Joined: Thu Jan 05, 2017 9:03 pm

Re: Radio controlled airplane

Postby Kunda1 » Wed Oct 09, 2019 8:35 pm

Maybe one of the Finite Element Analysis folk would run this through a solver or 2 and generate some interesting images
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montagdude
Posts: 29
Joined: Tue Jan 08, 2019 9:04 pm

Re: Radio controlled airplane

Postby montagdude » Wed Oct 09, 2019 8:48 pm

I actually have some interesting computational fluid dynamics results for it, not done in FreeCAD though. Hopefully linking to another site is okay...

https://www.rcgroups.com/forums/showthr ... tral-point
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Zolko
Posts: 472
Joined: Mon Dec 17, 2018 10:02 am

Re: Radio controlled airplane

Postby Zolko » Thu Oct 10, 2019 2:01 pm

montagdude wrote:
Wed Oct 09, 2019 7:14 pm
1) The servo on top is for the ailerons.
Ah, didn't see them. But then, if you have ailerons why did you put dihedral ? Especially on such high wings. And why the swept wings ? For such a small and light plane with constant chord, straight wings would greatly simplify (and strengthen) construction.
try the Assembly4 workbench for FreCAD v0.19
install with Tools > Addon Manager > Assembly4 — simple tutorial here
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bill
Posts: 376
Joined: Fri Jan 09, 2015 9:25 pm

Re: Radio controlled airplane

Postby bill » Thu Oct 10, 2019 3:43 pm

Zolko wrote:
Thu Oct 10, 2019 2:01 pm
why did you put dihedral
For level flight stability; it looks like a camera-ship!

Does the wing come off for repair? Is it elevator/aileron? Is it electric; then where does battery fit?
montagdude
Posts: 29
Joined: Tue Jan 08, 2019 9:04 pm

Re: Radio controlled airplane

Postby montagdude » Thu Oct 10, 2019 6:01 pm

Zolko wrote:
Thu Oct 10, 2019 2:01 pm
montagdude wrote:
Wed Oct 09, 2019 7:14 pm
1) The servo on top is for the ailerons.
Ah, didn't see them. But then, if you have ailerons why did you put dihedral ? Especially on such high wings. And why the swept wings ? For such a small and light plane with constant chord, straight wings would greatly simplify (and strengthen) construction.
The dihedral is because I want it to be stable. One goal is for it to be able to fly itself for awhile in case I happen to lose the video feed at any point. It doesn't need ailerons since it has dihedral and sweep, but I enjoy flying planes much more when they have ailerons. I did consider not including them, since it would have made it lighter and simpler, but in the end I decided to go for it.

As for the sweep, originally I had a straight wing, but after making some CG estimates, I realized it would probably be too far back. After that, I moved the wing back by 1/2", swept it like you see here, and also moved the stabilizers farther away from the wing, all of which move the neutral point aft to allow sufficient longitudinal stability without having to add ballast.