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Old Sep 22, 2014, 03:27 AM
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Build Log
Twin engined Bixler 2

This is my second twin engined Bixler, after countless flights with my first one (http://forum.flitetest.com/showthrea...gined-Bixler-2) it had a rather unfortunate crash in a tree and was a little too damaged to be worth repairing. It was extremely fun to fly so I decided to build a new one, however give it even more power and try to make it even stronger without adding much weight. The first one I modified after I had already built it, but this one will be a twin from the beginning. The first one had 2 Turnigy D2826-6 2200kv motors with 2 40A speedcontrollers mounted right behind the motors on the wings, and was already capable of unlimited vertical at 3/4 throttle. The one I'm making now will have a little bit less than twice the power and it weighs only 50 grams more.

I am using 2x NTM prop drive 28-36 2700Kv motors (+- 500Watt on 3S each) with a 6X4 prop and powered by 2x Turnigy Plush 60A speed controller. Should give about 2.4kg thrust in total in a plane that will weigh 1.3kg.

This is a vid of the previous one:

Twin engine Bixler 2 doing flat spins etc (6 min 39 sec)


Picture time (sorry for the bad quality, I need a better camera):

First I made more room for the batteries, It'll use 2x 2200Mah 3S lipos, but due to the weight of the engines forward of the CG, I'll need to move the batteries back quite far in order to get the balance right. So, out go the two plastic tubes and cut out some more foam for 1 of the 2 batteries to fit underneith the wing.



I strenthened the wing this time by taking a saw blade and making a slot in the wing, in which a 6mm wide flat strip of carbon goes vertically. Do this both the top and on the bottom of the wing. This adds very little weight but makes the wing increadibly strong. The whole wing, including wires and servos weighs 350 grams, but If you support it at each wing tip you can place a full bucket of water (+- 10kg) in the middle without the wing even bending. I built the wing as a single piece first and later bolted and hot glued it to the top of the fuselage. On the fuselage i cut the top part off so you can do this.









The engine mounts are 3D printed this time, I designed one that slides right over the wing and has a 3 degree down angle compared to the wing chord. This, together with the positive angle of incidence of the wing puts the motors at about a 0.5 degree downwards angle, which results in no pitch moment when you add full power. Once I have tested everything I'll put the files online so people with a 3D printer can make these mounts as well. They have a normal bolt pattern for 28mm motors in them. The ESC's go in the side of the fuselage, below the wing. I posted the STL file for the mount on thingiverse: http://www.thingiverse.com/thing:469613















Everything completed, ready for a test flight soon. I also reinforced the control surfaces the same way as the wings, to stop them from flapping about at high speeds. The tail is reinforced with 2 extra carbon rods on the top left and right, creating a triangle shape with the bottom one (if you take a cross section of the tail) making it very strong as well, there is no more flex in the tail. The horizontal stabilizer got a carbon rod in it as well. I also ditched the standard control linkages as they have quite a bit of play in them. With the things I have now, there is no play in the control surfaces. I cut off the top of the wing and the whole engine mount until right on the wing and gave it some shape again with depron.











Another work in progress will be a retractable gear set for it. I'm working on a sort of pod you can bolt to the bixler which houses the retracts. The nose retract (it will be a tricycle gear with stearable nose wheel) can go where the battery would normally go and will get gear doors too. I will post the STL files for that as well once they are finished.

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Old Oct 08, 2014, 03:36 AM
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The retracts are almost done now. Designed a mount which you can easily remove in case you want to fly without gear, as it adds about 200 grams to the whole plane. I'll make some fairings out of foam to make it a bit more aerodynamic. The main gear retracts towards the back, and the nose gear retracts forward and rotates 90 degrees while it does it. It also steers on the ground so you can taxi. The retract unit is also mounted on a 3d printed piece, which is glued in. As you can see in the pictures, all control surfaces are removed. I'm making new ones out of foam and fiberglass as the old ones are just too weak and bendy.

















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Old Oct 15, 2014, 02:23 PM
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Joined Aug 2006
380 Posts
Nice Looking Build.
How did you end up replicating the wing's profile in CAD to create you motor mounts? I'm a regular SW user, but i'm not sure what process you would use to get those dimensions.

cheers,
Brian
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Old Oct 16, 2014, 07:19 PM
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Joined Apr 2012
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Very interesting reading this thread, it never ceases to amaze me at the ingenuity shown taking a humbvle epo kit and doing amazing things with it.

Good work with the 3d printer too and thanks for posting your mods on thingiverse, nice of you to share.
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Old Oct 20, 2014, 09:30 AM
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Quote:
Originally Posted by TooSLow2Care View Post
Nice Looking Build.
How did you end up replicating the wing's profile in CAD to create you motor mounts? I'm a regular SW user, but i'm not sure what process you would use to get those dimensions.

cheers,
Brian
I couldn't find what profile the bixler uses, so I measered several points and the thickness etc and took the profile that was the closest to it. You can download the coordinates for most airfoils online. You end up with a file with 2 colums, the first are the X axis coordinates and the second the Y axis, and everything is still dimensionless, so just a number between 0 and 1. I used Excel to multiply all coordinates by the size in mms of the bixler wing, add a Z axis column (just 0 in this case) and then import it via the Curves through XYZ points feature and made it an extruded cut through the engine mount which I made on a plane tilted at the right angle.

Here is a nice tutorial about it (not mine):

Design a Wing in Solidworks (20 min 55 sec)


Quote:
Originally Posted by jhkiom View Post
Very interesting reading this thread, it never ceases to amaze me at the ingenuity shown taking a humbvle epo kit and doing amazing things with it.

Good work with the 3d printer too and thanks for posting your mods on thingiverse, nice of you to share.
Thanks! I'll share the parts for the gear as well, once they are finished and tested. I still have to make a gear door for it too.
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Old Oct 20, 2014, 10:17 AM
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Very interesting about the profile dimensions.

I look forward to seeing the finished project and the flight footage and if you get round to posting the stl's, I would definitely have a go myself. (It would be my first trike undercart, all my fleet are taildraggers!).

Do I see you are a SouthPark fan too, looking at the TV in the background?
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