The Murphy Builders Site

We use a 3D printer in our business for product development and prototyping.

Both the 3D printer and I have had a few free hours to dabble with aviation parts. Boeing, Airbus and NASA aren't the only show in town. I'm sure there are other builders already using 3D printers too. For my first Murphy project, I used our CAD software to design a fairing for the wing flaperon/aileron pushrod. I've printed and installed the plastic fairing for our Rebel with flaperons. I modeled it after the fiberglass faring I did the old fashion way years ago for our Elite. Haven't tested it for fit on the Elite, but should work. There is a SuperRebel at our airport so I'll check it out, but I think they may need different and/or bigger fairings.

I placed the files for 3D printing as well as the CAD file for modifying up for anyone to use for free on Thingiverse. This is a website where countless thousands of free 3D printable objects reside.

http://www.thingiverse.com/thing:824279

Here is a picture of the 3D printed part on the Rebel.

Eric
N112R & N645E

that looks great
I may have to look into that for the wing strut fairings

Looks great Eric! What's the long term durability of that material?

Many 3D printers for home use can print in several plastics. Two most common are PLA and ABS.

ABS is great, since many fairings on planes (experimental and certified) are made of ABS. Acetone can smooth it and it can be sanded and painted. Should be painted as UV affects it. But ABS stinks when printing.

So, most people use PLA which is corn or potato based and the very slight smell just makes you crave corn nuts or potato chips. Surprisingly, PLA is bullet proof. It laughs at acetone. Gasoline is a joke. Even MEK won't mess with it. Sand paper and files just fuzz it up. You can drill it. Nothing likes to stick to it so painting is not realistic. But, it softens at a low temp...like 140F. So, I'll see how they do when Redding gets to 115F in the shade this summer. Realistically the PLA should be used for fiberglass molds...or used forever, as-is, if you live in Canada (kidding).

ABS should be fine for real parts. Mass producing on 3D printers is not ready for prime time yet. I think it took 5 hours to print *each* fairing that I attached to the Rebel. One printed over night. You don't need to supervise printing (sometimes you do wake up to some amazing creations when a part tips over sometime during printing...another story).

I'm looking at designing some fairings for the wing strut where it attaches to the fuselage and the wing. I've heard that these are great areas for cleaning up drag and gaining airspeed.

I'll share whatever I create so others can use or improve as they see fit...

Eric
N112R & N645E

I will take 2 of these and 2 wing strut fairings too! LOL. Seriously though what would it cost to get a commercial printer to do it

Thanks Ray,

Hope that this isn't a repeat. I started typing and then had dinner, so the original post timed out...I think.

There are commercial 3D printers out there. We've used Shapeways for limited use. They are far too expensive and when we used them the plastic was not structural. Since there are now tens of thousands of underutilized home 3D printers out there, I'm surprised that someone hasn't harnessed these resources to produce 3D parts cooperatively. The plastic for the fairings is a few dollars...maybe. The printers run about $2000. But, it takes time to print. The pushrod fairings took 5 hours each to print in rough-draft mode. So, 3D printing is here for good and is only going to get more amazing from Boeing all the way down to home use. Still early days right now...

I put the fairing files up on Thingiverse for open and free use. If you can find a commercial printer, use them. If you modify and improve them, awesome. If you share your improvements openly and freely..great...but no need to. The design is open to anyone to do anything. I'll do the same with the strut fairings when I find the time...

Enjoy,

Eric
N112R & N645E

That's pretty neat for sure.

that's really cool that your using 3d printing
I did 3d printing 25-30 years ago, was one of the first to try it in Canada but we could not give it away
now look, everybody is using it

cheers

mike#007

Great topic.
Now brace yourselves for topic creep.

Seems there is some plastic expertise on this thread....
so maybe someone could answer a question
I've wondered about for a long time.

Why has no one made and sold a plastic extrusion, airfoil shaped,
that could slip over the bracing wires on floats?

I'm visualizing something like those booklet binders that
squeeze the left hand side of the pages to hold them together,
but airfoil shaped. Light and cheap. And aerodynamic.

Surely there'd be a reasonable market in the u/l and
homebuilder markets, w/o the hassle of STC certification.
Sorry for the thread topic creep.

John

Good point and not much topic creep really. Everyone on floats has been watching for that to develop. Probably has to be extruded and sold by the foot. Would have to fit a variety of flying wire sizes I guess, and for safety should be transparent for inspections. If it fit loosely it could simply turn and align itself with the wind, cutting the drag to as little as 1-3 or less. We have the diagonals exposed to the wind head on, the horizontals in the wake of other equipment may not make much difference. It would also have to be UV resistant, and of course cheaper than stainless. Since the stainless is ludicrously expensive, this stuff could pay for itself fairly easily. Each rebel would use about 24' of it and I bet every one of us would part with $4 a foot to get some. A small tech problem would be putting it on so that it would align with the wind easily without sticking.

Steve Sloan at Arlington had a lot of success with fairing his Rebel, both on wheels and floats. Don't recall the numbers, but I think his 125 hp Cont 240 on amphibs was faster than a 320, maybe even the 360, can't remember for sure, and used a way less fuel. Haven't met up with him for years now, but wish I would have taken some pics. I know he did a lot of experimenting, and he knows what works, or biggest bang for the buck (effort).

Now with the 3D printers, should be a lot easier to trial and error the best shape, before the final product, maybe in just simple shaped aluminum. Hint, hint,... Eric... And then let the rest of us know.

With my 360 Rebel amphib, I cruise mostly at pretty low power (<65%) and about 120 mph or less. I can go faster (when I used to fly with a 185 friend), but my fuel usage goes way up at anything over 120. So fairings would be nice. The other benefit would be better engine cooling, as it would take less power at cruise speed.

skidaddy20000 wrote:Great topic.
Now brace yourselves for topic creep.

Seems there is some plastic expertise on this thread....
so maybe someone could answer a question
I've wondered about for a long time.

Why has no one made and sold a plastic extrusion, airfoil shaped,
that could slip over the bracing wires on floats?

I'm visualizing something like those booklet binders that
squeeze the left hand side of the pages to hold them together,
but airfoil shaped. Light and cheap. And aerodynamic.

Surely there'd be a reasonable market in the u/l and
homebuilder markets, w/o the hassle of STC certification.
Sorry for the thread topic creep.

John

John,

Creative thinking on your part to be sure, however I would have a concern about flutter. My feeling is that they would flutter and disintegrate. Even if you could find an effective way to secure them to the cable, the cable can still twist....and flutter could still develop. That is why biplane aileron slave pushrods are round, or the airfoiled ones require a bead along one side to cause drag that keeps the tube always trying to twist in one direction....and not hunting back and forth. And that bead causes DRAG.

Cheers,
Nigel

Walter,

I met Steve Sloan years ago and his fellow Rebel builder who's name escapes me right now. Couple of characters and lots of fun. They had all kinds of speed mods, shorter legs on their floats, custom fairings, etc. I think they may have been Boeing engineers having tons of fun with their Rebels.

Until you mentioned proving some designs in 3D plastic, I hadn't thought about aluminum. Yes, soon, but not cheap enough for us, we'll be able to 3D print aluminum. But, you got me thinking. Along with making forms for laying up fiberglass, it may be possible to 3D print plastic forms for forming aluminum. Probably lots of limitations, but this plastic is strong. The Rebel wreck (now flying 112R) purchase came with a bunch of very useful Murphy parts and a bunch of aluminum 2'x2' aluminum of various gauges and alloys.

I have several sheets of 2024-0 and 6061-0 soft aluminum to play with. I'll see what some simple forms and a lot of little hammering and shaping can produce over a 3d printed mold. Sometimes after hammering for non-structural parts it may have enough temper. If you need more, then I think you send your soft part out to get tempered, but don't know if this has a reasonable cost for small quantities. First, I'll see what it is like to form over plastic forms.

Thanks for the idea Walter.

Eric
N112R & N645E

It's a little bit off subject .....

But check out this 3D printed jet engine !!!

http://www.gizmag.com/ge-fires-up-all-3 ... nge/37448/


WOW !

ericfo wrote:Along with making forms for laying up fiberglass, it may be possible to 3D print plastic forms for forming aluminum. Probably lots of limitations, but this plastic is strong.

Yes, that is exactly what I was thinking. Like Wayne, I hate working with fiberglass... But yeah, printing aluminum would indeed be the ultimate... I am sure it is coming. After all they can print human organs with them now...