Welcome to Boomtown!

aLAcrity Boomerangs is a group of boomerang enthusiasts from Los Angeles. At the moment, it is comprised of three people: Manny (a.k.a. v12aero), phnxhawk and Charles (a.k.a. hey_kuya).

Manny and I (phnxhawk) started this blog to share our interest in boomerangs--throwing and tuning, making our own rangs, as well as unraveling the science behind them. As we continue our journey into the world of boomerangs, we hope to make new friends and to expand our horizons. In this blog, we will post such things as videos from our regular throwing sessions, musings and lessons learned from throwing, and thoughts on making our own rangs.

Manny and I started throwing boomerangs since Spring 2009. It has been a long road as we developed a semblance of technique for throwing 'rangs. Nevertheless, after many a bruised hand or windy day, our fascination with these returning throwing sticks remains undimmed. We most certainly have more to learn about boomerangs, but we'll keep at it as long as we continue to have many happy returns.

--phnxhawk--

Friday, May 11, 2012

Carver's Corner #1 - phnxhawk's Prototypes

--by phnxhawk--

Well, folks, my work schedule has quieted down for now.  So, I can, hopefully, get back to throwing sticks and writing about all the great things I learn while doing it.  For this, my inaugural post for the throwing year of 2012, I will discuss my introduction to the world of carving boomerangs.

Introduction


I started flying remote control airplanes a few years back.  I mostly fly craft of the park flyer class--at one of the athletic fields where I now sometimes throw boomerangs, of course.  When I started, I learned to fly on an Easy Star, a prefabricated kit that was essentially ready to fly out of the box.  (Some minor assembly required for the RTF version.)   Many of the RC planes in my fleet are similar: great-flying airplanes that arrived at my doorstep already built.  Nevertheless, I have often said to myself, "You know, such-and-such would be an awesome airplane to fly.  If only someone made one like it!"  A couple years ago, I finally became fed up with waiting for those great airplanes to show up in stores and started cutting out my own versions of them.  They were crude and sometimes a terrific (and unintended) challenge to pilot, but full of all sorts of cool that only my imagination could imbue onto a few hunks of foam sheet glued together. 

Similarly, I was possessed last year by the notion that I should start creating my own boomerangs.  At once, my mind was filled with visions of the possibilities.  I could make my own Colorado replicas to supplement the precious few originals in my collection.  Or...I could implement my own intuitions for design into boomerangs that could be flight tested.  Or...instead of desperately searching for one boomerang or another to fit a certain niche in my collection, I could, with some effort, at least in principle, create it myself.  For all these reasons and more, this seemed to me to be a natural step in my development as an avid boomerang enthusiast.

Since this would be my initial foray into making my own boomerangs, I knew I would need a standard to which I could compare my creations.  I needed a boomerang whose performance was predictable and with which my technique was already mature.  In other words, I needed to generate a replica of a boomerang with which I am intimately familiar.  Fortunately, in my relatively short period of throwing 'rangs, I had developed an almost preternatural sense for achieving excellent returns with my Rainier and Phoenix.  I ultimately opted for the Rainier, boomerang #1 in my collection and my go-to warm-up boomerang.


From phnxhawk's Boomerang Collection


Preparation: Materials


Based on my initial research into the materials of choice by various boomerang carvers, it seemed to me that anybody who's anybody uses Finnish or Baltic birch plywood.  However, at the time, the 5-mm thick variety was out of stock with my prospective supplier, Anderson Trading, and I was bent on starting sooner rather than later.  So, I settled instead for a 2 ft x 1 ft sheet of 3/16 in thick, 4-ply birch from my local hobby shop.  Although it was not the ideal material to use, it would serve well as a test piece on which to test my carving techniques. 

Incidentally, I also gave some thought to the application of 3-D printers.  I consider myself an able CAD (computer-aided design) software driver, so I was understandably curious how I might leverage that skill in making my own boomerangs.  The grand dream, of course, is to model the boomerang in CAD software, export that data to some sort of computer-controlled manufacturing machine, and watch with detached glee as a boomerang popped out the other end.  This ought to be a topic for discussion another day, so suffice it to say that I am not yet convinced that 3-D printing is a cost-effective way for me to go.  (Among other things, I have no room for setting up any machinery in the long term.)

Preparation: Tools


Speaking of tools...every other year or so, I get this strange hankering to buy a scrollsaw and power sander not unlike the ones that got me through my student years.  2011 was no exception.  On the other hand, I already had a Dremel rotary tool in my toolkit.  With the routing/cutting bits and the various sanding drums, combined with careful handling, the Dremel could do the lion's share of the work.  After some quiet debate, I decided to put off the acquisition of the scrollsaw and instead picked up a folding work bench, the Dremel Workstation, and a generous amount of sandpaper.

Preparation: Boomerang Contours


The last remaining "first steps" were to generate a template from which to draw the blanks and to create a plan for fashioning the contouring that would give rise to the airfoil shape on the carved boomerang.  A Sharpie, some construction paper and a pair of scissors were all I needed to trace the Rainier's outline and generate a rough template, but the contour plan would require a little more effort.

I decided to draw once more from my experience as a CAD designer to fashion a rough 3-D solid model.  The surfaces would not need to be production quality--merely good enough for creating planar intersects corresponding to the interfaces between plies.  These would be adequate for producing a 2-D contour map that I could look at as I whittle away the excess plywood.

For the basic airfoil shape used in the 3-D surfacing, I used profiles based on the Clark Y airfoil.
From May 11, 2012


This is a relatively well-behaved airfoil that also happens to have a nearly flat underside, which, like the airfoil shapes I have seen on boomerangs I own, facilitates manufacture.  So, instead of committing time to carving both sides of the blank, I need only focus on the perimeter and the upper surface.  In general, I scaled this airfoil in height and chord as necessary to achieve the constant 3/16 in max thickness.  I also clipped the trailing edge to have a constant thickness of about 1 mm.  The trailing edge of the idealized airfoils looked too thin and would easily break; a nonzero trailing edge thickness would leave enough material so as not be as frail.


From May 11, 2012

From May 11, 2012


All in all, I was satisfied with how the 3-D model and 2-D contour map turned out.  They looked reasonably like the original, enough that I was willing to move forward with the real meat of the work.

Carving: My Humble Workshop



From May 11, 2012


For this "test run," I decided to cut three boomerangs from the plywood sheet (about as many as could be comfortably fit).  I labeled them Rainier V0001 through V0003.  (The "V" just clues me in to the fact that the next character is a numeral, even if I write it like an "O.")

To my surprise, simply applying the template to the wood sheet came with its own lessons learned.  In particular, it was not until after I had finished carving the airfoils into the first blank that I realized I had not scribbled the word "TOP" on the blank.  I had a 50/50 chance of choosing the wrong side when I picked up the blank to do the airfoil contouring, and as fate would have it, I chose poorly.  (The Rainier is not completely symmetrical about its "centerline.")  I was more vigilant in clearly identifying the top and bottom side with the subsequent versions.

From May 11, 2012


The second major lesson has to do with the grain direction of the plywood.  I had anticipated the plywood would have a pronounced grain direction and would be especially stiff in one direction (along the long edge of the sheet).  To explore the effect grain direction would have on the boomerangs, I laid them out on the sheet in three different directions.  (V0002 and V0003 were laid out and cut a week after V0001.)  After cutting the blanks, I was surprised by the degree of stiffness they exhibited.  V0001 is stiff along the trailing arm, which resists being bent to a different dihedral angle.  V0003 is the opposite, being stiff along the lead arm.  V0002 falls in between and is pliable along both arms.  All three seem to respond equally well to added twist.

Cutting the blanks was straightforward.  I used the multipurpose cutting bit for cutting the plywood and employed the cutting guide attachment so that I could focus exclusively on following the 2-D pattern I had stenciled with marker.  I took care to avoid diving inside of the lines and preferred instead to leave a small amount of excess material that I could sand down later.



From May 11, 2012




From May 11, 2012


I did all my Dremel sanding, for both refining the 2-D outline of the blank and working in the airfoil contouring, with the Dremel screwed into the Workstation, which was then securely clamped to my workbench.  I mostly used the 0.5-in sanding drum with the coarse sanding bands.  As you might imagine, I "burned" through a few of those bands over the course of sanding down three boomerangs.  I "eyeballed" my progress with the airfoiling by progressively comparing the in-work boomerang to my 2-D drawing.  After getting as close as I could to the desired shape, I smoothed out the curves by hand with finer grit sandpaper.

V0001 turned out pretty nicely.  V0002 and V0003 came out with a few dings and scratches from some overly aggressive power sanding.  (I cut and sanded both in the same afternoon...to the detriment of the final product.)  Still, all three were acceptable.  For these initial prototypes, I also applied a coat of wood finish and sealer.



From May 11, 2012
From May 11, 2012


Flight Performance: The Moment of Truth



First flight of the prototypes took place on a nippy day at the beach, and I can attest to the fact that they do, indeed, boomerang.  (Forsooth, my Boomerang Man bumper sticker reminds me daily that "a boomerang is not a boomerang if it doesn't boomerang.")  The first flights were not without some hiccups, however.

Rainier 0001 flies quite well.  In fact, it seemed to work the best out of the three, despite being "backwards."  Although the range does not seem quite as far as the original Rainier, the boomerang's flight path seems fairly typical and well-behaved, as expected.  The returns usually exhibit a large degree of hover and seem to have a propensity to continue spiraling in.  Rainier 0002 also flies pretty well.  Like the 0001, it still seems to "fly light," hovering extensively on the return.  Both benefited from the application of some rubber bands to serve as drag devices, which helped slow them down in the final stage of the return.

Rainier 0003 seems to have been laid down in a particularly unfavorable orientation with respect to the warping of the wood sheet from which it was cut.  The lead arm may have been bent too far down, but since that was also the arm aligned with the grain direction, it was also resistant to attempts to tune it.  Although its flight usually seems promising at release, it tends to promptly dive from a level return and into the ground.  After some aggressive wing twisting, this undesirable behavior was largely eliminated.

Charles also had a chance to weigh in on the prototypes several weeks later.  From what I could tell, he was quite pleased with the results.  Rainier 0003 gave him some trouble at first, but it was nothing that his "solar hands" could not tune.



From May 11, 2012
From May 11, 2012


Future Work


For the next iteration of Rainier replicas, I plan to utilize 5mm, 10-ply Finnish birch plywood, which I have acquired in the months since I made those first three boomerangs.  I will also try to produce a replica of a different boomerang; I am currently putting the Eagle at the top of that list. 
As I did with the plywood sheet I used for these initial boomerangs, I will want to examine how pronounced the grain direction is in the new material.  I also expect that having extra ply lines will help improve the fidelity of my airfoil contouring.

To reduce the excessive hover, I will transition from the airfoils to the flat plate of the elbow further out along the arms.  For these initial boomerangs, I took the airfoil contouring closer to the elbow than was present on the original.  At the time, I was unsure what the effect might be other than that it would improve the appearance.  If I have the time, I will want to do two versions, one for each variation of this detail, to investigate whether this has a noticeable effect on the flight characteristics.

I also need to continue my campaign to create a digital database of boomerang silhouettes corresponding to the 'rangs currently in my collection.  As with the Rainier, I scan the pen-and-paper outlines of the boomerangs and, with some manipulation in GIMP, create a digital version.  These have a variety of potential applications, such as facilitating advance planning of carving multiple boomerangs from a single sheet of plywood.  More directly, I use them to create 2-D outlines in my CAD suite from which I may generate the 3-D surfaces.

Overall, I am encouraged by these initial results.  Although I would be at pains to deliver replicas such as these under a tighter schedule, the tools and manufacturing skills I have suffice for my current purposes.  Furthermore, emboldened by the flight performance of Rainiers V0001 through V0003, I am eager to put together replicas of more boomerangs and to start working on my own designs.  Stay tuned for more news on this topic in future editions of the Carver's Corner with aLAcrity Boomerangs, and as always, feel free to comment below.

"Putting my spin on boomerangs..."

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