There's a new development brewing in the boomerang world. An eccentric edge in boomerang performance. It's an aerodynamic enhancement called turbulators. In the recent past and today, modern boomerangers have attached and crafted wind taming devices to their boomerangs such as flaps, tape, ribbons, string, wire, velcro, rubber bands, holes, slots, comb cuts, etcetera... to increase stability in stronger winds. We've even used them to increase lift when necessary. Turbulators ("turbs" for short) are various devices that actually channel airflow in a manner that increases overall efficiency. The results are quite different than what we get from the more commonly used flight altering modifications listed above. Turbulators agitate (or turbulate) the trapped air on the boomerang's immediate surface, which normally gets stuck there between the wing and the pressure from the air stream flow, causing an increase in drag. This agitation of the "laminar separation bubble" sort of shakes it off of the wing surface, allowing the two opposing forces to pass by each other with less conflict. Replacing the trapped air with turbulated air makes the boom more slippery in flight, decreasing aerodynamic drag and resulting in greater distance and stability against the oncoming wind. It also helps the boom to more easily maintain its pattern of flight. Some turbulators can actually be fashioned to increase drag on certain areas of the boomerang if desired, but this dynamic has been less explored. For example you can slow airflow at, say the wingtips and increase it elsewhere on the boom. This is a tricky strategy but it could be worth investigating. It's nice to know there's such a potential to play with.
Having followed this subject for a few years now, I've found that turb users have various different methods for applying them. Some are carved or burned in with a hot iron. Some are applied using flat stickers and even polyurethane tabs made for cabinetry. Even booms painted with that special decorative paint that leaves a rough or gritty textured finish have been considered to be turbulated to some degree. As for me, I started experimenting with turbs after reading a small paragraph about them in MHR. I used a homemade branding iron, burning small V shaped impressions in a specific pattern. Later, I switched to an easier faster method which imitates this pattern. Turbulation technology has been used mainly on aircraft, but has also been found on sailboats, Olympic ice skaters' clothing, tall buildings (to reduce wind load) and heat transfer equipment such as infra red and water heaters and boilers. They make stream flow more efficient.
Although turbulators have been found on aboriginal boomerang artifacts (previously presumed to be only for decoration), Georgi Dimantschev of Bulgaria, aeronautical engineer and highly acclaimed boomerang designer has been considered the originator of modern boomerang turbulators. I've interviewed four boomerang craftsmen who have done a considerable amount of experimentation with turbs. They all had something different to say about them. Well, different and yet the same. All quite inspiring.
Eric Brasseur of Belgium, an inventor and scientific journalist says "Turbulators are used on some gliders and airplanes to force the air to follow the shape of the wing. The little turbulences triggered by the turbulators seem to "hammer" [bring closer] the airflow on the wings upper side. This for example, is useful for wings with little chord flying at low speed and for flat wings flying at a high angle of attack. It is also useful to get a correct airflow around very thick boomerang wings. Turbulators can be used for two more effects on a boomerang. They can be used as aerobrakes to slow the boomerang down on purpose. This can be useful for short range jugglery boomerangs. The other effect is the turbulators force the air to travel around the boomerang wings in a predictable way. You get a constant and reliable lift on the wings that no more depends on random events like gusts of wind or slight changes in the launch."
"I knew about many turbulator shapes but I was attracted to the polyurethane flat domes for several reasons. Holes or deep carves would make the boomerang fragile and need more time and work to experiment and try different sizes and places. Polyurethane flat domes could be bought in a local store for peanuts and be glued and removed at will on the boomerang surface." The domes Eric has used are 8 mm in diameter and less than 2 mm thick, manufactured to soften the closing of kitchen cupboards. "The best place seemed to be on the upper side of
the leading edge, about 4 mm from the edge, with a distance of a little more
than a dome diameter between each dome. Close to the middle of each wing I added a second
Eric Brassuer's dome-turbed rang.
row of a few domes, 15 mm from the edge and forming triangles with the first row." Eric says if you use the self-adhesive domes he uses, make sure the boomerang's surface is clean when applying them. this can be done with some sticky tape. When the removed tape appears clean, the wing surface is ready for applying turbs. He also suggests trying different sizes of domes.
Georgi Dimantschev has taken the most scientific approach to his experimentations. He tested many of his own well designed boomerangs with and without turbulators. His tests have shown a definite benefit by applying turbs in the right place. There are a number of his findings posted on boomerang websites throughout the net. Here is Georgi's advice to new and future turb users:
The first information on turbulators which I encountered was in magazines and books about aeromodels in the early 70s. I had just begun to build little airplanes and boomerangs too at this time. It was many years later that I found the absolutely right information on this topic. For people who like to read technical manuals, I could recommend F.W. Schmitz' "Aeromodel Aerodynamics - Wind tunnel experiments at low speeds", written by the German expert, as the best such book. Throughout my way from aeromodeler to aircraft engineer and later to boomerang-designer, I have been coming back to turbulators myriad of times. In the beginning of the 90s I started to experiment with turbulators on boomerang-arms. I went maybe through all possible ways to make an air stream turbulent. In my first article concerning this, published in the German Bumerang Welt (3/1996), Swiss Boomerang Newsletter (4/1996) and the Italian Club Bollettino (#17, 1997), I explained my experience with 0.4 mm in diameter thread turbulators on 30-50m range boomerangs, made of 4 up to 6 mm thick plywood. There, using some graphic data excerpted from Felix Hess' Thesis on Boomerangs "Aerodynamics and Motion" (1975), I proved the connection between my experimental results and the theory. Bringing the project to the next level, I used lines of pin holes in combination with special slots in the middle of the arm-chord (GD-BoomArmProfile) on thin AR boomerangs made of 3.2 mm paper-phenolic. The best material for this experiments turned out to be my Factor FC/Endurance triblader and the 50+m range Atlas (the effect of the experiment was reported in Bumerang Welt, 3/1997). My first original MTA-designs Magic and Impulse were made of 1.5 mm glassfiber plates and had sharp edges that worked as turbulators (similar to the classic Ted Bailey plywood MTAs). I wrote about these experiments in the article "My Way To The MTA", published in Bumerang Welt (3&4/1995, 1/1996) and DBC Info (#61, 1997). In the middle of the 90s I began to manufacture Composite MTA boomerangs. The first of them, Vector, had turbulators resembling 2 parallel strips on the leading edges of the lead arm and elbow. The next Composite model, Gradus, had much more effective zig-zag turbulators of 0.15 mm thick sticker-paper. In my article "About The MTA-Boomerang Aerodynamics" (SBN , 1&2/2000) I presented the effects of turbulators on MTA arms supporting this with a lot of results of scientific studies. Nowadays, I use zig-zag turbulators for all the Composite MTAs that I make - the 2-blader Gradus, Sensor, Primer and Eventus and the 3-blader Trigger and Revolver and for all my LD-hooks (Concorde and Voyager). The most effective prove to be the zig-zag strips on the Gradus and Sensor MTAs, which need such strips, because their arm-profiles have relatively big thickness and camber.
What do I use turbulators for?
* On MTA boomerang-arms - to make the MTAs more stable at the process of transaction between the climbing-up phase and the hovering phase (as an anti-stall device) and to make the hover longer (for less vertical speed).
* On AR (30-50-m-range) and LD (80-100-m and greater range) - to provide higher lift-to-drag ratio, which reduces the throw-power, and gives the LD a chance for surer surfing on its backward journey.
Actually, what is a turbulator? A turbulator could be any device that changes the character of the air stream around the boomerang arm - from laminar to turbulent. What brings the necessity of such transformation? The turbulent flow is much more stable. In the first place, more stall-stable. And this automatically means higher flight stability. What could bring a turbulator on the right place? It gives higher lift, more stall-resistance, higher lift-to-drag ratio (also known as glade ratio). Any more sophisticated explanations are excessive if you just look at the graphics [Abb.17.]. Every influence of the turbulators is shown there.
Using turbulators on boomerang arms is nothing revolutionary or sensational. This is just a fine aerodynamic tuning and it is a matter of simple logic. The really "big deal" is to find the right place to add the turbulator depending on the boomerang's geometry (shape and arm-profiles). And this "deal" needs really deep practical aerodynamics understanding and something more. It costs a lot of time for throwing experiments. Looking for the right places, I personally came to need to know the air stream distributions on the boomerang's surfaces. Not having computers and/or wind tunnels like those in NASA at hand, I found my own very simple and effective method for this. Having found some of the particularities of the stream-fields, which act on the boomerang's surface, I found some "revolutionarily" new places to position turbulators.
Warning! The turbulators are not a universal "pain-killer", they are only a device for fine aerodynamic tuning. A geometrically wrong tuned boomerang cannot be corrected by turbulators.
In conclusion, even though it could sound like a paradox, it is true that the most important thing for modern boomerangs' tuning and their flight are turbulent flow and controlled drag forces. Along with BOOMERANGS FOREVER, I would say comes the slogan: TURBULATORS FOREVER!
Georgi Dimantschev
, Sofia, Bulgaria, Europe
Georgi's turbulated MTAs. From Pierre Kutek's collection.
Richard Harrison, known by most of us as The Boomerang Man, has had much to say about turbulators in recent years. He saves and uses borders from self-adhesive postage stamps, labels from vcr blank tapes and similar material. "At first, I used a zig-zag edge (using pinking shears). Rusty Harding said a straight edge was just as effective. He was correct. The turbs are applied to the top side of the leading edge. I use small sections, .25 to .5 inch long, 3/16 to 1/4 inch wide is typical." Rich began using turbs in effort to make his MTAs work better. He'd seen a picture of one of Georgi's MTAs that had some zig-zag material applied along the
leading edges. "Since I was not having much success with my Jonas carbon mtas, I figured
turbs might help. THEY DID :) ". He has turbs on all 10 of his MTA rangs (wood, paxoline and composite), a small turb on a Colorado Aspen (4mm symmetrical wing), a Wasp Polycarbonate and an aluminum triblade. "I've tested them on other rangs but turbs were not effective for the conditions used."
Turb instructions from The B-Man
HOW TO USE TURBS:
Collect self adhesive paper materials, such as postal stamp borders. Select a boomerang that you know. Apply a turb to the top of the leading edge, on the leading wing, and as
near to the tip as you can, but will not be touched by your fingers. THROW. Several throws should be all you need to know if the turbs are effective. This is trial-n-error testing. Apply a turb to the trailing wing. Toss. Apply a turb to the elbow. Toss. Reposition a turb, remove a turb. Toss. You can test a turb on the underside of your rang. Toss.
If you have a rang that is working well before turbing, you probably will not have any improvement after you apply the turb. However, for windy conditions a turb might make a difference. Like adding lead tape to fine-tune a rang, applying turbs is very much hands-on, trial-n-error. Don't ask for help...JUST DO IT :)
Rich adds, "I am enjoying success with my MTAs, thanks to turbs....over time I have noticed that I can remove a small part of a turb and the rang continues to work well. Maybe I've gotten better with my mta throwing, or perhaps the turb was simply a sort of 'training wheel' for me as I perfected my MTA throwing."
[b-man's stick-on turbs]
Renan Guillou of France, a wonderfully creative boomeranger, organizer and all around good guy has also done work with turbulators. I was impressed by what he told me. "I used turbs on MTA and Aussie Round booms. Maybe because I use to throw on North Brittany beaches, near St Brieuc, where there are often strong winds. NNW to ENE is okay, regular breeze coming from the sea. But SE to SW is hazardous, squally. Turbs are supposed to make a boom more able to endure this kind of weather."
"I make turbs with a woodburning tool. It's like a soldering iron, but made for decorating wood. This works quite well on bakelite, epoxy, polypropyl�ne etc. and plywood
As the picture shows, every leading edge is engraved with turbs, I throw it here, specially on windy conditions (up to 4 -5 on beaufort scale), when no other flies."
details of a wing. Renan's Bretzel
"Well, except in particular cases, I try now to find shapes, or work on them, that prevents me from making turbs in the first place. They're good to improve an existant boomerang, or to fit one to windy weather. But for example, I don't dare make turbs to improve my LDs!"
I hadn't yet tried using turbs on a plastic rang until Renan mentioned that he has. Well, now I've tried it on a small plastic triblader made of a soft plastic material about 1.5mm thick. I quickly and casually etched in a criss cross turb pattern with a sharp pocket knife when the wind picked up. Know what? It works! More range, better wind stabilility, nice return but with less hovering at the end of flight. This is a very light boomerang that previously had trouble standing up to more than a delicate breeze.
(left) The authors first turb application on a plastic rang. Works great!
(right) Renan's Bretzel wind boom plan
Renan discovered turbs somewhat by accident. When I first met him 5 years ago (via the internet) he related a story about his first known experience with turbulators...
"Let me tell you about one of the last booms I've crafted. It's a very simple, smooth sized shape of 6.5 to 7 mm 5 plies wood. But it works really good, as far as 70 to 80 m, and specially with strong wind.(up to 4 to 5 in Beaufort scale) It began with a stroke of luck. A children-asleep-nothing-on-TV evening when the idea came to me to pyro-engrave (woodburn) with V shaped patterns an old classic boom I'd already improved with 2 weights and undercut workings. As you can see on the file, V shaped patterns are perpendicular to the leading edges. The first purpose was just to decorate it, but I was really amazed when I threw it again. Characteristics have strongly changed. Very more far, more regular in height, more accurate, more resistant to strong gusts. This last point is spectacular: I use to throw on a large beach, with southern wind from november to may; that wind comes from the cliffs and is quite irregular, and usually pushes booms down at the end of the first part of their path. This particular boom seems not to be affected (or much less) by sudden changes of wind, keeping its own height energy. The really best is when you succeed in a very long flight, with constant height of 3 or 4m! The way to throw it has changed, too : between LD throw and aussie throw, very horizontally, and a bit more powerfull."
"So, you can get a high performance boom, using a simple shape and just
ordinary plywood...and some luck!"
Renan's Simple Bois plan that he describes above.
After hearing Renan's story, I believe that other boom makers may be using turbs without having considered the concept. The famous Bob Burwell of Australia decorates his wood rangs with engraved snake scales. I've wondered if Bob's snake engravings were intended as turbs and if he saw an improvement in his rangs' performance after applying them. Bob's reply:
"Turbulators. I have not been familiar with that word or meaning. I have heard the word in passing but have never made friends. For many years I have aimed at improving boomerang flight performance. Now I have a better understanding of the meaning, I realize that my efforts to modify airflow in relation to boomerang wing modification. Yes I have been using turbulators for some time.
In 1981 when the first USBA tour of Australia happened we discussed the application of wing surface modification. We tried to imagine what changes may result. Two obvious common practices were in the forefront of the discussions.
1. Dimples on golf balls.
2. Longitudinal grooves in traditional Australian Hunting style boomerangs.
I have tried to implement dimples by using a countersink bit to distribute dimples on the wing surface. I also tried longitudinal grooves. There may have been a resultant change in flight performance but I did not see it. Certainly not enough for me to see it as worth the effort.
I have seen a small improvement with flight stability after adding two scored grooves near the centre of the wing chord. Scored about, 1/3 length from the wingtip towards the elbow. I have never incorporated it in manufactured boomerangs for sale. Buyers would be asking for a discount because of the scratch marks.
I have two current ways of decorating boomerangs. I burn small indentations to give the boomerang that snake like appearance. I also dot decorate along the transition point of the leading and trailing edge of the wing surface. I use small blobs of turps based paint to leave
the effect of small mounds that may also act as turbulators.
Bob and Cecil Burwell engraved boomerangs
Alas I am but a simple man and have done no structured testing to be able to express a definitive change resulting from the application of those turbulators. My measure is pleasure. When I implement a change, if it results in giving me pleasure it stays as part of the manufacturing process.
I figure the most successful application I have seen to cause a successful wind flow disruption that causes me pleasure is with the application of rubber bands. They are most effective as their application causes no permanent change to the boomerang."
- Bob Burwell
Interesting comments indeed from Mr. Burwell. Bob is one of the world's greatest makers and throwers and his response further supports the evidence that he has seen and done it all in the boomerang world. Anyone who's had the pleasure of throwing one of Bob's rangs and experiencing its flight knows of his profound talent as a boomerang craftsman. At the same time, Bob's word on rubber bands raises the question as to what distinguishes a turbulator modification from a standard boomerang modification. Though all flight altering adjustments alter airflow turbulence in some way, in most cases turbulators are characterized by qualities specific to turbulator mechanics. Many and most devices increase drag in some way while retarding the wind's force against a flying rang. A turb device diverts airflow in a manner less disruptive to the differing forces of projectile vs. airflow. Georgi Dimanchev's answer to this question is as follows. "All devices used for greater wind resistance like holes, flaps, ribbons etc. are not typical turbulators with respect to the original meaning of this word. They are more accurately considered vortex generators. The effect of these vortexes could be advantageous. Dimples, grooves, engravings etc. with a depth of 0.5 to 1.0 mm are closer to classic turbulators. All my competition boomerangs (2 and 3-bladers) have row surfaces and edged and row LE."
My Own Methods:
As I mentioned, I began experimenting with turbs after reading a very small reporting about them in MHR. Following the given suggestions, I applied small v-shaped cuts to the upper surface of the boom. Not just on the leading edge but in rows all about the upper surface of the wings. Staggering the v-cuts within the rows resulted in minimized drag, while lining them up straight behind one another gave an increased force of drag. I would burn in the little Vs with an electric woodburning tool, as Renan prefers to use. The specific turb formations proved to be quite effective, but it took a long time to complete a full arrangement of these little turbs.
The two types of turb engravings I've used the most on my rangs
Eventually, through experimentation and a desire to incorporate the turbs into the decor of my booms, I got the idea to cut angular lines instead of individual V-cuts, creating a field of diamond shaped etchings, all connected with each other. Conversely, I've used a checkerboard pattern for increasing drag. It's much faster to cut a series of straight lines with a mini diamond cutting disc than it is to burn or carve them in individually. To me, the individual V shaped brandings seem to be considerably more effective than the other, but the diamond pattern works also. I usually put these cuts in a patch about 3 inches or so along the outer middle part of the wing, covering the width (or cord) of its upper surface. Results aren't as dramatic as turbing the entire upper wing surface but there is a more stable flight. Most people who see or throw my boomerangs won't recognize the art to be a performance enhancing device and I don't know why but I kind of like that. I've also found that a mini diamond cutting disc will do a fast job of cutting the lines whereas the standard mini cutting discs are not up to the task. I use a Dremel type rotary tool and I recently bought a flex shaft for it which makes a straight vertical cut easier to do.
What I've noticed about turbed boomerangs is that they fly farther and more swiftly than they did before I applied the turbs. They return more obediently but with less end hover, descending more quickly and less prone to wander. It seems that as long as they're moving along their path, they're buoyant and swift. But once they "put on the breaks" they're done. I happen to enjoy a little bit of end hover, but it doesn't stop me from using turbs. I prefer the overall behavior of turbed boomerangs.
Here are a few other comments people have made about turbs...
[Rusty Harding:]
What I saw used for turbulators with model RC sailplanes was 1/16 inch wide, .006 inch thick, black draftsmans tape. As a suggested start for those wanting to try this on booms, I'd use 1/32 wide tape, .006 inch thick, and put it at 20% chord with a reasonably well carved airfoil (not my semi-crude airfoil), and with the semi-crude airfoils, on the 45 degree leading edge, right where the aft edge of the tape touches the flat wing top. I'd also put it only on the outward 30% of the wing tips. Just a suggested starting point, and available
material.
Rusty.
3-27-02
Turbulators can be anything from machined or cut in grooves or dimples to tapes, straight or zig zag, stickers, sandpaper, strips of Velcro, beads of glue, textured sprayed paints, etc. My personal experience with turbulators on boomerangs is small, and the results and recommendations, inconclusive!
I have flown sailplanes with one to seven turbulating tape strips added to the leading part of the wings from tips to fuselage. All of these tapes were straight (ie. not zig zag), and all improved performance by decreasing sink rates up to 15%. Placement and number of strips was
critical, with five strips, the third strip on the 22% chord line and the others spaced in 5% increments fore and aft of that one.
In the Experimental Aircraft Association, one powered single engine airplane had a zig zag pattern turbulator located at the 15% chord line on the BOTTOM half of the wing. It added 16 MPH at the same throttle setting. On another airplane, turbulator strips (three) added to the outer 30% of the propeller blade span of both blades, I don't know chord position, added 5 MPH at the same RPM while dropping propeller noise a significant 63 DB! RC sailplane pilots I know claim a 10% reduction in sink rate with one 1/8 inch wide, .008 thick strip of automotive pin stripping tape. Now, all of you know as much about turbulators as I do.
Rusty
3-28-02
[John Cross:]
Did anyone notice the speed skaters at the olympics? They (the canadians anyways) had turbs built into their uniforms. They experimented with many different types including dots (like golf balls), little Vs, little ribs and a few others they didn't specify. They settled on the ribs. They said it was subtle but they felt they saw a significant lowering of drag. At their level, gaining even half a second over the course of a two minute race is pretty significant. They even addmitted the effect could have been psychosomatic but at that level, even thinking you have an edge is an edge. The turbs on their uniforms were about as high and as long as the ones I've seen used on booms. They were a bit narrower and were spaced about 1-2 cm apart.
John Cross Calgary
3-28-02
[Pierre Kutek on a method of Georgi's:]
Georgi has several methods to test the turbs (he has an access to a "real" wind tunnel , but knows xfoils too) , and he has a funny "system" to show him how the air "works" on the boomerang , before and after the placement of the turbs ... He puts quickly and as accuratly as he can glue (high speed glue!) on all the leading edges , and then ..he throws the MTA ! when the MTA is down , he quickly puts water on the boomerang, so he can see the movements of the glue .. then , he can place the turbs ! (don't forget Georgi is an aerodynamical specialist + aeronautical engineer , he craft ULM) . Ok , this method show the work of the air on blades in the first part of the flight BUT he told me that this is the most "critical" part of the flight and the higher Re (reynolds number) . You can try this method not with glue but with "high viscosity " paint too (non destructive testing :-)).
About the Reynolds numbers (Re), he said that the Re's range is not "planes" Re but "low scale" planes ("models") Re. That's why he believes that MTAs don't need a planes airfoil, but other specific airfoils because of the much lower Re. If you read German, I got a verrry complete and accurate article from Georgi on this topic (be carefull , 19 pages in German "technological language").
Best from Marseille !
Pierre K.
Okay, now you know as much about boomerang turbulators as just about any of us. Don't you want to get in your shops and boom fields and give it a try? Go ahead. Try it! You'll be amazed by the results :) .
John V.
