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BAGGRESSiVE forum  |  Long Distance  |  General ld Discussion  |  Topic: Easy to build easy to throw?
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rikbeter
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« on: Jul 08, 2009, 08:22 »

Hi

I am new to LD boomerangs, but have some experience with conventional booms.
I live in the Netherlands and happen to work at the national aerospace laboratory. So i have some knowledge about airfoils and reducing drag around me. I hope to share some information with you in the near future about this.
But first i have to get familiar with LD boomerangs. I would like to make an easy to build and to throw model. I have 3 mm pertinax available.
What can you advise me to start with?

Paul Admiraal
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laurent
141 m
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« Reply #1 on: Jul 08, 2009, 18:19 »

hello

LD booms are not easy to build by definition, but with 3mm you can try a 90% reduced "voyager" with simple airfoils (simple = you must work with care and accuracy BUT not too sharp. Sharp airfoils are most of the time disappointing. Build symetrical but just rounded airfoils). Don't add any lead at the beginning. I guarantee you will have an easy boomerang in order to try and discover the long distance flights.

If you have ideas abount redducing drag you are very welcome.  Wink
The problem is always the same: a boom is a small spinning object, not an airplane wing. I think most people want to have wing inspired airfoils, which is maybe not relevant for our boomerangs.

laurent
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rikbeter
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« Reply #2 on: Jul 09, 2009, 02:45 »

Thank you for your response. I will try the voyager 90%.
I agree with you on round trailing and leading edges. When the wing is at 12 o'clock, the leading edge is the leading edge, but at 6 o'clock, the trailing edge becomes the leading edge. and sharp leading edges are bad news for airflow. This might even cause the noise as discussed in the discussion about airfoils. Sharp leading edges are only used on supersonic airplanes.

In order to say something about reducing drag i need some parameters such as:
Throwing speed [m/s]
Rotational speed [Hz]
Wing span [m]
Wing chord [m]
Wing thickness [m]

I already made some calculations in a spreadsheet which calculated the lift, drag, relative airspeed and Reynolds number over the wing span, but only guessed (and with my experience with LD boomerangs these guesses might be very wrong) the above parameters. So input is needed.

Paul
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laurent
141 m
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« Reply #3 on: Jul 09, 2009, 07:36 »

Hi,

As a good starting point you could try:

Chord: 0.03 to 0.045m  (depending on design, size and part of the boom)
thickness: 0.0025 to 0.003m
Speed: say 150km/h at launch = approx. 40m/s
rotation: 10 to 20 rpm = approx 0.15 to 0.3 Hz

Of course speeds depend on the thrower ability but let try this.

Laurent
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rikbeter
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« Reply #4 on: Jul 09, 2009, 08:10 »

0.3 Hz? one rotation every 3 seconds?  Huh That seems very slow to me.
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b_der_k_te
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« Reply #5 on: Jul 09, 2009, 08:20 »

Im sure he wanted to write 10-20 rps. (600-1200 rpm)
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laurent
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« Reply #6 on: Jul 09, 2009, 08:35 »

Yes, sorry. 10-20 rotations per second.

laurent
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Tibor
136 m
BAGGRESSiVE
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« Reply #7 on: Jul 09, 2009, 13:06 »

We have done measurements for different throwers last summer on release speeds (unfortunatly Manuel was not available)
Rotation was almost always the same for all throwers, close to 15 Hz
Translation velocity did vary from 80 - 120 km/h

These are real measurements using a high shutter speed camera.

Paul, please consider buying the ld book to get a good idea of what is required to get successful ld throwing.
Most 'good' ld booms have quite sharp leading and trailing edges!
Once you read the ld book, try to get to physically meet ld boom throwers and see what they do and how the booms fly. This will give you the needed inputs to be successful.

my two Credits, Canadian Smiley
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hakkapeliitta
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« Reply #8 on: Jul 10, 2009, 15:50 »

 I suggest LDPR, but 3mm paxolin is very weak if the boomerang lands badly. My 2 friends had a very little experience on booms but they did over 100m with 3mm gfec LDPR(so actually LDGFECR)
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rikbeter
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« Reply #9 on: Jul 11, 2009, 05:48 »

I have already drawn on my raw material:
3 voyagers, 2 miniathlons (which are easy to throw as mentioned on this site.)
1 tigarang, and i have designed a triblader for long distances which i have drawn 3 times. Unfortunately no more room left for the LDPR  Embarrassed. Thanks for all the tips. In a couple of weeks i will have the first results about what is easy to build and throw and i will report it in this subject. I will also experiment with carborundum turbulence strips, which i hav plenty at my work. If things work out well i will meet you next year on a LD tournament in Germany.
« Last Edit: Jul 11, 2009, 07:39 by rikbeter » Logged

laurent
141 m
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« Reply #10 on: Jul 12, 2009, 06:17 »

I suggest LDPR, but 3mm paxolin is very weak if the boomerang lands badly. My 2 friends had a very little experience on booms but they did over 100m with 3mm gfec LDPR(so actually LDGFECR)

I began long distance with 3mm paxolin and I did not break so much booms. It is not too weak for small boomerangs, like the 90% Voyager I suggested.

By the way I threw 130m with such a boomerang and relatively round airfoil (quite "elliptical "airfoil, I would say)... Not bad compared to my carbon ar glassfiber booms.
Without lead these king of boom are very easy to throw and can pass 100m. With more tuning work and leads they are more competitive.

I think pax is a matreial of choice for LD beginners as it is unexpensive.
It is true that the quality may be quite differentfrom a batch to another: the matreial is sometimes more elastic or breakable.

Laurent
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rikbeter
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« Reply #11 on: Aug 18, 2009, 10:23 »

Hi,

Maybe i should have called this subject : easy to build, easy to throw and easy to tune.

I think i managed to finish my first voyager, it was not very easy but not impossible too.
The problem with my piece of pax (cloth impregnated) was that it was bend in the first place. with both a (very) negative dihedral on lift and dingle arm and the elbow had a severe angle of attack. I ironed (!) the rang, which worked only temporary. So i had to take more drastic measures: after the first layer of paint i held it under warm water (80 degrees C) flow and after the tune was made i cooled it down again quickly. this seems to fix the tune. Now the rang is more or less flat, but its very difficult to determine the AOA of both wings.
I tested to throw with very little power and the rang flew out straight (same height same direction) and after some distance it bended to the right and crashed. The book calls this a screw flight. But my rang did not gain any height at all.

How can you measure very small angles of attack? Where on the rang is the reference?

I am very scared to throw 'my precious'. I will follow up the tuning advise from the book and hope things will improve soon, before my boom is lost.
Is this fear normal? How many booms get lost?

Paul
« Last Edit: Aug 18, 2009, 10:44 by rikbeter » Logged

hakkapeliitta
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« Reply #12 on: Aug 18, 2009, 13:06 »

 wow....welcome to LD-world! Grin its not easy to build and tune a good boomerang. What I have learned is that boomerang should be flat so if it is warped forget it... measuring AOA? I compare leading and trailing-edge and try to estimate it, easiest way would be if you dont shape the bottom of your rang at all or at least not the trailing-edge.
- Voyager is not easy boomerang to tune, I guess you have too much lift in arm2 and too less in arm1...
I havent lost many LD-rangs, but it depends how low grass you have on your field and the number of friends with you. Good luck anyway
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Conair
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« Reply #13 on: Sep 03, 2009, 04:42 »

Hi rikbeter,

I think I am currently in the same situation you are. I have some experience with standard plywood booms. I made a few well performing weighted aussie rounders that go about 70m. I also have a few wooden Big Al hooks that work nicely for the 80-100m range.

Now I wanted to take it one step further and purchased some paxolin. Following the advice on this page I went with the Voyager shape. But my results have not been very promising (screwed up flight path, not returning).

I wanted to manufacture several booms and work my way up to a fully grown ld boom.
  • start with a standard airfoil and get a well returning boom that goes 80 -100m
  • increase the undercut on the leading and trailing edges and get a higher distance
  • put some lead in the lift arm for even more distance

This approach worked well for my plywood big al hooks. But I dont know whether I can transfer it to an advanced ld-shape (voyager, buzzwhip , etc.).

 Basically I just want to know if you can produce an advanced ld-shape with a more conservative airfoi and paxolin, or if the designs require gfc and advanced airfoils.

/Conair
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Hard Knox
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« Reply #14 on: Sep 03, 2009, 13:08 »

Hello Conair and Rikbeter,

The LD shapes such as Voyager and Buzz Whip have very forward swept wings to balance the effects from the undercuts.  The undercut foils at the tips force the boom to fly straight for some portion of the flight.  Without the undercuts the boom will turn more, but because of the forward swept wings the boom will also have a strong negative layover tendency.  So LD shapes with standard airfoils (no undercuts) will roll inward, spiral and crash.

I tuned a Voyager with standard foils using BoomSmith1.2 to see what it looks like.  See Below.

Anyway good luck!!

Andrew

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