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Old Aug 29, 2008, 10:05 PM
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Enrique K.'s Avatar
Montevideo, Uruguay
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Large aerobatic foamie - Chimango II

Hello.

After building a Le Fish look-alike and being very happy with it, I started to think in developing a larger version of it. A friend of mine argues: "Anything over 100 inches flies much better!" I was also impressed by the Toons from France's Aeromod.

Basic specs are: 3 meter span (118 inches), 88 square dm (1360 square in.), fuse length 170 cm (67 in.).

Initially, I was planning to make a proper build, with fiberglass finish, all RC gear buried inside, etc. After cutting the fuselage I realized this build would be quite an effort, and unfortunately I do not have much time for that. More doubts crept in as I thought that maybe the design needed improvements and, furthermore, the place I usually fly in might not be appropriate for this kind of sailplane -I fly on the beach of Montevideo, my hometown, using the tall buildings as a "slope".

So now I am thinking of making the sailplane as a test-of-concept but with "foamie technology". But I cannot completely duplicate this technology here in Uruguay because we have no EPP -just EPS-, no gorilla glue and carbon rods are almost impossible to get.

Where I am not clear is how to obtain an adequate structure using aluminum rods/tubes and tape covering -which are available here- to obtain sufficient strength to withstand flight loads and normal landings -landing on the beach is extremely friendly!

My main concern now is how to make the fuselage with enough strength. I am thinking of inserting an aluminum rod inside it, placing the elevator and rudder servos in the rear and the receiver in a hole carved between the two wing roots.

What do you think of this? Any suggestions?
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Old Aug 29, 2008, 11:28 PM
FSD
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Wow...I think I have fuselage envy.

-P
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Old Aug 29, 2008, 11:33 PM
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Joined Feb 2003
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I have nothing helpful to add re: build techniques, but I have to say I'm totally stoked to see such a huge piscine creature in... Uruguay! Awesomeness

If in doubt, my maxim: "Just say #### it and chuck it!"

Steve
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Old Aug 30, 2008, 12:15 AM
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Can you get carbon golf club shafts?

Mark
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Old Aug 30, 2008, 09:24 AM
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Enrique K.'s Avatar
Montevideo, Uruguay
Joined Apr 2006
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Quote:
Originally Posted by markktm
Can you get carbon golf club shafts?

Mark
This is something I had not thought about. I will check. Thanks! I had looked at arrow shafts, but these are too short.

Surfimp: the Le Fish influence is very far reaching!

Will keep you posted.


Enrique
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Old Aug 30, 2008, 10:18 AM
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A man after my own heart: going beeeeg ! Good luck with the project, hope it works well!
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Old Aug 30, 2008, 06:17 PM
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Montevideo, Uruguay
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When looked at obliquely and against sunlight, it was easy to see the sanding on the fuse was pretty poor. I then prepared a longer and wider sanding block than my standard one -as long as the longest sandpaper I had available- and headed for the Montevideo coast (understandably, my wife had raised hell with the thousand little pellets I had produced in the initial sanding!). It worked like a charm.

The complete fuselage -including the rudder- is too long to fit in my car. So I am developing a removable fin-and-rudder assembly. I am now working on the insertion device -for lack of better words- of this assembly onto the fuselage. It consists of a rail made essentially of telephone cards (I love this material!) that will accept an "I" shaped aluminum spar. The whole system is not completely finalized in my mind but I believe it will finally work out OK.

I went to the golf club to check if they had any carbon shafts. They don't. But maybe I can find an adequate shaft in a fishing shop. I will tackle this next week.
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Old Aug 30, 2008, 07:00 PM
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Montevideo, Uruguay
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Some additional details

* The EPS is 30 kg/cu.mt. -or 1.87 lb/cu.ft.

* Wing span is 300 cmts. (118 inches)

* Root chord is 37.5 cmts. (15 inches), tip chord is 20 cmts. (8 inches)

* Wing area (without fuselage) 86.25 sq.dm. (9.28 sq.ft)

* I am aiming at an all up weight of max. 3,5 kgs. (123 ounces) for a maximum wing loading of some 40 grs./sq.dm. (13 ounces/sq.ft). I hope my calculations are OK.

* The planned airfoil is TP 66 - TP66S by Thierry Platon. Maybe Thierry is around and may comment on my choice!
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Old Aug 30, 2008, 08:38 PM
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Adelaide, Australia
Joined Jan 2008
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If you're using white foam, tape and stuff and not planning on hard landings, why not just use square dowel or some other wood instead of CF for spars and stringers? Its worked well for the last 50 years. Fishing rods are tapered, with different flex qualities from one end to the other. Good luck with it, looking forwrd to seeing it in the sky!
Cheers, simon
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Old Sep 07, 2008, 09:50 AM
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Montevideo, Uruguay
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The fin-and-rudder insertion device is now finished. First, I took some weight-reduction measures. The initial piece weighed 45 grams (one-and-a-half ounces); after shaping it and taking the cardboard backing away it came down to 25 grams (less than an ounce.) I feel now comfortable with this device, I believe it will withstand not only the flight and landing loads but also the repeated placing and removing of the fin-and-rudder assembly.

In order to make this insertion device practical, I have decided to hinge the rudder on one side with silicone and use a single pushrod from a servo in the fuselage placed under the stab.

Here are some pictures.
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Old Sep 12, 2008, 05:21 PM
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Montevideo, Uruguay
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I am travelling for a couple of weeks to Germany for a teaching stint, so I will not be able to get to the building board.

To take advantage of this time, can anybody out there recommend servos for elevator, rudder, ailerons and flaps? I fly Futaba/Hitec.
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Old Sep 12, 2008, 06:20 PM
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Pacific Palisades, CA
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I would think some large, cheap standard servos would be fine. The 425 comes to mind. Run it off a 6 volt battery and you should have plenty of torque.
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Old Sep 13, 2008, 12:48 AM
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I 2nd the golf shaft call, I got a whole heap from my local golf shop for free (broken ones they couldn't repair) and the salesman promised to put some aside for me when they came in. Don't expect to get anything too exciting, but they work great as you can bury a brass sleeve in them for the wingrod joiner. Would probably work well for a fuse longeron too.

Neat idea on the removable rudder!!
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Old Sep 13, 2008, 02:25 PM
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Montevideo, Uruguay
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Thanks Flyonline! Looks very powerful.

I plan to put both the rudder and elevator servos in the tail close to the control surfaces. Isnīt 45 grams -about an ounce and a half- too much in these conditions?

Thanks!
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Old Sep 20, 2008, 02:10 PM
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Montevideo, Uruguay
Joined Apr 2006
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I took advantage of being in Germany to buy some goodies for the Chimango II.

I bought six Dymond D 300 MG servos, which seem to be very powerful and small size. Not only do they have metal gears but also ball bearings. To sweeten the deal, Staufenbiel -www.modellhobby.de- offers them at Euros 16,90 -some $ 24,50. Here are its specifications:

28 x 29,8 x 14mm, 28g, 54 Ncm, 0,17 sec to 60°, all at 4,8V. It can also be operated at 6,0V, but no data are provided in Staufenbiel's website.

I checked the German modelling forums for some comments by modellers -almost all of them praised the servo.

Bought also a 2400 mAh five-element Sanyo battery and other small stuff.

And also looked for carbon tubes. I finally decided to go all the way and cover the Chimango with fiberglass -the traditional way I finish all my foam-cored sailplanes. It will take more time but I will have more pleasure with the finished plane. So no carbon tubes for the fuselage. Neither for wing spars. I found some tapering tubes for this last purpose - http://www.carbon-vertrieb.com/pdf/15_pdf_preise.pdf- but then decided against them because I would have trouble putting them into my luggage and -more importantly- I was not sure I would be able to cut the passages adequately in the wing cores. I will most probably make the spars in aluminum. Nevertheless, I also bought some carbon rovings just in case.
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