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Old Feb 21, 2011, 01:31 AM
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Brisbane, Queensland, Australia
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4.5mtr SZD 9 Bocian- Wing rod advice please

I'm starting to organize myself to build a 1:4 scale SZD 9 Bocian 1E, which makes it about 4.5 metre wingspan, which is the largest sailplane I've built.
I need advice with the main wing rod.
It was suggested to me to use high tensile aluminium tube, as it's cheaper compared to a full length of carbon fibre rod, but the problem I see with this is the diameter and length I'd need to use (for enough strength) will be extremely large compared to the actual thickness of the wing. It won't leave much rib ply above & below the tube. I'm affraid whether the wings under load will break the ribs around the tube therefore result in complete wing failure.

If I was to use aluminium tube, can anybody suggest what diameter and length into each half of the wing I'd need for 4.5m wingspan?

Or if I was to use carbon fibre rod, what diameter and length would I need for this same wingspan?

If anybody could help with any suggestions, it would be greatly appreciated.
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Old Feb 21, 2011, 01:52 AM
Thermal Wrangler
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Launceston Tasmania
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Get in touch with Bananman; he's in Brissy I understand and has the know-how on big-scalies:

http://www.rcgroups.com/forums/member.php?u=1772

Chris.
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Old Feb 21, 2011, 08:24 AM
LSF 4685
Winchester, KY
Joined Sep 2009
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You may also consider using a smaller diameter tube with and even smaller diameter tube nested inside for strength. I am not competent enough to make strength calculations, but it seems to me that doubling the wall thickness would still save weight and might add enough strength to do the job.

Dave
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Old Feb 21, 2011, 08:54 AM
Vintage wood is the best!
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In my 1/3 scale 4.5 meter SZD-16 I have a 20" x 3/4" carbon rod and have had no problems..... You could also use a 6061 solid aluminum rod.
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Old Feb 21, 2011, 11:57 AM
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Hi there happy depending upon which approach you want to take you could quite happily use 14x2mm flat steel blades from Graupner crossed over and soldered together. Pbg composites in New Zealand make a nice range of carbon tube and sockets with both being in stock at The hobbyman in Melbourne or for round rod you could use 18mm solid glass rod from quador in Mitcham (Melbourne) but you will have to make your own sockets for the rod. As to length you only need the width of your fuselage into each wing half, any more is just adding weight formno real benefit.
Hope tuis Helps Rossco
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Old Feb 22, 2011, 07:25 PM
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Brisbane, Queensland, Australia
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Thanks guys for your suggestions.
I'm going to change the wing profile from the original plans, therefore will give me a thicker wing to work with.
It's also been suggested to me to laminate carbon fibre to the full length of the main spar, which I thought was a good idea for extra strength.
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Old Feb 23, 2011, 04:19 AM
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Quote:
Originally Posted by Big Nuts 181 View Post
As to length you only need the width of your fuselage into each wing half, any more is just adding weight formno real benefit.
Hope tuis Helps Rossco
Surely there is a more accurate formula for the required lenth of a joiner?
wouldnt it be based on more variables such as overall span,intended use and spar type etc rather than simply the "the width of your fuselage into each wing half"???
Maybe someone with some real engineering experience can chime in and offer a better solution?
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Old Feb 23, 2011, 04:32 AM
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Hasn't failed so far.

How many scale models have you desined and built again?
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Old Feb 23, 2011, 04:44 AM
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Originally Posted by Big Nuts 181 View Post
Hasn't failed so far.

How many scale models have you desined and built again?
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Old Feb 23, 2011, 03:21 PM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
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aufwind article on wing joiner engineering

Latest Dec. edition of Aufwind (apparently because my copy is yet to arrive) has an article on just that; engineering a joiner:

"The wing joiner system of a glider, the mysterious beast? Tobias Pfaff illuminates the dark secrets of calculations, lay-out, design, and sizing."



Chris.
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Old Feb 23, 2011, 03:40 PM
dare to thermal
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Joined May 2004
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Itīs in german, but worth reading:

http://wiki.rg.htmldesign.de/images/...t%C3%A4ben.pdf

What you need to know is the weight of the fuselage and the g-load.

fast sailplane (n = 12g); fuselage weight 3.7kg (app. 7lb) -> 20mm diameter carbon rod.
fast sailplane (n = 12g); fuselage weight 6.1kg (app. 12lb) -> 24mm diameter carbon rod.

With a steel rod i would use at least 16mm diameter.

Lenghth of the rod = width of the fuselage + (10% to 15% span)

Bernd
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Old Feb 23, 2011, 07:23 PM
Thermal Wrangler
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Launceston Tasmania
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Great find Bernd!
Just out of interest I ran the PDF through Google Translate and it worked! or at least it translated all the copy but removed the arwork.

Chris.
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Old Feb 23, 2011, 08:19 PM
Windburner Factory Pilot
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Quote:
Originally Posted by DrFragnasty View Post
Latest Dec. edition of Aufwind (apparently because my copy is yet to arrive) has an article on just that; engineering a joiner:

"The wing joiner system of a glider, the mysterious beast? Tobias Pfaff illuminates the dark secrets of calculations, lay-out, design, and sizing."



Chris.
Thanks for the heads up Chris.I am planning a project later in the year and are looking for some engineering tips to properly calculate and engineer the joiner system for a large scale model that will be used for high speed aerobatics and need it done right....cheers.
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Old Feb 24, 2011, 12:16 AM
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Brisbane, Queensland, Australia
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Quote:
Originally Posted by DrFragnasty View Post
Latest Dec. edition of Aufwind (apparently because my copy is yet to arrive) has an article on just that; engineering a joiner:

"The wing joiner system of a glider, the mysterious beast? Tobias Pfaff illuminates the dark secrets of calculations, lay-out, design, and sizing."



Chris.
Hi Chris,
Where do you normally get the Aufwind mag from? I can't find it in Brisbane. I noticed on the web you can subscibe for it, but at this point in time would like to get the December edition only. Maybe later subscribe.
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Old Feb 24, 2011, 03:28 AM
Thermal Wrangler
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Launceston Tasmania
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get a local to loan you a copy

Hi,

For single editions put the word out and "borrow" a copy from somebody local. You'll find the cost to get a single one and the shipping hassles isn't worth it.

Subscriptions are well worth 67 euro = AUD$95 for 6 editions sounds expensive but like any quality product you pay it. The articles,advertising (although the ads are in German) and photography is for me, worth it.

You can't get it through any local distributor, subs only from Aufwind.

Chris.
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