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Old Jan 25, 2013, 02:27 PM
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Holland
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Steve,

When you look at the construction of the original wing panel you can see it's made out of puzzle parts, all clicked together. The long thin walled aluminium tube hidden in the D-box probably hasn't any structural purpuse but was used for alligning the ribs during the build and letting the glue set. The new rear aluminium rear tube is just a simple addition in order to make the wing seem more rigid.

When I get to reinforcing my replacement wing panels with carbon tow I will make some pictures describing the process
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Old Jan 25, 2013, 03:05 PM
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Foam

What would foaming dtube and main tube to spar webbing do. there is a1/4 inch gap between rear wing tube and new aluminum tube! would spar made from good pine as in yard sticks laminated and then slid in place and then fill gap betweem main spar and webbing. would this stiffen and transfer loads to wing tube a little better?
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Old Jan 25, 2013, 04:07 PM
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To fill the tube with carbon tow, cut carbon tow about 2.2X of the length of the tube. Fold them in the mid point and tie a pull string at the mid point, pull the bundle thru the tube, keep trying and add more tow until you are happy with the amount. Remember, the epoxy will take up some space.

Then lay the carbon on the work bench, lined with butcher paper or something. Use the same weight of epoxy as the weight of the bundle of carbon tow. Pour the mixed epoxy onto the bundle and work it with your gloved hands to get all the tow wet. Get some one to hold the tube while you pull the bundle thru with the pull string (or rope). Cut off the tow on both end and let it cures.

It is messy, best to cover the outside of the tube with masking tape. Make sure the inlet end is smooth.

Good luck,

Brian, an EAJ
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Old Jan 25, 2013, 08:16 PM
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Quote:
Originally Posted by bhchan View Post
To fill the tube with carbon tow, cut carbon tow about 2.2X of the length of the tube. Fold them in the mid point and tie a pull string at the mid point, pull the bundle thru the tube, keep trying and add more tow until you are happy with the amount. Remember, the epoxy will take up some space.

Then lay the carbon on the work bench, lined with butcher paper or something. Use the same weight of epoxy as the weight of the bundle of carbon tow. Pour the mixed epoxy onto the bundle and work it with your gloved hands to get all the tow wet. Get some one to hold the tube while you pull the bundle thru with the pull string (or rope). Cut off the tow on both end and let it cures.

It is messy, best to cover the outside of the tube with masking tape. Make sure the inlet end is smooth.

Good luck,

Brian, an EAJ
I understand all that........that's the easy part....the hard part is how do you do all that with the tube hidden behind the D-tube sheeting without buggering up the sheeting and making a general mess of the wings?
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Old Jan 25, 2013, 10:13 PM
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Bottom spoiler location

Hey guys, I plan to add bottom spoilers. The top spoiler box is located about 3/4 inch behind the D-box sheeting & spar webs, leaving a 3/4" space between d-box sheeting & spoiler box. When mounting the bottom spoiler/box, would it be OK to put it right behind the d-box, glued to the web, without having the 3/4" space? This would place the bottom spoiler about 3/4" ahead, or forward, of the top one. It seems it would be stronger, and easier to install. The top one should probably also be reinforced to the webs, instead of just floating in the rib notches. Thanks, Bob.
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Old Jan 26, 2013, 04:52 AM
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Quote:
Originally Posted by SZD16 View Post
I understand all that........that's the easy part....the hard part is how do you do all that with the tube hidden behind the D-tube sheeting without buggering up the sheeting and making a general mess of the wings?
How big are the ali tubes again? That could be an awful lot of carbon and resin and there might be a risk of thermal runaway once the exothermic reaction starts. I agree with SZD - sounds rather tricky to me!....

Plus the carbon might cost more than the plane did!.....

Edit: I just read back and I guess the tubes are 18mm, so is probably OK from a cost and heat viewpoint. I just had a bunch of resin go "thermal" on me and it is quite exciting!

Simon
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Last edited by swarrans; Jan 26, 2013 at 04:55 AM. Reason: Read the forum!
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Old Jan 26, 2013, 04:06 PM
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Holland
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As I was preparing my new replacement wing panels for reinforcing I just made a nice discovery.

I was making the hole up front in the root rib in order to prepare the hidden aluminium tube inside the D-box for filling up with carbon tow. To my surprise I found that the original thin walled 18 mm Aluminium tube, to be found in the first series wing panels, has been replaced by an 32 mm aluminium tube. This is exactly the same size and quality tube as is used for the joiners. This tube starts in front of the second rib and ends 141.4 cm measured from the root rib.

Needless to say that with this my trust in the rigidity of the new wing panels has increased dramatically.

At this moment I'm considering to just glue in a vertical piece of wood plate in this front tube, starting in the root rib and running over the full length. This inceases the strength under bending loads considerably. The shorter 18 mm rear aluminium tube could be filled up with round stock, also starting at the root.

The center of the front tube at the root rib is situated 85 mm from the leading edge and exactly in the middle height wise.
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Old Jan 26, 2013, 05:19 PM
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Sounds great, Harm. Would greatly appreciate photos as you make progress.

Regards,

Steve
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Old Jan 27, 2013, 12:41 AM
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As long as the tube stayed round, it is strong. All you have to do is to insert a vertical shear web into the tube, can be balsa or pine. Something in the tube to keep it from changing it shape to not being round.

Brian, an EAJ
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Old Jan 31, 2013, 11:30 AM
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Wing upgrade pictures

Guys, I noticed on the RCNetwork.de site, p.109, reply #1630, grhe, Austria has posted some pretty good pictures showing the replacement wing upgrades. He peeled back the bottom covering. The pictures show the same web cutouts, and the 32mmx141mm tube added in the d-box. It also notes the alum. tube is only glued intermitently in holes in the ribs, with no extra reinforcement. Google translate didn't work on the picture captions, but the pictures do show most of the wing structure from the bottom. Bob
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Old Feb 04, 2013, 06:59 AM
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Hi,
I am the Austrian K8-owner, who opened the new wing. Bob has noticed that Google translate didn´t work on the picture captions, therefore I add the photos with some English explanations.
New wing – bottom peeled
you look from the root rib to the outside
Serial-number maybe 0001 ???

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You see a thin al-tube (diameter 19,13mm) reaching from rib 2 to rib 11, this is about the middle oft he airbrake.

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Between the main spar and the leading edge is a new al tube (diameter 32mm) beginning at rib 2 and ending at rib 16 = 141cm from root rib. The bonding of this tube is only spotty (hope this is the correct word)

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I try to reinforce this al tube with a vertical shear web (as Brian has recommended). At the picture you see the position oft he tube and the shear web in relation to the root rib.


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Maybe I will fix it carefully with PU foam, but I´m not shure about that.

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Greetings from Austria
Heinz
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Last edited by grhe; Feb 04, 2013 at 07:02 AM. Reason: wrong word
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Old Feb 04, 2013, 07:10 AM
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Hi Heinz,

Welcome to RC Groups and thanks very much for your ideas on strengthening the inner panels. Is this model popular in Austria and have you heard of any wing failures from Austrian pilots?

TIA,

Steve
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Old Feb 04, 2013, 09:35 AM
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Austria, OÖ, Altmünster
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Hi Steve,

I read your and the German RC-network site as you do, but just since a few weeks ago I heard of some Austrian pilots discussing the K8b. Maybe this is due to that the plane is available only at one or two dealers nearby. For this reason some of us just start building at this winter and do not have any flight experience and the others maybe do not have K8´s of the first edition with the fragile wings.

Heinz
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Old Feb 04, 2013, 09:57 AM
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Thanks Heinz. How did injecting foam into the aluminum tube work out. Do you think it added additional strength?

Steve
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Old Feb 04, 2013, 02:20 PM
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Holland
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I have been busy this weekend too reinforcing my new wing panels.

I made a sheer web from pine 7 x 30 mm which fills up the front hidden aluminium tube. It runs the whole length of the panel from the root rib till the end rib. In order to do this I made an opening in the end rib and filed out the oval holes in the last three ribs on order to let the shear web pass. I glued all with a copious amount of Larit, a very viscous type high quality epoxy.

Furthermore I fitted an 950 mm long and 18 mm diameter pine stick in the shorter rear aluminium tube. This stick starts at the root rib, I haven't glued it in yet.

I haven't done any other strengthening because I don't want to open the wing removing the covering. All the reinforcing has been done from the external, taking little costs and time.

The strength of the wing should be tremendously increased this way. One thing I will do is filling up the hollow carbon wing tip joiner tubes with carbon tow. These two joiners look puny now compared to the rest of the wing.

I also cut out the 500 mm long air brakes from my first set of wings and fitted them in the new wing. The upper metal is flush with the wing surface and will be masked with a good quality white tape. By putting red tape on the moving part you hardly will notice the white tape.
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