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Old Sep 14, 2012, 08:24 AM
Vintage wood is the best!
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Originally Posted by DanJudson View Post
HMM. A lot of creative thinking going on here. But after reading I have some questions. I read things like "high speed" and "6 g loads" Isn't this a vintage ship designed for low speed and more like 3-4 g loads? And if you need to pull 4 g's to do a loop, by inference there are many examples already doing that all over the world. Might not the one that broke be the exception? An MDM Fox with two up is only rated at +7 and -5.
I think one has to put this in perspective, this is an under engineered product offered a a ridiculously low price considering the shipping costs added to the airframe costs. I think your putting a silver dollar fix on a nickel plane, but none the less its interesting reading, and its nice to see so much interest in helping with a solution.
How do you plan to fix yours? New big wood spar, smaller carbon tow spar, or the carbon tube approach?
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Old Sep 14, 2012, 08:30 AM
Vintage wood is the best!
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Originally Posted by AllanK1 View Post

Tom can you measure up this tube in the broken wing?

Allan
Damn....you are bad with names...
My plane is still in one piece....Pat is the one with the broken up plane.

As far as design goes.....this airframe will never be a Fox but it does need to do loops and rolls and survive the occasional "oh crap brain fart momment".
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Old Sep 14, 2012, 11:26 AM
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Quote:
Originally Posted by DanJudson View Post
HMM. A lot of creative thinking going on here. But after reading I have some questions. I read things like "high speed" and "6 g loads" Isn't this a vintage ship designed for low speed and more like 3-4 g loads? And if you need to pull 4 g's to do a loop, by inference there are many examples already doing that all over the world. Might not the one that broke be the exception? An MDM Fox with two up is only rated at +7 and -5.
I think one has to put this in perspective, this is an under engineered product offered a a ridiculously low price considering the shipping costs added to the airframe costs. I think your putting a silver dollar fix on a nickel plane, but none the less its interesting reading, and its nice to see so much interest in helping with a solution.
You are absolutely right, but remember: earlier on some people were complaining that this glider couldn't take any abuse... Of course this is up to each individual to quantify what "abuse" they expect their glider to handle.

To compare full scale with large models is not right as when flying remotely you don't have the "feel". Believe me it is very easy to put over 4G's on a large model glider as soon as you fly far away and overhead... If you are a seasoned smooth pilot and fly in relative smooth conditions you might enjoy the K8 for a long time. Until something happen and you do an over correction at too high of a speed. Or simply you get in a fairly unstable air mass and get strong thermals with good shear, misjudge the rate of turn and pull a bit too harshly...

Luckily this specific glider has a lot of area and is on the (very) light side. So what you might lose in performances is compensated by the fact that the loads are pretty low. Unfortunately the structure is not exactly sound and the probability of having a structural failure could be considered as too high. This is each individual choice to assess the problem and decide what to do. One thing is for sure: if an accident happen and someone gets hurt (at best) what the outcome will be for everyone involved with large glider flying?

BTW: a full scale glider rated to +7 -4 will withstand a higher load before structural failure and ultimately catastrophic failure.
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Old Sep 14, 2012, 09:29 PM
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Originally Posted by fnev View Post
You are absolutely right, but remember: earlier on some people were complaining that this glider couldn't take any abuse... Of course this is up to each individual to quantify what "abuse" they expect their glider to handle.
Forums tend to amplify practical considerations sometimes, There seems to have developed a lynch mob lets get em mentality , Obviously the one that broke was an exception, at least if we believe the poster, who knows maybe there was undetected shipping damage, we can't say, perhaps the wing rod was improperly inserted, not maligning the guy, but there are several plausible explanations. Your observations are well thought out and obviously you understand the technical considerations.

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Originally Posted by fnev View Post
To compare full scale with large models is not right as when flying remotely you don't have the "feel". Believe me it is very easy to put over 4G's on a large model glider as soon as you fly far away and overhead...
That's very true, and Yes 4 g's is a reasonable figure for safety, apparently most of these have experienced 4g's and survived while looping. But 6 plus g's As mentioned somewhere is a little extreme to expect for a vintage glider, There is a reasonable limit in all things. Fly it like the full scale prototype, not a Fox.

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Originally Posted by fnev View Post
Luckily this specific glider has a lot of area and is on the (very) light side. So what you might lose in performances is compensated by the fact that the loads are pretty low.
Exactly the point. These large floaters, are so lightly loaded they shouldn't be compared to full scale examples. It is why modelers can get away with unscale like maneuvers with Models. If flown in a scale fashion (the one defective plane notwithstanding), There should be and have been few problems with failure even with the poor wing design.

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Originally Posted by fnev View Post
BTW: a full scale glider rated to +7 -4 will withstand a higher load before structural failure and ultimately catastrophic failure.
Certainly true,But What pilot might be willing to do that sitting in the cockpit. The load factors thrown around this thread, not necessarily by you, have bordered on ridiculous for a ship this size and type.
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Old Sep 14, 2012, 10:22 PM
Vintage wood is the best!
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Dan, you still have'nt answered how you plan to fix yours? Have you opened it up and actully looked at the ply used for the spar caps? Have you looked at the junction between the joiner and the existing spar structure? How about the way he tip joiners are attached?
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Old Sep 14, 2012, 10:58 PM
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You better support bottom of spoiler box also, and sides
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Old Sep 14, 2012, 11:05 PM
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It can be done with stripping wings if you use 3/8 x1 1/2 blsa,and must trim one slot for clearance to ribs, by using thread to pull into position and thread to pull up to bottom of existing ribs below spoiler box bottom, than add spacers, and then final bedding and clearance with silicone, with release agent or wrap to prevent poiler sticking, thenuse 3 or more screws provide in electric spoilers, on could also make spoiler tops like an Grob !03 were springs are used from top of spoiler to top of spoiler that fits flushand also provides more resistance for air flow
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Old Sep 15, 2012, 07:52 AM
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Twin towed our 6 meter KA8's today behind my mates hanger 9 Pawnee today, no problem, was pretty cool will upload video soon.
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Old Sep 15, 2012, 08:35 AM
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Rossco...pretty cool tow!

Looking at your photos, I now understand how you guys do things we can't. Living "down under", it's obvious you have a much weaker gravitational pull, hence no K8 wing failures, easy twin tows and the no worries when you carry that 6 meter beastie one-handed. Just don't jump too high when you celebrate a great flight!

Steve
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Old Sep 15, 2012, 07:16 PM
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Haha nice theory Steve. Both of our ka8's were from the first production run with that silly flappy thing on the bottom. Now neither of us have altered the tailplane incidence and there fore can't fly as fast. How fast was the aircraft flying before it broke up in flight as I have only been able to find reference to one aircraft in the world breaking up, a Friday build perhaps?
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Old Sep 15, 2012, 10:47 PM
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Shame, Shame
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Old Sep 15, 2012, 10:57 PM
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CF tube spar location with aluminum joiner location

Quote:
Originally Posted by AllanK1 View Post
Sounds great, nice solution.
The Carbon tube approach will have a square ply peice with a hole in it This glues to the ribs top anf bottom and buts up on the rear face of the existing front spar web. The tube is glued into these squares and glued to the webs along its length. It should be less disruptive to the existing structure I'm thinking.

.

Allan
I'm attaching some pictures showing the location of the existing forward 1 1/4" joiner, which is just behind the existing spar web, and a view from the outer end showing the square rib cutouts you refer to, and the "circle" showing the end of the alum. joiner. Will the cf tube be behind the existing cardboard receiver tube? If so, will a new joiner also be needed, or just stronger 1 1/4" joiners that use the existing receivers? If a new joiner and location is needed, note the pictures of the fuse joiner rod reciever fiber tubes, and how they are fixed to the fuse structure. Just thought the pictures might help in case a new joiner system, as you mentioned earlier, had to be engineered along with the spar. (hopefully not) Thanks.
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Old Sep 15, 2012, 11:10 PM
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Originally Posted by flyingfever View Post
I'm attaching some pictures showing the location of the existing forward 1 1/4" joiner, which is just behind the existing spar web, and a view from the outer end showing the square rib cutouts you refer to, and the "circle" showing the end of the alum. joiner. Will the cf tube be behind the existing cardboard receiver tube? If so, will a new joiner also be needed, or just stronger 1 1/4" joiners that use the existing receivers? If a new joiner and location is needed, note the pictures of the fuse joiner rod reciever fiber tubes, and how they are fixed to the fuse structure. Just thought the pictures might help in case a new joiner system, as you mentioned earlier, had to be engineered along with the spar. (hopefully not) Thanks.
The outer wing view picture is poor, but if you enlarge it to full screen, the "circles" on the rib mark the location of the joiner tubes location.
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Old Sep 16, 2012, 06:18 PM
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This is a scale glider...

...and as such, should be flown in that manner. That means, if the original is not intended for aerobatocs, why should you try that on a model? Just becaus there are videos on Youtube showing consecutive loops? In my opinion, this is a glider intended to thermal, which it does really well. I had my maiden flight on it yesterday, without any reinforcement, and it was really nice to hear the hight gaining sound from my variometer. In few minutes, I went from 350 meters to 420. The second trip was also very nice. I think that a lot of people tend to fly scale models on a non scale manner, often with bad results to the model. That said, I too belive that there are "lemons" amongst products, as is the case with many products.
However, I think it is unwise to fly a scale model in a none scale manner. Before buying a scale model, one should read about the full size counterpart and see what it is intended for, and capable of. And, not least, the don'ts. Besides this glider I fly a 1:3 Grunau baby (4.5 meters), a 1:3 Minimoa (5,5 meters) ASH 26 (4,5 meters) and a ASW 24 (4 meters). I try to fly them in a scale manner, and have never had structural problems with either of them.
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Old Sep 16, 2012, 06:42 PM
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My ka8 flys in a bery scale manner and does beautiful loops and stall turns in a very scale manner. Remember these were a club aircraft intended as a follow on from the ASK 13 trainer and were rated for light aerobatics..... Loops spins etc and were built to survive a winch launch as a cost effective alternative to the more expensive racing class kind of like a 1-26 Schweizer. just as many are today..... Not all though mind you.
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