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Old Jan 05, 2013, 12:01 PM
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Fotor's Avatar
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Papaalpha, could you point out where your cg is on the wing?
I have a Ka-7 with 4m span, which has the cg about 2 cm behind the LE at the wing root. The overhead view of the wing is about the same as an ASK-13, so I would suspect you should be fine with the cg about 1 cm behind the LE at the wing root (as your span is about half of mine).
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Old Jan 05, 2013, 03:46 PM
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The pic on page 9 shows the c o g with a red stripe about 1.5''/37mm behind the leading edge. To have a co g any further forward would mean so much weight in the nose as never to be able to soar let alone even glide on the slope in a light breeze which is always what I aim for and achieved with my same size Blanik and Bocian.
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Old Jan 05, 2013, 08:42 PM
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One of the humorous comments on the 1/4 scale Flair KA8 plan is something like "balance as shown, even if it takes the kitchen sink"

If the CG isn't right, it won't fly well. If it turns out heavy, it will at least fly, and fast! Just need a little more slope wind
You do what you have to do, or make it a hanger queen.

Scott
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Old Jan 05, 2013, 08:49 PM
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Exactly! Now that's the attitude. MoF, I just rebalanced my Radian again today with a whole new cockpit, pilot, landing gear with skis and recovering the fuselage with 3M packing tape. I thought for sure it was going to be nose heavy. Nope. The extra clear tape on the tail did it. Needed the battery to go more in the nose for proper CoG. Took my time got it to balance level before flying it.
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Old Jan 05, 2013, 08:52 PM
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Ok so getting back into my thread I will go on a race spec lightening spree Porsche factory style and get the ASK-13 tail feather light and strong.
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Old Jan 06, 2013, 02:47 AM
*** gravity sucks ***
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I agree with Scott. Your CG needs to be right, even if it takes more weight than you want. With a light and wrongly balanced model you will not fly at all, with a heavy but well balanced plane you can at least fly, be it faster. Sure it's better to be light, but this is something all pure gliders are dealing with. They miss the natural ballast that's present in the real planes (the fat belly of the pilot in front).
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Old Jan 06, 2013, 05:27 AM
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I want and aim for 'dream flyers' that stay up in a light/5mph breeze but also fly perfectly for slow lazy turns and spot landings and yet can cope with 15/18 mph winds.
I am only trying to save some 3ozs of lead in the nose which may add up to only one ounce needed to be saved rear of the c of g.
Always rewarding when everyone else has had no choice but to land and your scale model continues to quietly fly along the slope remaining airborne.
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Old Jan 06, 2013, 01:59 PM
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In for a penny,in for a pound so removed top fuselage planking and hacked away at fuselage formers/cross members as much as possible to try and reduce the weight rear of the c o g . Thought about doing such when building and to mention such to StudioRS but was too lazy and polite.
On checking the balance on c o g stand as per pic with no top decking , no extra weight is needed even with the lighter 4 cell battery. The thing is can I put back a lighter decking - maybe of thinner balsa and still achieve this position?
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Old Jan 06, 2013, 03:13 PM
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Quote:
Originally Posted by papaalpha View Post
In for a penny,in for a pound so removed top fuselage planking and hacked away at fuselage formers/cross members as much as possible to try and reduce the weight rear of the c o g . Thought about doing such when building and to mention such to StudioRS but was too lazy and polite.
On checking the balance on c o g stand as per pic with no top decking , no extra weight is needed even with the lighter 4 cell battery. The thing is can I put back a lighter decking - maybe of thinner balsa and still achieve this position?
I'm planning to remove ALL the rear decking from F5 back to F10 similar to Chris Williams designed Scheibe-Bergfalke Mü 13 and replace with thin diagonal bracing, then cover with white. Fortunately, I haven't glued in the top sheeting and most the bottom should come off easily. Rudder and and elevator with just be thin ribs and covering.
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Old Jan 06, 2013, 03:17 PM
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Like this...

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Old Jan 07, 2013, 02:45 AM
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I doubt if that will give a satisfactory result on an ASK-13. Your fuselage top is round, you will probably not be able to get a nice round finish without the sheeting. On my Ka-7 it worked well without sheeting, but there it's all flat surfaces.
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Old Jan 07, 2013, 06:55 AM
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Using card stock instead of balsa for the rounded edges might work well if any type of strnegth is not needed.

If it were me, I'd just put the weight in it and fly it. There is a such thing as being too light for a scale ship to fly correctly (that whole renolds number thing which I can't explain).
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Old Jan 07, 2013, 08:56 AM
Segelfliegen
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The most important aspects of this build are to fine tune my scratch building skills and make adjustments to the CAD files so the 4 meter ASK-13 can be built sucessfully. The 4 m size will use a different airfoil with more undercamber anyway.

I am kind of proud of the curved balsa sheeting I formed for the rear fuselage and would be a shame to not use this.

All of this building is all fun anyway, totally enjoying this as I go along. If it flys, great! if it needs loads of wieght, oh well I'll save it for my Cape Cod slope soaring fleet.

Cheers, Thompson
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Old Jan 07, 2013, 08:58 AM
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Quote:
Originally Posted by Fotor View Post
I doubt if that will give a satisfactory result on an ASK-13. Your fuselage top is round, you will probably not be able to get a nice round finish without the sheeting. On my Ka-7 it worked well without sheeting, but there it's all flat surfaces.
Right, I meant to say that I will be removing all of the sheeting from F5 below the curved top deck line.
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Old Jan 07, 2013, 02:59 PM
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Quote:
Originally Posted by studioRS View Post

All of this building is all fun anyway, totally enjoying this as I go along. If it flys, great! if it needs loads of wieght, oh well I'll save it for my Cape Cod slope soaring fleet.

My thoughts exactly. I spent the better part of 2 hours on Saturday building ONE RIB for a new scale project I'm working on. Building, and enjoying it, has it's own set of crazies.

Sunday I tore apart the rear suspension on my classic Porsche. I can't get enough self-inflicted project pain.
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