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Old Nov 02, 2012, 11:27 AM
Segelfliegen
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@papaalpha - thank you for your input on and speedy building skills - OMG ! on the K-13 and these other kits. When you maiden your ASK-13, I'm sure we would all love to see photos and video if possible. Cheers, Thompson
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Old Nov 06, 2012, 11:30 AM
Segelfliegen
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Northern Vermont
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More progress on the left wing. I wish I could post more, I'm just so slow and doing my first build very carefully.

Need to finish
- Spar box uprights
- Install top 1/16" sheeting
- Mount servo wires
- Mount servo between R15 and R16
- Root trailing edge
- Final sanding
- Glue in carbon spar rods
- Cover with econocoat
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Old Nov 06, 2012, 05:07 PM
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I assume you are building in some washout on the trailing edges of the wings which is essential.
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Old Nov 06, 2012, 07:14 PM
Segelfliegen
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Northern Vermont
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Quote:
Originally Posted by papaalpha View Post
I assume you are building in some washout on the trailing edges of the wings which is essential.
Yes, I've built some in, need to keep this in mind while I'm building the other wing and wings for the 2m and 4m versions! The 4m version will have a different wing profile with more undercamber too.
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Old Nov 06, 2012, 07:58 PM
Segelfliegen
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Northern Vermont
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Question from a newbie builder... What would be an optimal amount of washout on this 1,6m span wing? Basic amount for it to fly well and hopefully not tip stall?

Currently the trailing edge of R27 is higher than the traIling edge of R4 by about 3-4mm, is that enough or does it need to be more exaggerated ?
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Last edited by studioRS; Nov 06, 2012 at 08:28 PM.
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Old Nov 06, 2012, 07:59 PM
Vintage wood is the best!
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I would build the wing straight without washout.....the negitive affects out weigh any perceived benefits.
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Old Nov 06, 2012, 08:31 PM
Segelfliegen
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Well you guys see the photos, the trailing edge at R27 is really only 3-4mm higher than at the root trailing edge. I'll just build it out as is.
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Old Nov 07, 2012, 03:02 PM
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Washout is essential if you don't want tip stalling at slow speed.There are no negatives to having such. 3/4 mm should be fine on your model.
Had a few test throws down a grassy bank with my K13 and after adjusting the tailplane incidence with temporary packing and adding more weight to the nose threw it off the main slope for a 'hairy' 10 minute flight. At least established that the c of g is a good one and a quarter inches ahead of the online c of g calculator that I used ( as occurred with my Bocian). Does anyone know of an accurate on line c of g calculator?
So back home lightened the tail feathers by stripping and sanding thinner the tailplane,elevators and fin as even an ounce saved at the tail can be a saving of 3 to 6 ozs at the nose. With 2 ozs of lead right in the nose and the flight battery the weight is some 3lbs 5 ozs which is very similar to my Bocian at 3ibs 2 ozs which needed no nose weight.
Also discovered a 3mm discrepency in the angle of incidence of the left wing compared to the right which was a real pain to fix having to cut out and extract the wing tube and reposition and fix. Took 3 attempts to get near right. So ready for the next flight straight off the main slope and believe it should fly ok when everything sorted! All part of the fun of scratch building and getting the satisfaction when it eventually flys smoothly!
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Old Nov 07, 2012, 04:40 PM
Vintage wood is the best!
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Washout is not "essential" ......don't fly it so slow in a turn and it won't tip stall. "Twisting" a wing to add "washout" plays havoc with the performance of the airfoil. If you feel you must have the crutch of "washout" introduce it via the airfoils you use accross the wing......not by "twisting" the wing.
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Old Nov 07, 2012, 06:14 PM
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On a small model of 2 or less metres span the standard modelling way is to introduce it by the method as you say 'twisting' but by 3 or 4 mm on a 1.6 or 2 metre span is deminimus. Slingsby had it on all their gliders as do Boeing and Airbus on all their airliners albeit not induced by twisting as you say but they are slightly larger span! Don't you want safe slow flying whilst 'scratching' for lift or landing?
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Old Nov 07, 2012, 06:44 PM
Segelfliegen
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I plan to fly this little ASK-13 like I stole it, flat out. . Yes, would be nice to fly slowly and not induce a tip stall. Great information from both sides of the discussion, keep it flowing!
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Old Nov 08, 2012, 04:35 AM
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Getting a scale model like that you are making to fly at a scale like speed when the span is less than 6 feet/2 metres is very difficult as the 'Reynolds effect' takes hold and from my experience unless a basic wing profile one will be disapointed. Even on my Ka 6cr with its some 7 ft span because of all the above I had to make a simple, is it Clark Y (?) profile to get it to give any lift, using my first scale profile wing to light the fire! At least now the model flys ok in winds of 5/6 mph thru to say 15mph and at a scale like speed which is always pleasing to the eye.
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Old Nov 08, 2012, 06:23 AM
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Scale speed is impossible to reach for smaller models. For scale speed you would have to get the weight down by a factor scale^4.
This model is scale 1/10. For scale speed (original speed / 10) the weight would need to be 450 kg (that's a guess, don't know the exact weight of the fullsize) / 10^4 = 45 grams.
Only on very large scale models you can come close to scale speed.
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Old Nov 08, 2012, 07:46 AM
Segelfliegen
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Northern Vermont
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Gentlemen, thank you for the valuable input, I am learning so much! Please do not stop, keep adding to each and every topic and sub-topic that arises, this is really good.

My intentions with this ASK-13 1:10 scale build are to learn the process of construction and apply different techniques as I go. I can fine tune the drawings when fitment issues arise and adjust the build from your input and suggestions. Believe it or not, this 1,6m is practice for me building additional larger sailplanes. I want to thank you all again, your photos, flying experience and build knowledge are what keep me inspired to build more!

Of course I am keeping my fingers crossed that it flys well. If I need to "fly it like I stole it" to keep the speeds up, then that is ok too. I think the wings can handle it, the one I built feels strong. Keeping it light is very important. For ref. my EPO 2m ASW-28 is only 730g (1.68 lb) and floats very well, this includes a motor, spinner, folding Graupner propeller, pilot AND 1300mHa 3S battery! The biggest problem with lighter sailplanes is they lack inertia.

I will try aerotowing with this on a hot thermal day in the summer with some of you supervising ( SZD-16 ) and also try slope soaring with some good winds. Trimming it out on a nice tall grassy field first to minimize damage.

So, I'll just keep plugging away at building, posting photos and learning as I go, asking more beginner questions added along for your entertainment. Cheers, Thompson
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Last edited by studioRS; Nov 08, 2012 at 07:56 AM.
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Old Nov 14, 2012, 02:44 PM
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Well here is another sub topic for you! Had another test flight off the slope today before the wind dropped completely and whilst my K13 (off your plan but larger span) is ok in level flight, the battery and 2ozs of lead in the nose are so far forward being a two seater with a longer nose than that of a single seater all is well until a nose drop when it is 'pulled' down into too much of a dive i.e., like everyone on an airliner standing in the front of the cabin which is fine whilst level flight is maintained but if into a nose down position arises, it just steepens into a dive with massive up elevator needed if even effective. So back to the work bench to remove the tailfin and rudder to try yet again to lighten the tail with a profile thin and lighter weight one. At the same time will replace the wing servos with lighter micro ones and the main micro elevator and rudder servos in the fuselage with standard size heavier ones on the basis that it is not just having the necessary weight to balance a model but where the nose weight is positioned, as relatively close to the c of g rather than extreme nose position can be equally important to avoid nose down dives if the nose drops.
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