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Old Yesterday, 08:59 PM
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David Forbes's Avatar
United States, FL, Gainesville
Joined Dec 2005
2,773 Posts
Chadman,

Yes to the Morgan Mill stiffener. Foam is wonderful stuff, but it benefits from some structure, especially if you are going to put a big motor on it and start towing stuff with it.

I used two kinds of paint. Fuse was done with Top-Flight Cub yellow from the LHS. Expensive, hard to use (lousy nozzle), and it alligatored the foam. Wing was done with Krylon Fusion. 1/3 the $$, can't tell the difference with the color, easy to spray and no ill effects to the foam. I did splurge for the decals from Calliegraphics.

Dave
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Old Yesterday, 09:16 PM
Registered User
United States, OR, Portland
Joined Feb 2011
139 Posts
Quote:
Originally Posted by David Forbes View Post
Chadman,

Yes to the Morgan Mill stiffener. Foam is wonderful stuff, but it benefits from some structure, especially if you are going to put a big motor on it and start towing stuff with it.

I used two kinds of paint. Fuse was done with Top-Flight Cub yellow from the LHS. Expensive, hard to use (lousy nozzle), and it alligatored the foam. Wing was done with Krylon Fusion. 1/3 the $$, can't tell the difference with the color, easy to spray and no ill effects to the foam. I did splurge for the decals from Calliegraphics.

Dave
Well it looks great! Thanks for the tips on the stiffener and paint
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Old Today, 03:06 AM
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BAF23's Avatar
Belgium, Vlaams Gewest, Hasselt
Joined Aug 2012
174 Posts
Quote:
Originally Posted by surfimp View Post
BAF23 have you checked the incidence of your tailplane relative to your wing? Sounds almost like you have a negative decalage situation (wing at negative angle of attack relative to the the angle of attack of the stab).

I've seen a few KA-8s fly locally and none of them have the problems you're describing. In fact the plane appears to be quite docile and pleasantly aerobatic.
The way the Ka8 comes out of the box there is no possibility to adjust the tailplane incidence unless you scrape away foam to allow the leading edge of the tailplane to sit deeper in the fuselage. I can only think that the designer of the model tried to put the CG intentionally too far back, so the horizontal stabilizer also produces positive lift (as opposed to negative lift in a stable conventional aircraft). This allows the Parkzone Ka8 to be flown in thermals at very slow speed (so you can fly closer to the center in the thermal), and allows it to be landed "clean" at very slow speeds.

The drawback to that is that the lack of positive stability much limits the speed envelope of the model, and if assembled as per Parkzone instructions it can only be aerotowed by slow planes (yes, the Funcub or Mentor are good at that). Towing it with faster airplanes can only be done by pulling this lightweight almost vertically in the sky.

The positive lift of the tail also results in a greater pitching movement when the spoilers are deployed fully open. With my 50mm CG I eliminated both those problems and have a glider that can be towed by stronger faster towships, still thermals relative slowly compared to the modern glass gliders, but allows me to travel faster from one thermal to the other, perform nice loops and rolls, and does not need any elevator to spoiler mix at all.

The small pitching moment associated with spoiler operations just controls the glide angle and does not require much elevator movement. I have no problems flying it even in stiff winds because my higher speeds allow it to battle those strong winds in final. When necessary (during gusts) I dare to open or retract those spoilers a foot from the ground without surprises, but found out landing it with about half spoiler allows better control of the touchdown point and still leaves enough up elevator to flare into a smooth touchdown.

It now is even more docile and aerobatic. This setup (together with a towhook in the nose and carbon reinforced main wings) works very well for me and the many very strong and faster towships our club members provide. Glider pilots not needing that versatility might fly the Ka8 as pert Parkzone specs, I just provided some info about possibilities to modify the box model and improve its overall handling.
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