ALO 111,
If the fuel tank is located behind the CG, the model should be balanced
with the tank being full, which is the tail-heaviest condition.
While the fuel is used, the CG moves forward, which is safer.
This site you can find video, review, manual and specifications of a model that is very similar to yours:
http://www3.towerhobbies.com/cgi-bin...&I=LXKEW6&P=ML
Nitroplanes Seawind Seaplane 60
Wing span: 70 in / 1780mm
Wing area: 703 sq in / 45.5 sq dm
Flying weight: 9.1lb / 4130g
Fuselage length: 57 in / 1450mm
Engine Required: 2c 0.61 cu in
4c 0.91 cu in
Great Planes Seawind Amphibian
Wingspan: 71" (1805mm)
Wing Area: 676 sq in (43.6 sq dm)
Weight: 10.25 - 12.25lb (4620 - 5555g)
Length: 56" (1410mm)
Engine: .60 cu in (10cc) 2-stroke
.70-.91 cu in (11.5-15cc) 4-stroke
Center of Gravity: 1-1/32" (26mm) Back from the wing's leading edge.
This aircraft does not have a CG range, do not move the CG forward
or aft of the above figure.
Control Throws Low Rate High Rate
Ailerons: Up & Down 3/8" (10mm) ½" (13mm)
Elevator: Up & Down 7/16" (11mm) 5/8" (16mm)
Rudder: Right & Left 1-1/8" (29mm) 2" (51mm)
Flaps: ½" (13mm) 1-1/8" (29mm)
http://www.greatplanes.com/techsupport/technotes.html
However, in your post #8 you stated that “The factory CG is 90 mm”, which shows a great discrepancy between two equivalent models of
64 mm (2”-1/2)!!!!!!!!!!!!!
Here you can find a RCUniverse review of the Great Planes Seawind (sorry, couldn’t find a review for Nitro Planes’):
http://www.rcuniverse.com/magazine/a...article_id=723
Finally, you are not alone.
This thread illustrates how others have faced similar problem with that model:
http://www.rcuniverse.com/forum/m_4780929/tm.htm
Copied from post #6 there:
“My NP Seawind had the CG set @ 3.54" behind the wing LE. It went totally out of control. Since the plane fairly screams "TAIL-HEAVY," I set the CG to 1" behind the wing LE (following the Great Planes instructions instead). The Seawind took off (without a water rudder), flew beautifully and landed very smoothly. It required 3lbs of dead weight in the nose to balance it. It now weighs 11lbs with 3 lbs of useless weight. I am thinking of installing an electric motor and battery in the nose with a l-o-n-g shaft to a steerable water propeller in the tail. Might as well make the weight useful.
It is unfortunate that, as useless as the NP Seawind manual is, one of the few solid pieces of information (the CG point) is disasterously AND INEXCUSABLY WRONG, WRONG, WRONG! Maybe they meant 3.54 centimeters”.