Great Planes Seawind: CG within 1/32" ?

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LeeH - 14 Sep 2005 15:50 GMT

>From the Great Planes Seawind ARF manual:

--
1. Very Important: ...The C.G. is located 1-1/32" [26mm] back
from the leading edge of the wing.

IMPORTANT: The stated C.G. is where your model must
be balanced. The Seawind ARF does not have a C.G.
range like most R/C planes. Do not move the C.G.
forward or aft. Doing so will cause the plane to become
difficult to control. This C.G. point has been extensively
tested and you should not deviate from it.
--
Beautiful plane, IMHO
More info at <http://tinyurl.com/8z5bs>
Cheers -
LeeH, lusting for a Seawind ARF

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Double Ace - 14 Sep 2005 20:21 GMT

WOW! Sounds lilke it's just a litle unstable.

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Marlowe - 15 Sep 2005 01:11 GMT

You might be right. According to the website the wing loading is 35-41
oz/ft2. Pretty high loading which generally aggravates stability problems.
And look at the pictures. The horizontal tail looks pretty small and is
probably negated by the large, flat hull section in front of the wing.
Finally, since this is a scale model of a working full scale plane, the
Reynolds number (scale effect) reduces horizontal tail effectiveness. These
three effects could lead to a marginally unstable configuration and hence
the CG location is critical.

Bottom line however is that it is a very beautiful model. If I had one I
would try to figure out how to add another 15% to the tail area.

> WOW! Sounds lilke it's just a litle unstable.

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Dave - 15 Sep 2005 02:16 GMT

Annnnnnnnnnnnd.....

    If you like the trivia around the Seawind, It was designed and
built in Canada, scheduled for certification sometime this winter,
making it the only Certified amphib available.

    (lake Co's assets are being auctioned as I write this) :(

    ...some are considering it one of the most beautiful aircraft
designs ever........

    Dave

>You might be right. According to the website the wing loading is 35-41
>oz/ft2. Pretty high loading which generally aggravates stability problems.
[quoted text clipped - 9 lines]
>
>> WOW! Sounds lilke it's just a litle unstable.

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rcmob - 28 Sep 2005 03:25 GMT

There are a lot of factors that can complicate the design of an airplan
and the Seawind is not your typical plane. The CG needs to be at th
specified location because of several factors that include forwar
fuselage lift, landing gear location and hull step location as well a
engine thrust line. The airplane does not have any stability issues a
the specified CG as it is extremelly stable, no-surprises flying, wit
a soft stall, no spinning even when induced and 3rd or 4t
airplane-type performance (speed wise). The wing has been designed t
deal with the higher-than-average wing loading and it uses
combination of airfoils to make this a very honest airplane. The reaso
the CG is specified to a 1/32" resolution is because the dimension wa
measured in Metric and then converted to SAE and that is the rounde
number that came out

--
rcmo

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Model Forum / Radio Controlled / Air Models / September 2005

Great Planes Seawind: CG within 1/32" ?