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I would like to obtain the C.G. location for the Sterling Fokker D-7

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I would like to obtain the C.G. location for the Sterling Fokker D-7

Old 05-22-2006, 06:23 PM
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rustydog
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Default I would like to obtain the C.G. location for the Sterling Fokker D-7

[:-]I have just completed recovering a very old Sterling R/C model of the Fokker D-7.
I do not have the plans for the model and would like to obtain plan information as to the C.G. location.
I have measured the top and bottom wing to obtain a wing cord of 10 1/2" the rule of thumb is the C.G. should be 25% of the wing cord. According to my calculations thats about 3 7/8" back from the leading edge. If anyone has the plans I would appreciate a verification as to the C.G. location.
Old 05-22-2006, 06:59 PM
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da Rock
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Default RE: I would like to obtain the C.G. location for the Sterling Fokker D-7

The D7 you have is a control line model isn't it? Sterling had the SE5 and the D-7 in 35 size for CL. They were semi-scale and had symmetrical wings. What engine are you planning to use? I built the SE5 back then. I'd think a .35 in one for RC would be rather powerful.

Since you have the model and have already measured some things, take a look at the following site's application and what it requires for input. It will give you a very good answer (or answers) to your question. This application will work just as good for a biplane if you consider the two wings as one. To do that, consider the wings as one with the LE of the forward wing being the LE for the application, and the TE of the back wing as the TE for the application.

The CG location for pitch stability takes into consideration far more than just the wing. It considers the tail volume (tail area and the distance the tail is behind the wing are used to compute the tail volume) while working out the CG location, for example.

http://www.geistware.com/rcmodeling/cg_super_calc.htm
Old 05-22-2006, 08:06 PM
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rustydog
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Default RE: I would like to obtain the C.G. location for the Sterling Fokker D-7

The Fokker D-7 is an R/C model with a max. wing span of 58". I plan to use an OS 70 4-stroke to power the plane.
Thanks for your response.
Old 05-22-2006, 09:24 PM
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JohnBuckner
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Default RE: I would like to obtain the C.G. location for the Sterling Fokker D-7


ORIGINAL: rustydog
I have measured the top and bottom wing to obtain a wing cord of 10 1/2" the rule of thumb is the C.G. should be 25% of the wing cord. According to my calculations thats about 3 7/8" back from the leading edge. If anyone has the plans I would appreciate a verification as to the C.G. location.


I beleve what you described if I read it correctly is correct. Its a simplified method of figuring mean aerodynamic chord reasonably accurately of any positive or negatively staggered biplane, triplane. Not perfect and allows some error when the lower wings are shorter in span but I,ve used this on many aircraft and always get into a safe reasonable ballpark.

Measure the distance from the trailing edge of the lowest wing forward to a point even with the leading edge of the top wing. For our purposes this is the mean aerodynamic chord and is the distance that that will be divided by four ( 25% ) . This figure is then measured back from the leading edge of the top wing to mark our target CG point.

An airplane with zero stagger (wings superimposed can be measured just like a monoplane). Airplanes with one or more wings swept the problem becomes more involved but yours is unswept and untappered so everything is pretty straight forward.

John
Old 05-22-2006, 09:52 PM
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JohnBuckner
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Default RE: I would like to obtain the C.G. location for the Sterling Fokker D-7

Forgot, you may want to peruse this site:
http://home.mindspring.com/~jeff.coo...els/index.html

Your D-7 is model #SF21.

John

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