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Old Mar 01, 2015, 02:28 PM
StayQuiet is offline
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United States, MA, Oxford
Joined Jul 2011
101 Posts
Question
My first "real" scratch build

After building several available kits, doing a bit of "kit bashing" (Sig MidStar 40 conversion to twin electric power), and building from published plans (redrawn in CAD and laser cut for accuracy), I've decided to jump into the deep end, so to speak, and try my hand at designing my own plane.

Not being an aerodynamics genius, I'm using a set of 3-views of an Avro 625 Avian monoplane (as seen in Flying Models - July 2000 issue) as a basis for general layout. However, my design will be shoulder wing vs. low wing, and a simple box-style fuselage for simplicity, both in design and construction. I plan on incorporating something I've been thinking about for awhile in the design - a modular wing mounting system, that allows different wing designs (flat bottom, semi-symmetrical, symmetrical) with varying amounts of dihedral to change the flight characteristics of the model, without the need to re-design (and build) a fuselage to match the wing shape.

There are two rather important questions I'm still unsure of, though:

1) how do you estimate the weight of a model design that has yet to be built? The size of the motor, battery, and ESC have to be determined. I know construction and design will make a difference in the finished weight, and plan on building as light as possible while maintaining integrity.

2) how do you determine proper CG? I'd hate to go through all the design and build process, only to end up tail heavy and crash on the maiden flight. (The CG is not noted on the 3-views)

Some design goals - 48" wingspan with 8 1/4" constant chord, fuse length of 34". Aiming for somewhere around a 450 watt motor for power.

Thoughts? Am I on the right path, or about to walk off a cliff?
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Old Mar 01, 2015, 02:56 PM
eflightray is offline
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An itch?. Scratch build.
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South Wales U.K.
Joined Mar 2003
14,578 Posts
The Avian, that brings back memories, must have been around '89-'90 I built a flew one, from a plan if I remember right.

Still in my build log book, (worth doing one),
44.5" span
38oz flying
600 brushed motor
Olympus belt drive
7 cell Nicad pack.

A CG Calculator is always a useful tool -- http://adamone.rchomepage.com/cg_calc.htm
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Old Mar 01, 2015, 03:12 PM
StayQuiet is offline
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United States, MA, Oxford
Joined Jul 2011
101 Posts
Very pretty bird!

Your link to the CG calculator lit up my anti-virus software, though.
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