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Old Jan 12, 2011, 08:24 AM
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United States, OH, Bradford
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Originally Posted by Perdu View Post

Thanks, I'll start drafting the plan next week.
Both sections at minus 1.5 degrees from the fuselage datum line and 1.5 degrees down thrust?
Well, if you like an airplane that putters around with the fuselage's nose pointed up several degrees.

So the main wing zero lift line and the fuselage datum line is parallel is a good starting point for a tractor.
Well, um, NO.

What airspeed do you want to fly at? What angle of attack ("alpha") do you need for the wing to make the necessary amount of lift at that airspeed? What incidence angle between the wing and the fuselage do you need to make the fuselage level when the wing is at its required angle of attack? For example, if at your intended flying speed the wing needs an alpha of 1.2 degrees relative to its chord line to support its share of the plane's weight, then you need an incidence angle between the wing's chord line and the fuselage of that same 1.2 degrees.

The camber of each flying surface determines its aerodynamic pitching moment. You need to know the pitching moments and lifts of all the flying surfaces, the moments about the C/G that those lifts create, and if anything is well above or below the C/G you might need to figure in pitching moments due to drag as well. Add up all the moments and figure the canard lift, canard alpha, and therefore the canard incidence you need to bring all of those moments into equilibrium with each other.

John Roncz had an outstanding series of articles on preliminary aircraft design, in the EAA's "Sport Aviation" magazine from the Feb. '90 issue to Feb. '91, which included Excel spreadsheets to help figure all of this out. It was oriented around a full-scale single-engine tractor arrangement, but applies equally well to canards. The articles give an outstanding plain-English explanation of all these issues, where they come from and how to deal with them. You might check at your public library, or you might be able to get reprints thrugh the EAA.
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