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Old 02-02-2003 | 08:25 PM
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Ben Lanterman's Avatar
Ben Lanterman
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From: St. Charles, MO
Default elevator control on canards

May I second the use of small models to determine settings and physical layout of potential designs. I use 1/8 inch foam from trays or whatever to make small electric RC models as a way of evaluating airplanes. They are not perfect for this application but are a step up from the basic glider (still a good starting place).

Look at

http://142.26.194.131/aerodynamics1/...ty/Page11.html

for an nice interactive idea of stability and control of a canard.

To get some more information of how the stabillity of a canard will effect the loadings on the forward surface look at

http://www.desktopaero.com/appliedaero/appliedaero.html

Section 14.4.4

There are no equations in this page, very basic assumptions - No fuselage, no wing section pitching moment, just basic stuff. The graphics could be more exciting though.

The definitions of the inputs in the figure are below

sm = static margin, the measure of stability based on the reference chord. Distance between the CG and the Neutral Point.

Wing AR and Tail AR = changes in the picture as you change the numbers. What you see is what you get

St/SW = the ratio of tail area to wing area, easy stuff.

The Figure changes to show the changes, you can click/drag the tail left and right and see how the changes occur.

If the Lt/Lw printed out is positive it indicates a tail up load.
e is the induced drag and is not too interesting.

For a typical canard

sm = .10
Wing AR = 8
Tail AR = 6
St/Sw = .2

Push the compute button.

Use the mouse and move the red horizontal tail left and right and see the load on the horizontal change. If the term Lt/Lw is positive then the load is up.

Notice that the upload on the canard is from 25 to 30 percent of the wings load. Since the canard area is only 20% of the wing it indicates that the canard will probably stall sooner than the wing if the airfoil is the same.

I notice that Rutans canard airfoil as seen in Profili is creating sightly more lift at the same angle of attack as the wing airfoil.

It is a good tool to find out what is happening. Of course if the airfoil has a big moment input or the fuselage, flaps, etc it will change the answer. Sometimes not easy to guess at.