# How to calculate position of a canard?

does anybody know how one can calculate the position, shape and size of an aircraft with a canard?

So the main goal of a canard configuration: increase lift + increase agility/maneuverability

So at least I can calculate the centre of pressure of the whole aircraft, which has to be behind the CoG to guarantee static stability in pitch.

But still, I have a range in x-direction , where I can place the canard. What do I have to define or know in order to place my canard?

Lift: I can design my main wing and its lift A_W_wing. In horizontal flight A=W=A_Wing +A_Canard ; So I could now design my A_Canard (shape, size).

But what about the maneuverability? What do I need to now?

So for my opinion: for a curve to fly with a specific rotating rate, my control surfaces (tail + canard) need to create a specific moment. Since Moment = Force * Arm I could make calculate the needed Arms/ positon ?

Thank you for any tips on literature or calculations

• This is really a quibble unrelated to your actual question, but not too sure about the agility/maneuverability part, in a configuration that is intended to never let the main lifting surface get close to stall. I don't think the Rutan designs were more agile in the pitch axis than conventionally tailed airplanes of similar overall configuration, because of the limited pitch authority baked into the design. Commented Nov 19, 2019 at 18:47
• Agility is possible with a canard (Wright Flyer), but practically requires computer control. en.wikipedia.org/wiki/Canard_(aeronautics)#Control Commented Nov 19, 2019 at 19:48
• The best canard is placed behind and not ahead of the wing. If you insist on putting it ahead of the wing, make sure its wake will flow above or below the wing in cruise. Commented Nov 19, 2019 at 20:25
• @Helmut K. you may wish to work with roll and yaw rate as well to increase agility. Possibilities include increasing control surface travel and or size. These are your "destabilizers". There may not be as great a need to destabilize the aircraft when they are not in use. Commented Nov 21, 2019 at 19:58

There are several factors to consider, and depending on your preferences there is not one ideal size and place for a canard. For a first rough concept look at similar designs and use the same canard volume. That is the product of canard area and the distance between its and the wing's neutral points, relative to the aircraft's reference parameters.

$$V_{Canard} = \frac{S_{Canard}}{S_{ref}}\cdot\frac{X_{NP, wing}-X_{NP, Canard}}{l_{ref}}$$

Collect as many canard volumes as you can from different but similar designs and use that for a first draft.

Next, decide on your priorities. Do you want good pitch damping for a pleasant ride even in rough air, use a smaller canard area on a longer lever arm. Damping grows with the square of the canard lever arm while its stabilising effect is only linear. Do the opposite if you prefer more agility.

Next, what center of gravity range do you desire? If, for example, you plan a tandem two seater where due to engine weight and pilot position the second seat is at some distance from the center of pressure, increase canard area accordingly.

So far we looked only at area and lengthwise position. But the vertical position must also be considered. Ideally, the wake of the canard will be above the wing for all practical angles of attack (from cruise to stall), which can be achieved by placing the canard wing high on the fuselage and the wing low. In that position, however, the canard wing might obstruct the pilot's view, so maybe you want to strike a compromise where the wake is below the wing in cruise but above near stall. This can only be achieved with a short lever arm, however.

Regarding the shape: A straight, high-aspect-ratio wing will be best. After all, the canard will fly at the highest lift coefficient of all surfaces so it should have the highest aspect ratio. Use a trapezoidal planform with a ratio of tip chord to root chord of 0.6 - 0.7, or, for simplicity, a rectangular planform which needs only one rig/mold for both sides.

But if what you really want is a good airplane and aren't determined on making it a canard: Place that smaller surface behind the main wing.

This diagram is from the book Design for Flying by David Thurston and might be of use.

• Do you have a reference to this book (e.g. isbn)? Commented Nov 20, 2019 at 8:27
• isbns here: amazon.com/Design-Flying-David-B-Thurston/dp/0070645574. Be forewarned it's more of a "guide for laypeople" kind of book on light aircraft design and he only devotes a page and a half and that illustration to canards. Commented Nov 20, 2019 at 13:43