Canards

Close coupled or long arm?

What is canard

French for “duck”Ducks have a layer of feathers around the neck which improves aerodynamics

Canard is a control surface in front of the wing

Lifting canardControl canard

General effects

Loaded canard decreased drag at supersonic speeds

Provides upload vs traditional tail downloadReduced need for elevon trim

Less drag in level flight

Unloaded canard only adds minor drag, but improves lift and reduces drag in turnImproved STOL performance

Close coupled canard

Increases instability levelLow pressure area at forward part of the wing > dynamic instability

Does not shift to stability during supersonic flightImproved pitch rate through angle of attack rangeImproved pitch onset and turn onset rate

Close coupled canard

Improved lift at high angles of attackImproved instantaneous turn rateLittle effect at speeds above Mach 0,9

Reduced necessary wing twistReduced drag for a given angle of attack

Delayed stall; reduced trim dragSignificant improvement in L/D ratio

Close coupled canard

Vortexes improve wing response to control surface inputs and improve control surface effectiveness

Improved transient performanceRoll onset rate in particular

Improved control effectiveness at high angles of attack

Close coupled canard

Reduced drag during supersonic cruiseReduced centre of lift shift

Less trim drag

No effect on lift or drag during supersonic maneuversStall and spin recovery

Long arm canardCanard vortex bursts early due to lack of influence from the parent wing

No drag improvement at high AoANo improvement in roll onset rateLift improvement limited to increase in reference area caused by addition of canard; no effect on the parent wingRequires greater static instability margin to achieve same overall amount of instability > no dynamic instability

Conclusions

Close coupled canard is a better choice for applications where maneuverability is requiredLong arm canard may be better for cruise performanceBoth canard configurations are superior to a traditional wing-tail configuration

Presentation by Picard578http://defenseissues.wordpress.com/http://defenseissues.wordpress.com/2014/08/23/close-coupled-vs-long-arm-canard/