Why are there so few canards?

[Trevor Lyons]

The vast majority of GA aeroplanes are conventional in layout, with a main wing forward and the tailplane aft, and it is a rare sight to see a canard. Why are there so few canards, when their advantages are so well known?

I used to go boating in monohulls, but having sailed in catamarans, I would never choose to return to a single-hulled vessel. Catamarans are faster, more comfortable, with a shallower draft (allowing access to beaches unavailable to monohulls), lighter (no deadweight ballast required for stability), more easily pushed with a smaller sail area or smaller motor (so, again, lighter and more economical), and vastly roomier. If catamarans had been invented first, no-one might ever have bothered with monohulls!

But with aeroplanes, the better design (the canard) DID come first, in the form of the Wright Flyer. What went wrong?

To rehearse the benefits: both main wing and canard provide lift, whereas a conventional tail is always providing downforce. (Yes, in a conventional aircraft one is burning fuel for the empennage wing to push you down, not up!) A canard aircraft cannot stall, since the canard wing stalls first, the nose drops and recovers, and the mainwing never stalls. If it doesn't stall, it can't spin, and must be safer. Visibility will be good, as the mainwing is aft of the pilot. The canard wing itself does not significantly obstruct the view; rather it provides a horizon reference. Canards often have tandem seating, which further enhances visibility. They also tend to have pusher engines, which allows for a very clean nose design.

Yet the few available canards comprise only the advanced Rutan Long-Ezes, Vari-Ezes and Cozys, and cruder fare like the Goldwing single-seat open-cockpit microlight, or the rather nice French Ibis (as yet unapproved by the LAA). You have to be very keen and really competent to build a Rutan; and anyway, plans are no longer available.

It is said that it is easier to lose a fortune in aviation than in other markets; but that doesn't stop the regular appearance of new designs that are utterly conventional. Canards are a niche market with little competition for the available demand; so again, one wonders, why are canards ignored?

[Penguin]

Arrivisto,

It may appear on the surface that the canard configuration is "better", but that really depends what you want the aeroplane to do. NASA studied the best ratio of canard to mainplane size (I think from the performance perspective) and concluded that it was 5:1, that is canard 5 times larger! Not sure that visibility is that much better (especially for passengers). The greatest draw back of the canard config is the lack of cg flexibility. A normal aeroplane will have a greater cg range, and so will be easier to load. There is also the problem of stopping the prop from hitting the ground and of getting in and out. Good yaw control is also problematic as is fitting powerful flaps. So if you want a fast cruiser that lands quite fast (that is needs a long hard runway), then a canard aeroplane might fit the bill. If you want some aerobatic capability then perhaps not. Stall resistance isn't everything. So, perhaps canards are not ignored they are just not everyone's cup of tea? Every aeroplane is a compromise, those made when the Vari-eze was designed are perhaps more of an acquired taste than for some other aeroplanes?

Pete

[J.C.]

The simple truth is that if canards were so good there WOULD be more of them .
Come up with a good practical design and they DO become popular,e.g Piper Cherokee, Cub ;Cessna 150,172; Jodel;and more recently Vans and Sportcruiser to name a few.

[Trevor Lyons]

Arrivisto, It really depends what you want the aeroplane to do. Pete

True, the canard's inability to stall may rule it out for aerobatics; but for those wanting to fly from A to B efficiently, the canard has a lot to offer. It is true that canards are associated with CG inflexibility, vulnerable props, difficult access, and yaw control: but these are all matters that can be addressed with good design. Its small wheels and long take-off run may make the Long-Eze unsuitable for our short grass strips; but there is no reason why a canard cannot have tundra tyres and STOL capability. The canard lends itself to the efficient delta wing, with wingtip fins and rudders which eliminate the weight and drag of a lengthy fuselage; and the rudders can serve as airbrakes when used together. But if you are determined to drag a fuselage along behind you, a canard can have a pod and boom layout (say, to protect the prop). Rutan designs show how easily a retracting nosewheel can be incorporated.

Let's do some tailplane arithmetic. If an airframe need a 100sqft of wing to fly, with a canard layout, the main wing need be only 80sq ft, and the canard 20. If the conventional equivalent has a 25sqft tailplane, the main wing might need a further 25 on the wing to compensate. Total 150sqft; or 50% more! The extra wing area will need extra strength which involves extra weight. A vicious circle! (Yes, I know it's not quite this simple, but the point is made.)

The simple truth is that if canards were so good there WOULD be more of them.

I'm not so sure. I suspect it is rather the inherent conservatism of aviators and the lack of available designs. G-BUXP was a UK example of the microlight canard Falcon XP. It looked a clever little aircraft, and it's a shame there aren't more like it!

[Charles E Taylor]

arrivisto

The answer to your question is possibly "Sheep"

But then, like you I'm probably biased and anyway it's really all in the name.


Kind Regards


Charlie

[Brian Hope]

I'm not convinced that it is the conservatism of the aviation community that has held back the canard. If that was the case we'd never have moved away from wood and fabric aeroplanes (what am I saying!), would not have trusted monoplanes, and the jet engine would still be a quaint curiosity. As in all walks of life, good design and inventiveness will win through if they are an improvement on existing products. Clearly the canard has yet to surpass the merits of existing designs.
Regarding the Falcon. Somebody who once flew one commented to me that the best thing that happend to 'XP was that it was damaged beyond repair (some years ago now). He reckoned tha handling was awful.

[Trevor Lyons]

Regarding the Falcon. Somebody who once flew one commented to me that the best thing that happend to 'XP was that it was damaged beyond repair (some years ago now). He reckoned tha handling was awful.

A bit harsh! Some time ago, I read a flight test of 'XP by (I think) Tim Cripps; and I seem to remember that he waxed lyrical!

[Penguin]

Arri,

I think your tailplane sums are a little out. The Cl of a tailplane section is not the same (lower) as that of the main wing, so you cannot sum the areas on a canard or subtract on a conventional layout. While you are correct that a tailplane will always exert a downward force, the magnitude of that force can be minimised by careful selection of the wing section (to achieve a low cruise pitching moment) and by arranging for the cg to be toward the aft limit. For both types of aeroplane it is desireable (for efficient cruising) for the tailplane or canard not to be working very hard. Look at conventionally configured aeroplanes, how many have a tailplane 1/4 the size of the main plane? Not many! I don't really think you have made the point.

I think you have also underestimated the difficulty in making a highlift canard mainplane - I seem to remember that it is difficult to fit powerful flaps to a canard mainplane (can't remeber why off the top of my head). So you could fit the largest tundra tyres available, but it would be difficult to get enough Cl out of the mainplane to get off the ground very quickly.

It is easy to say that the weak points of canards can be addressed by good design, but how many good designers have tried and been successful, not may I would suggest. To take yaw control as an example, ideally the rudder should be a long way from the cg. Putting one on the front of the aeroplane is not good for lateral stability, so the wing tips are the only other place. Thus the wings must be swept back to gives the rudder a reasonable moment arm on the cg (that makes the wings heavier than they need to be). If you do choose a forward rudder, then the fins have to enlarged (again heavier) to provide static lateral stability. The point here is that everything is a compromise.

If you would like an efficient long distance cruiser, then a Long-eze is a great aeroplane. Perhaps you should go buy one and find out what the true pros and cons are? I have no idea, I've never flown one. However, there is an Aussie called Jon Johanson (sp?) who has flown around the World several times in his ... RV-4. If a Long-eze was so superior why did he not chose one ? Again I don't know the answer, just posing the question.

Why don't you design & build a good STOL canard with a fine turn of speed and show the conservative conventional configuration pilots what they are missing out on?

Pete