Canards

[Ian Swadling]

G'day.

Can anyone please explain how Canards-foreplanes operate in relation to elevators?

Ian

[Martin Dance 1]

In simple terms for a canard which has a fore plane with elevators. The elevators move in the opposite sense to conventional elevators at the rear of an aircraft. So with the elevator moving downward the aircraft pitches up and with up moving elevator the aircraft pitches downwards. With an all moving fore plane with the leading edge moving higher than the trailing edge, i.e more positive angle of attack the aircraft climbs and vice versa when the trailing edge moves higher relative to the leading edge, reduced angle of attack.

Note however you will need to ave the fore plane at about 5 degrees of positive incidence to get stable flight.

[Piers Bowlan]

Hi Ian, this is my simple take on it!

First, canard fore-planes (generally) contribute to the overall lift of an aircraft whereas tailplanes tend to produce some negative lift on a conventional aeroplane. It is this downward force which contributes to the longitudinal stability of a conventional aircraft. This difference is important if elevators are attached to a canard fore-plane, as, if the elevators are deflected downwards, for example, this increases the lift produced by the canard and causes the nose of the aircraft to pitch upwards. This is the reverse of what happens in a conventional aircraft with a tailplane - downward elevator deflection causes a reduction of 'negative lift' causing the tail to move upwards (and the nose of the aircraft to pitch down).

Some canard configuration aircraft have an all-flying canard control surface as opposed to separate elevators but they operate in the same way as a canard with elevators.

Famously, Burt Rutan produced many canard designs including his Vari Viggen, Very/Long-Easy, which all featured canard fore-planes. As his canard fore-planes are quite highly loaded compared with the main wing and also of high aspect ratio, they tend to stall before the main wing, which tend to make the aircraft handling benign, as far as stalling is concerned. I think this was part of the attraction of the configuration. Also, as the canard contributes to overall lift they would also appear to be more efficient, although in reality the downwash and turbulence from the canard has an adverse effect on the efficiency of the mainplane. Notwithstanding, they are brilliant designs and thousands have been built.

Many jet fighters feature all-flying canards but these are more for control than for generating lift (Typhoon, Rafael Griffon etc.) - but I digress!

[Piers Bowlan]

Beat me to it Martin and much more succinct!

Are you planning to build a canard Ian? How about Nigel Hawes very popular Can-Doo? Plan here.

Edited By Piers Bowlan on 31/12/2019 09:06:37

[Ian Swadling]

Hi Martin and Piers.

Thank you both for your replies and information.

No Piers, I'm not planning to at the moment. I was just reading about a model jet and wanted to find out why foreplanes work the way they do.

Thanks again.

Ian

[Cuban8]

This is a fascinating subject worthy of some historical reading and research if one's interested. For me, the Wright Brothers have a lot to answer for by sticking to a forward mounted pitch control surface for much too long, until their Model B around 1910 that carried the elevator at the rear - although still very much a 'dead end' design.. Personally, I think Mr Bleriot got it pretty much right all along apart from a few early oddities. Must have been exciting times.

Edited By Cuban8 on 31/12/2019 11:42:37

[Erfolg]

Here is my canard

To go up, the elevator trailing edge goes down, to go down, I am sure you get it.

My model had to have the fins increased to provide directional control. If the main wing was swept back, it would not have been necessary]y.

[J D 8]

In the early 80's I flew a type of microlight called an "eagle" Lateral/yaw control was by tip dragger rudders and pitch control was a combination of weight shift and canard with elevator.

It was not possible stall it in the conventional way, the canard would stall if you went slow enough but the wing itself would remain flying resulting in just a nodding flight path.

Another feature was the up elevator movement [ down pitch remember ] was linked to the control with a section of bungee cord so as you dived increased air speed would lower the elevator and along with the greater incidence of the canard increase its lift and you had an automatic dive recovery.

In the early days of microlights there were many odd control systems tried that very much mirrored the early days of aviation.

[Former Member]

[This posting has been removed]

[Nigel R]

Worth noting that if canard configurations could be made more efficient than the usual arrangement, Boeing et al would move straight to it.

Not sure concordski's failings were onky due to having canards?

[Simon Chaddock]

Ian

Canards correctly set up can produce a stable and efficient layout (as found out by the Wright Brothers!) but it can become unstable more easily than a conventional layout at the limits of the flight envelope. This fact tends to restrict their use in light aircraft and civil airliners.

Modern fighter jets have the benefit of sophisticated 'computer' flight control systems so any stability issues can be negated and can actually become a benefit.

As mentioned the Russian Tu 144 canards were only used to improve control at low speeds. They only added a nose up force and were retracted for supersonic flight. The huge Mach 3 American XB70 Valkyrie used them for the same purpose but they were not retractable. Concord on the other hand moved fuel about to alter the CofG position to suit the requirements of low speed and supersonic flight.

On my EDF model of the XB 70 I had to use both the canards and the elevators working in opposition to give sufficient pitch control at very low speed.

Edited By Simon Chaddock on 01/01/2020 11:45:58

[Erfolg]

Over the years many full size designers have been attracted to canards. Similarly to flying wings many claims have been made as to why they could result in a efficient design. It is a similar situation with the delta plan form. In reality those claims have generally never been realised.

In the case of the canard, many have been attracted to the possibility that the volume of the aircraft fuselage could be free, presenting the possibility of an uninterrupted space for the bombs, no spars, or transfer frames, cluttering up , dividing, the space. In practical terms, the next issue becomes fuel storage, it no longer is easily arranged around the CG, that is where the bombs would be. Sensibly the tankage has to be at the rear, so the CG moves forward with usage. In doing this other issues or solutions have to be incorporated..

The demonstrators produced have apparently been flawed in some way, never delivering what had been hoped for. The downwash from the fore plane has often contributed to the issues.

The Variezy took advantage of the load being fixed at the CG, enabling a pretty shallow body to be produced. There does appear to be a number of crashes, put down to stalling, perhaps not quite the same scenario as with conventional layouts.

In the case of many military aircraft with fore planes, I gat the impression, the aircraft does not operate strictly as a canard layout. Under normal conditions the fore planes are not generating any pitching loads (hence inducing drag from the process), the aircraft seem in general to be designed with neutral stability, where electronics maintain the intended path, the control surfaces on the main plane are primarily used to ensure stability is managed. The fore planes are there to augment maneuvering in the more aggressive flight envelope.

My model canard was initially born out of a project for non conventional BARCS League comps. Towing was an issue. The project put to one side, then re-emerged with electric powered flight in a much reduced size. As a model it flies well, is inclined to dutch roll in turns (slightly). Does not stall as easily as a conventional type, it will stall doing aggressive maneuverers. If the rear surface should be lifting in theory, in practice both wings have stalled. Although in standard approach type scenarios this will not happen, In the round, it is a good flyer.