The Wright Bros. Aeronautical Designs

[bobthefish50]

It took seven years years of advancement, 1903 to 1910, before the brothers placed their rudder and elevator aft of the wing, having been forward of the wing until 1903.

Why such a long time? By 1909, the Bleriot's stabilizers were placed aft of the wing.

Bob

[Tom Harper]

The Wright Bros. were business men who had patented their 'flying machine'. A major claim was their method of directional control. Even though it was unsatisfactory they were reluctant to give it up.

Tom

[kcaldwel]

I believe the rudders were always aft of the wing.

Chanute and Lillenthal had rear stabs before Bleriot too, and they had thousands of successful flights.

The Wrights believed the canard stabilizer helped their aircraft recover from stalls quicker. They were very wary of stalls, because of Lillental's death. The Wright's aircraft were pitch unstable. Fortunately they were slow enough, and the Wrights quick enough that they could fly them. Once they started going faster they would have had to keep moving the CG forward to make the aircraft more pitch stable. They would have eventually run into a problem with developing enough lift from the thin, low camber canard airfoils they used. They would have been forced to eventually move to a rear stabilizer until airfoil design would provide higher Cl airfoils for canard designs.

Kevin

[vintage1]

Take a look also at the 14bis: http://en.wikipedia.org/wiki/14_Bis

There is nothing wrong with a canard configuration: it can be as stable or more stable than a conventional arrangement. Indeed one source I read stated categorically that the reason the canard was abandoned for many years was nothing to do with aeronautical issues at all: it was totally due to the fact that in a crash, having a large heavy engine behind the pilot was lethal. This applied as much to the rear engine, rear tail pusher planes like the gun bus etc..once synchronised machine guns became available the advantages of a big lump of metal in front of the pilot were overwhelming..

The Bristol boxkite had a fore and aft plane..

Canards really didn't appear again until the jet age and delta planforms. I am not sure of the reasoins whty they are now prefreed in e.g. the Eurofighter..possibly because having the control surfaces well clear of the wing wash allows better control. Although that plane is deliberately unstable...

[kcaldwel]

Yep, canards can work just fine. Rutan is very fond of them. But I've seen a paper that analyzed the Voyager, and it could have made it around the world with 10% less fuel if it had had an optimized aft stabilizer design. Rutan's Solitaire canard sailplane also flew OK, but was a terribly inefficient sailplane.

Highly swept jet fighters are always odd creatures, and the elevons are probably short of control power at high alpha, and of course add flaps going the wrong way when you don't want them. So canards probably help pitch control and vortex control.

Canards are never as efficient as an aft tail layout, particularly for low speed flight. The canard just ends up far too heavily loaded if you want to make sure the fore wing stalls first. You end up with the main wing far from it's max Cl, and the lower Re canard providing huge amounts of lift inefficiently. Some of the early homebuilt canards used to uncontrollably descend in rain, because the droplets disturbed the critical laminar flow on the high lift canards. The downwash from the canard also effects the rear wing, which you can't really compensate for with twist because it is angle of attack related. And it is always hard to get the vertical tail back far enough without running a fuselage back there anyway.

Look up Ilan Kroo's papers if you want detail of optimized tail configurations. Canards fly, but you would always be better off with an aft tail, unless there is some particular engine or cargo reason that drives the design that way. That is why you don't see canard sailplanes, where efficiency is everything.

Kevin

[HugePanic]

but: at a canard-plane i have two surfaces generate lift, at a conventinal the tail is creating negaive-lift.
from this point a canard has a big advance agains a convetional tail-design.


eurofighter typhoon for example is a highly unstable aircraft, flow by an computer.
the design goal was a interceptor, for close combat, not a bomber....
the canard helps to achieve a compact design.

[Brandano]

I think the main reason for canards in the eurofighter is because they are always outside the wing wake, which helps with maneuverability, while at the same time the canard surfaces have better control authority compared to a pure delta. The delta wing gives a lot of volume for relatively low drag and good high AOA performance, and is a tried and tested planform. Also, the canard lifts the nose from the runway rather than pushing down the tail, which helps with short takeoffs. Another interesting feature present in the JAS39 Gripen is that while the plane is pitch-unstable, in the case of a flight computer failure the canards can be left feathering and the pitch control is transferred to the elevons. In this configuration the canards don't contribute to lift or control, and the plane is stable in pitch like all the older euro-delta's. I am not sure the EF2000 can do the same, but it wouldn't surprise me.
Incidentally, while th EF isn't meant to be a bomber, it has plenty of wing, plenty of hardpoints, can refuel in flight, can supercruise, has a small frontal area RCS and can fly NOE with no active emissions. All in all it makes a quite decent bomber, and could be an excellent one with a bigger fuel load. I have seen concept drawings with a conformal fuel tank on the wing root.

[MarkusN]

but: at a canard-plane i have two surfaces generate lift, at a conventinal the tail is creating negaive-lift.
Having two lifting surfaces is overrated. Especially if the front one is forced to carry much higher load, leaving the large one in an ineffective state, as it is apparently the case for a safe flying canard.

BTW, conventional designs can also be configured that the tail is carrying load in many situations. (This is not to say that one should aspire to do so, but they can.) You wouldn't use such a configuration for a highly maneuverable plane, though.

Birds don't fly canard either, not even ducks, which were used as their namesake.

[kcaldwel]

but: at a canard-plane i have two surfaces generate lift, at a conventinal the tail is creating negaive-lift.
from this point a canard has a big advance agains a convetional tail-design.

Nope. A rear tail design can have the tail lifting, no load on the tail, or the tail providing a down force. All can be pitch stable, it depends on the tail volume and stability margin.

And even with the stabilizer providing a slight down load, a tail aft design will be more efficient. Chech out some of Ilan Kroo's work from Stanford. Some are available on the web:

http://aero.stanford.edu/Reports/MultOp/multop.html

http://aero.stanford.edu/People/KrooPubs.html

Kevin

[Brandano]

The canard is normally less efficient than a correctly engineered conventional tail, because since it has to stall before the main wing it usually flies at a larger AOA, and generates more induced drag. It also flies in a different, less advantageous Reynold range when compared to the main wing, so it's much harder to maintain a laminar flow, and this naturally spoils the airflow for everything trailing it. This is the main reason why canard gliders are rare and usually not as efficient as conventional designs, or even flying wings. Naturally this changes when the plane is an unstable design, controlled by a computer.

[MCarlton]

I think in the case of Eurofighter, Gripen, Rafale et el, you can't really call them canards.

My understanding is that a Canard is an aircraft where the pitch stabiliser is in front of the main wing.

What you see on modern fighters isn't really that, its a means of controlling, by computer, an inherantly unstable aircraft at high AOA where conventional controls would be blanked out by the wing.

Modern fighter aircraft can get away with bending the rules of physics a bit, certainly in terms of stability and controllability.

As far as the original question is concerned, remember aerodynamic theory was in its infancy at the time, so most things were done on the basis of trial, error and hunch. If something worked, as it did in the Wright's initial designs, then it would have been tempting to stick with it until something else turned up.

Mind, if you look at Percy Pilcher's "Hawk" he had a rear mounted stabiliser of sorts and arguably would have been flying under power first were it not for a fatal accident. Even then, some argue with the Wright Bros. claim as first

[mnowell129]

Just to add my portion and reinforce what some have said.. The FAA requires that human carrying aircraft have a nose down stall recovery, for a canard this implies a higher loading on the canard surface than would be required for just trim. This makes the generally lower aspect ratio, smaller surface more draggy than if it just trailed behind where it can be effectively zero loaded, producing virtually no induced drag. To add insult to injury the main wing now has to fly in the dirty wake of the canard. The optimum tail is likely the t-tail where it can have low induced drag, and because it operates in clean air it can be smaller, thus have lower profile and parasite drag. Full sized sailplanes have T tails for good reasons.
Canards on jets probably have a whole different purpose since the AC shift to 50% occurs once you are supersonic. You get a nose down moment at this point and canards may be a good solution for this. Also the canards are used post-stall for combat maneuvers. The dirty wake may be an advantage as well, similar to the strakes on the F18.
The canards will also work subsonic, through transonic on into the supersonic region without much ballyhoo. Everything changes in supersonic land....

mick

[Brandano]

The dirty wake may be an advantage as well, similar to the strakes on the F18.
That's very likely. Initial studies on the X29 FSW research plane predicted it would depart in a spin once reaching about 40 degrees AOA, while flight testing turned out the plane would still mantain control over 60 degrees AOA. This obviously puzzled the NASA researchers, but eventually they found that the interaction between the close coupled canards and the wing created vortices pretty much like LERXes did. This on a plane that was pitch stable, and not completely under the control of a fly-by-wire system.

[admodesi]

...The FAA requires that human carrying aircraft have a nose down stall recovery, for a canard this implies a higher loading on the canard surface than would be required for just trim. This makes the generally lower aspect ratio, smaller surface more draggy than if it just trailed behind where it can be effectively zero loaded...

You meant to say higher aspect ratio right? Non-computerised tandem wing (conventional or canard) designs need the fore-plane to stall first to have a nose down recovery. Right? ...regardless of which surface is the main or even shared lifting surface.

[Brandano]

Well, you can also have a strongly down-lifting tail stalling before the main wing, and in that case the plane will still recover with a nose-down attitude. This can happen on planes where the CG is too far forward, it usually results in a gentle stall at low AOA, that takes a long time to recover from. Normally however the wing stalls first, the tail transitions from down-lifting to lifting and the plane recovers. On planes with a "flying tail" design and non computer assisted controls the stall recovery can be counterintuitive. On the Tornado for example if the plane enters a stall you have to pull on the stick rather than push, to try and reduce the angle the tailerons have with respect to the airstream.