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Shin_kazama

Canard real purpose in life....

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Canards can perform several functions.

 

In a tailless delta, if the canard is movable as on the XB-70, it replaces the elevator.

It has a big advantage in this role since the elevator must push down on the tail to stabilize the aircraft and therefore subtracts from the lift of the wing.

The canard on the otherhand, pulls up the nose to stabilize the aircraft, which adds to the lift.

The Wright brothers chose to use a canard on the original Flyer for this very reason (they were struggling to get the best possible lift/drag ratio to make up for their lack of power).

The disadvantage to the canard in this role is that having the stabilizing force forward of the wing is inherently unstable.

Almost all planes after the Wright Flyer used a tail instead of a canard for this reason.

Modern fly-by-wire solves the stability problem and makes the canard superior to having a tail in most situations.

A movable canard is a huge advantage for tailless delta winged aircraft.

Without the canard, they cannot have landing flaps, as the trailing edge flaps are the sole means of controlling pitch.

With a canard, the wing can lower the trailing edge flaps and the canard can push up to counter the resulting pitch moment, providing the maximum amount of lift possible for STOL.

 

Small fixed canards are not nearly so useful, but can provide much better airflow over a wing at high angles of attack for very little cost in drag and weight.

They pretty much provide the same benefits as leading edge root extensions by helping the air flow stay attached to the wing at angles where is would normally separate and lead to stalling.

The canard generate vortices which energize the air over the wing to keep it flowing despite the high angle of attack.

Vortices are a drag penalty, but the turbulent separation of airflow from the wing is both a huge drag and lift penalty.

So there is a useful net gain in lift and drag despite the drag caused by the canards.

 

The only time you should see canards moving down on an aircraft is when the pilot wants to lower the nose and/or reduce the angle of attack.

In level flight and sustained turns, the canard should generally be in a position to cause lift or be in a neutral position.

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StreakEagle is mostly right, however if you look at the video a few years back from the Typhoon display at Fairford where it nearly hit the ground you'll see something odd.

As the aircraft is at the bottom of it's loop and about 6' off the deck, and with the pilot presumably having both feet on the instrument panel to pull back as hard as he can the canards are pointing down, i.e. providing a downwards pitch moment. However the Typhoon continues to loop up away from a very expensive and slightly embarrassing crash. Why? Well the Typhoon is a dynamically unstable aircraft with computers doing all the clever stuff. The pilot has told the computer he wants to pull up, lots, the aircraft gives itself a massive nose up pitching moment in response, at this point being unstable the aircraft would keep pitching up until the wings stalled and it crashed horribly. To prevent this the canard applies just a enough pitch down moment to hold the aircraft on the edge of controlled flight so it changes direction as quickly as possible without stalling. The canard is basically opposing the aircraft's tendency to continue moving/rotating in any given direction once the initial movement is made, you only get this with dynamically unstable aircraft with FBW control systems.

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Also I think sometimes the canards are directing airflow onto the wings behind them to prevent accelerated stalls and create vortices and so on. They're quite small on the Typhoon compared to say the Viggen and their overall lift is minor.

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The Typhoons canards are pretty big and bear in mind compared to the Viggen they're all moving.

 

 

but seing this berkut video, i still need enlightenment.

 

notice both elevatros and canards point down.

 

 

 

the thing i am saying is a 1:30.

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The Su-30, Su-33, and the Su-34 have canards that work in unison with the AC's flight control computer to prevent the pilot from exceeding alpha limits, and to stabilize the aircraft while in level flight (an advantage when delivering weapons at low altitudes).

 

On, the Su-33 in particular, you will often see the canards opposing the elevators during a carrier approach, helping the aircraft maintain the proper glide slope with as little interaction on the pilot's part, as possible.

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Also with most of these newer fly by wire systems, the computers will not allow the airframe to be over stressed by pilot input. One more possible reason that the canards could have been pointed down, as pointed out by skippybing.

Edited by MAKO69

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- the Berkoot is a special case...it was a maneuverability demonstrator essentially

 

- the quick answer...canards make the front end of the plane stall before the wing stalls...while instantaneous direction delta is improved by essentially changing the moment arm, it makes the plane more stable because it reduces the chances of stalling the wing...which can be bad

 

- yes I know about post-stall maneuvering...any airplane can post-stall maneuver...usually that is called falling out of the sky...some airplanes like the Berkoot and some Flankers are the exception for a very long explanation

 

- and dont forget...3wire is a GAME...not a sim...while fun, dont use it to write your term paper

 

- enter fast cargo to disagree with me

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- the Berkoot is a special case...it was a maneuverability demonstrator essentially

 

- the quick answer...canards make the front end of the plane stall before the wing stalls...while instantaneous direction delta is improved by essentially changing the moment arm, it makes the plane more stable because it reduces the chances of stalling the wing...which can be bad

 

- yes I know about post-stall maneuvering...any airplane can post-stall maneuver...usually that is called falling out of the sky...some airplanes like the Berkoot and some Flankers are the exception for a very long explanation

 

- and dont forget...3wire is a GAME...not a sim...while fun, dont use it to write your term paper

 

- enter fast cargo to disagree with me

 

thanks all for the info...

 

BTW, i still enjoy 3wire sims........

 

and not making a term paper, :biggrin:

 

just want to learn...

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