tspear
Well-Known Member
Ok, I have searched this forum, the Velocity Forums, canardaviation and a dozen or so others.
I know the following basic information.
-- Everyone says do not put flaps on a canard airplane
-- Too complicated for a home built aircraft
-- If you add flaps to the main wing, you need to add them to the canard...
and so on.
So with that stated, I am computer geek, not an engineer. So tell me where I am wrong.
Case one: Add flaps to the main wing, changes the chord on the main wing, effectively increasing the lift, depending on the flap type may move the center of lift of the wing. As a result, to maintain the same attitude, the angle of attack on the canard increases causing it to stall earlier.
Case two: Add flaps to both the canard and the main wing. Adds massive complexity, failure mode can cause asymmetric lift situations were it would be possible to stall the main wing and not the canard (probably not recoverable)
Case three: Swing the canard (e.g. Beech Starship) as the flaps deploy on the main wing, changes the center of lift of the canard placing a greater load on the main wing. The side effect is to reduce the amount of lift needed by the canard which reduces the angle of attack required by the canard, allowing the plane to slow further before the canard will stall.
Aerodynamically, slats can extend the chord of the wing forward which moves the center of the lift forward. Depending on the design of the slats, many include slots which are usually good for increasing the energy of the boundary layer allowing the wing to fly at a higher angle of attack before stalling.
Historically in a traditional airplane, moving the center of lift forward is contraindicated because it can either create a tail stall or actually place the CG behind the center of lift leaving the plane in an unrecoverable situation. In a canard, you could actually end up in a situation where the canard can lift the nose to the point where main wing stalls and you back in an unrecoverable situation.
Since this is the case, why not combine slats and flaps on the main wing? The slats would move the center of lift forward increasing the ratio of weight carried by the main wing reducing the load on the canard. The canard carrying less weight would require a lower angle of attack, allowing the plane to fly slower. Since you would not want the slats to change the center of lift too much, combine the slats with flaps increasing the chord of the main wing increasing its lift.
From what I have read, this should just be a math problem to determine how much we want to move the center of lift forward, and then design the slats and flaps to match. By using a Gouge style flap, you can control the amount of movement in the center of lift. Since asymmetric lift would still be an issue, a worm drive connected to both the slat and flap would keep them in sync. This could dramatically lower the stall speed of the plane, allow shorter fields...
If I am correct, and this is a math problem. What are some of the design and calculation problems? If you are a home builder, how do you design test this in a safe manor? (e.g. you do not want to actually stall the main wing, how do you just build it with a guess and find the right slat/flap ratio via trial and error)
Note: This is purely an academic exercise for me, I am trying to get a feel what could be possible, what the effect would be, and how hard the effort. How much from a schedule perspective would I need to work with the factory. I would not even consider this kind of change without the factory/designer support.
Tim
I know the following basic information.
-- Everyone says do not put flaps on a canard airplane
-- Too complicated for a home built aircraft
-- If you add flaps to the main wing, you need to add them to the canard...
and so on.
So with that stated, I am computer geek, not an engineer. So tell me where I am wrong.
Case one: Add flaps to the main wing, changes the chord on the main wing, effectively increasing the lift, depending on the flap type may move the center of lift of the wing. As a result, to maintain the same attitude, the angle of attack on the canard increases causing it to stall earlier.
Case two: Add flaps to both the canard and the main wing. Adds massive complexity, failure mode can cause asymmetric lift situations were it would be possible to stall the main wing and not the canard (probably not recoverable)
Case three: Swing the canard (e.g. Beech Starship) as the flaps deploy on the main wing, changes the center of lift of the canard placing a greater load on the main wing. The side effect is to reduce the amount of lift needed by the canard which reduces the angle of attack required by the canard, allowing the plane to slow further before the canard will stall.
Aerodynamically, slats can extend the chord of the wing forward which moves the center of the lift forward. Depending on the design of the slats, many include slots which are usually good for increasing the energy of the boundary layer allowing the wing to fly at a higher angle of attack before stalling.
Historically in a traditional airplane, moving the center of lift forward is contraindicated because it can either create a tail stall or actually place the CG behind the center of lift leaving the plane in an unrecoverable situation. In a canard, you could actually end up in a situation where the canard can lift the nose to the point where main wing stalls and you back in an unrecoverable situation.
Since this is the case, why not combine slats and flaps on the main wing? The slats would move the center of lift forward increasing the ratio of weight carried by the main wing reducing the load on the canard. The canard carrying less weight would require a lower angle of attack, allowing the plane to fly slower. Since you would not want the slats to change the center of lift too much, combine the slats with flaps increasing the chord of the main wing increasing its lift.
From what I have read, this should just be a math problem to determine how much we want to move the center of lift forward, and then design the slats and flaps to match. By using a Gouge style flap, you can control the amount of movement in the center of lift. Since asymmetric lift would still be an issue, a worm drive connected to both the slat and flap would keep them in sync. This could dramatically lower the stall speed of the plane, allow shorter fields...
If I am correct, and this is a math problem. What are some of the design and calculation problems? If you are a home builder, how do you design test this in a safe manor? (e.g. you do not want to actually stall the main wing, how do you just build it with a guess and find the right slat/flap ratio via trial and error)
Note: This is purely an academic exercise for me, I am trying to get a feel what could be possible, what the effect would be, and how hard the effort. How much from a schedule perspective would I need to work with the factory. I would not even consider this kind of change without the factory/designer support.
Tim
