How do you turn a hydrofoil ?
Posted: Mon Jun 23, 2014 11:29 pm
Hi all
Think we should make a thread of its own on this topic, as it seems many dont agree at all (actually noone agree with me it seems ), but l think we are all openminded so lets discuss thoughts and experiences.
My take on how it works:
When going halfwind or upwind, the board is angled to windward.
We have a force vector from the kite, up, plus the force from the lifting front foil wing up.
These has to balance the weight of you (and your board), nothing more nothing less.
But when the wing is tilted, it also have an upwind force.
This has to be balanced exactly by the kite downwind force (and the kite forward force is balanced by the overall foil drag).
Then we have the steady state where we ride balanced.
If we have the board tilted like this, and suddenly let go of the kite - what would happen ?
Two things can happen - we could fall backwards into the water, OR, we could initiate an upwind turn by twisting, thus making an arc as long as the foil will keep foiling.
Meaning, when a turn is started and the foil is tilted, we can make an arc or circle, simply because the force from the wing going "inside" the turn, is equalled by the centripetal force.
Nothing new about this
But my experience and thoughts are, that because you (well, your feet) are elevated 105cm above the wing and center of effort, heel or toepressure has no noticeable effect at all.
On a surfboard, toe and heelpressure will directly change how much the board is "tilted" right away, so the feedback is immense and you turn on a dime just by putting a little pressure on your toes f.ex.
This does not hold for a hydrofoil, because your feet are more than 1 meter away from the wing, IMO.
The wing is self stabilizing - why is this ?
Because, if it starts to roll or fall to one side, the inside wingtip will experience a greater AOA, and the outside a decreased AOA, thus immediately creating an correcting force/moment that will stop this roll - GREAT, and this is why a foil is stable and does not immediately fall to one side or the other.
Okay, when we ride straight in balance, we have equilibrium.
To make a turn into a narrow jibe or turn, we lean forward (inside) and twist the board at the same time.
Leaning forward and accelerating a sharp turn, is improved greatly by flying the kite to the other direction, thus we get a sudden pull which can help us both lean forward and twist the board into the sharp turn
When into the turn it goes automatically, so no biggie apart from balancing yourself (which is hard to start with).
When we want to turn back upwind from a full downwind turn f.ex, we use the opposite method - we sheet the kite OUT when we carve upwind to drop the pull, thus we lean back and turn upwind.
Of course we use toe/heel pressure all the way for balancing and fine corrections - but IMO every big change of direction/turn is initiated by a twisting motion (yaw), and not by pressure on the toes or heels.
I might be wrong, but this is my experience, and when I think about it, it also makes sense.
Unfortunately it is also the reason why it took me so long to learn - as the well known toe/heel balancing and turning on a surfboard, does not work on a hydrofoil IMO
PF
PS: Came to think about Joyriders example with a bike.
Here you balance and can lean into the turn, thus accelerating the turn.
If you stood up on the bike on a plate on the seat, hands off the handle, you could still turn by doing weight shifts.
But you dont really turn anything directly, by using toe or heelpressure, as you are 1 meter or higher above the ground.
If you used the handle to turn though, while leaning inside - you can turn sharper than if just balancing and leaning inside.
This could maybe be compared to using/initiating with a twisting/yaw motion on a hydrofoil - and as we got the kite pull to counteract both ways, we can be quite agile in turning/arcs compared to what one would think
Of course it is two different principles of balancing and turning, but point is that you dont really apply any direct turning force by using heel or toepressure when so far away from the contact point.
Think we should make a thread of its own on this topic, as it seems many dont agree at all (actually noone agree with me it seems ), but l think we are all openminded so lets discuss thoughts and experiences.
My take on how it works:
When going halfwind or upwind, the board is angled to windward.
We have a force vector from the kite, up, plus the force from the lifting front foil wing up.
These has to balance the weight of you (and your board), nothing more nothing less.
But when the wing is tilted, it also have an upwind force.
This has to be balanced exactly by the kite downwind force (and the kite forward force is balanced by the overall foil drag).
Then we have the steady state where we ride balanced.
If we have the board tilted like this, and suddenly let go of the kite - what would happen ?
Two things can happen - we could fall backwards into the water, OR, we could initiate an upwind turn by twisting, thus making an arc as long as the foil will keep foiling.
Meaning, when a turn is started and the foil is tilted, we can make an arc or circle, simply because the force from the wing going "inside" the turn, is equalled by the centripetal force.
Nothing new about this
But my experience and thoughts are, that because you (well, your feet) are elevated 105cm above the wing and center of effort, heel or toepressure has no noticeable effect at all.
On a surfboard, toe and heelpressure will directly change how much the board is "tilted" right away, so the feedback is immense and you turn on a dime just by putting a little pressure on your toes f.ex.
This does not hold for a hydrofoil, because your feet are more than 1 meter away from the wing, IMO.
The wing is self stabilizing - why is this ?
Because, if it starts to roll or fall to one side, the inside wingtip will experience a greater AOA, and the outside a decreased AOA, thus immediately creating an correcting force/moment that will stop this roll - GREAT, and this is why a foil is stable and does not immediately fall to one side or the other.
Okay, when we ride straight in balance, we have equilibrium.
To make a turn into a narrow jibe or turn, we lean forward (inside) and twist the board at the same time.
Leaning forward and accelerating a sharp turn, is improved greatly by flying the kite to the other direction, thus we get a sudden pull which can help us both lean forward and twist the board into the sharp turn
When into the turn it goes automatically, so no biggie apart from balancing yourself (which is hard to start with).
When we want to turn back upwind from a full downwind turn f.ex, we use the opposite method - we sheet the kite OUT when we carve upwind to drop the pull, thus we lean back and turn upwind.
Of course we use toe/heel pressure all the way for balancing and fine corrections - but IMO every big change of direction/turn is initiated by a twisting motion (yaw), and not by pressure on the toes or heels.
I might be wrong, but this is my experience, and when I think about it, it also makes sense.
Unfortunately it is also the reason why it took me so long to learn - as the well known toe/heel balancing and turning on a surfboard, does not work on a hydrofoil IMO
PF
PS: Came to think about Joyriders example with a bike.
Here you balance and can lean into the turn, thus accelerating the turn.
If you stood up on the bike on a plate on the seat, hands off the handle, you could still turn by doing weight shifts.
But you dont really turn anything directly, by using toe or heelpressure, as you are 1 meter or higher above the ground.
If you used the handle to turn though, while leaning inside - you can turn sharper than if just balancing and leaning inside.
This could maybe be compared to using/initiating with a twisting/yaw motion on a hydrofoil - and as we got the kite pull to counteract both ways, we can be quite agile in turning/arcs compared to what one would think
Of course it is two different principles of balancing and turning, but point is that you dont really apply any direct turning force by using heel or toepressure when so far away from the contact point.