foil mount position

[Scuba]

Hi chaps

I have a new build under way, having built a foilboard already that flys well.
I thought I would ask the question on the foil mount position before I sink the tuttle box in the board.
I was just going to mount the foil in the same location 285mm from rear of board to trailing edge on the foil, but am thinking of moving the mount further forward.
I have noticed the spotz is mounted quite far from the back of the board, also the new liquid force is really far forward.
would you think that by having the foil mounted further forward that it would be more stable and less twitchy ie up n down , as your centre of gravity is more over the lifting forces?
your thoughts are much appreciated.
Steve

[davesails7]

Once you are on foil, the position of the foil to board does not matter. When on foil, the foot strap position relative to the foil is what matters.

The Tuttle box position in the board matters more for when the board is on the water. I think my Tuttle box is a little far forward on my board. Makes it tougher to do the touchdown Jibes. I have to keep weight forward to keep foil down, but that weight position is a little too far forward on the board and the nose digs in sometimes.

[Peter_Frank]

If you have straps/plugs on your board, there is only one correct box position, for a given hydrofoil in neutral trim.

You can not move it forward or rearward - then it wont work, has to be very precise.

If you take another brand hydrofoil, the mast should f.ex be mounted much further forward, or rear, to work.

When hydrofoiling you have to be in balance for things to work, so as said, you can not move it really

But you can mount it wrong, thus useless

So be careful and mount it correct, so it fits your hydrofoil.

This is easy with standard hydrofoils, as you can measure the distance to rear and front strap on a working board/hydrofoil and thats it.


On a homebuild, you can do one of the following:

1. Take a chance and cross your fingers, that everything is trimmed correct.

2. Have multiple inserts for straps, and cross your fingers you will be able to trim your foil within these.

3. Mount the foil on "something" that can hold together for a short while (an old beat up waveboard or similar), and ride strapless and find the position you need to mount it bulls-eye on your new board.

4. Adjust the AOA to change the COE forward or back, so you can use your existing mastposition even when quite off the neutral trim with your default AOA.


#2 and 3 is of course the best options.
#2 will often work, if you just aim your measurements/distances like what the manufacturers do at existing hydrofoils if yours are similar - but be prepared for a surprise, as it might also NOT work.
#3 only works if you are experienced.

IMO

PF

[WCH]

On a new set up; lay your fuselage, with wings mounted on it, on top of your board, put your feet in the position that you want them to be on your board.
1/3 back from leading edge of front wing will be your CG, move your fuselage front to back until that CG point is between your feet. Note where the mast will be. After mounting you can fine tune with your foot strap.
changing types of wings, high or low A, can make the mast position fall in a different place, most of the time you can adj your foot straps.
If you are in the design phase, try to put you CG of the front wing on the same spot each time on the fuselage.
You can shim your rear stabilizer to get good balance, but you will induce drag, and the foil will react differently at speeds.
This has been a good starting point fo me.
Using a Lift mast track board now and when changing front wings I note where the position works best and record that position for next time.
Have fun and be careful out there

[Scuba]

Thanks for the replies guys.
I was going to do option 3 ie mount it on an old board and move it around but hard to do with a tuttle,
Then I was going to make a tuttle to plate mount just for the purpose of finding the right location.
But I think I will take my chance and mount it in the same location as the other home build I have that works nicely.
I have wanted to start taking the shim out of the rear wing and moving the foot straps backwards to reduce drag, but have limited time at the mo, on my home build.

I was even going to offer it to ride with anybody down Melville with a tuttle mount just to see how it went, I may still do this option.

Still have to wait 3-4wks for my leg to heal so very frustrating.....

Thanks again guys will post pics when can.
Cheers
Steve

[Europ2]

1/3 back from leading edge of front wing will be your CG, move your fuselage front to back until that CG point is between your feet.

True if the wing is rectangular (constant chord) and perpendicular to fuselage ie not tapered.
What happens if your leading edge is not perpendicular to the fuselage or if the chord is not constant ? -> estimate the position of an equivalent rectangular wing perpendicular to fuselage !

I have never tested for a foil (only RC model) but an even finer method could be to apply this 1/3 method to the Mean Aerodynamic Chord (MAC) of your projected front wing.

What WIKI says

The MAC is a specific chord line of a tapered wing. At the mean aerodynamic chord, the center of pressure has the same aerodynamic force, position, and area as it does on the rest of the wing. The MAC represents the width of an equivalent rectangular wing in given conditions.

If your front wing is elliptical it can be approximated by 3 or 4 tapered segments from which you can calculate the equivalent MAC.

In practice, your CG should move aft towards the mast by 2 to 5 cm (1 to 2 in).
Please keep us posted and let us know which method brings the best results as center of your straps ie the most comfortable position with neutral (zero lift) stab position:
- 1/3 of root chord from leading edge = "raw" method,
- 1/3=33% of MAC chord of the shade of your front wing when "lit from above" (projected surface)

In fact, it's not your foil that you should lay over your board that will be useful but its outline/footprint drawn on a sheet of paper with mast position on fuselage - pen held vertically and contouring Fwing and fuse on 3 A4 taped sheets.

Example of graphical method for a tapered wing :
ACe = Aerodynamic Center Equivalent
ACw = Aerodynamic Center Wrong

[Europ2]

I was going to do option 3 ie mount it on an old board and move it around but hard to do with a tuttle,

It was true until the arrival of the arrow-foil.com (=TheKiteFoil.com) fin-box which is in fact a rail .... for tuttle plugs if used with an adaptor. Why not asking Renaud Barbier its availability in his own thread ?
Nobody has tested this 170USD method yet so you'd be a pioneer much looked after

If TheKF solution is demonstrated to be effective, no doubt a 100% tuttle rail or Ketos Fbox rail will emerge.



http://arrow-foil.com/products/tkf-fin-box

[Edge19]

Without getting to technical, I just put the foil on the floor and stood over the wing. One foot forward one behind, held the board in relation to where I wanted my feet and marked the position of the strut on the board.
I could have been lucky but it was bang on the button .
I left the rear strap off, To help find the balance point. It was central right over the rear strap holes.

Job done

Good luck