Mushin said..

Sandman1221 said..

Mushin said..

Sandman1221 said..
Mushin You mentioned above how you felt you were planing but could not get up on the foil. With my AFS W95 foil when I had that problem it was solved by putting a 0.5 mm AFS shim under the front of the stabilizer, then the foil came up easily! I think I saw a shim set on the Alpinefoil website. I now always run the AFS foil with the 1 shim on the stabilizer, with any of the 3 wings I have (F1080 F770 S670) and in any wind condition from 8-30 knots.

I mentioned the use of +0.7 shim in my first post, that made it easier also in lower wind i tried the +1.5 shim. But I think that a need for a shim in a broad range of wind conditions like that could really be a sign of the foil not being in balance. Maybe other experienced riders can comment on that.

I think the way AFS made the foil was for the stabilizer to be neutral, so that you could shim it based on the board maybe?, foil is perfectly balanced on my board with the 1 shim, they made the shims for a reason!

I understand it in the way an airplane works, elevators are used to make the plane fly with lower speed or even higher speed. When flying in a straight line at optimum speed they are set to neutral. There is also a control aspect to the elevators which is not relevant for foils. So the shims can be used to change the angle of attack to make the foil fly with lower speed. However changing the angle of attack from default neutral decreases the overall efficiency mainly by causing more drag. Also I think it might affect stability of the foil in a bad way at speeds the shims were not intended to be used. So in short elevators are replaced by the stabilizer shim and flaps are replaced by the main wing shim on the foil.

If the foil is to far back adding negative lift makes it counteract the imbalance of having the Center of Gravity to far forward from the Center of lift. But it comes at a cost of increased drag and possibly worse stability. The user might have the feeling of better stability because it's not necessary to constantly press on the back leg... but that might be misleading.

It is however possible that some foils might be deliberately designed this way but I think it would be mentioned explicitly in the user manual or something.

I am not actually an expert for foils or an airplane engineer so if someone is... your opinion is welcome!

I made a mistake in my previews post and cant edit it anymore so here is a repeat to fix the mistake.

I understand it in the way an airplane works, elevators are used to make the plane able to fly with lower speed or even higher speed. When flying in a straight line at optimum speed they are set to neutral. There is also a control aspect to the elevators which is not relevant for foils. So the shims can be used to change the angle of attack to make the foil fly with lower speed. However changing the angle of attack from default neutral decreases the overall efficiency mainly by causing more drag. Also I think it might affect stability of the foil in a bad way at speeds the shims were not intended to be used. So in short elevators are replaced by the stabilizer shim and flaps are replaced by the main wing shim on the foil.

If the foil is to far back adding negative lift to the stabilizer (pushing down) makes it counteract the imbalance of having the Center of Gravity to far forward from the Center of lift. Effectively correcting the incorrect foil pitch back to zero. But it comes at a cost of increased drag and possibly worse stability. The rider might have the feeling of better stability because it's not necessary to constantly press on the back leg... but that might be misleading.

It is however possible that some foils might be deliberately designed this way but I think it would be mentioned explicitly in the user manual or something.

I am not actually an expert for foils or an airplane engineer so if someone is... your opinion is welcome!

Now another question arises:
When one wants to get going earlier (in lighter wind) is it better to change the angle of attack of the main wing or the stabilizer?

Mushin said..
Now another question arises:
When one wants to get going earlier (in lighter wind) is it better to change the angle of attack of the main wing or the stabilizer?

The recommendation from Starboard for light winds is shimming the stabilizer (+1 is maximum for the IQFoil setup, which gives the stab more down lift, and thus pushes the nose up). I've found that shimming the stab while also pulling the mast base back definitely gives earlier takeoff with pumping, combined with a higher boom, looser outhaul, as well as better upwind/downwind angles in marginal wind.

Higher boom, if I understand correctly, equals less mast base pressure, so earlier flight. Same with stab shim and aft mast base. I drop the boom on the 9.0 at closer to 14-16kts on the IQ setup and it makes it much easier to ride, as well as about 1cm forward on the mast base.

I am unaware of anyone designing for shimming the fuse/front wing (may just be my own ignorance though), but it will change the relationship between the board and the wing. More shim on the front will add drag before flying as well as make the board fly nose-down for the same hydrodynamic lift. If anything, racers will rake, or shim, the mast board connection to give the front wing more down angle. This causes the board to ride nose-high which helps when in heavy waves/chop.

Forward rake or positive front wing shim, because it will cause the board to fly nose-down, will be more likely to stick/pearl/catapult.

Also, looks like the ones with the longer fuse (f4 or the other alpine line that's a little more forward) will be better in upwind/downwind and the jibes.

When the board tilts to the side, which you want for upwind, this spends a lot of the lift laterally to push against the wind, and requires more backfoot pressure. So, more forward wings give you more upwind power and ability to tilt the board, but it makes it harder to do a beam reach fully powered.

For jibing, in a carve, the board is tilting so you need some more lift/backfoot pressure, and you also slow down unpowered so a more forward front will give you more lift. Shimming will help too but I haven't done the math on how big the difference is.

aeroegnr said..

Mushin said..
Now another question arises:
When one wants to get going earlier (in lighter wind) is it better to change the angle of attack of the main wing or the stabilizer?

I am unaware of anyone designing for shimming the fuse/front wing (may just be my own ignorance though), but it will change the relationship between the board and the wing. More shim on the front will add drag before flying as well as make the board fly nose-down for the same hydrodynamic lift. If anything, racers will rake, or shim, the mast board connection to give the front wing more down angle. This causes the board to ride nose-high which helps when in heavy waves/chop.

Forward rake or positive front wing shim, because it will cause the board to fly nose-down, will be more likely to stick/pearl/catapult.

(reply refers only to a part of the post)
If I am understanding correctly you are referring to modifying the board - foil connection as changing the angle of attack for the front wing?
I don't think this would actually help with lift at all, it would only cause the board to fly nose-down as you said. Because the relative relationship between the front wing, fuse and stab angles is still the same. There would be no change in angle of attack.

If you are referring to adding a shim just to the front wing (for adding more lift to take off earlier)... I would not expect it to change the pitch of the whole assembly. Except maybe as a consequence of the stab producing less lift due to lower speed and thus causing overall pitching down. I think the rider would compensate for that possible pitching down intuitively and possibly not be aware of it at all.

With my Alpinefoil shims were included for both the front and the back wing.
I've seen a video of someone using the most powerful shims on the front and back of the alpine foil to get going at really ridiculously light wind.

Increasing the angle of attack should produce more dynamic drag when flying not just when pumping to get going or slogging.

I use a shim between the foil mast head and the DT box to align the fuselage/foil with the board so the board is parallel to the water when in flight. That shim was tricky to make, shimming the front wing would be easier, but with the foil mast head shim I now have a solid connection between the foil and board.

Grantmac said..
Can you use the ULW1200 with the 122cm fuselage? Generally the longest fuselage with biggest wing will offer the easiest learning.
Don't get too wrapped around shimming until you actually get flying.

Looks like yes! I asked Alpinefoil and looks like the ULW1200 is compatible but the answer was not specific so I have sent another email asking for details. Damien confirms that it should improve takeoff, feel and overall performance.
The trouble with shimming for me is that it is a necessary evil because my local spot has barely some wind in the summer time. This is part of the reason for my slow progress. I'm really keen to get the 122cm fuse because form my personal experience so far and the great information from the people here I conclude that the imbalance of the foil was setting me back especially in combination with the lack of wind.

The ULW1200 is compatible with the 122cm fuselage and looks like the midpoint of the wing will be just a bit in front of the F4 Race foil. The center between the straps is located somewhere in the White Shaded Area. I have decided to buy the 122cm fuselage.

Grantmac said..
Expect to move straps forward and run a negative shim on the tail. I'm betting that will be a very good combo once you adjust to it.

Thanks for the tips! I will try that as well and see what works best :-)