I have an F4 Freeride foil that I use on a Slingshot Wizard 130. At low speeds (taking off and stopping) it pitches up like crazy. But, at higher speeds, especially with power in the sail, it pitches down. At a narrow moderate speed band, it's stable. This makes sense to me, as the rear wing gets lower lift at slow speeds (letting the nose up) and gets lots of lift at high speeds (pushing the nose down).
But, I haven't experienced this "instability" on other foils (Slingshot HG, Starboard race and the F4 course and slalom setups). Why are those stable at a wide speed band?
I've certainly dealt with consistently needing backfoot or frontfoot pressure and know how to adjust for that. But, what do you do when it is both frontfoot and backfoot depending on the speed?
That sounds odd. A couple of thoughts / points to check:
- what's the mast rake?
- is the mast solid/fixed in the box, or does it move? (are the bolts loose after the ride)
- what's the rear wing trim/angle?
I've only experienced excessive lift with too much rear wing angle, that is, running 330 SB stab instead of 255... Was instantly noticeable. But all foils I've tried (various SB race setups, NP F4, etc.) were consistent, unless I was running wrong stab settings, or not shimming the rake-box.
If I recall correctly from Berowne's videos which helped me heaps with my speed. Long lines - always loaded, mast foot back and heel the board. Once you're loading the sail for power it generates downforce through the mast foot which needs to be countered by back foot pressure otherwise you're touching down and doing the dolphin up-down motion. So the equilibrium is achieved between these two in addition to your front foot. essentially the sail becomes your instrument of downforce.
For the front foot at low speeds: Maybe the front wing is positioned too much forward so it tries to take off even though there is not enough board speed for it. Try moving your feet/straps forward or the wing/foil back.
Select to expand quoteWillyWind said..
For the front foot at low speeds: Maybe the front wing is positioned too much forward so it tries to take off even though there is not enough board speed for it. Try moving your feet/straps forward or the wing/foil back.
+1. When the trim is wrong, it sometimes results in behavior that is quite unexpected, and does not seem to make sense.
I sometimes have situations that feel similar to what you describe. It usually happens when the wind picks up suddenly and a lot, and I end up very overpowered. Then, the foil often wants to pop up right away, and feels unstable until I manage to push down a lot with the front foot, and pick up some more speed. Switching to smaller gear, or at least adding shims to reduce lift, usually fixes this.
Sounds to me more like a mastfoot pressure problem more power in the sail means more downforce on the deckplate bring it back 10mm try it then 5mm steps
If trim changes significantly with speed it's almost always down to shimming. Usually the tail, in this case I'd shim for more down pressure from the tail.
Select to expand quoteUS85 said..
I have an F4 Freeride foil that I use on a Slingshot Wizard 130. At low speeds (taking off and stopping) it pitches up like crazy. But, at higher speeds, especially with power in the sail, it pitches down. At a narrow moderate speed band, it's stable. This makes sense to me, as the rear wing gets lower lift at slow speeds (letting the nose up) and gets lots of lift at high speeds (pushing the nose down).
But, I haven't experienced this "instability" on other foils (Slingshot HG, Starboard race and the F4 course and slalom setups). Why are those stable at a wide speed band?
I've certainly dealt with consistently needing backfoot or frontfoot pressure and know how to adjust for that. But, what do you do when it is both frontfoot and backfoot depending on the speed?
It's mast foot pressure? Low speed it's limited (sail pressure)and once your up & flying everything becomes balanced between mast foot body weight distribution & lift from below
I can't comment from personal experience as i don't have any to that specific foil, but found a review that speaks a little about the matter:
www.windfoilen.nl/en/f4-foils-freeride-windfoil-review/
from the link:
F4 Foils mast extra attention for trim As with the F4 Foils Freerace , we had to adjust the angle of the mast slightly to ensure that the nose of our board stayed up nicely. The angle of the fuselage to the bottom of the board is standard 0 degrees. We may easily get on the foil, but during wind foiling we have to tilt our sail quite far back to ensure that the nose of our board remains neatly horizontal in the air. In addition, the board slows down considerably as soon as we have a touch down.The solution is to use special spacers or shims to adjust the angle of the mast in the board. After some trial and error we arrive at an ideal angle of between 2 and 3 degrees. With this angle we have more lift and the nose of the board stays nicely in the air. We feel a better balance in the complete set and that also gives a little more power on average. We stay also more comfortable, which also gives us more control. As an additional advantage, the nose of the board rises nicely again when we have a touch down. We also give the back wing with the included shims a slightly more positive angle to get a little more lift. These 2 adjustments ensure that we have sufficient lift at all times and have a good balance in the set.
so maybe same thing going on for you?
I think seaanchor has it. Downforce from the sail makes a big difference. The more the sail is powered and sheeted in, the more downforce it exerts. It is the third point of balance besides the two feet. This is what differentiates windfoiling from wingfoiling and kitefoiling.
A properly designed foil sail with push down with more wind power. This helps prevent porpoising at speed.
That's weird, almost like the tail is stalled or doesn't have enough angle for low speed.
I've lost control like that sometimes when getting caught in weeds wrapped in the foil, but that caused me to not be able to fix it and then crash, it wasn't uniform up and down issues but also roll.
OK. So, I think I'll add a shim to depower the rear stab for less pitching up at low speeds. To try to make it not pitch down at higher speeds, I'll try moving foil and rig backwards in their tracks. I'll probably try just the stab first and see if that helps.
Select to expand quoteUS85 said..
OK. So, I think I'll add a shim to depower the rear stab for less pitching up at low speeds. To try to make it not pitch down at higher speeds, I'll try moving foil and rig backwards in their tracks. I'll probably try just the stab first and see if that helps.
The stabiliser has minimal impact at slow speeds. Depowering the stabiliser will make the foil even more rear footed at high speed. The foot pressure changes you describe are exactly what you would expect with insufficient stabiliser downforce. It's best to get the speed related balance changes minimised first and then adjust the foil in the tracks for your preferred front/rear foot balance.
Most large foils feel very front footed just before they stall. That's because you're riding with a very high angle of attack to get enough lift at low speed. The extreme board angle pushes your weight more over the tail of the board and makes the foil feel front footed. I wouldn't try to tune the foil for that scenario as it will ruin it for the rest of the speed range. Just try to throw your weight forwards in those situations or keep the nose lower and accept you'll either touch down or will need more speed to get on the foil.
The board will always pitch more nose down at higher speeds as you adjust the angle of attack to keep constant lift. If the nose is excessively low you could using a plate shim under the tracks to have a more nose up stance.
