yaw stability

[lovethepirk]

I rode a friends LP foil today and after getting the stabilizer to 3 degrees it is riding well but it felt crazy wiggly on the nose, just a weird uncomfortable feeling...one of those weird feelings that draws you into it and you try to investigate so I just wiggled the nose back and forth, which is completely impossible on my Delta foil.

The older Delta foil I'm riding has a rudder and it made me appreciate that, BUT if I remember I've ridden other foils without the rudder that didn't exhibit this yaw unstability.

Question....obviously a rudder would reduce this yaw...honestly I thought the mast would take care of this for you, but what is the reason a foil would be unstable in the yaw disregarding the rudder?

[Peter_Frank]

Not sure I understand, did you try to ride it without the 3 degree stabilizer adjustment and there was a difference, or is it not the topic ?
I assume you mean minus 3 degree adjustment so it pulls a bit more down thus initially feels stable, right ?
Assume it is beyond the topic though...

There are several parameters that determines yaw stability, fuselage outline, mast position, wing design, washout or not etc.

But if these are pretty given, then yes, the rudder is the determining factor.

A stabilizer which is swept up or down, or has winglets = rudder, exactly the same thing.

It is not that easy though - as many of us like a really "loose" foil for tricks and waves, and this requires at least a smaller stabilizer.

Stabilizer size and rudder is a bit different though, as some like a foil that can be turned yaw wise thus little or no rudder effect, others like to have a tracking effect of the rudder so it does not feel as nervous (like you describe, nose wiggly).
Exactly the same thing as with waveboards and fins - two different opposite likings with each their advantages.

Regarding stabilizer SIZE, somewhat the same applies, as a smaller stabilizer means a livelier foil in both yaw and pitch, so more twitchy and difficult to ride, but more fun.

Till some extent, as when too small, it becomes "no good".

I've got a supersmall stabilizer without winglets nor V, and it is really fun often, but can also be too twitchy and I opt for a still quite small but a bit more upswept shape, so still lively but still feels good in terms of desireable tracking

For learning things, a big stabilizer and rudder effect, is much easier.

I took a look at the LP stabilizer(s), and it is almost flat with only really small winglets, so not much rudder effect no, which explains your experience, some dont like it others love this.


Short story is, rudder effect means a lot, but you gotta try to find your personal liking for your specific style, to know what you like

It was not an answer to your question, I know, but the yaw stability is the outcome of many design parameters and not that easy to determine without looking a the complete foil design, and not just one or two factors.

PF

[FattyArbuckle]

We,ve found, trying various foils including dedicated wake foils / windsurf foils / kitefoils that a degree of yaw instability makes learning/ starting and recovering from some situations easier...Easiest of all foils we,ve tried is Crazy foil with no rudder at all...it means it can be steered twisting shoulders ( as on snow board) In some situations.(ie at slow speeds board can get crossed and wants to push mast clear of water behind you) you simply cant get enough pressure to get board back inline...but if you twist shoulders to.oppose direction board/ foil is wanting to go it is possible to recover situation where a foil with " heavy" directional stability simply cant be recovered..( Our experience of foiling at present is very limited to behind boat, on WS or kite it would be possible to depower and recover, obviously behind boat that is not an option)
Our Crazy foil cann be steered with shoulder twist...the NP flight can not..behind boat that helps...no idea about other situations...it would mean with WS you,d have to keep CoE lined up with CoR or it would turn up or down wind more than NP flight...but CF is designed specifically for wakefoiling...???!!;

[FattyArbuckle]

We,ve found, trying various foils including dedicated wake foils / windsurf foils / kitefoils that a degree of yaw instability makes learning/ starting and recovering from some situations easier...Easiest of all foils we,ve tried is Crazy foil with no rudder at all...it means it can be steered twisting shoulders ( as on snow board) In some situations.(ie at slow speeds board can get crossed and wants to push mast clear of water behind you) you simply cant get enough pressure to get board back inline...but if you twist shoulders to.oppose direction board/ foil is wanting to go it is possible to recover situation where a foil with " heavy" directional stability simply cant be recovered..( Our experience of foiling at present is very limited to behind boat, on WS or kite it would be possible to depower and recover, obviously behind boat that is not an option)
Our Crazy foil cann be steered with shoulder twist...the NP flight can not..behind boat that helps...no idea about other situations...it would mean with WS you,d have to keep CoE lined up with CoR or it would turn up or down wind more than NP flight...but CF is designed specifically for wakefoiling...???!!;
I,d guess the yaw instability of Crazy Foil would be problematic if used for kiting or WS ??? But behind boat its a bonus...( IMHO) I ,d leave a long fin in WS board if attempting to windfoil on CF..???

[davesails7]

Another way to add yaw stability is to move the strut attachment back on the fuselage. This greatly increases the stress on the board and on the fuselage, but many newer race foils have done this because race foils are all about going fast in a straight line.

As Peter pointed out, any vertical surface (including stabilizer wingitps) will add to yaw stability. The further they are from the center of rotation (the strut) will make that area more effective at increasing yaw stability. With the strut moved back on the fuselage, the front wing is further from the center of yaw rotation, so makes the foil much more directionally stable.

For waves and freestyle, yaw stability is not a good thing because you want to make tight carves.

[FattyArbuckle]

For waves and freestyle, yaw stability is not a good thing because you want to make tight carves.

Apologises, mid read this originally. Yes, I agree. Heavy yaw stability will interfere with carving tight turning.