With the introduction of the step/fence on the new GoFoil wings. Anyone playing with the idea of adding fences to existing wings and what are the results?!? I'm envisioning some sort of 3m stick on product. Probably have my head in the clouds.
yes, I think something like what's on a) will work great on a foil that has issues blowing out when breaching tips.
Select to expand quotefoilthegreats said..
With the introduction of the step/fence on the new GoFoil wings. Anyone playing with the idea of adding fences to existing wings and what are the results?!? I'm envisioning some sort of 3m stick on product. Probably have my head in the clouds.
The GoFoil uses a very abrupt twist change that forms a step but imho the breaching goodness comes more from the twist (unloaded wingtips) than from the step.
There is no fence on the top,low pressure side which is the one sucking air in a breach.
A true fence as in a) or vortex generators as in b) are going to add a lot of drag.
what airplanes do (expecial delta wings) is downward leading edge extensions to accomplish the decreased angle of attack on the tips (like the opposite of the gofoil) This has the added benefit of a notch to interupt spanwise fliow (on delta wings the flow has a tendency to run the span). Lots of fighter jets (delat wings) have bumps for this.
Bumps interupting spanwise flow might be one of the things that makes the kujira special. Also, those bumps might be giving areas of the wing different effective angles (peaks of bumps have higher AOA than valleys) making parts of the wing stay effective in adverse AOA scenarios. This might be part of what gofoil is going for with angled tips
If you look closely all foils that I have seen have the same angle of attack twist that GF does, just that most wings are continuous twist from root to tip and the GF wings have the abrupt change that also seems to act as a fence. I measured the twist carefully on a few wings and the tips are angled about two degrees more than the root and the progression is exponential from root to tip, so most of the wing isn't twisted until you get out to the ends.
Select to expand quotejondrums said..
If you look closely all foils that I have seen have the same angle of attack twist that GF does, just that most wings are continuous twist from root to tip and the GF wings have the abrupt change that also seems to act as a fence. I measured the twist carefully on a few wings and the tips are angled about two degrees more than the root and the progression is exponential from root to tip, so most of the wing isn't twisted until you get out to the ends.
Super interesting insights on the twist! Anyone knows a place to learn about airfoils applied to foiling?
the vortex generators are hillarious!
Tip stall is so bad and uncontrollable we're going to purposly screw with the flow on the other end to make sure it stalls there first!
I think some things don't translate well from airfoils to hydrofoils
Select to expand quotemcrt said..foilthegreats said..
With the introduction of the step/fence on the new GoFoil wings. Anyone playing with the idea of adding fences to existing wings and what are the results?!? I'm envisioning some sort of 3m stick on product. Probably have my head in the clouds.
The GoFoil uses a very abrupt twist change that forms a step but imho the breaching goodness comes more from the twist (unloaded wingtips) than from the step.
There is no fence on the top,low pressure side which is the one sucking air in a breach.
A true fence as in a) or vortex generators as in b) are going to add a lot of drag.
Agree it's mostly about unloading the tips, foils that handle tip breaches such as the lift just have similar de loading by running a more neutral section near tips, also I think it's worth noting that most foils will handle highly loaded breach with a decent amount of foil out, I think the 'goodness' is the ability to handle the slight tip breach with minimal change in feel. When you bank into a turn and kind of hear it but don't feel it, the **** is working
Select to expand quotejondrums said..
If you look closely all foils that I have seen have the same angle of attack twist that GF does, just that most wings are continuous twist from root to tip and the GF wings have the abrupt change that also seems to act as a fence. I measured the twist carefully on a few wings and the tips are angled about two degrees more than the root and the progression is exponential from root to tip, so most of the wing isn't twisted until you get out to the ends.
Interesting! That's hard to spot just eyeballing
Talking about multiple different things here.
The change in AoA from the wing root to tip is called wash out.
Wing fences are a great but crude way to stop spanwise flow on foil. Plus they are sharp and prone to damage. It has been done and yep it works.
Since 99% of foils are straight ie not highly swept or delta config simple works best. Biggest issue with foils as opposed to a plane is the large and constant AoA changes through a massive speed range. Never happen on a plane.
One of the best but least used aerodynamic tools used on planes that would work for foiling is a Vortilon. Never going to happen.
The GO foil line is currently using both a simple fence design and a cuffed leading edge amalgamation. It's all about stopping the boundary layer separating at high and changing AoA's. It works too. There is other stuff going on in the actual foil shape obviously.
Also if your interested have a gander at NACA aerofoils for basics shapes.
if it works in the air it will work in water to a degree.
Select to expand quoteTooMuchEpoxy said..
the vortex generators are hillarious!
Tip stall is so bad and uncontrollable we're going to purposly screw with the flow on the other end to make sure it stalls there first!
I think some things don't translate well from airfoils to hydrofoils
The vortex generators are used on the wing root on that illustration,not the tips.
They are supposed to create a higher energy turbulent flow to delay stalling where it occurs first.
www.boldmethod.com/learn-to-fly/aerodynamics/vortex-generators/
Anyway the problem with breaching is ventilation,not a stall.
They stick VG's anywhere on planes these days. 737's have them on front below the windscreen to quieten them down.
Fences or steps make the most sense as the work on the boundary layer.
I've used fences years ago on windsurfing fins to stop ventilation travelling down from the surface. They work really well, and they are relatively easy to make and attach, but are easily damaged. Worst of all they will pick up any weed that would normally slide off the end of the foil.
Gofoil's approach with the step seems like a better approach, I've got an RS 1150 now and it seems pretty immune to tip ventilation, it seems to be an extremely well behaved foil.
Select to expand quoteRichJam said..
Also if your interested have a gander at NACA aerofoils for basics shapes.
if it works in the air it will work in water to a degree.
Air and water aren't totally the same, aerofoils designed for air don't need to take ventilation/cavitation into account. Aerofoils designed for water need to use sections that have a flatter lift distribution curve if that are going to be used in conditions where ventilation (aerated water or close to the surface) or cavitation (high speed) are likely.
Older style aerofoils and many early hydrofoils used sections that had fairly fat leading edges and the maximum thickness well forward. For foiling it was felt that these were more stall resistant and less pitch sensitive. These sections produce a peak of negative pressure on their low pressure (upper) sides, and if this is lower than the local vapour pressure (i.e. how easy it is to suck air out of the water or down from the surface) the foil will aerate.
To get around this it is best to use a foil section that has a flatter lift distribution, and this is usually achieved by using a foil section that has maximum thickness and camber further back with.a finer leading edge.
These foils also have lower drag due to greater degrees of laminar flow, but can also be more sensitive in pitch. Most foil manufacturers are now going this way, particularly with their higher performance foils.
Select to expand quotefoilstate said..jondrums said..
If you look closely all foils that I have seen have the same angle of attack twist that GF does, just that most wings are continuous twist from root to tip and the GF wings have the abrupt change that also seems to act as a fence. I measured the twist carefully on a few wings and the tips are angled about two degrees more than the root and the progression is exponential from root to tip, so most of the wing isn't twisted until you get out to the ends.
Super interesting insights on the twist! Anyone knows a place to learn about airfoils applied to foiling?
Read up about "washout"- that's what it's called.
Select to expand quotePacey said..RichJam said..
Also if your interested have a gander at NACA aerofoils for basics shapes.
if it works in the air it will work in water to a degree.
Air and water aren't totally the same, aerofoils designed for air don't need to take ventilation/cavitation into account. Aerofoils designed for water need to use sections that have a flatter lift distribution curve if that are going to be used in conditions where ventilation (aerated water or close to the surface) or cavitation (high speed) are likely.
Older style aerofoils and many early hydrofoils used sections that had fairly fat leading edges and the maximum thickness well forward. For foiling it was felt that these were more stall resistant and less pitch sensitive. These sections produce a peak of negative pressure on their low pressure (upper) sides, and if this is lower than the local vapour pressure (i.e. how easy it is to suck air out of the water or down from the surface) the foil will aerate.
To get around this it is best to use a foil section that has a flatter lift distribution, and this is usually achieved by using a foil section that has maximum thickness and camber further back with.a finer leading edge.
These foils also have lower drag due to greater degrees of laminar flow, but can also be more sensitive in pitch. Most foil manufacturers are now going this way, particularly with their higher performance foils.
This is good info,thx!.
It is easy to find web info about airfoils,much harder about hydrofoils and there is very little about small,low speed foils like ours.
Select to expand quotemcrt said..
It is easy to find web info about airfoils,much harder about hydrofoils and there is very little about small,low speed foils like ours.
yes, there is very little available online for low Reynolds number hydrofoils. Tom Speer did some good work on the h105 and earlier foils (e.g. www.tspeer.com/Hydrofoils/h105/h105.htm) , but much of the in-depth research has been done by Americas Cup teams and has unfortunately been kept confidential.
