I'm hearing rumours of a HA tail release to complement the HA foils...anyone have any info on this...?

Yeah there's a screengrab in the HA1125 topic, page 5, here: www.seabreeze.com.au/forums/Wing-Foiling/Wind-Wings/Armstrong-HA-1125?page=5

I asked same question there but was perhaps a bit off-topic, so will re-state here: what would HA tail achieve? As in, which design requirement do they fulfill?

As I understand, tails generate drag and tails generate a downward force, and both these forces act in a stabilizing way to any pitch deflection of the entire foil system. Therefore, a tail with more surface area is more stable (because it creates more induced drag when its aoa increases), as well as a longer fuselage is more stable (because of the arm on which the force of the tail acts is longer, and therefore the stabilizing moment).

With this, if we would have two tails with exactly the same surface area, but a different aspect ratio, what would be the difference in how they behave? Again from my understanding, a higher aspect ratio wing has a steeper Cl-alpha curve than a lower aspect ratio wing, which would mean that the incremental increase in the stabilizing force (the lift of the tail, or its downward force) is higher for a higher aspect ratio tail, compared to a lower aspect ratio tail. So this would mean a higher stabilizing force for a given pitch deflection, for the high aspect tail. In layman's terms, this would mean a higher aspect ratio tail would be more stable than a lower aspect ratio tail, for the same tail surface area.

This sounds like all positive, but could the negative be that the stall angle is reduced with a higher aspect ratio tail? If that is the case, is a tail stall an undesirable phenomenon or does the drag that is generated in the stall a desired stabilizing force? But then I'm also thinking, in what situations do tails stall, given that they're upside down compared to the front wing? It seems that the only situation where the tail wing would stall, is in a severe pitch down situation, which is when the forward pitching moment of the front wing becomes too big as you go faster.

Curious to hear anyone else's thoughts and if my thinking is correct or if I'm mistaken in some way.

Also, it seems smaller stabs turn quicker.
HA would turn quicker at lower speeds, but be more stable directionally at higher boatspeeds?

the HA tail should be way more stable for the area and get up easier because you can run a shorter fuse for the same stability and it has less induced drag.

Induced drag is important at high load, which on tails happens at the extremes of the speed range. low speed is obvious but at high speed the tail is under a surprising amount of load. for unloaded scenarios like gliding medium speeds (12-16mph) profile drag is probably more important.

Turning should suffer compared to a low aspect tail given the same pitch balance. In this case it could turn better with the HA foils because of better tuning.

Tails actually stall a lot! Much of the font foot pressure from a foil on takeoff happens because the tail is stalled and not giving enough stabilizing lift. takeoff angles on foils are around 15-20 degrees, tail stall angles are way lower because the section is has to work upside down. This is where something like a V tail with flex/twist works well because it can actively reduce the Aoa to help prevent stall. The same flex can come at a cost at high speed and not give enough stabilizing force.

The HA tail will probably work better in situations where the tail is under high load like big front wings, long masts, high speeds, and short fuselages.

Select to expand quote

FoilAddict said..
the HA tail should be way more stable for the area and get up easier because you can run a shorter fuse for the same stability and it has less induced drag.

Induced drag is important at high load, which on tails happens at the extremes of the speed range. low speed is obvious but at high speed the tail is under a surprising amount of load. for unloaded scenarios like gliding medium speeds (12-16mph) profile drag is probably more important.

Turning should suffer compared to a low aspect tail given the same pitch balance. In this case it could turn better with the HA foils because of better tuning.

Tails actually stall a lot! Much of the font foot pressure from a foil on takeoff happens because the tail is stalled and not giving enough stabilizing lift. takeoff angles on foils are around 15-20 degrees, tail stall angles are way lower because the section is has to work upside down. This is where something like a V tail with flex/twist works well because it can actively reduce the Aoa to help prevent stall. The same flex can come at a cost at high speed and not give enough stabilizing force.

The HA tail will probably work better in situations where the tail is under high load like big front wings, long masts, high speeds, and short fuselages.

To your last point, can't wait to try the 725/100mast/50fuse/HAtail combo!

I just modified a SPG Sprint tail. Works well.


Bog came off but it works fine without it. No noise heaps of glide and works will with 1250/1550/1125. Turns surprisingly well for an 18-inch tail. No shim A+ 60 fuse. Solid carbon so can be cut down. Konrad have similar tail that has holes in the correct place.

Chopped down to 13.5" is the magic number for those race tails hilly.

Select to expand quote

wicka said..
Chopped down to 13.5" is the magic number for those race tails hilly.

I have a smaller KDMaui tail as well, so not cutting ATM. But it is tempting

Select to expand quote

FoilAddict said..
the HA tail should be way more stable for the area and get up easier because you can run a shorter fuse for the same stability and it has less induced drag.

Induced drag is important at high load, which on tails happens at the extremes of the speed range. low speed is obvious but at high speed the tail is under a surprising amount of load. for unloaded scenarios like gliding medium speeds (12-16mph) profile drag is probably more important.

Turning should suffer compared to a low aspect tail given the same pitch balance. In this case it could turn better with the HA foils because of better tuning.

Tails actually stall a lot! Much of the font foot pressure from a foil on takeoff happens because the tail is stalled and not giving enough stabilizing lift. takeoff angles on foils are around 15-20 degrees, tail stall angles are way lower because the section is has to work upside down. This is where something like a V tail with flex/twist works well because it can actively reduce the Aoa to help prevent stall. The same flex can come at a cost at high speed and not give enough stabilizing force.

The HA tail will probably work better in situations where the tail is under high load like big front wings, long masts, high speeds, and short fuselages.

Thanks Kane for bringing in your foiling experience and translating what the characteristics of a HA tails will mean in foiling terms.

How about that ;-)

More on IG: @thefoildesigner (www.instagram.com/thefoildesigner/)

Select to expand quote

Mokuleia said..
How about that ;-)

More on IG: @thefoildesigner (www.instagram.com/thefoildesigner/)

Interesting!!
Tell us more...!

Stoked! Any idea on release date?

Select to expand quote

longboard said..

Mokuleia said..
How about that ;-)

More on IG: @thefoildesigner (www.instagram.com/thefoildesigner/)

Interesting!!
Tell us more...!

This particular wing is 100% carbon fiber composite. Overall span is 15 inches. I love it for prone foiling and winging.

In a nutshell, I first designed the wing using a CAD design software, then CNC a mold out of plywood. The latter was then vacuum laminated and glossed. After this I filled the mold with carbon fiber and epoxy. The hard part with Armstrong comes from the fact that the tail has threaded inserts so I have to add this little pedestal and put it back into the CNC to get perfect alignment between the wing and the shim.

The whole process can be seen in this video:

www.instagram.com/p/CPgups5Ac9m/?utm_source=ig_web_copy_link

Select to expand quote

Mokuleia said..

longboard said..

Mokuleia said..
How about that ;-)

More on IG: @thefoildesigner (www.instagram.com/thefoildesigner/)

Interesting!!
Tell us more...!

This particular wing is 100% carbon fiber composite. Overall span is 15 inches. I love it for prone foiling and winging.

In a nutshell, I first designed the wing using a CAD design software, then CNC a mold out of plywood. The latter was then vacuum laminated and glossed. After this I filled the mold with carbon fiber and epoxy. The hard part with Armstrong comes from the fact that the tail has threaded inserts so I have to add this little pedestal and put it back into the CNC to get perfect alignment between the wing and the shim.

The whole process can be seen in this video:

www.instagram.com/p/CPgups5Ac9m/?utm_source=ig_web_copy_link

Awesome stuff! What's the reasoning behind the straight edges vs some type of rounded outline?

Primarily to maximize glide. It is inspired from a shopped Signature tail wing a friend of mine modified that he liked a lot. He asked me to make him one for Armstrong. I decided to keep the shape as is, and never felt the need to round the tips. Being 100% carbon it could be recut to any length and any tip shape.

The overall area is only 210cm2 but IMO it pumps better than the unchopped 232 cm2 and turns better too.

Select to expand quote

Mokuleia said..
Primarily to maximize glide. It is inspired from a shopped Signature tail wing a friend of mine modified that he liked a lot. He asked me to make him one for Armstrong. I decided to keep the shape as is, and never felt the need to round the tips. Being 100% carbon it could be recut to any length and any tip shape.

The overall area is only 210cm2 but IMO it pumps better than the unchopped 232 cm2 and turns better too.

yours is prob thinner than the 232? Do you have measurements to compare?

So its flat and looks much thinner than the 232. Would be much faster. Thats what we have found anyhow. Although ive been using the chopped 232 instread of the V tail for that reason - to slow the 925 down until i get my head around it.

Select to expand quote

FoilAddict said..
Tails actually stall a lot! Much of the font foot pressure from a foil on takeoff happens because the tail is stalled and not giving enough stabilizing lift. takeoff angles on foils are around 15-20 degrees, tail stall angles are way lower because the section is has to work upside down.

That's not how stabilisers work, they are designed to pull downward all the time. If they stall, the main foil will pitch down, not up. And the stabiliser section is not being asked to work upside down, the curvature is on the bottom surface of the stab because it is designed to pull downward.

Front wings run positive 15-20 degrees on takeoff, and generally run positive to about 20mph. the tail angle relative to flow is about 2-3 degrees less than that. How can a wing pull down while pointing up 10 degrees? It only takes a 5-10 degrees positive Aoa for a majority of tail wing designs to stall.

Most foils need a tail design that makes downforce efficiently to counteract diving at high speed. Part of the reason foils pitch up at low speed is because the tail wing is in partial or full stall and not pushing upwards to stabilize the foil.

Select to expand quote

FoilAddict said..
Front wings run positive 15-20 degrees on takeoff, and generally run positive to about 20mph. the tail angle relative to flow is about 2-3 degrees less than that. How can a wing pull down while pointing up 10 degrees?

Do you think the tail on this airbus is pulling down or up?


My point is that I think you are confusing the angle of attack in the global reference frame with the angle of attack relative to the motion through the fluid. You also need to account for the downwash from the main wing that the stabiliser operates in.

It's hard to say without a video or knowing the speed and angle of attack on the wings. Airplane takeoff probably isn't the best comparison either because flaps and engines reduce the loading on the stabilizer.

I have done calculation, video analysis, real life experimentation, Cfd simulation and countless prototypes. My testing has pretty clearly shown that hydrofoil tail wings make a significant upward force at low to medium speeds or under high load. It has also shown that tail wing stalling is a large factor in the takeoff performance of a foil. This is easily provable with a gopro and some yarn or just google, a calculator, and a piece of paper!

This might be better as it's own thread?

Select to expand quote

FoilAddict said..
It's hard to say without a video or knowing the speed and angle of attack on the wings. Airplane takeoff probably isn't the best comparison either because flaps and engines reduce the loading on the stabilizer.

I have done calculation, video analysis, real life experimentation, Cfd simulation and countless prototypes. My testing has pretty clearly shown that hydrofoil tail wings make a significant upward force at low to medium speeds or under high load. It has also shown that tail wing stalling is a large factor in the takeoff performance of a foil. This is easily provable with a gopro and some yarn or just google, a calculator, and a piece of paper!

This might be better as it's own thread?

For the case of the Airbus, it's not hard to say. Very simply, you pull the control column back, the stabiliser angles down, and the nose goes up. In this case it's extreme just after takeoff, so the plane clearly has enough speed and flaps to not stall the main wing. But there is no way that the tail is not providing downforce.

I appreciate that you have done substantial physical testing and experimentation on foils and I respect the development you have done, but without knowing the effect of downwash your measurements may be deceptive. Similarly, CFD is a double edged sword, results are very dependent on the nature of the software used and the setup. Are you interested in sharing some of your results that support your view that the stabiliser spends much of its time providing upwards lift?

That a380 picture looks fake as hell. Lighting is not right, and no plane will have its landing gear up that quick. I just googled a couple of vertical A380 takeoffs on youtube and there are none that look like that.

Select to expand quote

ninjatuna said..
That a380 picture looks fake as hell. Lighting is not right, and no plane will have its landing gear up that quick. I just googled a couple of vertical A380 takeoffs on youtube and there are none that look like that.

just thumbnails, til you watch the videos and dont see any plane in those positions,

now back to the HA tails on what we are riding

Very possible to stall a tail with an aft center of gravity, which is exactly what you get when pushing hard with the back foot.

Select to expand quote

Pacey said..

FoilAddict said..
It's hard to say without a video or knowing the speed and angle of attack on the wings. Airplane takeoff probably isn't the best comparison either because flaps and engines reduce the loading on the stabilizer.

I have done calculation, video analysis, real life experimentation, Cfd simulation and countless prototypes. My testing has pretty clearly shown that hydrofoil tail wings make a significant upward force at low to medium speeds or under high load. It has also shown that tail wing stalling is a large factor in the takeoff performance of a foil. This is easily provable with a gopro and some yarn or just google, a calculator, and a piece of paper!

This might be better as it's own thread?

For the case of the Airbus, it's not hard to say. Very simply, you pull the control column back, the stabiliser angles down, and the nose goes up. In this case it's extreme just after takeoff, so the plane clearly has enough speed and flaps to not stall the main wing. But there is no way that the tail is not providing downforce.

I appreciate that you have done substantial physical testing and experimentation on foils and I respect the development you have done, but without knowing the effect of downwash your measurements may be deceptive. Similarly, CFD is a double edged sword, results are very dependent on the nature of the software used and the setup. Are you interested in sharing some of your results that support your view that the stabiliser spends much of its time providing upwards lift?

It's pretty easy to conclude that stabilizers spend a lot of time providing upward lift. Front wings stall at around 15-20 deg depending on design, but tails are usually set at 2-3 less than that. So whenever we are at speeds close to stall speed, the tail will be angled upwards (wrt the flow). Let's say you're foiling at a low speed and the front wing is at 13 deg aoa, your tail wing will then be at 10 deg aoa. Even though the section is upside down (bc it's designed to work efficiently at higher speeds), at 10 deg aoa it will provide an upward force. You're right that downwash could reduce the "effective" aoa of the tail wing, but even if that's another 2 deg or so, you're still at 8 deg positive angle, which would mean an upward force.

Select to expand quote

greg87foil said..
It's pretty easy to conclude that stabilizers spend a lot of time providing upward lift. Front wings stall at around 15-20 deg depending on design, but tails are usually set at 2-3 less than that. So whenever we are at speeds close to stall speed, the tail will be angled upwards (wrt the flow). Let's say you're foiling at a low speed and the front wing is at 13 deg aoa, your tail wing will then be at 10 deg aoa. Even though the section is upside down (bc it's designed to work efficiently at higher speeds), at 10 deg aoa it will provide an upward force. You're right that downwash could reduce the "effective" aoa of the tail wing, but even if that's another 2 deg or so, you're still at 8 deg positive angle, which would mean an upward force.

It's important to consider that cambered sections typically have their angle of zero lift at negative 2-3 degrees. If you have a cambered section such as a NACA 63-412 used as both main foil and stabiliser, and you had the main foil set at 0 degrees angle of incidence and the tail set at -2, then the stabiliser would need to be rotated positively be about 5 degrees before it started to generate to positive (i.e. upward) lift. And that's not accounting for downwash, which is significant and increases with main foil AoA.

For example, if you crank a typical mid aspect (AR = 5) main foil up to 10 degrees AoA with a lift coefficient of about 1.3, the downwash will be approximately 9 degrees. The downwash angle would need to drop below 5 degrees for the stab to be generating positive lift.

These are approximate numbers based on rules of thumb for downwash (i.e. downwash angle = (35 x CL) / AR), but they are intended to illustrate that the assumptions that FoilAddict is using are not clear cut. I accept that at when getting up on foil there will be a short period where the main foil is stalled or very close to stall, and the stab may be producing positive (upward) lift, but the I think the assumption that the stab operates for extended periods generating upward lift is incorrect, and if true would bring into question the need to use a cambered section with its cambered side on the underside of the stabiliser. After all, camber is typically used to increase the available lift coefficient on the cambered side while decreasing the maximum lift coefficient available on the flatter side, and shifting the drag bucket of the foil over so that it is centred on the most commonly used lift coefficient. If FoilAddict is correct he is effectively saying that we have our stabiliser sections upside down and we would get better stall and drag performance if we switched.


NACA 63-412 lift and drag curves for reference:

Would it be possible to get a bunch of different foils and put them into something like this that could be adjusted to all the different angles and velocities see what is actually going on an improve our sport at much faster rate. I am talking about something big where you have 5-10 very good foil surfers that can describe in detail what they feel on each set up in a couple of different wave scenarios, wing riding scenarios, DW scenarios. Take the notes on those. Then put those set ups into something like this and observe flows to see what may coordinate with what each rider may be seeing. Optimistic? yes, VERY

Lots of geek talk going well past my care factor.
so when is the new HA tail coming out so we can try it in the real world.