Winging - I can pump to get up on foil, build speed and apparent wind in lulls, and much less well flagging on waves.
With a wing air goes backwards and I go fowards, but with no wing where does forward momentum come from and what's going backwards to equal it? How does pumping work?

You mean pumping the foil?
very basically it is doing the same thing that the handwing is doing to air but in the water. so as you pump you are pushing water off the back of the foil which pushes you farward. could go into a lot more detail but that's the very basics of how you go forward

Good advice I received from SUP Foiling is that it's easier to keep the speed up pumping the foil if you are at speed already so don't let the board speed slow too much before pumping to keep going.
Hope that makes sense.

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FarNorthSurfer said..
Good advice I received from SUP Foiling is that it's easier to keep the speed up pumping the foil if you are at speed already so don't let the board speed slow too much before pumping to keep going.
Hope that makes sense.

Drag is lowest at a middling speed. Ideally you want to pump just above minimum drag speed.

If you fall below this speed, then any further reduction in speed increases drag even more, resulting in a feedback loop to a stall.

Most of the forward propulsion from pumping actually comes from the stabiliser, not the front foil. The physics is similar to dolphin propulsion: dolphins can swim up to 30 km/h, propelled by their large horizontal tails, known as a "flukes".

The front wing/foil doesn't generate much propulsion but is responsible for a lot of drag. You know this form personal experience: 1) High aspect ratio foils pump and glide much better than low aspect foils because of increased parasitic drag from the low aspect foils BUT the high aspect foil itself is NOT generating much propulsive power compared to the stabiliser. 2) You need to change pumping cadence when you shorten the fuselage; this is because of the effect on the stabiliser, not the front foil.

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Fatboy3 said..
Most of the forward propulsion from pumping actually comes from the stabiliser, not the front foil. The physics is similar to dolphin propulsion: dolphins can swim up to 30 km/h, propelled by their large horizontal tails, known as a "flukes".

The front wing/foil doesn't generate much propulsion but is responsible for a lot of drag. You know this form personal experience: 1) High aspect ratio foils pump and glide much better than low aspect foils because of increased parasitic drag from the low aspect foils BUT the high aspect foil itself is NOT generating much propulsive power compared to the stabiliser. 2) You need to change pumping cadence when you shorten the fuselage; this is because of the effect on the stabiliser, not the front foil.

During a pump sequence there is an increase in AoA so more lift, then sailor pushes with front foot and board speeds up. Can you explain what stab is doing?

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Fatboy3 said..
Most of the forward propulsion from pumping actually comes from the stabiliser, not the front foil. The physics is similar to dolphin propulsion: dolphins can swim up to 30 km/h, propelled by their large horizontal tails, known as a "flukes".

The front wing/foil doesn't generate much propulsion but is responsible for a lot of drag. You know this form personal experience: 1) High aspect ratio foils pump and glide much better than low aspect foils because of increased parasitic drag from the low aspect foils BUT the high aspect foil itself is NOT generating much propulsive power compared to the stabiliser. 2) You need to change pumping cadence when you shorten the fuselage; this is because of the effect on the stabiliser, not the front foil.

I don't believe this is correct. Stabilizers are often less than 200 cm2, hence will produce very little propulsion. Dolphins have no front wings. In this analogy the front foil is similar to the dolphin's fluke and the stab is merely a stabilizing piece.

I believe most of the propulsion comes from being high on the mast and running the foil downhill, where you then unweight and increase the angle of attack to get high again. Sometimes my front leg will get tired first from pushing the front end down. The pump at the bottom of your stroke further propels you forward like the fluke.

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radair said..
I believe most of the propulsion comes from being high on the mast and running the foil downhill, where you then unweight and increase the angle of attack to get high again.

Agree with this, and so with pumping you're jumping "off" the front wing at the bottom of your pump, and then gliding back down. Which is why you can pump without a tail stabiliser.
Here is a video from someone that attempts to explain it. Note there is no correct answer just theories, this one is what I think is the best we have for how pumping works.


The dolphin aspect would require moving parts to make sense IMO

Select to expand quote

cornwallis said..

radair said..
I believe most of the propulsion comes from being high on the mast and running the foil downhill, where you then unweight and increase the angle of attack to get high again.

Agree with this, and so with pumping you're jumping "off" the front wing at the bottom of your pump, and then gliding back down. Which is why you can pump without a tail stabiliser.
Here is a video from someone that attempts to explain it. Note there is no correct answer just theories, this one is what I think is the best we have for how pumping works.

The dolphin aspect would require moving parts to make sense IMO

Thanks but the video is jibberish. He seems to think some circular motion form waves pushes you then you just go forward (that's the question how. He doesn't explain why the other side of the circular motion from waves doesn't push you down or how pumping still works in flat, calm water.
One of the other videos and something said here makes more sense; you start with some forward motion (from wing or funning dock start or paddle onto wave) then as the bend knees and take weight off board you take more off front foot so increase AoA and board lifts upwards even though rider centre of gravity may be lowered through bending knees. The rider presses more with front foot and levels foil/board and as gravity slowly sinks board and rider foil fall in a forward direction.

Select to expand quote

cornwallis said..

radair said..
I believe most of the propulsion comes from being high on the mast and running the foil downhill, where you then unweight and increase the angle of attack to get high again.

Agree with this, and so with pumping you're jumping "off" the front wing at the bottom of your pump, and then gliding back down. Which is why you can pump without a tail stabiliser.
Here is a video from someone that attempts to explain it. Note there is no correct answer just theories, this one is what I think is the best we have for how pumping works.

The dolphin aspect would require moving parts to make sense IMO

Its just physics, Lift is proportional to speed.

The easiest way I can explain pumping is we use the natural glide ratio of the foil to propel ourselves forward, we start with an initial speed and height on the mast. then as we glide down, we convert potential energy (height) to kinetic energy (speed). then before we touch down we must change the angle of attack (by shifting mass aft) and push against the lift force to essentially jump our way back up closer to the surface. Then we shift weight forward at the top of the pump to again point the foil down and glide. repeat.

So pumping is gliding and jumping (basically).

The better the glide ratio of the foil (generally) the easier it will be to pump efficiently.

I find the biggest technique challenge (and the biggest payoff) is to aim to stayhigh on the mast (higher than you think) This minimises drag and gives you more stored potential energy (height) to help cover up moments when you can't get a good pump due to waves / turbulence etc.

Good pumping technique is then a balancing act between speed and height. If you want more speed you will can burn some height and focus more force with the nose down, if you need to built height you need to focus more on the nose up phase of the pump and dig deep / burn some cardio.

A common mistake I see is thinking you have to go a million pecent, in fact you need to give the foil time to glide so it seems most people improve their pump by slowing down their cadance. I know I do.

ps im pretty **** at pumping, I can generally manage a 3 for 1 prone foiling but it's cool to see the legends who can that can ride around on tiny foils for 15 minutes in the surf zone ripping turns and connecting waves so efficiently

pps And if you watch the good guys pump they tend to stand quite tall or at least keep their lower body fairly straight. this is because a shallow squat motion going from slight knee bent to straight leg is far more effective than a low squat motion.

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Ju_foil said..

cornwallis said..

radair said..
I believe most of the propulsion comes from being high on the mast and running the foil downhill, where you then unweight and increase the angle of attack to get high again.

Agree with this, and so with pumping you're jumping "off" the front wing at the bottom of your pump, and then gliding back down. Which is why you can pump without a tail stabiliser.
Here is a video from someone that attempts to explain it. Note there is no correct answer just theories, this one is what I think is the best we have for how pumping works.

The dolphin aspect would require moving parts to make sense IMO

Its just physics, Lift is proportional to speed.

The easiest way I can explain pumping is we use the natural glide ratio of the foil to propel ourselves forward, we start with an initial speed and height on the mast. then as we glide down, we convert potential energy (height) to kinetic energy (speed). then before we touch down we must change the angle of attack (by shifting mass aft) and push against the lift force to essentially jump our way back up closer to the surface. Then we shift weight forward at the top of the pump to again point the foil down and glide. repeat.

So pumping is gliding and jumping (basically).

The better the glide ratio of the foil (generally) the easier it will be to pump efficiently.

I find the biggest technique challenge (and the biggest payoff) is to aim to stayhigh on the mast (higher than you think) This minimises drag and gives you more stored potential energy (height) to help cover up moments when you can't get a good pump due to waves / turbulence etc.

Good pumping technique is then a balancing act between speed and height. If you want more speed you will can burn some height and focus more force with the nose down, if you need to built height you need to focus more on the nose up phase of the pump and dig deep / burn some cardio.

A common mistake I see is thinking you have to go a million pecent, in fact you need to give the foil time to glide so it seems most people improve their pump by slowing down their cadance. I know I do.

ps im pretty **** at pumping, I can generally manage a 3 for 1 prone foiling but it's cool to see the legends who can that can ride around on tiny foils for 15 minutes in the surf zone ripping turns and connecting waves so efficiently

pps And if you watch the good guys pump they tend to stand quite tall or at least keep their lower body fairly straight. this is because a shallow squat motion going from slight knee bent to straight leg is far more effective than a low squat motion.

I thought drag increased on way up (so losing kinetic energy) due to greater AoA but just saw graph showing it doesn't for small changes in angle. So at the top of the pump when rider weights their front foot I guess the changing AoA sweeps water back and accelerates the board forward.

Select to expand quote

patronus said..

Ju_foil said..

cornwallis said..

radair said..
I believe most of the propulsion comes from being high on the mast and running the foil downhill, where you then unweight and increase the angle of attack to get high again.

Agree with this, and so with pumping you're jumping "off" the front wing at the bottom of your pump, and then gliding back down. Which is why you can pump without a tail stabiliser.
Here is a video from someone that attempts to explain it. Note there is no correct answer just theories, this one is what I think is the best we have for how pumping works.

The dolphin aspect would require moving parts to make sense IMO

Its just physics, Lift is proportional to speed.

The easiest way I can explain pumping is we use the natural glide ratio of the foil to propel ourselves forward, we start with an initial speed and height on the mast. then as we glide down, we convert potential energy (height) to kinetic energy (speed). then before we touch down we must change the angle of attack (by shifting mass aft) and push against the lift force to essentially jump our way back up closer to the surface. Then we shift weight forward at the top of the pump to again point the foil down and glide. repeat.

So pumping is gliding and jumping (basically).

The better the glide ratio of the foil (generally) the easier it will be to pump efficiently.

I find the biggest technique challenge (and the biggest payoff) is to aim to stayhigh on the mast (higher than you think) This minimises drag and gives you more stored potential energy (height) to help cover up moments when you can't get a good pump due to waves / turbulence etc.

Good pumping technique is then a balancing act between speed and height. If you want more speed you will can burn some height and focus more force with the nose down, if you need to built height you need to focus more on the nose up phase of the pump and dig deep / burn some cardio.

A common mistake I see is thinking you have to go a million pecent, in fact you need to give the foil time to glide so it seems most people improve their pump by slowing down their cadance. I know I do.

ps im pretty **** at pumping, I can generally manage a 3 for 1 prone foiling but it's cool to see the legends who can that can ride around on tiny foils for 15 minutes in the surf zone ripping turns and connecting waves so efficiently

pps And if you watch the good guys pump they tend to stand quite tall or at least keep their lower body fairly straight. this is because a shallow squat motion going from slight knee bent to straight leg is far more effective than a low squat motion.

I thought drag increased on way up (so losing kinetic energy) due to greater AoA but just saw graph showing it doesn't for small changes in angle. So at the top of the pump when rider weights their front foot I guess the changing AoA sweeps water back and accelerates the board forward.

For the foil there is no water being swept back, in fact a small component of the fluid close to the foil is being dragged forward (viscous drag / skin friction).

We are using gravity to accelerate down as we glide (just like a paper airplane) and a component of down is used to propel forward. We then jump / hop up to reset and do it again.

On the other hand, Pumping the wind wing is different because we are able to aggressively change the angle of attack to allow us to angle drag ourselves forward by pulling air back. Pumping the wind wing is a mix of 'rowing' the air and keeping the flow attached and accelerating the air across the surface to generate lift from the airfoil. This is the aspect that gives a good head start to guys coming from windsurfing because you develop a good feel for how hard you can pull and how far you can angle before the flow becomes detached from the wing.

Edit: I think the foil angle of attack (the flow the foil sees) probably does not change all the much because on the up portion we change the angle to horizontal, but we also un-weight the foil, angle it up and let it follow us up. You can ride smaller and smaller foils as you 'dial in' your pump because you get good at keep the foil at a relatively steady AoA thought the pump and so you won't end up stalling even on a small area foil. people tent to talk about stall speed but in fact an airfoil does not have a stall speed, it has a stall 'angle' and as you go slower it gets harder and harder to keep the angle small. Hopefully I'm making sense to someone hahah

Select to expand quote

Fatboy3 said..
You know this form personal experience: 1) High aspect ratio foils pump and glide much better than low aspect foils because of increased parasitic drag from the low aspect foils BUT the high aspect foil itself is NOT generating much propulsive power compared to the stabiliser.

High-Aspect reduces induced drag, not parasitic. In fact, HA normally increases parasitic drag (you have a bigger cross-section ploughing through the water).

It's because induced drag is cause by the high-pressure zone trying to return to the low pressure zone at the wingtips. A bigger AR means a percentage of the wing where this is happening.




As far as pumping goes, I think it is mostly as Ju_foil describes. Pump high by pushing water downward, then glide forward. There might be a little bit of forward thrust too from the pump, but I think that this isn't the main mechanism. Dolphins can really bend their tails so that their thrust stroke projects water backward, but we can't really do that so much with only a few degrees.

You aren't changing the AoA much when pumping. AoA is relative to the direction of travel, not the surface of the water, so even if you're following a sinusoidal path, the AoA can remain fairly constant.

There has to be an energy input from the rider in the pump, and it is the downward displacement of water (like the dolphin), pushing the rider higher, that does this. If you just changed the AoA, then there would be no energy input.

"pushing water downward, then glide forward." kinda misses the point of the question, how does pushing down generate forward momentum. Newton's Law, something must be going backwards i.e. water.

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patronus said..
"pushing water downward, then glide forward." kinda misses the point of the question, how does pushing down generate forward momentum. Newton's Law, something must be going backwards i.e. water.

I think that just because water is behind you doesn't mean you pushed it there. We are gliders without jets or propellers. It's like dragging your sled to the top of the hill and sledding down. Your legs are tired climbing up, but the ride down is fun. Like Woody says to Buzz, "You're not flying. You're falling with style."

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patronus said..
"pushing water downward, then glide forward." kinda misses the point of the question, how does pushing down generate forward momentum. Newton's Law, something must be going backwards i.e. water.

It doesn't, it generates the gravitational potential energy. It's the gliding that then generates the forward momentum (gravitational potential energy to kinetic).

If you want to see this in action, drop a paper aeroplane out of a tall building with no forward momentum. It will pick up both forward and downward momentum (trading gravitational potential energy for kinetic).

If you want to look at it from conversation of momentum, then it is in the gliding that water is propelled backward. With the paper aeroplane, it starts off dropping downward with zero forward momentum. As it builds up some speed, because it is at a slight nose-down angle, air particles are forced backward as it drops. Eventually, a steady state is reached where the drag (air particles gaining momentum in the direction of travel) is equal to the thrust (air particles gaining momentum in the opposite direction).

Select to expand quote

BritWinger said..

patronus said..
"pushing water downward, then glide forward." kinda misses the point of the question, how does pushing down generate forward momentum. Newton's Law, something must be going backwards i.e. water.

It doesn't, it generates the gravitational potential energy. It's the gliding that then generates the forward momentum (gravitational potential energy to kinetic).

If you want to see this in action, drop a paper aeroplane out of a tall building with no forward momentum. It will pick up both forward and downward momentum (trading gravitational potential energy for kinetic).

If you want to look at it from conversation of momentum, then it is in the gliding that water is propelled backward. With the paper aeroplane, it starts off dropping downward with zero forward momentum. As it builds up some speed, because it is at a slight nose-down angle, air particles are forced backward as it drops. Eventually, a steady state is reached where the drag (air particles gaining momentum in the direction of travel) is equal to the thrust (air particles gaining momentum in the opposite direction).

We are saying same thing:-)

I don't necessarily disagree with what was said above, but some things seem to be missing. Here's a different approach to explain why pumping the foil works.

Basically, pumping involves two types of weight shifts: up and down, and forward and backward.

If water would be compressible, then pushing down on the foil would move the foil down in the water. But water is (mostly) non-compressible, so that does not really happen. If the downward pushing force isbehindthe balance point of the foil, the push will do two things: push the foil forward (slightly), and change the orientation so the front wing goes up, and the stab goes down (higher angle of attack). Here's a screenshot from the Kitesurf College pumping tutorial at this point:

Pushing down with the body weight is next followed by a reduction of the downward force (think about the short moment at a top a jump). Bending the knees to reduce the pressure on the feet enhances the effect, as does pulling in with the arms to put some of the body weight onto the wing):
With less downward force on the foil, it will want to rise up, which is helped by the increased angle of attack and the forward momentum. It will rise only to a certain point before it looses all forward speed, so the next step is to push down with the forward foot to flatten out the board and reduce drag. Putting more weight back onto the board also pushes it down towards the water:


At this point, the board is flat again, and it is partly out of the water. That reduces drag, allowing the board to pick up speed in the next pump cycle.

The coordination of the up-down and forward-backward movements with board height and speed makes this a rather complicated movement. Fortunately for us less coordinated people, some of the coordination skill can be replaced by effort , especially when we also have a wing in our hands.

Select to expand quote

patronus said..
how does pushing down generate forward momentum. Newton's Law, something must be going backwards i.e. water.

Good question. But if you look at foiling videos without a wing, the foils are almost always started with and external force that creates the momentum: a wave, a bungee cord, someone pulling the foiler, or jumping onto the foil in a dock start. I think I have seen a video where someone started a foil SUP on flat water without any of these, but that looked like an awful lot of work, and there definitely was a lot of water being displaced while getting up to speed. Not sure how many people in the world could do this.

Select to expand quote

Ju_foil said..

patronus said..

Ju_foil said..

cornwallis said..

radair said..
I believe most of the propulsion comes from being high on the mast and running the foil downhill, where you then unweight and increase the angle of attack to get high again.

Agree with this, and so with pumping you're jumping "off" the front wing at the bottom of your pump, and then gliding back down. Which is why you can pump without a tail stabiliser.
Here is a video from someone that attempts to explain it. Note there is no correct answer just theories, this one is what I think is the best we have for how pumping works.

The dolphin aspect would require moving parts to make sense IMO

Its just physics, Lift is proportional to speed.

The easiest way I can explain pumping is we use the natural glide ratio of the foil to propel ourselves forward, we start with an initial speed and height on the mast. then as we glide down, we convert potential energy (height) to kinetic energy (speed). then before we touch down we must change the angle of attack (by shifting mass aft) and push against the lift force to essentially jump our way back up closer to the surface. Then we shift weight forward at the top of the pump to again point the foil down and glide. repeat.

So pumping is gliding and jumping (basically).

The better the glide ratio of the foil (generally) the easier it will be to pump efficiently.

I find the biggest technique challenge (and the biggest payoff) is to aim to stayhigh on the mast (higher than you think) This minimises drag and gives you more stored potential energy (height) to help cover up moments when you can't get a good pump due to waves / turbulence etc.

Good pumping technique is then a balancing act between speed and height. If you want more speed you will can burn some height and focus more force with the nose down, if you need to built height you need to focus more on the nose up phase of the pump and dig deep / burn some cardio.

A common mistake I see is thinking you have to go a million pecent, in fact you need to give the foil time to glide so it seems most people improve their pump by slowing down their cadance. I know I do.

ps im pretty **** at pumping, I can generally manage a 3 for 1 prone foiling but it's cool to see the legends who can that can ride around on tiny foils for 15 minutes in the surf zone ripping turns and connecting waves so efficiently

pps And if you watch the good guys pump they tend to stand quite tall or at least keep their lower body fairly straight. this is because a shallow squat motion going from slight knee bent to straight leg is far more effective than a low squat motion.

I thought drag increased on way up (so losing kinetic energy) due to greater AoA but just saw graph showing it doesn't for small changes in angle. So at the top of the pump when rider weights their front foot I guess the changing AoA sweeps water back and accelerates the board forward.

For the foil there is no water being swept back, in fact a small component of the fluid close to the foil is being dragged forward (viscous drag / skin friction).

We are using gravity to accelerate down as we glide (just like a paper airplane) and a component of down is used to propel forward. We then jump / hop up to reset and do it again.

On the other hand, Pumping the wind wing is different because we are able to aggressively change the angle of attack to allow us to angle drag ourselves forward by pulling air back. Pumping the wind wing is a mix of 'rowing' the air and keeping the flow attached and accelerating the air across the surface to generate lift from the airfoil. This is the aspect that gives a good head start to guys coming from windsurfing because you develop a good feel for how hard you can pull and how far you can angle before the flow becomes detached from the wing.

Edit: I think the foil angle of attack (the flow the foil sees) probably does not change all the much because on the up portion we change the angle to horizontal, but we also un-weight the foil, angle it up and let it follow us up. You can ride smaller and smaller foils as you 'dial in' your pump because you get good at keep the foil at a relatively steady AoA thought the pump and so you won't end up stalling even on a small area foil. people tent to talk about stall speed but in fact an airfoil does not have a stall speed, it has a stall 'angle' and as you go slower it gets harder and harder to keep the angle small. Hopefully I'm making sense to someone hahah

Great couple of posts mate. Totally agree with your insights. Whether or not they are entirely
correct from a physics point of view (some science egg heads will always argue) - you model is easy to follow and practical to use.


one thing to add . eventually no matter how good your balance between aoa, speed and mast height is - age and fitness play a part. Then eventually the former is the predominant factor.

You can be sure it takes time. When I first started getting two for ones I thought I have got this. Then you look back a year later and you think I was a **** pumper back then but I definitely got this now. Then another year later you think I was still a **** pumper but I am so much better now. I just think that is how it will always be in that you just slowly get better at pumping for years and years.
All of us thinking it must be the equipment is what has driven so many foil sales then I discovered the below.!

The last two days I have been riding the gofoil v2 mast where Alex moved the front foil further away from the mast and I can tell you this has taught me a lot about how pumping works. The pump is improved dramatically with this design change so that tells me the front foil porpoising through the water on a longer lever and is what is providing the better pump. Go figure.

Select to expand quote

Fatboy3 said..
Most of the forward propulsion from pumping actually comes from the stabiliser, not the front foil. The physics is similar to dolphin propulsion: dolphins can swim up to 30 km/h, propelled by their large horizontal tails, known as a "flukes".

The front wing/foil doesn't generate much propulsion but is responsible for a lot of drag. You know this form personal experience: 1) High aspect ratio foils pump and glide much better than low aspect foils because of increased parasitic drag from the low aspect foils BUT the high aspect foil itself is NOT generating much propulsive power compared to the stabiliser. 2) You need to change pumping cadence when you shorten the fuselage; this is because of the effect on the stabiliser, not the front foil.

you made my day as my experience in low winds is, that small stabs reduce pumping efficiency to get on foil.
Many mates state, that small stabs would support this procedure due to less drag,
The later will be the case once up on foil and accelerating, but if you can?t get there, drag doesn?t matter at all, does it ? !

Select to expand quote

Foxi said..

Fatboy3 said..
Most of the forward propulsion from pumping actually comes from the stabiliser, not the front foil. The physics is similar to dolphin propulsion: dolphins can swim up to 30 km/h, propelled by their large horizontal tails, known as a "flukes".

The front wing/foil doesn't generate much propulsion but is responsible for a lot of drag. You know this form personal experience: 1) High aspect ratio foils pump and glide much better than low aspect foils because of increased parasitic drag from the low aspect foils BUT the high aspect foil itself is NOT generating much propulsive power compared to the stabiliser. 2) You need to change pumping cadence when you shorten the fuselage; this is because of the effect on the stabiliser, not the front foil.

you made my day as my experience in low winds is, that small stabs reduce pumping efficiency to get on foil.
Many mates state, that small stabs would support this procedure due to less drag,
The later will be the case once up on foil and accelerating, but if you can?t get there, drag doesn?t matter at all, does it ? !

Following quote from Oskar reviewing latest Armstrong stabs proning. He distinguishes between front foot pressure and lift (which some don't) then says 220 stab has more lift than 235. I only wing and thought stabs affected front foot pressure and their force is downwards. So anyone know what Oskar's on about?

"A recent prone session riding the new Speed 180 tail with the MA800 and 795 performance mast. The 180 feels really predictable and smooth which I love, you just have the confidence to push your turns a little harder and lean over the foil more. Compared to the existing HA195 I find these new tails have more of a positive front foot feel. When you hit those higher speeds they add a little more pressure on the front foot but without just stacking on too much lift. The HA195 I had moments where it felt like it dived a little as the lift would level out at speeds and if I wasn't ready it could result in a dive. Having the extra front foot pressure means the foil drives out of turns easier and helps you roll from rail to rail. I will generally ride the Dart 140 as my go to for everything apart from downwinding where I use the 180, or when its very small, and then I use the 220 for dockstarts or when I want to get the most glide out of it. For me the 220 has more lift than even the Flow 235 and really helps with that low end if you're getting into downwinding or wanting to increase the stall speed while not sacrificing on glide and speed. "

There are many different types of pumping: getting going with a smallish wing foil board, pumping with a prone or with a wing foil while you are already foiling, etc. And slightly different rules apply for every different type of pumping I'd say.

For example, when pumping from standstill I do change the angle of the attack of the foil a lot, and in order to make it happen the most effective way the size of the stabiliser needs to be just right. With a too big stabiliser (for my weight) I wouldn't be able to push it through the water easy enough (which I need for changing the angle of attack of the front wing), and similarly, a too small stabiliser would go through the water too easily. Also, a too small stabiliser would reach the nice flight mode at higher speeds compared to a properly sized one.

Here's an example with a 195 cm2 stabiliser. With a noticeably bigger stabiliser that kind of pumping becomes noticeably more difficult for me.

Select to expand quote

Taavi said..
.................Also, a too small stabiliser would reach the nice flight mode at higher speeds compared to a properly sized one.................

Taavi - why does a small stabliser reach nice flight mode at higher speed, is it more pitchy?

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patronus said..

Taavi said..
.................Also, a too small stabiliser would reach the nice flight mode at higher speeds compared to a properly sized one.................

Taavi - why does a small stabliser reach nice flight mode at higher speed, is it more pitchy?

@patronus, at a too slow speed a too small stabiliser would start sinking, while a front wing at the same time could still be happy to fly. And that would trim the angle of the front wing pointing upwards, and unless you have extra power coming from the wing for example, and/or unless you make an extra effort to keep your weight on your front foot, you would stall and would not reach the stable level flight. But when the stabiliser matches well the intended speed range of the front wing, this would not happen. Of course, it's also rider dependent - a more light footed rider can get away with a smaller stabiliser if paying attention and bringing more weight forward when needed, but if the rider is back foot heavy a small stabiliser can be a nuisance at slow speeds.

Nobody knows... do they! It's probably Magic,

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patronus said..

Foxi said..

Fatboy3 said..
Most of the forward propulsion from pumping actually comes from the stabiliser, not the front foil. The physics is similar to dolphin propulsion: dolphins can swim up to 30 km/h, propelled by their large horizontal tails, known as a "flukes".

The front wing/foil doesn't generate much propulsion but is responsible for a lot of drag. You know this form personal experience: 1) High aspect ratio foils pump and glide much better than low aspect foils because of increased parasitic drag from the low aspect foils BUT the high aspect foil itself is NOT generating much propulsive power compared to the stabiliser. 2) You need to change pumping cadence when you shorten the fuselage; this is because of the effect on the stabiliser, not the front foil.

you made my day as my experience in low winds is, that small stabs reduce pumping efficiency to get on foil.
Many mates state, that small stabs would support this procedure due to less drag,
The later will be the case once up on foil and accelerating, but if you can?t get there, drag doesn?t matter at all, does it ? !

Following quote from Oskar reviewing latest Armstrong stabs proning. He distinguishes between front foot pressure and lift (which some don't) then says 220 stab has more lift than 235. I only wing and thought stabs affected front foot pressure and their force is downwards. So anyone know what Oskar's on about?

"A recent prone session riding the new Speed 180 tail with the MA800 and 795 performance mast. The 180 feels really predictable and smooth which I love, you just have the confidence to push your turns a little harder and lean over the foil more. Compared to the existing HA195 I find these new tails have more of a positive front foot feel. When you hit those higher speeds they add a little more pressure on the front foot but without just stacking on too much lift. The HA195 I had moments where it felt like it dived a little as the lift would level out at speeds and if I wasn't ready it could result in a dive. Having the extra front foot pressure means the foil drives out of turns easier and helps you roll from rail to rail. I will generally ride the Dart 140 as my go to for everything apart from downwinding where I use the 180, or when its very small, and then I use the 220 for dockstarts or when I want to get the most glide out of it. For me the 220 has more lift than even the Flow 235 and really helps with that low end if you're getting into downwinding or wanting to increase the stall speed while not sacrificing on glide and speed. "

Yeh weird hey - but different tails definitely give different lift characteristics given all other variables constant. Damn ive tried enough tails to know at least that much. How - dont know and dont care. They just do . magic as someone said.
Maybe this is not distinguisable with front foot pressure in the end as well.

like this

Select to expand quote

eppo said..

patronus said..

Foxi said..

Fatboy3 said..
Most of the forward propulsion from pumping actually comes from the stabiliser, not the front foil. The physics is similar to dolphin propulsion: dolphins can swim up to 30 km/h, propelled by their large horizontal tails, known as a "flukes".

The front wing/foil doesn't generate much propulsion but is responsible for a lot of drag. You know this form personal experience: 1) High aspect ratio foils pump and glide much better than low aspect foils because of increased parasitic drag from the low aspect foils BUT the high aspect foil itself is NOT generating much propulsive power compared to the stabiliser. 2) You need to change pumping cadence when you shorten the fuselage; this is because of the effect on the stabiliser, not the front foil.

you made my day as my experience in low winds is, that small stabs reduce pumping efficiency to get on foil.
Many mates state, that small stabs would support this procedure due to less drag,
The later will be the case once up on foil and accelerating, but if you can?t get there, drag doesn?t matter at all, does it ? !

Following quote from Oskar reviewing latest Armstrong stabs proning. He distinguishes between front foot pressure and lift (which some don't) then says 220 stab has more lift than 235. I only wing and thought stabs affected front foot pressure and their force is downwards. So anyone know what Oskar's on about?

"A recent prone session riding the new Speed 180 tail with the MA800 and 795 performance mast. The 180 feels really predictable and smooth which I love, you just have the confidence to push your turns a little harder and lean over the foil more. Compared to the existing HA195 I find these new tails have more of a positive front foot feel. When you hit those higher speeds they add a little more pressure on the front foot but without just stacking on too much lift. The HA195 I had moments where it felt like it dived a little as the lift would level out at speeds and if I wasn't ready it could result in a dive. Having the extra front foot pressure means the foil drives out of turns easier and helps you roll from rail to rail. I will generally ride the Dart 140 as my go to for everything apart from downwinding where I use the 180, or when its very small, and then I use the 220 for dockstarts or when I want to get the most glide out of it. For me the 220 has more lift than even the Flow 235 and really helps with that low end if you're getting into downwinding or wanting to increase the stall speed while not sacrificing on glide and speed. "

Yeh weird hey - but different tails definitely give different lift characteristics given all other variables constant. Damn ive tried enough tails to know at least that much. How - dont know and dont care. They just do . magic as someone said.
Maybe this is not distinguisable with front foot pressure in the end as well.

I agree, just wondered why. With big stab on downstroke I feel like push down lift board whereas with not much smaller stab it just sinks. Screengrabbed a shot of pumping on flat water reaches 16 degree AoA. Someone here said stabs start lifting if AoA greater than 6 degrees so maybe that helps a bit too