Can't get flying

It's not just in using bigger wings for flight in 11-15 knot gusts.
The lower drag of smaller foils allow for smaller sails to attain foil speed.
Increased drag from big foils need more sail power to get thru it's drag phase to attain foiling speed.
Look at foil racers. For the lightest 6-13 knot days, while they use 9 meter sails, the choice of wing is still around a 100cm wide, maybe 1,000 sq cm area front wing.
Lower drag has to account for something.

I foiled the Gamma 68, then the I76 and now a 1700cm2 wing on a 72cm freeride windsurf board with low tail volume. Largest sail is 6.3, I'm up and going in 10-12kts and I'm at least 200# in gear.
Your issue is pumping technique. Likely just wagging your back hand without any leg involvement. You can spot these sailors because they don't get flying very early and they tire quickly.

That said LeeD is entirely wrong about wing size and low speed drag. High aspect low area wings require large sails and volume to get useable bottom end, their lack of drag is only a factor once foiling at high speed. I've run both types on a low volume board and the difference was staggering.

I use the Naish Kitewing, 2019, 600 sq cm.
Same wind as I use the WS 2018 wing 1220 sq cm.
Naish 73 cm 122 Hover. Don't know about right or wrong, but both work for 6-14 knot breeze.
My buds, smaller than me, are using 1050 NP's and i76 with similar sail sizes.
I AM lightweight, but up to 30 lbs. heavier than my foiling buds.
I am also 17-40 years older than them.

Try to get in the front strap while pumping. If you have problems with this remove all straps and try to get your weight more back

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aeroegnr said..
Here's the math. The 99 takes off around 8mph or so, and lift is linear with area but squared with velocity. So, if 8mph is right, then takeoff speed of the 76 is right around 10mph by the math. It's too close to tell in the footage I have of myself though.

This is assuming that lift coefficient and weight difference is insignificant. Weight probably true, and because they are similar design it seems like the lift curve will also be quite similar.

That's probably a good first approximation, but not the whole story. The i99 has only 15% more area than the i84, which would give a 7% difference in takeoff speed. That would be less than 1 mph. But foilers who have both wings usually report a larger difference.

In the mathematically framework, that would probably be reflected by a higher lift coefficient for the i99. One way to look at that is that the wings have similar areas where the flow is more disturbed (the center and the outside wings), but the i99 has a larger area in the middle. The i99 also seems to have a sharper (and thus less draggy) trailing edge. The i99 also seems thinner than the i84, although that should effect top speed rather than takeoff speed, unless the i84 is too thick.

But in the end, the square relation of speed to lift will overwhelm the linear relation between lift and lift coefficient, so we're probably talking about differences like 7 and 10 mph vs. 8 and 10.

There's a fun way to see what the minimum speed of foils: have a cell phone announce the speeds to you through an app like "Talking GPS Speedometer" or WindsportTracker. That works well for foiling since everything is so quiet. Getting the takeoff speed may be hard since the speed changes quickly once you get on the foil, but you can get a good idea of the stall speed in lulls, when speed changes are more gradual.

At age 72 and 195 lb I have no trouble getting the i76 up into flight with a 6.8 in 12 mph winds (just barely the onset of whitecaps), and I'm no youthful jock that can pump like crazy. In my book (and this is just my book, I know), the i84 and i99 are overkill for light winds when the i76 is plenty.

In any of these wind sports, you have to have enough energy in the wind to get you moving. No move, no fly. The wind kinetic energy is a squared function of wind velocity. As a result wind of 12 mph has 2.25 times the energy of wind at 8 mph. Expecting to fly in 8 mph wind, even with a monster sail and monster wing, is wishful thinking.

The i99 might get flight at 11 mph, and the i84 at 11.5 mph (ok, let's be optimistic and call it 10 mph and 11 mph, respectively). You need board speed to fly. You need wind to get board speed.

Waiting to see a couple whitecaps out there with a i76 and 6.8 has worked for me. If I don't see at least a couple odd whitecaps, I go fishing.

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aeroegnr said..
Here we go, found one spot where I pumped just above the planing threshold with the i76 but probably stopped pumping too soon.

I'm sure there's plenty to criticize technique wise

.be

I won't criticize your technique because I don't know enough to do that so I want to share one thing about my pumping technique (or lack thereof). I have a formula board and a infinity 84 wing. I weigh 75 kilos and mainly use my sailworks NX 8.2 4 cam sail. when I pump, I am WAY more aggressive than you and bring the sail much closer to my chest (I Bend my arms much more than you). I sometimes start with very little pumps but as soon as I am at take off speed, I start pumping with bigger movements. Also, if the wind is pretty light, I will be pumping for much more time than you. Oone more thing, mast carbon content has a big impact on the way you pump and the way the sail reacts to your pumping. I think if you have the proper mast and the mast has high carbon content you could pump faster than with a lower carbon content because the mast with more carbon will react faster. I notice this with my 6.7 which I use with a 30% carbon content.

again, I am not sure if my technique is proper, just sharing what I do (and I works for me)

Board is planing...pilot needs to step back.
Standing forward in slog position will keep him from flying, since slog position promotes slogging.

Front foot in the strap. When you release the sail pressure pull the foot up and when you pump the sail push it down/forward.
This results in being airborne with the sail in a position to add forward momentum rather than having no way to accelerate once you are up.
The sail pump which works best for me is hands together, front hand starts the pump; back hand finishes it and the mast is brought forward again before sheeting out.

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Awalkspoiled said..


Is that you, Greg? If so, I'm probably the older guy (64 years old/215lb). I was actually on an i84 with that 10.0 Speedfreak but just because I was too lazy to rig my 7.0 Flyer which would have foiled up just as early. I'm eager to try the i99 but never have. I do like running big sails because I truly hate pumping, but with big sails I bet I'd be happier with higher-aspect wings than Slingshot offers.

I thought you looked pretty smooth yesterday, with nice height control. On that huge sail I was either WAY up near breaching when I stood right over the board, or sort of semi-slapping when I hiked out in the straps. I did fly in both front and back straps for a while (a first - usually I'm just in the front strap) but never felt really balanced on the new board. Its balance is amazing on a fin, but I wonder if I should move my straps back for foiling?

We should be on small sails tomorrow!

Hah yeah that's me, and thank you! Yeah, so far much better control, I think you saw me when I was heading toward shore and up on the I99. You had some good gybes earlier when you were finning, made me upset I didn't bring my 9.5 yesterday.

I think I breached a couple times but it was a very gentle drop and never came off the board or catapulted, just kept going.

Yeah, tomorrow should be very interesting indeed!

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aeroegnr said..
Here we go, found one spot where I pumped just above the planing threshold with the i76 but probably stopped pumping too soon.

I'm sure there's plenty to criticize technique wise

.be

honestly, did not look like you were pumping that much, I know you felt like you were, but in reality not much pumping of the board and really minor pumping of the sail.

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aeroegnr said..
Thanks guys, I'll get into the front earlier and try to get more aggressive. Before, when getting more aggressive, I have either rounded up or gotten way off balance, but I'll keep trying to improve. I actually liked pumping the bigger sails more in light wind because they're a better counterbalance but I'll keep trying with my 6.6 because I've been able to fly the 99 on it.

BTW this is with the foil as far forward as I can put it for both the I76 and I99.

FYI the 76 should be at least 6cm further back than the 99, assuming universal and straps are unchanged

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segler said..
In any of these wind sports, you have to have enough energy in the wind to get you moving. No move, no fly. The wind kinetic energy is a squared function of wind velocity. As a result wind of 12 mph has 2.25 times the energy of wind at 8 mph.

It's a cubed function of wind velocity. A 12 mph wind has 3.375 times the power available for extraction than the 8mph wind.

but it also takes 33% more power to drive a board at 11mph than at 10mph. (Assuming drag of the non-planing board goes up with the square of velocity -a huge assumption = but if it did). 10% more wind will get you that extra mph. It's going to be hard to measure!

Cubed or squared, it is definitely not linear. We need wind to move our gear. 8 mph is insufficient. 12 mph is sufficient.

Back to the physics. Above it says, "the power of the wind is a cube function, but the kinetic energy of the wind is a square function." I based my squared argument on the KE = 1/2*m*v*v equation. Power equals force times velocity. This is where the third velocity comes in.

Lift is not power. Lift is a force and is based on the velocity squared, as shown above.

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boardsurfr said..

That is incorrect with respect to foiling.
The idea that the energy is a cubed function of wind velocity seems to come from wind turbines.

It's not incorrect and it's not just an idea. Lift or power? They are just 2 different applications of F=ma. There's a few other mathematical tricks based on F=ma that are useful at times. You'll get the same answer no matter which method you use.

Don't think you're going to even get close with mathematics on this one though. All that pumping going on.

Not much difference in a wind turbine and a sailboat. They use similar wings. One goes around in circles, one in a straight line.