Jump to content

Naish Foil Board


SoutherlyBuster
 Share

Recommended Posts

Sea trials are complete, took the board out into the surf with the home made rear wing today. Took some shims along just in case the zero angle of incidence needed adjusting. The lower angle worked to my favour, lifting later but at speed needing to be less forward on the board, so was more managable to control pitch at higher speeds. Gave a nice stable flight. There was a hum though, will need to investgate possible causes. And the rear wing did not break, ya hoo.

After the sea trials:

20181114_131041ForWeb.thumb.jpg.abbd68924f8d3fb1dd2c8c79e90cfd82.jpg

20181114_131054ForWeb.thumb.jpg.fe62d0f4801fe734a5861fcdcf847579.jpg

(No fairing added between wing and fuselage, might be the cause the the hum.

20181114_131105ForWeb.thumb.jpg.456e0ee6df0ef1bb53eab80f0e4840ef.jpg

Counterbores applied to the wood were a neat flush fit, but when the glass was applied, the precision was lost, so this might also be the cause of the hum by way of turbulence. All final brush strokes of paint applied in the stream wise direction, to avoid roughness in the wrong direction.

Screenshot_20181114-130856.png.0c8dd5f276537ae0e3f6654da9b23b33.png

Highly approximate, but I remembered the frequency of the hum, then when I came back to my car, by memory I sang the same hum and used the stroboscope on my mobile phone to measure the frequency. 146 Hz, rather low frequency.

Foil thickness distribution was "eye" balled, so maybe there are some parts of it causing too negative a pressure, leading to cavitation which also might be the reason for the hum. The wing feels reasonably stiff so would not have thought the hum was due to the wing being too flexible.

 

Oh and pumping the board works better now, used this once standing with kite to get the board quicker up to speed.

Edited by SoutherlyBuster
Link to comment
Share on other sites

Some googling, reading and applying some engineering common sense ....

There appears to be a lot of “wive’s tales” and snake oil surrounding the source of the humming, but also a lot of good information out there. From my reading it appears the shape of the trailing edge is the most important aspect to reduce or eliminate the humming. As the two flow streams from the top and bottom sides of the wing come together at the trailing edge, where the vorticies peel off is the important bit. If they peel off consistently on either the top, middle or bottom then no vibraton; if they peel off alternatively between the top and bottom surfaces, this causes a vibration and this is what the hum is. From a Yatching design book, there are some guideliness to reduce or even eliminate this vibration, see below for extracts and source of the book:

20110417Principles%20of%20yacht%20design

A0880EB3-7033-45F7-8279-EA8D8EA3CE72.thumb.jpeg.68c01f29c6286de2a51bdfa22919071f.jpeg

A8641097-8AFE-434D-95CC-4BF1DA4043C2.thumb.jpeg.20dbb53a0be507fb0ad0dd79a29ce645.jpeg

What I have is a rounded squared off trailing edge — not a favourable shape. So what I need is some thing like option 5 or 8. The fibre glass is wrapped around a shape like option 1, so as not to expose the wood underneath the fibre glass protective layer, I need to add some fairing to the trailing edge to make it one of the more favourable shapes, but also ensure I don’t make it too sharp to avoid cutting myself.

 

Thanks @Kamikuza for the suggestion, it lead me to find the above information. By the way your name appeared in some of the searches :) . Looks like a lot of other foilers experience the same problem. Also one suggestion was to apply some tape to one side of the trailing edge to stop the fluctuatin of where the vortices peel off, might be a quick way to see if this is where the vibration problems come from.

 

Link to comment
Share on other sites

That's interesting. I wonder if it matters that the article is talking about vertical surfaces rather than horizontal, and surfaces that are much further apart than kite foils are...

5 or 8 is going to lead to cuts when you kick the foil under water. I think I still have scars from kicking a stab last year.

I think my name pops up because I've asked questions and commented on my experiences, rather than offering anything useful :D Searching images for "axis kite foil" used to turn up my photo in first spot, but now for me it's the end of the second row :(

This topic is interesting to me because I've ridden two different foils of one brand, and one has whistled like a steam train, the other has been completely silent. We've got a guy with an Alpine foil that whistles so loudly you can hear him literally hundreds of meters away. He's swapped the wings and it still whistles. Another guy with the same foil is silent. Why?

Is the whistling related to vibrations, or is that something else? Both my Axis foils are smooth as silk through the water, but the kite foil would squeak softly if I loaded it up in a carve, and the S-series has a gentle whistle when running flat out. Neither are as bad as the Alpine, which is bloody loud.

So I think it comes mostly from the stab, or interaction between stab and water flow around mast and stab.

 

Is it vibration you're feeling too, or just the sound? With the tape residue on the other wing, it was feeling like I was driving over shingle rather than any noise...

 

Link to comment
Share on other sites

I applied some tape to the trailing edge starting on the top side level out extending beyond the trailing edge by about 2mm fold over and stick to the bottom surface of the foil. Humming gone (which I could hear and feel).Screenshot_20181117-201031.thumb.png.180c76eb21e4489a6653d3fc912ec9b6.png

The tape is very sticky, I use it for reinforcing my foam gliders, sticks like sh@#$/ $# on a blanket. Did not come off during the light wind session 6.6 to 9 knot wind with 18m FlySurfer Lotus.

Link to comment
Share on other sites

17 hours ago, Kamikuza said:

That's interesting. I wonder if it matters that the article is talking about vertical surfaces rather than horizontal, and surfaces that are much further apart than kite foils are...

5 or 8 is going to lead to cuts when you kick the foil under water. I think I still have scars from kicking a stab last year.

Is the whistling related to vibrations, or is that something else? Both my Axis foils are smooth as silk through the water, but the kite foil would squeak softly if I loaded it up in a carve, and the S-series has a gentle whistle when running flat out. Neither are as bad as the Alpine, which is bloody loud.

 

Vertical or horizontal makes no difference as gravity makes no difference here on the formation of the vorticies, and it is the vorticy formation alternating between either side of the foil that causes the vibration.

Surfaces being further apart, yes agree. I thought about this too, there must be some sizing effect going on. If you zoom in close enough there will always be a blunt end of the trailing edge. I suspect the characteristic length would be the boundary layer thickness. I expect the above article was an A to B comparison, same foil size, just alter the taper angle. So at some point a blunt end would make no noticable difference.

Agree some of these sharp edges look nasty for rider safety. Reckon the blunt hard trailing edge plus the relatively soft tape I used is a good solution, just a mater of find tape that lasts long enough. Helicopters use a special tape for the leading edge for abrasion resistence ... hmmm.

10 hours ago, Kamikuza said:

That's very interesting too. You stuck the tape to itself past the trailing edge? Basically just longer and thinner trailing edge, eh. So are you going to thin out your trailing out to a point? Or just slim it down some more?

Yes the tape was double backed onto itself to creat a thinner trailing edge. At the moment I am thinking, don’t mess with the foil, just use tape, main motovation is rider safety against cuts. The tape lasted well for one session, will see how long it lasts. Longer term solutions would be tapes with heat activated glue applied to the resin coating.

I suspect if the foil wing and mast were made of a very heavy highly damped material with zero vibration transmision you would not hear the wistling. Apart from the very low frequency vibrations that one would definitely feel through your feet, the high pitched frequnecies may be more noticable depending on the stiffness and mass of the mast and board, if the whistling frequency excites one of the natural frequencies of the mast and board, then it would be clearly audible, like a sounding board of a piano.

Link to comment
Share on other sites

I was thinking more differences in water pressure at different depths, and how they might travel.

My foil's TE are noticably squared, the front thicker than the rear.

Tape would be good for free ride but I doubt the racers would countenance it :D

I think the relative stiffness of the fuselage matters too -- wouldn't stiffer transmit more "sound"?

"Rumbles" are the turbulence in the water I think, and the trim difference between wing and stab feel similar but more rearward to me...

So where is the whistling actually coming from?

Link to comment
Share on other sites

14 hours ago, Kamikuza said:

I was thinking more differences in water pressure at different depths, and how they might travel.

So where is the whistling actually coming from?

Depth, ah right the p=density x depth x g. For the mast can be important but I doubt important for whistling.

Where is the whistling coming from? Well in my opinion, it is not just from one thing. Think of it like a guitar or violin, the sounds come from the vibrating string (our vortex sheet coming off the foilig trailing edge), the vibrations then get transfered to something which amplifies (the wing to mast to the board) the sound, then eventually to something that creates air pressure waves so we can hear it. If the vibrations were solely confined to the water, I doubt we would hear it. To amplify the vibrations, you need to tune the natural frequency of your strucutre to match the forced vibrations, hence why same foils with different mast/board some sing, some don’t. Ever pick a guitar and notice the sound rings nicely and others just sound dull? It is all about getting that resonnance right in the structure of the body and for guitars and violins the air space since it has it’s own set of natural frequencies.

Link to comment
Share on other sites

Is a whistle the same as a hum though? We're using them interchangeably but I think they're unique.

The Alpine is a definite hum by the character of the sound, and the DA would just start humming at a certain speed, like a switch was thrown.

My whistle grows in volume with board speed, and probably speed into the wind, I'd have to concentrate. There are mounting holes in the plate, I wonder if they're the source. It's really almost non-existent, very quiet -- unlike the DA or the Alpine.

Now I think of it too, the Alpine is a Tuttle mount on a Spots board...

Link to comment
Share on other sites

  • 1 year later...

Adding the tape to the trailing edge of my stabilizer wing initially stopped the whistling and vibrations, but gradually started coming loose, which attracted grit and gave overall a rough surface finish. The result was that the hydrofoil slowed down and became prone to stalling. The stalling was evident by riding along nicely, as speed increased I needed to put my weight further forward, putting high loads on the stabilizer wing, then a sudden pitch forward without the wings exiting the water. So it was time to remove the tape and fix it permanently by filing in a sharper trailing edge. In the above example from "The Principles of Yacht Design" figure 6.3, I went for option 5, with the exception of instead a knife edge a 0.5mm radius. I figured the finite radius would be more wear resistant, more robust to the edge breaking off and friendlier to the rider (besides I do not push my feed on the wings to kick them out). I cut a bit into the underlying ply wood, so had to re-coat with West System resin, let it cure, then file, sound down for a smooth finish -- no humps. Then used wet and dry sand paper. Finally, used some cut & polish for buffing up car paint jobs. The front wing was getting a bit dagy as well, so mixed up some resin with filler, then got the same treatment as the rear stabilizer wing. The wings felt smooth to the touch.

Gave it a burl yesterday in the surf. Straight away noticed the nice swish feel, so parasitic drag was significantly reduced. No more rear stabilizer stalls and usual speed was restored.

Still finding trouble at the higher speed that I can not lean further forward to balance out the board to keep lift constant, hydrofoil exits water and I go for a swim. Will try some shims on the stabilizer to tilt the trailing edge up to get more down force -- currently at zero degrees.

 

Also have in mind to make a new front wing, same method as the rear wing (plywood, hand shaped, covered in fibre glass), making the front wing a higher aspect ratio than the one that came with the Naish hydrofoil.

Link to comment
Share on other sites

  • 2 weeks later...

Adding the shims made the ride go horrible, so took them off. They probably also added some nasty flow separation.

@Kamikuza, your comment of don’t try and lean forward rather move your COG forward, makes no sense. Perhaps we are saying the same thing, when I say lean forward, I mean shifting my body forward which then shifts the COG forward. Yes I know simply pushing down on the front foot does nothing to balance the board out because the COG has not changed.

At the moment the biggest helper for me was to reduce the kite size now that my skill level is better, that way I can depower more once the board speed goes up. Launches are a bit harder but I have the knack of that now. Also a kite with good upwind capability helps greatly to body drag out past the breakers in the surf.

By the way, those FlySurfer Peak 4’s have caught my attention, some of the local foilers here in Christchurch New Zealand are using them in the surf with rediculously small kite sizes. Anyone try the Born Race Stars for hydrofoiling?

Link to comment
Share on other sites

It may well be cross-talk...

If you leaning from the waist over your front foot, you're doing a lot less to shift your CoG, and are upsetting your balance.

The answer is Yoga lunges -- keep your torso upright and bend your front knee.

Yeah I quickly went from 13m tube to 12m Speed3, then 10m Crossbow. Had the 21 for super-light winds, but as soon as I was overpowered (10 knots maybe) I'd go straight to the 10m.

It's the same now. If I can't water start on the 10m, it wouldn't be much fun anyway. 

Key thing is a good power stroke, then being able to turn the power right down. When you get used to loading up the kite and foil like a racer, power is less important.

Honestly, the estuary is great. Getting out through the waves at Brighton is still a bit tricky :D

Peak 4 interests me too. Hopefully get a Debi this year...

Link to comment
Share on other sites

  • 1 month later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

  • Similar Content

    • By BlindJP1600949559
      When I was still but a lowly newbie, and I MEAN newbie to kitesurfing I planned a trip to Egypt, Moonbeach to be exact, where the weather was warm and the winds were perfect. I owned a 12m and a 15m so what else would I possibly need!!
       
      Well... after booking and doing the inevitable EXTRA research on where I was going I discovered if I wanted to get the best out of the lpace I had better get my hands on a 9m! Fortunately due to the miracle of work (yes I do actually work folks!!....Occasionally!) I went to see Mark at Whitstable Windsurfing and got some great advice and left the shop £350 lighter and the proud owner of a new 06 Naish Boxer III 9m complete.
       
      Well I was desperate to use this kite before I went but lets be honest here! You buy a 9m kite 5 days before you go on a kitesurf holiday there is not a chance in hell that the wind gods are actually gonna let you fly it before you go!!!
       
      So I get to moonbeach and its perfect learners 9m weather! Well I was still at the stage where I could go right foot forward without a problem but left foot forward was definitely challenging! Well due to perfect wind, butter flat water and 90 degree sunshine I had both directions cracked on the first day and was finally in a postion to learn a bit about the kite!
       
      What I learnt was I LOVE IT!!!
       
      As a foil flyer I always though that a 9m kite was an absolute monster, and as foils go it is! It is also like flying a bus of beachy head, unless you get it right it just falls out of the sky!!!
       
      Well was I in for a shock! a 9m Lei flys like a wasp! The Boxer III is a medium aspect kite, it is fast through the window and had me grinning like a lunatic in minutes!
       
      By the 2nd hour of the 2nd day I was actually making 'upwind' progress!! Something that had seemed like some kind of Voodoo magik prior to this with my Hydros!
       
      The build quality of this kite is absolutely ROCK solid, the 5th line safety system is excellent, but I did find the leash banging against my leg a bit odd and after a couple of dunkings I diod notice it was wrapped around the chicken loop. Not something that is too essential but as Naish's safety system is an odd 'grab the web cover at the top of the chicken loop and slide forward' this did give me a minor amount of concern.
       
      The kite is marketed as an 'all terrain' kite and although I have no plans to landboard with this EVER! I am toying with the idea of snowkiting with it! Yes I am that impressed with the build quality!
       
      This kite gave me my first taste of jumps and as with all small kites like this it shoots you airborne very rapidly but it doesnt have a great deal of float! Not that I cared as I was too busy thinking "Ive just made it into orbit!!"
       
      Some say a beginner shouldnt even think about a small Lei but this was as friendly as you made it. Something that is often the case with kites. Granted I did learn the following day this isnt applicable to ALL kites! (I flew an 05 14m Rhino that scare the bejesus outta me!) Would I recommend this to a beginner, well in hindsight probably not, but not because its a dangerous kite but more because of the winds you take it out in. I am now loathed to get this baby out in anything less than 30mph where its an absolute beasty!!
       
      Its an amazing kite, great build quality and attention to detail. It flies well has a good fifth line system and in my opinion is only let down by its bizzarre relaes system. Something I didnt have to use in Egypt and as I now fly it on an 06 Slingshot bar system it is not an issue. Its a fast kite, will get you very high very quickly but DONT expect floaty landings. Its a high wind kite if you really want to get the best out of it. But it flys well, the sheet in/out doesnt make it too ugly to fly if you are horrible overpowered but at the time I only had 03 kites to compare it with.
       
      As with most Lei's this size, its not that much about aspect ratios as you are generally flying them in high winds anyway so you are going to be lit up regardless. I like my little Boxer and its price onhly made it more attractive and now its been superceeded by the SLE I have seen it for sale new kite only for £299 which in my opinion makes it a steal!
       
      By : BlindJP
    • By RaceKites
      The new Naish Element 10.5 depowerable foil.

      In the bag

      - Control bar
      - User's manual
      - Four 25m color coded flying lines
      - Light weight bag
      - Kite compression/packing strap
      - Backpack

      The one I had came in a stuff sack so I cannot comment on the backpack that will bew supplied on sale.

      Out of the bag
      As you would expect from all Naish equipment the build quality is excellent with and the Setup is a simple process.

      - Unfurl the kite Weigh the sail down with some sand on the trailing edge.
      - Attach the colour-coded.
      - Peg the safety leash down.
      - Attach the lines to the bar

      Hey presto you're ready to go.

      First impressions were its similarity in appearance to an Ozone frenzy only slightly more rounded which makes it appear smaller next to equivalent sized kites.

      The test
      The kite has been designed for use on snow but I have been testing it on a mountain board and in a buggy.

      7 - 10 mph is the highest wind speed I've tested in so far which really is not enough to test the more radical moves this kite will generate.

      Launching the kite is a snap, set the depower system to full by pulling the depower strap toward you. Attach the leash to your harness and pull tension on the leash lines which keeps the kite grounded, if the kite tries leave the ground put more tension on the leash lines. Hook the bar onto the spreader, push the bar away, let go of the leash and the kite climbs straight to the top of the window where its sits above you without over fly or too much lift.

      The Element turns quickly and develops good power throughout the wind window feeling very stable although the conditions were not gusty. The wing tips did tuck on occasion but this was due to a lack of wind and did not occur when the wind picked up. When it comes jumps redirect the kite and pull in the bar to develop extra power giving nice lift and floaty landings.

      In A buggy
      The kite works well in a buggy as it only has a small bar and is in easy reach when the bar is out. Its smooth consistent power lent itself to ground base tricks such as wheel stands offside and kite-side which were mainly all I could produce in the available wind. The few small jumps I achieved were floaty and the kite redirected well for a soft landing.

      On A Board
      The kite is well suited to kiteatb, again the even power developed, gave a feeling of security whilst leaning back against the kite. At no point in both in regular and toe-side stance did I feel It would let me go and id eat sand. Due to conditions most tricks were unattainable but as with the buggy the jumps achieved were floaty and I had no difficulty re-directing the sail to power up on landing.

      Conclusion
      On the whole a good kite with stability and smooth power. It gave the impression that in good wind it would give a good speed run or free ride without the rider having to concentrate on the kite leaving you free for tricks. This is certainly a good first depowerable foil kite.
      By : Phatdan
    • By RaceKites
      Naish released the X3 in 2003, the evolution of the X2. The X3 was a response to those riders who were looking for a more European style wing, more forgiving, wider range. Flysurf.com put one of the strong winter wind sizes to the test for you, the 8.0.

      Extras
      Adjustable carry bag, pump with leash, 50cm control bar fitted with de-power and Safety System, colour coded flying lines with differentiated connections (loop or knot), repair kit, instruction manual.

      Finish
      The kite is well finished with well positioned reinforcements. You just need to look at it and you can tell it's a great product. There are numerous adjustments you can make to improve performance at the light and heavy ends of its wind range : kite end adjustments. There are two valves on the leading edge, one of which serves as a rapid deflation valve. The kite has 5 inflatable battens, the leading edge tube extends to form the wing tip battens.


      Control bar
      The control bar is colour coded to avoid making a mistake when recovering in the water or following a no- hands jump. The de-power system adjusts by means of a strap with a stop-loop, you have to push it away from you to release the front lines. The small harness loop to the front lines has a quick release (trim loop quick release), you push away from you to release, there's no locking strap to impede your harness loop. The elasticised kite leash is connected along one of the front to your harness.

      Design remit
      The X2 surprised everyone with its build quality and its amazing flying characteristics! Naish have bettered that this year with the X3! Benefiting from the very latest technical developments, the X3 is the ultimate flying machine in terms of performance!

      Actioning the safety system
      The small harness loop releases if you push towards the bar (upwards), the leash retains the kite and it becomes a harmless flapping cloth. Nothing to add to the previous year's system.

      Re-launch
      It's a medium sized and wind kite, there aren't usually any problems re-launching given those criteria.

      Power
      Great depth of power. In lighter winds you can use its air speed to keep you planing although jumping's another matter once you get down to this size.

      Stability
      Nothing to say, it's got it in spades. In fact it's quite difficult to pull out of the sky, and it's stable also in the sense that it doesn't really deform (good rigidity).

      Flying - General handling
      It's pretty fast but a good deal calmer when you connect the rear lines further towards the inner attachment points. Very comfortable fly, no surprises, its rigidity makes it very reassuring. We also tested with 20 metre flying lines on which makes it more lively but more sustainable. It's a comfortable fly, not too fast if you connect the front lines towards the front-most connections.

      Lift
      In the appropriate wind range (powered-up / over-powered) it's got excellent lift for an 8.0.

      Range
      Very good wind range. A really good progression from the previous year. Riders of about 50 - 60kg and good skill level could see themselves holding this right up to 30 knots. Bigger riders up to 40 (top skill level only though!). Good de- power not least because it moves quickly to the edge of the window where it pulls a lot less.

      Conclusion
      It's a high performance 8.0 but is cool to fly. Lifts like nobody's business in its wind range, is stiff and controllable, doesn't kick or give nasty surprises and has a great wind range... On the negative side, perhaps you could fault the air speed you're going to have to adjust to, and of course, depending on your settings it's no butterfly...

      Pluses
      Great lift and carry for such a small kite, stability and range. Flysurf.com recommendation: Attach your rear lines towards the inside at first for less forward speed, afterwards go with whatever suits your style but bear in mind that it is an 8.0. Send it big for your first jumps!

      Recommended skill level
      Experienced to expert

      How does it meet the design remit
      A real high performer, oh yes!

      The testers' verdicts in a sentence

      Caro, 34 years old, 60kg
      I found the lift incredible but still gentle for its size. Flies really well. I preferred the 'slow' setting for strong wind.

      Marc, 29, 75kg
      Nothing but goodness ! Its speed, stiffness and range (up to 45 knots no problemo!)

      Alex, 24, 78kg
      I'm not a big fan of kites less than 9.0 m2 and as for riding in 40 knots plus, that seems mostly about survival to me. But hey, I found it a really good fly. It's brilliantly finished, it flies comfortably and it would suit a light weight rider in big beefy conditions!

      Sandrine, 36, 52kg
      Very forgiving and tune-able with those adjustments for more or less power. It's a good fly and very reassuring, no calamities if the wind really picks up.
       
       
      By : Team Flysurf
×
×
  • Create New...