Forums > Windsurfing Foiling

Does a longer fuselage make a more stable ride?

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Created by Heliboy999 A week ago, 7 Apr 2019
Heliboy999
21 posts
7 Apr 2019 9:35PM
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Hi.

Struggling with keeping airborne for longer on my kit.
Does a long fuselage make for a more stable ride in the pitch axis?

What is classed as a long fuselage length?

Would a wider stance help?

Cheers

HB

CoreAS
58 posts
8 Apr 2019 1:59AM
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A longer fuselage will help with stability, which foil and length are you using now?

if you're having level, pitch issues it could be more than fuse length though! What width board and type of rig are you using. Then there is mast base location, too far back and it's more sensitive to pitch, to far forward and the board feels sticky and hard to lift.

Fuse length, free riding anything over 85cm. Race guys are on 100-120cm for extreme angles, big boards, big rigs.

On a slingshot hover glide the combined length from wing tip to end of fuselage is 96.5cm that gives me a nice blend of stability and maneuverability.

WhiteofHeart
92 posts
8 Apr 2019 3:00AM
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Like said above, could have to do with your trim. Too much power on your backfoot makes it harder to keep it flying steady. You want front foot preassure. What foil/board combo do you ride and how far from the front screw do you have the mastfoot / backstrap frontscrews?

Heliboy999
21 posts
8 Apr 2019 3:06AM
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Thanks for coming back.

I am using the Naish Thrust set up but with a Naish Surf XL front wing.

Mast Size: 90 cm

Fuselage: 64.2 cm

64.2 seems short but I'm wondering if you need to include the wings in length?

Fronton front wing to rear of rear wing is 79cm.

Naish Hover 142.

Mast base is in the middle of the track.

The centre if lift is between my foot straps

I have my foot straps right at the front of the plugs for early planning and back straps are one back from the front.

The Foil mast is 1 cm back from the very front of the twin boxes.

Im 6 foot one.

I am using Naish Lift sails.

I posted a video of my last session on this forum under Big wings. You can see I'm touching down gently but find it hard to stay airborne for more than 10 seconds.

WhiteofHeart
92 posts
8 Apr 2019 3:49AM
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I have to say never tried the naish foil, but the fuse of my F-One is 66cm (including stab) and it is very stable.

i looked at your video and to be honest I find it hard to see whats happening exactly! I was wondering, how are your lines positioned? Can you let go of the sail with 2 hands while foiling?? (Way easier than on the regular windsurfboard tbh) maybe your lines are too far backward making you touch down in the gusts, or too far forward, making you control height with sailpreassure on the backhand (which is horrible). A longer fuselage is easier, but there's more aspects. A relatively bigger stab or more rake on the stab will make the setup more stable aswell. For me having the mastfoot further back (or shift the entire rest of the setup further forward) helps in keeping the board in the air! Same goes for higher boom, I ride it with the front of the boom at about eyeheight on Everything but my racekit, which i ride higher. A little more loose leech might also help.

CoreAS
58 posts
8 Apr 2019 4:07AM
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I used the thrust foil & 142 board last summer, you are taller than me (I'm 5' 10) but found both foot straps 2nd hole from front a good position but understand your back strap will differ. so maybe move front strap back one hole.

My Mast base quite far back in track. If yours in middle that's too far forward and maybe that's the significant factor. don't go all the way back though (Robby does) and I found it difficult to control at speed.

Sounds like the foil mast plate is in good location. Later I changed from the 70 mast to the 90 and it smoother out the height even more.


Heliboy999
21 posts
8 Apr 2019 4:11AM
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WhiteofHeart said..
I have to say never tried the naish foil, but the fuse of my F-One is 66cm (including stab) and it is very stable.

i looked at your video and to be honest I find it hard to see whats happening exactly! I was wondering, how are your lines positioned? Can you let go of the sail with 2 hands while foiling?? (Way easier than on the regular windsurfboard tbh) maybe your lines are too far backward making you touch down in the gusts, or too far forward, making you control height with sailpreassure on the backhand (which is horrible). A longer fuselage is easier, but there's more aspects. A relatively bigger stab or more rake on the stab will make the setup more stable aswell. For me having the mastfoot further back (or shift the entire rest of the setup further forward) helps in keeping the board in the air! Same goes for higher boom, I ride it with the front of the boom at about eyeheight on Everything but my racekit, which i ride higher. A little more loose leech might also help.


I do not foil hooked in. I only use the lines to have a rest when i am off the plane. I find it almost impossible to foil hooked in as I feel to locked in and prefer to move the sail around as needed to trim. If I did hook in the lines would allow me to sail hands off for a short time. they are probably too long anyway for hooked in foiling.
The sail is a dedicated foil sail, very long boom and tight leeched but most of the time I am feathering the power and its fingertip pressure.
The boom is eye height when sailing but I could give it another couple of cm next time.

I do feel that i am simply balancing the power between my feet and don't feel like I am controlling height with sail pressure. The sail simply tops of the speed. I am wondering if a wider stance may help to shift the weight back and forth quicker as i am riding fairly comfortably but touch down before I have had a chance to recover it. I look at others out on the water and they ride for ages on the foil but they are on different kit. Mostly slingshot.

When you say "More rake the stab" do you mean a greater angle of deflection on the rear stab? The Naish is adjustable and I have it 0.5mm adjusted downwards for better lift on the foil.

Things I will try next time.

Boom another 2cm higher
Mast track further back

Heliboy999
21 posts
8 Apr 2019 4:20AM
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CoreAS said..
I used the thrust foil & 142 board last summer, you are taller than me (I'm 5' 10) but found both foot straps 2nd hole from front a good position but understand your back strap will differ. so maybe move front strap back one hole.

My Mast base quite far back in track. If yours in middle that's too far forward and maybe that's the significant factor. don't go all the way back though (Robby does) and I found it difficult to control at speed.

Sounds like the foil mast plate is in good location. Later I changed from the 70 mast to the 90 and it smoother out the height even more.



Thanks CoreAs.

Ive always had it in the middle and its the one thing I haven't really changed so it could be the missing link.

There really isn't a lot of info out there regarding tuning and positioning of masts, straps, foils etc. It mostly extremes. i.e. Foil forward for beginners etc.

I did seem to figure out that the centre of lift needs to be between your feet so it doesn't matter where the straps are as long as they are equal distance from the centre of lift? I have my foil fully forward to have the Centre of lift between the straps because I want early planning on the board. I am 110kgs so need to accelerate any way I can.

I will try the mast base back another couple inches.

At the moment I have my back straps 2 holes back but the wind has been very strong erectly so lift control has kept me in front of the straps. I have been toying with taking them off completely.

I do not sail hooked in. I only hook in for a rest when off the foil

CoreAS
58 posts
8 Apr 2019 4:24AM
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Watched your video.

move the mast base back, put that back foot in the strap. Your not putting enough pressure on the foil, thus not flying for very long.

Get board speed, pop up using back foot, even out with front foot pressure to level off the height.

Heliboy999
21 posts
8 Apr 2019 4:38AM
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CoreAS said..
Watched your video.

move the mast base back, put that back foot in the strap. Your not putting enough pressure on the foil, thus not flying for very long.

Get board speed, pop up using back foot, even out with front foot pressure to level off the height.


Will.

Lets hope it works.

Thank you

CJW
NSW, 1507 posts
8 Apr 2019 10:35AM
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Heliboy999 said..

When you say "More rake the stab" do you mean a greater angle of deflection on the rear stab? The Naish is adjustable and I have it 0.5mm adjusted downwards for better lift on the foil.



When you say you have it adjusted downwards what do you mean? The rear edge of the stabiliser moves further away from the bottom of the board? If that's the way you have adjusted it, that is the wrong way for more 'lift', the rear stabiliser pushes down so it's effectively a wing flipped upside down (relative to the front lifting wing)

Max it out, so the rear edge of the stabiliser moves closer to the board, or up. This will give you more 'effective lift' as it increases the AoA of the front wing. It's more stable because of an effect called decalage. It will also increase front foot pressure etc so a few other changes may be needed but it will be much more pitch stable.

Heliboy999
21 posts
8 Apr 2019 8:33PM
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I have the Stab angled down as per diagram A.

I believe A will cause the front wing to pivot up and increase angle of attack and create more lift???

When I was using the WS front wing I had it fully angled to maximum. Now I am using the Surf XL wing I find it only needs a tiny bit of angle (0.5mm) or it lifts and I can't hold it down.



CJW
NSW, 1507 posts
8 Apr 2019 11:06PM
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Yep you've got it right. Basically you need a certain amount of decalage (longitudinal dihedral is probably a better term) or the foil has very poor pitch stability. The first gen Pryde Alu foils suffered massively from this. This is the phenomenon as related to aircraft en.wikipedia.org/wiki/Phugoid ...same thing applies to foils.

The problem you have is you've effectively moved you main lift component way forward by adding the big wing. To counter this you've reduced the stab trim but that reduces the pitch stability as above. I'd add more trim to the stab (diagram A style) but to combat this you'll have to adjust things around. I'd move the foil back in the box first, if that's not enough, move the mast forward too, move straps forward etc.

As WhiteofHeart said foils really need to be sailed with front foot pressure for best performance. Sheeting the sail also has a massive effect on the lift control...less so on smaller rigs. Sheet in and it will keep the nose down, sheet out and it will rise. On the race foils we sail them so powered up you basically have to keep the sail sheeted in hard most of the time to keep the lift under control, sheet out downwind at your peril

Paducah
307 posts
9 Apr 2019 12:45AM
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reposted because first post somehow caught infinite quote-box fever


Lots of good advice on this [CJW's post]. Many windsurfers (definitely including myself), when coming to foiling, are used to pressuring the back leg. It's really a strange animal to literally stand on the front leg. (Maybe we associate that with a pending catapult?) When you consciously do this, you may find the unruly foil suddenly back on the water. Then it's a matter of adjusting how much pressure you need to fly.

I'd also suggest beginning to hook in - to encourage staying sheeted in and making the mast base pressure more consistent. Where we sail a lot, because of the peculiar geography of our launch, the last 100 m. coming in we have to bend downwind and unhook to prepare for landing. I have to hang on the booms to keep enough pressure on the wing; otherwise, bad things happen in front of my friends on the beach.

Lastly, we should dispense with the idea that the we should be directly above the center of lift. Ideally, we should be forward of it for stability (and why we should feel pressure under the front foot). Again, aeronautics is our guide.
www.quora.com/Why-is-the-center-of-mass-of-an-aircraft-always-in-front-of-the-center-of-lift-of-the-main-wing

"Q: Why is the center of mass of an aircraft always in front of the center of lift of the main wing?
A: It isn't "always" located there, but if the aircraft needs a degree of inherent stability to be easily controllable, it helps to have the center of mass located somewhat ahead of the aerodynamic center. This introduces a slight nose-down pitching force that is easily compensated by an appropriate down-force at the elevator. The closer the center of mass approaches the aerodynamic center from that forward location, the more sensitive the aircraft becomes to pitch control input. If the center of mass is located aft of the aerodynamic center, the aircraft becomes inherently unstable in pitch & will require constant elevator inputs to keep it level. The aircraft will "hunt" in pitch & may even diverge from controlled flight altogether."

IndecentExposur
53 posts
9 Apr 2019 2:45AM
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my 2 cents:
I have both the 75cm and the 115cm fuselages from Starboard. I have found the longer one does indeed help maintain a more stable flight.
Also, the stab (stabilizer, rear wing) also is a critical part. The larger the rear wing, the more input (pressure) you need to provide for it to pitch up or down. I ran the smaller 255cm stab with the 115cm fuse and 1100cm front wing this weekend prior to switching out for the 330 on Sunday. There was a noticeable difference in stability. Since the season is early here in Colorado, US, I wanted every advantage for stability.

Hope this helps.

ZYX
59 posts
Wednesday , 17 Apr 2019 8:35PM
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WhiteofHeart said..
Like said above, could have to do with your trim. Too much power on your backfoot makes it harder to keep it flying steady. You want front foot preassure. What foil/board combo do you ride and how far from the front screw do you have the mastfoot / backstrap frontscrews?



Agree.
Make sure the angle of attack of the main wing is positive in relation to the angle of attack of the stabilizer.
larger stabilizer compensates for the length of the fuselage.
Thinner stabilizer profile adds pitch stability. I think Naish stab is some 15mm thick. My stab is 4mm thick. You can probably cut a better stub out of 2mm Al or SS sheet and shape it as a knife on both edges. Adjust angle by bending.
Longer fuselage helps but stiffness is more important. If you hang 10kg on the stabilizer the vertical deformation should be under 5mm.
Try to fly without stabilizer to see if your current stabilizer adds stability.
The best option would be to move the entire foil assembly to find the balance. I think Naish offers such of option for foil attachment so it can be moved. In your case the foil needs to be moved back so you can make the stab angle more negative.
Naish foil is not good on a short mast because of large wing chord. Large chord fails to fly when gets close to the surface. You need to subtract the chord of the wing from your mast depth in order to get effective depth of your mast. Also subtract the vertical tail and pitching angle as you show on your video. Very little room left for stable pitching control.
Wider board is less stable. Try old slalom and long board. More swing weight (moment if inertia) helps.
Try another foil. Perhaps you need to be as good as Naish to feel comfortable on Naish windfoils. I see only Naish himself stable flights on Naish foil on youtube. But even Naish himself does not show a foiling jibe on his foil yet. Pitch control is important on a foiling jibe.

segler
73 posts
Thursday , 17 Apr 2019 11:02PM
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The Starboard 115 cm fuse puts the front wing way forward for most boards. If you use a small sail (like the 5.0-7.0) you will not be able to keep the nose down. That is why the racers use big sails (8.0-11.0) sails with the 115 cm fuse. The big sails provide enough downforce to control the far-forward front wing.

WhiteofHeart
92 posts
Thursday , 18 Apr 2019 4:02AM
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segler said..
The Starboard 115 cm fuse puts the front wing way forward for most boards. If you use a small sail (like the 5.0-7.0) you will not be able to keep the nose down. That is why the racers use big sails (8.0-11.0) sails with the 115 cm fuse. The big sails provide enough downforce to control the far-forward front wing.


i know people who ride the sb long fuse with wave sails just fine, matter of technique and really learning to lean forward. For the rest completely agree. big sails load up the nose and make it easier to ride more powerful setups with the frontwing further forward. However I wouldnt know how this applies to the conext of the topicstarter.

In context, start hooking in. If you have to move your sail around to keep stable flight something is definately up, for the sail should be able to be kept steady as a rock, with only small movements in body position. I think you are currently using the "wrong" way of controling your height by loading the mastfoot with your sail. try controling the height with just your weight first bij hooking in and moving your hips fore/aft.

lastly, the technique you are using to control flight height becomes increasingly difficult with less stable sails in gustier wind. The naish hover is the definition of unstable with huge low end power and only 3 battens making it less than ideal. changing COE in the sail very much affects the downforce of the sail and thus amount of "uprightness" needed to push down the nose. yet another reason to hook in and keep the sail in a fixed location and to use your bodyweight to control height.



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"Does a longer fuselage make a more stable ride?" started by Heliboy999