Forums > Stand Up Paddle Foiling

Fuselage / foil lenght - what does it affect?

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Created by AlexF A week ago, 6 Nov 2018
AlexF
135 posts
6 Nov 2018 1:41AM
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Now that we learned a lot on how a longer/shorter masts affects foiling and what wing surfaces do for us, i wondered about the fuselage or total foil length.
In windfoiling the lenght of the fuselage heavily affects foil behaviour,
1. Long fuse = high lateral stability but lower agilitiy
2. Long fuse + small stab = high lift + low drag -> racefoil Setup
Some brands offer up to 3 fuse length for their windfoils.

Sometimes i wonder if a longer fuse on my Slingshot Setup (Infinity 84 + small/standard stab + short 61cm fuse = 80 cm total foil length) wouldn't help me learning by being more stable. The long SS fuse would add 17 cm to the length.
I'm in the beginner stage atm, and on my first flights i found the lateral balance the most difficult part.

So now i wonder:
1. How long are the foils/fuses of the other brands, e. g. Axxis and NP look longer than SS (best to compare total length of foil) ?
2. What do you think about using a longer (+17 cm) fuse on my setup (buy and try would mean $$$ / ??? for me) ?

Alex

Piros
QLD, 5257 posts
6 Nov 2018 4:45AM
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Yes the SS fuse is a bit shorter but it also has 2 mast positions. Will a longer fuse help in stability yes it will BUT they are heaps of other factors like the depth of the front wing ( the cord ) SS has the largest selection of wings to suit one fuselage so there is a good reason it's that length. In short it's a proven design that works really well so just keep at it you don't need to lengthen it.

With new Front wing swept back designs signs like the Fanatic , surf foils could one day have no fuselage and just be a front wing.

AlexF
135 posts
Wednesday , 7 Nov 2018 1:20AM
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Hi Piros,
i don't want to change my front (Infintiy 84) and rear (standard, not the big FSUP) wing, just gain stability by a longer fuselage.
In windfoiling elongating the fuselages seems a trend to give the foils more stability, but keeping the rear wing -> drag small.
As you say the distance between the front and rear wing with my SS setup is really short, the pics of other brands foils look like much more lenght resp. distance front to rear wing.

As the brands don't give the measure ot their foil length i was curious about this measure at some other brands foils.
Could you give me the length of some of your foils front of front wing to back of rear wing?
E. g. Gofoil, NP, Axis etc.
That would be helpfull for me. Thanx in advance.
Alex

colas
2793 posts
Wednesday , 7 Nov 2018 3:17PM
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For what it is worth, the Gong shaper found out that most foils on the market (kite, SUP/surf) tend to have a "bare" fuselage length (distance from rear of front wing to front of rear wing) equal to the width of the main wing. It seems it is kind of a sweet spot (a golden ratio?) for the general balance and handling of the current design of foils.

cf (in French) www.gongsup.com/forum/viewtopic.php?f=56&t=9330&p=129487

AlexF
135 posts
Wednesday , 7 Nov 2018 9:20PM
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colas said..
For what it is worth, the Gong shaper found out that most foils on the market (kite, SUP/surf) tend to have a "bare" fuselage length (distance from rear of front wing to front of rear wing) equal to the width of the main wing. It seems it is kind of a sweet spot (a golden ratio?) for the general balance and handling of the current design of foils.

cf (in French) www.gongsup.com/forum/viewtopic.php?f=56&t=9330&p=129487


Ok, that would mean with a 80cm wide frontwing the distance back of frontwing to front of backwing should be 80 cm too?
That would lead to a total length of about 110 cm, i don't know Supfoils that long
Alex

AlexF
135 posts
Thursday , 8 Nov 2018 1:18AM
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Just found the measure of the Ke Nalu fuse: 737 mm
That's nearer to the long SS fuse with 787mm than the 610mm fuse, that comes stock with the SS FSUP.
The Ke Nalu should have a total length around 900 - 950 mm i guess.

I guess Axis and Naish fuses also are around 750mm
Alex

colas
2793 posts
Thursday , 8 Nov 2018 1:27AM
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Oops, of course you are right AlexF. Looks like it is more half of the total wingspan rather than a full wingspan. I will check with him if it was a typo and he think his observation is still relevant...

Fishdude
6 posts
Thursday , 8 Nov 2018 3:27AM
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AlexF said..
Just found the measure of the Ke Nalu fuse: 737 mm
That's nearer to the long SS fuse with 787mm than the 610mm fuse, that comes stock with the SS FSUP.
The Ke Nalu should have a total length around 900 - 950 mm i guess.

I guess Axis and Naish fuses also are around 750mm
Alex

Allvator with 80cm front wing and large rear wing. (small rear wing)
Leading edge of front wing, to trailing edge of rear wing 771mm (762)
Trailing edge of front wing, to Leading edge of rear wing assembled 406mm (425)

I dont see how fuse length would effect lateral stability (side to side) very much, Longitude stability i can see.

Personally, im curious about how fuse length effects pumping, Along with the relationship with rear wing size and riders weight fuse length for pumping efficiency... seems that down-winders may want longer fuselages for best pumping, but im just guessing

Fishdude
6 posts
Thursday , 8 Nov 2018 6:38AM
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Oops I got lateral and longitude confused, i get your concern. Can giving your stabilizer more downward angle help you with more lateral stability?

Piros
QLD, 5257 posts
Thursday , 8 Nov 2018 11:27AM
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Fishdude said..
Can giving your stabilizer more downward angle help you with more lateral stability?



Yes......it creates more drag & reduces lift & speed making it more stable. Re the length of the fuse , it's not just stability but pumping and turning is also affected so by going longer it will make it more stable but harder to pump and turn. As I said above each brand has done it's homework for the most efficient fuse length. So I wouldn't go extending anything , if you are finding it unstable you can play with the wings but just doing more water time is the best remedy.

colas
2793 posts
Thursday , 8 Nov 2018 2:45PM
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colas said..
I will check with him if it was a typo and he think his observation is still relevant...


Yup, he said he meant the total length (fuz+ wings). Basically the foil planshape is included in a square.


Select to expand quote
Piros said..
just doing more water time is the best remedy.


+1000

AlexF
135 posts
Friday , 9 Nov 2018 1:44AM
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Fishdude said..
Oops I got lateral and longitude confused, i get your concern. Can giving your stabilizer more downward angle help you with more lateral stability?


Yes you were right i meant longitudinal stability, not lateral, sorry

AlexF
135 posts
Friday , 9 Nov 2018 2:01AM
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Piros said..

Fishdude said..
Can giving your stabilizer more downward angle help you with more lateral stability?




.... As I said above each brand has done it's homework for the most efficient fuse length. So I wouldn't go extending anything , if you are finding it unstable you can play with the wings but just doing more water time is the best remedy.



I want to believe what you're saying, but in the case of the FSUP i guess SS was just looking what was laying around, 610 or 780 fuse.
The short 610mm fuse might work perfect for the FSURF with the Infinity 76, but the 76 wing/trailing edge is far more forward on the fuse than the 84 and also provides more total lenght due to a more forward leading edge than the 84 (i measured that).

The SS FSUP has a total length wing edge to wing edge of 735 mm, and a wing distance edge to edge of 340 mm.
Compared to the above given Gong measures (which is also a rather short foil) that's about 50 mm "too short".

Could you take these measures from your Gofoil, NP or Axis?

For sure more water time does always help but being an 50y old fart living Inland opportunities are rare and i don't want to waist them on not 100% perfect stuff, to provide learing as fast as possible and have an high fun/watertime factor.

Alex

colas
2793 posts
Friday , 9 Nov 2018 3:42PM
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AlexF said..
Compared to the above given Gong measures (which is also a rather short foil) that's about 50 mm "too short".


Like Piros said, I don't think you should compare foils from different brands dimensions by dimensions. Foils are a whole setup, there are many factors that get into the mix, dimensions but also wing geometries, foils, angles of attacks...

For a specific foil, shortening only the fuz by 50mm will decrease stability and enhance maneuverability. But comparing fuz lengths across brands is not the whole picture, and is not as meaningful. Experience from people who have actually compared them on the water is what is important.

AlexF
135 posts
Yesterday , 13 Nov 2018 8:44PM
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Big Thanx to Piros, he posted some of the measures in the NP foil thread:
Axis;- Back of mast to front of rear wing 350mm
NP:- Back of mast to front of rear wing 280mm

My SS FSUP has a measure of only 200 mm Back of mast to front of rear wing, that's 150 mm less than the Axis!
That's with about the same position of the the mast on the fuse (Position B on the SS shiftfuse, Pos. A is a little useless on the FSUP imo).

For me it's clear now, that's the cause of the longitudinal agility of the SS FSUP, this Foil would need a longer fuse for more stability, maybe i give it a try with the longer 780mm switchfuse instead of the stock 610mm shiftfuse.
By using the small/standard rearwing i hope/guess the abiltiy to pump and turn shouldn't suffer too much.

Alex



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"Fuselage / foil lenght - what does it affect?" started by AlexF