Author Topic: Longer Fuselage for Stability and Pump  (Read 8415 times)

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Re: Longer Fuselage for Stability and Pump
« Reply #15 on: January 06, 2023, 12:52:23 AM »
Still, we should test that. My guess is that it would pitch like a donkey, but it's just a guess. I should ask Adrian Roper about it. I suspect he's tried everything he can think of, and from my discussions with him, he's thought of a lot of crazy shit.

This is really interesting to me and it is an important concept.  I don't think there is any direct relationship between mast distance from front foil in terms of pitch or any other movement.  That is provided that the front foil can be (and is) positioned in the same location for each mast configuration (not limited by track length or other board specs.).  That is to say that the mast could be mounted on the front foil, in front of the front foil on an odd fuselage, or behind the tail wing on a really odd fuselage without changing the spatial dynamics at all.  Notes, of course, would be that everything else would remain static (distance from front to rear foil, rear foil selection, etc.). Also, weight distribution and mast drag positioning (minor) would certainly be effected by a mast move and fuse reconfiguration but not to a problematic level in smaller, more realistic measures and likely equally beneficial in some scenarios.

« Last Edit: January 06, 2023, 02:12:39 AM by Admin »

PonoBill

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Re: Longer Fuselage for Stability and Pump
« Reply #16 on: January 06, 2023, 10:56:03 AM »
A longer fuselage means a longer arc for the tail to travel through. Pumping has a fairly strange dynamic in that the downward movement looks fairly flat, while the upward movement is angled up. For pumpers who seem to get the most out of pumping the upward angle gets fairly acute. This makes a lot of sense, with the board (and foil) flat, the foil is providing lift at somewhere close to the lowest drag the wing can offer. The foil coasts forward, losing altitude as slowly as it can. With the nose of the foil lifted up to a higher angle of attack and the rider unweighting, the drag of the foil is high, but so is the lift, less lift is required due to unweighting, and the board rises quickly.

I suspect the longer fuselage helps most with timing. The stabilizer moves through a longer arc, and has a longer lever arm to apply any force through so it moves slower. Watching people pump with no stabilizer demonstrates that the pumping is much faster, and is probably less efficient.

Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

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Re: Longer Fuselage for Stability and Pump
« Reply #17 on: January 06, 2023, 11:06:00 AM »
Hi Bill, Agreed that front wing to rear wing distance matters a lot to many dynamics.  I avoided calling that distance fuselage length because, as with our new concept, part of that distance may be on the foil itself, and because some fuses have space behind the mounts.  My point was actually about the distance from mast to front foil, not from foil to foil. 

PonoBill

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Re: Longer Fuselage for Stability and Pump
« Reply #18 on: January 06, 2023, 05:47:46 PM »
Ah, yes, I don't think that makes a huge difference (though I certainly might be wrong) except perhaps for drag. Most windfoilers, and certainly the early ones, had the mast plugged into a tuttle finbox, meaning an actual finbox on boards not designed to foil and the fuselages were super long from mast to front wing, to get the center of lift under the rider.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

EastCoastFoiler

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Re: Longer Fuselage for Stability and Pump
« Reply #19 on: January 07, 2023, 03:42:34 AM »
For me, more pitch stability is the antithesis of pump.  Less stability tends to help, with the caveat that you can’t pump if your out of control.  So you want the least stability that you can be 100% in control of all the time.

Next is understanding how you get that stability.  More downforce from the tail is going to produce a more forward Center of effort, and you move the foil back to compensate.  The more rearward foil position is inherently more stable.  A larger tail is also more stable both for this reason and the difficulty of moving it up and down in the water column.

The fuse length comes into play with leverage.  Longer fuse gives the rear wing more leverage letting you ride less downforce and a smaller rear wing for the same effect.  Less downforce required makes less induced drag on the rear and front(with less downforce the front has to work less for the same net lift). Also with more leverage you can ride a smaller rear wing for the same stability resulting in regular drag gains.

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Re: Longer Fuselage for Stability and Pump
« Reply #20 on: January 07, 2023, 04:12:00 AM »
Ah, yes, I don't think that makes a huge difference (though I certainly might be wrong) except perhaps for drag. Most windfoilers, and certainly the early ones, had the mast plugged into a tuttle finbox, meaning an actual finbox on boards not designed to foil and the fuselages were super long from mast to front wing, to get the center of lift under the rider.

Here is the mental exercise.  With all 3 masts in place, move on any axis or pivot point.  Then remove any two masts and repeat.  As long as the position of the foils are locked in relation to the board the results are identical. 
« Last Edit: January 07, 2023, 05:19:00 AM by Admin »

EastCoastFoiler

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Re: Longer Fuselage for Stability and Pump
« Reply #21 on: January 07, 2023, 10:48:07 AM »
Yaw stability changes

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Re: Longer Fuselage for Stability and Pump
« Reply #22 on: January 07, 2023, 10:58:31 AM »
Yaw stability changes

Hi East, yaw wouldn't change at all based on mast position except for potential flex in the extreme example.  Is that flex what you meant?  It is (additionally) interesting because that front foil is your lifting entity and that lift is prying at any mast mount which is positioned behind the front  foil.
« Last Edit: January 07, 2023, 11:04:01 AM by Admin »

Beasho

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Re: Longer Fuselage for Stability and Pump
« Reply #23 on: January 07, 2023, 01:36:54 PM »
Yaw stability changes

Yes YAW changes based upon where the mast is.  Think as though the mast is acting as a rear fin.  The fin in the center of the board vs. the tail of the board will significantly dampen the Yaw.  Said another way the further towards the tail the mast is the more Yaw stability and therefore less maneuverability.  In the interview between Robert Stehlik and Mike's Lab the designers said they tried almost everything including putting the mast on the front wing but moved the mast behind the front wing for the 'Stability' it added. 

The other 2 factors are

1) The center of mass.  The mast forward would keep the weight centered.  The Mast aft would add significantly to the swing weight in the tail.

2) Structural integrity.  As has been discussed the mast at the Tail end would put enormous stress on the fuselage.  The mast sitting on the front wing would eliminate most of the stress applied to the fuselage, other than what was applied by the tail wing. 
« Last Edit: January 07, 2023, 01:41:03 PM by Beasho »

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Re: Longer Fuselage for Stability and Pump
« Reply #24 on: January 07, 2023, 04:33:02 PM »
Thanks.  That is interesting, and a good point.  It would be particularly significant at the extremes.  I can see that being huge in kite racing.  Also interested in how much of a factor more modest changes are there in relation to fuse length (stabilizer further back - topic of this thread)  and how the two might be balanced against one another. 

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Re: Longer Fuselage for Stability and Pump
« Reply #25 on: January 08, 2023, 01:03:13 AM »
Mentally picturing now, on a plane the vertical stabilizer is providing similar directional stability although much further back.  Yaw is occurring around the vertical axis, passing through the COG and running parallel to the mast.  COG is not static, particularly for us, but this still all makes sense and could impact directional stability to some degree.

With Mikes Lab it is even more interesting because their Masts appear to be all Tuttle.  To test the foils in the same positions (to keep things equal as above) they would need to build boards with different Tuttle positions.  Without that, if they direct mounted to the wing for instance, they would be moving the front wing back and would be adding a whole new group of factors.  Also their front wings have such tiny cord lengths that a direct mount would make that backshift even more significant.  Heading to watch that vid to see what they did :). This stuff is awesome to keep the mind purring.
« Last Edit: January 08, 2023, 01:06:19 AM by Admin »

EastCoastFoiler

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Re: Longer Fuselage for Stability and Pump
« Reply #26 on: January 08, 2023, 06:42:02 AM »
Better responsiveness from decreased yaw stability is the goal of most of my tuning.  If I’m riding 2 different foils I’m always putting the mast in the same spot(slammed forward) for yaw consistency, then tuning the tail to mess with the center of lift to get that where I want.  Most of the time this means tuning for less lift more efficiency, giving the pump I want as an added benefit.

I’ve built enough setups from scratch where I can generally hop on a foil, feel what’s happening enough to get it rideable(too much lift vs too little). Then tune to get the feel I want.  Most of the time this means taking something from “doesn’t pump well needs more glide” to “ok this is pumping better now”.  The way you do this is by shimming the tail for less lift and moving the foil forward(hence developing a taste for yaw instability).  You get more and more efficiency this way until you run out of box length OR the instability of having the foil too far forward becomes too much for you.  I’ve had instances where my initial tune for “rideable” was back of the boxes and my ending desired tune was fully forward with 4.5 degrees of angle milled into the fuse.  Foil want from “couldn’t pump a double” to easy 4+.

A longer fuse is going to add stability in a way that’s neutral to efficiency and pump(every other way is a negative to efficiency). Letting you do a more efficient tune(less downforce mast forward) or run a smaller more efficient tail and keep it rideable.  This is why the foiling Moth sailboats have a giant rudder gantry - effectively doubling the distance from the front wing to the rudder foil(their stabilizer).  Increased stability with no loss of efficiency. 

« Last Edit: January 08, 2023, 06:48:51 AM by EastCoastFoiler »

Solent Foiler

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Re: Longer Fuselage for Stability and Pump
« Reply #27 on: January 09, 2023, 05:39:50 AM »
EastCoastFoiler - do you think that your setups are inherently more pitch stable than one which has more stab lift with mast further back. I understand that in a static state the two setups (forward with less stab lift, and back with more stab lift) achieve the same centre of lift, but I don't know if they behave the same once in use?

I currently positive shim my setup (799 and 899 with 325P on CS ADV fuse) for more pitch stability, and I enjoy the way it rides that way but would be interested to see if I can remove the shim but still keep the pitch stability and possibly increase glide too! Should add this is for winging but the physics will be similar...
I'm 5'10", 66kg riding:
Swift Foil Boards custom 4'10 x 19.5" 35L
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Axis ART 799, 899, 1099, HPS 880 US & CS Adv fuse, 85cm mast
Gong Fluid L-S, XXL-S on 85cm and 65cm mast
Takuma RS 5.1, 4.3, 3.5


PonoBill

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Re: Longer Fuselage for Stability and Pump
« Reply #29 on: January 09, 2023, 03:24:04 PM »
Gee whiz, it sounds like we're leading edge just by trying not to break a fuselage.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

 


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