Author Topic: The humble fuselage...  (Read 888 times)

Solent Foiler

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The humble fuselage...
« on: October 14, 2020, 09:08:47 AM »
In a perfect world, would a fuselage not exist, or should it fulfil a role more than joining everything together?

Or put another way, is the function of the fuselage to be as unobtrusive as possible, or is there merit in asking it to fulfil a hydrodynamic role?

I've been considering the Gong fuselage, which superficially looks pretty low tech, being a straight, square section, compared to other brands which have round sections with additional shaping.

Presumably Gong have made this a design decision and I can't believe that the only factor was ease of manufacture. Making aluminium parts is one thing but their carbon mast fuse units could have adopted a different shape in their design without adding too much manufacturing complexity.

If that is correct then their fuselage's flat sided shape is adding stability to their foil package which presents the possibility of separation of function between it and the foil. If the fuse gives you some stability, then you can design a foil that can better exploit other areas of the design envelope.

How much would this feature in foil designers' thinking? I've never seen it mentioned before...
« Last Edit: October 14, 2020, 09:14:48 AM by Solent Foiler »
I'm 5'10", 65kg riding:
Gong Flint 5'6 95L
Gong Catch 5'3 34L
Gong Veloce L and XL on 100 monoblock mast
Gong Pulse - 4m, 5m
Gong Superpower 6m

Thatspec

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Re: The humble fuselage...
« Reply #1 on: October 14, 2020, 11:44:18 AM »

How much would this feature in foil designers' thinking? I've never seen it mentioned before...

As far as Gong's fuse design, I'd guess simplicity and cost to manufacture were heavily weighted parameters. Their stabilizer design would also dictate keeping that square section through the entire length of the fuse. It's not elegant like an Axis fuse but I suspect there's no penalty in performance which is more important to me. It's likely also incredibly strong at that diameter.

One downside of the design is there's no factory fuse length adjustability. I haven't actually measured nor could I say what's the optimal way to measure (stab LE to wing TE maybe?) It does appear that distance changes based on the wing line be it Rise, Curve or Veloce. There's also always the option of bolting on an Axis or custom stab which would shorten things up maybe 1.5". I always found the Large Pro / 40 surf stab super maneuverable as is.


jondrums

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Re: The humble fuselage...
« Reply #2 on: October 14, 2020, 11:58:09 AM »
I expect that the fuselage shape has almost no effect on the performance of the foil while surfing, winging, or gliding.  The flow around there there is so turbulent that it won't matter if its sharp or rounded.  Probably the total surface area matters to drag, but they are all about the same.  I think the stiffness probably matters, but that isn't what you were asking.

That said - for pumping, I could see the shape mattering somewhat.  The fuse is moving around in the flow in such that it might be swinging into undisturbed water and no longer a turbulent ball around it.    There is anecdotal evidence from Piros that when he polished up his aluminum Neil Pryde fuse that it rode better.  You might be able to find it on his insta feed.

I did some experimentation on my gofoil setup with fairing the wing-to-fuse and tail-to-fuse joints with bondo. I tried really hard to notice a difference, but it wasn't there.  A fluid flow guy I know took one look and laughed about it because he said it was 100% guaranteed to make no difference.  There's a thread on here somewhere about that.

DavidJohn

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Re: The humble fuselage...
« Reply #3 on: October 14, 2020, 12:50:54 PM »
I’ve noticed the Naish fuselage changing over the years with the first being thick and round.. (and heavy). The next year became square’ish. (and a bit lighter)..The next year became triangle’ish (and even lighter) and now the new S25 version is scooped out and lightened more version of the triangle.
I wonder if that’s it now with its evolution?

surfcowboy

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Re: The humble fuselage...
« Reply #4 on: October 14, 2020, 01:09:49 PM »
Thatspec, one thing on length. If you rewatch the Veloce intro you will see that they shorten and extend the mount for wings and stabs so that’s how Gong gets different lengths for each series.

When I get around to making some tails I’m going to make mine flat and bolt them to the top of the tail section so I can shim them. Probably make a cover for the end of the fuse eventually to make it smoother.

Hdip

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Re: The humble fuselage...
« Reply #5 on: October 14, 2020, 02:41:14 PM »
KDMaui also mentioned somewhere that the Takuma LoL is partly so efficient due to it's fuse to wing connection.

DavidJohn

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Re: The humble fuselage...
« Reply #6 on: October 14, 2020, 03:13:01 PM »
A neat trick with the Naish fuselage is to drill and tap a third hole ahead of the two stabilizer holes (same spacing) and then you have two positions for your rear wing.. (short and long fuselage)

canada foiler

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Re: The humble fuselage...
« Reply #7 on: October 14, 2020, 03:53:20 PM »
If the fuselage shape makes no difference, then why are plane bodies curved instead of square? 

Teeing that one up for the hydrodynamic, aeronautic, fluid mechanica' engineer types.

 ;) ;D 8)

Fishman

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Re: The humble fuselage...
« Reply #8 on: October 14, 2020, 04:35:58 PM »
If the fuselage shape makes no difference, then why are plane bodies curved instead of square? 

Teeing that one up for the hydrodynamic, aeronautic, fluid mechanica' engineer types.

 ;) ;D 8)
There are a few reasons to have a round fuselage on a plane that don't have anything to do with aero/hydrodynamics. Cost and strength are 2 big ones that come to mind right off the bat. I'm not saying that aero/hydrodynamics aren't another factor, just not the only factor. There are planes with flat sides and bottoms.
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Wetstuff

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Re: The humble fuselage...
« Reply #9 on: October 15, 2020, 06:20:31 AM »
As a follow-up to fishman, there are thousands of both round and rectangular aircraft fuselages.  It's kinda amazing that they ask U$400k for a lowly Piper Archer that is remarkably similar since the boxy shape was introduced in the early '60s.

Jim
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PonoBill

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Re: The humble fuselage...
« Reply #10 on: October 15, 2020, 10:47:31 AM »
Generally, if you're going to pressurize an airplane you want a round fuselage--a lot easier to make it hold pressure. You don't see a lot of square pressure vessels.
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