A question about Moff foils....
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=11189
Printed Date: 15 Jul 25 at 12:14am
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Topic: A question about Moff foils....
Posted By: Bootscooter
Subject: A question about Moff foils....
Date Posted: 05 Nov 13 at 10:00pm
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Why do foiling Moths have "T" foils?
Aircraft that are designed to fly straight and level in flight use dihedral wings (angled up in a very shallow "V") to aid stability. Could this not be used on the Moth foils to make it "easier" to use, with the added benefit of the leeward "wing" giving more windward lift when the boat is heeled to windward when on the beat? To simple? Or is there something I'm missing? Additionally, do the rules preclude "winglets" to give the same lift for a smaller wing/foil, as on the C17 and others? |
Replies:
Posted By: JimC
Date Posted: 05 Nov 13 at 10:08pm
| The foiler has loads of roll stability anyway, so probably no need. |
Posted By: Bootscooter
Date Posted: 05 Nov 13 at 10:17pm
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OK, I've never sailed one (bit on the chunky side!) so sadly wouldn't know.
Would winglets/end plates make the foiler "more accessible" to the heftier sailor though, for very little extra drag (I realise that a big guy isn't going to be properly competitive against racing-snakes in most conditions)? ------------- |
Posted By: GarethT
Date Posted: 05 Nov 13 at 10:22pm
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sorry to break it to you Boots, but you cannae change the laws of physics.
You (and I) are destined for a life of lowriding. |
Posted By: Bootscooter
Date Posted: 05 Nov 13 at 10:26pm
Haha, (very) lowriding!
... I wish I could fly.... ------------- |
Posted By: JimC
Date Posted: 05 Nov 13 at 11:46pm
| I think its safe to assume that if there were advantages in endplating the foils they'd be doing it. Don't know whether its science or rules though. |
Posted By: aardvark_issues
Date Posted: 05 Nov 13 at 11:48pm
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Science, pays to go bigger on span. Winglets are good if you are span limited.
------------- http://www.aardvarkracing.co.uk" rel="nofollow - Home of Rocket Racing |
Posted By: Neptune
Date Posted: 06 Nov 13 at 9:25am
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Was the not a story at this years worlds where people where experimenting with wing tips? Presumable you have a limited span as you don't want the foil to break the surface as the boat is canted over to windward, therefore a shorter foil with winglets could potentially have some advantages ------------- Musto Skiff and Solo sailor |
Posted By: laser193713
Date Posted: 06 Nov 13 at 9:40am
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Unless you are 120kg plus then you have no excuse not to go foiling. Some of the top guys in the moth fleet are approaching 100kgs now. There is even footage from the worlds of one of them sailing with a bikini clad girl on the boat with them, on foils... As an aside, I did notice that some of the foils at the moth worlds had little downwards pointing wing tips...
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Posted By: yellowwelly
Date Posted: 06 Nov 13 at 1:16pm
much as I wish your sentiment were true, when your local average conditions is around 8 knots, then sadly foiling is still much the preserve of the sub 90kg folks... unless you like a lot of time on a expensive mountain bike instead of sailing. I've noticed that our club boats foil before us windsurfers are planing.... they are definitely winning on the light wind threshold, although I think we can still take them when it's properly howling.... twice a year, on a Tuesday afternoon when everyone's working...
 |
Posted By: laser193713
Date Posted: 06 Nov 13 at 4:37pm
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Well how are these heavier guys staying up there in the light stuff? They do, there are results to prove it. I think you may also need a fairly heavy wallet to get some of the most recent foils, I get the feeling the very latest kit has come on leaps and bounds over even a couple of years back. That said, I do question the science behind "cut down" foils. Surely this has got to be a bit of a bodge? I have seen people attacking moth foils with hacksaws and files just weeks before the worlds. Is that really the pinnacle of design and construction!? All seemed a bit Cherub to me! |
Posted By: Jack Sparrow
Date Posted: 06 Nov 13 at 4:42pm
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All seems a bit C-Class cat to me. Get with this century. ------------- http://www.uk3-7class.org/index.html" rel="nofollow - Farr 3.7 Class Website https://www.facebook.com/groups/1092602470772759/" rel="nofollow - Farr 3.7 Building - Facebook Group |
Posted By: yellowwelly
Date Posted: 06 Nov 13 at 4:55pm
What I am about to refer to is windsurfing experience relating to planing thresholds, it might be totally different in moth world (I hope it is) but I would remain skeptical... lulls... feckin' lulls!!! In marginal conditions, you can maybe foot off and pump up onto the plane, and you can plane on a halfway through the lull on apparent, then you drop off - either as you run out of momentum, or you simply need to gybe around. Then you can't get going again.... bogging back at 1/4 of the speed you were planing at. Light wind windsurfing... (on short boards) PITA!!! As a solution, the windsurfing industry has sold us wide boards, with big fins. De-tuned formula boards. However these have a very narrow wind range.... you can't plane that much earlier than on standard, good quality kit, but the upper end is sh*te... they can't handle the chop and you piss it in all over the place unless you are highly skilled with overpowered 'big kit'... which most of us aren't. We'd be better with recreational, good quality longboards... but they're unfashionable these days and as such, no one makes them new. I would imagine that if I bought a moth I'd have a very narrow wind range of operation- too heavy to foil in light winds, not skilled enough to handle much above a F3....  How I would love to prove myself wrong on that, they look totally awesome! http://vimeo.com/78717048" rel="nofollow - http://vimeo.com/78717048 |
Posted By: blueboy
Date Posted: 06 Nov 13 at 6:08pm
State-of-the-art open class glider i.e. no span limit. Note winglets.  |
Posted By: tgruitt
Date Posted: 06 Nov 13 at 6:24pm
I think there is probably a structural span limit! ------------- Needs to sail more... |
Posted By: blueboy
Date Posted: 06 Nov 13 at 6:52pm
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^ That's a 23 metre span which is nowhere near the structural limit. This, on the other hand at 31m span, may well be pushing the limits. Also with winglets.  |
Posted By: hobbiteater
Date Posted: 06 Nov 13 at 7:15pm
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Sailplanes are going for smaller spans as they are weight limited. (By caa regulation)
So smaller span equals smaller wing area equals higher wing loading equals faster glide, equals winning cross country races. http://en.wikipedia.org/wiki/Gliding_competition#Water_ballast So in effect the quintus is span limited, by a round about way. |
Posted By: Bootscooter
Date Posted: 06 Nov 13 at 7:22pm
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I know for a fact that the C17's wingspan is about 52m, and without the winglets it would require wings that were 30% longer to provide the same lift.
Are the Moffists possibly missing a trick here.... same lift, smaller foils (with winglets) = less drag/friction/cleaner flow = greater speed? Edited to add; same lift, smaller foils (with winglets) = less drag/friction/cleaner flow = greater speed = more lift..... ------------- |
Posted By: hobbiteater
Date Posted: 06 Nov 13 at 7:25pm
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Winglet design is very very tricky, also I have a hunch incompressable water reduces the benefits.
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Posted By: Slippery Jim
Date Posted: 06 Nov 13 at 7:47pm
------------- Pass the skiff, man! |
Posted By: Slippery Jim
Date Posted: 06 Nov 13 at 8:08pm
Ask what it is that the tips do physically... wiki quote Wingtip devices are usually intended to improve the efficiency of fixed-wing aircraft.[1] There are several types of wingtip devices, and although they function in different manners, the intended effect is always to reduce the aircraft's drag by partial recovery of the tip vortex energy. Wingtip devices can also improve aircraft handling characteristics and enhance safety for following aircraft. Such devices increase the effective aspect ratio of a wing without materially increasing the wingspan. An extension of span would lower lift-induced drag, but would increase parasitic drag and would require boosting the strength and weight of the wing. At some point, there is no net benefit from further increased span. Gliders like lift and by increasing the aspect ratio of the wing they get it. But then the wings get impracticable to make... So they put on their tiplets et voilį! I have the feeling however that the thing in foiling moths is that the optimum aspect ratio has already been reached in this fluid medium and the foils already provide enough lift for everyone to be able to go like cucking frazy...  I“ll get my coat...------------- Pass the skiff, man! |
Posted By: aardvark_issues
Date Posted: 06 Nov 13 at 8:46pm
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Gliders can't change wing camber, so they're looking for big lift in a different way. edit, And the tips break out of the water sooner if they're pointing up. Pointing down is being used though. ------------- http://www.aardvarkracing.co.uk" rel="nofollow - Home of Rocket Racing |
Posted By: hobbiteater
Date Posted: 06 Nov 13 at 9:01pm
Err if you look at the picture of the eta (the one on the ground) you will see full span camber changing flaps along the trailing edge err leech |
Posted By: aardvark_issues
Date Posted: 06 Nov 13 at 9:10pm
Fair enough, but I doubt the coefficient of lift of that wing changes much with the flaps full down as they're also tiny so as not to break up the laminar flow. More of a trim change thing once up to speed.
------------- http://www.aardvarkracing.co.uk" rel="nofollow - Home of Rocket Racing |
Posted By: hobbiteater
Date Posted: 06 Nov 13 at 9:20pm
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From +15 to -7deg or so. The boundary layer is artifically tripped to turbulent bl before it reaches the flaps as it is a lesser evil than flow seperation.
But you are right a big effect is to level the fuselage over the speed range reducing trim drag. |
Posted By: alstorer
Date Posted: 06 Nov 13 at 9:25pm
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the latest thinking with airliner wing tips is both up and down. Being fitted (and tretro fitted) on pretty much all airliners, especially the not-notably-space-limited B737s and A 32xs ------------- -_ Al |
Posted By: Phil_1193
Date Posted: 07 Nov 13 at 2:10pm
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From what I have been told the Moth foil has pretty much reached its optimum. Needs to be smaller to reduce drag to go faster, but when it gets too small needs more wind to get up - hence why theres an optimum size or you need two sets of foils at £(insert very high figure here)k for varying wind conditions. Would wing tips would add drag as water is thicker than air and reacts differently to a plane wing?? Also if it has plates on the end when the boat was healed, as its generally sailed, would the water rushing over a vertical plate now at an angle affect the line it was taking? Planes fly 'flat' in a straight line, boat foils are not 'flat' to the water when trying to go in a straight line. |
Posted By: hobbiteater
Date Posted: 07 Nov 13 at 2:19pm
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Famous last words "has reached its optimum" |
Posted By: iitick
Date Posted: 07 Nov 13 at 3:46pm
| One of our illustrious contributors ..........could invent a system to alter tip angles from within the boat.......... |
Posted By: Rupert
Date Posted: 07 Nov 13 at 3:52pm
It could be connected to neck angle - tilt head, change tip angle. ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: Mark Jardine
Date Posted: 07 Nov 13 at 7:42pm
Downward-facing winglets already in action at the worlds - this is Ben Paton comparing his foil to world champion Bora Gulari's. |
Posted By: Granite
Date Posted: 07 Nov 13 at 11:41pm
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There are scale issues, and flow reigeme issues that complicate things for foils. My understanding of the upward longer winglets on aircraft is that there is a vortex generated at the wing tip. The winglet is positioned so that the part of the vortex that is flowing back towards the aircraft impinges on the winglet. the shape of the end of the wing, together with the shape of the winglet and the toe in angle are all critical to performance. To get that right on the scale of moth foils would be fractions of a mm and fractions of a degree, so tricky to get right. One of the big effects that helps dihedral provide stability is side slip, I don't thinkt he moths side slip in the same way. ------------- If it doesn't break it's too heavy; if it does it wasn't built right |