3500 hits since june 7th… nice thread!
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Quote:More than anything I think Future’s market surge has been from really good hype.
Marker surge comes from a lot of things. I regularly watch shapers push Futures on surfers that otherwise requested FCS, the shapers I know do this because the reps treat them well AND because they take less time to install. They tell the surfers it is stronger/stiffer than FCS, and otherwise equivalent in function. But that isn’t why the shapers choose them - that is a function of the sales rep and ease of install.
I’ve even told them (as JJR mentioned) that Lokbox is supposed to be easier to install yet, but they seem too happy with Futures to care.
Another part is the FCS reps aren’t quite so good.
But from my vantage the change in selection for local boards is driven by the shapers choice.
Basically it was just good timing. The 5 to 7 year cycle has passed, and there is just nothing exciting about FCS anymore. The inside foils are spongy and the feedback is they just don’t perform that well. Feedback from the vectors are all over the place as well. Futures has done it’s groundwork for years, and it’s starting to payoff a bit for them. Most shapers I know don’t deal with the glassing end that much. If they did, the future explosion would be much smaller. It’s kinda hard to install a 6 inch long dead flat box, into a curved surface, without some issues. With it’s original longboard application, it was less of a problem. Flatter bottoms, using a small low cant fin. Shortboards are different, and have changed alot in the last 20 years.
Funny, as I was typing my last post, one of the installers that works at a few of the bigger shops around here walked in. He read some of this and just laughed. He said, “yeah, the futures are a piece of cake…if you don’t care about angles. You get what you get, because you can’t really manipulate them side to side. Throw a piece of tape over it, and slam it in. Easy money! Concave boards end up with very little cant”
But who cares about angles right? I guess the shapers don’t. They used to.
Hi Lawless
Sorry I am not being pickie I just think I see a flaw
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The washout decreases the angle of attack at the wing tips, thereby allowing the tip (and ailerons) to still be effective as the wing root stalls. For example, if you decrease the tip AOA by 3 degress and the wing root stalled at 20 degrees, the tips would still be creating lift (and aileron control) because they would only have a 17 degree AOA.
In surfboard terms, if you had a fin with washout designed into it, if you were looking at the board from the bottom, the base of the fins would have more toe to them and would decrease as you reached the tips of the fin (tips would be more parallel to the stringer).
I have attached a rather rough drawing to explain my self (I hope)
First to define I have allways measured AOA relative to a line drawn through the center of the foil (wing) root section
Now in level flight at say (all numbers in this and the drawing are for example only) 100 knots yes the wing tips have a lessened AOA compared to the root
Now lets slow down to 60 knots the nose of the air craft is now pointing up higher than at 100 knots the AOA over the entire wing has now increased the tips are at a AOA maybe near where the root was at when at the higher speed
Lets slow down some more,The entire AOA increases again as the air craft nose points higher. Now the air flow over the root section of the wing is at a AOA that is too high to sustain airflow and starts to breakup
indeed its stalling, While at the tip section of the wings AOA is still at angle where airflow can be sustained
The aircraft will maintain a relativly straight flight path, if it did not have the twist (washout angle) it is very likley that one of the wing tips would have stalled first resulting in a catastropic wing drop and the start of a spin.
Having said all that If you want to experience it your self go to the local gliding airfield ask for a trial instruction flight, once in the air ask the instructor to show you a straight ahead stall then a incipant spin or wing drop stall
You will be very impressed !!
Washout is allways up in a wing,that is towards the cambered side of the wing .Hense the explaination below
The drawing shows that if the fin has a tow in angle reative to the stringer of say 2 degrees and a washout of 3 degress then the tip will have a tow in relative to the stringer of 5 degress
So if in flat water going straight we assume that the fin is operating at near 0 degress AOA then the tip will have 5 degress negitive AOA which would be just drag
So end result you build a high lift fin with less rake put some washout in it so it has a progressive stall in changing AOAs great in turns but when you get on a flat it acts like a brake
There you go again there is no such thing as that free lunch
Regards Mike
here is the rough drawing to go with the post
Sabs, you’re absolutely correct. I had a brain fart, and got the fin example exactly opposite of how it should be. I went back and edited my post to clear up any confusion. The tip should have a lower AOA relative to the root is the point I was trying to make.
As for stalls in an airplane, I’ve spun my dad’s Bonanza practicing stalls with him. He is a much larger guy than me and it made the plane want to snap off to the right on a power on stall. Needless to say, it happened very quickly and we lost about 1000 ft before I recovered. Altitude is your friend. On the other end of the stall spectrum, I was doing stall/spin practice in a Cessna 150, and had a hard time trying to spin it even with full left rudder at the stall. Much less wing loading, hence a much more stable stall.
Sorry to digress, just my experiences with washout. It’s saved my ass more than a few times.
i didnt realise lawless got it wrong…but when he gave the % examples and the way he descibed it ,it was clear and easy to follow and made the process of washout easier to understand…i got the point but over looked the wording…
so you guys being plane buffs as well as having an interest in surfboards obviously…
do you agree then that the rake in a fins template , would better equip it to deal with washout (if that term could be used in that context??)
coz the more rake you have the more resistance it gets in a turn and wants to correct it self ,where as with out the rake , once it fails and stalls completly its harder to regain control,if a plane had raked wings youd be doing your best to try and make it stall???
sabs!!! so you agree with the fact surfboard fins have evolved more rake to deal with inadequate foils,especially not enough camber???
coz ill take it one step further and say surfboard design has evolved around inadequate fins ,
fins have got thinner and smaller in the last 20 years to the point that boards have been shaped to give a measure of control back…making up for poor fin foils…
i say make the board flat and fast give plenty of release and get your control back by having efficient foils that deliver hold and control…
on another subject ive been wanting to take some photos of the test fins i made for the vector experiment …but 3 out of the 4 sets i made have been poached by team guys , so i could either build some more , or try and get them back but some of them are hundreds of kms away…
if i post pics it will make things heaps clearer…
ill just make some more ,i made 4 identical templates (like halycons mental template) all with different foils a flat sided one,a flat sided one with a 15/85 leading edge,a concaved one with a 15/85 leading edge,and a concaved one…
another reason ive held off , is because i used the mental style template which is extremly effective …it may have clouded the effects of the other changes…
so just to be really sure im going to do the same tests but with a standard profile fin…
i personally feel the mental template made the fins work better than they should of , thus making it harder to assess the other aspects of the foils objectively…
im doing another north trip soon so the plan is take 8 sets , 4 mentals and 4 standard profiles with the configs mentioned above …and test them in some real punch…coz so far all my testing has been done from waist high to double head beachy’s …
i wanna see what happens in some square ledging coral set ups ,before im confident about posting the next observations…
halycon !!!if you want me to try anything in punch that will be a good opportunity…
ok another day gone again…
regards
BERT
Bert, great stuff. But do you ever sleep? I mean you are on most significant threads here with so much info. thx
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do you agree then that the rake in a fins template , would better equip it to deal with washout (if that term could be used in that context??)
PROGRESSIVE rake, or curvature, is an adaptation to prevent tip stall. It also reduces the contribution of the foil to lift. More rake is less lift at any given AOA.
It is interesting to see that nearly all low aspect ratio wings deal with tip stalling with tapered chord lengths at the tips, end-plates, or decreased AOA at the tip, whereas nearly all surfboard fins use progressive rake instead. There are notable exception (like the bong fin or starfin).
Is it because water is fundamentally different…because airplane wing design is backed by thousands of published studies and wind tunnel test…or do surfboard fin designers know something that airplane wing designers don’t.
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coz the more rake you have the more resistance it gets in a turn and wants to correct it self ,,,where as with out the rake , once it fails and stalls completly its harder to regain control,,,,if a plane had raked wings youd be doing your best to try and make it stall????
Very nearly all airplane wings have raked wings. Certainly all fighter jets do. They don’t stall easily.
But again you mention surfboard fin rake - and I think you mean PROGRESSIVE rake, curvature, which almost no airplane wings have. I think it is a lossy design inefficiency to get more chord length closer to the tip. You can easily make the leading edge straight and choose a rake to avoid stalling, but you’ll probably have less fin area near the tip than you are used to.
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sabs!!! so you agree with the fact surfboard fins have evolved more rake to deal with inadequate foils,especially not enough camber????
Low aspect ratio foils are not, generally, any thicker relative to chord length, than surfboard fins. I make my fins to have more chord length further from the board, tapered tips, and set the rake angle so it doesn’t stall in hard turns, with no progressive rake. Makes a big difference. The F14, F18, and Concorde all have very thin wings. relative to their chord lengths. Thicker foils are the rule in high aspect ratio wings that don’t work in a vortex mode.
Thruster fins work close to a ratio between root chord length and depth of 1. Longboard fins are generally between 1 and 2. Foil theory that predicts lift coefficients from NACA foils all BREAKS DOWN for foil aspect ratios under 5. Relations between thickness and lift are different.
Hey Dave,
I respect you for your technical knowledge and your ability to express theory. It’s way beyond anything I can ever hope to be able to do.
With that said, I have to follow by saying that you text reads very black and white when surfboard technology is by nature very gray. And yet what you say makes sense and is very informative.
The fin template you show is with the exception of on small arc something out of drafting magazine not a surf mag. It seems to me that this is the one you will want for you rotating fin box. If so I’m up for it. How deep?
Mahalo, Rich
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Is it because water is fundamentally different…because airplane wing design is backed by thousands of published studies and wind tunnel test…or do surfboard fin designers know something that airplane wing designers don’t.
I’ve been curious to this design difference as well. The majority of aircraft have straight leading edges regardless of what speed they are designed to operate at. They vary the rake to deal with higher speed. (with many exceptions) Most birds have progressive rake on their wings and bats can actually vary the camber of their wings and are one of the most agile flying creatures (interesting sidenote that bat wings have multiple cutaways).
Curious as to why surfboard fins have always had progressive rake with very few exceptions.
I’ve only recently really gotten into fin design as I finally got my boards dialed in to a point where I was very satisfied with them. Fin design, seems to be the next logical place to look for more fine-tuning. I approach it more with my limited aeronatical knowledge which may or may not be applicable to fin design. Seems the guys like Bert and Halycon have a good real world understanding of what works and what doesn’t and it seems they’ve actually tried alot of different concepts.
blakestah, any initial impressions on that fin template you’re working on? I shaped a couple of wood side fins for a thruster set up based on the template you posted on page 2 or 3 of this thread. I still need to glass them and some waves would help. It seems you’ve moved on in your r&d of that template, care to share what you found so far? I was very curious to see how a straight leading edge acted.
I’m curious what the latest race boats are using as far as leading edge shape on their keels and rudders.
I started with the straight leading edge, and fixed the root chord length, a basic trapezoid. Then I rounded the leading tip edge to help with tip stall.
The first 3 were altered in rake only. I made one more raked and one less raked. I used the less raked fin. I am a little reluctant to stand it up any more, because it will be tough to get enough fin area and keep the trailing edge perpendicular to the board, or raked. The rake series was really clear. More raked fins have a much softer feel. But I just couldn’t make the board come around like I could on the less raked (more upright) fins. All the testing was with the rotating fin system, so you cannot assume it will behave the same as a fixed fin - it will always have less AOA than a fixed fin.
Then I added root chord, 1/2 inch at a time. It got stronger and stronger, and then felt kinda funny - like the base was stalling. Just kinda mushy when you push on it. So I made the rear cutaway. Then I made it bigger. Another good adaptation.
Although the template looks funny to the eye, if you hold a standard 7.5 inch fin up against it, you will see the fin area and leading edge are quite similar - certainly in the same ballpark. I really doubt having the leading edge straight makes much difference - except that it makes it tough to have a long chord length near the tip.
The adaptation is that, with the rear cutaway, the chord length in the middle is unusually long. This is an idea from the Halcyon mental template. I wanted to keep the tip tapered to about 1.5 inches and have longer chord lengths in the middle. I didn’t want them too close to the board, because the board pulls water with it, and the fin is less efficient there. And too close to the tip long chord lengths make it prone to tip stall. You can use progressive rake instead, but using that also reduces the lift from the tip. Either way it is hard to get much lift from the tip or the base. The long middle chord was, in my mind, the way to try. The middle region of the fin depth gives you the most lift for your chord length.
I had this idea when I was playing with cutaways a few months ago - why not a cutaway with a long middle chord, but Halcyon’s Mental template was what really made me try it. And he was onto this decades ago.
If you want to try it for a fixed fin system, email me. I can easily tilt the leading edge another 5 degrees to make it more amenable for fixed fin systems and send you the image of the template, or shrink it etc. The image I posted was for a 7.5 inch depth fin.
Hi guys
Yes I agree with your conclusions Bert about the evolution of fins with rake and leading edge curve,it makes them very forgiving
Which is in itself not a bad thing and many surfers like what they are riding
But for people like us there is a huge area for improvment and innovation
I would caution every one on using aircraft wing plan shapes with regard to rake ,curve and taper,most air craft have tailplanes they are there to provide stability to the main wing.So that the rake etc are doing different jobs
There is a lot of data out there on flying wings IE aircraft with out tailplanes,this data may be more relevant to our application
All that said for many years I have played with slated fins,moderate rake, straight leading edges.high aspect with the front fin having a concave high pressure side that overlaps the secondary fin and sits within 10mm of the low pressure side of the secondary fin
These need each other to perform and interact as one foil not two separate fins
The lift is good,the stall resistance is unbeatable and drag quite low
I have only just recently again started playing with the much more conventional thruster setups This is to try an see for myself why they are still so popular
My recent conclusions are that they are still very much as they were many years ago I think that this stems from the surfers general dislike of any thing away from the popular standard
Others who have tried my prefered fins have said that they felt fast,gripie but a little looser than what they are used to
They then go straight back to there more conventional fins again,I dont know maybe they think that my ideas are just a little too strange to be seen in puplic with.
So, I like the cutaway fins that i have tried these seem to be an improvment, as also is having correct leading edge radiuses ,but I must admit that I feel my slated fin may have more potential though.
I think that I my start toying with some of the cut away benefits on my slated fins
Maybe between us all we can eventualy change things
I am envious of you guys that can try your ideas out with the team riders,that level of fedback must be great
Cheers Mike
on a slightly random note what abot twist between the front and back of the main fin. we have experimented with a few fins and in my 10’6 longboard i am currently using a 9 inch fatboy shape with a thin strip of uni directional carbon fibre running up the leading edgethis means lots of twist along the fin between leading and trailing edges but a stiff fin up and down seems to be fast. racing keelboats have trim tabs on the back of the centerboard that do the same thing they push these tabs the right way for extra lift when going upwind. the natural shpae of a wave and the way water flows up it means fins with a stiff leading edge do the same thing and help lift the board into a wave
also as surfboards do a slightly lower speed than aircraft shouldnt the shape be further forward in most fins. i also yacht and in yachting the thickest part of the foils is determined by the speed of the yacht, the same is true for aircraft look in the difference between fighter jet and jumbo jet wings the thickest part of the wing is further forward also the slower the plane the less rake on wings. a fighter jet i have seen has wings that actually rake back after a certain speed is obtained a system like that would be cool on a fin
Hi James
Im not to sure about your twisting fin can you do a drawing or photo
The camber point on the wings
Powered air craft are a whole different kettle of fish The lift of the wing just needs to match the avaliable thrust and weight to keep it airborne
You may have noticed that many larger aircraft use leading edge slats and flap extensions to provide more lift at lower take off speeds
once these aircraft have gained height and airspeed the need for that much lift is reduced
In effect they have variable camber foils
Glider wings mostly have the camber much further back and have differing leading edge radius,for the lift verces gravity results in speed
Hang gliders have the camber way forward they also have reflex (a slight upward tilt on the trailing edge near the keel,the reason for this is that they are flying wings with no horizontal stabilizer and so to remain pitch stable they cannot have camber too far aft
There are similar reasons for yachts and wind surfers if the camber is too far back it becomes pitch unstable which creates weather helm in a yacht,to correct that you need lots of rudder,too much rudder means too much drag and you go slow
On a wind surfer if the max camber is back at say 45 % the sail will be pitch unstable,you would have a hard time trying to control it as all it would want to do is climb into the wind.So you would have to push on the mast hand while pulling on the clew (aft )hand.The net result is that usually the sail will crash into the water in front of you mast first !
As I have said before we on surfboard are luckly as pitch stability does not really affect us that much so we can use foils with the camber further back which at our speeds should provide better lift
They are different in application, but have a look at some aircraft propellers and some low rotational speed water props,the camber points are quite different.
Regards Mike
hey sabs…
2 questions???
what would be better?
a fin that has good lift but poor ability to deal with high AOA…
a fin with average lift but the ability to handle massive AOA and still be providing lift…
which would be better for a surfboard…???
its a rhetorical question…im curious …
it seems like you have a good grasp of foil concepts and whats happening…
but from what i read of your posts you still need to link the various factors ,and apply the most important points ,that are more relevant to surfboard design…
coz the principals of lift dont really change from craft to craft regardless of whether they are used in water or air…
but what does change is the functions were asking of our foils…
we can isolate our needs …
1 whats the speed range were operating in ???
2 what range of angle of attack do our fins need to tolerate???
3 how much load will we put on a given amount of fin area???
4 do we need to cater for turbulence???
were not just in water or just in air , were on the boundry dealing with both, so then ventilation becomes an issue …
5 what foils deal better with ventilation???
6 where on our fins do we need more lift ? further forward or further back??
in surfboards we have very particular needs ,so its a matter of isolating the various foil characteristics we need the most and discarding the ones of least value…
so we have a foil purpose built for our requirements…
are there any other craft that have similar needs???
can we learn something from them???
a number of years ago i went on a quest to find those answers…
first i tried aircraft , went to the libary and got every book i could get for about 2 years…but still theres alot of conflicting theories…
next i went and got a stack of books on fish…took them to an old fisho friend , i asked him to show me the fastest most agile and manouverable fish in the ocean…he pointed quite a number out …then i had a closer look at all of them …
after that did the same thing with birds ,which are the fastest most agile birds??
it ends up theres animals out there that are already placing real similar loads on there wings and fins…
proven designs …
i once heard halycon say he gets his inspiration from marine animals and our feathered friends ,something like that…
i firmly believe the best templates and foil profiles will be found there…
thats not the end of it …but at least were on the right track…
regards
BERT
sabs think about that question i asked up front…
I have been following this thr. right along. I think the right questions have now been asked. TK to Bert. How fast does a surfboard go? Unless your at jaws it is going to be less then 30 MPH. Much slower then even our sail board friends. At that slow of a speed does the flow of the water really cause problems? I don’t think so. I think that the correct foil, is the most important, and in order to get that you need some thickness. Halyon made me a fin and used foam in it to keep it light, but still make it thick enough to get a good foil. It is one of his Mental templets. I have not had a change to really try the fin but it looks like it should work just fine. Are we really in that air/water zone with our fins? I don’t think we are, at least not most of the time. Most of the time we are in green water, and there is not much turbulence since we are not going all that fast. If the fin is not foiled right or is set at an angle, then you will have turbulence, but the fin would humm or viberate. Eather one of these you would feel or hear. Now remember I’m just talking about a singel fin board. That is my thought on this subject.
Template shape has a pronounced impact on fin performance. Using fins fixed in chord length and area, I only varied the leading edge rake angle, and the differences were easy to notice when riding the board.
Similarly, shifting the distribution of chord lengths has a noticeable impact as well. It is hard for me to think that anyone would not easily notice the change in fin action from a Mental to a standard 'dolphin" shape fin, even if the leading edges, foiling, and fin template areas were the same!
Of course, foiling matters too, but I think it is naive to dismiss the impact of the template shape. Fin design is a combination of many inter-relating factors to achieve the desired lift and drag and hold combinations at different angles of attack. It is not too difficult to isolate one variable, try 3 different fin combinations, and determine if its impact is easy to notice.
Blakestan, I’m sorry I did not make myself very clear. All I was really trying to say was that I do not feel that we are going fasting enough to worry about turbulence. Yes the area of the fin does make a big differance in the way a fin feels, as does the rake, base, length, and shape. I surf only longboards and most of them have only one fin. So I don’t have all of the experance that most of you guys have with the shortboard and the 3 to 7 fins. Haylon and I are working on a new fin for me. We just don’t have it all worked out yet. I get my speed from trim. I need a fin to hold me on the wave once I get in trim. If you look at one of the fastest swimming fish.(the sail fish) he tucks his fins in to his body when he wants to go fast, thus reduceing his fin area to 0, as does a lot of other fish. When a bird want to go fast they just tuck in there wings. So if you want to go fast use as small a fin area as you can, and still control the board.
I have been thinking about this fin retraction thing to lessen drag for a while- (just can’t think the bugs out), but it’d be with a semi-flex panel in the tail, ( maybe a Jim Richardson-type flex foam construction) with the fins attached to the deck and coming out through slots. That way, back foot pressure would engage the fins more through turns, and the flex would retract them back a bit ( 1" max I suppose) during trim when fin length is not needed?