aerodynamics vs hydrodynamics

General Discussion
1

Well, this kind of about winglets, but please don’t lock it down, yet…

Someone mentioned that industry studies showed a 5% increase in efficiency (with winglets). This is for a design feature on a aircraft made to go 700 miles per hour in a straight line through the air. Now we (we, as in we surfers, the tribe) are applying this feature on a craft meant to be constantly turning at about 10-15 miles per hour, in water. Is the 5% still applicable? Would a surfer notice 5%? And what of the trade off- you decrease turbulance, but you reduce draft (depth) or increase wetted surface. So maybe that eats away your 5%?

Finally, if the winglets are so efficient why aren’t there winglets on the winglets???

Oh, and boys, like keep the discussion on design, not marketing.

2

Wings cause a lot of drag on airplanes (as well as lift to :slight_smile: ). I dont remember a specific drag breakdown, but a 5% increase in the airline industry makes a huge difference, especially when it costs em $25k to throw winglets on a plane, whereas a new-fangled engine with install would cost millions. They make up the cost in fuel savings pretty quickly, and it is a very easy mod. Winglets on winglets… I think that would be pushing the structural limitations and at that point it might not be cost-justified. One big winglet helping to cut drag by 5%, then a small winglet that helps to cut 5% of drag from the winglet… that would be negligable imo.

IMO, based purely on theory with no hands on experience with “finlet” fins, I can only see them being useful on side fins. If they are on a center fin as in the FCS red tip or the star fin, the so-called winglet is more of a hydrofoil, which generates lifting forces. I am 99% confident that design does not reduce drag.

A winglet is basically a vertical wing setup on the end of the wing so that it sits in the vortex that comes from the bottom of the wing, around the tip, to the top of the wing. It doesnt “interrupt” the vorticy, it sits at an angle such that the flow of the vortex over the winglet creates a forward component of lift, also known as thrust. Yes it does reduce the magnitude of the vortex, but that is not the primary reason for reduction of drag, imo.

So for a center fin with finlets on it, during a turn the finlet on one side may be helping, but the other will be hurting (drag… though this may not be the only design consideration for such products). With a side fin, and a finlet correctly engineered it could definitely help, to what degree, i dont know.

3

Swaylocks quote of 2009.

4

“Oh, and boys, like keep the discussion on design, not marketing.”

LOL, so you know the true reason why to add “winglets” to a surfboard fin.

There is probably something to be gained in performance but as with all things surf-related, it’s really hard to get any empirical hard numbers. Surfing is so subjective, one person could love a certain setup and another could totally hate it.

In my opinion, fins still have a long way to go in simple areas like foil. Guys like Halcyon are making a nice little niche market by really paying attention to the details.

5

Winglets on airplanes are an advantage in high lift situatiions, landing, takeoff, climbing, thats when the pressure differential from top to bottom of wing is greatest so inefficient exchange of those pressures over the end of the wing area are greatest. The winglets can block or take advantage of the pressure exchange vortices. I read that in an aerodynamics text.

6

It’s all about the Reynolds number. The flow rate of water across a foil can be much less than the flow rate of air across a foil to gett he same lif and drag numbers. But, the point about rate of change of angle of attack and the amount of turbulence in the medium each are attacking within would increase the the efficiency gains that an airplane wing feels with fences or winglets as compared to a performance shortboard set of fins. But, hey sometimes all it takes is the perception that there is a performance gain.

I do think that this type of feature would be appreciated more by a big carvey kind of surfer.

7

Fractal design, no-go!

8

“winglets on the winglets”

Careful - Carry that far enough and you’ve got a loop/hoop/tunnel…

9

air compressible fluid

water non compressible fluid (at least at surfboard level of forces…)

just my 2 cts…

10

An interesting excerpt from the attached article, with emphasis added for illustration purposes:

“However, previous winglets are designed to provide maximum drag reduction and ideal improvement to the lift-to-drag ratio under cruise flight conditions. Consequently, these winglets may not provide optimal fuel efficiency during non-cruise conditions, such as during climbs, takeoffs, and landings. Since non-cruise conditions generally make up significant portions of a flight, maximum efficiency may not be realized by such designs.”

To me, surfing seems more like non-cruise conditions. Just found that part interesting when I was reading through the patent.

http://www.pat2pdf.org/patents/pat20080308683.pdf

11

tomatdaum got it right - the Reynolds numbers are different. When I hear someone talking aero and hydronamics in the same paragraph, I glaze over. The flow conditions are just too different.

It was long ago noted and used by the Hobie Cat racers: a sanded finish is faster. But do you see any useful number of sanded finishes on boards? NO. Why? I think because for too many, a board is a (disposable) fashion item that may be more valued for flash and glam rather than performance, though everyone speaks of the latter.

Aircraft: 5% over 3,000 miles and five hours of flight time is a large savings in fuel, crew time, airframe time, engine time… all adding up to serious money. Surf: 5% on a 20-second surf is only a tenth of a second, inconsequential. And: 5% on a 75-yard ride is just under a foot. You’d be better off taking one more stroke on takeoff, or losing a few pounds, if you wanted to make a difference.

12

" When I hear someone talking aero and hydronamics in the same paragraph,
I glaze over. The flow conditions are just too different."

Man. Throw the baby out with the bathing fluid medium, why dont ya.

13

Janklow. How many guys here can understand Reynolds versus Froude number, compressible versus incompressible flow, inertial versus gravitational forces, and know the appropriate times to use them?

More to the point, who is gonna try, and what is the audience for those that do?

No, let’s not through out the baby, etc., and I do encourage dreaming, but at some point the obvious should enter the discussion.

14

You have a point, but foils and planes and fluids do the same kinds of things, and you have to break out Reynolds v. Froude and incompressible etc to make your point.

Also consider that guys with no idea at all what youre talking about have made highly functional surfboards and fins with only a rudimentary understanding of how foils produce lift.

Anyway, I have no wish to make this into a micturition championship…

http://www.grc.nasa.gov/WWW/K-12/airplane/lifteq.html

15

This photo fascinates me:

So much going on there with that outside fin - tip vortices, flow seperation, etc.

There is a lot to be gained by understanding what is going on there. Whether you relate it to Reynolds numbers or just how it feels when you’re riding, it’s a fun area to explore and it’s wide open to interpretation.

16

An aeronautical engineer friend, Walter Majcan, commented that ‘‘in general’’ high speed air, and low speed water, behave in a very similar manner. Walter spent his spare time, for years in the 50’s and early 60’s, photographing surfers at Windansea. Butch, Diff, Curran, Nelson, Land, Patterson, Cannon, etc. All the top riders of that era. I observed an Al Nelson balsa board, in 1957, with a trailing edge winglet on a D-fin. Windansea, in those years, was a real center of innovative applications in surfboard design and performance, going back to Woody Brown, and Bob Simmons. Lots of interesting history there.

17

Winglets eh? A lotta throwing around of terms and concepts here.

I just want to chime in a little and add some perspective to the airline industry as far as the fuel savings part of this conversation. Whoever said 5% is a lot would be correct. My wife flew for many years for TWA before they eventually were swallowed up by American then they all got fenced in to their hub, then furloughed, then basically got the shaft.

After Pan Am went under, TWA had to be very resourceful in order to survive through many challengiing times. One of the fuel saving practices that TWA pilots imparted to the rest of the airline industry was using one engine to taxi out to the runway for takeoff.

Jet fuel ain’t cheap, and I still wince when I think of the regular practice of dumping fuel once they are up, but they have to have it for saftey’s sake. The comment about the savings being once the planes are up at cruising altitiude is probably pretty on…you notice how they try to get up to crusing altitude as quickly as possible, and this of course has many considerations surrounding it: air traffic, weather conditions, surrounding topography, plane model, freight and pax (passenger) load, etc. .It was Howard Hughes that figured drag coefficients were less way up high, where the air is thin, and that was before jet propulsion.

You don’t see winglets on every type of plane though…can’t recall seeing them on 747, 757 767 or 777’s…maybe their on L1011’s or some RJ’s (regional jets)? I’d have to look it up. Maybe winglets are on McConnell Douglas designs verus Boeing??? Are any on Airbuses? I’d really have to research.

Anyway, I’ll let you guys bash out the details on whether winglets are worth it. I don’t know about the estimated cost of $25K being correct or not, but that wouldn’t be terribly prohibitive on a $10 mil. plane IF it paid big dividends on fuel savings…a lot of these planes are in service for decades, and flying a helluva lotta routes and miles. The 747’s are disappearing becuz although they were like comfy Caddies of yesteryear, they are also gas guzzlers.

A lot of domestic flights that once ran 737’s (United has retired all theirs) are now running smaller more ecnomical RJ’s.

Survival is the name of the game for the airlines, winglets or not.

Just did a quickie little research…winglets retrofit $725,000. Fuel savings and hundreds have been added on 737’s and other types of plane. See this article:

http://www.usatoday.com/money/biztravel/2006-06-05-winglets-money-x.htm

Crap, I just tried this link and it didn’t take it to the article…hmmm. Anyway if you put in Yahoo Browser USA Today Planes with Winglets,…it should come up…article title is "Get Used to Seeing Planes with…

Winglets or not, my vote was for The Concorde…IMO the most beautiful plane ever designed albeit not practical.

18

Part of a paper that a friend wrote “Hydrodynamics of Surfboard Fins” did a little analysis of introducing a fence on a symetrical fins. It starts on page 144.

http://cetic.swan.ac.uk/surfs/pdf_files/Carswell_(2007)_Hydrodynamics_of_Surfboard_Fins.pdf

19

WOW. I just took a look at that real quick… looks like some really solid work. Is that your friends masters thesis, or is it beyond that? I wish I could get funding to research surfing…

gonna file that away to read this summer after classes are done.

Thanks for the link

20

That was Dave’s doctorial thesis. Now, he’s running the mainframe at Swansea University