A more stable efoil for bigger guys


#1

I am a bigger guy (225 lbs) and not an acrobat. Has anyone ever experimented with one big front foil and two smaller rear foils to give a more stable ride and perhaps create more lift? I would be satisfied to have a seat and not have to stand initially. And I think that going from a prone position to standing would be a challenge for me.


#2

And I think that there are probably a lot of people that are physically challenged that would enjoy the thrill of flying! Even if speed and run times are limited. Sure would appreciate any feedback from this community.


#3

A SUP foil makes a huge difference for using big guys, I’m 255 lbs, I can ride the Liquid force kite foil, but sup foil allows for slower more comfortable flight vs faster with kite foil. Two smaller wings in the back I don’t think will make it more stable.


#4

My thought was that a big foil front and center and two smaller foils on each rear corner like the setup used on racing yachts would be more stable. But as I think about it the rider still has to be able to balance and shift side to side for turning. I’ve seen all your videos so you have a lot more experience with it than I. Thanks for the input.


#5

You are 255, use an SSS 56104 and a sup foil. what kind of speed and run time do you get?


#6

Sup/Surf Foil is the way to go - they have massive amounts of lift.
I know plenty of big guys who are using these for SUP and kiting with good results.

GoFoil Maliko
Takuma V100
Naish Thrust
Lift 170
etc

If you use a big enough board with enough volume, you can start from a standing position and don’t have to pop-up while moving. This type of big board will be heavier and run time will be impacted, but ease of use will be better.


#7

You just made my day! Now I’ve got to get busy building…


#8

@Wade, Check out my build - 'foil-piercing foil board.
It’s being designed for a 200Kg lift. - I’m 130Kgs (286lb)
Would be happy to share info
Dave


#9

That front foil is huge! Are you building this from scratch? Using CF or fiberglass?


#10

The whole board is being scratch-built.
Pretty much all of the systems being built on this forum or soon to be on-sale from manufacturers are typically for riders in the 70 - 85 Kg weight range and a heck of a lot fitter than old bloaters like me :slight_smile: I need something that is a./ capable of supporting my weight and b./ stable enough to allow me to stand without wobbling all over the place. (Incidentally I’ll be able to add a motorcycle-style seat to it that will take either one of me or two average weight riders)

Essentially this board needs to lift around double the mass of other boards you see elsewhere. Add to that I’m more into cruising so a more modest cruising speed of 15mph with a more sedate take off speed of only 5mph is why I need bigger and two wings to create the lift.
Stability is a big thing for me which is why I’ve arrived at this design. There are multiple points to improve the balance at rest, moving sub-take-off, take-off and cruising:-
• There are two wings widely spaced apart. I’m hoping this should eliminate much of the pitching issues you see many riders struggling with when they are learning to ride.
• The shape of the front foil provides a variable lift that ultimately means the whole board is self-levelling and a little less sensitive to throttle. – I.e. The slower you go the board sits a little lower. The greater lift on the front wing will cause the rear of the board to sit lower and change the angle of attack to generate more lift at slower speed. The faster you go and the less front wing is in the water.
• Having three supports allows a tripod-style support rather than a mono style single mast which should be in-errantly more stable
The front wing has quite a complex geometry. Not only is it curved in three directions but there are three airfoil section types along the curve ranging from a low drag type in the centre through a high lift section on the sloping sections and lastly a symmetrical streamlined section for the support sections. The front wing, rear mast & rear wing are made of a 3D printed core with a carbon fibre and Kevlar coating.
Well that’s the theory at least 
I’ve added a few pictures of a 1:10 scale 3D print of the whole board plus a 75% test print of the latest wing design.
Dave

IMG_1372IMG_1376


#11

Incredible! Any chance you live in the Tampa area?


#12

That looks amazing. Does anyone know the difference in width between a kitefoil and a sup foil? It should be easy to take a good wing shape and to just scale it up. Then we can 3D print it and cover it with glass. Use a Space Bag to vacuum it.


#13

First time I ever saw a foil in action was when my lakeside neighbor, an avid water skier, bought an “Air -Chair” in 1999.

See one in action HERE

image

image


#14

I heard that they are quite dangerous.


#15

Actually quite safe. The rider is strapped in on the waist/thighs and also has a foot boot. So when you crash, there is no risk of rider hitting the foil. It hurts as much as falling on a wakeboard going 18mph.


#16

@Wade - Cheers mate - I live in the UK but am more than happy to exchange info via this forum.

The thing FANTASTIC thing about forums like this is sooooo much info is shared anyway. Couple that with the wonders of Google means that much of the questions you will ask on your own journey to creating your own masterpiece will be answered as if you had your own consultants :slight_smile:

Rgds Dave


#17

Hi @MaxMaker,
While I don’t have a simple answer to your question I wonder if there is a fantastic opportunity for an Engineer with experience in Hydrodynamics/ aerodynamics that visits this fantastic forum to come up with a simple design and spreadsheet where the rest of us just add the numbers of what we need to acomplish.
For my design I’m using a book called ‘Hydrofoils Design Build Fly’ by Ray Vellinga (ISBN No: 0980982236116). In that book he attempts to simplify the design process and even suggesting some aerofoil types.
In simplistic terms lift is determined by a number of key factors:-
• Foil or wing details i.e. :-
o Profile of the foil/ wing section.
o Shape of the wings in in plan (i.e. Looking from above)
o Speed of the wing
o Angle of attack of the foil/ wing section
• drag – i.e. :-
o Parasitic Drag which is made up of a number of different types of drag…… See http://www.aircraftnerds.com/2016/06/types-of-drags-on-aircraft.html for more description.
o Induced or Lift drag – Basically cross section, plan shape and size influence drag
Staying with the simple descriptions then…… Essentially getting a foil (wing) to fly comes down to just two things………

  1. Having enough lifting force to equal the weight you need to overcome (i.e. weight (mass) of rider and board)
  2. Having enough thrust to overcome the drag and get the foil (wing) up to speed.
    Simples huh? Sadly - Some considerations that add complexity to any solution:-
  3. The Wing:-
    a. Decreasing the thickness of the section reduces frontal area drag (Part of the parasitic drag) at the expense of lift and strength.
    b. The plan view shape can substantially affect the induced drag – i.e. a long thin tapering wing. (like you see on a glider) and/or with little Winglets (Like you see on passenger aircraft) are all tools to reduce induced drag.
    c. A higher angle of attack increases lift at the cost of increased drag – both parasitic and induced.
    d. Running depth below the surface:-
    i. Most boards will tilt-in towards the centre of the turn. If the turn is too sharp or there is angle (Also known as dihedral which is primarily used to aid stability and turning) in the wings – The wing will broach (break) the surface of the water causing a reduced/ sudden loss of lift.
    ii. If the depth of water to the top surface of the foil is less than the width of the foil then an additional drag is introduced
  4. Weight – Naturally reducing weight (otherwise known as mass) means many things including reduced area of wing, thinner sections, slower take-off speed and so on.
  5. Drag – We’ve already touch on some of the points of induced drag but other things need to be considered such as:-
    a. Smoothness of the skin or surfaces – polished is good.
    b. Interfaces – i.e. the interface between the mast and the board and the wing and the mast/ motor mount etc can set up significant drag at the interfacing. Eliminating sharp angles at these points (Also known as fairing) significantly reduces this part of parasitic (Interference) drag. The way this is done is to add radii to these intersections. Not only does this reduce drag but adds strength.
  6. Power or thrust – The frustration is that as speed increases then drag is increased by the square – i.e. increasing speed from 2mph to 4mph (just 2mph) increases drag by a factor of 4. Drag is at its worst just before take-off which is why you need much additional power. After take-off parasitic drag is substantially reduced as the board and any interfaces etc are no longer in the water – Which is why the power requirement (And therefore range) is substantially reduce.
    Clearly then a board designed for a small child/ tiny adult who doesn’t want to fly that fast wins hands down in this race. And explains that my Jumbo board has significantly more wing area and loads of power even though my take off speed is only 5mph.
    All in all the concept of a hydrofoil is easy but you need a little thought and understanding to put it all together.
    Enter an Engineer that has the experience and understanding to come up with a standard design where you can add simple inputs such as weight, speed etc and the spreadsheet will calculate the area of board required, mast etc utilising a series of standard foil sections. Either that or copy the ‘crap’ out of someone elses in which someone who’s already bought one and has a digital scanner can be everyone’s new best friend 
    I guess it’s over to you Mr @pacificmeister as our leader and spokesperson for this exciting new sport to see if you could garner some interest out there. That’s of course if you think it a good idea 
    Rgds
    Dave

#18

I love the enthusiasm many here have about engineering and building foils. There is a lot of good discussion and I enjoy reading it.

Luckily we are not alone and we have sup/surf/kite foils makers figuring things out too. Lots of innovation. After kite foils we now have the sup/surf foil market exploding. I am on Maui right now, sup/surf foilers everywhere. More than regular sups! Totally insane. GoFoil is offering about 7 different wing sizes now. I saw their biggest wing yesterday and oh my, it’s huuuge. My point is that there is a foil for every speed and rider weight now and many of them will work great for efoils. But there is not one size that fits all styles and weights. Many sup foilers here have multiple front wings and change them depending on conditions. Same is possible with efoils.

So here is where I think we should innovate. Rather than designing another foil similar to all the sup/surf/kite foils out there, let’s figure out a way how we can adjust the foil while riding. I imagine a wing that has more surface during takeoff and for slow cruising (or heavier riders or beginners) and can be reduced for high speed riding. And all that combined with actuators adjusting winglets for electronic lift adjustment and stabilization… a foiling Segway.


#19

I have been thinking about the segway function. There are model airplanes like the Easystar, that get away without ailerons. They only have a rudder and elevator at the back and fly very well. The wings form a slight V-Shape when looked at from the front. This causes them to passively stabilise their roll. They are called dihedral wings.

Maybe this could be a good starting point to design something that does only needs two control surfaces on the back wing.


#20

Another approach is to have a flap on the trailing edge of the main wing. A flap would allow slower take off with a relatively small wing, Then reduce the flap setting as speed increases for minimal drag.

Now make it automatic… use pitot static water pressure to actuate the flap. Flap could be spring loaded in down position, as water velocity increases, a small piston is pressurized and the flap setting could automatically be reduced.