Mast Profile - rule of thumb performance impact


#1

Without getting into the woods with detailed hydrodynamics on the subject, is there some good rule of thumb logic why the mast nose should be thicker then the tail on an efoil?

I’m researching the mast (keel) and have spent a fair amount of time reading about the various options. After looking at the various masts from different manufacturers (both efoil and no motor) and it appears the profile (shape, aeroprofile, hydroprofile) is typically symmetrical on both sides (equal nose and tail thicknesses).

I assume this is mostly because it decreases production costs / complexities making, but there must be some good rule of thumb logic for making the nose side of the mast thicker than the tail.

My understanding is that the thickness primarily drives the strength and stiffness, so it should be as thin as possible without losing structural integrity (10mm is likely minimum, 20mm max and 15mm average, all based on materials). Thinner is better as it creates less drag. The mast itself is not providing any lift necessarily, so does having a wider nose than tail have any advantage at all? If so, what’s the “back of the napkin” logic for deciding that thickness…

Thanks


#2

I think it is the best hydrodynamic profile,


#3

Right, but most that I have seen (mostly in pictures) have a symmetrical profile (nose & tail of the mast are equal thicknesses) vs. the “Airfoil” in your image has a thicker nose than tail.


#4

i have 3 mast from different suppliers and they are asymetrical. Maybe the cheap one are symetrical to reduce production costs…


#5

Even on the example you show (liquid force) the wide point is slightly toward the front (you can see the shape the the small triangles in the end after the screw holes) , i guess that make the profile more stable.

So it will always be symmetrical side to side as you don’t need lift, but never symmetrical front to back to be more stable.


#6

I see, thanks.

https://www.grc.nasa.gov/www/k-12/airplane/foil3.html

Using the NASA configurator, tweaking the airfoil to the smallest thickness creates less drag than the symmetrical ellipse with the same thickness, so that makes sense (I think).

Still not sure how to determine what that thickness should be… make the nose as thin as possible while still keeping the airfoil shape and structural integrity?


#7

Leading edge, trailing edge, … This post should be useful to you:

The parameters that matter: airfoil section, profile thickness and thickness to chord ration, same thing with front wing airfoil sections… demonstrated with figures here:

Today, in kitefoil, to go beyond 45 knots (70mph or 80 kmph) without motor (just wind), the best mast thickness is ~11.6mm, built in UHM carbon (Ultra High Mofulus). That’s half the 2008 Carafino kitefoil mast thickness (22mm) which had a very draggy elliptical airfoil section.

For me, the ideal efoil or kitefoil board should look like this (half joking :wink:)
Laugh_efoil_board


The twix-efoil project
#8

Thanks for the great links. Very helpful… I’ll stop using the “nose” and “tail” language and go for leading edge / trailing edge.

Did you ever try your half joking config? Seems like it would work for a larger board… :slight_smile:


#9

Never took the time :wink: Problem is that this config introduces at least 2 issues: 1 - the depth of each leg (angle with respect to board bottom) influences the angle of attack of front and rear wing (stabilizer) which are supposed to stay at 0 and -3 degrees with respect to board deck horizontality 2 - serious rigidity issues.

If you overcome this, you get a plane without fuselage (which has never been tested so far) PLUS a very handy set to travel with. But where do you place the motor of your efoil ? :grinning:


#10

On your point #2, do you mean rigidity issues in the board itself or the masts?


#11

Each mast around its axis.


#12

Could be a good start for the rear plate :Hinged_plate_efoil


#13

Here’s a start for a ironing board configuration foil set-up. Missing the retractable aspect of it…:

https://a360.co/2HEvE24


#14

Very very nice ! I wonder if the fore mast leading edge on your drawing is not facing downwards …:wink:

Let’s open a dedicated thread to this exciting project !