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Wing profile info for backyard hydrofoil builders

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Europ2
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Re: Wing profile info for backyard hydrofoil builders

Postby Europ2 » Wed Jan 20, 2021 1:42 am

Hey PrfctChaos, could you evaluate these sections according to your protocol ? They are praised for their low drag and AoA tolerance with UAVs.
Curious to see what these slightly reflexed profiles could bring to hydrofoils.
https://www.aerodesign.de/profile/phoenix.txt 8.2%
https://tracfoil.com/airfoils/uploads/f ... /PW51i.dat 8.9%

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Re: Wing profile info for backyard hydrofoil builders

Postby Biggles » Wed Jan 20, 2021 4:51 pm

Hi PrfctChaos , a real wealth of information in this thread!!
Any chance I could pick your brain on the project I am working on?

I have 3D drawn and made a few hydrofoils which work well for kiting and prone surfing. I have used the AG11 and Aquila 9.3. I stumbled upon your inputs here researching a better profile. I was shocked to see that the dedicated thinner hydrofoil profiles (YS930 / Eppler818 etc ) that I was going to now use were actually not optimum. My mission is to design and make a semi high aspect wing that is decent to prone surf and pumps extremely easily to connect small mushy waves. That said, it must still turn well and be fun to ride. The Fone Phantom 1480 comes close but is still a little tricky to turn for newer foilers....and costly!

So far, I have worked the calcs possibly differently using Re numbers and studying the patterns of different airfoil polars for the thickness of profile wanted. (Around 18 to 20mm max thickness) A SUP paddles forward around 8km/h and a surfer around 4km/h. This gives a range between 200000 and 600000. I use the CL/CD vs alpha to find the optimum angle for efficiency (graph peak) and set the wing angle slightly less than that. I also studied/measured the board pump angles of different riders and found for the higher aspect wings a shallower pump is used but still moves to around 11 deg upwards and 6 deg downwards.

1.Any suggestions as to how to optimize the wing and stab incidence angles for minimum drag and best forward propulsion between these angle limits. (My current design uses a fixed -3deg stab and 0 deg wing and flat bottom profiles on both .... I noted your suggested NACA0008 profile). I understand that it may be key to get a design/setup that accelerates quickly to more efficient speeds from the prone paddle speed. That said its probably not going to be more than 10km/h when surfing / pumping back.

2. The drawn design is: 955mm span 258mm root chord and has 168463mm^2 area. Full setup including rider is 90kg. What profile would you suggest? Do the YS930/Epplr818 make sense.....or even the Aquila9.3 again. Are these dedicated foil profiles designed more for boats around 40km/h where cavitation is the issue? It is easy enough to change all these parameters given. For interest the Phantom 1480 has 960mm span and 203mm root chord.

3. I was looking at adding 2 deg or so washout towards the tips. Changing the root wing incidence progressively to 0 deg at the tip and starting from the half span. Would this just increase drag too much in the downward pump as the negative angles are reached rather than adding the benefit of less induced drag & better turning?

Any help much valued & appreciated !!

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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Thu Jan 21, 2021 5:27 am

Europ2 wrote:
Wed Jan 20, 2021 1:42 am
Hey PrfctChaos, could you evaluate these sections according to your protocol ? They are praised for their low drag and AoA tolerance with UAVs.
Curious to see what these slightly reflexed profiles could bring to hydrofoils.
https://www.aerodesign.de/profile/phoenix.txt 8.2%
https://tracfoil.com/airfoils/uploads/f ... /PW51i.dat 8.9%
Hello Europ2,

I show some results below for a generic Small, Medium and Large wing. With both Phoenix and PW51i results added to the same graphs for comparison.

The Phoenix seems to have a very narrow sweetspot, with drag increasing quickly in its upper range. The PW51i does better, with a wider sweetspot. Still getting beaten by about 10% by the optimised selection. MH30 is the winner for all three the wings shown. Interesting to note that MH23, MH30, S2055, rg14a147 and NACA1406 are very often the best or very close to the top.

Fast/Small:
Capture - Comparison fast.PNG
Medium:
Capture - Comparison Med. PNG.PNG
Slow / Large:
Capture - Comparison Slow. PNG.PNG
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PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Thu Jan 21, 2021 6:15 am

Biggles wrote:
Wed Jan 20, 2021 4:51 pm
Hi PrfctChaos , a real wealth of information in this thread!!
Any chance I could pick your brain on the project I am working on?

I have 3D drawn and made a few hydrofoils which work well for kiting and prone surfing. I have used the AG11 and Aquila 9.3. I stumbled upon your inputs here researching a better profile. I was shocked to see that the dedicated thinner hydrofoil profiles (YS930 / Eppler818 etc ) that I was going to now use were actually not optimum. My mission is to design and make a semi high aspect wing that is decent to prone surf and pumps extremely easily to connect small mushy waves. That said, it must still turn well and be fun to ride. The Fone Phantom 1480 comes close but is still a little tricky to turn for newer foilers....and costly!

So far, I have worked the calcs possibly differently using Re numbers and studying the patterns of different airfoil polars for the thickness of profile wanted. (Around 18 to 20mm max thickness) A SUP paddles forward around 8km/h and a surfer around 4km/h. This gives a range between 200000 and 600000. I use the CL/CD vs alpha to find the optimum angle for efficiency (graph peak) and set the wing angle slightly less than that. I also studied/measured the board pump angles of different riders and found for the higher aspect wings a shallower pump is used but still moves to around 11 deg upwards and 6 deg downwards.

1.Any suggestions as to how to optimize the wing and stab incidence angles for minimum drag and best forward propulsion between these angle limits. (My current design uses a fixed -3deg stab and 0 deg wing and flat bottom profiles on both .... I noted your suggested NACA0008 profile). I understand that it may be key to get a design/setup that accelerates quickly to more efficient speeds from the prone paddle speed. That said its probably not going to be more than 10km/h when surfing / pumping back.

2. The drawn design is: 955mm span 258mm root chord and has 168463mm^2 area. Full setup including rider is 90kg. What profile would you suggest? Do the YS930/Epplr818 make sense.....or even the Aquila9.3 again. Are these dedicated foil profiles designed more for boats around 40km/h where cavitation is the issue? It is easy enough to change all these parameters given. For interest the Phantom 1480 has 960mm span and 203mm root chord.

3. I was looking at adding 2 deg or so washout towards the tips. Changing the root wing incidence progressively to 0 deg at the tip and starting from the half span. Would this just increase drag too much in the downward pump as the negative angles are reached rather than adding the benefit of less induced drag & better turning?

Any help much valued & appreciated !!
Don't hold back on the tough questions Biggles :o :D :lol:

Just a quick response for the easy ones, will have to come back to the more in-depth questions. Although, I am not sure how easy it is to quantify pumping with handcalcs, there is a lot of dynamic weighting and unweighting as well as angle changes happening (Also, with the dynamic movement, one would need to look at the angle of the wing relative to the movement direction instead of compared to water surface, since there is dynamic up and down components involved. Not easy for steady state type calcs). My approach would be to rather look at a few more NYfoiler youtube videos and see what kind of average pumping speeds he is getting on which wings. Can then optimise a wing for low drag near that sped range. When pumping the speed is definitely well above 4 km/h.

Having a quick look at the wing size for point 2, below are some results. MH23 looks really good. AG11 (you mentioned) is added as a comparison, it has a very narrow sweetspot for this wing / speed range.

AG11 comparison:
Capture - Biggles.PNG
YS930 comparison: (Looks better than AG11, but nothing to write home about, that I can see.
Capture - Biggles YS930.PNG
Aquila 93 comparison: Nah.
Capture - Biggles Aquila93.PNG
Both our calcs use Reynolds numbers, airfoil polars etc. We should definitely get to the same values. And if you double check one of my results at a single speed for a single wing (using the plots on Airfoiltools.com, for example) you should get exactly the same results as me.

For example, if you take MH23 at a single speed of 23.75 km/hr you get a Reynolds number of close to 1000000 (for the wing size above). Required lift coefficient is 0.23 to lift 90 Kg at this speed. Alpha of just less than 1 degree. Cl/Cd of 54. Cd of 0.0045. Giving profile drag of around 1.7 Kg, then adding induced drag of 1.2 Kg. You get to the total drag of 2.9 Kg, shown on the graphs above. Easy to doublecheck on Airfoiltools.com, although they just show a few reynolds number plots there and not too easy to read accurately, but good enough for a quick check.

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Re: Wing profile info for backyard hydrofoil builders

Postby Biggles » Thu Jan 21, 2021 11:19 am

Thanks so much for the amazing help here!!

I watched this last night and it had a ton of useful info regarding speeds and glides etc. Great twist towards the end too ...

"Aspect Ratio + Area + Speed Performance = 3 key attributes to the perfect lake wing"

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Sun Jan 24, 2021 2:36 am

Biggles wrote:
Thu Jan 21, 2021 11:19 am
Thanks so much for the amazing help here!!

I watched this last night and it had a ton of useful info regarding speeds and glides etc. Great twist towards the end too ...

"Aspect Ratio + Area + Speed Performance = 3 key attributes to the perfect lake wing"
Okay, first things first. From everything I can see / find / experience I believe most pumping and small wave prone foiling happens around the 12.5-25 km/hr speed range (~8-15 knots). So will be concentrating on that range. Now if we look at the results for a wing with the F-one phantom 1480 dimensions (960 mm wingspan and 1480 cm^2 area), see results below. Then we can see that at the low end the drag is completely dominated by induced drag. This means it really does not matter what airfoil is selected, until you get up to around 15-20 or so km/hr, because that drag is just dominated by that induced drag, which is largely a function of the wingspan.
Capture.PNG
Increasing the wingspan to 1050 mm and the results start to look pretty good.
The optimiser 5000 says that area of around 1450 cm^2 is a good area for this speed range / wingspan.
Capture2.PNG
Increase the wingspan some more to 1150 cm^2 and results improve some more.
Capture3.PNG
If I can use foilingNY as a reference. I think the clip below does a good job of illustrating that even the big Starboard 2400 wing does a good job of initiating a turn, because of the downward sweep of the wing (compared to the very very flat axis wings). So I would not be too worried about losing turnability with the increased wingspan, but I would suggest adding more downward sweep to the wings (definitely more than the axis 1150 wing) to keep it turning in a fun way. The 1050 mm wingspan above could be a good compromise of low drag vs wingspan, but I would personally go for 1150 mm and add a healthy amount of downward sweep if I was making another pump / small surf wing.



Hope some of it helps. Happy to run some more scenarios if any of the above gives you a good idea to look at in more detail.

Wing angle, stab angle:
I am still happy to suggest 0 degrees for the front wing (since they are often very close to that angle near the middle of their speed range.). Stabs, I would still suggest using a fast low drag, high aspect ratio stab for all occasions (except learning) and shimming it to the angle where it feels right. I don't have much to contribute here, but I have noticed I get better pumping distance with a slightly larger stab (compared to the funner smaller stab), I guess it just helps to give something to push against harder on the upward pump. Basically if I had to make a stab for a pumping setup I would just copy the axis 460 stab dimensions (since it gets the results), and use a NACA0008 profile (good stall angle range and low drag) and set it to around 2.5 degrees compared to the front wing. Then ride it a few times and shim until perfect. Sorry I don't have much fancy analysis for stab setups.

Almost forgot, wing washout angle:
In aeroplanes it is used to help keep some control when the wing starts stalling (so that one can still turn the plane, since some of the control surfaces are not stalled yet), something that is not applicable to hydrofoils (the whole wing is a control surface). I have ridden a few wings with washout, like the moses 590 and it just feels super draggy to me, but maybe it has nothing to do with the washout and more to do with other features of that wing. Anycase, I haven't done definitive calcs on washout. One would have to remember that if washout is added, then the plan shape of the wing will also need to be adjusted to still keep a theoretically optimum elliptical LIFT DISTRIBUTION, otherwise if one does not change the plan shape then the suboptimal lift distribution will just increase induced drag. So in summary I would only add washout if you are going to do a complete detailed design and optimise the plan shape to maintain the elliptical lift profile. It is possible, but I just don't see what the advantage would be.

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Re: Wing profile info for backyard hydrofoil builders

Postby Biggles » Mon Jan 25, 2021 12:37 pm

Yes , this helps a ton...thanks.
On the washout question : Would washout not reduce the amount of induced drag as less lift is produced towards the tips. Hence less tip vorticies. Also as one turns , less lift is being produced at the outer portion of the wing hence increasing roll stability.
On Wing Angle: The critical part of the whole prone saga is the paddle and trying to be as efficient as possible to catch mush. Surely aligning the wing at the optimum cl/cd vs alpha for an Re between 300000 & 500000 will give the easiest/most efficient paddle & start? I find this to be around 2.5 - 4 degrees for most profiles.

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Re: Wing profile info for backyard hydrofoil builders

Postby tweoistom » Mon Jan 25, 2021 6:03 pm

Hi there,

I'm looking to make a foil to learn on while being towed behind a tender. I think this realistically won't be able to go much faster than 6-7kts with the outboard it has + drag etc. Ideally the wingspan will be less than 1m as this is the width of the glass fibre I have to make glassing easy. I guess really 950mm would be best. Are you able to help me out with a wing profile? For such a low speed? I'm about 70kg + maybe 15kg of kit

Many thanks in advance.

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Re: Wing profile info for backyard hydrofoil builders

Postby tweoistom » Mon Jan 25, 2021 6:07 pm

tweoistom wrote:
Mon Jan 25, 2021 6:03 pm
Hi there,

I'm looking to make a foil to learn on while being towed behind a tender. I think this realistically won't be able to go much faster than 6-7kts with the outboard it has + drag etc. Ideally the wingspan will be less than 1m as this is the width of the glass fibre I have to make glassing easy. I guess really 950mm would be best. Are you able to help me out with a wing profile? For such a low speed? I'm about 70kg + maybe 15kg of kit

Many thanks in advance.
Looking at the question and answer above naca 1406 could be a goer...

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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Tue Jan 26, 2021 2:18 am

Biggles wrote:
Mon Jan 25, 2021 12:37 pm
Yes , this helps a ton...thanks.
On the washout question : Would washout not reduce the amount of induced drag as less lift is produced towards the tips. Hence less tip vorticies. Also as one turns , less lift is being produced at the outer portion of the wing hence increasing roll stability.
On Wing Angle: The critical part of the whole prone saga is the paddle and trying to be as efficient as possible to catch mush. Surely aligning the wing at the optimum cl/cd vs alpha for an Re between 300000 & 500000 will give the easiest/most efficient paddle & start? I find this to be around 2.5 - 4 degrees for most profiles.
More washout should increase induced drag. Here is a guestimate prediction formula for how much washout increases induced drag by. Sure only a few % maybe, but a increase of drag, not decrease.

However, this level of detail is very much in the realm of detail design. I would highly recommend installing a program for further detail design, such as a CFD program or XFLR5. Then making changes to washout, sweep angle, anhedral etc to the wing and the program will show you the results for that change. The goal of my calcs is just to get DYIers to that 95% stage where they are close to a good / ideal wing design. Already having the main dimensions and profile selected means it is feasible to investigate detail design after that stage (Trying to design the first 95% of a wing from scratch using one of the detail design tools will be a huge waste of time, but they are very useful for getting that last 5% over the line).
Capture.PNG
Capture.PNG (24.63 KiB) Viewed 2698 times
Wing angle: Well remember increasing the wing angle for more lift also increases drag. So for the added wing angle to be of benefit when paddling you would need to be sure that that extra lift and drag is helping to offset even more drag by lifting board and rider further out of the water. So that the total drag is a minimum. If you just look at the wing itself it has minimum drag at close to 0 degrees. At paddle speed for 0 degree wing, you might have 3.7 Kg lift and 0.1 Kg drag. While at 4 degrees you might have 7.3 Kg lift and 0.28 Kg drag. So you would need to decide if the extra lift is worth the extra drag.
It is easy to test, since it is the same result as shimming between the base plate and board to have the board angle -4 degrees nose down compared to the mast. Then take it for a paddle back-to-back with the normal 0 degree setup. (All this assumes that the bottom of your board is at exactly 0 degrees while paddling, which is not necessarily correct.). Not sure if it will be irritating having the board pointing down when at normal cruising speed either?


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