Whilst spinning fins around the pool I discovered Bernard Smith 'the 40knot sailboat' and then Sail Rocket2. Then I noticed Paul Larsen made a 1:5 scale model to test before committing to build the current world record machine. Since there is no wind here and I'm nursing a minor injury seemed like a good idea to build an exact scale RC model. Opted to start with 10.5 scale (chosen as the biggest airfoil that fits my 3D printer) to sort out design. Uploaded a current work in progress video for the Printables 'make it fly' contest so for sure model is not finished as yet. This will be an FPV machine with camera on mast tip as could be a lethal weapon if can't see where you are going. Will be named "Spirit of Reg" after recently deceased sailing buddy who loves this sort of stuff. Curious if anyone else out there has made RC wind powered speed craft and if so, what sort of speeds reached.

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Flex2 said..
Whilst spinning fins around the pool I discovered Bernard Smith 'the 40knot sailboat' and then Sail Rocket2. Then I noticed Paul Larsen made a 1:5 scale model to test before committing to build the current world record machine. Since there is no wind here and I'm nursing a minor injury seemed like a good idea to build an exact scale RC model. Opted to start with 10.5 scale (chosen as the biggest airfoil that fits my 3D printer) to sort out design. Uploaded a current work in progress video for the Printables 'make it fly' contest so for sure model is not finished as yet. This will be an FPV machine with camera on mast tip as could be a lethal weapon if can't see where you are going. Will be named "Spirit of Reg" after recently deceased sailing buddy who loves this sort of stuff. Curious if anyone else out there has made RC wind powered speed craft and if so, what sort of speeds reached.

Looks cool! Or is it an April fools prank ;)

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Freezer said..

Flex2 said..
Whilst spinning fins around the pool I discovered Bernard Smith 'the 40knot sailboat' and then Sail Rocket2. Then I noticed Paul Larsen made a 1:5 scale model to test before committing to build the current world record machine. Since there is no wind here and I'm nursing a minor injury seemed like a good idea to build an exact scale RC model. Opted to start with 10.5 scale (chosen as the biggest airfoil that fits my 3D printer) to sort out design. Uploaded a current work in progress video for the Printables 'make it fly' contest so for sure model is not finished as yet. This will be an FPV machine with camera on mast tip as could be a lethal weapon if can't see where you are going. Will be named "Spirit of Reg" after recently deceased sailing buddy who loves this sort of stuff. Curious if anyone else out there has made RC wind powered speed craft and if so, what sort of speeds reached.

Looks cool! Or is it an April fools prank ;)

no prank. This is Flex to a tee.
Love the name, Flex.

What a beautiful sailmachine ! I did not know that this design was made in 1963, which make it even more astonishing ! I was 2 years old at that time...

Love the project, and love the dedication to Reg.

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rp6conrad said..
What a beautiful sailmachine ! I did not know that this design was made in 1963, which make it even more astonishing ! I was 2 years old at that time...

To clarify, the original concept of the aerohydrofoil and the trimaran launch system was Bernard Smith's in 1963. You can read all about it for free on Google docs by searching "the 40 knot sailboat google docs". Bernard made many models and experiments but never made a full sized version. What's interesting is that he seems to have come up with the concept playing with a butter knife in the bath. The Sail Rocket 2 design was inspired by Bernard and essentially driven by Paul Larsen who was also the sailor with the principle designers being Christopher Hornzee-Jones, Malcolm Barnsley and Wang Feng. You can learn more at www.sailrocket.com

I uploaded a pile of photos at www.printables.com/model/438587-sail-rocket-2-1105-scale

How do they decide who wins?

Flex, how does scale affect performance?
There's that square/cube relationship, where volume/weight and area happen at very different rates.

So if I have this correct, a small scale mode is going to be much lighter for it's size.
Do you have to compensate for this?
I guess, construction materials wont scale down as well and could end up a bit heavier, but I don't think that will compensate enough.

As a heavy guy , I know I take a lot more power to get going but not much more to keep planing.

Amazing. well done. Will you try and make the foil super cavitating? The Sailrocket story is amazing.

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tarquin1 said..
Amazing. well done. Will you try and make the foil super cavitating? The Sailrocket story is amazing.

yes, entire project came about based on the foil and it needing to be supercavitating. So it is razor sharp at leading edge and 90deg at trailing edge.

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decrepit said..
Flex, how does scale affect performance?
There's that square/cube relationship, where volume/weight and area happen at very different rates.

So if I have this correct, a small scale mode is going to be much lighter for it's size.
Do you have to compensate for this?
I guess, construction materials wont scale down as well and could end up a bit heavier, but I don't think that will compensate enough.

such an easy question but so complicated:-

There is a bunch of stuff going on at scale.

1: there is the basic chop issue: small ripples for a 1/10 vs 1/5 scale when trying to get enough speed to fly
2: the control electrics are essentially the same mass for both scales so bigger is best
3: doubling the scale, squares the wing/sail area, the current 3d printed sail with carbon mast/stiffeners etc comes in at 637g at 0.2245 m^2 area excluding the wing extension (mass includes wing ext) 1/5 scale has 0.99m^2 area and pretty sure I can build for same mass or less using conventional model techniques. i.e. 3D printed ribs, or balsa and heat shrink film so the sail will have 4x power to weight
3.5: Doubling the float size gives ^3 volume so can be much smaller/closer to scale
4: Engineering issues of making the floats, fuselage etc...so much easier to trim weight, and so much easier to do all the controls i.e. same wall thickness but 4+ times volume for very little weight gain. Less weight = more likely to fly
5: Then there is the non trivial stuff and in my extremely limited understanding Mr Froud and Mr Stokes describe how scale works for fluid effects and they both work opposite each other. Froud says gravity effects scale in proportion to square root of their length (i.e. a 1/10 scale model needs to go slower by 0.316 to show same effects as full scale) and Stokes says viscous effects scale opposite in direct proportion so a model needs to go 10 times faster to show same effects as real scale. It all does my head in so thus the fin spinner and/or just build it to see how it goes. Add in how supercavitation works at scale size....arg! (and I was just trying to clean the gutters today) My basic understanding is closer you can get to real scale the better

So roughly speaking if can make the model double the size for same or at least less than 4x mass (seems easy but remains to be seen) gives 4 times the power, so far more likely to work like the real thing.

Its all quite a rabbit hole of intrigue.

I thought the leading edge was blunt or angled. I know Paul kept it quiet for awhile.
The idea was to create Cavitation at low speeds so it wasn't a problem at high speeds.

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tarquin1 said..
I thought the leading edge was blunt or angled. I know Paul kept it quiet for awhile.
The idea was to create Cavitation at low speeds so it wasn't a problem at high speeds.

I'm no expert but definitely sharp leading edge and 90 deg trailing edge. Bernard said the boat needs the foil to be bullet shape. Take a look at all the supercavitating torpedo designs, all feature sharp leading edge and 90deg trailing edge..what you hide behind on the trailing edge doesn't add drag..i.e. rocket motor, electronic attachment etc

Wired magazine, yachting world articles from 2013 was pretty clear foil was wedge shape, photos attached..

Also pretty clear on Sailrocket.com pictures that it's a definite wedge shape. (not sure what the guy is doing in the pic with a hacksaw though!)

Too funny! My mistake i think.
I think that is after they broke the record and they cut the foil off for Paul to keep.
There were a couple of shots after they broke the record with him with a piece of foil in his hand. He said this was the secrect. He held it up with the sharp edge in his palm and the trailing edge out. I just thought the blunt leading edge was the secret!!
I was going to ask about the scale thing as well. You will have to try it in pretty flat water. They also chose that spot for various reasons not just wind. Hell I might be wrong though!!
The blog was amazing. He didn't give up and lived in a container on the beach to make it happen.
Aparently somebody offered him a lot of money for that piece of foil. He said no F'n way!

Finally got some time to check some vids and this CNN one is a good summary of the 10 year effort to get Paul and Helana's world record with SR2 and shows off some model action (only of SR1) for basic concept

edition.cnn.com/videos/sports/2013/03/14/mainsail-paul-larsen-a.cnn

Small update with V2 build....whilst nice after this build pretty convinced need 1/5 scale to make it all work as power to weight is not right for 1/10.5. Paul Larsen got it right with his 1/5 scale models....

Amazing stuff! Love it.

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Flex2 said..
Small update with V2 build....whilst nice after this build pretty convinced need 1/5 scale to make it all work as power to weight is not right for 1/10.5. Paul Larsen got it right with his 1/5 scale models....

So you need a bigger 3D printer and a bigger pool !

Really cool project, fun to see.

Also, seems like something I'd do (forget to remove the pool cleaner before the test...)

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Flex2 said..
Small update with V2 build....whilst nice after this build pretty convinced need 1/5 scale to make it all work as power to weight is not right for 1/10.5. Paul Larsen got it right with his 1/5 scale models....

But ... but .. but ... you need a bigger pool!!!!!!!!!!!

(amazing stuff!)