NALSA decided to adopt FISLY class 3 platform rules for NALSA class 4 . My existing wingboat didn't fit the new rules so I decided to make a new class3 sized wing for it. It took about 3 months to build. Just in time for the Worlds.

WOW !!!!!!

So very impressive. Pea green with envy.

The very best of luck with your racing.

PS; There is no way you could build a structure like that here in Western Australia.
I have studied your construction and cant find a single knot hole in the timber anywhere.

Absolutely FIRST CLASS!!!

Likewise, I am very impressed with your craftsmanship and envious of the materials available to you but the thing that I cannot understand is the use of the two close-coupled symmetrical aerofoil shapes to create the wing. The need to have an articulated wing for low speed lift is obvious but in all the many radio controlled power planes and high performance gliders I have built or observed it seems to me to defy logic to deliberately disrupt airflow like that over control or lifting surfaces at speed. We did find that making the forward control surface of an elevator or fin rudder about 1/3 thicker did stop flutter of the control surface at speed and that would have been due to the same interrupted airflow and loss of some effective control. Is that the theory of the dual wing perhaps as there has been instances described of the sails shaking violently at times?

For my education I would like to have the theory of air flow over the double wing explained. All the best wishes for your ventures, you are an inspiration to others.

My understanding is that the front aerofoil acts similarly to a jib on a boat, when, for speed the front aerofoil is separated slightly leeward which creates a slot for the slower windward(higher pressure) air to transfer to the leeward side of the rear aerofoil speeding up creating a greater low pressure. As the slower air speeds up it sucks the faster air from the leeward side of the front aerofoil through faster increasing its speed and therefore reducing the pressure which translates into a greater pressure differnce between windward and leeward sides of front aerofoil resulting in more speedI think.
If I am wrong some one will surely correct me

The way I understand it is - a plain single airfoil will have the boundry layer (airflow close to the foils surface) separate near the rear of the section at high angles of attack. This causes it to have little lift particularly in our low speed ranges(getting started, pointing high and going deep downwind). When an external flap is added it creates a slot. The Slot allows some air to go from the windward side to the lee ward side. This air slipping through helps the boundary layer to not separate. This allows the slotted wing to perform well in high lift situations. I make my main wing and flap elements 50 /50. Some go 60/40. The 60/40 will have more strength because the first element will be larger. On my new wing I made the wing non tapered until the hound resulting in a much stiffer wing compared to my old one. I found through my own tests that the 50/50 has more lift. It should have a better lift coefficient ( more even lift in it's span) than a conventional tapered wing.

flap study - naca.central.cranfield.ac.uk/reports/arc/rm/2622.pdf
flap.




You can see how the slotted flap reattaches on the flap in the video at 8:00. This is a asymmetrical slotted flap where as mine are symmetrical.



There is a slotted flap study related to the video some where on the net that shows the slotted flap to be the most superior of lift devices with the least amount of drag at high lift.

Hi TP1, a slot on the top of commercial passenger plane wings utilises that idea to enhance airflow and reduce stalling speed but my understanding is that the two aerofoils in the yachts are hinged together - no slot, so no air can pass thru. The idea of two foils on their own individual pivots would be excellent as is the jib on a yacht with adequate slot makes a tremendous difference to air flow. We see that with the fine tuning of our radio yacht sails.

Gizmo, you would have studied the wings, how are they configured? On another question now we have awakened you!!.... I haven't had anyone give me an explanation as to why/why-not a racked mast is/is-not better than an upright mast. It must lie in the centre of pressure changing on or off wind, spilt wind, change in camber or something like that......Wok

A study done in the 1930's showing slotted flaps a king. - ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091677.pdf

The pivot points on the hinges are key in determining the amount of slot (gap) one wants to achieve. I choose 12% x flap chord length = 21'' x 12% = 2.5''
That means the pivot point of the flap hinge is 2.5'' forward of the main elements trailing edge.

Excellent video 772. I can see therefore you must have included a slot between the two aerofoils as TP1 suggests. The Wright brothers would be proud of you. I was too slow in getting my spelling correct earlier and you were able to slip the video in. Thank you....wok

Select to expand quote

wokelliott said...
Gizmo, you would have studied the wings, how are they configured? On another question now we have awakened you!!.... I haven't had anyone give me an explanation as to why/why-not a raked mast is/is-not better than an upright mast. It must lie in the centre of pressure changing on or off wind, spilt wind, change in camber or something like that......Wok

Have a look at things around you..... In nature have a look at soaring birds (seagulls, albatros, eagle etc) and their wing shape and rake angle and wonder why......
Have a look at aircraft with high lift (and not being pushed by jet engines) and ask why the wing shape is like that.
Why did the air force F1-11 aircraft have a swing wing?

Rather than give a straight out answer doing some thinking will give people a greater understanding of wing / sail shapes.

Ok, so it looks like I will need to attack my back-up radio yacht and fit it out with a raked mast. The usual common setup is a vertical mast, sails are a regulated size within very strict rules but there are trimming limits I can legally work within. Will be very interesting to see what effect a raked mast does once I rebalance. If nothing improves should I stick tail feathers up the rear end ??

I think you missed it..... Vertical mast more lift, raked mast less lift.
BUT a raked mast has a wider angle or window of usable sail shape. A thin vertical sail / wing has higher lift but needs very precise air flow control.

Then why do most of the landyachts have such steeply raked masts? Years ago I sailed against an identical 20" Spacesailer with a raked mast and we couldn't point like him.

Yes wok, you've got it, by raking the mast it gives a greater tolerance for wind direction and speed, just like a QANTAS aircraft where they need an aircraft to accommodate various loads and takeoff angles.
A 'sailplane' glider with straight wings are high performance (great lift) but very precise in their flying.

So why are landyachts mast so raked..... the Old class5 rules gave a 'defined' height to the tip of the mast 'vertically', I forget what the measurement was but if the mast was raked you could get more mast on the yacht and that meant a higher aspect ratio sail (better performance).
So we know that the 'sweet spot' for lift on a sail is 1/3 from the leading edge, A vertical mast has a long sweet spot. A raked mast 'sweet spot' moves up and down the sail depending on sheeting angles.

Manta design yachts were originally made by a hang glider maker and they have used their design knowledge to make the yacht. Hence the very raked mast.

With land sailing design tend to follow the winning yachts pilots, so if you have a medium performance yacht sailed VERY well up against a high performance yacht poorly sailed the medium yacht will often win.... People see it win and then the yacht design goes down that path often because of a good pilot rather than by good design.

Thanks for that Gizmo. My second back-up yacht is identical to my usual one and I can get sneaky enough with wind changes to outpoint most of the others but I lack downwind speed for some reason, think it must be hull width/shape and thought the raked mast may trap more wind so I'll give it a go....nothing to loose. Our underwater hull shapes are allowed some variations but hull length, weight, draft, sails, boat length are controlled. So it is mostly up to the trim and sailing skill that wins races, just as it should be in landyacht competition. I am surprised that the landyachts do not utilise a boom vang.

No boom vang needed.... when you set up a water yacht (with boom vang) you set up for a very narrow wind band ie;15 knots with boat speed you might get to 20 knots.

But with a landyacht in 15kmh wind you might get to 80kmh with apparent wind, for a landyacht the wind range is huge...... Remember that a landyacht is sailing 'upwind' virtually all the time.