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      Abbreviated rules   07/28/2017

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Xlot

Are Z foils that much slower?

130 posts in this topic

12 minutes ago, Rawhide said:

Why is a guy sitting on a bike or pump less of a sailor than someone who is just wt on the rail for most of the race and only pulls sails up and down once every half hour?

Better question... why is a guy on a bike less of a sailor than the guy on coffee grinders from the previously century of AC's?

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From an A-Cat regatta held during the Garda Foiling Week:

"Interestingly, the new prototype of Thilo Keller, known as AC nano, is based on an automatic board drill (cant or rake?) system designed to maximize the propensity of the leeward one to generate vertical thrust while minimizing resistance of the windward one. The remarkable feature of this boat is to get up from the water already with about 7 knots of real wind. According to Thilo's statement, there are already plans for serial production of the prototype by Advanced Sailing Technologies."

 

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Wow.  Great thread.  Re-reading now a few times.  Usually pass these over assuming they are all polluted by he who cant be named and un-readable.  What a pleasant change!!!

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On 7/7/2017 at 4:46 PM, Rawhide said:

Why is a guy sitting on a bike or pump less of a sailor than someone who is just wt on the rail for most of the race and only pulls sails up and down once every half hour?

In this version of the cup all the grinders (cyclors or coffee grinders) were human oil pumps. How many sailors have you met who spend entire voyages continuously pumping? (Usually if constant pumping is required it means something is very wrong with the boat).

I don't think it is how they deliver the power that people take issue with - hell, let them use rowing machines if it generates more power in an efficient manner (although it would make the boats look like slave galleys)- it's the fact that hydraulic pumping needed to be constantly delivered to perform a non-sailing function (pumping oil) that most people I know didn't like.

Non-sailors  just wanted to know why they need to cycle constantly? When I explained it was to pump oil the replies were "what kind of sailing requires continuous oil pumping?", and "Why don't they just hook them up to a propeller?"

 

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6 hours ago, Xlot said:

From an A-Cat regatta held during the Garda Foiling Week:

"Interestingly, the new prototype of Thilo Keller, known as AC nano, is based on an automatic board drill (cant or rake?) system designed to maximize the propensity of the leeward one to generate vertical thrust while minimizing resistance of the windward one. The remarkable feature of this boat is to get up from the water already with about 7 knots of real wind. According to Thilo's statement, there are already plans for serial production of the prototype by Advanced Sailing Technologies."

 

Thilo's boat foils downwind in 5 knots and upwind in 7. It has a clever cant system which works automatically and it uses C foils. It has caused a bit of a firestorm, mainly because many class members who understand the rules believe it is not class legal. We await action and clarification from the technical committee.

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  ^

Thanks. Wonder if he'll be at the Italian A-Cat Nats, which will be held on the Bracciano lake near Rome at the end of the month

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1 hour ago, KoW said:

In this version of the cup all the grinders (cyclors or coffee grinders) were human oil pumps. How many sailors have you met who spend entire voyages continuously pumping? (Usually if constant pumping is required it means something is very wrong with the boat).

I don't think it is how they deliver the power that people take issue with - hell, let them use rowing machines if it generates more power in an efficient manner (although it would make the boats look like slave galleys)- it's the fact that hydraulic pumping needed to be constantly delivered to perform a non-sailing function (pumping oil) that most people I know didn't like.

 

I'm all for the slave galley look, the cup needs more theater. Maybe the only comms allowed should be a drum. 

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2 minutes ago, Rawhide said:

I'm all for the slave galley look, the cup needs more theater. Maybe the only comms allowed should be a drum. 

KMEE117.pvw.jpg

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1 hour ago, Rawhide said:

I'm all for the slave galley look, the cup needs more theater. Maybe the only comms allowed should be a drum. 

To be honest all big boat racing has always had it's galley slaves, I think they only thing they got wrong this time was the ratio of drummers to rowers.  I think you have to have at least 3 people on the back who's only jobs are about sailing the boat.  Watching people like slingby's huffing and puffing while also attempting to make tactical decisions detracted from the event in my opinion.  One more person on the boat would have made a big difference.

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Thanks for reporting Xlot,

Your comments make a lot of sense to me if I understand what you report

because, despite a reading of Tom Speer's A-cat foils Workpaper,

I have not yet understood everything about Z-Foils, so it is an opportunity to share my ignorance and lack of brain power.

I feel there is a kind of  lift "paradox" with the current A Cat Z foil concept

If you assume you are already foiling (phase 1 Low speed),

then wind increases and the boat accelerates to (phase 2, higher speed)

My question regards what actually happen for both foils during the acceleration.

Phase 1 at low speed both foils provide vertical lift and lateral forces, which are proportional to the vertical lift but substract to each other while vertical lift add to each other.

So if the boat accelerates, the leeward foil will have too much vertical lift to stay at the same heigh unless its AoA decreases accordingly

If AoA decreases on the leeward foil, It will increase by the same angle on the windward foil.

That is why I do not really understand how you can foil an A-cat with good foil efficiency without changing both Foils AoA separetly, not just changing symetrically the "toe-in"

Hope it is clear enought, sorry if it is not.

 

Cheers

 

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14 hours ago, Bench Warmer said:

...If AoA decreases on the leeward foil, It will increase by the same angle on the windward foil.

...

Decreasing the pitch attitude will decrease the angle of attack on both foils.  Increasing the leeway angle will increase the angle of attack on the leeward foil and decrease the angle of attack on the windward foil.  You need to solve for both angles to get the foil to balance the weight and side force at a particular speed.  You also need to either solve for the center of gravity (crew position) to balance the heeling moment, or you need to vary the side force to balance the righting moment available from the crew.  So at a minimum, it ends up being a problem with three unknowns to solve for simultaneously.

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On 2017-7-13 at 6:23 PM, A Class Sailor said:

Thilo's boat foils downwind in 5 knots and upwind in 7. It has a clever cant system which works automatically and it uses C foils. It has caused a bit of a firestorm, mainly because many class members who understand the rules believe it is not class legal. We await action and clarification from the technical committee.

Really C foils? Werent those discarded as good full foilers?

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4 hours ago, sail(plane) said:

Really C foils? Werent those discarded as good full foilers?

Thilo seems to have done this for a number of reasons, not least because his foils aren't limited by the rules and because he feels it best suits his system that cants the windward foil to a different angle to the leeward one

 

19 hours ago, Bench Warmer said:

That is why I do not really understand how you can foil an A-cat with good foil efficiency without changing both Foils AoA separetly, not just changing symetrically the "toe-in"

A year ago, a few of the top boats were set up so that you could alter the AoA of each board independently. It was found to not help at all and might have actually been slower. I think the main answer to your puzzle is found in leeway which means that the 2 foils work differently to each other. I also suspect that is what drives Z foil development, although this is getting a bit beyond my pay grade!

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Bit of thread drift: I keep being intrigued by Basiliscus' seemingly innocuous comment,

"whether the rudders are forward or aft of the foil could be an interesting question and left to the teams to decide."

 

I do remember canard rudders were used on some (Formula 40 ?) cats many years ago with reportedly good results, although the rationale is not clear to me. But when you get into foiling and horizontal lifting surfaces, I sense there could be significant advantages. For one thing the canard stabilizer lifts instead of pushing down (and effectively increasing the boat weight). But mainly, there's the old saying that canard planes don't stall - provided the unit loading on the forward stabilizer is higher than on the rear wing. Shouldn't this feature be very much appreciated in a foiler?

 

Quote

 

 

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35 minutes ago, Xlot said:

Bit of thread drift: I keep being intrigued by Basiliscus' seemingly innocuous comment,

"whether the rudders are forward or aft of the foil could be an interesting question and left to the teams to decide."

 

I do remember canard rudders were used on some (Formula 40 ?) cats many years ago with reportedly good results, although the rationale is not clear to me. But when you get into foiling and horizontal lifting surfaces, I sense there could be significant advantages. For one thing the canard stabilizer lifts instead of pushing down (and effectively increasing the boat weight). But mainly, there's the old saying that canard planes don't stall - provided the unit loading on the forward stabilizer is higher than on the rear wing. Shouldn't this feature be very much appreciated in a foiler?

 

Another advantage of the canard is that it prevents rudder wash out causing pitchpole, as what happened to TNZ.

However I think that planes with canard need computers to pilot it as they are very sensitive.

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^ Well they already have that covered...if they want to continue down that route.

Rudder/foil on each corner, use as many as you like, for whatever you like, whenever you like!?

 

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Thank you Basilicus,

Of course, the crew weight position + main sheet control,with good coordination will manage the pitch of the boat.

Anybody knows how long is the foiling part of today's A-Cat foil ?

I guess the chord at the "knee" of the foil is around 15 cm ?

Cheers

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7 hours ago, Xlot said:

Bit of thread drift: I keep being intrigued by Basiliscus' seemingly innocuous comment,

"whether the rudders are forward or aft of the foil could be an interesting question and left to the teams to decide."

 

I do remember canard rudders were used on some (Formula 40 ?) cats many years ago with reportedly good results, although the rationale is not clear to me. But when you get into foiling and horizontal lifting surfaces, I sense there could be significant advantages. For one thing the canard stabilizer lifts instead of pushing down (and effectively increasing the boat weight). But mainly, there's the old saying that canard planes don't stall - provided the unit loading on the forward stabilizer is higher than on the rear wing. Shouldn't this feature be very much appreciated in a foiler?

 

Canard planes do not stall because they cannot be allowed to stall the wing.  If they did, they'd flip over backwards.  The canard is designed to stall before the wing, which results in the nose dropping before the canard develops enough control power to stall the wing.  You can avoid stall with an aft tail by limiting the control power - the Ercoupe is a good example.

Every study looking at the drag of trimmed aft tail vs canard vs tandem wing configurations has shown the aft tail has the least drag and the tandem wing has the most drag.  You can make an aft tail have positive lift for trim by putting the center of gravity far enough aft and enlarging the tail to maintain stability.  This is commonly done on freeflight model airplanes.

Some friends and I tried a canard configuration for controlling a wingsail, and we quickly found we couldn't make it work.  The drag on the canard contributed to the unstable moment from the canard, and at a certain angle of attack it was impossible to bring the wingsail back.  We switched to an aft tail, and that was entirely successful.

With regard to sailing hydrofoils, the best location for producing the side force and the best location for producing the vertical lift may not be the same.  That's one reason to consider alternative locations for the rudder.

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6 hours ago, Tornado-Cat said:

...However I think that planes with canard need computers to pilot it as they are very sensitive.

Computer control is not needed for a canard.  Just look at all the successful Burt Rutan homebuilt designs - Variviggin, VariEze, LongEze, Quickie, Voyager - none of which used computer control.  Computer control is needed for supersonic designs that have the c.g. so far back that they are unstable at subsonic speeds, but this isn't required to make a canard stable.

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Thanks Basiliscus, I was thinking to supersonic planes, you are right that Rutan planes do not need computer.

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The Wright Flyer was a canard, pretty sure it didn't need a computer...

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In the ongoing debate "Are Z foil that much slower ?"

After Basilicus explanation, I try to crunch basic numbers, and according to the reduction in righting moment I would state that the "Sail driving force " with full righting moment is around

(with apparent wind à 17°/ windward):

1- 150 N for a Z foils package both @ 45° (lift breakdown: 70% leeward / 30% windward)

2- 250 N for a "open L" foil @ 67° instead of 90° (leeward foil only)

Well it is not the result of sophisticated CFD program,

just my HP12C (a collector hand computer)

Hope it can help in the debate

Cheers

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Please read

2- 200 N for a "open L" foil @ 67° instead of 90° (leeward foil only)

Instead of 250 N

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On 7/16/2017 at 5:34 PM, Basiliscus said:

Decreasing the pitch attitude will decrease the angle of attack on both foils.  Increasing the leeway angle will increase the angle of attack on the leeward foil and decrease the angle of attack on the windward foil.  You need to solve for both angles to get the foil to balance the weight and side force at a particular speed.  You also need to either solve for the center of gravity (crew position) to balance the heeling moment, or you need to vary the side force to balance the righting moment available from the crew.  So at a minimum, it ends up being a problem with three unknowns to solve for simultaneously.

Thank you Herr Professor.

"a problem with three unknowns" is simply the best and most concise explanation of twin z foil sailing I have encountered - and at last my understanding of this phenomena has progressed out of the chop and on to smooth water.  

thanks again.

 

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1 hour ago, Sailbydate said:

Puffer Jacket for yachts.

No twist evident. Looks a convenient foil, but pretty inefficient. 

Agree, but the general idea could have a lot of potential with the possibility to alter more than just the twist of the wing.

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Imagine if you broke a conventional mast at sea and were able to rig one of these - not sure about racing but maybe as jury rig?

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2 minutes ago, Alpina said:

What happens if inflated with helium instead of air?

Up up and away on my beautiful.....

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