Forums > Land Yacht Sailing Construction

Class Five Design

Reply
Created by blake52 > 9 months ago, 3 Dec 2010
landyacht
WA, 5921 posts
8 May 2011 8:24PM
Thumbs Up

couple of things to note. with the RAF you had the sheeting forward of mid boom , so no matter how hard you sheeted you were never getting all the sail had to offer. now you have a rear sheeted unit you are able to get the power out of the sail to the yacht. Tall skinny sails get twitchy at speed, especially on a frame the size of a 5.
couple this with your soft Y frame chassis and heavy centred body weight, the yacht will want to get out of balance fairly easy.
can i suggest to get a freind to help and do Kiwi 307's tests for the 3 centers and report back

Nikrum
TAS, 1972 posts
9 May 2011 12:16AM
Thumbs Up

C'mon Paul,p happened.. Do we have to go back to the CofG's and CLR's etc.? That is where it all happened with Kiwi307. I can find the C of G OK but what are the other 2 again??
Ron

Clemco
430 posts
9 May 2011 6:00AM
Thumbs Up



The Center of Gravity will do fine Ron. Now rake the mast back so the estimated centre of effort is directly above your C of G when the sail is fully sheeted in. Simple.
You will need that mast extended too.

Nikrum
TAS, 1972 posts
9 May 2011 10:27AM
Thumbs Up

Clemco,
That is lookin' highly techanogicle but not too confusing.. I will try it and see.
Thanks,
Ron

landyacht
WA, 5921 posts
9 May 2011 8:32PM
Thumbs Up

kiwi307 said...

[The other 2 points of interest for a design on paper are, 1) the centre of gravity with pilot in place, and 2) the centre of lateral resistance. Neither of these have I been able to find anything other than a "suck it and see" method (except huge amounts of complicated maths). Bill Finch showed me his method about 29 years ago and I still use it.
Centre of gravity, balance the whole yacht (with pilot) on a brick and move the yacht back and forwards till you have the CofG noted, it's where it balances.
Centre of Lateral resistance is found by tying a rope on and try to drag the whole yacht sideways (peagravel or wet grass is easiest). With a bit of luck and a fair bit of empirical testing (otherwise known as messing about) you will find this point.
If all 3 points line up, ie Cof E directly above the C of G which co-incides with the CLR, you will have a really sweet yacht with minimal steering input to keep straight. Strangely it also seems to be the fastest ones too!


thats how you find them . the Bill Finch method as shown to kiwi307, and never improved on . It was hidden in a post back on page 7
glad i could help clear that up I will be trying it on my new mini myself

Gizmo
SA, 2865 posts
10 May 2011 12:28PM
Thumbs Up

landyacht said...
. the Bill Finch method as shown to kiwi307, and never improved on . It was hidden in a post back on page 7
glad i could help clear that up I will be trying it on my new mini myself



That's actually a method used 25+ years ago... things have moved on since then just like plastic seats and near vertical steering on land yachts, what you are measuring in that method is the "Centre of Gravity" of that object. It might have been a guide then but hardly reliable particularly in the current information technology age.
www.grc.nasa.gov/WWW/K-12/airplane/cg.html

Infact you should be looking at is "Aerodynamic Centre"
www.grc.nasa.gov/WWW/K-12/airplane/ac.html

also keeping in mind the "Centre of Pressure"
www.grc.nasa.gov/WWW/K-12/airplane/cp.html

"It has been found both experimentally and theoretically that, if the aerodynamic force is applied at a location 1/4 chord back from the leading edge on most low speed airfoils, the magnitude of the aerodynamic moment remains nearly constant with angle of attack."

The "Centre of Effort" as it has become known DOES vary up and down this has been known for years and is NOT a static point, water sailors have used this concept in strong wind sailing to reduce the healing motion of the yacht.



nebbian
WA, 6277 posts
10 May 2011 5:22PM
Thumbs Up

Gizmo said...

Infact you should be looking at is "Aerodynamic Centre"
www.grc.nasa.gov/WWW/K-12/airplane/ac.html

also keeping in mind the "Centre of Pressure"
www.grc.nasa.gov/WWW/K-12/airplane/cp.html

"It has been found both experimentally and theoretically that, if the aerodynamic force is applied at a location 1/4 chord back from the leading edge on most low speed airfoils, the magnitude of the aerodynamic moment remains nearly constant with angle of attack."



That NASA site is great, hey It's got a really good explanation on there as to why the traditional "Air flows further over the top" explanation of lift is completely wrong.

However I think you may have those terms mixed up -- the aerodynamic centre is useless in a landyacht because you've still got a moment. What you need is a point that is given by the aerodynamic centre plus the offset for the torque given by the moment....

which is called the Centre of Pressure

From the site:
The aerodynamic force can then be resolved into two components, lift and drag, which act through the center of pressure in flight.

So the centre of pressure is just another name for the term "centre of effort" that we sailor-types use.

Aerodynamic centre is useful when designing an aeroplane, but not really all that useful for sails.

Gizmo
SA, 2865 posts
10 May 2011 8:17PM
Thumbs Up

Aerodynamic centre is usually the combined vectors of the main wing (port & starboard sides) AND the horizontal tail wing but also applies to a single wing / delta wing, but they are formed from the vectors of each separate wing section.

So when is the transition point of a sail to a soft wing?

I had a similar conversation with a sail maker (and one of those that made Australia 2 sails) His attitude changed after sailing a land yacht, he then regarded land yachts as having a vertical soft wings. Land Yacht sails are more a kin to high performance hang glider wings or sailplanes.
I have often thought if you were traveling below true wind speed it acts like a sail when you get above true wind speed and generating significant amounts of apparent wind it performs totally differently and much more like a wing.
Water sailors that try fast land yachts are often staggered at the difference.

Nikrum
TAS, 1972 posts
10 May 2011 8:58PM
Thumbs Up

Yeah Right! I ain't being sucked into this one!! Don't want to get misunderstood again.. Next time I get a Sail Re-cut I will send it to one of you Boffins.. You've stuffed my head.
Ron
PS you build 'em I'll Fly 'em.

nebbian
WA, 6277 posts
10 May 2011 7:43PM
Thumbs Up

Gizmo said...

Aerodynamic centre is usually the combined vectors of the main wing (port & starboard sides) AND the horizontal tail wing but also applies to a single wing / delta wing, but they are formed from the vectors of each separate wing section.


Again I believe that it's the centre of pressure that you're talking about, not the aerodynamic centre. The thing that gets calculated for the whole aircraft is the centre of pressure, while aerodynamic centre is used in isolation when considering a specific airfoil.

But I'm happy to be proven wrong

landyacht
WA, 5921 posts
10 May 2011 8:12PM
Thumbs Up

Gizmo said...

landyacht said...
. the Bill Finch method as shown to kiwi307, and never improved on . It was hidden in a post back on page 7
glad i could help clear that up I will be trying it on my new mini myself



That's actually a method used 25+ years ago... things have moved on since then just like plastic seats and near vertical steering on land yachts, what you are measuring in that method is the "Centre of Gravity" of that object. It might have been a guide then but hardly reliable particularly in the current information technology age.
www.grc.nasa.gov/WWW/K-12/airplane/cg.html

Infact you should be looking at is "Aerodynamic Centre"
www.grc.nasa.gov/WWW/K-12/airplane/ac.html

also keeping in mind the "Centre of Pressure"
www.grc.nasa.gov/WWW/K-12/airplane/cp.html

"It has been found both experimentally and theoretically that, if the aerodynamic force is applied at a location 1/4 chord back from the leading edge on most low speed airfoils, the magnitude of the aerodynamic moment remains nearly constant with angle of attack."

The "Centre of Effort" as it has become known DOES vary up and down this has been known for years and is NOT a static point, water sailors have used this concept in strong wind sailing to reduce the healing motion of the yacht.





are you suggesting we should be leaning out more , I stopped doing that 25 years ago , when Bill and Stan made his first layback seat?
I must agree with the CE moving back as you sheet in and accelerate, weve kinda accepted that for 20 years

Gizmo
SA, 2865 posts
10 May 2011 10:04PM
Thumbs Up

Landyacht, The picture shows by feathering the top of the sail the CE moves down and with a raked mast and strong down haul it will then move forward just a bit.

The lift on an airfoil is a distributed force that can be said to act at a point called the center of pressure. However, as angle of attack changes on a cambered airfoil, there is movement of the center of pressure forward and aft. This makes analysis difficult when attempting to use the concept of the center of pressure. One of the remarkable properties of a cambered airfoil is that, even though the center of pressure moves forward and aft, if the lift is imagined to act at a point called the aerodynamic center the moment of the lift force changes in proportion to the square of the airspeed.

en.wikipedia.org/wiki/Pitching_moment

As we have said before land sailing is a bit more than just bunging a sail on a 3 wheeled frame, most things in the sport have been a case of trial and error, and it has changed a lot over the years

nebbian
WA, 6277 posts
10 May 2011 8:54PM
Thumbs Up

Well, you can use aerodynamic centres if you want. You can even choose to take moments around the leading edge if you feel like it, which would make more sense for a landyacht.

Using the centre of pressure method means you don't have to do all that tedious mucking around with moments and torques just to calculate where the sail will pull from.

Nikrum
TAS, 1972 posts
10 May 2011 11:27PM
Thumbs Up

Posted - 09/05/2011 : 6:00 am Was supposed to happen today but "Life" once again got in the way. No matter as a couple of Rare Steaks, a rasher of Bacon and some Roasted veg washed down with a couple of good bottles of red was most definitely enjoyed by all So. Munyana. Munyana is good enough for me

Hasta Munyana amigos
Ron

Clemco
430 posts
11 May 2011 8:23AM
Thumbs Up

That raked position would be a good place to start with Ron. You do the fine tuning of the mast rake on the beach. It's the only way.
You also mentioned you felt the yacht seemed to be breaking out at the rear. Could this possibly just be the fiberglass axles bending back and causing the yacht to round up into the wind? If you find the yacht snaking all over the place I think that could be the reason. By the way,.. Nice looking sail.

Nikrum
TAS, 1972 posts
11 May 2011 1:40PM
Thumbs Up

Clemco said...










The Center of Gravity will do fine Ron. Now rake the mast back so the estimated centre of effort is directly above your C of G when the sail is fully sheeted in. Simple.
You will need that mast extended too.


Thanks Clemco, It don't look too bad even if I do say so meself.. Looks close to '100Kmph to me. Now Alls I needs if a Gentle Zephyr around 25Kts.[}:)]
Ron

landyacht
WA, 5921 posts
12 May 2011 8:27PM
Thumbs Up

ron , you will need to adjust that rear pulley posn on the boom. get it running straight up and down, not angled, otherwise you are wasting energy trying tp push the boom into the mast.
dont be shy to let the foot of the sail off quite a bit , it will then be able to accelerate from low speedsrather than have you dribbling around trying to get going. the skinny sails are hopeless for trying to get going from a start in lighter breezes, so always try to start off upwind or at worst reaching to get speed before turning off downwind

Nikrum
TAS, 1972 posts
12 May 2011 10:47PM
Thumbs Up

I can do that Paul.
You're right it is a right P in the A to get moving in lighter winds.. I am just going to not be so Bloody Stubborn and use the other sails until the winds cooperate with me. I am becoming paranoid thinking that nature has it in for me.. Winds look good until I break out the LY's jump in and get 50mtrs and they just go away. Bugger.
Ron

landyacht
WA, 5921 posts
12 May 2011 8:57PM
Thumbs Up

skinnies are always tricky to get going, really let that foot out, and keep an eye on it as it will want to flatten out on its own

Nikrum
TAS, 1972 posts
13 May 2011 9:06PM
Thumbs Up

Moving this over to Nikrum's Page
Ron

landyacht
WA, 5921 posts
13 May 2011 7:57PM
Thumbs Up

Gizmo said...

Landyacht, The picture shows by feathering the top of the sail the CE moves down and with a raked mast and strong down haul it will then move forward just a bit.

The lift on an airfoil is a distributed force that can be said to act at a point called the center of pressure. However, as angle of attack changes on a cambered airfoil, there is movement of the center of pressure forward and aft. This makes analysis difficult when attempting to use the concept of the center of pressure. One of the remarkable properties of a cambered airfoil is that, even though the center of pressure moves forward and aft, if the lift is imagined to act at a point called the aerodynamic center the moment of the lift force changes in proportion to the square of the airspeed.

en.wikipedia.org/wiki/Pitching_moment

As we have said before land sailing is a bit more than just bunging a sail on a 3 wheeled frame, most things in the sport have been a case of trial and error, and it has changed a lot over the years


you got me thinking Gizmo, having just tryed bill/kiwi's method on the new minimini, given all your newly found up to date info, can you please suggest a simple set of ways to balance up a new yacht for us, one that can be done on the back lawn , with tools as simple as a rope and a brick.
that way we laymen can get up to date as well

Gizmo
SA, 2865 posts
13 May 2011 10:30PM
Thumbs Up

How about we start a new thread on the subject?

www.seabreeze.com.au/forums/Land-Yacht-Sailing/Construction/How-to-find-the-balance-points-for-a-Landyacht/

Nikrum
TAS, 1972 posts
15 May 2011 11:50AM
Thumbs Up

Clemco


New Zealand

264 Posts

Posted 09/05/2011, 6:00 am

HMMMMMMMMMMMM!!![}:)] Clemco, are you suggesting I am FAT!!!!??

It would appear that you have a pretty fair eye for balance.. I have just come in from the shed, buggering about with the CofG of Occum's Razor.. As near as I can make out your estimate would suggest I am a tad on the tubby side..Move your suggested CofG forward by around 25 to 32MM and you would have it Dead On, not bad though, not bad.
The sail/mast cant/rake would feel pretty well on though on wet, low friction Tarmac it tends to move the whole thing sideways.

Ron

Clemco
430 posts
15 May 2011 10:13AM
Thumbs Up

Ah... But did you have your Helmet goggles and drysuit on Ron???

landyacht
WA, 5921 posts
15 May 2011 8:52PM
Thumbs Up

how smooth have your A/C tyres become ron.
you may need to consider cutting some grooves into thetyres, but Im starting to wonder about those carbon axles

Nikrum
TAS, 1972 posts
15 May 2011 11:22PM
Thumbs Up

Thanks Paul,
They are pretty smooth. I probably should turn them on the Rim. The Carbon Axles are Stiff and don't bend a lot under heavy gusts. The razor stands on one wheel quickly. As soon as I can get some footage you will be able to see for yourself. The footage from a couple of days broke in the saving of it, Andre is going to take a look and see if he can repair it. The alternative is to re-shoot it when I get some favorable winds.
The tires grip fine on dry tarmac, I think most of the trouble is the Gravel that is spread liberally about.
The Razor does perform well on clean tarmac
Ron

aus230
WA, 1659 posts
20 May 2011 9:03PM
Thumbs Up

I have sourced a length of aluminum tube for my next yacht axles, maybe someone could tell me if it would be suitable for axles, it is 6082 and t5 temper. is there a lot of strength difference to 6061 t6 temper. all other measurements are the same

dia 48.40
wall thickness 4.47

Cheers
Vic

landyacht
WA, 5921 posts
20 May 2011 9:15PM
Thumbs Up

aus230 said...

I have sourced a length of aluminum tube for my next yacht axles, maybe someone could tell me if it would be suitable for axles, it is 6082 and t5 temper. is there a lot of strength difference to 6061 t6 temper. all other measurements are the same

dia 48.40
wall thickness 4.47

Cheers
Vic

T5 temper means it basically annealed for use in benders. ie specialyy made for bending.
I have a 1.3m peice of old T6 scaff from that you can have on your next visit . I will look out for some more

aus230
WA, 1659 posts
20 May 2011 9:22PM
Thumbs Up

Thanks Paul , I thought that was the case, There is another place that I have not tried in Bundury. Failing that I need 3 pieces 1.2m. Dam it was a lot easier to get things when I worked in the mines.
Cheers
Vic

cisco
QLD, 12310 posts
21 May 2011 1:09AM
Thumbs Up

aus230 said...

Thanks Paul , I thought that was the case, There is another place that I have not tried in Bundury. Failing that I need 3 pieces 1.2m. Dam it was a lot easier to get things when I worked in the mines.
Cheers
Vic


Smart Aluminium list four sizes in T6 tube.
Extruded:- 63.5mm X 6mm (6060 T6), 63.5mm X 6mm (6061 T6) and 76.2mm X 4.75mm (6060 T6). Those two sizes will telescope with 3.2mm slop.

Scaffold:- 48.41mm X 4.47mm (6061 T6) That size will telescope into the 63.5mm tube with 3.09mm slop.

Their nearest shop to you is or was 34 Boulder Road, Malaga, Perth. Ph. (08) 9248 7148

Should be a couple of yachts in it if you buy a 6m length of each.



Subscribe
Reply

Forums > Land Yacht Sailing Construction


"Class Five Design" started by blake52