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