Finding the balance points for land yacht can achieve better performance and easier control.

Many people just bung a mast and sail on a 3 wheel buggy and hope for the best but there is a better way.

For the frame firstly you need to have enough weight on the front wheel to steer safely and for good maneuverability, the exact weight needed will vary for every sailor and surface.

OK if the balance point was exactly in align with the back axle with the pilot seated the front wheel would have zero weight on the ground... if it was further back than that the front wheel would rise.

So knowing that.... the balance point MUST be in-front of the rear axle line.... to get the exact point try a bit of 4x2 timber or a brick on the ground place the yacht frame with the mast fitted on it [try about 300mm in-front of the axle line] and do a few trial tests to find the balance point... when you find it mark that point with a permanant marker.
That point WILL vary from an adult to a teenager to a small kid

That balance point is a start to finding the centre of resistance CR which will be some where between the balance point and the rear axle line.
The CR will vary depending on tyre size of the front/ rear tyres, tyre tread / pattern, inflation pressure and the pilot weight.
In theory you should be able to push or pull on the CR point with pilot seated and the yacht should equally move sideways..... now this in practicality would be extremely hard to do.

I will try and answer this as we go along..

desertyank said...

Is there a point on the yacht, either a measurement from the rear axle, or a % of the wheelbase from the rear axle that works better than others? Seems like anywhere between the 2 axles could work, but I'm guessing there is a 'sweet' spot for any given yacht.

Over the years it has been found that lots of weight over the front wheel is not good (like the Manta) move the mast back and the steering becomes easier... move it to far back and the back wheels break traction to easily.... and that point will vary depending on the pilot weight and the wheels and tyres.

Also, on the 'class-5 design' thread, someone mentioned that 10 kilos was about right for the loaded yacht front wheel weight. Does anyone out there have a different weight they use with good results?

That weight I can't recall but could be right it will depend in the surface, the class5 promo actually has a minimum weight specified. A soft and loose surface WILL need more weight on the front wheel to enable turning.

My LLM works great, but must have a balance point pretty close to the rear axle, because it will pop a wheelie on some quick spin turns. I will measure its front wheel weight, and balance point when I can

Gizmo said...

I will try and answer this as we go along..

desertyank said...

Is there a point on the yacht, either a measurement from the rear axle, or a % of the wheelbase from the rear axle that works better than others? Seems like anywhere between the 2 axles could work, but I'm guessing there is a 'sweet' spot for any given yacht.

Over the years it has been found that lots of weight over the front wheel is not good (like the Manta) move the mast back and the steering becomes easier... move it to far back and the back wheels break traction to easily.... and that point will vary depending on the pilot weight and the wheels and tyres.

Also, on the 'class-5 design' thread, someone mentioned that 10 kilos was about right for the loaded yacht front wheel weight. Does anyone out there have a different weight they use with good results?

That weight I can't recall but could be right it will depend in the surface, the class5 promo actually has a minimum weight specified. A soft and loose surface WILL need more weight on the front wheel to enable turning.

My LLM works great, but must have a balance point pretty close to the rear axle, because it will pop a wheelie on some quick spin turns. I will measure its front wheel weight, and balance point when I can

Thanks Gizmo !

Now if you have your head around that, the whole things changes when you get up on 2 wheels.
As the yacht now pivots in a line between the front wheel and one of the rear wheels the direction of resistance now changes to right angle to that line. And the CR moves forward because the sideways traction is now spread over 2 wheels instead of 3, and this again is dependant of tyres and inflation pressures.
And at this point add in wheel camber angles and bearing twist BUT the CR should by my thoughts should still be around the Centre of Balance point.

Sails: and finding the various point on them.....
The terminology of sails, wings, soft wings ALL mean the same... and all work the same to move a land yacht by having a different air pressure on each side of the sail.
For more info on this just google "How a sail works" or "How a wing works"

What we also know is that a low aspect sail will give more power and less speed for a given area, and the opposite of that a higher aspect ratio sail gives greater speed but less power.

The rig setup on a land yacht (class5, promo, + Mini Yachts) is quite different than other wind powered yachts by using an unstayed mast. Yes there are water yachts that use an unstayed mast like the 'Finn', 'OK' and 'Laser' classes but they adjust those rigs in a totally different way to land sailors. Water yachts normally set their rig to suit a wind speed and apparent wind speed is normally not of a huge concern apart from craft like High speed sail boards and Catamarans.

Land sailing needs a rig that will give maximum power at slow speeds and as the yacht increases in speed the rig needs to change to accommodate the increase of the apparent wind speed and direction. (like an auto transmission in a car)

The use of sailboard masts on land yachts in recent years has changed the sport some what, Class5 and Promo Class yacht rules still specify an aluminium mast set up where as the mini class can use any material including aluminium, fibre glass or carbon fibre.

Gizmo said...


As the yacht now pivots in a line between the front wheel and one of the rear wheels the direction of resistance now changes to right angle to that line.

I'm not sure that it does -- if so then you would accelerate uncontrollably. The yacht will tip around the axis between the leeward wheel and the front wheel, sure, but the vector of resistance will always be at 90 degrees to the direction that the wheels are pointed in. I guess if you've got a lot of toe-in on the rear wheels then it might just change...

You could test this by raising the point at which you attach the bridle, so the yacht would start to tip before it started to skid.

I had a lot of trouble sorting out aus230, mainly in strong winds, I found that if I moved my body back to get some weight of the front wheel the back of the yacht washed out and I had poor steering around corners. I had more success changing the sail rake. I was surprised to see how much the mast racked back with only a couple of degrees adjustment. (I found it best to only adjust a couple of degrees at a time)

I think it all goes out the window when sailing on a different surface, the surface at the sandgropers is loose,on top of a hard surface and combined with lots of corners is the hardest to set up. Lake Lefroy salt provides plenty of traction so maybe the weight could be further back.

On sand the pics of class5 yachts of the I have seen have there sails racked right back. Is this because sand has plenty of grip stopping the back of the yacht from washing out.

So the more I can learn about this balance thing the better.

Cheers
Vic

nebbian said...

I'm not sure that it does -- if so then you would accelerate uncontrollably. The yacht will tip around the axis between the leeward wheel and the front wheel, sure, but the vector of resistance will always be at 90 degrees to the direction that the wheels are pointed in. I guess if you've got a lot of toe-in on the rear wheels then it might just change...

You could test this by raising the point at which you attach the bridle, so the yacht would start to tip before it started to skid.

If some would like to try this it would be great but on the yachts that I have sailed when a rear wheel is lifted even slightly the front wheel normally flattens out a little more, and often in sand the yacht crabs sideways slightly, the steering is altered just a bit to compensate, this is easy to see by the tyre marks left on the sand.

Nikrum said...

Going on what has recently been discussed I would tend to think that the apparent wind is a weaker force requiring a Free Rolling system and High Sideways resistance in order to make full use of it ie; Low resistance bearings and a smooth Tarmac surface. Whereas the Water Craft, a for, mentioned would have too higher forward resistance to get any great value from the apparent wind??? No?(Perhaps I can upset someone else[}:)]) It seems the New Skinny has what it takes to get moving well given the room to accelerate to a reasonable working speed or Air Movement high enough to have the same effect.
Ron

Apparent wind is NOT weaker than normal wind its all the same stuff.... Try this, go for a drive in a car.
Find a road where the med / strong wind is coming over the back of the car, then drive down the road at 60kmh and put your arm out the window how much force is on your arm? If the true wind was 20kmh [from behind the car] and you are now driving at 60kmh in that same direction you will have 40km/h wind hitting your arm. And think about how much area is on your arm then think how big a sail is.... that's how much wind force your playing with.... LOTS then turn around and lets feel what 80kmh wind feels like 20kmh [true wind + 60kmh car speed] = 80kmh

How about we explain apparent wind this way.....
For example, you are riding your bicycle on a completely calm day with no wind. However, you can feel wind on your face and it feels stronger as you pedal faster. That is because as you move forward, the motion creates its own wind.

Now imagine you are riding your bicycle but there is a strong breeze coming at you from the right. This natural wind is called "true wind".

When you add this side wind to the cycle ride, the wind the rider feels is now somewhere between the true wind (from the side) and the man made wind (from ahead). This resultant wind is know as the 'apparent wind' and will have a speed and apparent wind angle, measured from the direction of travel to the apparent wind angle.




www.greenbird.co.uk/about-the-greenbird/how-it-works

Sails...
I'm going to start at the very basics and going to work up from there to try and get people across the subject.

Lets start with a VERY basic sail...simple triangle, no luff curve, no battens. (A)



(B) Shows what the cross section of that sail would approx be, the maximum curve would be at about 1/2 way across the sail, this would give lots of side force but would give only a small amount of forward force.

(C) Shows what the cross section of that sail would approx be, the maximum curve would be at about 1/3 way across the sail, this would give some side force but would also give forward force.

(D) Shows what the cross section of that sail would approx be, the maximum curve would be at about 1/4 way across the sail, this would give less side force but would also give lots of forward force.

To change the shape from B-C-D, this can be easily done by using a downward force at the 'tack' of the sail wich is where "Downhaul" comes into action.

Any quesions so far?

Ron we are a l-o-n-g way from the end, just need to cover the basics first.

Now with a real life sail thats not square-ish you will need to do some guess-timations to find the balance mid point along the force line or "Aerodynamic Centre" of a sail (not quite but is acting as one).
That balance point is in relation to area and shape of the sail.
The "Centre of Effort" point does and will change in real life depending on downhaul and actual sail setup.
Using what I have explained in this thread here is what it might be on a real sail...



People with a setup sailboard rig can test this... put the mast step on the ground and hold the boom with 1 hand at about 1/4 - 1/3 from the front there is a point that the sail will sit there, not wanting to swing forward or back..... your hand is now in align with the "Aerodynamic centre" and futher up that line on the sail will be the "Center of effort"

Gizmo said...


Any questions?

You've shown how to calculate the centre of effort for a sail with a fat head, but haven't taken twist into account -- why is this? Experimentally the centre of effort is a long way further down than is indicated in the diagrams above.


Note the twist in this sail: