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New Build - Steering geometry question

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Created by markkiwi 1 month ago, 18 Jan 2019
markkiwi
6 posts
18 Jan 2019 2:36PM
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I'm looking into building my first land yacht, simply for leisurely cruising along a beach (rather than competition or feeding the speed demon) so not at all worried about conforming to class standards or sizes for my build.

I like the look and simplicity of the Lake Lefoy Mini plans but also like the compactness of the blokart design for transporting it in the back of a car. (The jury is still out on which way I'll go.)

I'm thinking I'll try picking up a cheap windsurfer sail during the off season, and if I'm lucky, perhaps carbon mast, else I'll have to make an aluminium mast as per the Lefoy plans.

While studying the Lake Lefoy Mini plans, I started to think about the detail of the steering side of things..I found a post by PiperPawnee entitled 'my-homebrew-build', that mentioned aligning the steering axis so that an imaginary line through the steering axis would ideally touch the ground directly under the centre of the wheel (for avoiding nasty speed wobbles)

I did some googling about the subject of steering geometry and came across a BMX web site that explains if the wheel contacts the ground behind the steering axis line, it creates stability and wondered if this would be useful in my future build. www.gsportbmx.com/2004/05/steering-geometry/

I've hunted through the forums but can't find anything specific that discusses this subject (other than PiperPawnee's post) so wondered what advise the forum members could offer.

sn
WA, 2509 posts
18 Jan 2019 5:38PM
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Kiwi - those Lefroy plans are gold!!
Don't mess about too much with them as they are proven to be simple to build, and they sail very well.

Landyacht's gospel = "LIGHTER IS RIGHTER"

Follow the guidelines, keep it simple, keep it light.
The biggest expense in a Lefroy mini, is the cost of the wheels and pulley blocks, virtually everything else can be scrounged [if you are good at scrounging!]

Buying a Blokart - new they start at a couple of thousand.....

The Lefroy mini breaks down for easy transport - the rear axles and the back rest can both be "unplugged, being secured by either bolts - or spring clips.

The front axle assembly can also be removed easy enough as well.

Stick to plastic wheels [fallshaw are the ducks guts - being virtually indestructible.]

About the only improvements to the original Lefroy plans are:
: vertical mast step - works well with unmodified sails.

: reinforcing strap stitch welded down the side of the mast step, under the chassis spine and up the other side.
[with severe thrashing, mast steps were eventually being torn out at the welds due to metal fatigue]

: seal up the rear of the chassis spine tube by welding a plate over the open tube.
[stops mud, salt water etc from accumulating inside the hollow tube, and helps prevent cracking of welds due to twisting of the chassis spine.

markkiwi
6 posts
19 Jan 2019 4:59AM
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Thanks sn. As usual I'm probably overthinking things! It's quite possible the Lefroy mini plans do set the wheel contact point at or behind the axis of rotation and hence produce stable steering...is a bit hard to tell from the plans.
Yup I found those mods...but just to make it clear for a newbee...If I set the mast to 90 degrees there is no requirement to modify a sailboard sail as described in the plans? (I doubt the wife's sewing machine or nerves would cope with something like that! )

Looking at pictures of sailboard sails, their booms/handle things go around the sail whereas a guess we want more of a single boom system so maybe a sail mod is required....better do more research!

I'll have to find a local supplier in NZ for those fallshaw wheels everyone raves about...sounds like that's the way to go. So far I've only seen barrow wheels in places like Bunnings and they don't look the best. Lots to learn.

(Am trying to make 2019 the year I do the things I've been wanting to get into for some time but keep putting off)

Cheers!

Bynorthsea
95 posts
19 Jan 2019 6:54PM
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For steering angle I have always set mine up to be neutral, the point of contact and the steering angle centre line coinciding, for angle I prefer 35/40 deg, just that bit more positive than 30 particularly on soft surfaces. When your thinking about sails to use uncut requires engineering and a little sewing, cut sails require a lot of sewing. I started of on cut sails but now use uncut for performance. Both choices really need you to start off with the right shape of sail, so not any old windsurf sail. Have a look back at my photos they should give you an idea of what's involved.
Good luck

Hiko
1189 posts
24 Jan 2019 3:48AM
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Specialist Wheels and Castors Ltd in 24 Sylvia park Road Auckland have Fallshaw Wheels ,bearings, ribbed tyres ,tubes etc.

I bought some from them about a year ago

PiperPawnee
8 posts
24 Jan 2019 10:50AM
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I'm glad someone read my old thread! (also - it was a huge fluke that I happened to read this forum today, haven't been landsailing in ages...)

From what I remember, the steering geometry of my landyacht was basically stolen from the Lefroy. The imaginary line being neutral gives nice handling that doesn't get too scary when the wind picks up. A super lightweight build may give you the edge when racing but given the unavoidable weight of the pilot, personally I'd rather be stronger for a fairly small % increase in weight.

Good luck with your build - take pics!

markkiwi
6 posts
24 Jan 2019 4:44PM
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Select to expand quote
Hiko said..
Specialist Wheels and Castors Ltd in 24 Sylvia park Road Auckland have Fallshaw Wheels ,bearings, ribbed tyres ,tubes etc.

I bought some from them about a year ago


Thanks Hiko.
I had found that supplier but wasn't sure if they were the Fallshaw wheels everyone talks about.. I'm still trying to get my head around what the codes mean ie their 4.80 / 4.00 - 8 Pneumatic Wheel I'm assuming is the one to use...it has dimensions as 395mm Diameter x 78mm Hub Width x 25.4mm Bore.
From this I assume the wheel diameter is 395mm, and the 78mm Hub width will determine axle length but what is the hub diameter/tyre inner diameter? ... I'm guessing I need to know this to get replacement tyres and tubes... there must be some standard sizes.

markkiwi
6 posts
24 Jan 2019 4:45PM
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Select to expand quote
PiperPawnee said..
I'm glad someone read my old thread! (also - it was a huge fluke that I happened to read this forum today, haven't been landsailing in ages...)

From what I remember, the steering geometry of my landyacht was basically stolen from the Lefroy. The imaginary line being neutral gives nice handling that doesn't get too scary when the wind picks up. A super lightweight build may give you the edge when racing but given the unavoidable weight of the pilot, personally I'd rather be stronger for a fairly small % increase in weight.

Good luck with your build - take pics!


Cheers! Will do!

Hiko
1189 posts
24 Jan 2019 6:05PM
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SWC code for these wheels is 8x250PW(NB) They don't call them Fallshaw but they are
The code for the ribbed tyres is TKE 813-A 480/400 x8 2 ply industrial S369. You don't want the knobbly ones
The tubes are TKW 820. 480/400x8 TR13
You need to decide what bearings you are going to use and ask them to supply both bearings and bushes to suit the wheels Their prices on the bearings are the best I have found in NZ I used 47x20 6204 2rs bearings but I think the
42 x20 6004 bearings are a better bet as the plastic bushes for them are thicker
20 mm axles are a good size for these yachts

markkiwi
6 posts
25 Jan 2019 7:56AM
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Select to expand quote
Hiko said..
SWC code for these wheels is 8x250PW(NB) They don't call them Fallshaw but they are
The code for the ribbed tyres is TKE 813-A 480/400 x8 2 ply industrial S369. You don't want the knobbly ones
The tubes are TKW 820. 480/400x8 TR13
You need to decide what bearings you are going to use and ask them to supply both bearings and bushes to suit the wheels Their prices on the bearings are the best I have found in NZ I used 47x20 6204 2rs bearings but I think the
42 x20 6004 bearings are a better bet as the plastic bushes for them are thicker
20 mm axles are a good size for these yachts


Sweet! Thats the detail I need. I'll flick them an email and ask for a quote.
Cheers!

markkiwi
6 posts
Sunday , 17 Feb 2019 1:47PM
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Wheels ordered! ($270 delivered)
I had some problems getting quotes using the online form and via phone, but an email has done the trick
I couldn't get the spacers for the 42mm OD bearings as they have to get them in, so have gone with the 47mm bearing setup for now.
I've told the supplier I'll buy the 42mm spacers when they come in late this month. Then I'll source some bearings and have them on hand to swap out as required.

Picked up a kawasaki 355mm metal cut-off saw using airpoints, and scrounged some 1" square small gauge tubing to practice welding on.
I'm thinking I'll make some jigs to help hold everything in place when I weld the frame and steering sections. Good opportunity to practice welding (I've got my brothers mig welder lined up to borrow)

Now I'm trying to source the steel, It was suggested to me I try a scrap metal dealer, else I'll have to find a local engineering place.

Also keeping my eye out for a cheap wind surfing sail....not sure what the normal cost is for a second hand sail.

At least I'm progressing....

Hiko
1189 posts
Sunday , 17 Feb 2019 6:21PM
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Most of the steel I used on my minis I sourced from a local exhaust tube shop Main spine ,mast step, steering head,etc
I used old snow skis back to back for the axles mounted in a section of channel across the rear of the tube spine
Snow skis can be picked up second hand here for next to nothing I know of a house locally that has used them for fence palings! They make great mini landyacht axles.
My exhaust shop had a great range of tube sizes and he would cut and supply any length unlike a lot of steel suppliers.
May be suitable for you
Second hand windsurf sails I have paid from 20 dollars to a really nice suitable one that required minimal alteration 120 dollars



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"New Build - Steering geometry question" started by markkiwi