Howdy all

have been trawling though some past posts and see there has been some discussion re chassis tube material.
It appears at present due to mining BOOM, drill core tube is in short supply. I have contacted some steel/tube supply co's. and a supplier of the specific product, they all plead insanity or are unable/dont want to help! Here in sleepy hollow (SA) salvage yard operators look at you with blank stares.

What sort of material have you used? It appears majority of chassis are steel grades, have many tried aluminium? Lets talk about all materials that have been sourced and used!

When posting, sometimes acronyms are employed, can we please spell out the term early in the post so we understand the meaning then revert, eg. CRW350 (?). Thanks blokes and girls.

The RC landyacht site that I was directed to by Landyacht is very informative, same rules apply to full as scale models. In fact scale need to be more accurate than full . Who remembers Hardi Krueger in "Flight of the Phoenix". Gee I must be old, but, the film is aired at least annually.

Hillsie, you are a regular contributor, can you tell me if Test is away, have sent message re LY plans and regatta this weekend at Pt Gawler, no reply yet. I will send message to you re this event.

Constructors and designers, lets help each other and get this dialogue going.

Hey Sandflyer,
How go dude. "The Flight of the Phoenix". You ain't old if you watch that movie. There's been a recent remake but I'll bet it isn't a scratch on the original. And you only mentioned Hardy Kruger. How about Jimmy Stewart, Ernest Borgnine, George Kennedy and the great Australian actor, Peter Finch. Plus the other great actors whose names I don't know or remember. The whole cast was brilliant.

Hang on, we're supposed to be talking about land yachting here aren't we??

I intend building a class VI and possibly class V yacht using aluminium scaffold tube. It is apparently the only high grade aluminium form made in Australia. It is sold by Smart Aluminium "www.smartaluminium.com.au". The tube is graded 6061 T6, outside dia 48.41mm, wall thickness 4.47mm and comes in 6.1m lengths. There is also a 63.5mm dia, 6mm wall tube of the same grade that is extruded. If this makes a difference in strength, I do not know. Get hold of their catalogue. It has lots of useful info.

My yacht will be bolted together as the temper of the ally is lost where welded. It will have steel or stainless steel fittings for joiner, axle carriers and mast step. It will have steel tube struts between the rear cross member and the top and bottom of the mast step. I will attempt the use of this tube on it"s own for the mast.

The yacht will be based on class VI or V measurements but will possibly not be compliant with class rules in full. Cest la vie but it is sure going to be fun.

Unfortunately it will be a while before any of this happens. A house refurb (nearly finished) and water yacht refurb (not yet started) take precedence. I anticipate getting the first land yacht built this year though.

Will certainly be posting to the construction forum during construction.

What is the address of the RC land yacht site. Sounds like it has some valueable info.

Cheers for now from cisco.

You bet I've heard that line before. Christmas a year ago my wife found and bought for me a 5 DVD disk, 25 episode collection of "The Cisco Kid". I've even got my 11 y.o. son saying "Oh Cisco; Oh Pancho!!" There is something really good but very simple about that era. Look out, I'll get weepy soon.

Found the RC land yacht link thanks mate but it does'nt want to load at the moment. Will try again later as well as do a related search. If I find some good stuff I will post it.

See ya round like a rissole.

Interesting what you are saying there Lachlan about you and your Dad's first yacht.

My following comments are analytical and definitely not critical. My view is that there is no such thing as constructive criticism. All criticism is negative.

You built a 3m x 2m chassis using 40 x 40 x 2.5mm steel. There is quite a lot of weight in that. To get that amount of weight moving you then needed a sail 8.5 sqm in size. That amount of sail area then required the chassis to be braced with extra steel (more weight) to counteract downforce.

Seems to me that you got caught up in a viscious circle of adding, adding, adding to counteract the effect of overbuilding in the first place.

By the same principle that, weight for weight, hollow section material (steel or any other material) is stronger than solid material, your chassis could have been built using say, 60mm round x .75mm wall thickness steel and ended up being stronger and lighter and therefore faster for the same sail area.

From there we could go into use of higher tech materials like aluminium, fibre glass and carbon fibre, but that is getting away from the home builder's workshop.

Got onto the RC landyacht site eventually and like you say, a lot of good info there. Another great site to get a bit of design philosophy from is "www.f-boat.com" .

Keep da faith brudders.

Old father time here time here come to edumicate all you kids.
I have enough NQ core tube for 2 cl 5 chassis , I can bring it as far as Gilles. First in best dressed , send measurements for precutting,add 50mm just in case. . On our promos we substituted 2mm wall Galv fencepost steel for the back axles, it works good. the T6 mentioned is imperial and ancient , check the milling date as t6 can lose temper over the years. On our lefroy minis we use 30mm,2mm wall for axles,even for the big guys, cheap and good. tested the axle by caving in the sidebar protected door of a Camry,no damage to yacht.
One of the advantages of the small minis is that materials get .cheaper.
The next mini we do I plan to build one with a main spine from the same Galtube that we use for the promo axles. I believe that it will work fine.
Lesson ends

Just a question to all the engineers out there?
lets assume i have a 50x50 x 3mm SQ tube AND a 50 Dia x 3mm Round tube both about 1.5m long .. could be steel or aluminium do they have the same resistance to twisting length way or are they different( and is there any formula to calculate this)
im not talking different materials for each im just talking shape at this stage..
Thanks

Gizmo is asking about a torsional load, not a bending load. To begin with, the circumference of the 50mm round is much less than the perimeter of the 50 x 50 square rhs. As torsion is applied to the rhs, the corners of the square will try and open up. The rhs will definitely be strained (strained - forced out of original shape)more than the round tube, The round tube will resist the stress of twisting much better than the square tube (rhs) all other things being equal.
If a bending load is applied, the square tube will distort (flex) much less as there are two vertical side webs (or walls) to support the load. You never see round tube used as a beam. A zig-zag truss made of round tube is different, (Warren Girder truss). Aluminium is never as strong as steel in bending or torsional (twisting) loads. The aluminium will deform badly compared to a steel tube. If you want material to use as the "spine" of a yacht, then steel will produce the results and be far lighter than an aluminium equivalent. Hope this helps.

Kody

I think two new threads are needed here. "Ultra Technical Tips" and "Tech Tips for Illicit Substance Users".

My brain went into a downward helical spin after reading that one Brian.

Definitely the full spectrum has been covered in those last few posts.
Cheers All really good stuff though.

Here is a little more material on round vs square tube...found on www.auf.asn.au/scratchbuilder/metals.html

Effect of shape on stiffness
Structural stiffness in bending or torsion is as important as strength; for example if the aft fuselage bends under changing aerodynamic loads on the tailplane surfaces the angle of attack of those surfaces will change, thus again changing the load ... and so the cycle continues. In the turbulent atmospheric conditions often encountered near the surface lack of structural stiffness substantially increases pilot work load and adds to airframe fatigue — see below.

The modulus of elasticity expresses the stiffness value of standard test pieces but stiffness of formed metal is also dependent on the geometry of the material. For example the stiffness of a solid metal bar of particular cross-section area can be substantially changed by reforming it as an angle section, channel section, 'T' section, 'I' section or a round, rectangular or streamlined tube, of the same length and mass. An aircraft designer will be looking for the most efficient material shape for each structural element i.e. the shape that provides the required stiffness and strength with the least weight.

Structural elements loaded only in tension or compression are, except for long columns, generally very stiff and that stiffness is dependent on the cross-section area [as is the strength] not the cross-section shape. However the resistance to bending and torsion loads [which are combinations of tension and compression stress acting opposite to each other] is allied to the shape of the element; for example:
Round or rectangular tubes and other enclosed shapes resist torsion well and are more rigid against torsion than an 'I' section.
An 'I' section resists bending better than round or rectangular tubes and that bending stiffness is proportional to the section depth cubed: see properties of beams.
A hollow circular shaft is the most efficient shape for carrying a torque — hence torque tubes.
a round tube has the greatest resistance to buckling in compression — and tubing trusses nearly always fail in compression by buckling, see long column buckling below.

The bending and torsional stiffness of a tube is a function of diameter and wall thickness. If a round tube of particular outside diameter is reformed into a larger diameter tube of the same length but reduced wall thickness the wider tube will be stiffer than the original tube even though the mass is the same. (The increase in stiffness is in proportion to the square of the diameter.) Or a round aluminium tube of 50 mm outside diameter and 2 mm wall thickness will be eight times stiffer than a tube half its diameter with the same wall thickness, even though the larger tube has only slightly more than twice the mass. (The increase in stiffness is in proportion to the cube of the diameter if the wall thickness is maintained — or if the wall thickness is doubled the bending stiffness is also doubled.)

However as you might imagine there is a limiting relationship between outside diameter and wall thickness before buckling potential might become a problem; also very thin walled steel tubing is difficult to weld so there is a minimum wall thickness associated with welded tube structures.

Round rather than square metal tubing is the material of structural choice because a given mass of metal can be formed into a larger diameter [and thus stiffer] tube of the same wall thickness and length if round rather than square. The mass of metal contained in a 10 mm × 10 mm × 2 mm wall thickness square tube would produce a 12 mm outside diameter × 2 mm wall thickness round tube of the same length, which would be considerably stiffer and more resistant to long column buckling. Conversely a round tube can provide the same stiffness as a square tube but with considerably less weight.

However square steel tube greatly simplifies welded truss fabrication as parts can be mated with simple straight angled cuts whereas round tube requires more complex radius cutting [a fish mouth] to properly mate the parts prior to welding. This advantage may be appealing to someone who is prepared to trade the long term weight penalty [for example reduction in payload and rate of climb, increase in fuel bills] for the short time saved in construction. Round tubing is the primary material in most factory built steel truss fuselages. There may be advantages in using square tubing for fuselage longerons and round tubing for the other members.

To cut a long story short..... ROUND is stronger than SQUARE as Landyacht main spine

I suppose the next step is put away the welder and make a mini chassis completely from composite tubes. It wouldnt weigh alot!

For those of us who have a similar attitude to metric as Kody has and would prefer to work in imperial units but find it a pain in the butt to have to convert all the time, here is a little gem.

Joshua F. Madison, who in my opinion must be an absolute gentleman, has written a little program called "Convert". It will convert just about anything. It certainly converted me.

Get it for free by visiting "joshmadison.com/" and click on the software tab. If memory serves it will even fit on a floppy (what's that).

It settles all arguements when talking knots, mph and kmh.

This little gem rates with the likes of "Irfan Viewer", possibly the best graphics viewing and editing program around. Get IT free from "www.irfanview.com" but make sure you download "all plugins" as well to get full functionality.

Have Fun, Adios Amigos.

Not going to enter the metric vs imperial debate. Im a scientist so metric is the ONLY system I can use (SI units).

Right, a chassis material question. Who may venture an opinion and reasoning to the idea of using 75x50x2.0 steel RHS for a class 3 sized landyacht frame? Same goes for using 50x? round as the rear beam? It is a 'stayed' yacht of conventional T design. Thanks for any input.

Any plans in metric are ok Landyacht, its a brave new world .