Why don't all areoplanes have reserve wings? same logic.

IF you are planing a tilt up tower you will be well advised to study the 4 guy tilt-up posts here. It would then be prudent to raise the tower by itself a couple of times before placing any hardware on the top.

I actually wonder if one should warn folks of the dangers of some of these processes or let them waste money or get themselves or others killed or injured. Letting the stupid get hurt and/or killed is called 'natural selection'.

the three guy system as seen on commercial applications are highly engineered and not just some scheme penciled out on the back of a napkin.

presumably one uses guys to not only stabilize a tower but place them under tension
to increase the strength of the assembly.

the mega disaster series on the discover channel illustrated what happens
when aomething bad takes place, the texas city TV/Radio tower is an example.

the guys in that case were tensioned to something on the order of 20k lbs each
and when the jib crane broke loose allowing the antennae to fall, the antennae cut
a set of guys (one leg of the 3 guy system, allowing the other two sets of guys that were under 20k lbs of tension to pulled the tower and the whole thing came down.

if your tower is strong enough to be self supporting by itself and you are useing guys just to stabilize it you will probably be ok with a 3 wire system.

however if the tower needs tensioned guys in order to be stable, and you are not an engineer, then you might seriously consider the 5 guy system.

i would think long and hard about this part of your project, bad things do happen
and when they do you will be liable for the results.

simply put if one is to err, err on the side of caution.

We all  have opinions on this stuff.  To be honest though - in my opinion ;-)  - if 1 guy breaks on a tower with 3, the tower will fall over.  If one breaks on a system with 5, I expect two more would be quick to break - the forces on the remaining two could be extreme if you think about the angles involved.  Almost all guyed towers that do not tilt have 3 guy wires of suitable size with suitable anchors and properly setup they are quite safe.   That said - other than larger foot print/more land used up and more cost, there is certainly no harm in 5 cables.

 'It seems that a properly designed three guy system is all that is needed, after all that is what the big boys use.'

Right - it also takes up less land.  

'  Also I dont really see it as absolute necessity to have a four pattern for a tilt up, one could use a truck or a tree as a temp for the tilt up procedure.  Seems more a matter of convenience and how often, if at all, one intends to lower and re-raise the tower.'

I have to agree with Ron - you'd be nuts to go with less than 4.  You can put in temps/use trucks or whatever as you describe.  It's dangerous stuff - forces involved with tilt up towers get extreme.  It needs to be done such that you're sure the guys loosen on the way down and tighten (but not too much) on the up.  You cannot tell by looking just how tight a cable is or when it's about to break.  A tilt tower should be as safe, and convenient as possible.  It should have 4 guy wires.  The side cables should slightly loosen on the way down and they should tighten back into adjustment on the way up. Anything else seems inconvenient and dangerous.  Most of the small wind turbine towers that do fail are tilt up towers - again, the forces get pretty extreme.  You can easily do the numbers and figure out what the forces 'should be' but - a bit of wind, or a slight 'bounce' on the way up or the way down can change things drasticly.  The rule of thumb as I understand it - calculate the forces involved and throw in a 500% safety factor.

You can experiment with a small wind turbine - try thinking out of the box and do strange stuff, odds are it wont work well and it will fall apart (maybe not)... and hopefully if that's the case you had fun, it's unlikely to cost a great deal or cause property damage, hurt/kill somebody etc.  That is not the case with towers.