Hi
I am looking to build a trike unit for a microlight aircraft as in the photo.
but using CF tubes in place of the aluminium tubes.
Some tubes needs to be rigid with good tensile and compressive strength but with little or no flexibility.
The pair of undercarriage legs, 1 meter each, need to flex about 3 to 4 inches when landing.
Total weight including pilot is 170 kg.
Recommendations please on the type of CF tubes by Easy Composites.
Also is there a website or calculator to figure out how much a particular type of tube will flex for a given load?
Thanks!

As you got an engineering background, you should be able to calculate the propertys of the tubes.
There are usually no data sheets with mechanical propertys available for cured composites parts. But you can usually assume the carbon to be ht-type and the resin to be at least standard epoxy. For products like tubes you can also assume the fibre content to be about 60%.
There are basically two types (plus filament winding, if you want custom taylored tubes) of commercially  available cf tubes. Pultruded tubes consist of fibres, wich are all parallel to the tube axis. I would not recommend those for your project, as they are not very damage resistant.
Roll wrapped tubes consist of 50% of the fibres parallel to the tube axis, and 50% fibres at 90% (usually. You may contact the manufacturer for detailed information).
With this information, the tube dimensions and your background, you should be able to calculate the flex of the tubes quite easily.

I would be looking at our Roll Wrapped Carbon Fibre  range of tubes for this application.  Mechanical data is available for the tubes which means you can calculate the deflection based on the loads you are likely to experience. Remember that the static load weight you give will be considerably less than the experienced loading on initial landing impact so you will need to take this into account in your calculations.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

The properties are similar based on our experience, due to similar construction (except for the surface finish).  However we do not have formal mechanical data for the woven finish tubes yet. 


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

The landing is more of an energy problem, then an ultimate strength problem. The question is if the tube can store up enough energy before hitting the critical deflection (ground contact).

Does anyone know of a Round Tube Beams Deflection Calculator where material property values of a material (eg. roll wrapped of CF tube) can be entered manually?
Thanks!

for iterations i simply use excel

Yes, good idea to use Excel.
Due to the orientation of the fibers, 'Roll Wrapped' and 'Woven Finish' CF tubes have different ultimate tensile and compression strengths.
What are the appropriate formulae to use to calculate deflection load?

f=(F*l^3)/(3*E*I)
f= deflection
l= length between support and wheel
E= Young's modulus
I= Moment of inertia

E depends on the laminate