Is using all aluminum struts on a himax OK to do, the plans call for the front strut to be made from 4130 steel. The minimax uses all aluminum struts. I have read the original stress report and that is with aluminum struts. My gross flying weight will be near the same as the minimax 470 lbs . team stopped replying to my questions so I assumed lawyers.

I will stick with what the plans say, gonna be fat but skinny by himax standards. Much love!

I suspect the Himax uses steel in the front strut to take a higher compression(-g) load since it is longer than the Minimax strut and therefore buckling strength becomes the problem.  


I calculate the buckling load for a 1.25" diameter .0625 wall 6061T6 tube of 74" length to be 742 lbs. which would be marginally sufficient.  The steel struts would be nearly three times stronger in compression.

But the airbike uses all aluminum?

If steel is specified, it will not be without good reason. I wouldn't like to find out the hard way. What is the weight penalty? It may put the CG further back than ideal.

Steel is about 2.8-2.9 times denser than aluminum.  A 72"x1.25"x0.0625" aluminum tube would weigh about 1.75 lbs and the same tube in steel would weigh 5 lbs.  I should think it better to put less "useful ballast" further from the cg, maybe into the engine mount for instance, if that is indeed the reason for steel struts.  The safety factor for the front strut in the Minimax is 3.7 according to the TEAM analysis when in tension (flight load, positive g).  I believe this is determined by the strength of the bolted connections at the strut ends and not the tensile strength (>8000 lbs.).

British Maxes have to have larger diameter front struts, by the way.

I edited my previous post to correct an embarrassing math error which doubled the calculated compressive load the strut could resist! The correct value reinforces my opinion that the strut was modified to better handle compressive loads (-g flight loads). Either changing to steel or increasing the diameter of the strut, as the Light Aircraft Association did, will increase the compressive force resistance (and the tensile resistance as well though the original strut was already over-strength for tension).

Thanks Bob. Aircraft designers don't specify steel if AluminIum will do instead!

I assume some mid wing versions of the Max ( heavier wing loading ) also use steel for front strut.

No, not to my knowledge.

Being 17" shorter, the Minimax main strut is 1.7 times as resistant to buckling under compression as the Himax strut of the same material, diameter and wall thickness.  

Quoted from Keith103

I assume some mid wing versions of the Max ( heavier wing loading ) also use steel for front strut.

The Eros uses steel for the front strut.