About Perch

After asking both my Mongolian perch reference (Batsugar Tsendjaev) and my Russian perch reference (Alexander Gavrilov), the answer was clear : a perch should be made out of “Dural”. But, what is dural ? It is an old name to call the alloys of aluminium used to build airplanes. In Europe these are now standardized and named by the EU norm EN 573-1. I then started to dig into the website Euralliage, where all the data of this norm about the different alloys of aluminium are clearly displayed.

The aluminium I am using is : 2017a T3 and T4. The alu 2024 was also on my list, but was harder for me to find.

The reason why “Dural” was such an unanimous answer is that the bending point of this kind of aluminium is a lot further to its breaking point than with the more common aluminiums. So practically, you will notice if you have been applying too much load to it, because it will then bend. Whereas with the common aluminiums there is a chance you might not have the luxury to see it bend before it just snaps broken (which can be deadly when it comes to acrobatics). This being said, the main contraint that would actually make a perch brake is happening when the flyer(s) center(s) of gravity goes away from the perch. For just one person doing a basic climb and staying close to the perch, I have been using a bit whatever, like a big branch, a pipe of the theater, an alu ladder, a Chinese pole… So, if you intend to do flags, spins, or all sorts of crane pieces on the top (for attaching aerials), “Dural” is my recommendation.

The calculations of the forces in the main pole of a crane are a well known thing, but these are always a function of the size and strength of the foot. In the case of the perch, the foot is supposed to have only a vertical force, and this makes this calculations impossible. I have had a couple of math and engineers geek friends to look into this problem, and they did not come to a solution for calculating properly the bending force applied to the perch while having an acrobat flagging on it. If you know better please tell me. All this to say that I will only be able to give my empirical experience for the dimensions of a perch :

With a flyer about 90kg and about 1m90 doing a flag on a 4m high perch, we use a perch in 2 pieces of 2m each made of a pipe of 50mm diameter and 2,5mm thick walls of alu 2017a T3 with a connecting piece of 45mm x 5mm of 2017a T4.

I used the same kind of pipe with the same connections to make a perch of 6m with a crane on top to make a rigging point for a rope about 50cm away from the pole. With this the flyer was about 60kg.