Thought I would start a new thread on his subject as I didn't want to polute the question previously asked about suitable extrusion and I saw a response to my post that was both incorrect and incomplete and which I consider to be a safety issue.. I have no bone to pick with anyone here but when mis-information is posted as fact or out of context it needs to be corrected.

 My experience is with the 701 and I am using that as a reference. This is my opinions backed up by the math and common sense, I am not an engineer and any changes I have made during my build rely on that common sense and often following the path of others after gaining any information I feel is relevent and researching available resources and I suggest everyone does the same.

 The final word is Zenith they are your most valuable resource and in their construction standards which they supplied with your plans they list materials and possible substitutes, for extrusion in my plans they call for 6061 T-6 with possible substitutes as 2024 T-3, 2024 T-4, Why would you use any other materials and compromise the structural integrity of your plane?

 The 3/4" extrusion Zenith calls for is 6061 T-6 in .093 thickness and I have never heard of it being available from anyone except Zenith which in my opinion makes it propreitary, the acceptable substitute approved by Zenith has been 3/4 x 3/4 6061 T-6 .125 thick. If in doubt call Zenith.

  I stated that 6063 alloy should not be used as it is an arcitectural grade and not a structural grade which 6061 and 2024 are. It is not just a question of strength in my opinion as the inside angle of the structural alloys have a radius where as the sharp inside angle of the 6063 has the potential to be a stress point and could begin to crack or fail. Do not Use 6063.

  After just checking some data sheets on 3/4" 6061 T-6 the inside leg radius is stated as .094  and not .125.

 The final note is on weight. Over the years when this has been discussed (yes it has been discussed before) the only thing  I have ever seen is that peple will say that "your plane wll be significantly heavier'  where it was magicaly "calculated" that you were adding 10 to 12 pounds or more. I have never seen anyone actually give any real world numbers so lets break it down at least a little.

  I purchased 2 twenty five foot lengths of 3/4" x 3/4" 6061 T-6 .125" thick, I did not need all of it for

the build but we will use that number, I calculared it a couple of ways using 2 different sources (aircraft spruce/online metals) and came up with the same numbers but you can easily check for yourself. For the Zenith thickness number I used the weight given in the previous posters chart he provided a screenshot of.

If that weight is correct for .093 thickness which is stated as .158 pounds per foot then for 50 feet the weight of the Zenith extrusion is 7.9 pounds.

If we take the posted weight of the .125 extrusion of .212 pounds per foot then for 50 feet the weight is 10.6 pounds.

The difference is 2.7 pounds so for my build I suspect that I added 2 1/4 to 2 1/2 pounds by using the heavier material. decide for yourself what you are going to do but make a wise decision. 

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Well stated Dan.

I had considered using the 0.125 longeron material as I think I can buy it locally from Vans Aircraft, if it's good enough for an RV, it's good enough for a Zenith. I had though about the extra weight too, as I am very conscious of weight from unnecessary changes. I had also determined that the extra weight will be well under 5 pounds, mostly added around CG. Not a big deal.

Thank you, I realize this was a controversial post when I typed it but I do consider it to be a safety issue. You should be able to source the .125 thickness 6061 T-6 from any local metal supplier.


Interesting and worthwhile discussion.   Have you installed the thicker longeron?   Did you come across any times when the extra thickness caused a need for any other alterations, like longer rivets, etc?

Yes, all of the extrusion is installed in the airplane and I didn't notice anything that needed to be changed. The Avex rivets grip range easily acommidates the extra thickness. I may have changed the length of the solid rivets in the fuselage sides, but I had extra lengths of rivets on hand and just chose the appropriate length. Don't remember, and when I ordered solid rivets the cost was minimal for extra lengths in 1/4 pound quantities.


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