I can't seem to find the right grade 6061 t6 aluminum channel for the tail brackets. These are used where the tail strut bolts up. Wicks appears to have the right material but when you click the link its listed as 6063-t52 grade. Can't find it at aircraft spruce either. I could buy 3/4" square channel and make it work but the wall thickness might be too thin?
To make my tail brace fittings, I carefully cut one side off of 3/4" X .062" wall square steel tubing to end up with the 1/2" inside width channel. I cut it in such a way to preserve the full 3/4" height of the channel, but it did have the slightly thinned edges from the radiused outside corners of the square tubing I used. If you decide to go the "ripped" steel tubing route, look for sharp bend corners on square tubing not the really "rounded" corner stuff.
Please, always take my input as suggestions only. I admit that I have more of a car building mentality and that might not always be appropriate for aircraft.
For any load-bearing application, like the tail brackets, it is important to use angle with an internal radius at the corner. The outside corner is less important, but angle with no inside radius will fatigue & crack much earlier than that with a 'fillet'.
Well I cant remember who told me, or where I read it, but T5 and T6 are pretty much interchangeable. And if your looking for T6 and find T6xyz, ...same thing. Again, just going by foggy memory so you do what you feel comfortable. I would feel fine with T5 in my plane.
Doh! I didn't see you wrote 6063 ! If you could find 6061 T5 it looks slightly weaker, 35ksi ultimate vs 38 for T6. Moot pint though. 6063 is weaker still.
Doh! I didn't see you wrote 6063 ! If you could find 6061 T5 it looks slightly weaker, 35ksi ultimate vs 38 for T6. Moot pint though. 6063 is weaker still.
No big deal dog, I think I will make mine from steel fittings, I thought of bending my own aluminum channel from flat plate clamped in a vise but I have seen how easily 6061 will crack at that thickness. I also got to thinking where else channel is needed in the plans. Looks like the spar carry through uses a one inch channel. luckily it looks like wicks carries a 1x2 rectangular tube in the right grade I can saw into the correct dimensions.
Jeff, Another resource you could tap into when you are stuck for a raw material is to check with Dave Cooper at TEAM. He will get you the part. Plus, he knows exactly what item is suitable etc. I have ordered quite a few metal parts from Dave in the last 2 years, and his prices are almost same as Aircraft Spruce. Sometimes he will have it even drop shipped to you from ACSpruce.
ACSpruce obviously has a bigger set-up and if you order from them you may get the item possibly a day sooner, but in a 2 year build process, I found that one day by itself makes no real difference. You need to email Dave at theecoop@comcast.net if you need some item. This is just an added resource you could keep in mind.
My R1100 plans specify for all the AL channel including the tail strut attachments either 6061-T6 or 6063-T52. With a yield strength of 21 kpsi, the 6063 bracket will withstand 1575 lbs. Even if we assume the strut bracing takes all the spar bending (it does not take even most of the bending), the bracket is ten times as strong as it needs to be. Fatigue is not an issue. The aircraft would have to be stressed to the design limit something like ten million times before fatigue failure in the bracket.
Keith is right. Talk to Coop. I would not be happy making that bracket out of steel and I would be very unhappy indeed to see a bracket without an internal radius.
No inside radius in my TEAM-supplied AL channel for those brackets either. Couldn't be, the AN3 bolt head wouldn't seat right. Has TEAMMinimax done additional stress analysis beyond that done by Jim Collie and found his work lacking?
Bob is right. The channel that came with the kit does not have rounded corners on the inside. Also, why not use a slightly wider channel, so it is easier to insert a wrench to tighten the nut and bolt ?
That is a 6063 t5 bracket Keith same thing lawn chairs are made from. I'm not saying its not strong enough. Its impossible to find 6061 grade at that size.
Sorry, I was reading the original question to be referring to the tailplane mounting brackets, not the bracing struts. It's true the channel has square internal corners, so that the bolt head sits snug to the base.
The lack of an internal radius is not a problem on a lightly loaded cleat such as the tail brace. But it would be on a more highly stressed bracket like the one that secures the tailplane to the fuselage. Here, you would certainly want a radiussed internal corner, as a sudden change of section greatly influences fatigue life (the main mount item is radiussed internally on my plane). Steel also generally has a lower fatigue life than aluminium, even though it is 'stronger'. Something to bear in mind if you are sourcing your own metal parts.
On the same theme, try to make your holes as smooth as possible, and spend some time getting all cut edges as smooth & polished as possible. Any small notch or scratch is a stress raiser. Of course, the Max is a very lightly loaded structure with lots of reserve in these items of detail design, but it is good practice to avoid building in a potential failure point. When I worked in the aerospace industry, apprentices were taught never to use pencil in marking material to be shaped, only to use felt tip pens. Even the notch caused by the pencil graphite was a potential site for a crack to start & so was forbidden!
I'm sure many builders already know these things, but there may be some who don't.
That is a 6063 t5 bracket Keith same thing lawn chairs are made from. I'm not saying its not strong enough. Its impossible to find 6061 grade at that size.
Didn't you build and fly a plane made out of foam house insulation?
Burt rutan built a pretty amazing airplane from foam. I emailed David cooper, he said 6063 grade would be fine on the channel because there is only a push and a pull. I think I will give my money to Dave because he doesn't give me what I want.to hear
I think that is correct - there is only a side-to-side force on these components. That basically translates to an up-and-down longitudinal force at the hole where the bolt goes through. So the stress would likely be localized on the floor of the channel where the bolt hole is. I doubt the sides of the channel serve any function at all except maybe to add overall strength and prevent fore and aft movement of the strut in some situations. You might want to regularly check the area around the through-bolt for cracks.
I want to go carefully here so not to offend anybody but when technical information MIGHT be misleading or incorrect I think it proper to speak up - if only for clarification purposes.
Regarding: "Steel also generally has a lower fatigue life than aluminum, even though it is 'stronger'. Something to bear in mind if you are sourcing your own metal parts."
Steel does not have a fatigue life if it is cyclically stressed at loads lower than a certain limit. The design engineer usually designs under that limit so you don't have anything to worry about. Aluminum always has a fatigue life. (See: https://en.wikipedia.org/wiki/Fatigue_limit) In the certified airplane world, if you use steel and it is stressed above the fatigue limit, it will become a "limited life item" and must be replaced - usually based on cycles. The main landing gear on lots of Beechjets fit into this category.
Regarding: "When I worked in the aerospace industry, apprentices were taught never to use pencil in marking material to be shaped, only to use felt tip pens. Even the notch caused by the pencil graphite was a potential site for a crack to start & so was forbidden!"
This is really good advice but a note of clarification is in order - the pencil does not (under normal usage) put a notch on the part but it does leave graphite which can lead to a corrosion induced failure.
Along the same lines though - that is why you should never use a scribe to layout a part on aluminum - if not sawed off - that is a scratch that could become a stress riser and lead to a crack/failure.
BTW - It can be a very poor practice to substitute materials in a loaded application - go forth really carefully because you might be in uncharted waters. What usually gets folks is the relative stiffness of the two materials. For a simple example: say you are trying to increase the strength of a spar (because you are going to add some sort of load it was not originally designed to carry) and add a piece of very strong (i.e., stiff) steel to the existing aluminum cap. So the steel, because it is stiffer, carries most of the load until it fails and then the aluminum comes into play but, alas, it is now the weak link in the load carrying system and it too fails.
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