Monty
Well-Known Member
I don't know.......I always second guess. So far my hand calcs and the FEA results are in tune, with the hand calcs being on the conservative side. I've just been using FEA to tweak things.
What I'm finding so far is that durability and manufacturing are driving most of the design rather than material strength. The exception is the spars. Even so, my design is winding up looking rather flimsy compared to a lot of other aircraft I have seen. For instance, I am using mostly .025 6061, because it is easy to handle and it is durable. I could get by with thinner material, but it really doesn't save much wt in an airplane where most of the weight is the useful load and the engine. Going with lighter material means more stiffeners bulkheads etc. It makes a lot of extra work and since most of the little bits and pieces aren't doing anything structurally, doing so really just makes the aircraft harder to build. In the end all this extra work only saves a few pounds. Especially when you add in all the extra rivets.
The spar shown here is a built up spar. The caps consist of a 1X1X1/8in angle, and a 1X1/8 bar 2024 T3. The shear web is .030 the shear doubler is .035. The angles and the bar are tapered to spread the stress along the spar. The outer portion is just a .030 C with a .040 angle doubler near the root. Also tapered. The load case is at 7.5G (ultimate) with a constant load distribution (should be conservative). The stress is only just getting to yield. I have yet to do the asymmetric load case.
Am I crazy???
ara:
Well maybe I should re-phrase that. :gig:
Does this make sense to those in the know?:nervous:
Monty
What I'm finding so far is that durability and manufacturing are driving most of the design rather than material strength. The exception is the spars. Even so, my design is winding up looking rather flimsy compared to a lot of other aircraft I have seen. For instance, I am using mostly .025 6061, because it is easy to handle and it is durable. I could get by with thinner material, but it really doesn't save much wt in an airplane where most of the weight is the useful load and the engine. Going with lighter material means more stiffeners bulkheads etc. It makes a lot of extra work and since most of the little bits and pieces aren't doing anything structurally, doing so really just makes the aircraft harder to build. In the end all this extra work only saves a few pounds. Especially when you add in all the extra rivets.
The spar shown here is a built up spar. The caps consist of a 1X1X1/8in angle, and a 1X1/8 bar 2024 T3. The shear web is .030 the shear doubler is .035. The angles and the bar are tapered to spread the stress along the spar. The outer portion is just a .030 C with a .040 angle doubler near the root. Also tapered. The load case is at 7.5G (ultimate) with a constant load distribution (should be conservative). The stress is only just getting to yield. I have yet to do the asymmetric load case.
Am I crazy???
ara:Well maybe I should re-phrase that. :gig:
Does this make sense to those in the know?:nervous:
Monty
