Much of my time is spent completing projects for people that have little more than a vague idea of what they need with even less of an idea for how it might be fabricated.
"Could you design me something to barely fit <here>, CNC it, TIG weld it, finish it, then install it? All by next Tuesday?"
The project I am about to describe here was nothing of the sort.
In this installment of design-build with Dave, we are going to scratch build a Super Duper Cubby Ruddy for no other reason other than to simply learn how one could do it.
I was curious where the design of a new Cub rudder might go, how I might model the structural stresses expected in normal and abnormal operations, how I might fab thin walled 4130 tube into tight repeatable bends for the trailing edge, how I might jig the full part to keep it straight during welding, and how an oversized rudder might change the feel of my ugly duckling Cub in all corners of the flight envelope.
In short, it sounded like a good time at the time, and the full journey was quite indicative of the ups and downs experienced by those truly experimenting in experimental aviation.
Inspiration
To each their own, but to my eyes there is nothing more brutally beautiful than the Wolf Pitts Pro.
Specifically, I adore the Wolf Pitts Pro rudder. I would move a mountain to work with that team someday, but until then...
Working Constraints to Software Modeling
Armed with some inspiration and a new target surface area, a new rudder took shape entirely in digital space. The full design-build process is best shown through pictures.
Digital rudder jig
Nothing is real until you can hold some cold hard 4130 parts in your hands
3D printing has been a total game changer in every area of my design and fabrication process. I feel bad for anyone hand coping 4130 tube without some sort of jig.
Jig on the table with the first rudder ready for the TIG
Bending jigs bolted to the weld table to allow me to form the trailing edge of the rudder
Test fitment of the new rudder on the fuselage
Superflite covering system, medium weight fabric
Installed after endless hours of sanding, priming, sanding, then painting
Is it any lighter?
No, in fact it is roughly 20% heavier than the under-built J3-sized rudder that was previously installed.
Is it any stronger?
Undoubtedly yes. Depending on the location and direction the force vector is applied to the new rudder, it could be as much as 40% stronger than the previous rudder.
Is it any better?
Possibly.
The extra surface area was immediately noticeable and the rudder feels more balanced, albeit the extra heft is also noticeable.
I always break down this specific question into three distinct sections:
- Is the change noticeable?
- Is the change provide more (or less) of what I am looking for?
- Do I like the change?
In the case of this new rudder, the change was immediately noticeable. The control in almost every phase of flight was superior. I still don't know if I like the change. The new rudder feels slightly heavier underfoot and with the heft it feels slightly less sensitive at very slow speeds. Most pilots would never notice, and even fewer would ever care.
I am not most. Someday I will probably redesign and then rebuild this rudder with a goal of ~25% weight reduction with additional leverage applied at the rudder horn.
To those of you out there that are brave enough to dream up a idea, fabricate it into reality, then test it in a controlled manner to determine if the reality of the component matches the dreams you had for said component, I salute you.