Stef wrote: I am using 4130 steel for my roll bar but my plane is a radical departure from a standard KR so I don't know how carbon fiber would work. I think that strength is only 1/2 the equation here. Abrasion resistance is just as important if your scraping down the runway upside down at 30-40 knots. I would go as many layers as you can afford.
Stef, Steel will work, though it MIGHT be overkill depending on the thickness. I am planning an aluminum bar for my own plane based on my own experience. While it is unlikely you will ever be upside down on the runway, I have proven it can happen, regrettably. >From a practical perspective it is unlikely you will be sliding down the runway upside down at 30-40 knots, as the failure of the nose strut (or pitching over the nose of a tail dragger), and flipping the plane perpendicular to the relative wind will take a huge amount of speed off the plane. Here is what I believe happened to us in our mishap: Nose wheel fold: 60 MPH Edge of the runway: 40-45 MPH Begin rotation over nose strut as it dug into the ground: 35 MPH Tail impacting the ground: 10 MPH or less. In going over, we probably lost 25 MPH or more. This is based on the fact there was no dragging of the tail or fuselage visible in the dirt under the plane (no witness marks). We flipped, we stopped. The biggest reason to have the roll bar is to prevent the crushing in of the fiberglass and canopy bow when weight is put on it from the vertical. Jim did not have his seatbelt cinched down tight (I did). The result was his face and head made contact with the ground and broken canopy while we were upside down and the turtledeck compressed ~ 4-6 inches. Even a light roll bar will delay or eliminate that crush. The key was the inability of the fiberglass to withstand the weight placed on it out of plane. It only took one person to lift the whole plane off of us from the tail, so the amount of weight the roll bar would need to hold is not hundreds of pounds (in our mishap, anyway). Of course, if you impact the ground at high speed (100+ MPH) and the plane flips you are out of Schlitz no matter how big your roll bar is.
