I heard about two rigid wing launch accidents this year that I believe had the same cause, launching with a low angle of attack, then not changing the angle of attack during the launch run. I believe it was the late Steve Daleo who first described the phenomenon and coined the term "sticky pitch". Here is his description:
"Rigids are very easy to launch. They have lots of directional stability because they have control surfaces to initiate roll. However, there are some differences that are worth discussing. I’m going to introduce the concept of “Sticky Pitch”. It’s the tendency for the nose angle to just stay where you put it with very little additional input required. It’s really only noticeable on launch and landing. Even then it’s a subtle effect.
During a flex wing launch, the pilot is usually pulling in slightly during the run to keep the glider accelerating. As the speed builds up, the effort required to keep the glider on the ground increases. This is due to the fact that the airfoil becomes more defined as the sail fully inflates and the airframe flexes some as it loads up. The rigid is different. Since the airfoil is completely defined by the ribs and D-Spar, there is no appreciable change in the airfoil or airframe geometry as you begin to move and load up the wings. If the pilot either sets the initial nose angle too low or pulls in too much during the launch run, the glider will just go faster. There is almost no tendency for the glider to pull you off the ground. That’s the “Sticky” part. The pitch will just stay glued where it is and continue to accelerate unless the pilot acts to change it. Once you get up to flying speed you will instinctively ease out a bit and you’ll be away."
I highlighted the sentence above for added emphasis, It is possible to run all the way to the bottom of a launch (or into obstacles) without the glider ever lifting you off the ground, even though it easily could have. I have found that when launching a rigid you should ease out the bar and let the nose slowly increase in pitch. Below are two links of two pilots launching the same model of glider (Atos VR) in the same conditions. Pilot 1 has the tendency to keep the nose angle constant during launch, pilot 2 (me) tends to let the nose angle rise during launch. This is one of the just a couple of differences between rigid wing and flex wing gliders that will get a rigid wing pilot in trouble.