Are you referring to the crash near Taylorville (I think it was Taylorville....)? Given that there were witnesses who said the aircraft was maneuvering to avoid the buildings, I don't think that is probably the case. However, the chances of knocking one's head hard enough to knock oneself out is a real one in a lot of the "faux fighter" type homebuilts because of tight fit necessary to maintain the desire aestetics. Even in non-fatal crashes, it's not uncommon to find blood, hair or even pieces of skin stuck in the frames on the sides of the canopy or on the instrument panel. Somewhere I have a picture of a "faceprint" from the face of a RV pilot being bounced off the side of his canopy during a crash. He survived (thankfully there was not a post-crash fire) but had to have his face bolted back together by a maxillofacial surgeon.Here in central IL I believe it was two years ago there was a plane they used for jumping. After everyone jumped it looked as the plane stalled and one wing dropped. They believe there was such a force when the plane stalled the pilot hit his head and was knocked out. Not sure if that is what happened.
I did the same thing but I am working on my design around a 6'3" 230 lb occupant. If someone that size can fit in there, my 5'9" 170-something pound frame should be able to easily accommodate a helmet with some room to spare.I would not fit in my airplane with a helmet so I modified my airplane by lowering my seat.