I too get concerned when I see people running up engines in that manner.I plan on going 50-100 cc gas soon and I do not feel comfortable wacking that prop from the front. I see some guys at the field starting 100 cc engines by themselves.They are tied down on the tail,but could one not flip the prop by stradling the firewall behind the prop? I have seen a large motor fire up and launch into the operator at 3/4 throttle.not cool