On two occasions I've had very near misses with large model aircraft. On the closer occasion, whereas my steed was audible and visible for probably about 8 miles, the model, which probably had a 6-8ft winspan was invisible until it was within a couple of hundred yards or about 3 secs away. The resultant hard, aggressive manoeuvring at 50 agl just avoided a collision. Having seen the damage a small bird can do, I'd hate be in the cockpit when the engine block of one of these things comes through the windscreen at about 200kts.