Hi, I want to shoot a question past some of the aerodynamic wizards here to get some opinions on possible causes of erratic behavior in one of my aircraft. My main question is, if an engine is starting to separate from the firewall in flight, could this cause the aircraft to pitch in different directions erraticly? Namely down and to the left to be precise. Here's the dope on the story. Its an approx 45" span Fokker DVI bipe. I've flown it many times before and it always behaves beautifully. Anyway, on this particular day I took off from my strip, climbed up about 100 to 200 feet and was just tooling around a bit. Then the wierdness occured. Every once a while the nose would drop/dip sharply and quickly, but then stop and be level again. (Ok, I know what your thinking "servo glitch" but hear me out) So, I'm thinking hmmmm. not good, but not deadly either so lets keep cruising and see what happens. Just in case I thought, lets do this observational/diagnostic cruising over near the end of the strip so I can land in a hurry if things go south rapidly. As most of you know who have had anything to do with aircraft, this can happen quickly.....and did. I turned, then I flew parralel past the strip to my ingress end and was preparing to turn back when the nose not only dipped sharply, it flat out dove! I threw in full up elevator. She leveled out. I still had about 120 feet in alt. so I started the turn back into the strip again. She turned to face the strip and then dove severely yet again as I approached! Again I hit full up elevator, she leveled off but maintained a severe right bank, I fed in full rightrudder but she just flew straight with this crazy right bank thing going on, almost like a held knife edge. At this point she was 25 feet out fromt he strip and about 30 feet up dropping fast. I startred to chop the throttle and she slowed. There is deep hay before you reach the strip so I thought this might save some damage. She smacked into the deep grass roughly end over ending, but the damage was minimal. Four bent and separated cabane struts that need repair, amazingly enough that was about it!! But the clincher was the engine was barely hanging in place. When I removed the cowl it simply fell off the plane! Now this could have been crash induced, but I'm thinking it may hav been the culprit all along. I would like to know if anyone else thinks this is valid? It was only held on with wood screws anyway......sooo...... guess its time to install some blind nuts. I'm thinking they mey have worked loose and caused this whole thing. I have found the engine mount loose before and retightened them more than once. I'm going to do a range check this week with the current battery charge and see if I get any glitches, but right now I'm thinking the problem may have entirely been due to this engine mount getting worse and worse and finally pulling loose. Anybody out there think this is realistic? TIA for your replies!!