Here is a quote about using a negative-g in a defensive maneuver from Kyösti Karhila, a finnish fighter ace with 32 1/4 victories.
I've used the exact same maneuver in similar situations as Karhila describes succesfully in AH many times.
"- What was the absolutely worst you experienced?
- It was on the 20th August 1943 as four of us took off at Kymi. Puhakka led us, there had been an alert: bombers approaching Kotka. Puhakka had a wingman and he ordered me and Flt.Mstr. Tuominen as top cover, but Tuominen did not manage to start his engine in time. The three of us took off, and as we turned our radio on, we heard that the enemy had retreated. Puhakka flew straight to the area between Seiskari and Lavansaari islands. Enemy aircraft could always be found there, and we did. Puhakka announced that he is going to engage, and I stayed behind to see to it that they should not be surprised. Puhakka and his wingman dived, soon I heard over the radio that they were in a dogfight. I checked the horizon, the weather was clear and sunny, nothing was seen. I looked down for targets to attack. I was just about to dive as there was a tap on my shoulder: it is true. As I looked back, there was a big white spinner at the distance of 20 or 30 meters behind my tail.
- That is the worst situation you can find yourself in, but I was prepared for it. Should I ever be surprised, I should engage evasive action at the same moment. I kicked my right foot down and shoved the stick ahead and to the right, resulting in outside barrel manouver. At the same moment the La fired, tracers flew all over my fighter.
- Do you hear the sound of passing enemy projectiles?
- No, it is masked by the sound of your engine and the airflow, but I heard the tac-tac-tac of the enemy guns. As I manouvered, the sand in the bottom of the fuselage was thrown about by the negative G force. Since I did not have my goggles on, some of the sand got in my eyes. I did some external barrel rolls, it is an uncomfortable manouver because you are hanging by your belt and straps. In the same time I tried to see where the La was, but I did not see anything. I recovered, but immediately dived again and looked back: there he was, a little farther behind already. I tried to think what the heck to do now, I thought of the situations I had experienced, of the standing orders, but in vain. I decided to keep on diving. If the enemy is going to shoot, it is more difficult for him to hit me because he has to dive deeper to get a lead on me. The La did not shoot, I continued the dive and thought that I really must do something. I recollected my teacher of Finnish in the school, he was a Home Guard officer and he used to say: " Remember, lads, attack is the best defense!" I never found out why he kept repeating this phrase, but now for some reason I remembered it. I thought: how to get to attack ? I must do something! I pulled the stick and climbed, I saw the La follow, but then I ran out of speed. I turned and kept watching the Russian. Due to my turn he was climbing higher than I was, I saw that now I have a chance to attack him although I am below. I picked some speed, then I gave the La some lead and fired. It was a good shot because the La pulled a turn immediately. Again I took deflection and fired, and he changed his turn. This manouvering enabled me to get behind his tail fairly easily. Then I just waited for a chance to get a good deflection. When I had a chance to shoot, the salvo hit the La and the plywood fuselage broke behind the cockpit. The front part dived, the rear part fell slowly and the red star was flashing as the rudder kept going. The pilot bailed out immediately and opened his chute. I may have flown around the man, making a gesture to him, and he may have shaken his fist at me, but I cannot swear what happened really... I often used to hope that I could meet with this pilot and learn what he was thinking as he had had the winning hand and yet he lost."
http://www.elknet.pl/acestory/karhi/karhinv2.htm
