Pilot reported an inadvertent gear up landing during a training scenario with an instructor.

Narrative

Chain of events leading to a gear up landing on Date.Here are the events just prior to our gear up landing as I recall them. We had just conducted a simulated engine out with gear failure in the pattern. On this round I identified a 'popped' circuit breaker and pushed it in. The gear came down and I focused on the 'engine out'. I flew the airplane to a very soft landing with the engine at idle. The softest of the day. On the next take off my instructor indicated that he wanted to do another such emergency practice and stated he wanted me to use the emergency gear extension this time. I stated I was familiar with the one on a 172 RG and asked if they were similar. He instructed me to hold the emergency gear selector down until the gear was down and locked; simple I thought. We approached the abeam point of the downwind leg. My instructor pulled the power to idle as he had done before. I attempted to lower the gear with the primary gear selector knowing that it would not work. It did not. I reached for the emergency gear down and held it until I had 'three in the green.' At this point he reminded me to continue to the runway as I had entered a shallow bank in the direction of the runway. I increased my bank angle and keyed the mike to make a radio call saying that we were now base to final for a sim engine out landing. I immediately looked to the runway and evaluated our glide path. It appeared we would make the runway; we were slightly lower than normal; right at 90. I verbalized this and my instructor agreed. I reached for the flaps; short final; I decided against it; concerned that we would need the airspeed. I verbalized the same. I took my hand from the flaps to the base of the throttle just in case. Squared up with the runway; I began my round out right around the end of the runway and waited to feel the airplane sink. It began to sink and I began to lightly pull back on the yoke. My instructor coaching me; 'Hold it off; hold it off.' It appeared we were about to touch down softly. Then I felt and heard a scraping sound. For a split second I was confused. Then it hit me. I said out loud; 'Oh no!' At this point I realized what was happening and that we were going to ride this landing in. There was no time left for a go around. My instructor responded saying something like; 'Keep the airplane straight.' And I did. I focused on the controls; applying rudder and pulling the nose up. We scraped until the aerodynamic forces gave out and the prop struck the runway followed by the plane settling down to the surface and then we slid a short distance to the left of the centerline. We quickly confirmed that neither of us were hurt and began shutting down the airplane. My instructor asked if there was fire. I saw none. I made a hasty radio call about being down on the runway gear up. We quickly exited the airplane. I walked to the grass looking at the plane; I was nauseous; it had a bent propeller and was sitting on the ground. The entire event from the point we began to scrap to the skid to a stop lasted only a couple of seconds. From the abeam point to getting out was just a few minutes. We began to call emergency numbers. The control tower and the FBO operator were notified. I never heard a gear warning horn on final. I did not input flaps so that safety switch was not in use. We were at idle and I would have expected to hear the warning horn if there was a problem with the gear. I did not. I know I did not recheck the gear down indicator lights on short final as I had just confirmed this seconds before when I extended them with the emergency extension and we were quickly approaching the runway. I anticipated a normal landing. Human performance considerations. Consider practicing engine failures and gear extension failures separately. Possibly avoid emergency circle to land maneuvers to allow for more time in the pattern. Recognize that an attempt to go around after ground contact may have led to a worse outcome. Always confirmgear down on short final regardless of the situation.