General aviation pilot reported they did not extend the landing gear resulting in a gear up landing and damage to the aircraft.

Narrative

I departed ZZZ1 for a training flight to practice landings. I proceeded Southeast following the coastline south until turning southwest to proceed direct to ZZZ. I performed four landings on runway XX; staying in the pattern each time. There were multiple aircraft in the airport area with which I was sharing the airspace. There were three training aircraft; two students who were reporting that they were on student solo flights and a Seminole practicing instrument approaches; including circling to a missed approach. While conducting my fifth circuit in the pattern; a Learjet performed an ILS approach to a full stop landing. I permitted the Learjet to proceed unimpeded to the runway as I extended my left downwind for my fifth landing. I had planned to land long to stay above any wake produced by the Learjet. When I flared for the landing; the landing gear was not in the extended position and the propeller and aircraft impacted the runway. Upon stopping on the runway; I secured the aircraft and shut down fuel and electricity. No other property was damaged other than the aircraft. One item of note is that the gear warning horn did not sound when I brought the power back to idle in the flare for landing. To prevent this in the future; I will add to my preflight briefing a discussion on the differences of the flight. The nature of the flight in question was unusual - a training flight to practice landings in an airport traffic pattern. In this particular instance; very different from the normal mission profile in the Mooney from point to point with one landing. There were also multiple distractions at the destination airport - multiple student pilots practicing procedures; including student solos; and circling approaches as well as a Learjet performing an ILS to the landing runway presenting an additional distraction. In such a busy airport environment; it would be best to abandon the original plan and find an airport with fewer distractions. In addition; strict adherence and discipline in performing multiple GUMP (Gas; Undercarriage; Mixture; Propeller; and Fuel Pump) checks need to be employed and stable approach criteria implemented to ensure that a gear up landing is avoided. In the immediate future; I plan to coordinate instruction with a Mooney expert instructor to ensure that my procedures and techniques are adequate and acceptable to prevent any other incident in the future.