The pilot of the retractable-landing gear-equipped airplane reported that, during approach, he noticed the airplane was a little high, so he reduced power to idle and heard an alert horn. He quickly scanned the engine gauges and saw that the manifold pressure gauge was "pegged at the bottom with no indication." He considered conducting a go-around but decided to land and assess the situation on the ground. The pilot landed the airplane with the landing gear retracted. The pilot added that he did not see the landing gear position light because his iPad, which was sitting on the yoke, blocked his view. He added that, leading up to the approach and landing, the flight was fast paced, and he felt rushed, which attributed to his assumption that he was in his "typical" fixed-landing gear airplane. The airplane sustained substantial damage to the fuselage. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.