Air temperature and humidity do have an effect on aircraft performance (models and full size). A term used in full-size flying that combines the affects of temperature, humidity, and pressure is called "density" altitude. On a hot, humid day the measured altitude might be 300 meters but the density altitude might be 1000 meters. The aircraft would perform as if it were flying at 1000 meters rather than 300. The engine would develop less power, the propellor less thrust, and the wings less lift at a given airspeed.