Huge, clearly- defined saucer hovers at treetops

I was a teenager & watching TV when I heard what sounded like a huge vacuum cleaner ououtside. I went out & saw a huge saucer -about the size of a football field- hovering just above the woods. We lived in the county about 3 miles from the small airport. The UFO was huge, made a humming, vacuum sound, domed on top & bottom with rotating lights around both domes & around the middle, except the lights around the middle didn't rotate but seemed to flash randomly. I felt no fear, just awe. I ran into the house & got my mother so she could see it & she did. Being mechanically-minded I focused on the sound of the craft to try to determine its power source & was very conscious to pay attention to details of appearance. I took a Polaroid picture after getting my mother but it didn't take. The photo background was brownish-black with 3 scarlet red smears in the center. I don't know what happened to the photo but now think the red smears were heat indicators. I've drawn this craft several times over the years & keep one with me in case I run into someone who claims to have seen the same thing. I was intelligent & didn't use drugs. I saw this craft, I am not crazy, & I have been trying to figure out its power source for 29 years. I am a technical mechanical engineer by trade & now have a pretty good idea about the craft's power source. I believe there's a reason some of us see these things & some don't. I don't know what that reason is but I know that my life changed when I saw that UFO & feel there was a purpose for it. Maybe submitting this report is the reason. If anyone from this area also saw this, please submit your report. I reported this sighting to the airport nearby & the sheriff's department immediately after my sighting.
Date of incident may be approximate.  PD