I am working on a project and would like to hear your guys' thoughts or experiences. I am building an x8 that I need to fly for 45 minute flight times with a 2.5-3.5 lb camera payload. I am thinking the new KDE 7 series motors and 26-28'' props with 6s... Thoughts or what it would take to achieve this?
I don't think those are the right motors. What you want is one of the new pancake-type "efficiency" motors like the T-motor U8 and large props (26" or more). And with those, you can do it with a quad.
HobbyKing just announced some new 100kv motors. They're 8S-12S, which makes things interesting, but they're a good deal. http://www.hobbyking.com/hobbyking/...gy_Multistar_Brushless_Multi_Rotor_Motor.html
I think 45 minutes is a tough ask for any multicopter. Your best bet as Steve is saying is to maximize the size of the props and get a low-kV efficiency motor. Also try to maximize the "energy fraction" - meaning the weight of the battery as a percentage of the overall aircraft weight. Think of it this way: the higher the percentage of the weight you are lifting as energy instead of dead weight (the frame, motors, electronics, cameras), the longer the flight times will be. Eg. the Space Shuttle or any space rocket is mostly fuel by weight. This might mean you have a massive battery pack and have to get bigger motors as a result to lift the added weight (keep in mind maximum current limits of your flight board). But the flight time doesn't necessarily depend on how much your aircraft weighs overall, just on the fraction of the overall weight that is usable energy.