@Howard: I was just going to ask what Avroto was similar to on the Tiger site. i could not find any similar specs for Avroto the way Tiger does it for their motors. At one point I think I read that the Avrotos were Tigers with white exteriors, bigger bearings, etc and thought maybe the MN3520s would be a comparable spec. If so, here is the chart for the Tiger 3520s: If you want to hover at 50% throttle at 28 pounds you need about 1600 grams per motor of thrust. Using the tiger 3520 specs below you could only guess that an 18 inch prop would do it, but if you see the motor temp column going from 16 to 17 takes a big temp jump. Going to 18 might be too much for this...just a guess. That leaves you with about 60% throttle using 16 inch props - or over 65% with 15x5 props. The U7s-420s would get you 1600 at roughly 60% staying with a 15x5 prop and the U7-490s would get you 1600 at 50% with a 15x5 prop. Both of the U7s would be running very cold at that level as well. Efficiency while providing 1600 grams of thrust seems to be very similiar for the 3520s, U7 420s and U7 490s. All getting in the upper 7s for g/W and all pulling about 9 amps to do it. I like the idea of the U7 490s to have the power to swing an 18 inch prop with no problem or the flexibility to be very efficient with a lighter load and deliver long flight times. At 50% / 100% throttle (6 cell battery) the U7 490s kick out: 15x5 props - 3.5 pounds per motor / 9 pounds per motor 16x5.4 props - 4 pounds per motor / 10.2 pounds per motor 17x5.8 props - 4.6 pounds per motor / 11.2 pounds per motor 18x6.1 props - 5.3 pounds per motor / 11.6 pounds per motor The max thrust at 100% throttle may not be something we ever need, but sure is impressive. There is a lot of lift available between 50% and 100% with these.