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Help! Running a 90mm EDF motor on 6s with a 7x6 prop

Ryan O.

Out of Foam Board!
Now, the Help! prefix is for 2 reasons. 1: I don't know if this would work, and 2: I need help because I may have gone insane... I saw how fast David was able to get his spit going on 4s, so what if I were to take a motor from a 90mm EDF and slap a 7" prop on it and hope for the best? I think that if I were to run this on a FT BF-109 with clipped wings, a modified firewall, and metal gear servos I could get it going much faster than the Spit did. Maybe another 10-15 mph. The motor is an outrunner, and it is rated to 6s on a 90mm 12blade EDF, so I think it might be able to consistently use a 7" prop on 6s without getting too overheated. What do you think?
Last edited:


Legendary member
What do you think?
That’s too large of a prop, 90mm is about 3.5 inches. I’d start with a 4 inch prop and not a cheap one. I have had props explode from spinning too fast. Stay in front or behind the prop, don’t stand in line with it.

Start with a 10 second run, then stop and hold the motor & esc to check for heat. Warm is OK but if you can’t hold them, stop, that’s too hot. If it passes, try a 30 second run, then a 60 second run. If it passes the 60 run, try a larger prop.

I’ve got a 3000kv motor on 3S, that gets warm on a 5 inch prop. If the air temperature is above 95, I’ve got to back off the throttle or it will get hot.