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What's a good FAST motor for FT Racer and Versa Wing?

#1
My dad is getting into RC planes and so he bought the FT Racer, Baby Blender, and Versa Wing, and I am picking out the electronics. The plan is to get two powerpod setups to use on the three planes. One will be just a simple 3s 25A system with ample thrust that'll work well on all three planes. He also wants a powerpod with a fast motor on a 4s that we can use on the Racer and Versa Wing (maybe the blender too just for fun, but it's not built for speed).

I scratchbuilt a Racer and I use an NTM 28-36 2700kv with a 3s and a 7x4 prop. I speculate that setup goes about 70-80mph. It works well but we want to try a 4s setup with hopefully even more speed and more fun!

I don't know if I should find a high kv motor with a small prop, or a lower kv with a higher pitch prop. Any suggestions guys?

Bottom line, I'm looking for a motor:
  • to be used with a 4s (1800-3000mAh)
  • 80+ mph speeds on Racer and Versa Wing
  • 45-60 amps
  • Hopefully in HobbyKing US warehouse

Thank you very much!
 
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Craftydan

Hostage Taker of Quads
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#2
**Theoretically** that motor swinging a 7x4 on a 3S will become most effecient at 113.5mph, and frankly, it's overpropped at 7" -- if the 6x4 prop can keep it airborne (it should) there's a better than fair chance your racer will fly *faster* becasue the motor can generate a higher RPM while still overcomming the drag. No doub about it, that's a haus of a motor!

**Theoretically** if the 4.75x4.75 prop can do the same, it will become most efficent around 180MPH (!!!), while generating nearly 2.5lbs of thrust.

how'd I get to those numbers?

Voltage x KV x pitch = most efficent speed at WOT(Wide Open Throttle) in inches/min

to get the speed to a sane unit (like MPH):

in/min x 60 min/hr / (12 in/ft x 5280 ft/mi) = mi/hr

This assumes first, that the KV = 2700 under load -- aproperatly propped, it's not too far off, but the more over-propped it gets, the slower the motor spins, and the slower your max speed will be.

It also assumes 2.5 lbs of thrust is enough to overcome 100+MPH worth of drag to get this motor up to that speed . . . that depends on the design -- FT planes aren't the sleakest airframes, but the versa and racer aren't horible. Making a slimmer wing on either (and streamlining the V&H Stab on the racer, and replacing the cockpit and rear turtle deck with a shorter, streamlined profile), with that power system will likely go farther to increase speed than adding a faster stronger motor.
 
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#3
Thanks Crafty Dan, I've crunched those numbers before and I've had that motor on three different planes with different props too and I've been running the 7x4 just for preference. Maybe I'll try modifying the plane to make it a bit sleeker and faster like you said.

However, my dad is building a separate Racer and it'd be fun to fly both at the same time so I figured I'd try a new setup on a 4s to see how we like it.
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#4
4S on the *MUCH* smaller 4.75" prop may give you the boost you want w/o slimming -- a simple change that hopefullty will let you smoke you dad's plane ;)

only potential headache I see is the fuse blocking too much of the prop disk, robbing you of power. Not much can be done about that . . . except slimming the nose :p