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So I want to make a fast plane...

#1
I need someone to explain KV to me. Keep it simple. Ive read the technical definition and understood very little.

Act as if Im five :p

Also, Id like to keep it in the traditional electric motors. No etf rocket jet type motors :)
 

Revere

New member
#2
It is the rpm of the motor (under no load and with no prop attached) using 1 volt of input current.

Think of it as "revs per volt".
 

CrashRecovery

I'm a care bear...Really?
Mentor
#3
There are a few more factors as well. You also have to look at your aircraft size. if the motor you want to use does not have the ability to move the weight of your plane then that won't work. Its a balancing act.
 
#4
If you want to build a fast one, you might want to consider the nnChipmunk from Nerdnic.

The plans for Chipmunk Version 2 include two wing patterns; one for standard flight, and one for outright speed. I've seen this one perform at Flite Fest, and it's flat out amazing. I intend to build one myself shortly, but will probably go with the standard wing and 3S power. I don't need a plane that flies faster than my reflexes. ;-) Meaning, 100+ mph, which the Chipmunk can do easily with the speed wing and a 4S pack.

Gryf
 
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nerdnic

nerdnic.com
Mentor
#5
Gryf thanks for suggesting my chip! You've got the v1 link in your post though.

For kv, Revere is right, RPM is what you're looking at. The trick though is to pair that kv with the right prop. Kv is to RPM as prop is to what gear you're in. For a car your Lamborghini engine might be able to handle 12k RPM but if you're in first gear you're not gonna go very fast. For your prop it's a combo of diam and pitch. Your prop pitch is the direct measure of how many inches it travels through the air on one rotation and is directly related to top speed. Diam is going to give you the punch speed, your thrust. So think of it like the bigger the diam the more torque you have, insta power sport plane feeling. The bigger your pitch the greater top speed.

High kv != high speed on its own. Your prop is just as important as the motor.

There are general guidelines of what kv goes with what prop, but it would be best if you tells us about your plane and then we can talk to that use case.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#7
Here is my 2 cents worth.
The higher the KV the smaller prop diameter. When comparing 2 motors of the same wattage or power rating the high KV will give the same thrust with a smaller propeller.

When designing a high speed model keep it light if you want to land at slower speeds without a fullhouse setup of flaps etc.
Also keep the wing profile clean and if possible fully symmetrical. The wing must be strong to reduce twisting as well as possibly a total failure during high speed maneuvers.

Dual rate and Expo on the control surfaces is highly recommended as the forces generated are speed related for the same deflection. This means that a roll rate of one full rotation every 2 seconds at slow speed can increase to approximately 2 rotations per second at twice the speed. A loop will tighten with speed and put great forces on any wing joint. When using foamboard I always fit paddle pop sticks to the inside of the wings at the joint as well as a dihedral brace even if the wing is flat

Also consider a flight stabilization system with return to field feature because a small model at high speed can quickly leave your sight and your radio control if you are not careful.

When you take your plane out for its first flight bring a bag to take it home in:black_eyed:. Try to get a veteran flier to check your settings and even do the first flight. If you are to do the flight yourself then gain height ASAP and then cruise at moderate throttle to check your controls and trim the control surfaces. When at height and all the trimming is done then you can "Open her up". Once you have done a few passes at high speed and you are happy with all start practicing low speed flight whilst still at height to get a feel of how slow it can go.

Slowly decrease height and practice low speed landing approaches and then your landing. When I mention low speed I do not mean the same slow speed you would get on a trainer but rather the slowest speed at which you have positive control responses.