hey there,

I'm fairly new to rc flying and building (depron), but i bought a robbe f-18 nano-jet ARF epo or epp some foam not shure , anyway to go short, i shortened this f-18 on first fl.. crash ..hehe.
So i build a new one, a mirage and the building plans are trusted, put the edf 55mm in it and the esc, servo's, battery and receiver, it flew and landed exactly on a branch, wich broke off al the blades of the edf fan....
Now i repaired the mirage and bought a prop to make it a pusher jet, my question is... can i do that and what (size/pitch?) prop do i need, i do not now the specs of the brushless bl motor, but it came with a 20 amp esc and a 950mah 11,1V 3s lipo.
I was trying to make a "cheap" cool plane, so it doesn't have to be fancy or anything, i like it simple as possible.....

Hope you can help me (this is a cool hobby )

Thx Martijn

What is the KV of the motor?

I don't no, there is nothing in the manual or on the motor, i guess it's something standard, i hoped the other specs could help, because it was pre installed in this f-18 so it matches the esc and batt, or am i lost with this answer.
Maybe some more specs..
weight 350gr. all-in
wingspan 475 mm
lenght 688 mm

thnx

can't find it on internet either..

There is no such thing as a standard KV for any motor.

Most EDF motors will ahve much too high a KV for use with a propeller.

Do you have a tachometer?

Nope, i don't have it, can i use it with reduced throttle if the kv's to high, you have to excuse me, but i am learning.
I guess i have a Mc gyver status at the moment

this is the one

http://wn.com/Blue_Angels_Mini_F-18_EDF_Jet

!@#$ i can't find any specs on this motor... grr

Originally Posted by jocker edf55

Nope, i don't have it, can i use it with reduced throttle if the kv's to high, you have to excuse me, but i am learning.
I guess i have a Mc gyver status at the moment

NO - due to the way a brushless motor works, your setup needs to be able to handle the full-power usage. What happens is the controller pulses very quickly, and each pulse is full voltage IF that pulse is "ON" - the apparent average voltage can then vary, depending on what percentage of the pulses are ON and which are OFF... but during the ON pulse, it is like your motor is running at full power. However that has very little to do with the kV.

THEORETICALLY, you could run a small prop at high RPM and get about the same power usage as you would if you were turning a big fan - and this will actually get more power to the air, due to propellers being more efficient. However, your particular motor might not be capable of this, as there may not be a real propeller which would work. That is, there is always a theoretical propeller which would spin up to around the same RPM as your EDF - but maybe that's a 4x0.5 or something else we can't actually buy off the shelf, and then you're looking at making your own props, and it becomes so complicated that your project has a high chance of failure.

Tell you what Joker, I have a big bunch of BL moters a friend gave me, I'm sure one of them will work for what you want to do. I'll find a motor that will work and give it to you for just the shipping charge.

What's teh weight of the motor you have? & what size prop?

OK?

Crunch

thnx jasmine,

Then i guess i need to just try it and see what happens...
Otherwise i have to order a new fan and make it edf again...

What motor do you advise if i would like to go with the prop idea

oke capt crunch sir, that;s very nice

I will weight the motor tomorrow, for i am not at home at the moment.
thnx again..

Originally Posted by jocker edf55

thnx jasmine,

Then i guess i need to just try it and see what happens...
Otherwise i have to order a new fan and make it edf again...

What motor do you advise if i would like to go with the prop idea

That's a tricky test to do when you don't have specs on the motor. You could put too much prop on it and it could melt before you have time to shut it down.

If you want to design a power system for a particular airplane, you need to know all the specs about that plane - its weight in particular. Some planes need lots of speed to stay up, but they aren't very heavy. Some planes are light and slow, some are big and slow, some are big and fast... we need to know what you're looking at. With electrics though, it's almost always possible to find a perfect motor for a given plane, if you know enough about it. Tricky for you, but not so much for me... experience is required.

i see,
the fly-weight of this plane is 286 gram
it's a mirage 2000 nano jet out of depron.
it needs some speed to stay in the air, it's pretty fast with the 55mm edf. guess... 70 km/u, and the plane was very stable, needed a little trim on ele and the cg was good, little nose heavy, then i hit the branch........ i am more a flyer then a technision, but i have learned a lot already today...

so it's a parkflyer size jet. i will have to dig up the plans somewhere to give you more detail..

thanx

so a 7 inch prop is probebly to heavy..