Yikes...Is that the top speed? That is well below what I was hoping for and expecting. I really hope it's not such a dog with the stock setup.

1) EDF fans do not use centrifugal force to move air - here's a centrifugal compressor, doesn't quite match what's in an EDF



2) This is for electric motors: unlike fuel motors, which are constant power, electric motors are constant rpm, i.e., the motor will work to maintain rpm for a given voltage, drawing more current as the loading is increased until it reaches stall torque. As the number of blades increase, the point of maximum efficiency drops as the torque/rpm increases (i.e. at a lower current level), resulting in more heat loss compared to power delivered as current draw increases at higher rpms.



Here is an interesting article about ducts: http://4wings.com.phtemp.com/tip/tpdduct.html

Addendum: In some cases the fan blades can hit stall speed, so the stall torque is never reached.

Originally Posted by ViperVJG73

Thanks!
Can you please check the correct CG with a 4000mA 35C battery weight 650 grams?

Many thanks
Erich

You can fly with 4000 but i dont recommend it.
Flying time will be at 2min or 2min30sec i think.
CG won't be a problem, you will have to add about 30 or 40 grams of lead in the nose.


Best regards


Roman
Ready2fly.com

Originally Posted by mymia

You can fly with 4000 but i dont recommend it.
Flying time will be at 2min or 2min30sec i think.
CG won't be a problem, you will have to add about 30 or 40 grams of lead in the nose.

Best regards
Roman
Ready2fly.com

Hi Roman,
that is what I would know! Whether I extra weights need in the nose.
40 grams are no problem.

Thanks again.

Kind regards
Erich

Originally Posted by henke

Blade count have nothing to do with thrust

Originally Posted by AirX

+1, the number of blade does not add more load, the average pitch of the blade does that.

Eric B.

Originally Posted by AirX

Because the twelve bladed fan has a higher overall pitch than the 5 bladed fan, I have a Wemotec Midi and a Stumax 89/45 the differences are the number of blades the blade shapes and the stators are matched to the fan. Both fans put out ~7lbs to 8lbs thrust on 8s, each uses a different kv motor to get the job done and both draw ~80amps on 8s 4000mah.
The pitch on the midi lower than the pitch on the Stumax thus requires a higher kv to do the same job. The motor kv on the midi is 1400kv and the kv of the Stumax is 1250kv.

The disc area of the fan drives part of the thrust equation, acceleration drives another part of the thrust equation, and air density drives the final part of the thrust equation. Thrust = (1/2density*area*velocity^2), Power needed for that thrust is: Power = (1/2density*area*velocity^3). No where in that equation is there a need for a lower number of blades or a higher number of blades just the air being pushed thru a tube at a defined velocity. This works on turbofans and electric driven fans.

Cheers,
Eric B.

BTW the reason the Pitch is higher on most high blade count fans is the root needs to be about 70degrees pitch to be able to fit all the blades arround the hub. Thus the overall pitch is higher, the problem is most people try to use the wrong motor on a given fan and the results are the fan load causes the motor to over heat as it is drawing way to much amps than it was designed for.

This notion is like saying which came 1st the chicken or the egg. Pitch and blade count go hand in hand, if not all fans regardless of count would all be the same pitch. So in order to have a higher blade count such as a 12B the pitch increases, where as a lower blade count has less pitch and in order to compensate for those increase or decrease in blade count and pitch, a different motor is used. So it's like saying pitch and blade count don't make a difference in thrust...it's the motor. See these all work together so they all make a difference in thrust of a plane as do the shroud, stators, and ducting. Perfect ex. is my inboard Sanger wakeboard boat uses a 4 blade acme prop on a Scorpion 350 (chevy) motor top end and low end speed is great as well as pulling power when I'm pulling a boarder or a tube full of ppl. Same motor but switch to a acme 911 3 blade prop and I loss that top end speed and pulling power , but boy does she shoot the hole and accelerate like a bat outta hell. Same motor but, different props, different pitch, different blade count...you can't have one without the other. So there is reason blade count and pitch go hand in hand even on real Toy , hey I guess I could always swap boat motors lol!

Originally Posted by v8truckin

This notion is like saying which came 1st the chicken or the egg. Pitch and blade count go hand in hand, if not all fans regardless of count would all be the same pitch. So in order to have a higher blade count such as a 12B the pitch increases, where as a lower blade count has less pitch and in order to compensate for those increase or decrease in blade count and pitch, a different motor is used. So it's like saying pitch and blade count don't make a difference in thrust...it's the motor. See these all work together so they all make a difference in thrust of a plane as do the shroud, stators, and ducting. Perfect ex. is my inboard Sanger wakeboard boat uses a 4 blade acme prop on a Scorpion 350 (chevy) motor top end and low end speed is great as well as pulling power when I'm pulling a boarder or a tube full of ppl. Same motor but switch to a acme 911 3 blade prop and I loss that top end speed and pulling power , but boy does she shoot the hole and accelerate like a bat outta hell. Same motor but, different props, different pitch, different blade count...you can't have one without the other. So there is reason blade count and pitch go hand in hand even on real Toy , hey I guess I could always swap boat motors lol!

Ok what is the pitch of the two props specifically? What are the exact diameters of both props. IIRC from my meager boating experiences it still took a different pitch to get pulling power and a different pitch for top end. To absorb the same ammount of power it requires that a specific ammount of fluid is moved at a specific velocity. Defining force in physics is pretty specific: Force = 1/2mass * velocity^2, in our case we call it thrust. Mass in your boat case is defined by the 1/2 water density * disc area of the prop * the distance the water was moved, multiply by the velocity^2. Pitch like a screw pitch gives us the distance that the water is moved. Multiply this mass component by the velocity^2 and you have the force produced. Number of blades will figure into the loss side becasue of the tip vortice produced by each blade and the miniscule parasitic drag each blade has as it moves thru the water, but even these are very small losses and will probably relate to ounces per revolution however much power that will take..

Eric B.

OK now you explain how you come up with your answer?

It's not the blade count that matters, it's the combined chrod of all blades! A 2 bladed fan would be very long/thick while the high blade count fans are short with less chord per blade for the same power input.

How many blades you choose is more a matter of what's practical for your application in terms of fan dimensions.

Just grab this, as this is they way it works!

Originally Posted by AirX

Ok what is the pitch of the two props specifically? What are the exact diameters of both props. IIRC from my meager boating experiences it still took a different pitch to get pulling power and a different pitch for top end. To absorb the same ammount of power it requires that a specific ammount of fluid is moved at a specific velocity. Defining force in physics is pretty specific: Force = 1/2mass * velocity^2, in our case we call it thrust. Mass in your boat case is defined by the 1/2 water density * disc area of the prop * the distance the water was moved, multiply by the velocity^2. Pitch like a screw pitch gives us the distance that the water is moved. Multiply this mass component by the velocity^2 and you have the force produced. Number of blades will figure into the loss side becasue of the tip vortice produced by each blade and the miniscule parasitic drag each blade has as it moves thru the water, but even these are very small losses and will probably relate to ounces per revolution however much power that will take..

Eric B.

OK now you explain how you come up with your answer?

Originally Posted by henke

It's not the blade count that matters, it's the combined chrod of all blades! A 2 bladed fan would be very long/thick while the high blade count fans are short with less chord per blade for the same power input.

How many blades you choose is more a matter of what's practical for your application in terms of fan dimensions.

Just grab this, as this is they way it works!

A 3 bladed prop isn't going to do what a 4 bladed prop with the same pitch does and vice versa. There's a reason for the increase in blades and different pitches.

I'm not arguing that pitch isn't the reason, I'm just stating that they all have a factor work together. Like I said you can't have one without the other.

If you want an equation 1 + 1 = 2 , they go hand in hand.

Here you can clearly see the diffrence in chord of the blades. Pitch is about the same but chord differs. Both fans rated the same thurust and RPM.

Originally Posted by ViperVJG73

henke, can you please send us a pic from the YAK battery compartment?
I'm very interested at the place under the canopy.

Thanks in advance.

Again not arguing yours and airX points, they are true. However the above 2 Wemo pics show what I'm trying to say and you said it yourself " they have about the same pitch". They don't have the same pitch, "about the same" isn't the same, although it slightly differnce in pitch there is one. So I'll say it one last time pitch and blade count go hand in hand.

Originally Posted by henke

EXCELLENT work!
Nice to see it.

Thanks again.
Erich

Henk,

Thanks for the pics!

Originally Posted by v8truckin

Again not arguing yours and airX points, they are true. However the above 2 Wemo pics show what I'm trying to say and you said it yourself " they have about the same pitch". They don't have the same pitch, "about the same" isn't the same, although it slightly differnce in pitch there is one. So I'll say it one last time pitch and blade count go hand in hand.

Ok... I give up on this OT, back to the Yak.

Originally Posted by henke

Ok... I give up on this OT, back to the Yak.

Have you already flown the YAK?

How is your impression?

Thanks.