Does it work ?Modifying 6 blade to 3 blade EDF

[Warbird]

hihi just pulling your leg

[Unorthodox_Sniper]

some control lines only use one blade

[Babylon5]

Schübeler or Schübi It is German

Why not? One blade for sure has lower amp draw

Hi Eric, check this link at NASA. One blade propeller does work.
they use a counter balance to make it work properly.

http://www.hq.nasa.gov/office/pao/History/SP-445/ch4-5.htm

[Warbird]

yes I know it works. control line and some pylon racers use it. But has anyone tried it in a ducted fan yet ?? Babylon you might be the first

[Babylon5]

Hi Eric,did tried on two blade but could not run at very high rpm because of resonace problem. Because of the resonace problem limit too very low current low thrust setup. I stop experiment after I got better result with the 3 blade EDF.

[Babylon5]

One more thing , on 1 blade maybe more tricky because of the counter balance require. As you reduce the number of blade arrangement you also need to run at higher rpm to get back sufficient thrust. May not be a bad idea to use high KV motor running at high rpm because higher KV rated motor has lower internal resistance and hence have lower IsquareR lost than lower KV rated motors of the same type.

[ER69]

Hi Babylon,
Just FYI,
I had came across this thread Discussion - "Cutting down 6 blades EDF to 3 blades made the jet fly faster" in RC Groups started by this guy called "galactica". Asking about the same question as you had mentioned here.
Reason for me to post this is because I do not wish to mislead flyers who are new to EDF, thinking that by cutting off some blades will increase the thrust.
Well, Yes, it will lower the amp draw but will not increase the thrust and make the plane fly any faster.
Anyway, check it out.

http://www.rcgroups.com/forums/showthread.php?t=557669

May the force be with you.

[Babylon5]

Hi Babylon,
Just FYI,
I had came across this thread Discussion - "Cutting down 6 blades EDF to 3 blades made the jet fly faster" in RC Groups started by this guy called "galactica". Asking about the same question as you had mentioned here.
Reason for me to post this is because I do not wish to mislead flyers who are new to EDF, thinking that by cutting off some blades will increase the thrust.
Well, Yes, it will lower the amp draw but will not increase the thrust and make the plane fly any faster.
Anyway, check it out.

http://www.rcgroups.com/forums/showthread.php?t=557669

May the force be with you.

Hi ER69, was busy with other project like the SU27 converted to single EDF.
Maiden sucessfully last weekend to reply.

In my earlier thread I have already mentioned why the three blade modification will work for some and will not work for other setup.
Without information like power ,motor type, KV it is hard to ascertain why it doesn't work.

Instead we should focus on what works and analyse on the technique.
Let us go back to the cut down 3 blade modification that works . If you recall, the cut down 3 blade EDF from SFM was carried out sometime ago by Flightpower by a person Andy Kirby. I have to salute to him for his creativity and ingenuity to modify the micro-jet to fly 100++MPH . A US$10 buck EDF unit can fly a plane at 100MPH is a EDF Buffs dream . Don't you agree?

Before I go on ,can you tell me what type of motor, weight KV that was use in the "Flightpower " setup?
To be fair ,the Flightpower setup is not perfect and there are potential problem with this setup. Do you know what it is?


Cheers

[ER69]

Congrats on your maiden.

I think you got me wrong. I am not saying that by cutting off blades from 6 to 3 will not work.
My point is, by cutting off some blades it will lower the amp draw but will not increase the thrust and make the plane fly any faster.

For example only :
1) 6blades EDF + xxxxkv motor + 3s lipo drawing @18A= 100g of thrust
2) 3blades EDF + xxxxkv motor + 3s lipo drawing @14A= Should be lesser than 100g of thrust with the same set up.

However, if you change the motor to a higher yyyykv motor ofcouse there will be a slight increase of thrust.

So end of the day, I personally think that why dont just get a suitable motor to match the fan rather than by cutting down blades and change to higher KV motor to increase the thrust.

Hey, if you are able to recall, you had told us that your mirco jet set up is almost the same as " Andy Kirby" and is doing about 100mph with a mirco fan drawing @ less than 15 or 16A.
Btw Fyi 100mph is = to 160.9km/hr

Anyway, I try to think "inside and outside the box" like what u said, but I still have lots of doubt about it. (mirco fan @ 15A draw doing at 100mph??)
I dont think that the airframe or the fan can take it man..

If you need a radar gun to clock your 100mph mirco jet, do let me know..

Cheers

[Babylon5]

ER69, you are right when you mention correct key word is match motors.
Anything
Just curious what is the thrust when you run the 3 blade at 18amps same as 6 blade setup . I think the result is going to be varied depending on the type of motor weight,KV ...just my opinion.


However, it is difficult to match the 6 blade with a lighter motor without drawing excessive current or encountering high temperature just to get enough thrust. One will be likely to be tempted to use heavier duty motor which will increase the weight and the cost significantly.

Try to use the ordinary 2025 motors on the 6 blade and check out the current or feel the temperature of the motor and you will get my meaning.


When you mention lower current at lower thrust that is correct. Thrust must come from the electrical power...but this thread is about efficiencies base on the lighter weight motors. It is how much efficiencies you gain or lost for the two type of setup(3 blade Vs 6 blade)

To make things interesting and keeping this forum alive here is puzzling quiz.
Which of this statement is truth or fiction related to EDF?
If so give your reasoning.

1) More Thrust =higher level flying speed
2) More Thrust= lower level flying speed


Besides ER69, invite others to join this forum.
By the way this is not a million dollar question so there is no prize for getting the right answer but perhaps I can treat you to cup of coffee or tea one of this days.

Note: Anyone know what kind of motors and weight and KV was use in the original 3 blade Microjet EDF conversion UK Flight power setup?

Cheers

[ER69]

ER69, you are right when you mention correct key word is match motors.
Anything
Just curious what is the thrust when you run the 3 blade at 18amps same as 6 blade setup . I think the result is going to be varied depending on the type of motor weight,KV ...just my opinion.


However, it is difficult to match the 6 blade with a lighter motor without drawing excessive current or encountering high temperature just to get enough thrust. One will be likely to be tempted to use heavier duty motor which will increase the weight and the cost significantly.

Try to use the ordinary 2025 motors on the 6 blade and check out the current or feel the temperature of the motor and you will get my meaning.


When you mention lower current at lower thrust that is correct. Thrust must come from the electrical power...but this thread is about efficiencies base on the lighter weight motors. It is how much efficiencies you gain or lost for the two type of setup(3 blade Vs 6 blade)

To make things interesting and keeping this forum alive here is puzzling quiz.
Which of this statement is truth or fiction related to EDF?
If so give your reasoning.

1) More Thrust =higher level flying speed
2) More Thrust= lower level flying speed


Besides ER69, invite others to join this forum.
By the way this is not a million dollar question so there is no prize for getting the right answer but perhaps I can treat you to cup of coffee or tea one of this days.

Note: Anyone know what kind of motors and weight and KV was use in the original 3 blade Microjet EDF conversion UK Flight power setup?

Cheers

Well, it will be a no ending story if you keep going round the bush..
Try post this topic in rc group and see what the other have to say.. I bet you have already got the answer ya.
cheers

[Babylon5]

ER69, sound like you are offended by the question I post. It was meant as a harmless way of stimulating a person creative thinking. Man, shouldn't take it so seriously.

Cheer up man

[ER69]

ER69, sound like you are offended by the question I post. It was meant as a harmless way of stimulating a person creative thinking. Man, shouldn't take it so seriously.

Cheer up man

Don't worry, I am not offended by it.
Anyway, forum is a place to post and share our experiences.
Well, ofcouse we do not want to mislead others, don't we?
Sorry if you are offended by my replies as I am a very stright forward person.

Cheers

[Jeff]

Hi,

Wow it's been awhile. Sorry I missed your question. If it's still of any interest I am using the following motor.

Cool Red 3600kV

As mentioned in my earlier post it draws 18 to 19A on 3S 2000mAH li poly.

I've heard somewhere that it is more efficient if the rotor blades cover the whole fan swept area rather than leaving gaps where blades have been removed. Presumably it is not the number of blades per se that is important but whether they have been designed to work properly and cover the area of the shroud. I am sure that a fan will still work with blades removed but what is important for efficiency is thrust produced for same power input.

Again sorry for the late reply.

Jeff

Hi Jeff, would like to find out how many amps and the type of motor is use on the 6 blade wattage EDF.


In my case with the 6 blade I was using 60 grams 28-xx class motor which is the same weight as the 2025.
The motor is 3.55KV when I ran on 3 cells lipo it was drawing about 24-25 amps at around 28000rpm. I had it tested on the micro-jet.
Next I cut down the 6 blade to 3 blade and using the same motor , the current drops from 24-25 amps to 16 amps at around 30,000rpm.

As I mention when cutting the 3 blade without changing the motor and still able to fly almost the same speed as the 6 blade is itself an improvement.
It is a pity I don't have a video to take the speed at level flight before and after the change but the comment from my fellow Rc witness it was fast.

I am trying to change to another motor at higher rpm on 3 blade so that the current drawm would be about 24-25 amps. This is a fairer test.
I would expect that the plane on 3 blade running at 24-25 amps setup would be much faster than the 6 blade running at the same current.

Here is my analysis.....

This is like comparing smaller prop size at high rpm versus larger prop size at lower rpm .
The 3 blade is equivalent to a small prop.
The 6 blade is equivalent to a larger prop(in this case it is twice the blade area of the 3 blade.)

Assuming same amount of electrical power is available to both setup
With the smaller blade load is lighter therefore will spin at higher rpm than bigger blade .

The EDF rotary impeller is basically a propeller. When the smaller prop ( impeller) spin at a much faster speed not only does it create the slip stream, it will cockscrew" thru the air at a much faster rate than the larger propeller hence propelling the plane at a much faster speed.
Another problem with larger prop size in a plane is the drag created by the blade larger surface area hence reducing air speed.

On the other hand....
Some EDF with multiblade(number of blade greater than 4) are already optimized with certain motors,usually the very powerful and high end model by the manufacturer. In this situation, reducing the number of blade would not work. I have mentioned this situation in my earlier thread.

Anyway, check the internet, the 3 blade EDF works very well with the Super Flying model and some GWS EDF. I think wattage fan is also one of them but not sure.

If you are still not convince go to this link http://www.flightpower.co.uk/microjetedf.htm

(sorry I posted this link many times but you probably miss it.)



This guy uses the same fan as what I have and runs 30 amps with the 3 blade conversion see the video on 3 cells (top of the line) lipo .
I do not how the EDF blade can survive at over 300watts of setup

There is no way I am going to run the 3 blade EDF at this high current settings.

Anyway I could be wrong in my analysis and this is just a discussion.

Ok to share your views.

[Babylon5]

Hi Jeff, coming back to this topic. The cut down 3 blade offer some advantage and some disadvantage. According to my observation, the speed of the Jet on EDF do not always rely on thrust although most of the time it does.


1.)more thrust=higher flying speed--->generally true

2.)More thrust does not necessary translated to higher flying speed.
Some multiblade EDF are design at lower rpm like the Super Flying Model is spec at 25,000rpm max. To improve the jet level flying speed in some practice, a hollow taper cone is delibrately place at the exhause to reduce or act to constrict and force the air out at a higher speed thereby increasing the jet flying speed. (There is a limit you can reduce the exhause opening and improve the level flying speed before flowback air pressure reduces efficiencies . )
The tail cone /tube do not increase the static thrust but actually decreases static thrust..
In this case you have the following:
When constricting the exhause air opening....
Lower Thrust=higher exit air speed=faster flying speed

This is a situation where not all the thrust develop by the EDF is translated to higher level flying speed.


3) matching the motor to the 3 blade EDF

When you cut down the 6 blade to 3 blade, and do not change the motor.
The electric current and power will drop approximately 1/3 .This is good for the motor but you will lose some thrust.
If you were to change to a higher KV and matching motor and runs the 3 blade at higher rpm. As the rpm increases, the thrust will increase until a point where the thrust is almost equal to that of the 6 blade. There is another bonus in doing this...the air that is force out of this 3 blade setup would very much be at higher velocity than that of the 6 blade . The result is you will have a faster flying jet setup.

For this reason, I remove or shorten the tail cone or increase the air exhause openings for the 3 blade setup .

Since this 3 blade EDF modification require short or no tail cone at the exhaust for better performance, it may not work properly on scale jet where the EDF is buried deep inside the fuselage.

The amount of current and power depend on the motor that matches with the 3 blade.(you will find that quite a number of motor will readily match with the 3 blade without exceeding the motor max current ratings.)
If you matched the motor and fan correctly you will get high efficiencies and faster flying speed.

For small jet about 150-200 sq inches , on 3 cells lipo between 21-26 amps is reasonable. I know some RC buff go beyond 30amps.


As for your motor, can't tell if it is optimised. Try to measure the ESC frequencies or the rpm of the EDF and static thrust if you can . Measuring the ESC timing can roughly tells you the rpm of the fan or indicate improvement.
Example 24 amps at 32,000rpm vs 24 amps at 36,000rpm.(Later is more efficient)

Lastly , some very high efficiency EDF have very low blade count and are only 3 or 4 blade arrangement like the Schubeler EDF.

I hope this will answer to your query.

Cheers