Fan type/ size question

[bigfilsing]

Hi , i need some advice from the "ducted side" guys.

I've been doing a bit of reading up on the web and can see there's a lot out there!!

I need a single prefered ( maybe a double) fan set up for a project i'm working on.
As i dont have an unlimited budget i need to use the 3S 11.1 2200mah lipos i have.
So i think i'm looking at 30 maybe 35 amp draw..... max

Do you guys have any recommendations of fan/motor please. I'm more interested in a good static thrust rather than airspeed once flying!

All help appreciated

Cheers

[Babylon5]

Hi a twin 55-60mm size will give you a good thrust.

see link http://shop.singahobby.com/?q=node/14957

http://www.tahmazo.com/products/catalogue/75/160

If you want efficiencies ask for the 3.7Kv motor version instead of 4Kv version at the LHS.(the later suck more current.)
If I am not wrong price of the EDF with the motor is pretty attractive which I think is a good buy considering how well this EDF is made. Shop also sells impeller should you need replacement.


The current drawn on each ducted is around 15-17 amps so two ducted is around 30 -34 amps using the 3.7kv reno motors but more if you are using the higher kv motor.
A good 2200mah should able to handle this current.



Wellcome to the duct side.

[edmond22]

Hi a twin 55-60mm size will give you a good thrust.

see link http://shop.singahobby.com/?q=node/14957

http://www.tahmazo.com/products/catalogue/75/160

If you want efficiencies ask for the 3.7Kv motor version instead of 4Kv version at the LHS.(the later suck more current.)
If I am not wrong price of the EDF with the motor is pretty attractive which I think is a good buy considering how well this EDF is made. Shop also sells impeller should you need replacement.


The current drawn on each ducted is around 15-17 amps so two ducted is around 30 -34 amps using the 3.7kv reno motors but more if you are using the higher kv motor.
A good 2200mah should able to handle this current.



Wellcome to the duct side.

Sorry Babylon5,

How do you come to the conclusion that using a 4kv motor is less efficient that 3kv motor?

The efficiency is determined by the motor specs. If a 4kv motor max efficiency is 85% with current at say 45amp and max 500watts and you mate that to a 55mm fan and found that with 3s it is generating 500 watts at 45 amp, I think you are quite there with the motor already.

Do not think a general statement like this suffice to support your stated logic. Drawing more current doesn't mean less efficiency, it is only so if the resulted higher amp draw did not bring about increased RPM/ thrust/ efflux velocity. Are you trying to say that say paying an additional increase of 20% current draw did not bring about 20% increase in power? Or maybe even just by saying 20% more current brings about only 5% increase in power, not worth the effort. That will make more sense and this however greatly depends on your chosen power setup, not general 3kv or 4kv logic.

I think one should play the EDF game by asking yourself what watt per pound range you want to settle in, plan you power combo to that and whatever battery/ motor constraints you have.

Taking the test done by RC-Warbirds (see below), people normally go for lower KV motors to facilitate the use of higher cell count and achieve same watt output with higher voltage and lower current. If you were to take the same results below and run both with 3s setup for example, it doesn't make sense to run the 3w at 3s at all.

Example 1:

Motor: 2W (4740 KV)
-Max Current: 40 A
-Max efficiency: 88%
-Power Nominal: 450 Watts
Fan: Wemotec Mini480 Fan
ESC: CC 60 Amp
Battery: 3s1p 3200 mAh Lipo (20C)

Max Amp draw of 44.9 Amps max and +400W of power for most of the pack capacity.


Example 2:

Motor: 3W (3020 KV)
-Max Current: 35 A
-Max efficiency: 88%
-Power Nominal: 450 Watts
Fan: Wemotec Mini480 Fan
ESC: CC 60 Amp
Battery: 4s1p 3200 mAh Lipo (20C)

Max Amp draw of 30.3 Amps max and +400W of power for most of the pack capacity.

[bigfilsing]

Thanks babylon . I do like the look of the tahmazo stuff just worried the 3mm shaft is a bit restrictive in motor choice. I'll pop down there later today and see what kind of deal i can get.

It's looking more likely that a single fan is the way to go so maybe the 69mm.

Cheers

[bigfilsing]

Hi Edmund.

I can see where you are coming from more volts = less amps. Your 2 examples equate to the same power output but the 4s would have a longer duration time. Is this correct?

What does the "w" refer to in your 2W (4740) . Motor windings??

Given my imposed restriction of 3s 11.1V lipos 2200 , would i be better off with the 3.7 or a 4 + k motor ??

Cheers

[edmond22]

Hi Edmund.

I can see where you are coming from more volts = less amps. Your 2 examples equate to the same power output but the 4s would have a longer duration time. Is this correct?

What does the "w" refer to in your 2W (4740) . Motor windings??

Given my imposed restriction of 3s 11.1V lipos 2200 , would i be better off with the 3.7 or a 4 + k motor ??

Cheers

Yes, you will better flight duration due to the face that you are using less current with the increased voltage. This however will need some consideration. You will have increased weight due to the additional cell. To give you another example, I used to have a AJ Extra 330 that flies on 3cell 2500 driving a 14x7 prop. That is good for the 4-5mins of my style flying, I switche dto 4s 2500 driving a 13x6.5 prop and realised I needed less throttle power to do my usual flying and gained about 6-7 min flight time. It is easier on the batt but harder on the esc and motor (in terms of watt throughput)

I am not sure about the "W", could be marketing terms or winding lol.

For your last question, it depends on the brand you are dealing with. What is your project weight AUW est? Let us derive the watt per pound we want to achieve and then we can decide what fan motor combo is best. Assuming you are talking about a typical 20c 3s2200 lipo. Continous current run for that cell is about 44 amp.

For 500-650 gram AUW, I like GWS edf55mm with Himax 2025 4200 motor, this mate with 25 amp esc will give you about close to 250watts which is over the 175w limit for that motor, so be careful with newer high discharge batts.

For 1kg - 1.3kg AUW, I like HET 6904 fan or Wemotec minifan 480 with HET 2w20 on 4s or 2w23 on 5s. The 2w20 combo on 4s will give you about 40ish amp draw with about 500++ watt power. The motor is capable of 700 watt. I am currently pushing the motor further with 5s and my latest results tells me I am getting about 850-900 watts on about 50amp draw.

I never bother about static thrust (quite irrelevant with EDF in a way), only bothered with watt per pound rule and efflux velocity. When launching the model becomes a problem, I either think about ROG or bungee launch. When the model gets on step and "bites" the air, you can pull loop and whatever and instead of theorizing whether it is capable of unlimited vertical, I just fly straight up till my eyes give up and is being forced to turn it back down.


Good article for EDF introduction, tells you about the wattperpound guide.

http://www.rcuniverse.com/magazine/article_display.cfm?article_id=1077

150w/lb for Fair EDF performance
200w/lb for Good EDF performance
250w/lb for Great EDF performance
300w/lb (or greater) for Extreme EDF performance

[edmond22]

Btw,

FYI, some people will talk about theoritical unlimited vertical vs static thrust and I have this to say.

I have a EFRC Extra 300 that is capable of unlimited vertical. More than 1.5 to 1 thrust weight ratio but seeing this plane going up vertical is quite a pain if I were to just let my eye be the limit. It is just plain slow.

Now, when I have a F20 Tigershark that has less than 1:1 static thrust weight ratio, it is quite another to see this fellow climb vertically using your eye as a limit. It doesn't have unlimited vertical, it will bleed speed and drop eventually, but because it is moving at 100 over miles per hour, it climbs and cover so much distance that you and your eye will think it has unlimited vertical. It is more spectacular and that is the way you want it. Static thrust to me is easier for takeoff and launch, not for unlimited vertical, when you haven't got the efflux velocity, it is going to be a pain to watch it do unlimited vertical. Illusion works better.

[bigfilsing]

Great replies and link ( wish i'd found that earlier) Explains a lot.

I know what you mean about the static thrust versus verticle climb. Even on my simple dupron F22, it will vertical climb but the "load" it puts on the power system is crazy and by the very nature of a dupron plane all the components are light and operating on the limit of power/heat so it's just not worth it.
It currently flies great and i'm not going to ruin that by overloading the power setup with vertical

AUW ? Well it's a scratch build so i have some control over things. I'm aiming 450 grams max.

[viper1990]

More than 1.5 to 1 thrust weight ratio but seeing this plane going up vertical is quite a pain if I were to just let my eye be the limit. It is just plain slow.

Now, when I have a F20 Tigershark that has less than 1:1 static thrust weight ratio It doesn't have unlimited vertical, it will bleed speed and drop eventually, but because it is moving at 100 over miles per hour, it climbs and cover so much distance that you and your eye will think it has unlimited vertical.

Illusion works better.

Yessss..., totally agree with those sentences.

Months back i always see those people at the field doing vertical climbs with ducted fan planes and i wondered how they did it even with 1:1 or lesser thrust to weight ratio. Until i played around with efflux velocity with my F-16 blackknights and tried it myself. Works beautifully. You just have to give it time to pick up speed on a straight and level flight then gently ease up the elevator and watch it climb vertically! Though it won't be "unlimited vertical" a few seconds is "shoik enough" , sensational feeling!

[SKYHOBBIES]

Thanks Edmund for your explaination on the efflux velocity... it makes me easier to explain to the customers who has the negative impressions that the EDF model can go vertical the moment it leaves your hand...

Thanks again for your input... +points for you

[bigfilsing]

Wit Edmunds help and from my research it's clear.
Static thrust is the fans ability to suck in stationary air and push it out.

Whats more important is the fans abilty to take in air at 20 kph ( or whatever speed the plane is traveling at) and accelerate it into thrust .
I'm getting there slowly

[Babylon5]

Sorry Babylon5,

How do you come to the conclusion that using a 4kv motor is less efficient that 3kv motor?

The efficiency is determined by the motor specs. If a 4kv motor max efficiency is 85% with current at say 45amp and max 500watts and you mate that to a 55mm fan and found that with 3s it is generating 500 watts at 45 amp, I think you are quite there with the motor already.

Do not think a general statement like this suffice to support your stated logic. Drawing more current doesn't mean less efficiency, it is only so if the resulted higher amp draw did not bring about increased RPM/ thrust/ efflux velocity. Are you trying to say that say paying an additional increase of 20% current draw did not bring about 20% increase in power? Or maybe even just by saying 20% more current brings about only 5% increase in power, not worth the effort. That will make more sense and this however greatly depends on your chosen power setup, not general 3kv or 4kv logic.

I think one should play the EDF game by asking yourself what watt per pound range you want to settle in, plan you power combo to that and whatever battery/ motor constraints you have.

Taking the test done by RC-Warbirds (see below), people normally go for lower KV motors to facilitate the use of higher cell count and achieve same watt output with higher voltage and lower current. If you were to take the same results below and run both with 3s setup for example, it doesn't make sense to run the 3w at 3s at all.

Example 1:

Motor: 2W (4740 KV)
-Max Current: 40 A
-Max efficiency: 88%
-Power Nominal: 450 Watts
Fan: Wemotec Mini480 Fan
ESC: CC 60 Amp
Battery: 3s1p 3200 mAh Lipo (20C)

Max Amp draw of 44.9 Amps max and +400W of power for most of the pack capacity.


Example 2:

Motor: 3W (3020 KV)
-Max Current: 35 A
-Max efficiency: 88%
-Power Nominal: 450 Watts
Fan: Wemotec Mini480 Fan
ESC: CC 60 Amp
Battery: 4s1p 3200 mAh Lipo (20C)

Max Amp draw of 30.3 Amps max and +400W of power for most of the pack capacity.

Very simple, if the Tahmahzo EDF is using the same class of motor, same magnet, except turn, there is a electrical to mechanical loading to consider or "matching ".
Initially(some years back) tahmahzo uses the 3.7KV motor generating 480 grams of thrust at around 17amps on 3 s lipo.
Now they change the winding of the motor to get 4Kv++ and draw 20 amps just to get 520grams , just 40grams more thrust at 3amps ... that is not efficient.
By the way you won't find the old data but I have kept the old advertised data by Tahmazo years ago and post it in Daddyhobby forum Tahmazo cannot remmember which old thread.
My early experiment shows if you use a higher KV motor of the same size and class (apple to apple in comparison). The Higher KV motor will generate more static thrust but at much more expense to the electrical power as compare to the lower KV motor.

My definition of efficiency= Static Thrust/ total electrical input power or electric current

Tahmazo 3.7Kv motor 55EDF=480gram/ 17=28.23grams per amp
Tahmazo 4KV motor 55EDF=520/20 =26 grams per amp.



Cheers

[edmond22]

Very simple, if the Tahmahzo EDF is using the same class of motor, same magnet, except turn, there is a electrical to mechanical loading to consider or "matching ".
Initially(some years back) tahmahzo uses the 3.7KV motor generating 480 grams of thrust at around 17amps on 3 s lipo.
Now they change the winding of the motor to get 4Kv++ and draw 20 amps just to get 520grams , just 40grams more thrust at 3amps ... that is not efficient.
By the way you won't find the old data but I have kept the old advertised data by Tahmazo years ago and post it in Daddyhobby forum Tahmazo cannot remmember which old thread.
My early experiment shows if you use a higher KV motor of the same size and class (apple to apple in comparison). The Higher KV motor will generate more static thrust but at much more expense to the electrical power as compare to the lower KV motor.

My definition of efficiency= Static Thrust/ total electrical input power or electric current

Tahmazo 3.7Kv motor 55EDF=480gram/ 17=28.23grams per amp
Tahmazo 4KV motor 55EDF=520/20 =26 grams per amp.



Cheers

Bro that is to be expected right? You never heard of law of diminishing returns? And that is only 1 brand you are talking about.

You specifically pick a 3 and 4 kv motor for comparison, you might as well take a 1kv motor and compare a 4kv motor of the same brand class and whatever and you will find that you get even better efficiency than ever before. But that is not going to fly your plane.

Do you not think the point you make about the 3kv and 4kv motor applies specifically to the brand Tazmazo only, information is only good if they are timely and delivered correctly. The first post you made seems to give the impression that all 3kv and 4kv motor behaves like you have pointed out.

When I have a plane that needs a 500w power input, I will find a motor that has a reasonable eff like 75-80% to give me that output, you can find many brands like Mega, hacker, Medusa, Neu. I do not think I should go for a 400w setup just because 10-15% difference in effieciency.

Dun forget you can simply throttle down a little and get a 400w system out of a 500w for example, bet you never measure the efficiency of that.

See the attachment Motocalc, If I were to throttle down, I get nearly the same efficiency you are talking about but most importantly, I have the choice to go faster or go as you say efficient, what would you pick? 2 options or only 1 option?

[Babylon5]

Hi Edmond, if you look at thread #1, our friend has limited budget using
2200mah 3S lipo with limited current of 30-35 amps.
Recommending Wemotec on 4S is clearly not helping our friend nor responding to his query.
As far as law of diminishing return I am fully aware of this .

On the other hand I have come across other twin set up(not a Tahmazo fan) on 3s 2200mah lipo drawing a mere 25amp capable of hauling a 720grams aircraft with good vertical performance.

Would our bigfilsing be interested to know about this setup ?
I leave this query to him.

Cheers and all the best.

[edmond22]

Hi Edmond, if you look at thread #1, our friend has limited budget using
2200mah 3S lipo with limited current of 30-35 amps.
Recommending Wemotec on 4S is clearly not helping our friend nor responding to his query.
As far as law of diminishing return I am fully aware of this .

On the other hand I have come across other twin set up(not a Tahmazo fan) on 3s 2200mah lipo drawing a mere 25amp capable of hauling a 720grams aircraft with good vertical performance.

Would our bigfilsing be interested to know about this setup ?
I leave this query to him.

Cheers and all the best.

If you read properly, I wasn't recommending that setup to him, I am telling you that blindly recommending 3kv motor in favour of 4kv quoting better efficiency is plain wrong. The way to do it is ask yourself what watt per pound range you want to achieve, you then work backward from there and THAT IS exactly what I recommended to Bigfilsing and he did find it useful. If you read carefully again, you would have noticed I offered a setup that is completely within his constraints.

I have given you the example of why your logic doesn't make any sense (can't be any subtle anymore cos you asked for it) and you are clearly unable to answer. I am not against you recommending advice and such, but you must learn to accept that people can tell bad advice from good ones and they CAN tell. Deal with it.

On the honest side, I am pretty sick of it time and time again how you similarly try to advocate cutting 6 blades to 3 blades and claim better efficiency. So before you talk about using 3kv motor instead of 4kv for better efficiency, learn to throttle down first and see if it makes any diff.

I dun want to start with your "good vertical performance" really. It took you long enough time to phrase it that way and not incur some of the member's wrath here on the claim to unlimited.