Topic: which fan units for lander rafale?

Hi all, I'm trying to find an alternative fan set up other than the lander edf units.. for me they are quiet costly so if anybody has any experience/info as to what fan units I could use, it would be very helpful .
Thanks in advance.. Codfather 

Has anybody any info for me? 68mm fans are required & I want to run them on 3s

Wemotec Minifan or HET fans are popular in the 68-70mm size, but depends on your budget. One of those with a decent motor from the HET range say may not be much cheaper than the Lander fans, but will be a fair bit lighter. I have had good performance from the Minifan with HET 2W-20 motors on 4S myself. The HET motor for 3s is the 2W version.
There is quite a lot of info on the Rafale on the well known US based forum as well as the UK ones.

Iv been looking around and found some 'less costly' Dan units along with 3600kv inrunners ...put it this way all that has has come in at a lot less than 1 lander fan unit :-) just fingers crossed that it gets it airborne 

Following on from this, would it be possible to run some 6904 het fan units with my 3500kv in runners ? They are 28mm diameter with a 3.17mm shaft

I'm not sure what size shaft the HET fan adaptors use, I know you can get different sized ones for a Minifan. I'm pretty sure the HET motors I have are 3.17mm or 1/8 in old money, so they should be ok. Best check!!

What fans you need will depend on how much thrust you need, that in turn will depend on wing loading, all up weight, style of model, and personal preference.

With a Rafale type model 1:1 thrust to weight or better is presumably going to be your goal.

Whether your 28mm inrunners will work in a 6904 will depend not only on shaft size although you can buy various adapters, but also on whether they can work at the amperage the fan will draw on 3s with 3500kv.
As a very rough guide that is likely to be around 27-31,000 rpm probably about 450-500 watts and about 700g- 900g of thrust, on 3s 450-500w that is going to mean roughly 42-47 amps. If your motors can take this they will be fine.

If the model is a twin and weighs about 1.3-1.4kg then you should be OK.

I think Dizz has better figures for the 6904 and they maybe on a spreadsheet somewhere on RCMF, have a quick look at his build logs.

FWIW I bought the Lander 6s fan/motor combo for my Hunter.  Paid premium price, but I have to say it's proved superb - very safe bet.  Overlander were flogging them off for less than £50...

Mike

BRC hobbies have some cheap 70mm fans at the moment http://www.brchobbies.co.uk/?page=shop&action=additem&item=575
I have no idea on quality but they are cheap and a UK supplier, but unfortunately they are for 4s
I am rather doubtful of their claimed thrust figure as usually somewhere between 1.2grams/watt and 2grams/watt is about what you expect at 450 watts whereas they are claiming 3grams/watt and I haven't come across a fan that will do that. If I was buying them I would budget on getting about 700-900grams of thrust. Unless their claimed wattage is wrong and then who knows. Max amps for their motor is 43 and on 4s that is about 600 watts and I would reckon about 900grams -1.1kg of thrust if it was achieving that, but without testing it I cannot really say what the figures would be.

I'm now thinking it would be better economy for me to run on 2x 4s for my fan units as I already have a 4s 2300 which I recently bought for my squall. Only problem is, I'm not sure if my inrunners (black mantis 3500kv) will cope with 4s ? ?
Also found out that gc have the het fan units in stock with the 3.17mm shaft so iv gone ahead and ordered 2 :-)

I think they will really struggle if they are the 2846 which is rated for a max of 37 amps.

I think they will really struggle if they are the 2846 which is rated for a max of 37 amps.

Is this because the current will possibly exceed 37amps or the inrunners can't cope with the higher voltage of 4s lipo? 

There are only two limits on an electric motor.
1)The amperage that it can handle as this causes heating and heat has to be disipated either by the weight of the motor or by cooling. So too many amps causes too much heat which either melts the insulation on the windings and shorts them or damages the magnets. Your motor is rated at 37 amps and is likely to draw more than this if on 4s but until you test it with a meter it is difficult to know precisely what it will draw. If it is drawing more than this it will either slow down as the magnets over heat, or more likely start to emit smoke and stop working and either need rewinding or replacing. 

2) The physical speed it can rotate at without suffering from mechanical damage either bearings or shedding internals. This is likely to be close but under that point using 3500kv*15volts*80%efficiency =rpm but I do not know what the actual figure for that motor is.

Otherwise volts and watts do not really mean very much in terms of danger to the motor. As the voltage goes up, the motor will draw more current because it spins faster doing more work. The way round this is to use a lower KV motor so when someone says that they are using 6s because it means a lower amp draw they are saying that they are using a lower kv motor than the bloke with 4s set up and running a similar rpm.

Well I tested one of my fan units on a 4s lipo and fully wound up it was pulling 45amps at nearly 700watts. What comparisons would a 3s lipo produce?

Difficult to say without knowing the fan but expect roughly half the power requirement so 45 A would drop to 30-34A probably. Thrust will drop quite a lot as well but again difficult to say as fans become progressively less efficient at converting power into thrust as the rpm increases.
Lets assume that at 4s making 45A and 666W you got about 1200 grams of thrust at round about 1.9 grams thrust/watt
Then you may get on 3s 600-800 grams thrust at say 300-350 watts at 2-2.5grams /watt

It did occur much later to ask you if you measured how hot the motor got when running on 4s. The reason I ask is that I have found with EDF that quite often you can get away with being a little bit over the maximum Amperage at the initial start up values as they will come down a bit over the course of the run.
I think that is also because the motor cooling in a ducted fan is quite good compared to say a typical propeller sport model. with a semi enclosed motor. However I now tend to use outrunners with a stand off adapters which are fairly cheap and have most of the motor in the airflow rather than in the motor tube so with an inrunner in a plastic fan this might not be quite the same.

I am going to run up a fan on my 4s loong max for a 10 second wot with my watt meter wired through and Il check the temperature too. I did notice it was quiet hot last time, but iv got a digital thermometer with sensor probe so Il keep that attached to it for a minute afterward to see how the heat dissipates ...

You may if it is a twin find that you get a voltage drop that means that you pull fewer amps as well when both fans are hooked up depends on the battery and set up that you use.

Il be using 2 esc's with 2 lipos hooked up and the throttle leads y leaded into the rx

It is more a question of one battery or two. For example if you use a 3000 mah 4s 30c  battery and two fans that would pull 90 amps then the battery is likely to run at 13.8V rather than say 14.8
If you use 2  4s 2500mah 30c batteries in parallel then so long as your wiring is thick enough the voltage drop would be minimal.

I don't think I can wire my lipos in parallel with me having 2 esc's and 2 fan units can i?

Yes if you want to, or separately to each ESC. The advantage to parallel is same voltage to each ESC and motor. The disadvantage if one pack collapses you lose power completely. Advantage if one pack collapses you don't get a massive assymetric power change not too good on a low pass. disadvantage you may lose the good pack as well. advantage more even discharge of packs, and so on. So pros and cons but I daresay the manual has a reccomendation .

Hi, yes the manual suggests each pack per esc to fan unit ,with the esc's y leaded.. Il look into your other option though.
In the meantime I ran a few tests on one fan with my loong max 2300 25c 4s . After 3 10 second bursts of wot I achieved 45 amps at 700 watts and the motor/ esc temp was approx 31c so I'd say I'd get away with that , but I'm guessing Il have relatively short flight times on these lipos.

Well you should be able to get (2.3*60)/45 about 3 minutes at full throttle so 2minutes 45 seconds for 80% useage, throw in plenty of throttle management and you may get to 4 minutes or more depending on your flying style.

Iv started to put this together now, fan units and fuselage all built up now.. looking good I have to say

 


Rafale ready for Its maiden flight ..

Good luck 

Have you got about 1:1 thrust? With 700 watts I would think that you have, so it should go really well.

looking good coddy...i`m sure it will go well.
we`ll have to drag race beside my funjet...

Had its maiden today! With about 1400 watts of power its more like 2:1 thrust ratio! It leapt out of the launchers hand and quickly climbing out so fast !
@tsr I got about 2minutes or so on my first 2 flights ,I had about 35%  left .
Just need to move cg forward slightly but, what else can I say but wow!
 

Excellent stuff so where's the video?
With 700w per fan I'll bet it went like a "homesick angel"

Nobody willing to do a video this time , hopefully next time il get one done!

Glad to hear it went well. Whats the vertical performance like? Top speed is nice, but some airframes will never be that fast. But a good bit of shove is nice to have 

Are they cheater holes underneath?

@tsr the back 2 are cheater holes , the recesses for where the retracts would go make good grab handles for launching.
@ stuey on my maiden I only managed oval circuits with the odd low(ish) pass, be sure il be finding out its vertical performance next time out!

I have a bit of a thing about cheater holes. For static and low speed thrust they are useful but based on my experiences I think that they ultimately damage top speed. This I think is because they cause a turbulent flow in front of the fan from the main intake cheater hole flow intersection, so when they are present  the system is not as efficient as a single duct.
So it all depends on what you want out of the model. Easy hand launch then yes cheater holes have their place. Otherwise I am tempted not to include them. I haven't ever used them on my own designs but then they are by no means perfect, so perhaps that is where I am going wrong

I know cheater holes are the 'marmite' of edf models, & as this model had cheater holes already in, and with this being my first edf build I didn't want to interfere with the model design too much.
Also I need low end thrust for my hand launches so it works out ok for me :-)

I was wondering how it would be possible to run my lipos in parallel with 2 esc's ... I'm thinking of trying it if its possible to see if it will increase flight times.. not that iv had any flights since my maiden :(

It will not increase flight times.
However you make a double X so both red wires from the batteries in one connector and both Esc red wires to a single connector repeat for the black wires of each. Then connect the red battery connector to the red Esc connector repeat for black connectors. Both are then in parallel. However flight times should remain the same, and so long as the connectors are of sufficiently low resistance there will be no drop in power delivery.

Well il probably leave it as it is then  , had another successful flight today, better battery consumption with over 3 minutes flight time in moderate wind 
Iv got a video here of my flight which was filmed by a clubmate.. it isn't the best video but you can see how it's performing! Unlimited vertical too! 
 https://www.youtube.com/watch?v=IayfTOlj7lQ&feature=youtube_gdata_player

Cheers!

Very nice too. Glad to see it flying so nicely.

Very nice too. Glad to see it flying so nicely.

Thanks! , your input has helped me a lot with this build