UK EDF retailer?

[Tony Kenny]

HI,
I need to source a new 70mm EDF unit, fan and motor for my Sapac Hawk, can anybody suggest a good UK retailer? My usual model shop doesn't seem to have much in EDF but I've seen a lot on Amazon although the quality is unknown.

Also, some questions, if I may.

1. Is the diameter of an EDF unit measured across the fan or the outer diameter of the duct?
2. The model had a 5 blade, (i think), would I get any benefit from upgrading to more blades while I'm at it? I've heard it can achieve more air flow and potentially quieter running.

Many thanks!
Tony

PS. If anybody read my previous thread, turned out the ESC was fine, the motor was toasted which is why it was drawing so much current and delivering so little power!

[John Emms 1]

Hi Tony,

The diameter quoted on the Wemotec fans is of the rotor, and the OD of the housing on the 70mm Mini Fan is 72mm - I guess the others are the same, given that many are inferior copies!

The more blades, the higher the current draw on the same motor and battery, so that would result in greater power. The fans with more blades also tend to be quieter, but I never saw that as an issue with any EDF system.

My advice is to go straight to Wemotec where you will get very good quality and performance at sensible prices.

I did a search on this model to find the weight, but "lighter than normal for this type of model" wasn't the most help lol.

If you can give me a weight, I can help you a lot further.

Regards,

John

[Tony Kenny]

Hi John,

I found the product on line and they said the all up weight was approx 46oz = 1.3kg,

I've also found some EDFs online that can give 1.4kg thrust which sounds like it would be enough for getting used to EDF.

[Karl Jackson 1]

Hi Tony. It's not a uk supplier but turbines-rc in France is very good. Wide range of units with option of assembled fan and motor combos which are balanced. Only dealt by website and email but very good English and updated by email of order progress. Web address is www.turbines-rc.com

[John Emms 1]

Hi Tony,

Many will say you need far more power, but work on a minimum of 150W/lb, and aim closer to 250W/lb if that is practical (mainly considering space required for, and weight of, batteries). I work that out as between 430 and around 700W.

If you really must use 3S, then this would give you around 566W **LINK**

Ideally go for a minimum of 4S, and this would be around 670W **LINK**

Mad would be this on 6S at around 1200W (55A), but you would need to carry the weight of a 6S 3000mAh battery **LINK**

As general rules go for a low number of winds and longer motors to maintain higher efficiency at greater current levels.

Hope that helps,

John

[Tony Kenny]

Hi All, reporting back now I've got a new motor installed.

I picked up a cheap motor from China, worth a go. It's a Soldial 12 blade 3500KV 64mm. £24.81 on amazon, arrived in a couple of weeks so pretty impressed with that.

In the model on its wheels and nose pushed up against some scales, it's pushes about 400g of thrust. That's probably not the best way to measure thrust but gave me some idea. On the power meter I get the following, but forgot to read the Watts so my power values below are calculated from the current x standard voltage for the battery pack.

Model all up eight just shy of 800g (1.7 lbs). With the 150W/lb rule that would need 255W to fly.

On 3 cell. 40A, 435g thrust, so about 480W

On 4 cell. 60A, 600g thrust, about 960W - but, the larger pack will knock to CoG well off and I doubt the wing loading could take it and the wings would rip off if I try to pull any high-G moves.

At full throttle, the thrust starts to drop off pretty quickly, as does the battery capacity! No surprises there I guess though.

Does that sound like enough? Will be a while before I can fly as I need the right combination of weather, free day and available club member to assist with sound testing before I can fly it!

Final question, this model has wheels and rolls beautifully, but, would I get much difference in flight times if I remove the uc?

[John Emms 1]

Hi Tony,

Your figures are interesting, as with the 3600kv Mega 16EDF (16/17/2) in the Wemotec 70mm Mini Fan, we were just short of 1kg of static thrust with 3S at 40A using the intake ring, and an optimized outlet. However, historically, Mini Fan models were flying on less power than that, and your model is also lighter than a typical Mini Fan model (around 1kg). Model boats really need to be around 1:1 thrust to weight to perform well, but aeroplanes perform well on a lot less - only a tiny part of a loop is true vertical, and loops can be canted over so that none of the loop is vertical.

If 4S with your system is not working because of weight, and the current draw being too much for the batteries, then something needs to change, either lower resistance batteries, or reduce to 3S.

It has always struck me that the choice of wheels or not is a practical question. My only club at the moment has a tarmac runway, so it is difficult (and inconvenient for others) not to use wheels on the runway. Other clubs in the area only have grass, so a bungee launch is the answer there. Unlike a propeller, a fan does not unload, but keeps driving throughout the flight, so I doubt that wheels or not will make much difference to the flight time. No wheels will make a big difference to performance, due to lower weight and drag, particularly on lower thrust levels.

My thoughts are by no means definitive, but I hope they are of some help.

John

[Tony Kenny]

Hi John,

I must admit, I did expect greater thrust and it did fell less powerful that the old motor I took out even though it appears to be a similar, if not better, spec. With the old motor, if I held the model in my hand and went full throttle, it tried to pull away quite sharply, this one barely moves on 3S with 40A current draw. However, the old model had a 5 blade, this is a 12, but I thought that would be better rather than worse.

But, I just realised something, the ESC might be one I'd messed with in another model, so maybe the motor speed is set low? I'll try settings later and maybe a different ESC to see what happens.

Are there specific ESCs for EDFs? Could it be the ESC that actually burned out the previous motor and gave the blue smoke?

[Tony Kenny]

I just checked the ESC set up, starting with a reset then checking battery type and changed timing. It does try to pull from my hand when held up at 45 degrees but actually reads less on the scales. I suspect that my thrust reading may be very inaccurate given my method.

I looked at the power meter properly this time and it's around 400W and of course decreases by about 10 watts every few seconds. Just maybe 20 seconds or so of full power takes about 10% capacity from a fully charged 3S 2200mAh. Based on the Wattage, should be Ok to fly, we'll find out when the conditions are right at the field.

Re the wheels, I only fly on well trimmed grass but when I dead stick landed short, the uc was ripped off. So, just like my mini-switch, if they come off again, I might just leave them off and hand launch instead.

[John Emms 1]

Hi Tony,

If it's trying to pull out of your hands at 45 degrees, all will be fine. At 40A, I would be using 3300s, but half decent 2200s should be able to cope with 40A. Is the power reduced by 10% after 20 seconds? That would be quite normal.

The ESC just needs to be capable of the current that is being drawn, and not being used as a current limiting device. Classic ways of damaging an ESC are reverse connecting the battery, and having a poor connection between motor and controller.

Re the launching. I have seen EDF hand launched, but the super safe method is using a bungee to launch from a ramp. I have seen wallpaper paste tables set at about 15 degrees work really well for reliable launches.

Hope that helps,

John