DUCTED FANS

[MIKE S]

Having now scratch built a number of EDF planes, some a failure and some a great success, I decided that what I needed was a test rig. I built up a static frame from MDF and a floating EDF holder which sits on flexible strips allowing it to move along the thrust line. Various EDF units can be mounted in a vertical plate. To drive the EDF I used standard bits such as an old 60amp ESC, an old radio receiver and either a LiPoly or 12volt car battery.

To measure the thrust I bought a £9.99 kitchen scales. (Robert Dyass) Super bit of kit. Dismantled it had a 5Kg load beam connected to a control pnel and LCD display. Cut up in to separate bits, it proved possible to fit the load cell at one end so that the floating EDF holder pushed against it. The panel was now cut to only be what was needed, the two AAA batteries were mounted underneath in their holder cut away from the main moulding.  

 Reslults will follow later, but first test runs with an Airpower fan unit have shown that it works!

[Tim Mackey]

look forward to the build notes and pictures Mike !

[MIKE S]

Finished off the Thrust Test Bed now. All rigged up and ready to go. Unfortunately I have had a blade off my Airpower 70 unit and am waiting for a new fan from the supplier. I have two TowerPro 70mm units, one with 3.9Kv motor and one with 5.1Kv. It will be interesting to see which one produces the maximum static thrust. These are good cheap units, but do need a lot of balancing to make them run at a smooth full power.

Airpower EDF's are much better feeling and have a better motor adapter.

Next to try are the HyperFlow units from Great Planes, but so far I have not found a UK Supplier.

 I would post the photo's, but have not yet discovered how to achieve this. 

[Tim Mackey]

Michael, you need to post them first onan image hosting site such as photobucket.

Then copy " direct link to image" option from host, and use the link button on the forum ( picture of a tree ) and presto ! 

[Tim Mackey]

Green and brown thing, grows out the ground, some are deciduous, some not.

Branches and leaves, oh and yeh....its over on the right next to the ABC/ spellcheck button

However as once famously quoted  " I see no SHIPS! "

[MIKE S]

I know that the ducting has a big effect on thrust, but for the time being I am only doing comparison between vatios fans and motors of the same basic size.

So far I have recorded the highest thrust with a TowerPro EDF from RCM Direct using one of their 5.1Kv inrunner motors. This at 1 lb on my digital readout and 210 watts. LiPoly at 10 volts. The same fan with the RCM Direct 3.9Kv motor only gave  9 oz thrust. A cobination unit again from RCM Direct but with an outrunner built in was a poor 6 oz thrust.

My test rig has not been calibrated yet, so the thrust may be reading low, but the watts and volts are correct using a quality in line unit. This does not matter much as I have proved that the 5.1Kv motor in the TowerPro unit are my best option to fit in my North American Fury, which failed after one flight with a WemoTech. The fan broke up with the 5.1Kv motor.

 More work going on. Results later. New Hyperflow EDF's with AMMO motors on route from USA.

[scott cuppello]

I wish you luck! I have learned so much about EDF of late.....the hard way.....and from the guys in the USA.....who seem very knowledgable. They do a lot of static tests, but IN the model, very good for determining "cheater" hole sizes. And they do teach idiots like me not to leave the induction "rings" out [because they were such a pain to fit], when our cousins over the pond showed me tests of the fans/motors I was using with the rings out and in.....having those little round bit's of plastic in upped thrust by 200g!

I don't envy you for comparisons though, I mean there must be say, a dozen cheaper fan unit's on the market, several hundred motors, then voltages......what a headache!

[MIKE S]

Scott,

You are right, there are now so many EDF's on the market. Most of the cheap ones are flimsy and with fans that do not have the correct pitch change from hub to tip, resulting in uneven flow over the fan diameter. Some are fairly good, but have moulded fans in ABS which does not like 50,000 rpm. Some are very expensive and look like they are made from drainpipe. A friend has just bought the rolls Royce of EDF's and it looks home made. The fan is beautiful but the shroud and other bits are very amaturish, although with the correct motor they claim to produce the thrust.

Motors are another learning curve. Does one want a fine pitch fan with a high reving motor or a coarse pitch with a low revver? My tests do indicate that the best for static thrust is a fine pitch (like a propeller) with a high rev per volt. Then if the motor does not have enough power to reach the high revs, due to too large a fan, it is inificient at take off, but might be very fast in flight. Prices of motors for EDF vary from a few pounds up to hundreds. Once in the unit it is difficult to know which one you have spent your money on. Hence the need to test! All costing quite a lot though. All for the hope of building  a Gloster Meteor which can take off! 

[MIKE S]

We are getting on with testing EDF's and learning something every day. Using the 5.1Kv motor in a TowerPro 69mm fan, resulted in the best thrust for this size unit, but drew far too many amps, about 50. The 3.9 Kv motor reduced thrust, but not by much and the amps came down to 30 maximum.  Static thrust with the intake rings on averaged 23 ozs.

The much smaller Hyperflow EDF's with Ammo motors, bought direct from Tower Hobbies in USA are superb little units, giving 16 oz thrust at 200 watts. I am using two in a scratch built Gloster Meteor. In the air with good design of ducting, I expect 23 oz thrust.

My next phase is to get a data logger to record all my tests and produce graphs. One thing I have learned is that using LiPoly's for the power on the rig is not impossible but does not produce consistant results as the voltage drops quite fast and one has to charge up for every test. A Large car battery with a heavy duty charger provides a constant voltage and allows more testing with consistancy.

Another finding is that very careful balancing of the fan and nose is worth doing. 

[Paul Williams]

Hi Guys,

very new to all this, having read your threads I wonder weather you could advise? I just finished a muiltiplex twister I was bench testing and found the fan unit amps start to drop off at around 80% throttle. It runs up to 18amps then drops to 14 at full. I noted your comments on the induction ring the model as standard does not have cut outs for the ring so I just fitted it without. Could this be the problem? I have ample power 25c 2500mah 3s batteries and the esc should handle 45amp constant. its giving 680g of thrust at 80% with no improvement to full. Its a 5 blade set up with a 3600kv motor I cant measure the rpm though.