David Ashby - Moderator Posted February 19, 2010 Share Posted February 19, 2010 Hi chaps, one of my aims this year is to get stuck into EDF. It's an area that I've touched a few times but not really got my teeth into . I've been flying a nice F-16 for the last few months and thoroughly enjoyed it. I fly Futaba and Jeti 2.4 and recently fitted the Jeti telemetry module to the model to see what it draws in the air. On the ground my watt meter reads 33 amps at full chat and the Jeti system confirms this static figure. Tractor prop models draw a few less amps in the air (and my system has confirmed this in other models) but I think I'm right in saying that there's been a debate in EDF circles? Some think the EDF systems draw more current while others don't agree. My in-flight reading was 33/34 amps for the F-16 at full throttle. I wondered if anyone had any thoughts as to why there isn't the usual drop? I've been told it's because air going down the pipe can't go anywhere else and builds pressure (current draw) on the fan or something but don't quote me there I guess there will be variables but any other observations/steer would be interesting. Edited By David Ashby - RCME Administrator on 19/02/2010 15:11:44Edited By David Ashby - RCME Administrator on 19/02/2010 15:14:58 Quote Link to comment Share on other sites More sharing options...
Ady Hayward Posted February 19, 2010 Share Posted February 19, 2010 Hi David, I've no numbers to give, but found that running time on wide open throttle on the ground and wide open throttle flight time to LVC were within a couple of tens of seconds of each other. Not very scientific but seemed to concur that (my) fans do not unload that much in the air. I daresay that will change with higher performance setups. Regards Adrian Quote Link to comment Share on other sites More sharing options...
Dusty Posted February 19, 2010 Share Posted February 19, 2010 Efficieny of the ducting, balanced rotor blades etc etc... What model you going for David? A fast foam JEPE model, a review for the Mag? Quote Link to comment Share on other sites More sharing options...
Dusty Posted February 19, 2010 Share Posted February 19, 2010 My Jepe JET 90 on 6s is pulling a mere 54A! Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 19, 2010 Share Posted February 19, 2010 I am curious a) Is the current drawn the same when diving b)Is it the same when climbing I am asking, as I had always assumed that the current drawn would be affected by the mass flow through the duct. In my own mind I had assumed that this changed with the models speed. Also do you know the velocity of the model? Although I am very surprised that there is no difference amps drawn static to flying. Just goes to confirm my suspicions, I need a data logger, just to know what is happening and then to see if the data fits with the various propositions made. Although not relating to ducted fans. I recently was talking and observing a modeler who was setting up a competition electric glider, also using a Jeti 2.4 and data logger. He also reported that there was no unloading of the propeller in flight, which also surprised me. I did see a graph previously plotted, as I remember it, it was the heights that were discussed at length over the flight, so I do not think I saw any evidence on the current drawn. Other remembering my surprise. Erfolg Quote Link to comment Share on other sites More sharing options...
David Ashby - Moderator Posted February 19, 2010 Author Share Posted February 19, 2010 Thanks Adrian and Dusty. It's this F-16 from CML (Shenzen Co) and yup a review that'll appear in the March issue. 70mm fan, 4S 2200mAh. 515 watts and 33 amps. Erfolg - I tried that as, yes, the current draw does change on a tractor prop when the model is climbing (increases) but I couldn't really detect any change no matter where the F-16 was going. I'd say she goes at around 70-80 mph based on another model I fitted a speed sensor to a couple of years ago. I'll keep playing though....Edited By David Ashby - RCME Administrator on 19/02/2010 15:40:05 Quote Link to comment Share on other sites More sharing options...
David Ashby - Moderator Posted February 19, 2010 Author Share Posted February 19, 2010 oops - pic...... I think I'm getting hooked .... Edited By David Ashby - RCME Administrator on 19/02/2010 15:40:42 Quote Link to comment Share on other sites More sharing options...
Ady Hayward Posted February 19, 2010 Share Posted February 19, 2010 Thats the way it goes.... A jet shouldn't have a prop turning on it...even if you can't see it. Now EDF is getting quite plug and play it opens the doors to a lot more possibilities.........so many ideas, so little building time. Adrian Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 19, 2010 Share Posted February 19, 2010 I will be watching to see what postulations are made. The apparent facts do not seem to fit with any ideas I have, as both seem to suggest that the work done is constant, I think. How can that be? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted February 19, 2010 Share Posted February 19, 2010 No complex tecchy info I am afraid ( typical for me ) but I can pretty much confirm what you say David - EDF units dont "unload" to the same extent in the air as a prop model. early testing with a couple of my models showed around 5-6% difference ( eagle tree logger data ) between static runs and flight runs, whereas prop models can be as much as 30% different - depending of coure on flight conditions, prop and model size etc.I love the F16 Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted February 19, 2010 Share Posted February 19, 2010 At my age I've forgotten more than I ever knew but the answer probably lies in the transmissibility of fluid pressure and resultant thrust ie the difference between the thrusts/pressure on each side of the fan and its relationship to the total pressure. A graph/plot will show a straight line. Quote Link to comment Share on other sites More sharing options...
stuey Posted February 19, 2010 Share Posted February 19, 2010 Posted by David Ashby - RCME Administrator on 19/02/2010 15:39:23: oops - pic...... I think I'm getting hooked .... Edited By David Ashby - RCME Administrator on 19/02/2010 15:40:42 Looks good, although I think the shape of the fin looks a bit wrong?? Should be a bit more of an angle on the leading edge and narrower at the top compared to the bottom. Edited By stuey on 19/02/2010 17:53:55 Quote Link to comment Share on other sites More sharing options...
stuey Posted February 19, 2010 Share Posted February 19, 2010 Not sure why my text is so small on the above post? Quote Link to comment Share on other sites More sharing options...
David Ashby - Moderator Posted February 19, 2010 Author Share Posted February 19, 2010 The system does that sometimes Stuey, I think it gets bored. Yup, scale concessions or something...... Quote Link to comment Share on other sites More sharing options...
Chris Card Posted February 20, 2010 Share Posted February 20, 2010 I don't have any hard numbers to quote because I'm racking my brains from last year, which is when I last flew an EDF with the Jeti MUI sensor giving me live current info. I seem to remember a modest unloading but certainly not an increase in current draw in the air. Oh David! Now you've got me daydreaming about EDF again and I thought I'd managed to kick that addiction! I might have to revisit the torque rod aileron linkages on my HET F-20 and see if I can get it flying again. Edited By peevie on 20/02/2010 08:30:06 Quote Link to comment Share on other sites More sharing options...
Dizz Posted February 20, 2010 Share Posted February 20, 2010 You have to consider the fan as a propeller in a tube: the air reaching the fan face already has a significant velocity down the intake even when the aircraft is at zero airspeed. Obviously intake length, geometry and change in area along the duct will have an effect, but I think the fan is effectively already "unloaded". I would expect to see more of a difference on something like a GWS A-10 with the fan right at the front of the nacelle. Pete Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted February 21, 2010 Share Posted February 21, 2010 Yes it’s a fan or an impeller in a tube and as indicated by my earlier post, air is a fluid and with the impeller stationary the pressure is equal on both sides. As we throttle up we are transferring the pressure. The thrust is caused by a change in momentum not by a change in energy (Newtons second law). Therefore loading is relatively constant. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 21, 2010 Share Posted February 21, 2010 Brian Is the same argument relevant to propellers? Erfolg Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted February 21, 2010 Share Posted February 21, 2010 I think the difference is between the pressure in a confined column and in a free surface/space. Dynamic pressure is probably involved somewhere. Quote Link to comment Share on other sites More sharing options...
scott cuppello Posted February 21, 2010 Share Posted February 21, 2010 The loading is fairly minimal/constant in an EDF, however, the inefficiency of EDF is why certain factors [AUW, C of G and trim, all of which are far more critical than a prop driven model] are so important, and have such an effect. I never give much attention to loading [as it's not worth worrying about] as I work on the basis of MINIMUM 200w per 1lb for EDF and work on the afformentioned area's, this is the key, in my opinion, based on much experience to success with EDF. Quote Link to comment Share on other sites More sharing options...
James Hindle Posted February 28, 2010 Share Posted February 28, 2010 my 2p's worth would be that although the inlet recovers some of the pressure during flight it allows the motor to rev higher so balancing the load and keeping constant draw.... Hence the noise change in flight ? I'm not techie in a any way so don't flame my logic ! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 1, 2010 Share Posted March 1, 2010 JamesI suspect any noise change in flight has more to do with the doppler effect than changes in fan speed. Brian is right, the fan will hardly see the effect of the models speed as the air in the duct is already moving pretty quickly. Now if you fly supersonic and get clever with the shock waves......... Quote Link to comment Share on other sites More sharing options...
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