DH Flyer Posted July 18, 2013 Share Posted July 18, 2013 Hi all, Just bought a second hand edf unit, and am I am planning to mount it externally above the fuselage. As you can see in the picture it is quite basic with a simple plastic tube. Would it be helpful to build a sort of shroud/pod, maybe a larger inlet, or an extended, slightly tapered exit duct? Any advice greatly appreciated, Daniel Quote Link to comment Share on other sites More sharing options...
DH Flyer Posted July 18, 2013 Author Share Posted July 18, 2013 Sorry can't get the pic to show (I blame the iPad ) But it is just a straight sided plastic cylinder. There is a small cone over the fan hub, and the fan blades run flush with the leading edge of the tube) There is no ducting or anything behind, no exit cone, just the rear end of the motor Quote Link to comment Share on other sites More sharing options...
Dizz Posted July 18, 2013 Share Posted July 18, 2013 Difficult to be specific without pictures or knowing what performance you want, but you will definitely gain benefit of a higher static thrust (easier to hand launch) from a rounded intake lip (2 - 3mm radius). With the efflux it is a case of trading exit velocity for static thrust: up to a point, smaller the outlet area = higher exhaust velocity (higher potential top speed) but lower static thrust. Generally a good place to start is to add a cone to make the exhaust area between 85 and 90% of the fan swept area (FSA) (FSA = total area of the fan shroud - area of the motor housing). For more thrust increase the exhaust area to 95-100% FSA, for more speed reduce the area but never less than 75% FSA. HTH Pete Quote Link to comment Share on other sites More sharing options...
Tartan81 Posted July 19, 2013 Share Posted July 19, 2013 sorry dizz didnt follow that..but im not a fan of pods.pretty much unless there small and aerodynamic.but tbh i have not tryed many commercial products on the market so far but they look better than i could design.mayby its been my wood choice but this forum will never see pic of it, youll all laugh lol.i do..tee hee Quote Link to comment Share on other sites More sharing options...
DH Flyer Posted July 19, 2013 Author Share Posted July 19, 2013 Thanks for your inputs, Yes Dizz, I should be more specific: It is intended for a large, slow-flying model (I don't need 120mph!) so therefore I assume thrust is more important than exit velocity. Thanks for the numbers! Quote Link to comment Share on other sites More sharing options...
DH Flyer Posted July 19, 2013 Author Share Posted July 19, 2013 I can add a lip to the front but I am still not sure what to do for the motor end . . . Quote Link to comment Share on other sites More sharing options...
Dizz Posted July 20, 2013 Share Posted July 20, 2013 Google "Phase3 Fantom" and take a look at the pod on that for imspiration I have a photo of my Fantom here: http://forums.modelflying.co.uk/sites/3/images/member_albums/27405/img_0614.jpg Actually the efflux area is approx 105%FSA with this one - they have done that to help hand launching as it was sold as an intro to EDF. If you post the 2 diameter measurements of your unit (motor and inernal shroud) I can show the workings on here to explain if that would help. Admit that making an intake lip for your fan would be "challenging", but because the impeller is so close to the front edge it would be worth the effort. Lots of EF units come with a plastic intake ring though, so maybe you already have one. Pete Edited By Dizz on 20/07/2013 08:20:54 Edited By Dizz on 20/07/2013 08:27:01 Edited By Dizz on 20/07/2013 08:29:09 Quote Link to comment Share on other sites More sharing options...
DH Flyer Posted July 21, 2013 Author Share Posted July 21, 2013 Hi Pete, Thanks for your help. The Fantom looks a smart model and the sukhoi camouflage scheme suits it well! Funnily enough I think my edf was one that was removed form a Phase-3 Squall. I don't have a plastic intake ring unfortunatley. Although I have built a few models from plans I have never been tasked to produce a piece like that. I'll see what I can do, although as it is my summer holidays I have plenty of time for it. Your comment to do with hand-launching helped to steer me in a simialr direction as I will be hand-launching my model (no choice-the grass is nearly 2ft deep!). Maybe it would be a help if I described the model. I am intending mounting it on top of the fuselage of an own-design model. It is not designed for speed, imagine a Fournier RF4 for the looks. I wanted to power it and only chose an edf instead of a prop as I thought it would be fun (I know it is less efficient/appropriate for that purpose). If you could show me the calculations that would be very helpful thanks. The diameter of the of the motor-mounting shroud is 33mm and the inside diameter of the overall tube is 66mm. Many thanks, Daniel Quote Link to comment Share on other sites More sharing options...
Dizz Posted July 22, 2013 Share Posted July 22, 2013 Hi Daniel (Forgive me if I am teaching to suck eggs, I will use cm and 1 decimal place)) Area of a circle= pi x radius squared FSA = Area of the shroud - area of the motor So for your fan FSA = pi ( (3.3x3.3) - (1.65x1.65)) = 25.7sq cm and a radius of 2.9cm (100% FSA). Which then gives the following: 110% FSA 28.3sq cm radius 3.0cm 90% 23.1sq cm 2.7cm 85% 21.8sq cm 2.6cm 80% 20.6sq cm 2.5cm To get a template for whatever exhaust duct you decide on do a search for "cone layout" and you will find plenty of online calculators and free download software available (I actually use a programme called Cone Layout v2.0.4 from Pulse Rate Software). HTH Pete Quote Link to comment Share on other sites More sharing options...
DH Flyer Posted July 22, 2013 Author Share Posted July 22, 2013 Great, thanks for your help Daniel Quote Link to comment Share on other sites More sharing options...
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