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Dizz

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  1. Dizz

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  4. Dizz
    With a sealed duct to the fan the bell mouth/rounded lip is on the actual inlet opening, effectively increasing the area by allowing air to enter the duct from larger angles than with a sharp lipped intake. This has the greatest effect on static thrust. With a plenum chamber bell mouth the fan can't draw any more air than is being delivered by the duct infront of it unless of course the chamber is open to the fuselage. If that was the case then you would not have the efficiency gain from the claimed pressure increase ahead of the fan with forward speed (Stumax' explanation for the sealed duct recommend and one I subscribe to given the improved performance over expected of my M52, FD2 and P1091). Maybe the L39 scale intake area is too small wrt fan FSA and that is why Daniel has done it (to allow greater mass to enter the fan? Anyway, here is another conundrum for you theorists.............what is the prediction for this installation: The intake will have a large splitter plate standing off the fuselage side and the other 3 sides will have a rounded balsa lip. Am enjoying the discussion (again). Pete Edited By Dizz on 11/08/2012 13:26:24 Edited By Dizz on 11/08/2012 13:29:05
  5. Dizz
    Posted by Mark Powell 2 on 31/07/2012 12:47:31: INLET DUCTING. ................. 2) Try stopping the duct a few inches short of the motor rather than continuing it right up to the fan. This will give you a 'plenum chamber' and also allow you to use an inlet bellmouth (such as the one included with the Wemotec fans) on the fan unit. Schubeler now recommends this. The space between the end of the duct and the fan inlet does not have to be particularly smooth, but do not place deliberate obstructions. ................. An interesting situation and 100% opposite to what Stuart Maxwell of Stumax fans recommends. I can't see how the Schubler recomend would do anything other than disturb the air flow approaching the fan face, but I guess they must be basing it on something.
  6. Dizz
    Hi Grasshopper, i do build and fly EDF and given your criteria personally I would trade off some speed for static thrust (makes hand launches easier) and go for a 90-95% FSA exhaust area. That said, you ask 10 people an EDF related question and you will get 10 different answers! Good luck with your project Pete
  7. Dizz
    Nice one, always a big confidence boost when the first flight goes well. Pete
  8. Dizz
    Posted by David Ashby - RCME Admin on 17/01/2012 08:48:27: Looks interesting, a micro EDF eh?   Do you think they really mean 11750Kv?       Edited By David Ashby - RCME Admin on 17/01/2012 08:51:16 Having heard it in the video I also don't think that 11750kV unreasonable, particularly given the diameter of the fan is only 28mm.   Very rough calculation: 11750kV x 7.4v x 80% = approx 69,000 rpm   Pete
  9. Dizz
    Good to know you can actually get the spares.........good luck getting the old one off! I gave up on balancing the Sky rotor and bought a wemo min pro from Puffin. Pete
  10. Dizz
    OK, will keep an eye open for a 64mm Lander one in that case. Actually the Stumax test went very well, it is simply the smoothest fan ever and the sound is awesome! Everything held up under full power this time without collapsing, blowing up or catching fire, so I can crack on with the Viggen again now. That Sky fan on the other hand........................ It is still not running well so if it doesn't come in after the next balancing session I'll take all the tape off and start again. I have to persevere though because it will will look good down the intake of the P1154 I'm building next. Happy New Year   Pete @import url(http://www.modelflying.co.uk/CuteEditor_Files/Style/SyntaxHighlighter.css);@import url(/CuteEditor_Files/public_forums.css);
  11. Dizz
    It is rather - I have one in my Typhoon and 4 going in a Vulcan (when ever I get around to finishing the design), so I'll probably be in the same boat at some time. The more I think about it, the more I would be inclined to use a Wemo mini fan rotor. With a jig it would be a pretty esay job to take 2mm off each blade and the re-balance. Advantage over those other 64mm fans is that the material is pucker and the blade count/pitch/area seem closer to the original Lander item. I'm having an EDF morning today, currently on a break from balancing a 12 blade 70mm Sky fan then I have a Stumax 110-52 to run up on 12S . Pete Edited By Dizz on 26/12/2011 10:19:52
  12. Dizz
    @import url(/CuteEditor_Files/public_forums.css); Hi Stuey I checked the vendors I use and afraid no joy - in the UK or abroad. Found a potential option at Hobby King: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=4846  Or what about getting a 69mm fan and cutting it down? Merry Christmas Pete   @import url(http://www.modelflying.co.uk/CuteEditor_Files/Style/SyntaxHighlighter.css);@import url(/CuteEditor_Files/public_forums.css);Edited By Dizz on 23/12/2011 20:57:53
  13. Dizz
    @import url(http://www.modelflying.co.uk/CuteEditor_Files/Style/SyntaxHighlighter.css);@import url(/CuteEditor_Files/public_forums.css); My FD2 fuz based closely on the P1091 fuz which is basically a West Wings hunter. I have been lazy and used the triangular Hunter intakes (because they work and I had the vac-formings) rather than go through the process of making the FD2 rounded intakes. Not sure what you mean by "additional factor", but the intake area is just about 105% FSA.   I have quite a lot of thrust/power/velocity data from different EDF tests done over the last few years and will collate into a single spreadsheet this w/e, but I don't think this forum will allow me to post the file to share.   wrt the collapsing duct: I have used 2 different fixes in the past.   On the P1121 I simply laminated some glass cloth to the outside of the plastic vac-forming (keyed plastic first with coarse wire wool).  The second technique on my Viggen was to use Hysol areopoxy over carbon fibre tows wrapped around the GRP duct and additional balsa supports.  Looks a bit messy (it was! ), but does the job.     Pete    @import url(http://www.modelflying.co.uk/CuteEditor_Files/Style/SyntaxHighlighter.css);@import url(/CuteEditor_Files/public_forums.css);Edited By Dizz on 04/11/2011 11:06:11
  14. Dizz
    And so with that we are back to the point I tried to make on 19 Oct: without a wind tunnel and some decent insturmentation we are not going to be able to improve on what we can already achieve using basic testing and well know rules of thumb.   Regardless, I hope you can come up with something solid relevant to the higher power levels available now.   Afraid the weather put paid to any hope of flying the P1091 and getting a S&L speed today. However I'm moving along with a FD2 I'm building and should be able to provide a range of figures from that over the next couple of months.
  15. Dizz

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  16. Dizz
    WM400 with ARC 28-58-1, CC120HV ICE and Zippy 3000 40C 6S.FSA= 30.4cm^2 Exhaust area = 23.7cm^2 (78% FSA)  30 seconds into run: 1709W, 53,728rpm, Ve=189.5mph 84.7m/s (from How Fast system). Then I stopped the fan, reset the How Fast and ran it up to full power again, but this time I held the pitot tube against the side of the shroud with the opening about 3mm ahead of the edge (I didn't use a rounded intake lip).   vi=109.4mph 48.9 m/s......................not exactly "very low"  
  17. Dizz

    wm400 on test

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    wm400 on test
  18. Dizz
    But Richard it is you who makes the assumption vi=0 (in your 18/10/2011 18:57 post calculations). I agree with the other guys and think the static intake velocity is actually quite high. I am going to bed in a WM400 fan on the test stand tomorrow so will measure the intake velocity. It will not provide an accurate figure though because the static probe will not be facing into the flow, however it will give an indication..   Not sure about your mph to m/s conversions. I make 135mph=60.35m/s and that will obviously affect your calculated results. I'll still hold back on the P1091 Doppler speed I have and see what is predicted.   I could get the EF-16 intkae area from the replacement that I'm slowly progressing, but I don't have the exhaust area or efflux velocity so there is no point. Pete   PS Planning on an EDF session next Sunday, so (weather permitting) I should be able to get decent airspeeds for my  P1091, M52 and Typhoon - may be a few others too - to feed the verification process.Edited By Dizz on 22/10/2011 20:56:08
  19. Dizz
    Posted by Richard Sharman on 21/10/2011 21:51:28: Posted by Keith Simmons on 21/10/2011 21:26:20: I think the moving EDF has less work to suck the air in the intake so the fan was able to spin a bit faster and so a more thrust as a result. I have heard this "explanation" before, but admit to being a bit skeptical about it. Some people even say they can hear the motor note increasing (because it is running faster) in the air. But when challenged to tell the difference between that and the Doppler effect of an approaching model they usually can't. I can't hear anything that could be interpreted this way. And I've never seen the phenomenon of "on the step" which I suspect is a myth. Certainly my planes speed up as they get airborne and climb to cruising height, but so does my biplane, and my pattern ships. What we need is some observations of rpm, current draw and velocity in flight, which I want to do some day. Can't say I have heard any change in rpm - the Doppler analysis doesn't show it either. Stu Maxwell of Stumax EDFs fame is a member of the "the higher pressure in the duct ahead of the fan improves efficiency" school..........having followed his recommend to keep the intake duct sealed and seen positive results (in my opinion) I am too. Would an increase in pressure not mean that the fan is shifting a greater mass for the same rpm?  It is a fact that EDFs do not work so well at altitude (just read the US forum threats). Am asking Santa for a DX8 for Christmas - the telemetry options should be useful for in-flight EDF. Edited By Dizz on 21/10/2011 23:55:39
  20. Dizz
    Posted by Richard Sharman on 21/10/2011 21:14:12: Can you say what the entry area, fan swept area, and exit area values were? We could then use the theory to compare the static and dynamic cases.   P1091Wemo mini fan HET 2W-20 on 2650mAh 4S 40C pack.FSA=29.4cm^2 Exhaust =25.5cm^2 (87% FSA) Total Intake area 29.8cm^2 30s WOT figures:  Installed Static thrust = 1064g (10.43N); 800W on the Wattmeter; efflux velocity measured with the How Fast = 135mph Static thrust on the test stand=1140g ( 11.2N); 765W; efflux 146mph (no ducting)   I do have a Doppler speed for the P1091, but only one slightly into wind pass so I can't really declare an airspeed. Haven't got any fan figures for the dead EF-16, but I have several Doppler 'grams - max speed straight and level I have recorded is 122.8mph +/-1.8mph   Edited By Dizz on 21/10/2011 23:29:34
  21. Dizz

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  22. Dizz

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  23. Dizz
    "For example, no one has commented yet on the relationship between static thrust and dynamic thrust -- what is it? Because it's not obvious."   2 of my models have definitely generated more thurust once moving than when stationary (Modified Phase3 EF-16 and P1091): static thrust measured nose down on the scales indicated a T:W approx 0.9-0.95, but once in the air and "on the step" they will maintain a 90 degree climb without slowing. Both are(were) fast (120mph+ stright and level), have(had) bends in the intakes and sealed ducts (no openings for ESC cooling): I have a feeling that there is a gain from a dynamic pressure increase in the duct ahead of the fan - but lots of facors/variables involved and I have no way of finding out what is actually happening in flight..............especially the EF-16 because it exceeded Vne and is no-more
  24. Dizz
    Err..., well.....,no, actually! Because when designing a plane we need to work out what the exact geometry of duct is to build it, and when flying a plane we need to select the right battery for the desired duration/performance. So how would you do that? trial and error ? or theory and practice ? As our friends across the water would say, it's a no-brainer ! Third way...............experience ("rule of thumb").  Fourth way................use/adapt a proven design (use the experience gained by another).  
  25. Dizz
    Richard I appreciate you are looking at it as a system, but where are the system boundaries? I was taking the plane of the intake and exhaust faces. If you extend the boundary "a long way" from there both velocities will tend towards zero. However you were questioning where the missing Watts in your example calculation were going - I'm saying that without considering what is happening inside the system you wont be able to improve the Ploss figure.  wrt airframe characteristics: consider 2 aircraft with the same ducted fan units/motors/intakes/exhaust such that static thrust is the same - one a very large and draggy (but lightly loaded aircraft) that can only achieve an airspeed of x m/s where thrust=drag, then a second highly streamlined dart where thrust = drag at 5x m/s.How do the equations handle that?  Yep, reckon my money is pretty safe. If the static vent for the unit is inside a enclosed compartment with no openings it will relate to the pressure inside the enclosure when it was closed, not the current static atmospheric. The air inside the fuselage will tend towards the air pressure at the openings to the fuselage eg the gap around the canopy hatch. Where the local airflow accelerates (like over that lovely aerofoil shaped cockpit) it will be less than static, where it slows down it will be greater than static. Of course everything may balance out for a certain set of conditions, but that will change the next day.What is the % error between the "almost exactly" in agreement airspeed and averaged GPS ground speed? I have the How Fast pitot static system from BRC and that is claimed to have an accuracy (instrument error) of 2%, but as I said, small errors are magnified when a square appears in the equation. RegardsPete
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